// 阶段 2：revision 信息（siblings）与快照下载。

///|
/// 请求 revision 信息：commit sha 与文件列表（siblings）。
pub async fn fetch_revision_info(
  endpoint : String,
  repo_id : String,
  revision : String,
  token : String?,
) -> (String, Array[String]) raise HubError {
  let url = "\{endpoint}/api/models/\{repo_id}/revision/\{revision}"
  let (code, _headers, body) = get_follow(url, auth_headers(token), 5)
  if code == 401 || code == 403 {
    raise HubError::GatedRepo(url)
  }
  if code == 404 {
    raise HubError::RevisionNotFound(url)
  }
  guard code == 200 else { raise HubError::BadStatus(code, url) }
  let text = @utf8.decode(body) catch {
    _ => raise HubError::Parse("invalid UTF-8 from \{url}")
  }
  let json = @json.parse(text) catch {
    _ => raise HubError::Parse("invalid JSON from \{url}")
  }
  let obj = match json {
    Json::Object(o) => o
    _ => raise HubError::Parse("expected JSON object from \{url}")
  }
  let sha = match obj.get("sha") {
    Some(Json::String(s)) => s
    _ => raise HubError::Parse("missing or non-string `sha` field from \{url}")
  }
  (sha, parse_siblings(json))
}

///|
/// 从 JSON 中提取 siblings 文件名列表（缺失时为空数组）。
fn parse_siblings(json : Json) -> Array[String] {
  let files : Array[String] = []
  match json {
    Json::Object(o) =>
      match o.get("siblings") {
        Some(Json::Array(items)) =>
          for item in items {
            match item {
              Json::Object(s) =>
                match s.get("rfilename") {
                  Some(Json::String(name)) => files.push(name)
                  _ => ()
                }
              _ => ()
            }
          }
        _ => ()
      }
    _ => ()
  }
  files
}

///|
fn glob_to_regex(pattern : String) -> String {
  let mut out = "^"
  for ch in pattern {
    if ch == '*' {
      out = out + ".*"
    } else if ch == '?' {
      out = out + "."
    } else {
      if "\\^$.|+()[]{}".contains_char(ch) {
        out = out + "\\"
      }
      out = out + ch.to_string()
    }
  }
  out + "$"
}

///|
/// glob 风格匹配（* / ?），整串匹配。
pub fn matches_glob(filename : String, pattern : String) -> Bool {
  let regex = @string.Regex(glob_to_regex(pattern)) catch { _ => return false }
  regex.execute(filename) is Some(_)
}

///|
fn allowed(
  filename : String,
  allow_patterns : Array[String]?,
  ignore_patterns : Array[String]?,
) -> Bool {
  match ignore_patterns {
    Some(patts) =>
      for p in patts {
        if matches_glob(filename, p) {
          return false
        }
      }
    None => ()
  }
  match allow_patterns {
    Some(patts) if !patts.is_empty() => {
      for p in patts {
        if matches_glob(filename, p) {
          return true
        }
      }
      false
    }
    _ => true
  }
}

///|
/// 下载整个模型快照到 HF 兼容缓存，返回快照目录。
/// 离线模式下暂不支持（需要远端 siblings 列表）。
pub async fn snapshot_download(
  repo_id : String,
  config : HubConfig,
  allow_patterns : Array[String]?,
  ignore_patterns : Array[String]?,
) -> String raise HubError {
  guard !config.offline else {
    raise HubError::Offline(
      "snapshot_download is not available in offline mode",
    )
  }
  ensure_cache_tag(config.cache_dir)
  let (sha, files) = fetch_revision_info(
    config.endpoint,
    repo_id,
    config.revision,
    config.token,
  )
  let refs = refs_path(config.cache_dir, repo_id, config.revision)
  ensure_dir(dirname(refs))
  write_file_checked(refs, sha)
  let entries : Array[(String, Int, String)] = []
  for filename in files {
    if allowed(filename, allow_patterns, ignore_patterns) {
      let path = hf_hub_download(repo_id, filename, config)
      let size = file_size(path)
      let blob_id = (@fs.realpath(path) catch { _ => filename })
        .rev_after("/")
        .unwrap_or(filename)
        .to_owned()
      entries.push((filename, size, blob_id))
    }
  }
  write_tree_cache(config.cache_dir, repo_id, sha, entries)
  snapshot_dir(config.cache_dir, repo_id, sha)
}

///|
/// 写出 trees/.json（与 huggingface_hub 1.x 相同的缓存格式）。
async fn write_tree_cache(
  cache_root : String,
  repo_id : String,
  sha : String,
  entries : Array[(String, Int, String)],
) -> Unit raise HubError {
  let dir = "\{repo_cache_dir(cache_root, repo_id)}/trees"
  ensure_dir(dir)
  let buf = StringBuilder()
  buf.write_string("{\n \"format_version\": 1,\n \"files\": {")
  if entries.is_empty() {
    buf.write_string("}\n}")
  } else {
    buf.write_string("\n")
    for i = 0; i < entries.length(); i = i + 1 {
      let (name, size, blob_id) = entries[i]
      buf.write_string("  \"\{name}\": {\n")
      buf.write_string("   \"size\": \{size},\n")
      buf.write_string("   \"blob_id\": \"\{blob_id}\"\n")
      if i < entries.length() - 1 {
        buf.write_string("  },\n")
      } else {
        buf.write_string("  }\n")
      }
    }
    buf.write_string(" }\n}")
  }
  write_file_checked("\{dir}/\{sha}.json", buf.to_string())
}