// Theseus ID — the sign-in message (DESIGN-theseus-id.md §4), project IDs and
// origins (§3). Pure: no crypto, no I/O, so the same file runs in Theseus,
// the provider, browsers and tests.
//
// The message is built from fields and parsed back with an exact grammar.
// Signers never sign text a page wrote; verifiers never accept a message
// that does not round-trip through build(parse(text)) byte for byte.

export const MESSAGE_VERSION = "1";
export const ID_CHAIN = "tid:1";
export const WALLET_CHAINS = ["bch:mainnet", "bch:chipnet", "bch:regtest"];
export const MAX_WINDOW_MS = 10 * 60 * 1000;
export const BACK_SKEW_MS = 60 * 1000;

const LABEL_RE = /^[a-z][a-z0-9-]{0,31}$/;
const HOST_RE = /^(?=.{1,253}$)(?!-)[a-z0-9-]{1,63}(?:\.(?!-)[a-z0-9-]{1,63})+$/;
const NONCE_RE = /^[A-Za-z0-9_-]{16,128}$/;
const REQID_RE = /^[A-Za-z0-9._-]{1,64}$/;
const ISO_RE = /^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}\.\d{3}Z$/;
const ACCOUNT_RE = /^(tid|bitcoincash|bchtest|bchreg):[qpzry9x8gf2tvdw0s3jn54khce6mua7l]{42}$/;

// project-id = label / hostname / label ":" hostname   (§3.1)
export function parseProjectId(id) {
  const s = String(id ?? "");
  if (s !== s.toLowerCase()) return null;
  if (LABEL_RE.test(s)) return { id: s, kind: "first-party", authority: null };
  if (HOST_RE.test(s)) return { id: s, kind: "name", authority: s };
  const i = s.indexOf(":");
  if (i > 0 && LABEL_RE.test(s.slice(0, i)) && HOST_RE.test(s.slice(i + 1))) {
    return { id: s, kind: "family", family: s.slice(0, i), authority: s.slice(i + 1) };
  }
  return null;
}
export const isProjectId = (id) => parseProjectId(id) !== null;

// Exact origins only: scheme://host[:port], https, or http on a loopback host
// (development). theseus-addon://<id> is the pseudo-origin of a built-in add-on.
export function normOrigin(o) {
  const s = String(o ?? "");
  if (/^theseus-addon:\/\/[a-z0-9][a-z0-9-]{0,63}$/.test(s)) return s;
  let u;
  try { u = new URL(s); } catch { return null; }
  if (u.username || u.password || u.search || u.hash || (u.pathname && u.pathname !== "/")) return null;
  if (s.endsWith("/")) return null; // written without a trailing slash, as an origin
  const host = u.hostname.toLowerCase();
  if (u.protocol === "https:") return u.origin;
  if (u.protocol === "http:" && (host === "localhost" || host === "127.0.0.1" || host === "[::1]")) return u.origin;
  return null;
}

function domainOf(origin) {
  if (origin.startsWith("theseus-addon://")) return origin;
  return new URL(origin).host; // host[:port], port only when not the default
}

function oneLine(s, max) {
  const t = String(s ?? "");
  if (t.length > max || [...t].some((c) => { const n = c.codePointAt(0); return n < 0x20 || n === 0x7f || n === 0x2028 || n === 0x2029; })) return null;
  return t;
}

const HEADLINES = {
  signin: "wants you to sign in with your Theseus ID:",
  link: "wants you to link a wallet to your Theseus ID:",
};

// fields: { kind: "signin" | "link", origin, account, statement?, uri, chainId,
//           projectId, nonce, issuedAt, expirationTime, requestId?, resources?,
//           wallet?, walletChainId? (link only) }
export function validateFields(f) {
  const errs = [];
  const kind = f.kind || "signin";
  if (!HEADLINES[kind]) errs.push("kind");
  const origin = normOrigin(f.origin);
  if (!origin) errs.push("origin");
  if (!ACCOUNT_RE.test(String(f.account || ""))) errs.push("account");
  if (!isProjectId(f.projectId)) errs.push("projectId");
  if (!NONCE_RE.test(String(f.nonce || ""))) errs.push("nonce");
  if (!ISO_RE.test(String(f.issuedAt || "")) || isNaN(Date.parse(f.issuedAt))) errs.push("issuedAt");
  if (!ISO_RE.test(String(f.expirationTime || "")) || isNaN(Date.parse(f.expirationTime))) errs.push("expirationTime");
  else if (!errs.includes("issuedAt")) {
    const span = Date.parse(f.expirationTime) - Date.parse(f.issuedAt);
    if (span <= 0 || span > MAX_WINDOW_MS) errs.push("expirationTime");
  }
  // A statement that looks like a field line would parse back differently.
  if (f.statement != null && f.statement !== "" &&
      (oneLine(f.statement, 200) == null || /^(URI|Wallet): /.test(f.statement))) errs.push("statement");
  if (oneLine(f.uri, 2048) == null || !f.uri) errs.push("uri");
  if (f.requestId != null && f.requestId !== "" && !REQID_RE.test(String(f.requestId))) errs.push("requestId");
  const res = f.resources || [];
  if (!Array.isArray(res) || res.length > 8 || res.some((r) => oneLine(r, 2048) == null || !r)) errs.push("resources");
  const account = String(f.account || "");
  if (kind === "signin") {
    const isId = account.startsWith("tid:");
    if (isId ? f.chainId !== ID_CHAIN : !WALLET_CHAINS.includes(f.chainId)) errs.push("chainId");
  } else if (kind === "link") {
    if (!account.startsWith("tid:") || f.chainId !== ID_CHAIN) errs.push("chainId");
    if (!/^(bitcoincash|bchtest|bchreg):/.test(String(f.wallet || "")) || !ACCOUNT_RE.test(String(f.wallet))) errs.push("wallet");
    if (!WALLET_CHAINS.includes(f.walletChainId)) errs.push("walletChainId");
  }
  return errs;
}

