(defpackage #:flatbind
  (:use #:cl)
  (:local-nicknames
   (#:a #:alexandria-2))
  (:export #:do>))

(in-package :flatbind)

(defun variablep (thing)
  (and (symbolp thing) (not (keywordp thing))))

(defun values-binding-p (form)
  #+testiere
  (:tests
   (:is (values-binding-p 'a))
   (:is (values-binding-p '(a b)))
   (:is (values-binding-p '()))
   (:is (not (values-binding-p :x)))
   (:is (not (values-binding-p '(a b 4))))
   (:is (not (values-binding-p '(a :b 4)))))
  (or (variablep form)
      (and (listp form)
           (every #'variablep form))))

(defun destructuring-bind-list-p (form)
  #+testiere
  (:tests
   (:is (destructuring-bind-list-p '()))
   (:is (destructuring-bind-list-p '(a b)))
   (:is (destructuring-bind-list-p '(a &rest b)))
   (:is (destructuring-bind-list-p '(a &rest b &key (x 10) y)))
   (:is (destructuring-bind-list-p '(&optional a b)))
   (:is (not (destructuring-bind-list-p 'x)))
   (:is (not (destructuring-bind-list-p '(&rest x &optional y))))
   (:is (not (destructuring-bind-list-p '(&rest 10 &optional y)))))
  (and (listp form)
       (ignore-errors
        (multiple-value-bind (required optional rest kwargs allow-other aux keyp)
            (a:parse-ordinary-lambda-list form)
          (declare (ignorable required optional rest kwargs keyp))
          (not (or allow-other aux))))))

(defun slot-value-list-p (form)
  #+testiere
  (:tests
   (:is (slot-value-list-p '(a b c)))
   (:is (slot-value-list-p '((a slot-a))))
   (:is (slot-value-list-p '()))
   (:is (not (slot-value-list-p '(1 2))))
   (:is (not (slot-value-list-p '(:x)))))
  (and (listp form)
       (loop :for thing :in form
             :always (or (variablep thing)
                         (and (listp thing)
                              (= 2 (length thing))
                              (variablep (first thing))
                              (variablep (second thing)))))))

(defun expand-clauses (clauses)
  (flet ((collapse-progn (expanded)
           (if (and (listp expanded) (eq 'cl:progn (first expanded)))
               (rest expanded)
               (list expanded)))) 
    (loop :with expanded := nil
          :for (tag bindings form) :in (nreverse clauses)
          :do
             (setf expanded 
                   (ecase tag
                     (:simple
                      (cond ((null expanded) form)
                            ((eq 'cl:progn (first expanded))
                             `(progn ,form ,@(rest expanded)))
                            (t
                             `(progn ,form ,expanded))))

                     (:when
                         (cond ((null expanded) form)
                               ((eq 'cl:progn (first expanded))
                                `(when ,form ,@(rest expanded)))
                               (t
                                `(when ,form ,expanded))))

                     (:=
                      `(multiple-value-bind
                             ,(if (listp bindings) bindings (list bindings))
                           ,form
                         ,@(collapse-progn expanded)))
                     (:when=
                      `(a:when-let (,bindings ,form) 
                         ,@(collapse-progn expanded)))

                     (:slots=
                      `(with-slots ,bindings ,form
                         ,@(collapse-progn expanded)))
                     
                     (:match=
                      `(destructuring-bind ,bindings ,form
                         ,@(collapse-progn expanded)))))
          :finally (return
                     (if (and (listp expanded) (eq 'cl:progn (first expanded)))
                         `(block nil ,@(rest expanded))
                         `(block nil ,expanded))))))


(defun literals-equal (a b)
  (and (symbolp a) (symbolp b) (string-equal a b)))

(argot:deflanguage do> (:literals= #'literals-equal)
  (<start>
   :match (:seq (:* <clause>) (:eof))
   :then (expand-clauses (first <start>)))
  
  (<clause>
   :match (:or <binding-clause>
               <destructuring-clause>
               <with-slots-clause>
               <predicate-binding-clause>
               <predicate-clause>
               <simple-clause>)) 
  
  (<binding-clause>
   :match (:seq <values-bind> (:= :=) (:item))
   :then (destructuring-bind (bindings _ form) <binding-clause>
           (declare (ignore _))
           (list := bindings form)))

  (<values-bind>
   :match (:item)
   :if values-binding-p
   :note "Either a symbol or a list suitable for passing to MULTIPLE-VALUE-BIND")
  
  (<destructuring-clause>
   :match (:seq <destructuring-list> (:= :match=) (:item))
   :then (destructuring-bind (bindings _ form) <destructuring-clause>
           (declare (ignore _))
           (list :match= bindings form)))
  
  (<destructuring-list>
   :match (:item)
   :if destructuring-bind-list-p
   :note "An list that might be passed as the first argument to DESTRUCTURING-BIND.")
  
  (<with-slots-clause>
   :match (:seq <slot-value-list> (:= :slots=) (:item))
   :then (destructuring-bind (bindings _ form) <with-slots-clause>
           (declare (ignore _))
           (list :slots= bindings form)))
  
  (<slot-value-list>
   :match (:item)
   :if slot-value-list-p
   :note "A list that is suitable for passing to with-slots.")
  
  (<predicate-binding-clause>
   :match (:seq (:@ var (:item)) (:= :when=) (:@ form (:item)))
   :if (variablep var)
   :then (list :when= var form)
   :note "Bind variable to form, exit early if form evaluated to nil.")
  
  (<predicate-clause>
   :match (:seq (:= :when) (:item))
   :then (list :when nil (second <predicate-clause>)))
  
  (<simple-clause>
   :match (:@ simple (:item))
   :if (not (member simple '(:when= :match= :when := :slots=) :test #'literals-equal))
   :then (list :simple nil simple)))