import { tmpdir } from "node:os";
import { isAbsolute, join } from "node:path";

/**
 * Hub-as-OIDC-issuer configuration (files SSO, phase 1).
 *
 * The issuer, the single first-party client and its redirect URI are fixed by
 * the approved design (docs/design/2026-10-13-files-oidc-sso.md): a mismatch
 * anywhere breaks oCIS token validation, so production values are constants
 * and only the issuer / consent page may be overridden for local development.
 *
 * ENV CONTRACT (read per call, like loadMatrixSsoConfig — nothing at import):
 *
 *   OIDC_ISSUER        default https://api.occupymedia.cc/oidc (dev override only).
 *   OIDC_CONSENT_URL   Hub SPA consent route, default `${APP_URL}/oidc/consent`,
 *                      APP_URL defaulting to https://app.occupymedia.cc.
 *   OIDC_KEY_DIR       directory holding the sealed signing keyset. REQUIRED in
 *                      production (mount a volume). Dev default is under the
 *                      OS temp dir — never inside the repo, so a dev key can
 *                      not be committed by accident.
 */
export interface OidcConfig {
  issuer: string;
  consentUrl: URL;
  keyDir: string;
}

export class OidcConfigError extends Error {}

export const DEFAULT_ISSUER = "https://api.occupymedia.cc/oidc";
const DEFAULT_APP_URL = "https://app.occupymedia.cc";

/** The oCIS web app — the only registered client; public (no secret), PKCE-only. */
export const WEB_CLIENT_ID = "web";
export const WEB_REDIRECT_URI = "https://files.occupymedia.cc/oidc-callback.html";

/** Clients that skip the consent screen. Everything else fails closed. */
const FIRST_PARTY_CLIENTS: ReadonlySet<string> = new Set([WEB_CLIENT_ID]);
const REDIRECT_URIS: Readonly<Record<string, readonly string[]>> = { [WEB_CLIENT_ID]: [WEB_REDIRECT_URI] };

export const SUPPORTED_SCOPES: readonly string[] = ["openid", "profile", "email"];

/** Authorization codes are single-use and live at most this long (design: ≤60 s). */
export const CODE_TTL_SECONDS = 60;
/** id_token / access_token lifetime; oCIS re-runs the (silent) authorize flow after it. */
export const TOKEN_TTL_SECONDS = 3600;

function trimmed(env: Readonly<Record<string, string | undefined>>, name: string): string {
  return env[name]?.trim() ?? "";
}

function httpsOrLocal(name: string, raw: string): URL {
  let url: URL;
  try {
    url = new URL(raw);
  } catch {
    throw new OidcConfigError(`${name} must be an absolute URL`);
  }
  const local = url.hostname === "localhost" || url.hostname === "127.0.0.1";
  if (url.protocol !== "https:" && !(local && url.protocol === "http:")) {
    throw new OidcConfigError(`${name} must be https (http only for localhost)`);
  }
  return url;
}

/** Throws OidcConfigError on malformed or (in production) missing values. */
export function loadOidcConfig(env: Readonly<Record<string, string | undefined>> = process.env): OidcConfig {
  const rawIssuer = trimmed(env, "OIDC_ISSUER") || DEFAULT_ISSUER;
  const issuerUrl = httpsOrLocal("OIDC_ISSUER", rawIssuer);
  if (issuerUrl.search !== "" || issuerUrl.hash !== "") throw new OidcConfigError("OIDC_ISSUER must not carry a query or fragment");
  const issuer = rawIssuer.replace(/\/+$/, "");

  const rawConsent = trimmed(env, "OIDC_CONSENT_URL") || `${(trimmed(env, "APP_URL") || DEFAULT_APP_URL).replace(/\/+$/, "")}/oidc/consent`;
  const consentUrl = httpsOrLocal("OIDC_CONSENT_URL", rawConsent);

  const rawKeyDir = trimmed(env, "OIDC_KEY_DIR");
  if (rawKeyDir === "" && env.NODE_ENV === "production") {
    throw new OidcConfigError("OIDC_KEY_DIR is required in production (a persistent volume for the signing keyset)");
  }
  const keyDir = rawKeyDir === "" ? join(tmpdir(), "tmbh-hub-oidc") : rawKeyDir;
  if (!isAbsolute(keyDir)) throw new OidcConfigError("OIDC_KEY_DIR must be an absolute path");
  return { issuer, consentUrl, keyDir };
}

/** Raw authorize parameters, as received on GET /oidc/authorize or relayed by the consent page. */
export interface AuthorizeParams {
  response_type?: string;
  client_id?: string;
  redirect_uri?: string;
  scope?: string;
  state?: string;
  nonce?: string;
  code_challenge?: string;
  code_challenge_method?: string;
  prompt?: string;
}

export const AUTHORIZE_PARAM_NAMES: readonly (keyof AuthorizeParams)[] = [
  "response_type", "client_id", "redirect_uri", "scope", "state", "nonce", "code_challenge", "code_challenge_method", "prompt",
];