export function buildMessage(f) {
  const errs = validateFields(f);
  if (errs.length) throw Object.assign(new Error("bad message fields: " + errs.join(", ")), { code: "bad-request", fields: errs });
  const kind = f.kind || "signin";
  const origin = normOrigin(f.origin);
  const lines = [`${domainOf(origin)} ${HEADLINES[kind]}`, f.account, ""];
  if (f.statement) lines.push(f.statement, "");
  if (kind === "link") lines.push(`Wallet: ${f.wallet}`, `Wallet Chain ID: ${f.walletChainId}`);
  lines.push(
    `URI: ${f.uri}`,
    `Version: ${MESSAGE_VERSION}`,
    `Chain ID: ${f.chainId}`,
    `Project: ${f.projectId}`,
    `Origin: ${origin}`,
    `Nonce: ${f.nonce}`,
    `Issued At: ${f.issuedAt}`,
    `Expiration Time: ${f.expirationTime}`,
  );
  if (f.requestId) lines.push(`Request ID: ${f.requestId}`);
  if (f.resources && f.resources.length) lines.push("Resources:", ...f.resources.map((r) => `- ${r}`));
  return lines.join("\n");
}

// Strict parse: returns the fields, or throws. Accepts only what buildMessage
// produces for those fields.
export function parseMessage(text) {
  const t = String(text ?? "");
  const lines = t.split("\n");
  const fail = (why) => { throw Object.assign(new Error("malformed message: " + why), { code: "malformed" }); };
  if (t.includes("\r")) fail("CR");
  let i = 0;
  const head = lines[i++] || "";
  let kind = null;
  for (const [k, h] of Object.entries(HEADLINES)) if (head.endsWith(" " + h)) kind = k;
  if (!kind) fail("headline");
  const account = lines[i++];
  if (lines[i++] !== "") fail("blank after account");
  let statement;
  // A statement is any line that is not a field line, followed by a blank.
  const fieldStart = kind === "link" ? "Wallet: " : "URI: ";
  if (lines[i] !== undefined && !lines[i].startsWith(fieldStart)) {
    statement = lines[i++];
    if (lines[i++] !== "") fail("blank after statement");
  }
  const take = (label) => {
    const l = lines[i];
    if (l === undefined || !l.startsWith(label + ": ")) fail("expected " + label);
    i++;
    return l.slice(label.length + 2);
  };
  const f = { kind, account, statement };
  if (kind === "link") { f.wallet = take("Wallet"); f.walletChainId = take("Wallet Chain ID"); }
  f.uri = take("URI");
  if (take("Version") !== MESSAGE_VERSION) fail("version");
  f.chainId = take("Chain ID");
  f.projectId = take("Project");
  f.origin = take("Origin");
  f.nonce = take("Nonce");
  f.issuedAt = take("Issued At");
  f.expirationTime = take("Expiration Time");
  if (lines[i] !== undefined && lines[i].startsWith("Request ID: ")) f.requestId = take("Request ID");
  if (lines[i] === "Resources:") {
    i++;
    f.resources = [];
    while (i < lines.length && lines[i].startsWith("- ")) f.resources.push(lines[i++].slice(2));
  }
  if (i !== lines.length) fail("trailing lines");
  let rebuilt;
  try { rebuilt = buildMessage(f); } catch (e) { fail(e.message); }
  if (rebuilt !== t) fail("not canonical");
  return f;
}

// Move statement (§6.3): signed by both the old and the new key.
export function buildMoveStatement({ projectId, from, to, origin, nonce, issuedAt }) {
  if (!isProjectId(projectId) || !normOrigin(origin) || !NONCE_RE.test(String(nonce || "")) || !ISO_RE.test(String(issuedAt || ""))) {
    throw Object.assign(new Error("bad move fields"), { code: "bad-request" });
  }
  if (!/^tid:/.test(from) || !/^tid:/.test(to) || !ACCOUNT_RE.test(from) || !ACCOUNT_RE.test(to) || from === to) {
    throw Object.assign(new Error("bad move accounts"), { code: "bad-request" });
  }
  return ["Theseus ID move", `Project: ${projectId}`, `From: ${from}`, `To: ${to}`,
    `Origin: ${normOrigin(origin)}`, `Nonce: ${nonce}`, `Issued At: ${issuedAt}`].join("\n");
}

// Time check for a parsed message (§4.3 step 5).
export function checkTime(f, now = Date.now()) {
  const iat = Date.parse(f.issuedAt), exp = Date.parse(f.expirationTime);
  if (!(now >= iat - BACK_SKEW_MS)) return "issued-in-future";
  if (!(now <= exp)) return "expired";
  return null;
}

// Canonical JSON (sorted keys, no whitespace, nulls dropped) for signed
// origin lists and the registry.
export function canonicalJson(v) {
  if (v === null || v === undefined) return undefined;
  if (Array.isArray(v)) return "[" + v.map((x) => canonicalJson(x) ?? "null").join(",") + "]";
  if (typeof v === "object") {
    const keys = Object.keys(v).filter((k) => v[k] !== null && v[k] !== undefined).sort();
    return "{" + keys.map((k) => JSON.stringify(k) + ":" + canonicalJson(v[k])).join(",") + "}";
  }
  return JSON.stringify(v);
}