(.`` (.`` (.require
           [library
            [lux (.except open)
             [abstract
              ["[0]" monad (.only Monad do)]]
             [control
              ["[0]" pipe]
              ["[0]" maybe (.use "[1]#[0]" functor)]
              ["[0]" try (.only Try) (.use "[1]#[0]" functor)]
              ["[0]" exception (.only Exception)]
              ["[0]" io (.only IO) (.use "[1]#[0]" functor)]
              ["[0]" function]
              [concurrency
               ["[0]" async (.only Async)]
               ["[0]" stm (.only Var STM)]]]
             [data
              ["[0]" bit (.use "[1]#[0]" equivalence)]
              ["[0]" product]
              ["[0]" binary (.only Binary)]
              ["[0]" text (.use "[1]#[0]" equivalence)
               ["%" \\format (.only format)]]
              [collection
               ["[0]" array (.only Array)]
               ["[0]" list (.use "[1]#[0]" functor)]
               ["[0]" dictionary (.only Dictionary)]]]
             ["[0]" ffi (.only)
              (.,, (.for "JavaScript" (.,, (.these ["[0]" node_js]))
                         "{old}" (.,, (.these ["node_js" //control/thread]))
                         (.,, (.these))))]
             [math
              [number
               ["i" int]
               ["f" frac]]]
             [meta
              ["@" target]
              [macro
               ["[0]" template]]]]]
           [//
            [time
             ["[0]" instant (.only Instant)]
             ["[0]" duration]]])))

(type .public Path
  Text)

(`` (type .public (System !)
      (Interface
       (is Text
           separator)

       (,, (with_template [<name> <output>]
             [(is (-> Path (! <output>))
                  <name>)]

             [file? Bit]
             [directory? Bit]
             ))

       (,, (with_template [<name> <output>]
             [(is (-> Path (! (Try <output>)))
                  <name>)]

             [make_directory  Any]
             [directory_files (List Path)]
             [sub_directories (List Path)]
             
             [file_size     Nat]
             [last_modified Instant]
             [can_execute?  Bit]
             [read          Binary]
             [delete        Any]
             ))

       (,, (with_template [<name> <input>]
             [(is (-> Path <input> (! (Try Any)))
                  <name>)]

             [modify Instant]
             [write  Binary]
             [append Binary]
             [move   Path]
             )))
      ))

(def (un_rooted fs path)
  (All (_ !) (-> (System !) Path (Maybe [Path Text])))
  (let [/ (at fs separator)]
    (when (text.last_index / path)
      {.#None}
      {.#None}
      
      {.#Some last_separator}
      (do maybe.monad
        [[parent temp] (text.split_at last_separator path)
         [_ child] (text.split_at (text.size /) temp)]
        (in [parent child])))))

(def .public (parent fs path)
  (All (_ !) (-> (System !) Path (Maybe Path)))
  (|> path
      (..un_rooted fs)
      (maybe#each product.left)))

(def .public (name fs path)
  (All (_ !) (-> (System !) Path Text))
  (|> path
      (..un_rooted fs)
      (maybe#each product.right)
      (maybe.else path)))

(def .public (async fs)
  (-> (System IO) (System Async))
  (`` (implementation
       (def separator
         (at fs separator))

       (,, (with_template [<name>]
             [(def <name>
                (|>> (at fs <name>)
                     async.future))]

             [file?]
             [directory?]
             
             [make_directory]
             [directory_files]
             [sub_directories]
             
             [file_size]
             [last_modified]
             [can_execute?]
             [read]
             [delete]))

       (,, (with_template [<name>]
             [(def (<name> path input)
                (async.future (at fs <name> path input)))]

             [modify]
             [write]
             [append]
             [move]))
       )))

(def .public (rooted fs parent child)
  (All (_ !) (-> (System !) Path Text Path))
  (format parent (at fs separator) child))

(with_template [<name>]
  [(exception.def .public (<name> file)
     (Exception Path)
     (exception.report
      (list ["Path" file])))]

  [cannot_make_file]
  [cannot_find_file]
  [cannot_delete]

  [cannot_make_directory]
  [cannot_find_directory]
  )

(with_expansions [<for_jvm> (these (ffi.import java/lang/String
                                     "[1]::[0]")

                                   (`` (ffi.import java/io/File
                                         "[1]::[0]"
                                         (new [java/lang/String])
                                         (,, (with_template [<name>]
                                               [(<name> [] "io" "try" boolean)]

                                               [createNewFile] [mkdir]
                                               [delete]
                                               [isFile] [isDirectory]
                                               [canRead] [canWrite] [canExecute]))

                                         (length [] "io" "try" long)
                                         (listFiles [] "io" "try" "?" [java/io/File])
                                         (getAbsolutePath [] "io" "try" java/lang/String)
                                         (renameTo [java/io/File] "io" "try" boolean)
                                         (lastModified [] "io" "try" long)
                                         (setLastModified [long] "io" "try" boolean)
                                         ("read_only" "static" separator java/lang/String)))

                                   (ffi.import java/lang/AutoCloseable
                                     "[1]::[0]"
                                     (close [] "io" "try" void))

                                   (ffi.import java/io/OutputStream
                                     "[1]::[0]"
                                     (write [[byte]] "io" "try" void)
                                     (flush [] "io" "try" void))

                                   (ffi.import java/io/FileOutputStream
                                     "[1]::[0]"
                                     (new [java/io/File boolean] "io" "try"))

