;;; Copyright 2024 Masaya Tojo <masaya@tojo.tokyo>
;;;
;;; Licensed under the Apache License, Version 2.0 (the "License");
;;; you may not use this file except in compliance with the License.
;;; You may obtain a copy of the License at
;;;
;;;     http://www.apache.org/licenses/LICENSE-2.0
;;;
;;; Unless required by applicable law or agreed to in writing, software
;;; distributed under the License is distributed on an "AS IS" BASIS,
;;; WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
;;; See the License for the specific language governing permissions and
;;; limitations under the License.

(define-library (qklib infix)
  (export infix->prefix
          prefix->infix
          current-operator-rule-set)
  (import (scheme base)
          (scheme case-lambda)
          (only (srfi 1) car+cdr fold break! reverse! append! append-map! append-reverse!)
          (only (srfi 26) cut cute)
          (qklib infix rule-set))
  (begin
    (define (make-default-operator-rule-set)
      (rule-set
       (list
        (operator '+ 1 'both (unit 0))
        (operator '- 1 'left (unit 0 #t #t))
        (operator '* 2 'both (unit 1))
        (operator '/ 2 'left (unit 1 #t) (prefix '/))
        (operator '^ 3 'right #f (prefix 'expt #t)))))

    (define current-operator-rule-set
      (make-parameter (make-default-operator-rule-set)))

    (define infix->prefix
      (case-lambda
        ((expr failure)
         (call/cc
          (lambda (return)
            (let ((rs (current-operator-rule-set)))
              (map-all-list (cute infix->prefix-1 <> rs (lambda (e) (return (failure e))))
                            expr)))))
        ((expr)
         (infix->prefix expr (lambda (e) #f)))))

    (define (infix->prefix-1 expr rs fail)
      (cond ((and (pair? expr) (null? (cdr expr))) (car expr))
            ((and (pair? expr) (null? (cdr (cdr expr)))
                  (rule-set-infix-ref rs (car expr)))
             => (lambda (op)
                  (if (operator-unit-unary? op)
                      (let ((arg (car (cdr expr)))
                            (unit (operator-unit op)))
                        (if (rule-set-infix-ref rs arg)
                            (fail expr)
                            (if (unit-inv? unit)
                                expr
                                arg)))
                      (fail expr))))
            ((minimum-precedence expr rs)
             => (lambda (op)
                  (let ->prefix ((expr (list-copy expr))
                                 (op op))
                    (define (make-prefix left op-sym right)
                      (define (->infix left op-sym right)
                        (append left (cons op-sym right)))
                      (let ((left-op (minimum-precedence left rs))
                            (right-op (minimum-precedence right rs))
                            (not-binary-only? (not (operator-prefix-binary-only? op))))
                        `(,(operator-prefix-symbol op)
                          ,@(if (operator? left-op)
                                (if (and not-binary-only?
                                         (operator-left? op)
                                         (eqv? (operator-symbol op) (operator-symbol left-op)))
                                    (cdr (->prefix left left-op))
                                    (list (->prefix left left-op)))
                                (if (and (pair? left)
                                         (null? (cdr left)))
                                    (if (and not-binary-only?
                                             (operator-left? op)
                                             (pair? (car left))
                                             (eqv? (operator-symbol op) (car (car left))))
                                        (cdr (car left))
                                        (list (car left)))
                                    (fail (->infix left op-sym right))))
                          ,@(if (operator? right-op)
                                (if (and not-binary-only?
                                         (operator-right? op)
                                         (eqv? (operator-symbol op) (operator-symbol right-op)))
                                    (cdr (->prefix right right-op))
                                    (list (->prefix right right-op)))
                                (if (and (pair? right)
                                         (null? (cdr right)))
                                    (if (and not-binary-only?
                                             (operator-right? op)
                                             (pair? (car right))
                                             (eqv? (operator-symbol op) (car (car right))))
                                        (cdr (car right))
                                        (list (car right)))
                                    (fail (->infix left op-sym right)))))))
                    (if (operator-right? op)
                        (let-values (((lst op+rest) (break! (cute eqv? (operator-symbol op) <>) expr)))
                          (let-values (((op rest) (car+cdr op+rest)))
                            (make-prefix lst op rest)))
                        (let ((rev-expr (reverse! expr)))
                          (let-values (((rev-lst op+rev-rest) (break! (cute eqv? (operator-symbol op) <>) rev-expr)))
                            (let-values (((op-sym rev-rest) (car+cdr op+rev-rest)))
                              (make-prefix (reverse! rev-rest) op-sym (reverse! rev-lst)))))))))
            (else expr)))

    (define prefix->infix
      (case-lambda
        ((expr failure)
         (let ((rs (current-operator-rule-set)))
           (call-with-current-continuation
            (lambda (return)
              (let-values (((result _precedence) (%prefix->infix expr rs (lambda (e) (return (failure e))))))
                result)))))
        ((expr)
         (prefix->infix expr (lambda (e) #f)))))

