;;; -*-lisp-*-
;;;
;;; Method combination implementation
;;;
;;; (c) 2009 Straylight/Edgeware
;;;

;;;----- Licensing notice ---------------------------------------------------
;;;
;;; This file is part of the Sensble Object Design, an object system for C.
;;;
;;; SOD is free software; you can redistribute it and/or modify
;;; it under the terms of the GNU General Public License as published by
;;; the Free Software Foundation; either version 2 of the License, or
;;; (at your option) any later version.
;;;
;;; SOD is distributed in the hope that it will be useful,
;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;;; GNU General Public License for more details.
;;;
;;; You should have received a copy of the GNU General Public License
;;; along with SOD; if not, write to the Free Software Foundation,
;;; Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

(cl:in-package #:sod)

;;;--------------------------------------------------------------------------
;;; Message classes.

(export 'basic-message)
(defclass basic-message (sod-message)
  ((argument-tail :type list :reader sod-message-argument-tail)
   (no-varargs-tail :type list :reader sod-message-no-varargs-tail))
  (:documentation
   "Base class for built-in message classes.

   Provides the basic functionality for the built-in method combinations.
   This is a separate class so that `special effect' messages can avoid
   inheriting its default behaviour.

   The function type protocol is implemented on `basic-message' using slot
   reader methods.  The actual values are computed on demand in methods
   defined on `slot-unbound'."))

(defmethod slot-unbound (class
			 (message basic-message)
			 (slot-name (eql 'argument-tail)))
  (declare (ignore class))
  (let ((seq 0))
    (setf (slot-value message 'argument-tail)
	  (mapcar (lambda (arg)
		    (if (or (eq arg :ellipsis) (argument-name arg)) arg
			(make-argument (make-instance 'temporary-argument
						      :tag (prog1 seq
							     (incf seq)))
				       (argument-type arg))))
		  (c-function-arguments (sod-message-type message))))))

(defmethod slot-unbound (class
			 (message basic-message)
			 (slot-name (eql 'no-varargs-tail)))
  (declare (ignore class))
  (setf (slot-value message 'no-varargs-tail)
	(mapcar (lambda (arg)
		  (if (eq arg :ellipsis)
		      (make-argument *sod-ap* (c-type va-list))
		      arg))
		(sod-message-argument-tail message))))

(defmethod sod-message-method-class
    ((message basic-message) (class sod-class) pset)
  (let ((role (get-property pset :role :keyword nil)))
    (case role
      ((:before :after) 'daemon-direct-method)
      (:around 'delegating-direct-method)
      ((nil) (error "How odd: a primary method slipped through the net"))
      (t (error "Unknown method role ~A" role)))))

(export 'simple-message)
(defclass simple-message (basic-message)
  ()
  (:documentation
   "Base class for messages with `simple' method combinations.

   A simple method combination is one which has only one method role other
   than the `before', `after' and `around' methods provided by
   `basic-message'.  We call these `primary' methods, and the programmer
   designates them by not specifying an explicit role.

   If the programmer doesn't define any primary methods then the effective
   method is null -- i.e., the method entry pointer shows up as a null
   pointer."))

(defmethod sod-message-method-class
    ((message simple-message) (class sod-class) pset)
  (if (get-property pset :role :keyword nil)
      (call-next-method)
      (primary-method-class message)))

(defmethod primary-method-class ((message simple-message))
  'basic-direct-method)

;;;--------------------------------------------------------------------------
;;; Direct method classes.

(export 'basic-direct-method)
(defclass basic-direct-method (sod-method)
  ((role :initarg :role :type symbol :reader sod-method-role)
   (function-type :type c-function-type :reader sod-method-function-type))
  (:documentation
   "Base class for built-in direct method classes.

   Provides the basic functionality for the built-in direct-method classes.
   This is a separate class so that `special effect' methods can avoid
   inheriting its default behaviour and slots.

   A basic method can be assigned a `role', which may be set either as an
   initarg or using the `:role' property.  Roles are used for method
   categorization.

   The function type protocol is implemented on `basic-direct-method' using
   slot reader methods.  The actual values are computed on demand in methods
   defined on `slot-unbound'."))

