import { randomUUID } from "node:crypto";
import bcrypt from "bcrypt";
import type { FastifyInstance } from "fastify";
import { eq, roles, users, type Db } from "@parking/db";
import { ADMIN_ROLE_ID } from "@parking/shared";
import { permissionsFor, requirePermission } from "../auth.js";

// User management (admin). Users are created/edited at runtime here — the
// install-time seed-admin.mjs only bootstraps the FIRST admin. Each user has one
// role (RBAC); the role resolves to a permission set at request time. Passwords
// are bcrypt-hashed (cost 12) and never returned. See @parking/shared PERMISSIONS.
//
// NO-LOCKOUT INVARIANT: the app refuses to delete, or move off the `admin` role,
// the LAST user still holding `admin`. Administration can therefore never be
// locked out of the appliance. See wiki/entities/local-jwt-auth.md.
//
// PRIVILEGE-ESCALATION GUARD: a non-admin caller with `user:*` must NOT be able to
// (a) ASSIGN a role whose permissions exceed their own (e.g. hand themselves or a
// peer the admin role, or any role broader than theirs), nor (b) MODIFY a user who
// already holds a role broader than the caller's (resetting an admin's password is
// account takeover; deleting an admin is sabotage). Both are blocked below by
// comparing permission SETS. An admin holds the full set, so it is unrestricted.

// Optional profile metadata accepted on create/update. All nullable; "" is treated
// as "clear" (→ null). Trimmed before persisting.
interface ProfileBody {
  fullName?: string | null;
  phone?: string | null;
  email?: string | null;
  address?: string | null;
}
interface CreateBody extends ProfileBody {
  username: string;
  password: string;
  roleId: string;
}
interface UpdateBody extends ProfileBody {
  username?: string;
  roleId?: string;
}
interface PasswordBody {
  password: string;
}

const MIN_PASSWORD = 8;
const PROFILE_FIELDS = ["fullName", "phone", "email", "address"] as const;

/** Pull the optional profile fields out of a body → a patch of trimmed values
 *  ("" → null). Absent keys are omitted (so an update only touches what's sent). */
function profilePatch(body: ProfileBody): Record<string, string | null> {
  const out: Record<string, string | null> = {};
  for (const k of PROFILE_FIELDS) {
    const v = body[k];
    if (v === undefined) continue;
    const trimmed = typeof v === "string" ? v.trim() : "";
    out[k] = trimmed === "" ? null : trimmed;
  }
  return out;
}

export async function userRoutes(app: FastifyInstance, db: Db): Promise<void> {
  const readGuard = requirePermission("user:read");
  const createGuard = requirePermission("user:create");
  const updateGuard = requirePermission("user:update");
  const deleteGuard = requirePermission("user:delete");

  /** Count users currently holding the protected admin role. */
  function adminCount(): number {
    return db.select().from(users).where(eq(users.roleId, ADMIN_ROLE_ID)).all().length;
  }

  /** True if removing/relocating `userId` from admin would leave zero admins. */
  function isLastAdmin(userId: string): boolean {
    const u = db.select().from(users).where(eq(users.id, userId)).get();
    return u?.roleId === ADMIN_ROLE_ID && adminCount() <= 1;
  }

  /** A user row safe to return — never the password hash. */
  function publicUser(u: {
    id: string;
    username: string;
    roleId: string;
    language: string;
    createdAt: string;
    fullName?: string | null;
    phone?: string | null;
    email?: string | null;
    address?: string | null;
  }) {
    return {
      id: u.id,
      username: u.username,
      roleId: u.roleId,
      language: u.language,
      createdAt: u.createdAt,
      fullName: u.fullName ?? null,
      phone: u.phone ?? null,
      email: u.email ?? null,
      address: u.address ?? null,
    };
  }

  /** True if `targetRoleId` grants any permission the caller's role does NOT hold,
   *  i.e. assigning or touching it would let the caller act beyond their own
   *  privileges. (Admin holds the full set, so it never trips.) */
  function exceedsCaller(callerRoleId: string, targetRoleId: string): boolean {
    if (callerRoleId === targetRoleId) return false;
    const held = permissionsFor(callerRoleId);
    for (const p of permissionsFor(targetRoleId)) {
      if (!held.has(p)) return true;
    }
    return false;
  }

  // List all users (no password hashes) + their role names for display.
  app.get("/api/users", { preHandler: readGuard }, async () => {
    const rows = db.select().from(users).all();
    const roleRows = db.select().from(roles).all();
    const roleName = new Map(roleRows.map((r) => [r.id, r.name]));
    return {
      users: rows.map((u) => ({ ...publicUser(u), roleName: roleName.get(u.roleId) ?? u.roleId })),
    };
  });

