<?php

namespace qrCode;

class FrameFiller
{
    public array $frame;
    private int $width;
    private int $x;
    private int $y;
    private int $dir;
    private int $bit;

    public function __construct($width, $frame)
    {
        $this->width = $width;
        $this->frame = $frame;
        $this->x = $width - 1;
        $this->y = $width - 1;
        $this->dir = -1;
        $this->bit = -1;
    }

    public function setFrameAt($at, $val)
    {
        $this->frame[$at['y']][$at['x']] = chr($val);
    }

    public function next()
    {
        do {
            if ($this->bit == -1) {
                $this->bit = 0;
                return ['x' => $this->x, 'y' => $this->y];
            }
            $x = $this->x;
            $y = $this->y;
            $w = $this->width;
            if ($this->bit == 0) {
                $x--;
                $this->bit++;
            } else {
                $x++;
                $y += $this->dir;
                $this->bit--;
            }
            if ($this->dir < 0) {
                if ($y < 0) {
                    $y = 0;
                    $x -= 2;
                    $this->dir = 1;
                    if ($x == 6) {
                        $x--;
                        $y = 9;
                    }
                }
            } else {
                if ($y == $w) {
                    $y = $w - 1;
                    $x -= 2;
                    $this->dir = -1;
                    if ($x == 6) {
                        $x--;
                        $y -= 8;
                    }
                }
            }
            if ($x < 0 || $y < 0) {
                return null;
            }
            $this->x = $x;
            $this->y = $y;
        } while (ord($this->frame[$y][$x]) & 0x80);
        return ['x' => $x, 'y' => $y];
    }
}