                                   (ffi.import java/io/InputStream
                                     "[1]::[0]"
                                     (read [[byte]] "io" "try" int))

                                   (ffi.import java/io/FileInputStream
                                     "[1]::[0]"
                                     (new [java/io/File] "io" "try"))

                                   (`` (def .public default
                                         (System IO)
                                         (implementation
                                          (def separator
                                            (ffi.of_string (java/io/File::separator)))

                                          (,, (with_template [<name> <method>]
                                                [(def <name>
                                                   (|>> ffi.as_string
                                                        java/io/File::new
                                                        <method>
                                                        (io#each (|>> (try#each (|>> ffi.of_boolean)) (try.else false)))))]

                                                [file? java/io/File::isFile]
                                                [directory? java/io/File::isDirectory]
                                                ))

                                          (def make_directory
                                            (|>> ffi.as_string
                                                 java/io/File::new
                                                 java/io/File::mkdir))

                                          (,, (with_template [<name> <method>]
                                                [(def (<name> path)
                                                   (do [! (try.with io.monad)]
                                                     [?children (java/io/File::listFiles (java/io/File::new (ffi.as_string path)))]
                                                     (when ?children
                                                       {.#Some children}
                                                       (|> children
                                                           (array.list {.#None})
                                                           (monad.only ! (|>> <method> (at ! each (|>> ffi.of_boolean))))
                                                           (at ! each (monad.each ! (|>> java/io/File::getAbsolutePath (at ! each (|>> ffi.of_string)))))
                                                           (at ! conjoint))

                                                       {.#None}
                                                       (at io.monad in (exception.except ..cannot_find_directory [path])))))]

                                                [directory_files java/io/File::isFile]
                                                [sub_directories java/io/File::isDirectory]
                                                ))

                                          (def file_size
                                            (|>> ffi.as_string
                                                 java/io/File::new
                                                 java/io/File::length
                                                 (at (try.with io.monad) each (|>> ffi.of_long .nat))))

                                          (def last_modified
                                            (|>> ffi.as_string
                                                 java/io/File::new
                                                 (java/io/File::lastModified)
                                                 (at (try.with io.monad) each (|>> ffi.of_long duration.of_millis instant.absolute))))

                                          (def can_execute?
                                            (|>> ffi.as_string
                                                 java/io/File::new
                                                 java/io/File::canExecute
                                                 (io#each (try#each (|>> ffi.of_boolean)))))

                                          (def (read path)
                                            (do (try.with io.monad)
                                              [.let [file (java/io/File::new (ffi.as_string path))]
                                               size (java/io/File::length file)
                                               stream (java/io/FileInputStream::new file)
                                               .let [data (binary.empty (.nat (ffi.of_long size)))]
                                               bytes_read (java/io/InputStream::read data stream)
                                               _ (java/lang/AutoCloseable::close stream)]
                                              (in data)))

                                          (def (delete path)
                                            (|> path
                                                ffi.as_string
                                                java/io/File::new
                                                java/io/File::delete))

                                          (def (modify path time_stamp)
                                            (|> path
                                                ffi.as_string
                                                java/io/File::new
                                                (java/io/File::setLastModified (|> time_stamp instant.relative duration.millis ffi.as_long))))
                                          
                                          (,, (with_template [<flag> <name>]
                                                [(def (<name> path data)
                                                   (do (try.with io.monad)
                                                     [stream (java/io/FileOutputStream::new (java/io/File::new (ffi.as_string path)) (ffi.as_boolean <flag>))
                                                      _ (java/io/OutputStream::write data stream)
                                                      _ (java/io/OutputStream::flush stream)]
                                                     (java/lang/AutoCloseable::close stream)))]

                                                [#0 write]
                                                [#1 append]
                                                ))

                                          (def (move origin destination)
                                            (|> origin
                                                ffi.as_string
                                                java/io/File::new
                                                (java/io/File::renameTo (java/io/File::new (ffi.as_string destination)))))
                                          ))))]
  (for @.old (these <for_jvm>)
       @.jvm (these <for_jvm>)

       @.js
       (these (ffi.import Buffer
                "[1]::[0]"
                ("static" from [Binary] ..Buffer))
              
              (ffi.import FileDescriptor
                "[1]::[0]")

              (ffi.import Stats
                "[1]::[0]"
                (size ffi.Number)
                (mtimeMs ffi.Number)
                (isFile [] ffi.Boolean)
                (isDirectory [] ffi.Boolean))

              (ffi.import FsConstants
                "[1]::[0]"
                (F_OK ffi.Number)
                (R_OK ffi.Number)
                (W_OK ffi.Number)
                (X_OK ffi.Number))

              (ffi.import Error
                "[1]::[0]"
                (toString [] ffi.String))

              (def with_async
                (template (_ <write> <type> <body>)
                  [(template.with_locals [<read>]
                     (let [[<read> <write>] (is [(Async <type>) (async.Resolver <type>)]
                                                (async.async []))]
                       (exec
                         <body>
                         <read>)))]))
              
              (ffi.import Fs
                "[1]::[0]"
                (constants FsConstants)
                (readFile [ffi.String ffi.Function] Any)
                (appendFile [ffi.String Buffer ffi.Function] Any)
                (writeFile [ffi.String Buffer ffi.Function] Any)
                (stat [ffi.String ffi.Function] Any)
                (access [ffi.String ffi.Number ffi.Function] Any)
                (rename [ffi.String ffi.String ffi.Function] Any)
                (utimes [ffi.String ffi.Number ffi.Number ffi.Function] Any)
                (readdir [ffi.String ffi.Function] Any)
                (mkdir [ffi.String ffi.Function] Any)
                (unlink [ffi.String ffi.Function] Any)
                (rmdir [ffi.String ffi.Function] Any))

