#lang racket/base

(require 
  racket/promise racket/future racket/include racket/set racket/class racket/draw
  (rename-in racket/contract (-> ->>))
  ffi/unsafe ffi/vector)

(define stype (system-type))

(define gl-lib 
  (delay 
    (case stype
      [(windows) (ffi-lib "opengl32")]
      [(macosx) (ffi-lib "/System/Library/Frameworks/OpenGL.framework/Versions/A/Libraries/libGL")]
      [else (ffi-lib "libGL" '("1" ""))])))

(define windows? (eq? 'windows stype))

(define win32?
  (and windows?
       (equal? "win32\\i386" (path->string (system-library-subpath #f)))))

(define-syntax _fun*
  (syntax-rules ()
    [(_fun* x ...)
     (if win32? (_fun #:abi 'stdcall x ...) (_fun x ...))]))


;; The getProcAddress procedure dynamically loads a GL procedure.
(define getProcAddress 
  (delay 
    (if windows?
      (get-ffi-obj "wglGetProcAddress" (force gl-lib) (_fun* _string -> _pointer)
                   (lambda () (lambda (x) #f)))
      ; According to the Linux ABI, the correct entry point is glXGetProcAddressARB.
      ; But let's try the non-ARB version too.
      (get-ffi-obj "glXGetProcAddressARB" (force gl-lib) (_fun _string -> _pointer)
                   (lambda ()
                     (get-ffi-obj "glXGetProcAddress" (force gl-lib) (_fun _string -> _pointer)
                                  (lambda () (lambda (x) #f))))))))

(define (make-undefined-procedure name)
;  (printf "OpenGL procedure not available: ~a~%" name)
  (lambda args
    (error "OpenGL procedure not available:" name)))

(define (lookup-gl-procedure name type)
  (get-ffi-obj name (force gl-lib) type
               (lambda ()
                 (let ((ptr ((force getProcAddress) (symbol->string name))))
                   (if ptr
                     (begin
;                       (printf "Loaded dynamically: ~a~%" name)
                       (function-ptr ptr type))
                     (make-undefined-procedure name))))))

; Load everything lazily.
; This speeds things up in general and is essential on Windows
; where GL procedures can only be looked up once a GL context is bound.
(define (create-gl-procedure name arity type checker)
  (let ((proc (delay (lookup-gl-procedure name type))))
    (procedure-rename
      (procedure-reduce-arity
        (lambda args 
          (begin0
            (apply (force proc) args)
            (checker name)))
        arity)
      name)))

(define-syntax define-gl
  (syntax-rules ()
   ((_ name arity (type ...) contract checker)
    (begin
      (define name (create-gl-procedure 'name arity (_fun* type ...) checker))
      (provide/contract (name contract))))))

(define-syntax define-enum
  (syntax-rules ()
   ((_ name (constants ...))
    (begin
      (define name (let ((s (seteqv constants ...)))
                     (lambda (v) (set-member? s v))))
      (provide/contract (name (->> any/c boolean?)))))))

(define-syntax define-bitfield
  (syntax-rules ()
   ((_ name (constants ...))
    (begin
      (define name (let ((m (bitwise-ior constants ...)))
                     (lambda (v) (= v (bitwise-and v m)))))
      (provide/contract (name (->> any/c boolean?)))))))

; Check GL result
(define (check-gl-error name)
  (unless between-begin-end
    (let ((err (glGetError)))
      (unless (zero? err)
        (let ((msg (hash-ref error-messages err
                             (lambda () (format "Error code ~s." err)))))
          (error (format "OpenGL error in procedure ~a: ~a" name msg)))))))

(define (check-gl-error-begin name)
  (set! between-begin-end #t))

(define (check-gl-error-end name)
  (set! between-begin-end #f)
  (check-gl-error name))

(include "generated/gl_specs.inc")

(define (split-spaces str)
  (regexp-split #px"\\s+" str))

;; Query information in a convenient way.
;(provide gl-version gl-extensions gl-has-extension?)
(provide/contract 
  (gl-version (->> (listof exact-integer?)))
  (gl-extensions (->> set-eq?))
  (gl-has-extension? (->> symbol? boolean?))
  (gl-version-at-least? (->> (listof exact-integer?) boolean?)))

