<?php

namespace App\Services;

use Illuminate\Support\Facades\Http;

/** Public, content-addressed display copies. Network and hash work only runs on writes/sync. */
final class LocalIllustrations
{
    private ?array $manifest = null;

    public static function enabled(): bool
    {
        return (bool) config('illustrations.local_enabled');
    }

    private function read(): array
    {
        if ($this->manifest !== null) return $this->manifest;
        $path = config('illustrations.local_manifest');
        try {
            $value = is_file($path) && ! is_link($path) ? json_decode(file_get_contents($path), true, 512, JSON_THROW_ON_ERROR) : [];
            return $this->manifest = ($value['version'] ?? null) === 1 ? $value : ['version' => 1, 'assets' => [], 'selections' => []];
        } catch (\Throwable) {
            // Public requests never fetch Resource, hash files or repair a missing manifest.
            return $this->manifest = ['version' => 1, 'assets' => [], 'selections' => []];
        }
    }

    public function thumbnail(string $pool, string $slug): ?string
    {
        $state = $this->read();
        $id = $state['selections'][$pool][$slug] ?? null;
        $url = $id ? ($state['assets'][$id]['url'] ?? null) : null;
        return is_string($url) && preg_match('~\A'.preg_quote(config('illustrations.local_url_prefix'), '~').'/[a-f0-9]{64}\.(?:webp|png|jpg|gif)\z~D', $url) ? $url : null;
    }

    private function locked(callable $callback): mixed
    {
        $dir = dirname(config('illustrations.local_manifest'));
        if (! is_dir($dir) && ! mkdir($dir, 0700, true) && ! is_dir($dir)) throw new \RuntimeException('Local illustration state directory unavailable');
        if (is_link($dir)) throw new \RuntimeException('Local illustration state must not be a symlink');
        $lock = fopen($dir.'/state.lock', 'c');
        if (! $lock || ! flock($lock, LOCK_EX)) throw new \RuntimeException('Local illustration lock unavailable');
        try {
            $this->manifest = null;
            return $callback();
        } finally {
            flock($lock, LOCK_UN);
            fclose($lock);
        }
    }

    private function save(array $state): void
    {
        $state['version'] = 1;
        $state['updated_at'] = gmdate('c');
        $path = config('illustrations.local_manifest');
        $tmp = tempnam(dirname($path), '.manifest-');
        try {
            chmod($tmp, 0600);
            $bytes = json_encode($state, JSON_THROW_ON_ERROR | JSON_UNESCAPED_SLASHES);
            if (file_put_contents($tmp, $bytes) !== strlen($bytes) || ! rename($tmp, $path)) throw new \RuntimeException('Local illustration manifest update failed');
            $this->manifest = $state;
        } finally {
            if (is_file($tmp)) unlink($tmp);
        }
    }

    private function copy(array $image, array $assets): array
    {
        $id = $image['asset_id'] ?? '';
        $source = $image['url'] ?? '';
        $base = rtrim(config('illustrations.base_url'), '/');
        if (! preg_match('/\A[a-f0-9-]{36}\z/D', $id) || ! preg_match('~\A'.preg_quote($base, '~').'/media/[a-f0-9-]{36}\z~D', $source)) throw new \RuntimeException('Unregistered illustration source');
        $meta = $assets[$id] ?? IllustrationPool::assetMetadata($id);
        $sha = $meta['sha256'] ?? '';
        $mime = $meta['mime'] ?? '';
        $ext = ['image/webp' => 'webp', 'image/png' => 'png', 'image/jpeg' => 'jpg', 'image/gif' => 'gif'][$mime] ?? null;
        $size = (int) ($meta['bytes'] ?? 0);
        if (! $ext || ! preg_match('/\A[a-f0-9]{64}\z/D', $sha) || $size < 1 || $size > 20971520) throw new \RuntimeException('Invalid illustration metadata');
        $dir = config('illustrations.local_directory');
        if (is_link($dir) || (! is_dir($dir) && ! mkdir($dir, 0755, true) && ! is_dir($dir))) throw new \RuntimeException('Local illustration directory unavailable');
        $path = $dir.'/'.$sha.'.'.$ext;
        if (is_link($path)) throw new \RuntimeException('Local illustration file must not be a symlink');
        if (! is_file($path) || filesize($path) !== $size || ! hash_equals($sha, hash_file('sha256', $path))) {
            $tmp = tempnam(dirname(config('illustrations.local_manifest')), '.image-');
            $out = null;
            $stream = null;
            try {
                $response = Http::withOptions(['proxy' => '', 'allow_redirects' => false, 'stream' => true])->withUserAgent('FNA-V3/LocalIllustrations')->connectTimeout(3)->timeout(30)->get($source);
                if (! $response->successful()) throw new \RuntimeException('Illustration download failed');
                $stream = $response->toPsrResponse()->getBody();
                $out = fopen($tmp, 'wb');
                $bytes = 0;
                $hash = hash_init('sha256');
                while (! $stream->eof()) {
                    $chunk = $stream->read(65536);
                    $bytes += strlen($chunk);
                    if ($bytes > 20971520 || fwrite($out, $chunk) !== strlen($chunk)) throw new \RuntimeException('Invalid illustration download size');
                    hash_update($hash, $chunk);
                }
                fclose($out);$out = null;
                $info = @getimagesize($tmp);
                if ($bytes !== $size || ! hash_equals($sha, hash_final($hash)) || ! $info || ($info['mime'] ?? '') !== $mime || $info[0] * $info[1] > 10000000) throw new \RuntimeException('Illustration download integrity failed');
                chmod($tmp, 0644);
                if (! rename($tmp, $path)) throw new \RuntimeException('Local illustration publication failed');
            } finally {
                if (is_resource($out)) fclose($out);
                if ($stream) $stream->close();
                if (is_file($tmp)) unlink($tmp);
            }
        }
        return ['asset_id' => $id, 'sha256' => $sha, 'mime' => $mime, 'bytes' => $size,
            'url' => config('illustrations.local_url_prefix').'/'.$sha.'.'.$ext, 'source_url' => $source];
    }