  // Create a user. Username unique; password >= 8 chars; roleId must exist.
  app.post<{ Body: CreateBody }>("/api/users", { preHandler: createGuard }, async (req, reply) => {
    const username = (req.body?.username ?? "").trim();
    const password = req.body?.password ?? "";
    const roleId = (req.body?.roleId ?? "").trim();
    if (!username || !roleId) {
      return reply.code(400).send({ error: "username and roleId required" });
    }
    if (password.length < MIN_PASSWORD) {
      return reply.code(400).send({ error: `password must be at least ${MIN_PASSWORD} characters` });
    }
    if (!db.select().from(roles).where(eq(roles.id, roleId)).get()) {
      return reply.code(400).send({ error: "unknown roleId" });
    }
    // No-escalation: can't create a user with a role broader than your own.
    if (exceedsCaller(req.user.roleId, roleId)) {
      return reply.code(403).send({ error: "cannot assign a role with permissions beyond your own" });
    }
    if (db.select().from(users).where(eq(users.username, username)).get()) {
      return reply.code(409).send({ error: "username already exists" });
    }
    const id = randomUUID();
    const passwordHash = await bcrypt.hash(password, 12);
    db.insert(users).values({ id, username, passwordHash, roleId, ...profilePatch(req.body) }).run();
    const created = db.select().from(users).where(eq(users.id, id)).get()!;
    return reply.code(201).send(publicUser(created));
  });

  // Update a user's username and/or role. Guarded against orphaning admin.
  app.put<{ Params: { id: string }; Body: UpdateBody }>(
    "/api/users/:id",
    { preHandler: updateGuard },
    async (req, reply) => {
      const id = req.params.id;
      const existing = db.select().from(users).where(eq(users.id, id)).get();
      if (!existing) return reply.code(404).send({ error: "user not found" });
      // No-escalation: can't modify a user who already outranks you.
      if (exceedsCaller(req.user.roleId, existing.roleId)) {
        return reply.code(403).send({ error: "cannot modify a user whose role exceeds your own" });
      }

      const next: { username?: string; roleId?: string } & Record<string, string | null> = {
        ...profilePatch(req.body ?? {}),
      };
      if (req.body?.username != null) {
        const username = req.body.username.trim();
        if (!username) return reply.code(400).send({ error: "username cannot be empty" });
        const clash = db.select().from(users).where(eq(users.username, username)).get();
        if (clash && clash.id !== id) return reply.code(409).send({ error: "username already exists" });
        next.username = username;
      }
      if (req.body?.roleId != null) {
        const roleId = req.body.roleId.trim();
        if (!db.select().from(roles).where(eq(roles.id, roleId)).get()) {
          return reply.code(400).send({ error: "unknown roleId" });
        }
        // No-escalation: can't promote a user into a role broader than your own.
        if (exceedsCaller(req.user.roleId, roleId)) {
          return reply.code(403).send({ error: "cannot assign a role with permissions beyond your own" });
        }
        // No-lockout: don't move the last admin off the admin role.
        if (roleId !== ADMIN_ROLE_ID && isLastAdmin(id)) {
          return reply.code(409).send({ error: "cannot change the role of the last admin" });
        }
        next.roleId = roleId;
      }
      if (Object.keys(next).length === 0) {
        return reply.code(400).send({ error: "nothing to update" });
      }
      db.update(users).set(next).where(eq(users.id, id)).run();
      return publicUser(db.select().from(users).where(eq(users.id, id)).get()!);
    },
  );

  // Reset a user's password (admin sets a new one; >= 8 chars).
  app.put<{ Params: { id: string }; Body: PasswordBody }>(
    "/api/users/:id/password",
    { preHandler: updateGuard },
    async (req, reply) => {
      const id = req.params.id;
      const target = db.select().from(users).where(eq(users.id, id)).get();
      if (!target) {
        return reply.code(404).send({ error: "user not found" });
      }
      // No-escalation: can't reset the password of a user who outranks you
      // (that would be account takeover of a more-privileged account).
      if (exceedsCaller(req.user.roleId, target.roleId)) {
        return reply.code(403).send({ error: "cannot reset the password of a user whose role exceeds your own" });
      }
      const password = req.body?.password ?? "";
      if (password.length < MIN_PASSWORD) {
        return reply.code(400).send({ error: `password must be at least ${MIN_PASSWORD} characters` });
      }
      const passwordHash = await bcrypt.hash(password, 12);
      db.update(users).set({ passwordHash }).where(eq(users.id, id)).run();
      return { ok: true };
    },
  );

  // Delete a user. Refused if it's the last admin (no-lockout).
  app.delete<{ Params: { id: string } }>(
    "/api/users/:id",
    { preHandler: deleteGuard },
    async (req, reply) => {
      const id = req.params.id;
      const target = db.select().from(users).where(eq(users.id, id)).get();
      if (!target) {
        return reply.code(404).send({ error: "user not found" });
      }
      // No-escalation: can't delete a user who outranks you.
      if (exceedsCaller(req.user.roleId, target.roleId)) {
        return reply.code(403).send({ error: "cannot delete a user whose role exceeds your own" });
      }
      if (isLastAdmin(id)) {
        return reply.code(409).send({ error: "cannot delete the last admin" });
      }
      db.delete(users).where(eq(users.id, id)).run();
      return { ok: true };
    },
  );
}