import NextAuth from "next-auth";
import type { Account, DefaultSession, NextAuthConfig, Profile } from "next-auth";
import Authentik from "next-auth/providers/authentik";
import Credentials from "next-auth/providers/credentials";
import GitHub from "next-auth/providers/github";
import Google from "next-auth/providers/google";

import { rateLimit } from "@/server/lib/rate-limit";

const SIGNIN_RATE_LIMIT = { limit: 5, windowMs: 60_000 } as const;

/**
 * Best-effort IP extraction for the Credentials `authorize` callback.
 * Auth.js v5 doesn't hand us the request, so we reach for the Next.js
 * `headers()` helper — which works inside the route-handler context that
 * `/api/auth/[...nextauth]` runs in, but may throw in other contexts
 * (e.g. server actions during sign-in testing). On throw we return
 * `null` and the caller decides whether to skip the limiter (dev) or
 * lock the address as `"unknown"` (prod, so a header-stripping proxy
 * doesn't accidentally disable the guardrail entirely).
 */
async function resolveSignInIp(): Promise<string | null> {
  try {
    const { headers } = await import("next/headers");
    const h = await headers();
    const fwd = h.get("x-forwarded-for");
    if (fwd) {
      const first = fwd.split(",")[0]?.trim();
      if (first) return first;
    }
    return h.get("x-real-ip") ?? null;
  } catch {
    return null;
  }
}

/**
 * Session strategy is JWT (no `@auth/drizzle-adapter`). The callbacks below
 * are the manual replacement for what an adapter would normally do:
 *
 *   1. Credentials sign-in resolves to a `users.id` directly inside `authorize`
 *      because the row already exists (Credentials never creates users).
 *
 *   2. OAuth sign-in resolves via the linked `accounts` row when one exists
 *      (`(provider, provider_account_id)` is the canonical "this OAuth
 *      identity belongs to this user" record). When it doesn't, we fall back
 *      to looking up the OAuth-claimed email in `user_email_identities` and
 *      either link to that existing user, or mint a fresh `users` + primary
 *      identity row. The `accounts` row is then written so subsequent
 *      sign-ins use the fast path.
 *
 * Security model for OAuth:
 *   - Trust the provider's `email_verified` claim, but only after we've
 *     resolved it correctly per provider (Google/Authentik expose it on the
 *     OIDC profile; GitHub does not — we hit `/user/emails` with the access
 *     token and read the `verified` flag on the matching entry).
 *   - An unverified email never produces a verified identity row, which
 *     means the partial-unique constraint on `verified_at IS NOT NULL` can
 *     never be tricked into resolving the wrong human.
 *   - The "Bob claims alice's email via GitHub" attack is foreclosed two
 *     ways: (a) GitHub would not return `verified: true` for an email Bob
 *     doesn't actually own, and (b) if a verified identity already exists
 *     for the email under another user with an existing OAuth account, we
 *     reject the sign-in rather than silently re-linking.
 *
 * `db` is loaded dynamically inside callbacks so this module stays importable
 * from edge contexts (middleware, etc.); the actual SQL only runs on the
 * Node route handler.
 */

type Sql = (t: TemplateStringsArray, ...v: unknown[]) => Promise<unknown[]>;

async function getSql(): Promise<Sql> {
  const { db } = await import("@tasks/database/client");
  return (db as { $client: Sql }).$client;
}

/**
 * Per-provider resolution of `email_verified`. The provider's profile object
 * is the source of truth for Google and Authentik (both expose the claim on
 * the OIDC profile directly); GitHub does not, so we make a single REST call
 * to `/user/emails` and read the `verified` flag on the entry matching the
 * primary email.
 *
 * Authentik caveat: since the 2025.10 release, `email_verified` defaults to
 * `false` on the OIDC ID token unless an authentik admin has added a custom
 * property mapping that derives it. We honor whatever the provider says —
 * if it's false, the identity row gets `verified_at = null` and the user
 * will be prompted to verify via another provider (or, eventually, the
 * manual-verification flow) before they can accept invites to that email.
 */
async function resolveOAuthEmailVerified(args: {
  provider: string;
  profile: Profile | undefined;
  accessToken: string | null | undefined;
  fallbackEmail: string;
}): Promise<boolean> {
  if (args.provider === "google" || args.provider === "authentik") {
    return Boolean(args.profile?.email_verified);
  }
  if (args.provider === "github" && args.accessToken) {
    try {
      const res = await fetch("https://api.github.com/user/emails", {
        headers: {
          Authorization: `Bearer ${args.accessToken}`,
          Accept: "application/vnd.github+json",
          "User-Agent": "echodo-auth",
        },
      });
      if (!res.ok) return false;
      const emails = (await res.json()) as Array<{
        email: string;
        primary: boolean;
        verified: boolean;
      }>;
      const target = args.fallbackEmail.toLowerCase();
      const match = emails.find((e) => e.email.toLowerCase() === target);
      return Boolean(match?.verified);
    } catch (e) {
      console.warn("[auth] failed to fetch github /user/emails:", e);
      return false;
    }
  }
  return false;
}

