class UnifiedDiffOutputBuilder

final class UnifiedDiffOutputBuilder extends AbstractChunkOutputBuilder {
    private bool $collapseRanges = true;
    private int $commonLineThreshold = 6;
    
    /**
     * @psalm-var positive-int
     */
    private int $contextLines = 3;
    private string $header;
    private bool $addLineNumbers;
    public function __construct(string $header = "--- Original\n+++ New\n", bool $addLineNumbers = false) {
        $this->header = $header;
        $this->addLineNumbers = $addLineNumbers;
    }
    public function getDiff(array $diff) : string {
        $buffer = fopen('php://memory', 'r+b');
        if ('' !== $this->header) {
            fwrite($buffer, $this->header);
            if (!str_ends_with($this->header, "\n")) {
                fwrite($buffer, "\n");
            }
        }
        if (0 !== count($diff)) {
            $this->writeDiffHunks($buffer, $diff);
        }
        $diff = stream_get_contents($buffer, -1, 0);
        fclose($buffer);
        // If the diff is non-empty and last char is not a linebreak: add it.
        // This might happen when both the `from` and `to` do not have a trailing linebreak
        $last = substr($diff, -1);
        return '' !== $diff && "\n" !== $last && "\r" !== $last ? $diff . "\n" : $diff;
    }
    private function writeDiffHunks($output, array $diff) : void {
        // detect "No newline at end of file" and insert into `$diff` if needed
        $upperLimit = count($diff);
        if (0 === $diff[$upperLimit - 1][1]) {
            $lc = substr($diff[$upperLimit - 1][0], -1);
            if ("\n" !== $lc) {
                array_splice($diff, $upperLimit, 0, [
                    [
                        "\n\\ No newline at end of file\n",
                        Differ::NO_LINE_END_EOF_WARNING,
                    ],
                ]);
            }
        }
        else {
            // search back for the last `+` and `-` line,
            // check if it has trailing linebreak, else add a warning under it
            $toFind = [
                1 => true,
                2 => true,
            ];
            for ($i = $upperLimit - 1; $i >= 0; $i--) {
                if (isset($toFind[$diff[$i][1]])) {
                    unset($toFind[$diff[$i][1]]);
                    $lc = substr($diff[$i][0], -1);
                    if ("\n" !== $lc) {
                        array_splice($diff, $i + 1, 0, [
                            [
                                "\n\\ No newline at end of file\n",
                                Differ::NO_LINE_END_EOF_WARNING,
                            ],
                        ]);
                    }
                    if (!count($toFind)) {
                        break;
                    }
                }
            }
        }
        // write hunks to output buffer
        $cutOff = max($this->commonLineThreshold, $this->contextLines);
        $hunkCapture = false;
        $sameCount = $toRange = $fromRange = 0;
        $toStart = $fromStart = 1;
        $i = 0;
        
        /** @var int $i */
        foreach ($diff as $i => $entry) {
            if (0 === $entry[1]) {
                // same
                if (false === $hunkCapture) {
                    $fromStart++;
                    $toStart++;
                    continue;
                }
                $sameCount++;
                $toRange++;
                $fromRange++;
                if ($sameCount === $cutOff) {
                    $contextStartOffset = $hunkCapture - $this->contextLines < 0 ? $hunkCapture : $this->contextLines;
                    // note: $contextEndOffset = $this->contextLines;
                    //
                    // because we never go beyond the end of the diff.
                    // with the cutoff/contextlines here the follow is never true;
                    //
                    // if ($i - $cutOff + $this->contextLines + 1 > \count($diff)) {
                    //    $contextEndOffset = count($diff) - 1;
                    // }
                    //
                    // ; that would be true for a trailing incomplete hunk case which is dealt with after this loop
                    $this->writeHunk($diff, $hunkCapture - $contextStartOffset, $i - $cutOff + $this->contextLines + 1, $fromStart - $contextStartOffset, $fromRange - $cutOff + $contextStartOffset + $this->contextLines, $toStart - $contextStartOffset, $toRange - $cutOff + $contextStartOffset + $this->contextLines, $output);
                    $fromStart += $fromRange;
                    $toStart += $toRange;
                    $hunkCapture = false;
                    $sameCount = $toRange = $fromRange = 0;
                }
                continue;
            }
            $sameCount = 0;
            if ($entry[1] === Differ::NO_LINE_END_EOF_WARNING) {
                continue;
            }
            if (false === $hunkCapture) {
                $hunkCapture = $i;
            }
            if (Differ::ADDED === $entry[1]) {
                $toRange++;
            }
            if (Differ::REMOVED === $entry[1]) {
                $fromRange++;
            }
        }
        if (false === $hunkCapture) {
            return;
        }
        // we end here when cutoff (commonLineThreshold) was not reached, but we were capturing a hunk,
        // do not render hunk till end automatically because the number of context lines might be less than the commonLineThreshold
        $contextStartOffset = $hunkCapture - $this->contextLines < 0 ? $hunkCapture : $this->contextLines;
        // prevent trying to write out more common lines than there are in the diff _and_
        // do not write more than configured through the context lines
        $contextEndOffset = min($sameCount, $this->contextLines);
        $fromRange -= $sameCount;
        $toRange -= $sameCount;
        $this->writeHunk($diff, $hunkCapture - $contextStartOffset, $i - $sameCount + $contextEndOffset + 1, $fromStart - $contextStartOffset, $fromRange + $contextStartOffset + $contextEndOffset, $toStart - $contextStartOffset, $toRange + $contextStartOffset + $contextEndOffset, $output);
    }
    private function writeHunk(array $diff, int $diffStartIndex, int $diffEndIndex, int $fromStart, int $fromRange, int $toStart, int $toRange, $output) : void {
        if ($this->addLineNumbers) {
            fwrite($output, '@@ -' . $fromStart);
            if (!$this->collapseRanges || 1 !== $fromRange) {
                fwrite($output, ',' . $fromRange);
            }
            fwrite($output, ' +' . $toStart);
            if (!$this->collapseRanges || 1 !== $toRange) {
                fwrite($output, ',' . $toRange);
            }
            fwrite($output, " @@\n");
        }
        else {
            fwrite($output, "@@ @@\n");
        }
        for ($i = $diffStartIndex; $i < $diffEndIndex; $i++) {
            if ($diff[$i][1] === Differ::ADDED) {
                fwrite($output, '+' . $diff[$i][0]);
            }
            elseif ($diff[$i][1] === Differ::REMOVED) {
                fwrite($output, '-' . $diff[$i][0]);
            }
            elseif ($diff[$i][1] === Differ::OLD) {
                fwrite($output, ' ' . $diff[$i][0]);
            }
            elseif ($diff[$i][1] === Differ::NO_LINE_END_EOF_WARNING) {
                fwrite($output, "\n");
                // $diff[$i][0]
            }
            else {
                
                /* Not changed (old) Differ::OLD or Warning Differ::DIFF_LINE_END_WARNING */
                fwrite($output, ' ' . $diff[$i][0]);
            }
        }
    }

}