import { authenticateAppToken, getSessionUser, verifyAppToken, type User } from "@sttracker/core/auth";
import { AuthError, ImportError, NotFoundError, ValidationError } from "@sttracker/core/errors";
import type { Actor } from "@sttracker/core/history";
import { isUniqueViolation } from "@sttracker/core/matching";
import type { PluginRegistry } from "@sttracker/core/registry";
import type { Db } from "@sttracker/db/db";
import type { TokenScope } from "@sttracker/db/schema";
import { z } from "zod";

export type AuthMode = "none" | "session" | "token:read" | "token:write" | "any:read" | "any:write";
export type Method = "GET" | "POST" | "PATCH" | "DELETE";

export interface AppDeps {
  db: Db;
  registry: PluginRegistry;
  secret: string;
  dataDir: string;
  /** When it starts with `https:`, the session cookie is `Secure`. */
  publicUrl?: string;
}

export const SESSION_COOKIE = "stt_session";
export const CSRF_HEADER = "x-requested-with";
export const CSRF_VALUE = "sttracker";
export const MAX_JSON_BYTES = 1024 * 1024;
export const MAX_UPLOAD_BYTES = 50 * 1024 * 1024;
const SESSION_MAX_AGE_S = 30 * 24 * 60 * 60;

export interface Ctx<B, Q> {
  req: Request;
  url: URL;
  params: Record<string, string>;
  body: B;
  query: Q;
  /** The authenticated user. Throws on `auth: "none"` routes, which have none. */
  user: User;
  /** Who writes: `token:<name>` for Bearer requests, `"user"` for sessions. Pass it to every core write. */
  actor: Actor;
  /** The session token, when the request was authenticated by cookie. */
  sessionToken: string | null;
  /** Parsed multipart body, for `multipart: true` routes. */
  form: FormData;
  deps: AppDeps;
  ip: string;
}

export interface RouteDef<B = any, Q = any> {
  method: Method;
  /** Relative to `/api/v1`, with `:param` segments. */
  path: string;
  summary: string;
  auth: AuthMode;
  body?: z.ZodType<B>;
  query?: z.ZodType<Q>;
  /** Parse the body as multipart form data (upload limit) instead of JSON. */
  multipart?: boolean;
  /** Non-file multipart fields, for the OpenAPI document (handlers validate them). Every multipart route also takes `file`. */
  formFields?: z.ZodObject;
  /** Rate limit per client IP (login, register). */
  rateLimited?: boolean;
  /** Only admins may call it (403 otherwise). */
  admin?: boolean;
  handler(ctx: Ctx<B, Q>): Promise<unknown>;
}

/** Declare a route; returns it unchanged with the handler's body and query types inferred from the schemas. */
export function route<BS extends z.ZodType = z.ZodUnknown, QS extends z.ZodType = z.ZodUnknown>(
  def: Omit<RouteDef<z.output<BS>, z.output<QS>>, "body" | "query"> & { body?: BS; query?: QS },
): RouteDef {
  return def as RouteDef;
}

/** Throw from a handler to answer with a specific status and error code. */
export class HttpError extends Error {
  constructor(
    readonly status: number,
    readonly code: string,
    message: string,
  ) {
    super(message);
  }
}

export function json(data: unknown, status = 200, headers: Record<string, string> = {}): Response {
  return new Response(JSON.stringify(data), { status, headers: { "content-type": "application/json; charset=utf-8", ...headers } });
}

export function errorResponse(status: number, code: string, message: string, headers: Record<string, string> = {}): Response {
  return json({ error: { code, message } }, status, headers);
}

export const noContent = (): Response => new Response(null, { status: 204 });

const AUTH_STATUS: Record<string, [number, string, string]> = {
  invalid_credentials: [401, "unauthenticated", "Wrong username or password."],
  unauthenticated: [401, "unauthenticated", "Sign in first."],
  forbidden: [403, "forbidden", "You are not allowed to do that."],
  invite_required: [400, "invite_required", "Registration needs a valid invite code."],
  username_taken: [400, "username_taken", "That username is taken."],
  invalid_username: [400, "invalid_username", "Usernames are 2–32 characters: lowercase letters, digits and underscores."],
};