(defmethod shared-initialize :after
    ((method basic-direct-method) slot-names &key pset)
  (declare (ignore slot-names))
  (default-slot (method 'role) (get-property pset :role :keyword nil)))

(defmethod slot-unbound
    (class (method basic-direct-method) (slot-name (eql 'function-type)))
  (declare (ignore class))
  (let ((type (sod-method-type method)))
    (setf (slot-value method 'function-type)
	  (c-type (fun (lisp (c-type-subtype type))
		       ("me" (* (class (sod-method-class method))))
		       . (c-function-arguments type))))))

(defmethod sod-method-function-name ((method basic-direct-method))
  (with-slots ((class %class) role message) method
    (format nil "~A__~@[~(~A~)_~]method_~A__~A" class role
	    (sod-class-nickname (sod-message-class message))
	    (sod-message-name message))))

(export 'daemon-direct-method)
(defclass daemon-direct-method (basic-direct-method)
  ()
  (:documentation
   "A daemon direct method is invoked for side effects and cannot override.

   This is the direct method class for `before' and `after' methods, which
   cannot choose to override the remaining methods and are not involved in
   the computation of the final result.

   In C terms, a daemon method must return `void', and is not passed a
   `next_method' pointer."))

(defmethod check-method-type ((method daemon-direct-method)
			      (message sod-message)
			      (type c-function-type))
  (with-slots ((msgtype %type)) message
    (unless (c-type-equal-p (c-type-subtype type) (c-type void))
      (error "Method return type ~A must be `void'" (c-type-subtype type)))
    (unless (argument-lists-compatible-p (c-function-arguments msgtype)
					 (c-function-arguments type))
      (error "Method arguments ~A don't match message ~A" type msgtype))))

(export 'delegating-direct-method)
(defclass delegating-direct-method (basic-direct-method)
  ((next-method-type :type c-function-type
		     :reader sod-method-next-method-type))
  (:documentation
   "A delegating direct method can choose to override other methods.

   This is the direct method class for `around' and standard-method-
   combination primary methods, which are given the choice of computing the
   entire method's result or delegating to (usually) less-specific methods.

   In C terms, a delegating method is passed a `next_method' pointer so that
   it can delegate part of its behaviour.  (A delegating direct method for a
   varargs message is also given an additional `va_list' argument,
   conventionally named `sod__ap_master', which it is expected to pass on to
   its `next_method' function if necessary.)

   The function type protocol is implemented on `delegating-direct-method'
   using slot reader methods.  The actual values are computed on demand in
   methods defined on `slot-unbound'."))

(defmethod slot-unbound (class
			 (method delegating-direct-method)
			 (slot-name (eql 'next-method-type)))
  (declare (ignore class))
  (let* ((message (sod-method-message method))
	 (return-type (c-type-subtype (sod-message-type message)))
	 (msgargs (sod-message-argument-tail message))
	 (arguments (if (varargs-message-p message)
			(cons (make-argument *sod-master-ap*
					     (c-type va-list))
			      (butlast msgargs))
			msgargs)))
    (setf (slot-value method 'next-method-type)
	  (c-type (fun (lisp return-type)
		       ("me" (* (class (sod-method-class method))))
		       . arguments)))))

(defmethod slot-unbound (class
			 (method delegating-direct-method)
			 (slot-name (eql 'function-type)))
  (declare (ignore class))
  (let* ((message (sod-method-message method))
	 (type (sod-method-type method))
	 (method-args (c-function-arguments type)))
    (setf (slot-value method 'function-type)
	  (c-type (fun (lisp (c-type-subtype type))
		       ("me" (* (class (sod-method-class method))))
		       ("next_method" (* (lisp (commentify-function-type
						(sod-method-next-method-type
						 method)))))
		       .
		       (if (varargs-message-p message)
			   (cons (make-argument *sod-master-ap*
						(c-type va-list))
				 method-args)
			   method-args))))))

;;;--------------------------------------------------------------------------
;;; Effective method classes.

(export 'basic-effective-method)
(defclass basic-effective-method (effective-method)
  ((around-methods :initarg :around-methods :initform nil
		   :type list :reader effective-method-around-methods)
   (before-methods :initarg :before-methods :initform nil
		   :type list :reader effective-method-before-methods)
   (after-methods :initarg :after-methods :initform nil
		  :type list :reader effective-method-after-methods)
   (basic-argument-names :type list
			 :reader effective-method-basic-argument-names)
   (functions :type list :reader effective-method-functions))
  (:documentation
   "Base class for built-in effective method classes.