    (define (%prefix->infix expr rs failure)
      (let ->infix ((expr expr))
        (define (->infix-fst expr)
          (let-values (((x _) (->infix expr)))
            x))
        (if (not (pair? expr))
            (values expr -inf.0)
            (let-values (((op-prefix-sym args) (car+cdr expr)))
              (cond ((rule-set-prefix-ref rs op-prefix-sym)
                     => (lambda (op)
                          (let ((p (operator-precedence op))
                                (op-sym (operator-symbol op)))
                            (cond ((null? args)
                                   (cond ((and (not (operator-unit-inv? op))
                                               (operator-unit op))
                                          => (lambda (u) (values (unit-value u) -inf.0)))
                                         (else (failure expr))))
                                  ((null? (cdr args))
                                   (let-values (((r-expr r-p) (->infix (car args))))
                                     (cond ((operator-unit op)
                                            => (lambda (u)
                                                 (if (unit-inv? u)
                                                     (if (unit-unary? u)
                                                         (values `(,op-sym ,r-expr) -inf.0)
                                                         (values `(,(unit-value (operator-unit op))
                                                                   ,op-sym
                                                                   ,@(if (operator-right? op)
                                                                         (wrap-when (< r-p p) r-expr)
                                                                         (wrap-when (<= r-p p) r-expr)))
                                                                 p))
                                                     (values r-expr r-p))))
                                           (else (failure expr)))))
                                  ((null? (cdr (cdr args)))
                                   (let-values (((l-expr l-p) (->infix (car args)))
                                                ((r-expr r-p) (->infix (cadr args))))
                                     (values `(,@(if (operator-left? op)
                                                     (wrap-when (< l-p p) l-expr)
                                                     (wrap-when (<= l-p p) l-expr))
                                               ,op-sym
                                               ,@(if (operator-right? op)
                                                     (wrap-when (< r-p p) r-expr)
                                                     (wrap-when (<= r-p p) r-expr)))
                                             p)))
                                  (else
                                   (cond ((and (operator-left? op)
                                               (operator-right? op))
                                          (values (cdr (append-map! (lambda (arg)
                                                                      (let-values (((x-expr x-p) (->infix arg)))
                                                                        (cons op-sym (wrap-when (< x-p p) x-expr))))
                                                                    args))
                                                  p))
                                         ((operator-left? op)
                                          (let-values (((l-expr l-p) (->infix (car args))))
                                            (values (append! (wrap-when (< l-p p) l-expr)
                                                             (append-map! (lambda (arg)
                                                                            (let-values (((l-expr l-p) (->infix arg)))
                                                                              (cons op-sym (wrap-when (<= l-p p) l-expr))))
                                                                          (cdr args)))
                                                    p)))
                                         ((operator-right? op)
                                          (let ((rev-args (reverse args)))
                                            (let-values (((r-expr r-p) (->infix (car rev-args))))
                                              (values (reverse!
                                                       (append-reverse! (wrap-when (< r-p p) r-expr)
                                                                        (append-map!
                                                                         (lambda (arg)
                                                                           (let-values (((r-expr r-p) (->infix arg)))
                                                                             (cons op-sym (wrap-when (<= r-p p) r-expr))))
                                                                         (cdr rev-args))))
                                                      p))))
                                         (else (failure expr))))))))
                    (else (values (map ->infix-fst expr) -inf.0)))))))

    (define (minimum-precedence expr rs)
      (let ((dummy (operator 'dummy +inf.0 'both)))
        (let ((result
               (fold (lambda (x y-op)
                       (cond ((rule-set-infix-ref rs x)
                              => (lambda (x-op) (if (<= (operator-precedence x-op) (operator-precedence y-op))
                                                    x-op
                                                    y-op)))
                             (else y-op)))
                     dummy
                     expr)))
          (if (eq? dummy result)
              #f
              result))))

    (define (operator-unit-inv? x)
      (cond ((operator-unit x) => (cut unit-inv? <>))
            (else #f)))

    (define (operator-unit-unary? op)
      (cond ((operator-unit op) => unit-unary?)
            (else #f)))

    (define (operator-prefix-binary-only? op)
      (cond ((operator-prefix op) => prefix-binary-only?)
            (else #f)))

    (define (wrap-when b? x)
      (if b? (list x) x))

    (define (map-all-list f expr)
      (f (map-cars f expr)))

    (define (map-cars f expr)
      (if (pair? expr)
          (if (pair? (car expr))
              (cons (f (map-cars f (car expr)))
                    (map-cars f (cdr expr)))
              (cons (car expr)
                    (map-cars f (cdr expr))))
          expr))
    ))