              (def (any_callback write!)
                (-> (async.Resolver (Try Any)) ffi.Function)
                (<| (ffi.function (_ [error Error]) Any)
                    io.run!
                    write!
                    (if (ffi.null? error)
                      {try.#Success []}
                      {try.#Failure (Error::toString error)})))

              (def (value_callback write!)
                (All (_ a) (-> (async.Resolver (Try a)) ffi.Function))
                (<| (ffi.function (_ [error Error datum Any]) Any)
                    io.run!
                    write!
                    (if (ffi.null? error)
                      {try.#Success (as_expected datum)}
                      {try.#Failure (Error::toString error)})))

              (ffi.import JsPath
                "[1]::[0]"
                (sep ffi.String))
              
              (def .public default
                (Maybe (System Async))
                (do maybe.monad
                  [node_fs (node_js.require "fs")
                   node_path (node_js.require "path")
                   .let [node_fs (as ..Fs node_fs)
                         js_separator (if ffi.on_node_js?
                                        (JsPath::sep (as ..JsPath node_path))
                                        "/")]]
                  (in (is (System Async)
                          (`` (implementation
                               (def separator
                                 js_separator)

                               (,, (with_template [<name> <method>]
                                     [(def (<name> path)
                                        (do async.monad
                                          [?stats (with_async write! (Try Stats)
                                                    (Fs::stat path (..value_callback write!)
                                                              node_fs))]
                                          (in (when ?stats
                                                {try.#Success stats}
                                                (<method> stats)
                                                
                                                {try.#Failure _}
                                                false))))]

                                     [file?      Stats::isFile]
                                     [directory? Stats::isDirectory]
                                     ))

                               (def (make_directory path)
                                 (do async.monad
                                   [outcome (with_async write! (Try Any)
                                              (Fs::access path
                                                          (|> node_fs Fs::constants FsConstants::F_OK)
                                                          (..any_callback write!)
                                                          node_fs))]
                                   (when outcome
                                     {try.#Success _}
                                     (in (exception.except ..cannot_make_directory [path]))
                                     
                                     {try.#Failure _}
                                     (with_async write! (Try Any)
                                       (Fs::mkdir path (..any_callback write!) node_fs)))))

                               (,, (with_template [<name> <method>]
                                     [(def (<name> path)
                                        (do [! (try.with async.monad)]
                                          [subs (with_async write! (Try (Array ffi.String))
                                                  (Fs::readdir path (..value_callback write!) node_fs))]
                                          (|> subs
                                              (array.list {.#None})
                                              (list#each (|>> (format path js_separator)))
                                              (monad.each ! (function (_ sub)
                                                              (at ! each (|>> <method> [sub])
                                                                  (with_async write! (Try Stats)
                                                                    (Fs::stat sub (..value_callback write!) node_fs)))))
                                              (at ! each (|>> (list.only product.right)
                                                              (list#each product.left))))))]

                                     [directory_files Stats::isFile]
                                     [sub_directories Stats::isDirectory]
                                     ))

                               (def (file_size path)
                                 (do (try.with async.monad)
                                   [stats (with_async write! (Try Stats)
                                            (Fs::stat path (..value_callback write!)
                                                      node_fs))]
                                   (in (|> stats
                                           Stats::size
                                           f.nat))))

                               (def (last_modified path)
                                 (do (try.with async.monad)
                                   [stats (with_async write! (Try Stats)
                                            (Fs::stat path (..value_callback write!)
                                                      node_fs))]
                                   (in (|> stats
                                           Stats::mtimeMs
                                           f.int
                                           duration.of_millis
                                           instant.absolute))))

                               (def (can_execute? path)
                                 (at async.monad each
                                     (|>> (pipe.when
                                            {try.#Success _}
                                            true

                                            {try.#Failure _}
                                            false)
                                          {try.#Success})
                                     (with_async write! (Try Any)
                                       (Fs::access path
                                                   (|> node_fs Fs::constants FsConstants::X_OK)
                                                   (..any_callback write!)
                                                   node_fs))))

                               (def (read path)
                                 (with_async write! (Try Binary)
                                   (Fs::readFile path (..value_callback write!)
                                                 node_fs)))

                               (def (delete path)
                                 (do (try.with async.monad)
                                   [stats (with_async write! (Try Stats)
                                            (Fs::stat path (..value_callback write!) node_fs))]
                                   (with_async write! (Try Any)
                                     (if (Stats::isFile stats)
                                       (Fs::unlink path (..any_callback write!) node_fs)
                                       (Fs::rmdir path (..any_callback write!) node_fs)))))

                               (def (modify path time_stamp)
                                 (with_async write! (Try Any)
                                   (let [when (|> time_stamp instant.relative duration.millis i.frac)]
                                     (Fs::utimes path when when (..any_callback write!)
                                                 node_fs))))

                               (,, (with_template [<name> <method>]
                                     [(def (<name> path data)
                                        (with_async write! (Try Any)
                                          (<method> path (Buffer::from data) (..any_callback write!)
                                                    node_fs)))]

                                     [write  Fs::writeFile]
                                     [append Fs::appendFile]
                                     ))

                               (def (move origin destination)
                                 (with_async write! (Try Any)
                                   (Fs::rename origin destination (..any_callback write!)
                                               node_fs))))))))))