(define gl-version
  (let ((version 
          (delay 
            (map string->number
                 (regexp-split #px"\\."
                               (car (split-spaces (glGetString GL_VERSION))))))))
    (lambda () (force version))))

(define gl-extensions
  (let ((extensions (delay
                      (for/seteq ((ext (in-list (split-spaces (glGetString GL_EXTENSIONS)))))
                                 (string->symbol ext)))))
    (lambda () (force extensions))))

(define (gl-has-extension? ext)
  (set-member? (gl-extensions) ext))

(define (version>= v1 v2)
  (cond
    ((null? v2) #t)
    ((null? v1) #f)
    (else
      (let ((n1 (car v1))
            (n2 (car v2)))
        (cond 
          ((= n1 n2)
           (version>= (cdr v1) (cdr v2)))
          (else (> n1 n2)))))))

(define (gl-version-at-least? version)
  (version>= (gl-version) version))

; A "gl-vector" is any homogenous vector of a type which is used with the OpenGL API.
(provide/contract (gl-vector? (->> any/c boolean?)))

(define (gl-vector? obj)
  (or (bytes? obj) (s8vector? obj) (u16vector? obj) (s16vector? obj)
      (u32vector? obj) (s32vector? obj) (f32vector? obj) (f64vector? obj)))


;; Get the appropriate type enum for a Racket vector.
;; Useful for glVertexPointer and friends.
;; Also get length and cpointer in one operation.
(provide/contract 
  (gl-vector->type (->> gl-vector? exact-integer?))
  (gl-vector->cpointer (->> gl-vector? cpointer?))
  (gl-vector->length (->> gl-vector? exact-nonnegative-integer?))
  (gl-vector->type/cpointer (->> gl-vector? (values exact-integer? cpointer?)))
  (gl-vector->type/cpointer/length (->> gl-vector? (values exact-integer? cpointer? exact-nonnegative-integer?))))

(define (gl-vector->info vec)
  (cond
    ((bytes? vec) (values GL_UNSIGNED_BYTE values bytes-length))
    ((s8vector? vec) (values GL_BYTE s8vector->cpointer s8vector-length))
    ((u16vector? vec) (values GL_UNSIGNED_SHORT u16vector->cpointer u16vector-length))
    ((s16vector? vec) (values GL_SHORT s16vector->cpointer s16vector-length))
    ((u32vector? vec) (values GL_UNSIGNED_INT u32vector->cpointer u32vector-length))
    ((s32vector? vec) (values GL_INT s32vector->cpointer s32vector-length))
    ((f32vector? vec) (values GL_FLOAT f32vector->cpointer f32vector-length))
    ((f64vector? vec) (values GL_DOUBLE f64vector->cpointer f64vector-length))))


(define (gl-vector->type vec)
  (let-values (((type ->cpointer length) (gl-vector->info vec)))
              type))

(define (gl-vector->cpointer vec)
  (let-values (((type ->cpointer length) (gl-vector->info vec)))
              (->cpointer vec)))

(define (gl-vector->length vec)
  (let-values (((type ->cpointer length) (gl-vector->info vec)))
              (length vec)))

(define (gl-vector->type/cpointer vec)
  (let-values (((type ->cpointer length) (gl-vector->info vec)))
              (values type (->cpointer vec))))

(define (gl-vector->type/cpointer/length vec)
  (let-values (((type ->cpointer length) (gl-vector->info vec)))
              (values type (->cpointer vec) (length vec))))

(define error-messages (hasheqv
        GL_NO_ERROR "No error has been recorded."
        GL_INVALID_ENUM "An unacceptable value is specified for an enumerated argument."
        GL_INVALID_VALUE "A numeric  argument is out of range."
        GL_INVALID_OPERATION "The specified operation is not allowed in the current state."
        GL_STACK_OVERFLOW "This command would cause a stack overflow."
        GL_STACK_UNDERFLOW "This command would cause a stack underflow."
        GL_OUT_OF_MEMORY "There is not enough memory left to execute the command."))

