<?php
/*************************************************************
# 076 License

Copyright (c) テクニカル諏訪子

Permission is hereby granted to any person obtaining a copy of the software
Little Beast (the "Software") to use, modify, merge, copy, publish, distribute,
sublicense, and/or sell copies of the Software, subject to the following conditions:

    1. **Origin Attribution**:
       - You must not misrepresent the origin of the Software; you must not claim
         you created the original Software.
       - If the Software is used in a product, you must either:
         a. Provide clear attribution in the product's documentation, user interface,
            or other visible areas, **OR**
         b. Pay the original developers a fee they specify in writing.
    2. **Usage Restriction**:
       - The Software, or any derivative works, dependencies, or libraries
         incorporating it, must not be used for censorship or to suppress freedom of
         speech, expression, or creativity. Prohibited uses include, but are not
         limited to:
         - Censorship of so-called "hate speech", visuals, non-mainstream opinions,
           ideas, or objective reality.
         - Tools or systems designed to restrict access to information or
           artistic works.
    3. **Notice Preservation**:
       - This license and the above copyright notice must remain intact in all copies
         of the source code.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE
OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */
namespace Std\Lib\Git;

/**
 * オブジェクトの保存（objects/）：ルーズオブジェクトとパック、objects/info/alternates
 *
 * IDは16進数の文字列。読むと[種類, データ]（種類はcommit、tree、blob、tag）。
 */
final class ObjectDb {
  /** @var string[] オブジェクトのディレクトリ（自分とalternates） */
  private array $dirs;
  /** @var Pack[] パス => パック */
  private array $packs = [];
  private int $scanned = 0;
  /** 差分の元のキャッシュ（キー => [種類, データ]） */
  private array $cache = [];
  private int $cacheBytes = 0;
  private const CACHE_LIMIT = 33554432;

  public function __construct(private Repository $repo) {
    $this->dirs = [$repo->path.'/objects'];
    $alt = $repo->path.'/objects/info/alternates';
    if (is_file($alt)) {
      foreach (preg_split('/\r?\n/', (string)file_get_contents($alt)) as $line) {
        $line = trim($line);
        if ($line === '' || $line[0] === '#') continue;
        $dir = preg_match('#^(/|[A-Za-z]:[/\\\\])#', $line) ? $line : $repo->path.'/objects/'.$line;
        if (is_dir($dir)) $this->dirs[] = rtrim($dir, '/\\');
      }
    }
  }

  /** @return Pack[] */
  public function packs(bool $rescan = false): array {
    if ($rescan || $this->scanned === 0) {
      foreach ($this->dirs as $dir) {
        foreach (glob($dir.'/pack/pack-*.idx') ?: [] as $idx) {
          $pack = substr($idx, 0, -4).'.pack';
          if (!isset($this->packs[$pack]) && is_file($pack)) $this->packs[$pack] = new Pack($pack, $this->repo->hashLen);
        }
      }
      $this->scanned++;
    }
    return $this->packs;
  }

  /**
   * オブジェクトの場所
   *
   * @return array|null  ['loose', パス] 又は ['pack', Pack, オフセット]
   */
  public function locate(string $id): ?array {
    $id = strtolower($id);
    if (!$this->repo->isId($id)) return null;
    foreach ($this->dirs as $dir) {
      $p = $dir.'/'.substr($id, 0, 2).'/'.substr($id, 2);
      if (is_file($p)) return ['loose', $p];
    }
    $bin = hex2bin($id);
    foreach ([false, true] as $rescan) {
      foreach ($this->packs($rescan) as $pack) {
        $off = $pack->find($bin);
        if ($off !== null) return ['pack', $pack, $off];
      }
    }
    return null;
  }

  public function exists(string $id): bool {
    return $this->locate($id) !== null;
  }

  /**
   * オブジェクトを読む
   *
   * @return array|null  [種類, データ]
   */
  public function read(string $id): ?array {
    $loc = $this->locate($id);
    if ($loc === null) return null;
    if ($loc[0] === 'loose') return $this->readLoose($loc[1], $id);
    return $this->readPacked($loc[1], $loc[2]);
  }

  /** 必ず有るオブジェクト */
  public function get(string $id, ?string $type = null): string {
    $o = $this->read($id);
    if ($o === null) throw new GitException("オブジェクトが有りません：{$id}");
    if ($type !== null && $o[0] !== $type) throw new GitException("{$id}は{$type}ではなく{$o[0]}です");
    return $o[1];
  }

  /**
   * 種類と大きさだけ（データを全部は読まない）
   *
   * @return array|null  [種類, 大きさ]
   */
  public function info(string $id): ?array {
    $loc = $this->locate($id);
    if ($loc === null) return null;
    if ($loc[0] === 'loose') {
      $ctx = inflate_init(ZLIB_ENCODING_DEFLATE);
      $fh = fopen($loc[1], 'rb');
      $head = '';
      while (!str_contains($head, "\0") && !feof($fh)) $head .= (string)@inflate_add($ctx, (string)fread($fh, 256), ZLIB_SYNC_FLUSH);
      fclose($fh);
      if (!preg_match('/^(commit|tree|blob|tag) (\d+)\0/', $head, $m)) throw new GitException("壊れたオブジェクト：{$id}");
      return [$m[1], (int)$m[2]];
    }
    [$type, $size, $dataAt, $baseOff, $baseId] = $loc[1]->header($loc[2]);
    if (isset(Pack::TYPES[$type])) return [Pack::TYPES[$type], $size];
    // 差分：大きさは差分の頭、種類は元を辿る
    $head = $loc[1]->inflate($dataAt, $size);
    $target = Delta::targetSize($head);
    $pack = $loc[1];
    $off = $loc[2];
    for ($depth = 0; $depth < 10000; $depth++) {
      [$t, , , $bo, $bi] = $pack->header($off);
      if (isset(Pack::TYPES[$t])) return [Pack::TYPES[$t], $target];
      if ($bo !== null) {
        $off = $bo;
        continue;
      }
      $l = $this->locate(bin2hex($bi));
      if ($l === null) throw new GitException('差分の元が有りません：'.bin2hex($bi));
      if ($l[0] === 'loose') return [$this->info(bin2hex($bi))[0], $target];
      [$pack, $off] = [$l[1], $l[2]];
    }
    throw new GitException("差分が深過ぎます：{$id}");
  }