   This class maintains lists of the applicable `before', `after' and
   `around' methods and provides behaviour for invoking these methods
   correctly.

   The argument names protocol is implemented on `basic-effective-method'
   using a slot reader method.  The actual values are computed on demand in
   methods defined on `slot-unbound'."))

(defmethod slot-unbound (class
			 (method basic-effective-method)
			 (slot-name (eql 'basic-argument-names)))
  (declare (ignore class))
  (let ((message (effective-method-message method)))
    (setf (slot-value method 'basic-argument-names)
	  (mapcar #'argument-name
		  (sod-message-no-varargs-tail message)))))

(defmethod effective-method-function-name ((method effective-method))
  (let* ((class (effective-method-class method))
	 (message (effective-method-message method))
	 (message-class (sod-message-class message)))
    (format nil "~A__emethod_~A__~A"
	    class
	    (sod-class-nickname message-class)
	    (sod-message-name message))))

(defmethod slot-unbound
    (class (method basic-effective-method) (slot-name (eql 'functions)))
  (declare (ignore class))
  (setf (slot-value method 'functions)
	(compute-method-entry-functions method)))

(export 'simple-effective-method)
(defclass simple-effective-method (basic-effective-method)
  ((primary-methods :initarg :primary-methods :initform nil
		    :type list :reader effective-method-primary-methods))
  (:documentation
   "Effective method counterpart to `simple-message'."))

(defmethod shared-initialize :after
    ((method simple-effective-method) slot-names &key direct-methods)
  (declare (ignore slot-names))
  (categorize (method direct-methods :bind ((role (sod-method-role method))))
      ((primary (null role))
       (before (eq role :before))
       (after (eq role :after))
       (around (eq role :around)))
    (with-slots (primary-methods before-methods after-methods around-methods)
	method
      (setf primary-methods primary
	    before-methods before
	    after-methods (reverse after)
	    around-methods around))))

;;;--------------------------------------------------------------------------
;;; Code generation.

(defmethod shared-initialize :after
    ((codegen method-codegen) slot-names &key)
  (declare (ignore slot-names))
  (with-slots (message target) codegen
    (setf target
	  (if (eq (c-type-subtype (sod-message-type message)) (c-type void))
	      :void
	      :return))))

;;;--------------------------------------------------------------------------
;;; Invoking direct methods.

(export 'basic-effective-method-body)
(defun basic-effective-method-body (codegen target method body)
  "Build the common method-invocation structure.

   Writes to CODEGEN some basic method-invocation instructions.  It invokes
   the `around' methods, from most- to least-specific.  If they all delegate,
   then the `before' methods are run, most-specific first; next, the
   instructions generated by BODY (invoked with a target argument); then, the
   `after' methods are run, least-specific first; and, finally, the value
   delivered by the BODY is returned to the `around' methods.  The result
   returned by the outermost `around' method -- or, if there are none,
   delivered by the BODY -- is finally delivered to the TARGET."

  (with-slots (message (class %class)
	       before-methods after-methods around-methods)
      method
    (let* ((message-type (sod-message-type message))
	   (return-type (c-type-subtype message-type))
	   (basic-tail (effective-method-basic-argument-names method)))
      (flet ((method-kernel (target)
	       (dolist (before before-methods)
		 (invoke-method codegen :void basic-tail before))
	       (if (null after-methods)
		   (funcall body target)
		   (convert-stmts codegen target return-type
				  (lambda (target)
				    (funcall body target)
				    (dolist (after (reverse after-methods))
				      (invoke-method codegen :void
						     basic-tail after)))))))
	(invoke-delegation-chain codegen target basic-tail
				 around-methods #'method-kernel)))))

;;;--------------------------------------------------------------------------
;;; Method entry points.

(defparameter *method-entry-inline-threshold* 200
  "Threshold below which effective method bodies are inlined into entries.

   After the effective method body has been computed, we calculate its
   metric, multiply by the number of entries we need to generate, and compare
   it with this threshold.  If the metric is below the threshold then we
   fold the method body into the entry functions; otherwise we split the
   effective method out into its own function.")

