(.module:
  lux
  (lux (control [monad #+ do]
                ["ex" exception #+ exception:])
       (data [number]
             [text]
             text/format
             (coll [list "list/" Functor<List> Fold<List>]
                   [set #+ Set]))
       [macro #+ "meta/" Monad<Meta>]
       (macro [code]))
  (luxc [lang]
        (lang [".L" variable #+ Register Variable]
              ["ls" synthesis #+ Synthesis Path]
              (host [python #+ Expression Statement Except SVar @@])))
  [//]
  (// [".T" runtime]
      [".T" primitive]
      [".T" reference]))

(def: #export (translate-let translate register valueS bodyS)
  (-> (-> Synthesis (Meta Expression)) Register Synthesis Synthesis
      (Meta Expression))
  (do macro.Monad<Meta>
    [valueO (translate valueS)
     bodyO (translate bodyS)
     #let [$register (referenceT.variable register)]]
    (wrap (|> bodyO
              (python.lambda (list $register))
              (python.apply (list valueO))))))

(def: #export (translate-record-get translate valueS pathP)
  (-> (-> Synthesis (Meta Expression)) Synthesis (List [Nat Bool])
      (Meta Expression))
  (do macro.Monad<Meta>
    [valueO (translate valueS)]
    (wrap (list/fold (function [[idx tail?] source]
                       (let [method (if tail?
                                      runtimeT.product//right
                                      runtimeT.product//left)]
                         (method source (python.int (:! Int idx)))))
                     valueO
                     pathP))))

(def: #export (translate-if testO thenO elseO)
  (-> Expression Expression Expression Expression)
  (python.if testO thenO elseO))

(def: $savepoint (python.var "pm_cursor_savepoint"))
(def: $cursor (python.var "pm_cursor"))

(def: (push-cursor! value)
  (-> Expression Statement)
  (python.do!
   (python.send (list value)
                "append" (@@ $cursor))))

(def: save-cursor!
  Statement
  (python.do!
   (python.send (list (python.slice-from (python.int 0) (@@ $cursor)))
                "append" (@@ $savepoint))))

(def: restore-cursor!
  Statement
  (python.set! (list $cursor)
               (python.send (list) "pop" (@@ $savepoint))))

(def: cursor-top
  Expression
  (python.nth (python.int -1) (@@ $cursor)))

(def: pop-cursor!
  Statement
  (python.do!
   (python.send (list) "pop" (@@ $cursor))))

(def: pm-error (python.string "PM-ERROR"))

(def: (new-Exception error)
  (-> Expression Expression)
  (python.apply (list pm-error) (python.global "Exception")))

(def: fail-pm! (python.raise! (new-Exception pm-error)))

(def: $temp (python.var "temp"))

(exception: #export Unrecognized-Path)

(def: $alt_error (python.var "alt_error"))

(def: (pm-catch! handler!)
  (-> Statement Except)
  [(list "Exception") $alt_error
   (python.if! (python.= pm-error (python.apply (list (@@ $alt_error)) (python.global "str")))
               handler!
               (python.raise! (@@ $alt_error)))])

(def: (translate-pattern-matching' translate pathP)
  (-> (-> Synthesis (Meta Expression)) Path (Meta Statement))
  (case pathP
    (^code ("lux case exec" (~ bodyS)))
    (do macro.Monad<Meta>
      [bodyO (translate bodyS)]
      (wrap (python.return! bodyO)))

    (^code ("lux case pop"))
    (meta/wrap pop-cursor!)

    (^code ("lux case bind" (~ [_ (#.Nat register)])))
    (meta/wrap (python.set! (list (referenceT.variable register)) cursor-top))

    (^template [<tag> <format>]
      [_ (<tag> value)]
      (meta/wrap (python.when! (python.not (python.= (|> value <format>) cursor-top))
                               fail-pm!)))
    ([#.Nat  (<| python.int (:! Int))]
     [#.Int  python.int]
     [#.Deg  (<| python.int (:! Int))]
     [#.Bool python.bool]
     [#.Frac python.float]
     [#.Text python.string])

    (^template [<pm> <getter>]
      (^code (<pm> (~ [_ (#.Nat idx)])))
      (meta/wrap (push-cursor! (<getter> cursor-top (python.int (:! Int idx))))))
    (["lux case tuple left" runtimeT.product//left]
     ["lux case tuple right" runtimeT.product//right])

    (^template [<pm> <flag>]
      (^code (<pm> (~ [_ (#.Nat idx)])))
      (meta/wrap ($_ python.then!
                     (python.set! (list $temp) (runtimeT.sum//get cursor-top (python.int (:! Int idx)) <flag>))
                     (python.if! (python.not (python.= python.none (@@ $temp)))
                                 (push-cursor! (@@ $temp))
                                 fail-pm!))))
    (["lux case variant left" python.none]
     ["lux case variant right" (python.string "")])

