class Differ

final class Differ {
    public const OLD = 0;
    public const ADDED = 1;
    public const REMOVED = 2;
    public const DIFF_LINE_END_WARNING = 3;
    public const NO_LINE_END_EOF_WARNING = 4;
    private DiffOutputBuilderInterface $outputBuilder;
    public function __construct(DiffOutputBuilderInterface $outputBuilder) {
        $this->outputBuilder = $outputBuilder;
    }
    public function diff(array|string $from, array|string $to, ?LongestCommonSubsequenceCalculator $lcs = null) : string {
        $diff = $this->diffToArray($from, $to, $lcs);
        return $this->outputBuilder
            ->getDiff($diff);
    }
    public function diffToArray(array|string $from, array|string $to, ?LongestCommonSubsequenceCalculator $lcs = null) : array {
        if (is_string($from)) {
            $from = $this->splitStringByLines($from);
        }
        if (is_string($to)) {
            $to = $this->splitStringByLines($to);
        }
        [
            $from,
            $to,
            $start,
            $end,
        ] = self::getArrayDiffParted($from, $to);
        if ($lcs === null) {
            $lcs = $this->selectLcsImplementation($from, $to);
        }
        $common = $lcs->calculate(array_values($from), array_values($to));
        $diff = [];
        foreach ($start as $token) {
            $diff[] = [
                $token,
                self::OLD,
            ];
        }
        reset($from);
        reset($to);
        foreach ($common as $token) {
            while (($fromToken = reset($from)) !== $token) {
                $diff[] = [
                    array_shift($from),
                    self::REMOVED,
                ];
            }
            while (($toToken = reset($to)) !== $token) {
                $diff[] = [
                    array_shift($to),
                    self::ADDED,
                ];
            }
            $diff[] = [
                $token,
                self::OLD,
            ];
            array_shift($from);
            array_shift($to);
        }
        while (($token = array_shift($from)) !== null) {
            $diff[] = [
                $token,
                self::REMOVED,
            ];
        }
        while (($token = array_shift($to)) !== null) {
            $diff[] = [
                $token,
                self::ADDED,
            ];
        }
        foreach ($end as $token) {
            $diff[] = [
                $token,
                self::OLD,
            ];
        }
        if ($this->detectUnmatchedLineEndings($diff)) {
            array_unshift($diff, [
                "#Warning: Strings contain different line endings!\n",
                self::DIFF_LINE_END_WARNING,
            ]);
        }
        return $diff;
    }
    private function splitStringByLines(string $input) : array {
        return preg_split('/(.*\\R)/', $input, -1, PREG_SPLIT_DELIM_CAPTURE | PREG_SPLIT_NO_EMPTY);
    }
    private function selectLcsImplementation(array $from, array $to) : LongestCommonSubsequenceCalculator {
        // We do not want to use the time-efficient implementation if its memory
        // footprint will probably exceed this value. Note that the footprint
        // calculation is only an estimation for the matrix and the LCS method
        // will typically allocate a bit more memory than this.
        $memoryLimit = 100 * 1024 * 1024;
        if ($this->calculateEstimatedFootprint($from, $to) > $memoryLimit) {
            return new MemoryEfficientLongestCommonSubsequenceCalculator();
        }
        return new TimeEfficientLongestCommonSubsequenceCalculator();
    }
    private function calculateEstimatedFootprint(array $from, array $to) : float|int {
        $itemSize = PHP_INT_SIZE === 4 ? 76 : 144;
        return $itemSize * min(count($from), count($to)) ** 2;
    }
    private function detectUnmatchedLineEndings(array $diff) : bool {
        $newLineBreaks = [
            '' => true,
        ];
        $oldLineBreaks = [
            '' => true,
        ];
        foreach ($diff as $entry) {
            if (self::OLD === $entry[1]) {
                $ln = $this->getLinebreak($entry[0]);
                $oldLineBreaks[$ln] = true;
                $newLineBreaks[$ln] = true;
            }
            elseif (self::ADDED === $entry[1]) {
                $newLineBreaks[$this->getLinebreak($entry[0])] = true;
            }
            elseif (self::REMOVED === $entry[1]) {
                $oldLineBreaks[$this->getLinebreak($entry[0])] = true;
            }
        }
        // if either input or output is a single line without breaks than no warning should be raised
        if ([
            '' => true,
        ] === $newLineBreaks || [
            '' => true,
        ] === $oldLineBreaks) {
            return false;
        }
        // two-way compare
        foreach ($newLineBreaks as $break => $set) {
            if (!isset($oldLineBreaks[$break])) {
                return true;
            }
        }
        foreach ($oldLineBreaks as $break => $set) {
            if (!isset($newLineBreaks[$break])) {
                return true;
            }
        }
        return false;
    }
    private function getLinebreak($line) : string {
        if (!is_string($line)) {
            return '';
        }
        $lc = substr($line, -1);
        if ("\r" === $lc) {
            return "\r";
        }
        if ("\n" !== $lc) {
            return '';
        }
        if (str_ends_with($line, "\r\n")) {
            return "\r\n";
        }
        return "\n";
    }
    private static function getArrayDiffParted(array &$from, array &$to) : array {
        $start = [];
        $end = [];
        reset($to);
        foreach ($from as $k => $v) {
            $toK = key($to);
            if ($toK === $k && $v === $to[$k]) {
                $start[$k] = $v;
                unset($from[$k], $to[$k]);
            }
            else {
                break;
            }
        }
        end($from);
        end($to);
        do {
            $fromK = key($from);
            $toK = key($to);
            if (null === $fromK || null === $toK || current($from) !== current($to)) {
                break;
            }
            prev($from);
            prev($to);
            $end = [
                $fromK => $from[$fromK],
            ] + $end;
            unset($from[$fromK], $to[$toK]);
        } while (true);
        return [
            $from,
            $to,
            $start,
            $end,
        ];
    }

}