       @.python
       (these (type (Tuple/2 left right)
                (Primitive "python_tuple[2]" [left right]))

              (ffi.import PyFile
                "[1]::[0]"
                (read [] "io" "try" Binary)
                (write [Binary] "io" "try" "?" Any)
                (close [] "io" "try" "?" Any))

              (ffi.import (open [ffi.String ffi.String] "io" "try" PyFile))
              (ffi.import (tuple [[ffi.Integer ffi.Integer]] (Tuple/2 ffi.Integer ffi.Integer)))

              (ffi.import os
                "[1]::[0]"
                ("static" F_OK ffi.Integer)
                ("static" R_OK ffi.Integer)
                ("static" W_OK ffi.Integer)
                ("static" X_OK ffi.Integer)

                ("static" mkdir [ffi.String] "io" "try" "?" Any)
                ("static" access [ffi.String ffi.Integer] "io" "try" ffi.Boolean)
                ("static" remove [ffi.String] "io" "try" "?" Any)
                ("static" rmdir [ffi.String] "io" "try" "?" Any)
                ("static" rename [ffi.String ffi.String] "io" "try" "?" Any)
                ("static" utime [ffi.String (Tuple/2 ffi.Integer ffi.Integer)] "io" "try" "?" Any)
                ("static" listdir [ffi.String] "io" "try" (Array ffi.String)))

              (ffi.import os/path
                "[1]::[0]"
                ("static" isfile [ffi.String] "io" "try" ffi.Boolean)
                ("static" isdir [ffi.String] "io" "try" ffi.Boolean)
                ("static" sep ffi.String)
                ("static" getsize [ffi.String] "io" "try" ffi.Integer)
                ("static" getmtime [ffi.String] "io" "try" ffi.Float))

              (def python_separator
                (os/path::sep))

              (`` (def .public default
                    (System IO)
                    (implementation
                     (def separator
                       ..python_separator)

                     (,, (with_template [<name> <method>]
                           [(def <name>
                              (|>> <method>
                                   (io#each (|>> (try.else false)))))]

                           [file?      os/path::isfile]
                           [directory? os/path::isdir]
                           ))

                     (def make_directory
                       os::mkdir)

                     (,, (with_template [<name> <method>]
                           [(def (<name> path)
                              (let [! (try.with io.monad)]
                                (|> path
                                    os::listdir
                                    (at ! each (|>> (array.list {.#None})
                                                    (list#each (|>> (format path ..python_separator)))
                                                    (monad.each ! (function (_ sub)
                                                                    (at ! each (|>> [sub]) (<method> sub))))
                                                    (at ! each (|>> (list.only product.right)
                                                                    (list#each product.left)))))
                                    (at ! conjoint))))]

                           [directory_files os/path::isfile]
                           [sub_directories os/path::isdir]
                           ))

                     (def file_size
                       (|>> os/path::getsize
                            (at (try.with io.monad) each (|>> .nat))))

                     (def last_modified
                       (|>> os/path::getmtime
                            (at (try.with io.monad) each (|>> f.int
                                                              (i.* +1,000)
                                                              duration.of_millis
                                                              instant.absolute))))

                     (def (can_execute? path)
                       (os::access path (os::X_OK)))

                     (def (read path)
                       (do (try.with io.monad)
                         [file (..open path "rb")
                          data (PyFile::read file)
                          _ (PyFile::close file)]
                         (in data)))

                     (def (delete path)
                       (do (try.with io.monad)
                         [? (os/path::isfile path)]
                         (if ?
                           (os::remove path)
                           (os::rmdir path))))

                     (def (modify path time_stamp)
                       (let [when (|> time_stamp instant.relative duration.millis (i./ +1,000))]
                         (os::utime path (..tuple [when when]))))

                     (,, (with_template [<name> <mode>]
                           [(def (<name> path data)
                              (do (try.with io.monad)
                                [file (..open path <mode>)
                                 _ (PyFile::write data file)]
                                (PyFile::close file)))]
                           
                           [write  "w+b"]
                           [append "ab"]
                           ))

                     (def (move origin destination)
                       (os::rename origin destination))
                     ))))

       @.ruby
       (these (ffi.import Time
                "[1]::[0]"
                ("static" at [Frac] Time)
                (to_f [] Frac))

              (ffi.import Stat
                "[1]::[0]"
                (executable? [] Bit)
                (size Int)
                (mtime [] Time))

              (ffi.import File "as" RubyFile
                "[1]::[0]"
                ("static" SEPARATOR ffi.String)
                ("static" open [Path ffi.String] "io" "try" RubyFile)
                ("static" stat [Path] "io" "try" Stat)
                ("static" delete [Path] "io" "try" Int)
                ("static" file? [Path] "io" "try" Bit)
                ("static" directory? [Path] "io" "try" Bit)
                ("static" utime [Time Time Path] "io" "try" Int)

                (read [] "io" "try" Binary)
                (write [Binary] "io" "try" Int)
                (flush [] "io" "try" "?" Any)
                (close [] "io" "try" "?" Any))

              (ffi.import Dir
                "[1]::[0]"
                ("static" open [Path] "io" "try" Dir)
                
                (children [] "io" "try" (Array Path))
                (close [] "io" "try" "?" Any))

              (ffi.import "fileutils" FileUtils
                "[1]::[0]"
                ("static" move [Path Path] "io" "try" "?" Any)
                ("static" rmdir [Path] "io" "try" "?" Any)
                ("static" mkdir [Path] "io" "try" "?" Any))