    (^code ("lux case seq" (~ leftP) (~ rightP)))
    (do macro.Monad<Meta>
      [leftO (translate-pattern-matching' translate leftP)
       rightO (translate-pattern-matching' translate rightP)]
      (wrap ($_ python.then!
                leftO
                rightO)))

    (^code ("lux case alt" (~ leftP) (~ rightP)))
    (do macro.Monad<Meta>
      [leftO (translate-pattern-matching' translate leftP)
       rightO (translate-pattern-matching' translate rightP)]
      (wrap (python.try! ($_ python.then!
                             save-cursor!
                             leftO)
                         (list (pm-catch!
                                ($_ python.then!
                                    restore-cursor!
                                    rightO))))))

    _
    (lang.throw Unrecognized-Path (%code pathP))
    ))

(def: (translate-pattern-matching translate pathP)
  (-> (-> Synthesis (Meta Expression)) Path (Meta Statement))
  (do macro.Monad<Meta>
    [pattern-matching (translate-pattern-matching' translate pathP)]
    (wrap (python.try! pattern-matching
                       (list (pm-catch!
                              (python.raise! (new-Exception (python.string "Invalid expression for pattern-matching.")))))))))

(def: (initialize-pattern-matching! stack-init)
  (-> Expression Statement)
  ($_ python.then!
      (python.set! (list $cursor) (python.list (list stack-init)))
      (python.set! (list $savepoint) (python.list (list)))))

(def: empty (Set Variable) (set.new number.Hash<Int>))

(type: Storage
  {#bindings (Set Variable)
   #dependencies (Set Variable)})

(def: (path-variables pathP)
  (-> Path Storage)
  (loop [pathP pathP
         outer-variables {#bindings empty
                          #dependencies empty}]
    ## TODO: Remove (let [outer recur]) once loops can have names.
    (let [outer recur]
      (case pathP
        (^code ("lux case bind" (~ [_ (#.Nat register)])))
        (update@ #bindings (set.add (nat-to-int register))
                 outer-variables)

        (^or (^code ("lux case seq" (~ leftP) (~ rightP)))
             (^code ("lux case alt" (~ leftP) (~ rightP))))
        (list/fold outer outer-variables (list leftP rightP))

        (^code ("lux case exec" (~ bodyS)))
        (loop [bodyS bodyS
               inner-variables outer-variables]
          ## TODO: Remove (let [inner recur]) once loops can have names.
          (let [inner recur]
            (case bodyS
              (^code ((~ [_ (#.Nat tag)]) (~ [_ (#.Bool last?)]) (~ valueS)))
              (inner valueS inner-variables)

              (^code [(~+ members)])
              (list/fold inner inner-variables members)

              (^ [_ (#.Form (list [_ (#.Int var)]))])
              (if (set.member? (get@ #bindings inner-variables) var)
                inner-variables
                (update@ #dependencies (set.add var) inner-variables))

              (^code ("lux call" (~ functionS) (~+ argsS)))
              (list/fold inner inner-variables (#.Cons functionS argsS))

              (^code ("lux function" (~ [_ (#.Nat arity)]) [(~+ environment)] (~ bodyS)))
              (|> environment
                  (list/map (|>> (list) code.form))
                  (list/fold inner inner-variables))

              (^code ("lux let" (~ [_ (#.Nat register)]) (~ inputS) (~ exprS)))
              (list/fold inner (update@ #bindings (set.add (nat-to-int register))
                                        inner-variables)
                         (list inputS exprS))

              (^code ("lux case" (~ inputS) (~ pathPS)))
              (|> inner-variables (inner inputS) (outer pathPS))

              (^code ((~ [_ (#.Text procedure)]) (~+ argsS)))
              (list/fold inner inner-variables argsS)

              _
              inner-variables)))

        _
        outer-variables))))

(def: generated-name
  (-> Text (Meta SVar))
  (|>> macro.gensym
       (:: macro.Monad<Meta> map (|>> %code
                                      lang.normalize-name
                                      python.var))))

(def: #export (translate-case translate valueS pathP)
  (-> (-> Synthesis (Meta Expression)) Synthesis Path (Meta Expression))
  (do macro.Monad<Meta>
    [valueO (translate valueS)
     $case (generated-name "case")
     $value (generated-name "value")
     #let [$dependencies+ (|> (path-variables pathP)
                              (get@ #dependencies)
                              set.to-list
                              (list/map referenceT.local))
           @dependencies+ (list/map @@ $dependencies+)]
     pattern-matching! (translate-pattern-matching translate pathP)
     _ (//.save (python.def! $case (list& $value $dependencies+)
                             ($_ python.then!
                                 (initialize-pattern-matching! (@@ $value))
                                 pattern-matching!)))]
    (wrap (python.apply (list& valueO @dependencies+) (@@ $case)))))