(defmethod method-entry-function-name
    ((method effective-method) (chain-head sod-class) role)
  (let* ((class (effective-method-class method))
	 (message (effective-method-message method))
	 (message-class (sod-message-class message)))
    (if (or (not (slot-boundp method 'functions))
	    (slot-value method 'functions))
	(format nil "~A__mentry~@[__~(~A~)~]_~A__~A__chain_~A"
		class role
		(sod-class-nickname message-class)
		(sod-message-name message)
		(sod-class-nickname chain-head))
	0)))

(defmethod method-entry-slot-name ((entry method-entry))
  (let* ((method (method-entry-effective-method entry))
	 (message (effective-method-message method))
	 (name (sod-message-name message))
	 (role (method-entry-role entry)))
    (method-entry-slot-name-by-role entry role name)))

(defmethod method-entry-function-type ((entry method-entry))
  (let* ((method (method-entry-effective-method entry))
	 (message (effective-method-message method))
	 (type (sod-message-type message))
	 (tail (ecase (method-entry-role entry)
		 ((nil) (sod-message-argument-tail message))
		 (:valist (sod-message-no-varargs-tail message)))))
    (c-type (fun (lisp (c-type-subtype type))
		 ("me" (* (class (method-entry-chain-tail entry))))
		 . tail))))

(defmethod make-method-entries ((method basic-effective-method)
				(chain-head sod-class)
				(chain-tail sod-class))
  (let ((entries nil)
	(message (effective-method-message method)))
    (flet ((make (role)
	     (push (make-instance 'method-entry
				  :method method :role role
				  :chain-head chain-head
				  :chain-tail chain-tail)
		   entries)))
      (when (varargs-message-p message) (make :valist))
      (make nil)
      entries)))

(defmethod compute-method-entry-functions ((method basic-effective-method))

  ;; OK, there's quite a lot of this, so hold tight.
  ;;
  ;; The first thing we need to do is find all of the related objects.  This
  ;; is a bit verbose but fairly straightforward.
  ;;
  ;; Next, we generate the effective method body -- using `compute-effective-
  ;; method-body' of all things.  This gives us the declarations and body for
  ;; an effective method function, but we don't have an actual function yet.
  ;;
  ;; Now we look at the chains which are actually going to need a method
  ;; entry: only those chains whose tail (most specific) class is a
  ;; superclass of the class which defined the message need an entry.  We
  ;; build a list of these tail classes.
  ;;
  ;; Having done this, we decide whether it's better to generate a standalone
  ;; effective-method function and call it from each of the method entries,
  ;; or to inline the effective method body into each of the entries.
  ;;
  ;; Most of the complexity here comes from (a) dealing with the two
  ;; different strategies for constructing method entry functions and (b)
  ;; (unsurprisingly) the mess involved with dealing with varargs messages.

  (let* ((message (effective-method-message method))
	 (class (effective-method-class method))
	 (message-class (sod-message-class message))
	 (return-type (c-type-subtype (sod-message-type message)))
	 (codegen (make-instance 'method-codegen
				 :message message
				 :class class
				 :method method))

	 ;; Method entry details.
	 (chain-tails (remove-if-not (lambda (super)
				       (sod-subclass-p super message-class))
				     (mapcar #'car
					     (sod-class-chains class))))
	 (n-entries (length chain-tails))
	 (raw-entry-args (sod-message-argument-tail message))
	 (entry-args (sod-message-no-varargs-tail message))
	 (parm-n (let ((tail (last raw-entry-args 2)))
		   (and tail (eq (cadr tail) :ellipsis) (car tail))))
	 (entry-target (codegen-target codegen))

	 ;; Effective method function details.
	 (emf-name (effective-method-function-name method))
	 (ilayout-type (c-type (* (struct (ilayout-struct-tag class)))))
	 (emf-arg-tail (sod-message-no-varargs-tail message))
	 (emf-type (c-type (fun (lisp return-type)
				("sod__obj" (lisp ilayout-type))
				. emf-arg-tail))))