              (def ruby_separator
                Text
                (..RubyFile::SEPARATOR))

              (`` (def .public default
                    (System IO)
                    (implementation
                     (def separator
                       ..ruby_separator)

                     (,, (with_template [<name> <test>]
                           [(def <name>
                              (|>> <test>
                                   (io#each (|>> (try.else false)))))]

                           [file? RubyFile::file?]
                           [directory? RubyFile::directory?]
                           ))
                     
                     (def make_directory
                       FileUtils::mkdir)

                     (,, (with_template [<name> <test>]
                           [(def (<name> path)
                              (do [! (try.with io.monad)]
                                [self (Dir::open path)
                                 children (Dir::children self)
                                 output (loop (again [input (|> children
                                                                (array.list {.#None})
                                                                (list#each (|>> (format path ..ruby_separator))))
                                                      output (is (List ..Path)
                                                                 (list))])
                                          (when input
                                            {.#End}
                                            (in output)

                                            {.#Item head tail}
                                            (do !
                                              [verdict (<test> head)]
                                              (again tail (if verdict
                                                            {.#Item head output}
                                                            output)))))
                                 _ (Dir::close self)]
                                (in output)))]

                           [directory_files RubyFile::file?]
                           [sub_directories RubyFile::directory?]
                           ))

                     (,, (with_template [<name> <pipeline>]
                           [(def <name>
                              (let [! (try.with io.monad)]
                                (|>> RubyFile::stat
                                     (at ! each (`` (|>> (,, (template.spliced <pipeline>))))))))]

                           [file_size [Stat::size .nat]]
                           [last_modified [Stat::mtime
                                           Time::to_f
                                           (f.* +1,000.0)
                                           f.int
                                           duration.of_millis
                                           instant.absolute]]
                           [can_execute? [Stat::executable?]]
                           ))

                     (def (read path)
                       (do (try.with io.monad)
                         [file (RubyFile::open path "rb")
                          data (RubyFile::read file)
                          _ (RubyFile::close file)]
                         (in data)))

                     (def (delete path)
                       (do (try.with io.monad)
                         [? (RubyFile::file? path)]
                         (if ?
                           (RubyFile::delete path)
                           (FileUtils::rmdir path))))

                     (def (modify path moment)
                       (let [moment (|> moment
                                        instant.relative
                                        duration.millis
                                        i.frac
                                        (f./ +1,000.0)
                                        Time::at)]
                         (RubyFile::utime moment moment path)))

                     (,, (with_template [<mode> <name>]
                           [(def (<name> path data)
                              (do [! (try.with io.monad)]
                                [file (RubyFile::open path <mode>)
                                 data (RubyFile::write data file)
                                 _ (RubyFile::flush file)
                                 _ (RubyFile::close file)]
                                (in [])))]
                           
                           ["wb" write]
                           ["ab" append]
                           ))

                     (def (move origin destination)
                       (do (try.with io.monad)
                         [_ (FileUtils::move origin destination)]
                         (in [])))
                     ))))

       ... @.php
       ... (these (ffi.import (FILE_APPEND Int))
       ...        ... https://www.php.net/manual/en/dir.constants.php
       ...        (ffi.import (DIRECTORY_SEPARATOR ffi.String))
       ...        ... https://www.php.net/manual/en/function.pack.php
       ...        ... https://www.php.net/manual/en/function.unpack.php
       ...        (ffi.import (unpack [ffi.String ffi.String] Binary))
       ...        ... https://www.php.net/manual/en/ref.filesystem.php
       ...        ... https://www.php.net/manual/en/function.file-get-contents.php
       ...        (ffi.import (file_get_contents [Path] "io" "try" ffi.String))
       ...        ... https://www.php.net/manual/en/function.file-put-contents.php
       ...        (ffi.import (file_put_contents [Path ffi.String Int] "io" "try" ffi.Integer))
       ...        (ffi.import (filemtime [Path] "io" "try" ffi.Integer))
       ...        (ffi.import (filesize [Path] "io" "try" ffi.Integer))
       ...        (ffi.import (is_executable [Path] "io" "try" ffi.Boolean))
       ...        (ffi.import (touch [Path ffi.Integer] "io" "try" ffi.Boolean))
       ...        (ffi.import (rename [Path Path] "io" "try" ffi.Boolean))
       ...        (ffi.import (unlink [Path] "io" "try" ffi.Boolean))

       ...        ... https://www.php.net/manual/en/function.rmdir.php
       ...        (ffi.import (rmdir [Path] "io" "try" ffi.Boolean))
       ...        ... https://www.php.net/manual/en/function.scandir.php
       ...        (ffi.import (scandir [Path] "io" "try" (Array Path)))
       ...        ... https://www.php.net/manual/en/function.is-file.php
       ...        (ffi.import (is_file [Path] "io" "try" ffi.Boolean))
       ...        ... https://www.php.net/manual/en/function.is-dir.php
       ...        (ffi.import (is_dir [Path] "io" "try" ffi.Boolean))
       ...        ... https://www.php.net/manual/en/function.mkdir.php
       ...        (ffi.import (mkdir [Path] "io" "try" ffi.Boolean))

       ...        (def byte_array_format "C*")
       ...        (def default_separator (..DIRECTORY_SEPARATOR))

       ...        (with_template [<name>]
       ...          [(exception.def .public (<name> file)
       ...             (Exception Path)
       ...             (exception.report
       ...              (list ["Path" file])))]
       