/** Map a thrown error to the JSON error response (ruling 5). Unknown errors are logged and hidden. */
export function toErrorResponse(e: unknown): Response {
  if (e instanceof HttpError) return errorResponse(e.status, e.code, e.message);
  if (e instanceof z.ZodError) {
    const msg = e.issues.map((i) => `${i.path.length ? i.path.join(".") : "body"}: ${i.message}`).join("; ");
    return errorResponse(400, "validation", msg);
  }
  if (e instanceof ValidationError) return errorResponse(400, "validation", `${e.field}: ${e.reason}`);
  if (e instanceof NotFoundError) return errorResponse(404, "not_found", e.message);
  if (e instanceof AuthError) {
    const [status, code, message] = AUTH_STATUS[e.code] ?? [403, "forbidden", "You are not allowed to do that."];
    return errorResponse(status, code, message);
  }
  if (e instanceof ImportError) {
    const status = e.code === "account_not_empty" || e.code === "conflict" ? 409 : 400;
    return errorResponse(status, e.code, `Import failed: ${e.code}.`);
  }
  if (isUniqueViolation(e)) return errorResponse(409, "conflict", "That already exists.");
  console.error("[api]", e);
  return errorResponse(500, "internal", "Something went wrong on the server.");
}

export function sessionCookie(token: string, publicUrl: string | undefined): string {
  const secure = publicUrl?.startsWith("https:") ? "; Secure" : "";
  return `${SESSION_COOKIE}=${token}; Path=/; HttpOnly; SameSite=Lax; Max-Age=${SESSION_MAX_AGE_S}${secure}`;
}

export function clearSessionCookie(publicUrl: string | undefined): string {
  const secure = publicUrl?.startsWith("https:") ? "; Secure" : "";
  return `${SESSION_COOKIE}=; Path=/; HttpOnly; SameSite=Lax; Max-Age=0${secure}`;
}

function readCookie(req: Request, name: string): string | null {
  const header = req.headers.get("cookie");
  if (!header) return null;
  for (const part of header.split(";")) {
    const i = part.indexOf("=");
    if (i > 0 && part.slice(0, i).trim() === name) {
      try {
        return decodeURIComponent(part.slice(i + 1).trim()) || null;
      } catch {
        return null; // malformed percent-encoding: treat as no cookie
      }
    }
  }
  return null;
}

/** Read a request body, failing with 413 once it exceeds `max` bytes (whatever Content-Length claims). */
async function readLimited(req: Request, max: number): Promise<Uint8Array<ArrayBuffer>> {
  const tooLarge = () => new HttpError(413, "validation", `Request body is too large (max ${max / (1024 * 1024)} MB).`);
  const declared = Number(req.headers.get("content-length") ?? NaN);
  if (declared > max) throw tooLarge();
  if (!req.body) return new Uint8Array();
  const reader = req.body.getReader();
  const chunks: Uint8Array[] = [];
  let total = 0;
  for (;;) {
    const { done, value } = await reader.read();
    if (done) break;
    total += value.byteLength;
    if (total > max) {
      await reader.cancel();
      throw tooLarge();
    }
    chunks.push(value);
  }
  const out = new Uint8Array(total);
  let at = 0;
  for (const c of chunks) {
    out.set(c, at);
    at += c.byteLength;
  }
  return out;
}

/** Fixed-window-ish limiter: at most `limit` hits per `windowMs` per key. */
export function rateLimiter(limit: number, windowMs: number): (key: string) => boolean {
  const hits = new Map<string, number[]>();
  return (key) => {
    const now = Date.now();
    if (hits.size > 10_000) for (const [k, v] of hits) if (v.every((t) => now - t >= windowMs)) hits.delete(k);
    const recent = (hits.get(key) ?? []).filter((t) => now - t < windowMs);
    if (recent.length >= limit) {
      hits.set(key, recent);
      return false;
    }
    recent.push(now);
    hits.set(key, recent);
    return true;
  };
}

const SCOPES: TokenScope[] = ["read", "write", "ingest"];

/** Resolve the caller for `mode`. Returns the user and the session token used, if any. */
async function authenticate(
  req: Request,
  mode: AuthMode,
  db: Db,
): Promise<{ user: User | null; sessionToken: string | null; actor: Actor }> {
  if (mode === "none") return { user: null, sessionToken: null, actor: "user" };
  const authz = req.headers.get("authorization");
  const bearer = authz?.startsWith("Bearer ") ? authz.slice(7).trim() : null;
  const [kind, scopeName] = mode.split(":") as ["session" | "token" | "any", TokenScope | undefined];

  if (kind !== "session" && bearer) {
    const scope = scopeName!;
    const auth = await authenticateAppToken(db, bearer, scope);
    if (auth) return { user: auth.user, sessionToken: null, actor: `token:${auth.tokenName}` };
    for (const other of SCOPES) {
      if (other !== scope && (await verifyAppToken(db, bearer, other))) {
        throw new HttpError(403, "forbidden", `This app token lacks the '${scope}' scope.`);
      }
    }
    throw new HttpError(401, "unauthenticated", "Invalid or revoked app token.");
  }
  if (kind === "token") throw new HttpError(401, "unauthenticated", "Send an app token: Authorization: Bearer <token>.");

