(import (srfi :43)) ; vector extensions

; returns a list of numbers parsed from the first line of the file,
; separated by commas
(define (read-comma-separated-numbers file)
  (let loop [(draws '()) (n 0)]
    (let [(c (get-char file))]
      (cond
	[(char=? c #\,) (loop (cons n draws) 0)]
	[(char-whitespace? c) (reverse (cons n draws))]
	[else (loop draws (+ (* n 10) (string->number (string c))))]))))

; returns numbers 0 to 9 from ascii character
(define (char->number c)
  (- (char->integer c) 48)) ; 48 is ASCII's number zero

(define-record-type matrix (fields width height data))

; builds a matrix record from the given 2D vector
; vectors inside data vector are expected to all be the same length
(define (matrix-from-data data)
  (make-matrix
    (vector-length (vector-ref data 0))
    (vector-length data)
    data))

; returns value at x,y coordinates in matrix
; if coordinate is out of bounds, returns default
(define (matrix-get matrix x y default)
  (if (or (< x 0)
	  (< y 0)
	  (>= x (matrix-width matrix))
	  (>= y (matrix-height matrix)))
    default
    (vector-ref (vector-ref (matrix-data matrix) y) x)))

; set value at x,y in matrix with given one
; if coordinate is out of bounds, nothing happens
(define (matrix-set! matrix x y value)
  (when (and (>= x 0)
	     (>= y 0)
	     (< x (matrix-width matrix))
	     (< y (matrix-height matrix)))
    (vector-set! (vector-ref (matrix-data matrix) y) x value)))

(define (matrix-print matrix)
  (let y-loop [(y 0)]
    (printf "~a~%" (vector-ref (matrix-data matrix) y))
    (when (< y (- (matrix-height matrix) 1))
      (y-loop (+ y 1)))))

; parse 0-9 numerical data from file and return a matrix
(define (load-matrix file)
  (let y-loop [(heightmap '())]
    (let x-loop [(line '())]
      (let [(c (get-char file))]
	(cond
	  [(eof-object? c)
	   (matrix-from-data (reverse-list->vector heightmap))]
	  [(char-whitespace? c)
	   (y-loop (cons (reverse-list->vector line) heightmap))]
	  [(char-numeric? c)
	   (x-loop (cons (char->number c) line))])))))