#!/usr/bin/csi -s

(define MAX_ITERATIONS 27)

(define OUTPUT_RES_X 3.5)

(define OUTPUT_RES_Y 2)

(define OUTPUT_OFFSET_X -2.5)

(define OUTPUT_OFFSET_Y -1)

(define RESOLUTION_X 150)

(define RESOLUTION_Y 60)

(define (for start end fn)

    (if (>= start end)

        #t

        (begin

            (fn start)

            (for (+ 1 start) end fn))))

; turn # interactions into a char for display

(define (show val) 

    (if (<= val 26)

        (integer->char (+ val 

                          -1

                          (char->integer #\A)))

        " "))

; Calculate how many iterations are required.

(define (calc x y) 

    (let (

      (xi (+ OUTPUT_OFFSET_X (* OUTPUT_RES_X (/ x RESOLUTION_X))))

      (yi (+ OUTPUT_OFFSET_Y (* OUTPUT_RES_Y (/ y RESOLUTION_Y)))))

    (define (calc_inner x y iters) 

        (if (or (>= iters MAX_ITERATIONS)

                (< 4 (+ (* x x) (* y y))))

            iters

            (let (

                  (xnext (+ xi (* x x) (* -1 y y)))

                  (ynext (+ yi (* x y 2))))

                (calc_inner xnext ynext (+ 1 iters)))))

    (calc_inner 0 0 0)))

(define (draw_row y width)

    (for 0 width (lambda (x)

        (display (show (calc x y))))))

(define (draw_window width height) 

    (for 0 height (lambda (y)

        (begin

            (draw_row y width)

            (display "\n")))))

(draw_window RESOLUTION_X RESOLUTION_Y)