(define between-begin-end #f)

;;; Utility functions for dealing with textures
(provide/contract 
  (bitmap->texture 
    (->* ((is-a?/c bitmap%))
         (#:mipmap any/c
          #:repeat (one-of/c 'none 'x 'y 'both))
         exact-nonnegative-integer?))

  (load-texture 
    (->* ((or/c path-string? input-port?))
         (#:mipmap any/c
          #:repeat (one-of/c 'none 'x 'y 'both))
         exact-nonnegative-integer?)))

;; Convert argb -> rgba, and convert to pre-multiplied alpha.
;; (Non-premultiplied alpha gives blending artifacts and is evil.)
;; Modern wisdom is not to convert to rgba but rather use
;; GL_BGRA with GL_UNSIGNED_INT_8_8_8_8_REV. But that turns out not
;; to work on some implementations, even ones which advertise
;; OpenGL 1.2 support. Great.
(define (argb->rgba! pixels)
  (for ((i (in-range (/ (bytes-length pixels) 4))))
       (let* ((offset (* 4 i))
              (alpha (bytes-ref pixels offset))
              (red (bytes-ref pixels (+ 1 offset)))
              (green (bytes-ref pixels (+ 2 offset)))
              (blue (bytes-ref pixels (+ 3 offset))))
         (bytes-set! pixels offset (quotient (* alpha red) 255))
         (bytes-set! pixels (+ 1 offset) (quotient (* alpha green) 255))
         (bytes-set! pixels (+ 2 offset) (quotient (* alpha blue) 255))
         (bytes-set! pixels (+ 3 offset) alpha))))


;; Convert a Racket bitmap into an OpenGL texture.
;; (with lots of default settings.)
(define (bitmap->texture bm #:mipmap (mipmap #t) #:repeat (repeat-mode 'none))
  (let* ((w (send bm get-width))
         (h (send bm get-height))
         (pixels (make-bytes (* w h 4)))
         (texture (u32vector-ref (glGenTextures 1) 0)))

    (define (load-texture-data)
      (glTexImage2D GL_TEXTURE_2D 0 GL_RGBA8 w h 0 GL_RGBA GL_UNSIGNED_BYTE pixels))

    (send bm get-argb-pixels 0 0 w h pixels)
    ;; massage data.
    (argb->rgba! pixels)
    
    (glBindTexture GL_TEXTURE_2D texture)
    (glTexParameteri GL_TEXTURE_2D GL_TEXTURE_WRAP_S 
                     (case repeat-mode ((x both) GL_REPEAT) (else GL_CLAMP)))
    (glTexParameteri GL_TEXTURE_2D GL_TEXTURE_WRAP_T 
                     (case repeat-mode ((y both) GL_REPEAT) (else GL_CLAMP)))
    (glTexParameteri GL_TEXTURE_2D GL_TEXTURE_MAG_FILTER GL_LINEAR)
    (cond 
      ;; modern mipmap generation method
      ((and mipmap (gl-version-at-least? '(3 0)))
       (glTexParameteri GL_TEXTURE_2D GL_TEXTURE_MIN_FILTER GL_LINEAR_MIPMAP_LINEAR)
       (load-texture-data)
       (glGenerateMipmap GL_TEXTURE_2D))

      ;; old mipmap generation method
      ((and mipmap (gl-version-at-least? '(1 4)))
       (glTexParameteri GL_TEXTURE_2D GL_TEXTURE_MIN_FILTER GL_LINEAR_MIPMAP_LINEAR)
       (glTexParameteri GL_TEXTURE_2D GL_GENERATE_MIPMAP GL_TRUE)
       (load-texture-data))

      (else
        ; fallback to not using mipmaps
        ; this seems more useful than erroring
        (glTexParameteri GL_TEXTURE_2D GL_TEXTURE_MIN_FILTER GL_LINEAR)
        (load-texture-data)))

    texture))

;; Directly load a file from disk as texture.
(define (load-texture filename #:mipmap (mipmap #t) #:repeat (repeat-mode 'none))
  (bitmap->texture (read-bitmap filename) #:mipmap mipmap #:repeat repeat-mode))