const DRIVE_PATH = /^[A-Za-z]:[\\/]/;
const URI_SCHEME = /^[A-Za-z][A-Za-z0-9+.-]*:/;
const CONTROL_CHARACTER = /[\u0000-\u001f\u007f]/;

function invalidPath(message: "ASSET_PATH_INVALID" | "ASSET_PATH_OUTSIDE_PROJECT"): never {
  throw new Error(message);
}

function decodePath(sourcePath: string): string {
  let decoded: string;
  try {
    decoded = decodeURIComponent(sourcePath);
  }
  catch {
    return invalidPath("ASSET_PATH_INVALID");
  }
  // A canonical path must be safe to normalize again. Residual percent octets could otherwise
  // become separators or dot segments in a second decoder.
  if (decoded.includes("%")) return invalidPath("ASSET_PATH_OUTSIDE_PROJECT");
  try {
    encodeURIComponent(decoded);
  }
  catch {
    return invalidPath("ASSET_PATH_INVALID");
  }
  return decoded.normalize("NFC");
}

export function normalizeProjectAssetPath(sourcePath: string): string {
  if (typeof sourcePath !== "string" || sourcePath.length === 0 || sourcePath.length > 2048) {
    return invalidPath("ASSET_PATH_INVALID");
  }

  const blenderRelative = sourcePath.startsWith("//");
  if (sourcePath.startsWith("\\") || sourcePath.startsWith("/") && !blenderRelative) {
    return invalidPath("ASSET_PATH_OUTSIDE_PROJECT");
  }

  let relative = decodePath(sourcePath);
  if (relative.startsWith("//")) {
    if (!blenderRelative) return invalidPath("ASSET_PATH_OUTSIDE_PROJECT");
    relative = relative.slice(2);
  }
  relative = relative.replaceAll("\\", "/");
  if (relative.startsWith("/") || DRIVE_PATH.test(relative) || URI_SCHEME.test(relative)) {
    return invalidPath("ASSET_PATH_OUTSIDE_PROJECT");
  }

  const canonicalSegments: string[] = [];
  for (const segment of relative.split("/")) {
    if (segment.length === 0 || segment === ".") continue;
    if (segment === "..") {
      if (canonicalSegments.length === 0) return invalidPath("ASSET_PATH_OUTSIDE_PROJECT");
      canonicalSegments.pop();
      continue;
    }
    if (CONTROL_CHARACTER.test(segment)) return invalidPath("ASSET_PATH_OUTSIDE_PROJECT");
    canonicalSegments.push(segment);
  }

  const canonical = canonicalSegments.join("/");
  if (!canonical || canonical.length > 2048) return invalidPath("ASSET_PATH_INVALID");
  return canonical;
}