    public function storeSelection(string $pool, string $slug, array $image): string
    {
        return $this->locked(function () use ($pool, $slug, $image) {
            $state = $this->read();
            $asset = $this->copy($image, $state['assets']);
            $state['assets'][$image['asset_id']] = $asset;
            $state['selections'][$pool][$slug] = $image['asset_id'];
            $this->save($state);
            return $asset['url'];
        });
    }

    /** One atomic manifest switch after all downloadable files pass verification. */
    public function selectionBaseline(): array
    {
        $this->manifest = null;
        return $this->read()['selections'];
    }

    public function synchronize(array $snapshots, ?array $baseline = null): array
    {
        $baseline ??= $this->selectionBaseline();
        return $this->locked(function () use ($snapshots, $baseline) {
            $state = $this->read();
            $pending = [];
            foreach ($snapshots as $pool => $snapshot) {
                $available = [];
                foreach (array_merge($snapshot['items'], array_values($snapshot['selections'])) as $image) {
                    $id = $image['asset_id'];
                    if (isset($available[$id])) continue;
                    $state['assets'][$id] = $this->copy($image, $state['assets']);
                    $available[$id] = true;
                }
                $selections = [];
                foreach ($snapshot['selections'] as $slug => $image) $selections[$slug] = $image['asset_id'];
                foreach ($snapshot['unavailable'] ?? [] as $slug => $reason) {
                    $id = $state['selections'][$pool][$slug] ?? null;
                    $old = $id ? ($state['assets'][$id] ?? null) : null;
                    $local = $old ? config('illustrations.local_directory').'/'.basename($old['url']) : null;
                    // A healthy independent display copy survives physical loss at the source.
                    if (in_array($reason, ['file_missing', 'file_corrupt', 'file_symlink']) && $local && is_file($local) && ! is_link($local) && hash_equals($old['sha256'], hash_file('sha256', $local))) {
                        $selections[$slug] = $id;
                    } else {
                        $selections[$slug] = null;
                        $pending[$pool.':'.$slug] = $reason;
                    }
                }
                // Receivers may publish new mappings while the remote snapshot is in flight.
                // Never replace a local change made after this sync's baseline was captured.
                $current = $state['selections'][$pool] ?? [];
                $before = $baseline[$pool] ?? [];
                foreach (array_unique(array_merge(array_keys($before), array_keys($current))) as $slug) {
                    $exists = array_key_exists($slug, $current);
                    if ($exists !== array_key_exists($slug, $before) || ($current[$slug] ?? null) !== ($before[$slug] ?? null)) {
                        if ($exists) $selections[$slug] = $current[$slug];
                        else unset($selections[$slug]);
                        unset($pending[$pool.':'.$slug]);
                    }
                }
                $state['selections'][$pool] = $selections;
            }
            $this->save($state);
            return ['assets' => count($state['assets']), 'selections' => array_map('count', $state['selections']), 'pending' => $pending];
        });
    }
}