/**
 * Result of resolving an OAuth sign-in to a `users.id`.
 *
 * - `userId`: the canonical id the JWT should carry. Sign-in proceeds.
 * - `conflict: "cross_user_email"`: a verified identity for this email
 *   already belongs to *another* user who has at least one OAuth account
 *   already linked. We refuse to silently re-link — the original owner has
 *   primacy. Sign-in is aborted; the user sees the NextAuth error page.
 */
type OAuthResolution =
  | { userId: string }
  | { conflict: "cross_user_email" };

async function resolveOAuthUser(args: {
  account: Account;
  email: string;
  emailVerified: boolean;
  name: string | null;
  image: string | null;
}): Promise<OAuthResolution> {
  const sql = await getSql();
  const provider = args.account.provider;
  const providerAccountId = args.account.providerAccountId;
  const emailLower = args.email.trim().toLowerCase();
  if (!emailLower || !providerAccountId) {
    return { conflict: "cross_user_email" };
  }

  // Fast path: (provider, providerAccountId) is the canonical record of "this
  // OAuth identity belongs to this user." If we've seen them before, return
  // immediately and bump last_used_at on the matching identity row (if any).
  const linkedAccount = (await sql`
    SELECT user_id
    FROM accounts
    WHERE provider = ${provider} AND provider_account_id = ${providerAccountId}
    LIMIT 1
  `) as { user_id: string }[];
  if (linkedAccount[0]) {
    const userId = linkedAccount[0].user_id;
    await sql`
      UPDATE user_email_identities
      SET last_used_at = now()
      WHERE user_id = ${userId} AND email = ${emailLower}
    `;
    return { userId };
  }

  // New (provider, providerAccountId). Resolve which user this OAuth identity
  // should attach to.
  const verifiedClaim = (await sql`
    SELECT user_id
    FROM user_email_identities
    WHERE email = ${emailLower} AND verified_at IS NOT NULL
    LIMIT 1
  `) as { user_id: string }[];

  let userId: string;
  if (verifiedClaim[0]) {
    // The email is verified for an existing user. Two sub-cases:
    //   (a) They have no other OAuth accounts → this is their first OAuth
    //       sign-in for an email they previously used via Credentials. Link.
    //   (b) They have an OAuth account already → an OAuth account on a
    //       different provider is claiming an email another verified user
    //       already owns. Refuse.
    const ownerHasOAuthAccount = (await sql`
      SELECT 1
      FROM accounts
      WHERE user_id = ${verifiedClaim[0].user_id} AND provider != 'credentials'
      LIMIT 1
    `) as unknown[];
    if (ownerHasOAuthAccount.length > 0) {
      return { conflict: "cross_user_email" };
    }
    userId = verifiedClaim[0].user_id;
  } else {
    // No verified identity for this email. Check the legacy `users.email`
    // column (covers Credentials users whose primary identity is in the
    // identities table as well, but defensive against any drift).
    const legacy = (await sql`
      SELECT id FROM users WHERE lower(email) = ${emailLower} LIMIT 1
    `) as { id: string }[];
    if (legacy[0]) {
      userId = legacy[0].id;
    } else {
      const created = (await sql`
        INSERT INTO users (email, name, avatar_url)
        VALUES (${emailLower}, ${args.name}, ${args.image})
        RETURNING id
      `) as { id: string }[];
      userId = created[0]!.id;
      await sql`
        INSERT INTO user_email_identities
          (user_id, email, verified_at, source, created_at, last_used_at)
        VALUES
          (${userId}, ${emailLower}, now(), 'primary', now(), now())
        ON CONFLICT (user_id, email) DO NOTHING
      `;
    }
  }