       ...          [cannot_write_to_file]
       ...          )

       ...        (`` (def (file path)
       ...              (-> Path (File IO))
       ...              (implementation
       ...               (,, (with_template [<name> <mode>]
       ...                     [(def (<name> data)
       ...                        (do [! (try.with io.monad)]
       ...                          [outcome (..file_put_contents [path ("php pack" ..byte_array_format data) <mode>])]
       ...                          (if (bit#= false (as Bit outcome))
       ...                            (at io.monad in (exception.except ..cannot_write_to_file [path]))
       ...                            (in []))))]
       
       ...                     [over_write  +0]
       ...                     [append      (..FILE_APPEND)]
       ...                     ))

       ...               (def (content _)
       ...                 (do [! (try.with io.monad)]
       ...                   [data (..file_get_contents [path])]
       ...                   (if (bit#= false (as Bit data))
       ...                     (at io.monad in (exception.except ..cannot_find_file [path]))
       ...                     (in (..unpack [..byte_array_format data])))))

       ...               (def path
       ...                 path)

       ...               (,, (with_template [<name> <ffi> <pipeline>]
       ...                     [(def (<name> _)
       ...                        (do [! (try.with io.monad)]
       ...                          [value (<ffi> [path])]
       ...                          (if (bit#= false (as Bit value))
       ...                            (at io.monad in (exception.except ..cannot_find_file [path]))
       ...                            (in (`` (|> value (,, (template.spliced <pipeline>))))))))]

       ...                     [size ..filesize [.nat]]
       ...                     [last_modified ..filemtime [(i.* +1,000) duration.of_millis instant.absolute]]
       ...                     ))

       ...               (def (can_execute? _)
       ...                 (..is_executable [path]))

       ...               (def (modify moment)
       ...                 (do [! (try.with io.monad)]
       ...                   [verdict (..touch [path (|> moment instant.relative duration.millis (i./ +1,000))])]
       ...                   (if (bit#= false (as Bit verdict))
       ...                     (at io.monad in (exception.except ..cannot_find_file [path]))
       ...                     (in []))))

       ...               (def (move destination)
       ...                 (do [! (try.with io.monad)]
       ...                   [verdict (..rename [path destination])]
       ...                   (if (bit#= false (as Bit verdict))
       ...                     (at io.monad in (exception.except ..cannot_find_file [path]))
       ...                     (in (file destination)))))

       ...               (def (delete _)
       ...                 (do (try.with io.monad)
       ...                   [verdict (..unlink [path])]
       ...                   (if (bit#= false (as Bit verdict))
       ...                     (at io.monad in (exception.except ..cannot_find_file [path]))
       ...                     (in []))))
       ...               )))

       ...        (`` (def (directory path)
       ...              (-> Path (Directory IO))
       ...              (implementation
       ...               (def scope
       ...                 path)

       ...               (,, (with_template [<name> <test> <constructor> <capability>]
       ...                     [(def (<name> _)
       ...                        (do [! (try.with io.monad)]
       ...                          [children (..scandir [path])]
       ...                          (loop (again [input (|> children
       ...                                                  (array.list {.#None})
       ...                                                  (list.only (function (_ child)
       ...                                                               (not (or (text#= "." child)
       ...                                                                        (text#= ".." child))))))
       ...                                        output (is (List (<capability> IO))
       ...                                                   (list))])
       ...                            (when input
       ...                              {.#End}
       ...                              (in output)

       ...                              {.#Item head tail}
       ...                              (do !
       ...                                [verdict (<test> head)]
       ...                                (if verdict
       ...                                  (again tail {.#Item (<constructor> head) output})
       ...                                  (again tail output)))))))]

       ...                     [files ..is_file ..file File]
       ...                     [directories ..is_dir directory Directory]
       ...                     ))

       ...               (def (discard _)
       ...                 (do (try.with io.monad)
       ...                   [verdict (..rmdir [path])]
       ...                   (if (bit#= false (as Bit verdict))
       ...                     (at io.monad in (exception.except ..cannot_find_directory [path]))
       ...                     (in []))))
       ...               )))

       ...        (`` (def .public default
       ...              (System IO)
       ...              (implementation
       ...               (,, (with_template [<name> <test> <constructor> <exception>]
       ...                     [(def (<name> path)
       ...                        (do [! (try.with io.monad)]
       ...                          [verdict (<test> path)]
       ...                          (at io.monad in
       ...                              (if verdict
       ...                                {try.#Success (<constructor> path)}
       ...                                (exception.except <exception> [path])))))]

       ...                     [file ..is_file ..file ..cannot_find_file]
       ...                     [directory ..is_dir ..directory ..cannot_find_directory]
       ...                     ))

       ...               (def (make_file path)
       ...                 (do [! (try.with io.monad)]
       ...                   [verdict (..touch [path (|> instant.now io.run! instant.relative duration.millis (i./ +1,000))])]
       ...                   (at io.monad in
       ...                       (if verdict
       ...                         {try.#Success (..file path)}
       ...                         (exception.except ..cannot_make_file [path])))))
       
       ...               (def (make_directory path)
       ...                 (do [! (try.with io.monad)]
       ...                   [verdict (..mkdir path)]
       ...                   (at io.monad in
       ...                       (if verdict
       ...                         {try.#Success (..directory path)}
       ...                         (exception.except ..cannot_make_directory [path])))))

       ...               (def separator
       ...                 ..default_separator)
       ...               )))
       ...        )
       
