<?php
$input = file('input', FILE_IGNORE_NEW_LINES | FILE_SKIP_EMPTY_LINES);
$input = array_map(fn($line) => explode(',', str_replace(' -> ', ',', $line)), $input);

$map = array_fill(0, 1000, array_fill(0, 1000, 0));

foreach ($input as $coordinates) {
    if ($coordinates[0] === $coordinates[2]) {
        $start = min([$coordinates[1], $coordinates[3]]);
        $end = max([$coordinates[1], $coordinates[3]]);
        for ($i = $start; $i <= $end; $i++) {
            $map[$coordinates[0]][$i]++;
        }
    }
    if ($coordinates[1] === $coordinates[3]) {
        $start = min([$coordinates[0], $coordinates[2]]);
        $end = max([$coordinates[0], $coordinates[2]]);
        for ($i = $start; $i <= $end; $i++) {
            $map[$i][$coordinates[1]]++;
        }
    }
    if ($coordinates[0] !== $coordinates[2] && $coordinates[1] !== $coordinates[3]) {
        $startx = $start = min([$coordinates[0], $coordinates[2]]);
        $endx = max([$coordinates[0], $coordinates[2]]);
        $starty = $startx === $coordinates[0] ? $coordinates[1] : $coordinates[3];
        $endy = $startx === $coordinates[2] ? $coordinates[1] : $coordinates[3];
        $slope = $starty > $endy ? -1 : 1;
        for ($i = $startx, $step = 0; $i <= $endx; $i++, $step++) {
            $map[$i][$starty + ($step * $slope)]++;
        }
    }
}
echo count(array_filter(call_user_func_array('array_merge', $map), fn($el) => $el > 1)); //22213