(in-package #:parser)

(defun run (p input)
  (let ((result (funcall p input)))
    (if (parsing-p result)
      (parsing-tree result)
      result)))

(defstruct parsing
  tree
  left)

(defstruct failure
  place
  message)

(defmethod print-object ((obj failure) stream)
  (let ((file (input:file (failure-place obj))))
    (if file
      (multiple-value-bind (line column) (input:line-and-column (failure-place obj))
        (format stream "~a:~a:~a: ~a" line column file (failure-message obj)))
      (format stream "~a: ~a" (input:cursor (failure-place obj)) (failure-message obj)))))

(defun new (tree)
  (lambda (input)
    (make-parsing :tree tree :left input)))

(defun bind-with-input (p f)
  (declare (optimize (speed 3)))
  (declare (type function p f))
  (lambda (input)
    (let ((r (funcall p input)))
      (if (parsing-p r)
        (funcall (the function (funcall f (parsing-tree r) input))
                 (parsing-left r))
        r))))

(defun bind (p f)
  (declare (optimize (speed 3)))
  (declare (type function p f))
  (lambda (input)
    (let ((r (funcall p input)))
      (if (parsing-p r)
        (funcall (the function (funcall f (parsing-tree r)))
                 (parsing-left r))
        r))))

(defun discarding-bind (p f)
  (declare (optimize (speed 3)))
  (declare (type function p f))
  (lambda (input)
    (let ((r (funcall p input)))
      (if (parsing-p r)
        (funcall (the function (funcall f))
                 (parsing-left r))
        r))))

(defmacro comp (bindings &body body)
  (if (null bindings)
    `(new (progn ,@body))
    (let ((v (first (car bindings)))
          (p (second (car bindings))))
      (if (eq 'symbol (type-of v))
        (if (string= (symbol-name v) "_")
          `(discarding-bind ,p (lambda () (comp ,(cdr bindings) ,@body)))
          `(bind ,p (lambda (,v) (comp ,(cdr bindings) ,@body))))
        (if (and (eq 'cons (type-of v))
                 (eq 'symbol (type-of (car v)))
                 (eq 'symbol (type-of (cdr v))))
          `(bind-with-input ,p (lambda (,(car v) ,(cdr v)) (comp ,(cdr bindings) ,@body)))
          (error "Binding name/(name,input) must be either a symbol or a cons of symbols."))))))

(defun crit (p)
  (lambda (input)
    (let ((r (funcall p input)))
      (if (parsing-p r)
        r
        (error (format nil "~a" r))))))

(defun one-of (first-parser second-parser &rest other-parsers)
  (lambda (input)
    (labels ((one-of-rec (parsers failures)
                         (if (car parsers)
                           (let ((r (funcall (car parsers) input)))
                             (cond ((failure-p r)
                                    (one-of-rec (cdr parsers) (cons r failures)))
                                   ((listp r)
                                    (one-of-rec (cdr parsers) (append r failures)))
                                   (t r)))
                           failures)))
      (one-of-rec (cons first-parser (cons second-parser other-parsers)) nil))))

(defmacro unit (&optional predicate)
  (cond ((null predicate)
         (setf predicate '(characterp it)))
        ((symbolp predicate)
         (setf predicate `(,predicate it)))
        ((characterp predicate)
         (setf predicate `(char-equal ,predicate it)))
        (t (setf predicate
                 (nsubst-if 'it
                            (lambda (x)
                              (and (symbolp x)
                                   (string-equal (symbol-name x) "IT"))) predicate))))
  `(lambda (input)
     (if (input:has-data? input)
       (let ((it (input:peek input)))
         (if ,predicate
           (make-parsing :tree it :left (input:advance input))
           (make-failure :place input
                         :message (format nil "Expected: ~a, Got: ~a" ',predicate it))))
       (make-failure :place input :message "Reached end of input."))))

(defun literal (target)
  (lambda (input)
    (if (input:has-data? input)
      (if (input:prefix? target input)
        (make-parsing :tree target :left (input:advance input (length target)))
        (make-failure :place input :message "Predicate not satisfied."))
      (make-failure :place input :message "Reached end of input."))))

(defparameter nothing
  (new nil))

(defun optional (p)
  (one-of p nothing))

(defun many (p)
  (comp ((x p)
         (xs (optional (many p))))
    (cons x xs)))

(defparameter whitespace
  (comp ((_ (optional (many (unit char:whitespace?)))))
    nil))

(defun separated-list (p separator &key include-separator)
  (comp ((v p)
         (sep (optional separator))
         (vn (if sep
               (crit (separated-list p separator))
               nothing)))
    (if include-separator
      (cons v (cons sep vn))
      (cons v vn))))