;;  Copyright (c) Eduardo Julian. All rights reserved.
;;  This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0.
;;  If a copy of the MPL was not distributed with this file,
;;  You can obtain one at http://mozilla.org/MPL/2.0/.

(ns lux.parser
  (:require [clojure.template :refer [do-template]]
            clojure.core.match
            clojure.core.match.array
            (lux [base :as & :refer [deftags |do return fail |case]]
                 [lexer :as &lexer])))

;; [Utils]
(do-template [<name> <close-tag> <description> <tag>]
  (defn <name> [parse]
    (|do [elems (&/repeat% parse)
          token &lexer/lex]
      (|case token
        [meta [<close-token> _]]
        (return (&/V <tag> (&/fold &/|++ (&/|list) elems)))
        
        _
        (fail (str "[Parser Error] Unbalanced " <description> ".")))))

  ^:private parse-form  &lexer/$Close_Paren   "parantheses" &/$FormS
  ^:private parse-tuple &lexer/$Close_Bracket "brackets"    &/$TupleS
  )

(defn ^:private parse-record [parse]
  (|do [elems* (&/repeat% parse)
        token &lexer/lex
        :let [elems (&/fold &/|++ (&/|list) elems*)]]
    (|case token
      [meta (&lexer/$Close_Brace _)]
      (if (even? (&/|length elems))
        (return (&/V &/$RecordS (&/|as-pairs elems)))
        (fail (str "[Parser Error] Records must have an even number of elements.")))
      
      _
      (fail (str "[Parser Error] Unbalanced braces.")))))

;; [Interface]
(def parse
  (|do [token &lexer/lex
        :let [[meta token*] token]]
    (|case token*
      (&lexer/$White_Space _)
      (return (&/|list))

      (&lexer/$Comment _)
      (return (&/|list))
      
      (&lexer/$Bool ?value)
      (return (&/|list (&/T meta (&/V &/$BoolS (Boolean/parseBoolean ?value)))))

      (&lexer/$Int ?value)
      (return (&/|list (&/T meta (&/V &/$IntS (Long/parseLong ?value)))))

      (&lexer/$Real ?value)
      (return (&/|list (&/T meta (&/V &/$RealS (Double/parseDouble ?value)))))

      (&lexer/$Char ^String ?value)
      (return (&/|list (&/T meta (&/V &/$CharS (.charAt ?value 0)))))

      (&lexer/$Text ?value)
      (return (&/|list (&/T meta (&/V &/$TextS ?value))))

      (&lexer/$Symbol ?ident)
      (return (&/|list (&/T meta (&/V &/$SymbolS ?ident))))

      (&lexer/$Tag ?ident)
      (return (&/|list (&/T meta (&/V &/$TagS ?ident))))

      (&lexer/$Open_Paren _)
      (|do [syntax (parse-form parse)]
        (return (&/|list (&/T meta syntax))))
      
      (&lexer/$Open_Bracket _)
      (|do [syntax (parse-tuple parse)]
        (return (&/|list (&/T meta syntax))))

      (&lexer/$Open_Brace _)
      (|do [syntax (parse-record parse)]
        (return (&/|list (&/T meta syntax))))

      _
      (fail "[Parser Error] Unknown lexer token.")
      )))