#!/local/gauche/bin/gosh

(use srfi-1)
(use srfi-13)

(use gauche.uvector)

(define (string->dim s)
  (let ((x (string->number s)))
    (cond 
      ((<= x 0) (error "Dimension less than or equal to zero:" x))
      ((> x 5000) (error "Dimension suspiciously large:" x))
    )
    x
  )
)

(define (get-width-height hdr-line)
  (let ((dim-list (map string->dim (string-tokenize hdr-line))))
    (values (first dim-list) (second dim-list))
  )
)

(define (traverse-height maxval img-data y height x width)
  (if (< y height)
    (let ((pos (* (+ (* y width) x) 3)))
      (if (and (= (u16vector-ref img-data pos) maxval)
               (= (u16vector-ref img-data (+ pos 1)) 0)
               (= (u16vector-ref img-data (+ pos 2)) 0))
        (print x " " y)
      )
      (traverse-height maxval img-data (+ y 1) height x width)
    )
  )
)

(define (traverse-width maxval img-data x width height)
  (if (< x width)
    (begin
      (traverse-height maxval img-data 0 height x width)
      (traverse-width maxval img-data (+ x 1) width height)
    )
  )
) 

(define (find-red maxval img-data width height)
  (let ((rv (read-block! img-data)))
    (if (= rv (* width height 3))
      (traverse-width maxval img-data 0 width height)
      (error "Should've read " (* width height 3) " but read " rv)
    )
  )
)

(define (main args)
  (if (not (string=? (read-line) "P6")) (error "Incorrect signature"))
  (let ((dim-line (read-line))
        (maxval   (string->number (read-line))))
    (receive (width height) (get-width-height dim-line)
      (find-red
        maxval
        (cond
          ((= maxval 65535) (make-u16vector (* width height 3)))
          ((= maxval 255) (make-u8vector (* width height 3)))
          (else (error "Don't know how to deal with maxval of " maxval))
        )
        width height)
    )
  )
)