  private function readLoose(string $path, string $id): array {
    $raw = @file_get_contents($path);
    $data = $raw === false ? false : @zlib_decode($raw);
    if ($data === false) throw new GitException("壊れたオブジェクト：{$id}");
    $nul = strpos($data, "\0");
    if ($nul === false || !preg_match('/^(commit|tree|blob|tag) (\d+)$/', substr($data, 0, $nul), $m) || (int)$m[2] !== strlen($data) - $nul - 1) {
      throw new GitException("壊れたオブジェクト：{$id}");
    }
    return [$m[1], substr($data, $nul + 1)];
  }

  /**
   * パックの中のオブジェクト（差分は元を辿って当てる）
   *
   * @return array  [種類, データ]
   */
  public function readPacked(Pack $pack, int $offset): array {
    $key = $pack->path.':'.$offset;
    if (isset($this->cache[$key])) return $this->cache[$key];
    // 差分の連鎖を集める
    $chain = [];
    $p = $pack;
    $off = $offset;
    while (true) {
      $k = $p->path.':'.$off;
      if (isset($this->cache[$k])) {
        $base = $this->cache[$k];
        break;
      }
      [$type, $size, $dataAt, $baseOff, $baseId] = $p->header($off);
      if (isset(Pack::TYPES[$type])) {
        $base = [Pack::TYPES[$type], $p->inflate($dataAt, $size)];
        $this->remember($k, $base);
        break;
      }
      $chain[] = [$p, $off, $dataAt, $size];
      if (count($chain) > 10000) throw new GitException('差分が深過ぎます');
      if ($baseOff !== null) {
        $off = $baseOff;
        continue;
      }
      $hex = bin2hex($baseId);
      $o = $p->find($baseId);
      if ($o !== null) {
        $off = $o;
        continue;
      }
      $l = $this->locate($hex);
      if ($l === null) throw new GitException("差分の元が有りません：{$hex}");
      if ($l[0] === 'loose') {
        $base = $this->readLoose($l[1], $hex);
        break;
      }
      [$p, $off] = [$l[1], $l[2]];
    }
    for ($i = count($chain) - 1; $i >= 0; $i--) {
      [$cp, $coff, $dataAt, $size] = $chain[$i];
      $base = [$base[0], Delta::apply($base[1], $cp->inflate($dataAt, $size))];
      $this->remember($cp->path.':'.$coff, $base);
    }
    return $base;
  }

  private function remember(string $key, array $obj): void {
    $n = strlen($obj[1]);
    if ($n > self::CACHE_LIMIT / 4) return;
    while ($this->cacheBytes + $n > self::CACHE_LIMIT && !empty($this->cache)) {
      $k = array_key_first($this->cache);
      $this->cacheBytes -= strlen($this->cache[$k][1]);
      unset($this->cache[$k]);
    }
    $this->cache[$key] = $obj;
    $this->cacheBytes += $n;
  }

  /**
   * ルーズオブジェクトとして書く（既に有れば何もしない）
   *
   * @return string  ID
   */
  public function write(string $type, string $data): string {
    if (!in_array($type, ['commit', 'tree', 'blob', 'tag'], true)) throw new GitException("不正な種類：{$type}");
    $id = $this->repo->hashObject($type, $data);
    if ($this->exists($id)) return $id;
    $dir = $this->dirs[0].'/'.substr($id, 0, 2);
    $this->repo->mkdir($dir);
    $level = $this->repo->config->getInt('core.loosecompression', $this->repo->config->getInt('core.compression', -1));
    $this->repo->writeFile($dir.'/'.substr($id, 2), (string)gzcompress($type.' '.strlen($data)."\0".$data, max(-1, min(9, $level))), true);
    return $id;
  }

  /**
   * 短いIDを解決する
   *
   * @return string|null  一意に決まれば完全なID
   */
  public function resolvePrefix(string $prefix): ?string {
    $prefix = strtolower($prefix);
    if (!preg_match('/^[0-9a-f]{4,}$/', $prefix) || strlen($prefix) > $this->repo->hexLen) return null;
    if (strlen($prefix) === $this->repo->hexLen) return $this->exists($prefix) ? $prefix : null;
    $found = [];
    foreach ($this->dirs as $dir) {
      foreach (glob($dir.'/'.substr($prefix, 0, 2).'/'.substr($prefix, 2).'*') ?: [] as $f) $found[substr($prefix, 0, 2).basename($f)] = true;
    }
    foreach ($this->packs(true) as $pack) foreach ($pack->findPrefix($prefix) as $id) $found[$id] = true;
    return count($found) === 1 ? (string)array_key_first($found) : null;
  }

  /** 全部のID（重複あり得る） */
  public function ids(): \Generator {
    foreach ($this->dirs as $dir) {
      foreach (glob($dir.'/[0-9a-f][0-9a-f]/*') ?: [] as $f) {
        $id = basename(dirname($f)).basename($f);
        if ($this->repo->isId($id)) yield $id;
      }
    }
    foreach ($this->packs(true) as $pack) yield from $pack->ids();
  }

  public function dir(): string {
    return $this->dirs[0];
  }
}