  const token = readCookie(req, SESSION_COOKIE);
  const user = token ? await getSessionUser(db, token) : null;
  if (!user) throw new HttpError(401, "unauthenticated", "Sign in first.");
  return { user, sessionToken: token, actor: "user" };
}

interface Compiled {
  def: RouteDef;
  segments: string[];
}

function matchSegments(pattern: string[], parts: string[]): Record<string, string> | null {
  if (pattern.length !== parts.length) return null;
  const params: Record<string, string> = {};
  for (let i = 0; i < pattern.length; i++) {
    const p = pattern[i]!;
    const v = parts[i]!;
    if (p.startsWith(":")) {
      if (v === "") return null;
      try {
        params[p.slice(1)] = decodeURIComponent(v);
      } catch {
        return null;
      }
    } else if (p !== v) return null;
  }
  return params;
}

/** Build the `/api/v1/*` request handler over a route table. */
export function apiHandler(routes: RouteDef[], deps: AppDeps, prefix = "/api/v1/"): (req: Request, ip: string) => Promise<Response> {
  const compiled: Compiled[] = routes.map((def) => ({ def, segments: def.path.split("/") }));
  const limit = rateLimiter(10, 60_000);

  return async (req, ip) => {
    try {
      const url = new URL(req.url);
      const parts = url.pathname.slice(prefix.length).replace(/\/$/, "").split("/");
      let found: { def: RouteDef; params: Record<string, string> } | null = null;
      for (const c of compiled) {
        if (c.def.method !== req.method) continue;
        const params = matchSegments(c.segments, parts);
        if (params) {
          found = { def: c.def, params };
          break;
        }
      }
      if (!found) return errorResponse(404, "not_found", "No such endpoint.");
      const { def, params } = found;

      if (def.rateLimited && !limit(`${def.path}|${ip}`)) {
        return errorResponse(429, "rate_limited", "Too many attempts. Wait a minute and try again.", { "retry-after": "60" });
      }
      // CSRF: every non-Bearer write (login and register included) must carry this header. Browsers cannot add it
      // cross-site without a CORS preflight, which the server never grants. Bearer requests are not ambient, so exempt.
      const bearer = req.headers.get("authorization")?.startsWith("Bearer ") ?? false;
      if (req.method !== "GET" && req.method !== "HEAD" && !bearer && req.headers.get(CSRF_HEADER) !== CSRF_VALUE) {
        throw new HttpError(403, "forbidden", `Browser requests that change data must send the header X-Requested-With: ${CSRF_VALUE}.`);
      }
      const { user, sessionToken, actor } = await authenticate(req, def.auth, deps.db);
      if (def.admin && user?.role !== "admin") throw new HttpError(403, "forbidden", "Only an admin can do that.");

      let body: unknown;
      let form: FormData | undefined;
      if (def.multipart) {
        const type = req.headers.get("content-type") ?? "";
        if (!type.startsWith("multipart/form-data")) throw new HttpError(400, "validation", "body: expected multipart/form-data");
        const bytes = await readLimited(req, MAX_UPLOAD_BYTES);
        try {
          form = await new Response(bytes, { headers: { "content-type": type } }).formData();
        } catch {
          throw new HttpError(400, "validation", "body: malformed multipart form data");
        }
      } else if (def.body) {
        const bytes = await readLimited(req, MAX_JSON_BYTES);
        let raw: unknown;
        if (bytes.byteLength > 0) {
          const type = (req.headers.get("content-type") ?? "").split(";")[0]!.trim().toLowerCase();
          if (type !== "application/json") throw new HttpError(415, "unsupported_media_type", "Send the body as Content-Type: application/json.");
          try {
            raw = JSON.parse(new TextDecoder().decode(bytes));
          } catch {
            throw new HttpError(400, "validation", "body: invalid JSON");
          }
        }
        body = def.body.parse(raw);
      }
      const query = def.query ? def.query.parse(Object.fromEntries(url.searchParams)) : undefined;

      const ctx: Ctx<unknown, unknown> = {
        req,
        url,
        params,
        body,
        query,
        get user(): User {
          if (!user) throw new Error(`route ${def.method} ${def.path} has no authenticated user`);
          return user;
        },
        actor,
        sessionToken,
        get form(): FormData {
          if (!form) throw new Error(`route ${def.method} ${def.path} is not multipart`);
          return form;
        },
        deps,
        ip,
      };
      const out = await def.handler(ctx);
      return out instanceof Response ? out : json(out);
    } catch (e) {
      return toErrorResponse(e);
    }
  };
}