/** A request that passed every check: safe to issue a code for. */
export interface ValidAuthorizeRequest {
  clientId: string;
  redirectUri: string;
  scopes: string[];
  state: string | null;
  nonce: string | null;
  codeChallenge: string;
}

/**
 * Validation outcome. `redirect: false` errors are shown to the user and never
 * sent to the redirect URI (RFC 6749 §4.1.2.1: an unverified client or
 * redirect_uri must not receive a redirect). `redirect: true` errors go back to
 * the client's (already verified) redirect URI as `?error=…&state=…`.
 */
export type AuthorizeValidation =
  | { ok: true; request: ValidAuthorizeRequest }
  | { ok: false; redirect: false; error: string; description: string }
  | { ok: false; redirect: true; redirectUri: string; state: string | null; error: string; description: string };

/** RFC 7636 §4.2: BASE64URL(SHA256(verifier)) is always 43 chars. */
const S256_CHALLENGE = /^[A-Za-z0-9_-]{43}$/;
/** RFC 7636 §4.1 verifier grammar. */
export const CODE_VERIFIER = /^[A-Za-z0-9._~-]{43,128}$/;
const MAX_STATE_LENGTH = 512;

export function isFirstPartyClient(clientId: string): boolean {
  return FIRST_PARTY_CLIENTS.has(clientId);
}

export function validateAuthorize(params: AuthorizeParams): AuthorizeValidation {
  const clientId = params.client_id ?? "";
  const allowed = REDIRECT_URIS[clientId];
  if (allowed === undefined) return { ok: false, redirect: false, error: "invalid_client", description: "unknown client_id" };
  const redirectUri = params.redirect_uri ?? "";
  // Exact string match — no prefix, normalisation or wildcard semantics.
  if (!allowed.includes(redirectUri)) return { ok: false, redirect: false, error: "invalid_request", description: "redirect_uri is not registered for this client" };

  const state = params.state === undefined || params.state === "" ? null : params.state;
  const fail = (error: string, description: string): AuthorizeValidation => ({ ok: false, redirect: true, redirectUri, state, error, description });
  if (state !== null && state.length > MAX_STATE_LENGTH) return fail("invalid_request", "state is too long");
  if (params.response_type !== "code") return fail("unsupported_response_type", "only response_type=code is supported");

  const scopes = (params.scope ?? "").split(" ").filter((s) => s !== "");
  if (!scopes.includes("openid")) return fail("invalid_scope", "scope must include openid");
  const unknown = scopes.find((s) => !SUPPORTED_SCOPES.includes(s));
  if (unknown !== undefined) return fail("invalid_scope", `unsupported scope: ${unknown}`);

  if (params.code_challenge === undefined || params.code_challenge === "") return fail("invalid_request", "PKCE code_challenge is required");
  if (params.code_challenge_method !== "S256") return fail("invalid_request", "code_challenge_method must be S256");
  if (!S256_CHALLENGE.test(params.code_challenge)) return fail("invalid_request", "code_challenge is not a S256 challenge");

  const nonce = params.nonce === undefined || params.nonce === "" ? null : params.nonce;
  if (nonce !== null && nonce.length > MAX_STATE_LENGTH) return fail("invalid_request", "nonce is too long");
  return {
    ok: true,
    request: { clientId, redirectUri, scopes: [...new Set(scopes)], state, nonce, codeChallenge: params.code_challenge },
  };
}

/** `redirectUri?error=…&error_description=…&state=…` for a redirectable failure. */
export function errorRedirect(redirectUri: string, state: string | null, error: string, description: string, issuer?: string): string {
  const url = new URL(redirectUri);
  url.searchParams.set("error", error);
  url.searchParams.set("error_description", description);
  if (state !== null) url.searchParams.set("state", state);
  // RFC 9207 §2: iss is required on error responses too when the server
  // advertises authorization_response_iss_parameter_supported.
  if (issuer !== undefined) url.searchParams.set("iss", issuer);
  return url.toString();
}

/** Picks only the known authorize params out of an untyped query or body. */
export function authorizeParamsFrom(source: unknown): AuthorizeParams {
  const record = typeof source === "object" && source !== null && !Array.isArray(source) ? (source as Record<string, unknown>) : {};
  const params: AuthorizeParams = {};
  for (const name of AUTHORIZE_PARAM_NAMES) {
    const value = record[name];
    if (typeof value === "string") params[name] = value;
  }
  return params;
}