/**  Human-readable constraints:
 *   - valid W3C DID (https://www.w3.org/TR/did-core/#did-syntax)
 *      - entire URI is ASCII: [a-zA-Z0-9._:%-]
 *      - always starts "did:" (lower-case)
 *      - method name is one or more lower-case letters, followed by ":"
 *      - remaining identifier can have any of the above chars, but can not end in ":"
 *      - it seems that a bunch of ":" can be included, and don't need spaces between
 *      - "%" is used only for "percent encoding" and must be followed by two hex characters (and thus can't end in "%")
 *      - query ("?") and fragment ("#") stuff is defined for "DID URIs", but not as part of identifier itself
 *      - "The current specification does not take a position on the maximum length of a DID"
 *   - in current atproto, only allowing did:plc and did:web. But not *forcing* this at lexicon layer
 *   - hard length limit of 8KBytes
 *   - not going to validate "percent encoding" here
 * @param did - DID to validate
 * @throws {InvalidDidError} if the DID is invalid
 */
export const ensureValidDid = (did: string): void => {
  if (!did.startsWith("did:")) {
    throw new InvalidDidError("DID requires 'did:' prefix");
  }

  // check that all chars are boring ASCII
  if (!/^[a-zA-Z0-9._:%-]*$/.test(did)) {
    throw new InvalidDidError(
      "Disallowed characters in DID (ASCII letters, digits, and a couple other characters only)",
    );
  }

  const { length, 1: method } = did.split(":");
  if (length < 3) {
    throw new InvalidDidError(
      "DID requires prefix, method, and method-specific content",
    );
  }

  if (!/^[a-z]+$/.test(method)) {
    throw new InvalidDidError("DID method must be lower-case letters");
  }

  if (did.endsWith(":") || did.endsWith("%")) {
    throw new InvalidDidError("DID can not end with ':' or '%'");
  }

  if (did.length > 2 * 1024) {
    throw new InvalidDidError("DID is too long (2048 chars max)");
  }
};

/**
 * Simple regex version of {@linkcode ensureValidDid} constraints
 * @param did - DID to validate
 * @throws {InvalidDidError} - if the DID is invalid
 */
export const ensureValidDidRegex = (did: string): void => {
  if (!/^did:[a-z]+:[a-zA-Z0-9._:%-]*[a-zA-Z0-9._-]$/.test(did)) {
    throw new InvalidDidError("DID didn't validate via regex");
  }

  if (did.length > 2 * 1024) {
    throw new InvalidDidError("DID is too long (2048 chars max)");
  }
};

export class InvalidDidError extends Error {}