       (these)))

(def .public (exists? monad fs path)
  (All (_ !) (-> (Monad !) (System !) Path (! Bit)))
  (do monad
    [verdict (at fs file? path)]
    (if verdict
      (in verdict)
      (at fs directory? path))))

(type Mock_File
  (Record
   [#mock_last_modified Instant
    #mock_can_execute Bit
    #mock_content Binary]))

(type Mock
  (Rec Mock
    (Dictionary Text (Either Mock_File Mock))))

(def empty_mock
  Mock
  (dictionary.empty text.hash))

(def (retrieve_mock_file! separator path mock)
  (-> Text Path Mock (Try [Text Mock_File]))
  (loop (again [directory mock
                trail (text.all_split_by separator path)])
    (when trail
      {.#Item head tail}
      (when (dictionary.value head directory)
        {.#None}
        (exception.except ..cannot_find_file [path])
        
        {.#Some node}
        (when [node tail]
          [{.#Left file} {.#End}]
          {try.#Success [head file]}

          [{.#Right sub_directory} {.#Item _}]
          (again sub_directory tail)

          _
          (exception.except ..cannot_find_file [path])))

      {.#End}
      (exception.except ..cannot_find_file [path]))))

(def (update_mock_file! / path now content mock)
  (-> Text Path Instant Binary Mock (Try Mock))
  (loop (again [directory mock
                trail (text.all_split_by / path)])
    (when trail
      {.#Item head tail}
      (when (dictionary.value head directory)
        {.#None}
        (when tail
          {.#End}
          {try.#Success (dictionary.has head
                                        {.#Left [#mock_last_modified now
                                                 #mock_can_execute false
                                                 #mock_content content]}
                                        directory)}
          
          {.#Item _}
          (exception.except ..cannot_find_file [path]))
        
        {.#Some node}
        (when [node tail]
          [{.#Left file} {.#End}]
          {try.#Success (dictionary.has head
                                        {.#Left (|> file
                                                    (has #mock_last_modified now)
                                                    (has #mock_content content))}
                                        directory)}

          [{.#Right sub_directory} {.#Item _}]
          (do try.monad
            [sub_directory (again sub_directory tail)]
            (in (dictionary.has head {.#Right sub_directory} directory)))

          _
          (exception.except ..cannot_find_file [path])))

      {.#End}
      (exception.except ..cannot_find_file [path]))))

(def (delete_mock_node! / path mock)
  (-> Text Path Mock (Try Mock))
  (loop (again [directory mock
                trail (text.all_split_by / path)])
    (when trail
      {.#Item head tail}
      (when (dictionary.value head directory)
        {.#None}
        (exception.except ..cannot_delete [path])
        
        {.#Some node}
        (when tail
          {.#End}
          (when node
            {.#Left file}
            {try.#Success (dictionary.lacks head directory)}

            {.#Right sub_directory}
            (if (dictionary.empty? sub_directory)
              {try.#Success (dictionary.lacks head directory)}
              (exception.except ..cannot_delete [path])))
          
          {.#Item _}
          (when node
            {.#Left file}
            (exception.except ..cannot_delete [path])

            {.#Right sub_directory}
            (do try.monad
              [sub_directory' (again sub_directory tail)]
              (in (dictionary.has head {.#Right sub_directory'} directory))))))

      {.#End}
      (exception.except ..cannot_delete [path]))))

(def (attempt! transform var)
  (All (_ a) (-> (-> a (Try a)) (Var a) (STM (Try Any))))
  (do [! stm.monad]
    [|var| (stm.read var)]
    (when (transform |var|)
      {try.#Success |var|}
      (do !
        [_ (stm.write |var| var)]
        (in {try.#Success []}))
      
      {try.#Failure error}
      (in {try.#Failure error}))))

(def (make_mock_directory! / path mock)
  (-> Text Path Mock (Try Mock))
  (loop (again [directory mock
                trail (text.all_split_by / path)])
    (when trail
      {.#Item head tail}
      (when (dictionary.value head directory)
        {.#None}
        (when tail
          {.#End}
          {try.#Success (dictionary.has head {.#Right ..empty_mock} directory)}

          {.#Item _}
          (exception.except ..cannot_make_directory [path]))
        
        {.#Some node}
        (when [node tail]
          [{.#Right sub_directory} {.#Item _}]
          (do try.monad
            [sub_directory (again sub_directory tail)]
            (in (dictionary.has head {.#Right sub_directory} directory)))

          _
          (exception.except ..cannot_make_directory [path])))

      {.#End}
      (exception.except ..cannot_make_directory [path]))))

(def (retrieve_mock_directory! / path mock)
  (-> Text Path Mock (Try Mock))
  (loop (again [directory mock
                trail (text.all_split_by / path)])
    (when trail
      {.#End}
      {try.#Success directory}

      {.#Item head tail}
      (when (dictionary.value head directory)
        {.#None}
        (exception.except ..cannot_find_directory [path])
        
        {.#Some node}
        (when node
          {.#Left _}
          (exception.except ..cannot_find_directory [path])

          {.#Right sub_directory}
          (when tail
            {.#End}
            {try.#Success sub_directory}

            {.#Item _}
            (again sub_directory tail)))))))

(def .public (mock separator)
  (-> Text (System Async))
  (let [store (stm.var ..empty_mock)]
    (`` (implementation
         (def separator
           separator)

         (,, (with_template [<method> <retrieve>]
               [(def (<method> path)
                  (|> store
                      stm.read
                      (at stm.monad each
                          (|>> (<retrieve> separator path)
                               (try#each (function.constant true))
                               (try.else false)))
                      stm.commit!))]
               