  // Write the accounts row so subsequent sign-ins take the fast path.
  await sql`
    INSERT INTO accounts (
      user_id, type, provider, provider_account_id,
      access_token, refresh_token, expires_at, token_type, scope,
      id_token, session_state
    ) VALUES (
      ${userId}, ${args.account.type}, ${provider}, ${providerAccountId},
      ${args.account.access_token ?? null}, ${args.account.refresh_token ?? null},
      ${typeof args.account.expires_at === "number" ? args.account.expires_at : null},
      ${args.account.token_type ?? null}, ${args.account.scope ?? null},
      ${args.account.id_token ?? null}, ${args.account.session_state ?? null}
    )
    ON CONFLICT (provider, provider_account_id) DO NOTHING
  `;

  // Write the oauth identity row only if the provider verified the email.
  // An unverified claim leaves the identities table alone — the user still
  // signs in (we know they control the OAuth account), they just can't yet
  // accept invites sent to that address until they verify it.
  if (args.emailVerified) {
    await sql`
      INSERT INTO user_email_identities
        (user_id, email, verified_at, source, created_at, last_used_at)
      VALUES
        (${userId}, ${emailLower}, now(), ${`oauth:${provider}`}, now(), now())
      ON CONFLICT (user_id, email) DO UPDATE SET
        verified_at = COALESCE(user_email_identities.verified_at, EXCLUDED.verified_at),
        last_used_at = EXCLUDED.last_used_at
    `;
  }

  return { userId };
}

function slugifyForWorkspace(seed: string): string {
  const cleaned = seed
    .toLowerCase()
    .replace(/[^a-z0-9]+/g, "-")
    .replace(/^-+|-+$/g, "")
    .slice(0, 50);
  return cleaned || "workspace";
}

/**
 * Idempotent: if the user already owns or is a member of any workspace, no-op.
 * Otherwise mint a personal workspace and add them as `owner`. Runs on every
 * first sign-in (credentials and OAuth alike) so freshly-created OAuth users
 * don't land in the app with no tenant scope and an unusable session.
 *
 * Slug collisions are handled by retrying with a random 6-char suffix; we cap
 * attempts so a misbehaving DB can't lock the sign-in flow.
 */
async function ensureUserHasWorkspace(args: {
  userId: string;
  displayName: string | null;
  email: string;
}): Promise<void> {
  const sql = await getSql();

  const existing = (await sql`
    SELECT 1
    FROM workspaces w
    LEFT JOIN workspace_members m
      ON m.workspace_id = w.id AND m.user_id = ${args.userId}
    WHERE w.owner_user_id = ${args.userId} OR m.user_id = ${args.userId}
    LIMIT 1
  `) as unknown[];
  if (existing.length > 0) return;

  const trimmedName = args.displayName?.trim() ?? "";
  const seed = trimmedName || args.email.split("@")[0] || "workspace";
  const baseSlug = slugifyForWorkspace(seed);
  const workspaceName = trimmedName ? `${trimmedName}'s workspace` : "My workspace";

  let workspaceId: string | null = null;
  let candidate = baseSlug;
  for (let attempt = 0; attempt < 5 && !workspaceId; attempt += 1) {
    const inserted = (await sql`
      INSERT INTO workspaces (slug, name, owner_user_id)
      VALUES (${candidate}, ${workspaceName}, ${args.userId})
      ON CONFLICT (slug) DO NOTHING
      RETURNING id
    `) as { id: string }[];
    if (inserted[0]) {
      workspaceId = inserted[0].id;
      break;
    }
    candidate = `${baseSlug}-${Math.random().toString(36).slice(2, 8)}`;
  }
  if (!workspaceId) {
    console.warn("[auth] Failed to provision workspace for user", args.userId);
    return;
  }

  await sql`
    INSERT INTO workspace_members (workspace_id, user_id, role)
    VALUES (${workspaceId}, ${args.userId}, 'owner')
    ON CONFLICT (workspace_id, user_id) DO NOTHING
  `;
}

declare module "next-auth" {
  interface Session {
    user: {
      id: string;
    } & DefaultSession["user"];
  }
}

const providers: NextAuthConfig["providers"] = [
  Credentials({
    name: "Email",
    credentials: {
      email: { label: "Email", type: "email" },
      password: { label: "Password", type: "password" },
    },
    async authorize(credentials) {
      const email = credentials?.email as string | undefined;
      const password = credentials?.password as string | undefined;
      if (!email?.trim() || !password) return null;

