<?php declare(strict_types=1);
/*
 * This file is part of sebastian/diff.
 *
 * (c) Sebastian Bergmann <sebastian@phpunit.de>
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */
namespace SebastianBergmann\Diff;

use const PHP_INT_SIZE;
use const PREG_SPLIT_DELIM_CAPTURE;
use const PREG_SPLIT_NO_EMPTY;
use function array_shift;
use function array_unshift;
use function array_values;
use function count;
use function current;
use function end;
use function is_string;
use function key;
use function min;
use function preg_split;
use function prev;
use function reset;
use function str_ends_with;
use function substr;
use SebastianBergmann\Diff\Output\DiffOutputBuilderInterface;

final class Differ
{
    public const int OLD                     = 0;
    public const int ADDED                   = 1;
    public const int REMOVED                 = 2;
    public const int DIFF_LINE_END_WARNING   = 3;
    public const int NO_LINE_END_EOF_WARNING = 4;
    private DiffOutputBuilderInterface $outputBuilder;

    public function __construct(DiffOutputBuilderInterface $outputBuilder)
    {
        $this->outputBuilder = $outputBuilder;
    }

    /**
     * @param list<string>|string $from
     * @param list<string>|string $to
     */
    public function diff(array|string $from, array|string $to, ?LongestCommonSubsequenceCalculator $lcs = null): string
    {
        $diff = $this->diffToArray($from, $to, $lcs);

        return $this->outputBuilder->getDiff($diff);
    }

    /**
     * @param list<string>|string $from
     * @param list<string>|string $to
     */
    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 $token) {
            while ((/* from-token */ reset($from)) !== $token) {
                $diff[] = [array_shift($from), self::REMOVED];
            }

            while ((/* to-token */ 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): 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 (count($newLineBreaks) === 1 || count($oldLineBreaks) === 1) {
            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(int|string $line): string
    {
        if (!is_string($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];
    }
}