               [file? ..retrieve_mock_file!]
               [directory? ..retrieve_mock_directory!]))

         (def (make_directory path)
           (stm.commit!
            (do [! stm.monad]
              [|store| (stm.read store)]
              (when (..make_mock_directory! separator path |store|)
                {try.#Success |store|}
                (do !
                  [_ (stm.write |store| store)]
                  (in {try.#Success []}))
                
                {try.#Failure error}
                (in {try.#Failure error})))))

         (,, (with_template [<method> <tag>]
               [(def (<method> path)
                  (stm.commit!
                   (do stm.monad
                     [|store| (stm.read store)]
                     (in (do try.monad
                           [directory (..retrieve_mock_directory! separator path |store|)]
                           (in (|> directory
                                   dictionary.entries
                                   (list.all (function (_ [node_name node])
                                               (when node
                                                 {<tag> _}
                                                 {.#Some (format path separator node_name)}
                                                 
                                                 _
                                                 {.#None}))))))))))]

               [directory_files .#Left]
               [sub_directories .#Right]
               ))

         (def (file_size path)
           (stm.commit!
            (do stm.monad
              [|store| (stm.read store)]
              (in (|> |store|
                      (..retrieve_mock_file! separator path)
                      (try#each (|>> product.right
                                     (the #mock_content)
                                     binary.size)))))))

         (def (last_modified path)
           (stm.commit!
            (do stm.monad
              [|store| (stm.read store)]
              (in (|> |store|
                      (..retrieve_mock_file! separator path)
                      (try#each (|>> product.right
                                     (the #mock_last_modified))))))))

         (def (can_execute? path)
           (stm.commit!
            (do stm.monad
              [|store| (stm.read store)]
              (in (|> |store|
                      (..retrieve_mock_file! separator path)
                      (try#each (|>> product.right
                                     (the #mock_can_execute))))))))

         (def (read path)
           (stm.commit!
            (do stm.monad
              [|store| (stm.read store)]
              (in (|> |store|
                      (..retrieve_mock_file! separator path)
                      (try#each (|>> product.right
                                     (the #mock_content))))))))

         (def (delete path)
           (stm.commit!
            (..attempt! (..delete_mock_node! separator path) store)))

         (def (modify path now)
           (stm.commit!
            (..attempt! (function (_ |store|)
                          (do try.monad
                            [[name file] (..retrieve_mock_file! separator path |store|)]
                            (..update_mock_file! separator path now (the #mock_content file) |store|)))
                        store)))

         (def (write path content)
           (do async.monad
             [now (async.future instant.now)]
             (stm.commit!
              (..attempt! (..update_mock_file! separator path now content) store))))

         (def (append path content)
           (do async.monad
             [now (async.future instant.now)]
             (stm.commit!
              (..attempt! (function (_ |store|)
                            (do try.monad
                              [[name file] (..retrieve_mock_file! separator path |store|)]
                              (..update_mock_file! separator path now
                                                   (at binary.monoid composite
                                                       (the #mock_content file)
                                                       content)
                                                   |store|)))
                          store))))

         (def (move origin destination)
           (stm.commit!
            (do [! stm.monad]
              [|store| (stm.read store)]
              (when (do try.monad
                      [[name file] (..retrieve_mock_file! separator origin |store|)
                       |store| (..delete_mock_node! separator origin |store|)]
                      (..update_mock_file! separator destination (the #mock_last_modified file) (the #mock_content file) |store|))
                {try.#Success |store|}
                (do !
                  [_ (stm.write |store| store)]
                  (in {try.#Success []}))
                
                {try.#Failure error}
                (in {try.#Failure error})))))
         ))))

(def (check_or_make_directory monad fs path)
  (All (_ !) (-> (Monad !) (System !) Path (! (Try Any))))
  (do monad
    [? (at fs directory? path)]
    (if ?
      (in {try.#Success []})
      (at fs make_directory path))))

(def .public (make_directories monad fs path)
  (All (_ !) (-> (Monad !) (System !) Path (! (Try Any))))
  (let [rooted? (text.starts_with? (at fs separator) path)
        segments (text.all_split_by (at fs separator) path)]
    (when (if rooted?
            (list.after 1 segments)
            segments)
      {.#End}
      (at monad in (exception.except ..cannot_make_directory [path]))

      {.#Item head tail}
      (when head
        "" (at monad in (exception.except ..cannot_make_directory [path]))
        _ (loop (again [current (if rooted?
                                  (format (at fs separator) head)
                                  head)
                        next tail])
            (do monad
              [? (..check_or_make_directory monad fs current)]
              (when ?
                {try.#Success _}
                (when next
                  {.#End}
                  (in {try.#Success []})
                  
                  {.#Item head tail}
                  (again (format current (at fs separator) head)
                         tail))
                
                {try.#Failure error}
                (in {try.#Failure error}))))))))

(def .public (make_file monad fs content path)
  (All (_ !) (-> (Monad !) (System !) Binary Path (! (Try Any))))
  (do monad
    [? (at fs file? path)]
    (if ?
      (in (exception.except ..cannot_make_file [path]))
      (at fs write path content))))

(def .public (copy monad fs from to)
  (All (_ !) (-> (Monad !) (System !) Path Path (! (Try Any))))
  (do (try.with monad)
    [data (at fs read from)]
    (at fs write to data)))