#lang racket

(provide (all-defined-out)) ; for testing module

(require racket/draw)

; a Grid is a list of lines. All lines in a grid must be specified as moving left to right, top to bottom ("to" coordinate higher than "from" coordinate")

; represents a point in 2d space.
(struct point (x y) #:transparent)

; represents a line drawn from one point to another and which player drew it.
(struct line (from to player) #:transparent)

; width and height of the playing grid.
(define GRID-WIDTH 6)
(define GRID-HEIGHT 6)

; size of one grid position in pixels
(define GRID-SCALE 16)

; image representing the empty grid
(define EMPTY-GRID
  (let* ([bitmap (make-bitmap (* GRID-WIDTH GRID-SCALE) (* GRID-HEIGHT GRID-SCALE))]
         [dc (new bitmap-dc% [bitmap bitmap])])
    (send dc set-brush "black" 'solid)
    (for ([x (in-range GRID-WIDTH)])
      (for ([y (in-range GRID-HEIGHT)])
        (send dc draw-ellipse (* x GRID-SCALE) (* y GRID-SCALE) (/ GRID-SCALE 2) (/ GRID-SCALE 2))))
    bitmap))

; Grid that contains all possible lines filled. Used for filtering valid moves. This is an ugly way, but i can't think of a better one right now.
(define ALL-LINES (flatten
                    (for/list ([x (in-range GRID-WIDTH)])
                      (for/list ([y (in-range GRID-HEIGHT)])
                        (list
                         (if (< x (- GRID-WIDTH 1)) (line (point x y) (point (+ x 1) y) 1) '())
                         (if (< y (- GRID-HEIGHT 1)) (line (point x y) (point x (+ y 1)) 1) '()))))))

; Line Line -> Bool
; tests if two lines are in the same position
(define (same-position? l1 l2)
  (or
   (and
    (equal? (line-from l1) (line-from l2))
    (equal? (line-to l1) (line-to l2)))
   (and
    (equal? (line-to l1) (line-from l2))
    (equal? (line-from l1) (line-to l2)))))

; Point Point -> Point
; adds two points together.
(define (point+ p1 p2)
  (point (+ (point-x p1) (point-x p2)) (+ (point-y p1) (point-y p2))))

; Grid -> List of Lines
; returns all valid moves on a grid.
; TODO optimise. This "filtering what is invalid out of all possible lines" method sucks.
; TODO write more tests
(define (valid-moves g)
    (filter (lambda (move) (valid-move? move g)) ALL-LINES))

; Point Grid -> Number
; given a point that is the top-left corner of a square on the grid, returns the amount of edges surrounding that square.
(define (count-square p g)
  ; explanation:
  ; for every item in the grid (g), test it against every edge of the box for equality. if any are equal, it matches.
  ; then only those that match are kept and this list is checked for length to determine the matching lines.
  (length
   (filter (lambda (item)
             (member #t
                     (for/list ([x (list (point 0 0) (point 0 1) (point 1 0) (point 0 0))]
                                [y (list (point 0 1) (point 1 1) (point 1 1) (point 1 0))]) 
                       (same-position? item (line (point+ x p) (point+ y p) 0))))) g))) ; for every position in the square, check if there's a line there

; Line -> Bool
; returns #t if the line is forwards (with forwards being moving right and down, higher end coord than start)
(define (forwards? line)
  (and
   (>= (point-x (line-to line)) (point-x (line-from line)))
   (>= (point-y (line-to line)) (point-y (line-from line)))))

; Line -> Bool
; returns #t if a line is valid in terms of length (only moving one point in one direction)
(define (valid-length? line)
  (= 1
     (+ (abs (- (point-x (line-from line)) (point-x (line-to line))))
        (abs (- (point-y (line-from line)) (point-y (line-to line)))))))

; Point -> Bool
; returns #t if a point is out of bounds (off the edge of the grid)
(define (out-of-bounds? p)
  (or
   (> 0 (point-x p))
   (> 0 (point-y p))
   (< (- GRID-WIDTH 1) (point-x p))
   (< (- GRID-WIDTH 1) (point-y p))))

; Line Grid -> Bool
; returns #t if adding the given move to the grid is valid.
(define (valid-move? line grid)
  (and
   (empty? (filter (lambda (l) (same-position? l line)) grid)) ; line doesn't already exist on board
   (valid-length? line)
   (forwards? line)
   (and
    (not (out-of-bounds? (line-from line)))
    (not (out-of-bounds? (line-to line))))))

; Grid -> Image
; renders grid to an image for showing humans the game.
(define (render-grid grid)
  (let* ([bitmap (make-bitmap (* GRID-WIDTH GRID-SCALE) (* GRID-HEIGHT GRID-SCALE))]
         [dc (new bitmap-dc% [bitmap bitmap])])
    (for ([l grid])
      (cond
        [(= (line-player l) 0) (send dc set-pen "red" 4 'solid)] ; player 1 draws in red
        [(= (line-player l) 1) (send dc set-pen "blue" 4 'solid)]) ; player 2 draws in blue        
      (send dc draw-line
            (+ 4 (* GRID-SCALE (point-x (line-from l))))
            (+ 4 (* GRID-SCALE (point-y (line-from l))))
            (+ 4 (* GRID-SCALE (point-x (line-to l))))
            (+ 4 (* GRID-SCALE (point-y (line-to l)))))) ; draw the line
      
    (send dc draw-bitmap EMPTY-GRID 0 0) ; overlay dot grid 
    bitmap))