<?php
namespace Relay\Files;

use Relay\Multisite\SubsiteFiles;

use Relay\Jobs\Budget;

/**
 * On the site receiving files: which listed files it needs (spec §5.2) and, in mirror mode, which of its own
 * items the other site doesn't have (spec §5.1). Uploads in "only new or changed" or "since a date" mode are
 * compared like rsync: a file with the same size and mtime is the same; same size but another mtime is
 * compared by sha1. Everything else that is listed is needed. Runs over as many requests as it takes.
 */
final class FileDiff
{
    private const BATCH = 500;

    private FileList $source;
    /** @var array<string, string> */
    private array $roots;
    private array $parts;
    private string $dir;
    /** @var array<string, string> */
    private array $policies;
    /** @var array<string, string[]> */
    private array $untouched;

    /**
     * @param array<string, string> $policies group => SubsiteFiles policy; a group taken "add-missing" keeps the items
     *        this site has (they are never sent, replaced or mirrored)
     * @param array<string, string[]> $untouched group => top-level items mirror never moves (the main site's uploads/sites)
     */
    public function __construct(FileList $source, array $roots, array $parts, string $dir, array $policies = [], array $untouched = [])
    {
        $this->source = $source;
        $this->roots = $roots;
        $this->parts = $parts;
        $this->dir = $dir;
        $this->policies = $policies;
        $this->untouched = $untouched;
    }

    public static function start(): array
    {
        return ['phase' => 'compare', 'pos' => 0, 'needed' => 0, 'bytes' => 0, 'scan' => null, 'scan_pos' => 0, 'extras' => 0, 'extras_bytes' => 0, 'kept' => [], 'done' => false];
    }

    public function needed(): IndexList
    {
        return new IndexList($this->dir . '/needed.bin');
    }

    /** One JSON line per item to move aside in mirror mode: {"g": group, "r": item or upload path}. */
    public function extras_path(): string
    {
        return $this->dir . '/extras.jsonl';
    }

    public function run(array $cursor, Budget $budget): array
    {
        $needed = $this->needed();
        $needed->truncate((int) $cursor['needed']);
        if ($cursor['phase'] === 'compare') {
            $cursor = $this->compare($cursor, $budget, $needed);
        }
        if ($cursor['phase'] === 'extras') {
            $cursor = $this->extras($cursor, $budget);
        }
        return $cursor;
    }

    private function compare(array $cursor, Budget $budget, IndexList $needed): array
    {
        $batch = [];
        $finished = true;
        foreach ($this->source->each((int) $cursor['pos']) as $i => $e) {
            if ($budget->exhausted()) {
                $finished = false;
                break;
            }
            if ($this->keeps($e)) {
                $top = RelPath::top($e['r']);
                if ($top !== 'index.php') { // WordPress's own file in themes/ and plugins/: kept too, but no theme or plugin to name
                    $cursor['kept'][$e['g']][$top] = true;
                }
            } elseif ($this->needs($e)) {
                $batch[] = $i;
                $cursor['bytes'] += $e['s'];
            }
            $cursor['pos'] = $i + 1;
            if (count($batch) >= self::BATCH) {
                $needed->add($batch);
                $batch = [];
                $cursor['needed'] = $needed->count();
            }
        }
        $needed->add($batch);
        $cursor['needed'] = $needed->count();
        if ($finished) {
            $cursor['phase'] = $this->parts['mirror'] ? 'extras' : 'done';
            $cursor['done'] = !$this->parts['mirror'];
            wp_delete_file($this->extras_path());
        }
        return $cursor;
    }

    /** A theme or plugin this site already has, when the group is only added to (a subsite). */
    private function keeps(array $e): bool
    {
        return ($this->policies[$e['g']] ?? '') === SubsiteFiles::ADD_MISSING && file_exists($this->roots[$e['g']] . '/' . RelPath::top($e['r']));
    }

    private function needs(array $e): bool
    {
        if ($e['g'] !== 'uploads' || $this->parts['uploads']['mode'] === 'all') {
            return true;
        }
        $path = Packer::path($this->roots['uploads'], $e['r']);
        clearstatcache(true, (string) $path);
        if ($path === null || !is_file($path) || filesize($path) !== $e['s']) {
            return true;
        }
        return filemtime($path) !== $e['m'] && sha1_file($path) !== $e['h'];
    }

    /**
     * Mirror: whole themes and plugins this site has and the other doesn't (when all of them are copied), and
     * uploads files the other site doesn't have (all or changed mode). Excluded and protected items stay.
     */
    private function extras(array $cursor, Budget $budget): array
    {
        $excludes = Groups::excludes($this->roots, $this->parts['excludes'], $this->untouched);
        if ($cursor['scan'] === null) {
            $lines = '';
            foreach (['themes', 'plugins'] as $group) {
                if ($this->parts[$group]['mode'] !== 'all' || isset($this->policies[$group])) {
                    continue;
                }
                $theirs = [];
                foreach ($this->source->each() as $e) {
                    if ($e['g'] === $group) {
                        $theirs[RelPath::top($e['r'])] = true;
                    }
                }
                foreach (Inventory::top_level($this->roots[$group], $excludes[$group]) as $item) {
                    if (!isset($theirs[$item])) {
                        $lines .= self::line($group, $item);
                        $cursor['extras']++;
                    }
                }
            }
            Fs::put($this->extras_path(), $lines);
            $cursor['scan'] = in_array($this->parts['uploads']['mode'], ['all', 'changed'], true) ? Scanner::start() : ['done' => true, 'list_bytes' => 0];
            wp_delete_file($this->dir . '/ours.jsonl');
        }
        $ours = $this->dir . '/ours.jsonl';
        if (empty($cursor['scan']['done'])) {
            $scanner = new Scanner(['uploads' => $this->roots['uploads']], ['uploads' => $excludes['uploads']], $ours);
            while (!$cursor['scan']['done'] && !$budget->exhausted()) {
                $cursor['scan'] = $scanner->run($cursor['scan'], 2000);
            }
            if (!$cursor['scan']['done']) {
                return $cursor;
            }
        }
        if (is_file($ours)) {
            $theirs = [];
            foreach ($this->source->each() as $e) {
                if ($e['g'] === 'uploads') {
                    $theirs[$e['r']] = true;
                }
            }
            $h = Fs::open($ours, 'rb');
            fseek($h, (int) $cursor['scan_pos']);
            $lines = '';
            $finished = true;
            while (($raw = fgets($h)) !== false) {
                if ($budget->exhausted()) {
                    $finished = false;
                    break;
                }
                $cursor['scan_pos'] += strlen($raw);
                $e = json_decode($raw, true);
                if (is_array($e) && is_string($e['r'] ?? null) && RelPath::valid($e['r']) && !isset($theirs[$e['r']])) {
                    $lines .= self::line('uploads', $e['r']);
                    $cursor['extras']++;
                    $cursor['extras_bytes'] += (int) ($e['s'] ?? 0);
                }
            }
            Fs::close($h);
            Fs::put($this->extras_path(), $lines, true);
            if (!$finished) {
                return $cursor;
            }
            wp_delete_file($ours);
        }
        $cursor['phase'] = 'done';
        $cursor['done'] = true;
        return $cursor;
    }

    private static function line(string $group, string $rel): string
    {
        return json_encode(['g' => $group, 'r' => $rel], JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE) . "\n";
    }
}