// Theseus ID — what a project's server checks (DESIGN §4.3, §6.3, §7).
//
//   const v = createVerifier({ crypto, projectId: "hephaestus",
//     origins: ["https://code.silentmode.st"], providerOrigin: "https://accounts.silentmode.st",
//     consumeNonce: async (nonce) => true_if_issued_by_me_and_unused });
//   const { account, origin } = await v.verifySignIn({ message, signature });

import { parseMessage, checkTime, buildMoveStatement, normOrigin, ID_CHAIN, WALLET_CHAINS } from "./message.mjs";

const bad = (code, msg) => Object.assign(new Error(msg || code), { code });

export function createVerifier({ crypto, projectId, origins = [], providerOrigin = null, consumeNonce, acceptWallets = false, now = () => Date.now() }) {
  if (!crypto || !projectId || typeof consumeNonce !== "function") throw new Error("createVerifier: crypto, projectId and consumeNonce are required");
  const allowed = new Set(origins.map(normOrigin).filter(Boolean));
  if (providerOrigin) allowed.add(normOrigin(providerOrigin));

  async function check(message, signature, wantKind) {
    let f;
    try { f = parseMessage(message); } catch (e) { throw bad("malformed", e.message); }
    if (f.kind !== wantKind) throw bad("malformed", "wrong message kind");
    if (f.projectId !== projectId) throw bad("wrong-project", `signed for ${f.projectId}`);
    if (!allowed.has(f.origin)) throw bad("wrong-origin", `origin ${f.origin} is not ${projectId}'s`);
    const late = checkTime(f, now());
    if (late) throw bad(late);
    const isId = f.account.startsWith("tid:");
    if (wantKind === "signin") {
      if (isId ? f.chainId !== ID_CHAIN : !(acceptWallets && WALLET_CHAINS.includes(f.chainId))) throw bad("wrong-chain");
    }
    if (!crypto.verifyAddress(message, signature, f.account)) throw bad("bad-signature");
    // Last, so a bad request cannot burn a good nonce.
    if (!(await consumeNonce(f.nonce, f))) throw bad("bad-nonce", "nonce unknown or already used");
    return f;
  }

  return {
    async verifySignIn({ message, signature, move }) {
      const f = await check(message, signature, "signin");
      const out = { account: f.account, projectId: f.projectId, origin: f.origin, kind: f.account.startsWith("tid:") ? "tid" : "wallet" };
      if (move) {
        // §6.3: the new key signs in; a statement signed by old AND new moves the account.
        const text = buildMoveStatement({ projectId, from: move.from, to: f.account, origin: f.origin, nonce: f.nonce, issuedAt: move.issuedAt });
        if (text !== move.message) throw bad("bad-move", "move statement does not match the sign-in");
        if (!crypto.verifyAddress(text, move.signatures?.old, move.from)) throw bad("bad-move", "old key did not sign the move");
        if (!crypto.verifyAddress(text, move.signatures?.new, f.account)) throw bad("bad-move", "new key did not sign the move");
        out.movedFrom = move.from;
      }
      return out;
    },
    // §7: { message, signatures: { id, wallet } } — both keys sign the same text.
    async verifyLink({ message, signatures }) {
      const f = await check(message, signatures?.id, "link");
      if (!crypto.verifyAddress(message, signatures?.wallet, f.wallet)) throw bad("bad-signature", "wallet did not sign the link");
      return { account: f.account, wallet: f.wallet, walletChainId: f.walletChainId, projectId: f.projectId, origin: f.origin };
    },
  };
}