      // Rate-limit by IP before doing any DB work. 5/minute is well above
      // the rate a human can plausibly fat-finger a password but tight
      // enough that an automated guesser hits the wall before it can
      // burn through a meaningful dictionary slice. In dev we skip the
      // limiter when we can't resolve an IP so a header-less local test
      // run doesn't lock itself out.
      const ip = await resolveSignInIp();
      const limiterKey = `signin:${ip ?? "unknown"}`;
      const skipLimiter = ip === null && process.env.NODE_ENV === "development";
      if (!skipLimiter) {
        const rl = rateLimit({
          key: limiterKey,
          limit: SIGNIN_RATE_LIMIT.limit,
          windowMs: SIGNIN_RATE_LIMIT.windowMs,
        });
        if (!rl.allowed) {
          console.warn(
            "[auth] credentials sign-in rate-limited ip=%s retryAfterMs=%d",
            ip ?? "unknown",
            rl.retryAfterMs,
          );
          return null;
        }
      }

      const devPassword = process.env.AUTH_DEV_PASSWORD;
      if (!devPassword) {
        console.warn("[auth] AUTH_DEV_PASSWORD is not set; credentials sign-in disabled.");
        return null;
      }
      if (password !== devPassword) return null;

      const sql = await getSql();
      const rows = (await sql`
        SELECT id, email, name, avatar_url AS "avatarUrl"
        FROM users
        WHERE lower(email) = lower(${email.trim()})
        LIMIT 1
      `) as { id: string; email: string; name: string | null; avatarUrl: string | null }[];
      const user = rows[0];
      if (!user) return null;

      return {
        id: user.id,
        email: user.email,
        name: user.name ?? undefined,
        image: user.avatarUrl ?? undefined,
      };
    },
  }),
];

if (process.env.AUTH_GITHUB_ID && process.env.AUTH_GITHUB_SECRET) {
  providers.push(
    GitHub({
      clientId: process.env.AUTH_GITHUB_ID,
      clientSecret: process.env.AUTH_GITHUB_SECRET,
    }),
  );
}

if (process.env.AUTH_GOOGLE_ID && process.env.AUTH_GOOGLE_SECRET) {
  providers.push(
    Google({
      clientId: process.env.AUTH_GOOGLE_ID,
      clientSecret: process.env.AUTH_GOOGLE_SECRET,
    }),
  );
}

if (
  process.env.AUTH_AUTHENTIK_ID &&
  process.env.AUTH_AUTHENTIK_SECRET &&
  process.env.AUTH_AUTHENTIK_ISSUER
) {
  providers.push(
    Authentik({
      clientId: process.env.AUTH_AUTHENTIK_ID,
      clientSecret: process.env.AUTH_AUTHENTIK_SECRET,
      issuer: process.env.AUTH_AUTHENTIK_ISSUER,
    }),
  );
}

export const { handlers, auth, signIn, signOut } = NextAuth({
  session: { strategy: "jwt" },
  pages: {
    signIn: "/sign-in",
  },
  providers,
  callbacks: {
    async signIn({ user, account }) {
      // OAuth providers must give us an email so we can map to a `users` row.
      if (account && account.provider !== "credentials" && !user?.email) {
        return false;
      }
      return true;
    },
    // The Auth.js v5 jwt callback receives `profile` on the initial sign-in
    // call (when `account && user` are present). We use it to read provider-
    // specific claims like Google/Authentik's `email_verified`. For GitHub
    // we fall back to a REST call inside `resolveOAuthEmailVerified`.
    async jwt({ token, user, account, profile }) {
      if (account && user) {
        let dbId: string | null = null;

        if (account.provider === "credentials") {
          dbId = user.id ?? null;
        } else if (user.email) {
          const emailVerified = await resolveOAuthEmailVerified({
            provider: account.provider,
            profile,
            accessToken: account.access_token ?? null,
            fallbackEmail: user.email,
          });
          const resolution = await resolveOAuthUser({
            account,
            email: user.email,
            emailVerified,
            name: user.name ?? null,
            image: user.image ?? null,
          });
          if ("conflict" in resolution) {
            console.warn(
              "[auth] OAuth sign-in refused: email %s already verified for another user (provider=%s)",
              user.email,
              account.provider,
            );
            // Returning a token with no `id` field denies the session — the
            // session callback below leaves `session.user.id` unset, which
            // protectedProcedure / workspaceProcedure both reject.
            return token;
          }
          dbId = resolution.userId;
        }

        if (dbId) {
          token.id = dbId;
          await ensureUserHasWorkspace({
            userId: dbId,
            displayName: user.name ?? null,
            email: user.email ?? "",
          });
        }
      }
      return token;
    },
    async session({ session, token }) {
      if (session.user && token.id) {
        session.user.id = token.id as string;
      }
      return session;
    },
  },
  trustHost: true,
});