    (flet ((setup-entry (tail)
	     (let ((head (sod-class-chain-head tail)))
	       (codegen-push codegen)
	       (ensure-var codegen "sod__obj" ilayout-type
			   (make-convert-to-ilayout-inst class
							 head "me"))))
	   (finish-entry (tail)
	     (let* ((head (sod-class-chain-head tail))
		    (role (if parm-n :valist nil))
		    (name (method-entry-function-name method head role))
		    (type (c-type (fun (lisp return-type)
				       ("me" (* (class tail)))
				       . entry-args))))
	       (codegen-pop-function codegen name type)

	       ;; If this is a varargs method then we've made the
	       ;; `:valist' role.  Also make the `nil' role.
	       (when parm-n
		 (let ((call (make-call-inst name
					     (cons "me"
						   (mapcar #'argument-name
							   entry-args))))
		       (main (method-entry-function-name method head nil))
		       (main-type (c-type (fun (lisp return-type)
					       ("me" (* (class tail)))
					       . raw-entry-args))))
		   (codegen-push codegen)
		   (ensure-var codegen *sod-ap* (c-type va-list))
		   (emit-inst codegen
			      (make-va-start-inst *sod-ap*
						  (argument-name parm-n)))
		   (convert-stmts codegen entry-target return-type
				  (lambda (target)
				    (deliver-expr codegen target call)))
		   (emit-inst codegen (make-va-end-inst *sod-ap*))
		   (codegen-pop-function codegen main main-type))))))

      ;; Generate the method body.  We'll work out what to do with it later.
      (codegen-push codegen)
      (let* ((result (if (eq return-type c-type-void) nil
			 (temporary-var codegen return-type)))
	     (emf-target (or result :void)))
	(compute-effective-method-body method codegen emf-target)
	(multiple-value-bind (vars insts) (codegen-pop codegen)
	  (cond ((or (= n-entries 1)
		     (<= (* n-entries (reduce #'+ insts :key #'inst-metric))
			 *method-entry-inline-threshold*))

		 ;; The effective method body is simple -- or there's only
		 ;; one of them.  We'll inline the method body into the entry
		 ;; functions.
		 (dolist (tail chain-tails)
		   (setup-entry tail)
		   (dolist (var vars)
		     (if (typep var 'var-inst)
			 (ensure-var codegen (inst-name var)
				     (inst-type var) (inst-init var))
			 (emit-decl codegen var)))
		   (emit-insts codegen insts)
		   (deliver-expr codegen entry-target result)
		   (finish-entry tail)))

		(t

		 ;; The effective method body is complicated and we'd need
		 ;; more than one copy.  We'll generate an effective method
		 ;; function and call it a lot.
		 (codegen-build-function codegen emf-name emf-type vars
		  (nconc insts (and result
				    (list (make-return-inst result)))))

		 (let ((call (make-call-inst emf-name
			      (cons "sod__obj" (mapcar #'argument-name
						       emf-arg-tail)))))
		   (dolist (tail chain-tails)
		     (setup-entry tail)
		     (deliver-expr codegen entry-target call)
		     (finish-entry tail)))))))

      (codegen-functions codegen))))

(defmethod compute-method-entry-functions
    ((method simple-effective-method))
  (if (effective-method-primary-methods method)
      (call-next-method)
      nil))

(defmethod compute-effective-method-body
    ((method simple-effective-method) codegen target)
  (basic-effective-method-body codegen target method
			       (lambda (target)
				 (simple-method-body method
						     codegen
						     target))))

;;;--------------------------------------------------------------------------
;;; Standard method combination.

(export 'standard-message)
(defclass standard-message (simple-message)
  ()
  (:documentation
   "Message class for standard method combinations.

   Standard method combination is a simple method combination where the
   primary methods are invoked as a delegation chain, from most- to
   least-specific."))

(export 'standard-effective-method)
(defclass standard-effective-method (simple-effective-method) ()
  (:documentation "Effective method counterpart to `standard-message'."))

(defmethod primary-method-class ((message standard-message))
  'delegating-direct-method)

(defmethod message-effective-method-class ((message standard-message))
  'standard-effective-method)

(defmethod simple-method-body
    ((method standard-effective-method) codegen target)
  (invoke-delegation-chain codegen
			   target
			   (effective-method-basic-argument-names method)
			   (effective-method-primary-methods method)
			   nil))

;;;----- That's all, folks --------------------------------------------------