import { TRPCError } from '@trpc/server';
import { and, desc, eq, isNull, ne, or, sql } from 'drizzle-orm';
import { z } from 'zod';
import { schema, type Db } from '@linkder/db';
import { PAST_JOB_STATUSES, sendMessageSchema, type JobStatus } from '@linkder/shared';
import { protectedProcedure, router } from '../trpc';

/**
 * Chat between the two parties on a job.
 *
 * A thread is a MATCH, not a job. One job can have several pros accept it, and
 * each of those is a separate private conversation — keying chat on the job
 * would put three tradespeople in one room with the customer and each other.
 *
 * `matches` already carries `lastMessageAt` and `messages` is already indexed
 * for both "this thread, newest last" and the unread badge. This router is the
 * first thing to read or write either.
 */

/** A page of history. Thirty is about two phone screens. */
const PAGE_SIZE = 30;

/**
 * A crude per-process send throttle.
 *
 * It is deliberately not a real rate limiter: it resets on deploy and does not
 * span instances. What it does buy is that a runaway client or a held-down send
 * button cannot write ten thousand rows before anyone notices. The real limiter
 * belongs with the shared Redis in M4 — this is the floor until then.
 */
const SEND_WINDOW_MS = 60_000;
const SEND_LIMIT = 30;
const recentSends = new Map<string, number[]>();

function assertSendRate(userId: string): void {
  const now = Date.now();
  const window = (recentSends.get(userId) ?? []).filter((at) => now - at < SEND_WINDOW_MS);
  if (window.length >= SEND_LIMIT) {
    throw new TRPCError({ code: 'TOO_MANY_REQUESTS', message: 'Slow down a moment.' });
  }
  window.push(now);
  recentSends.set(userId, window);
}

type Tx = Parameters<Parameters<Db['transaction']>[0]>[0];
type Executor = Db | Tx;

export interface MatchContext {
  matchId: string;
  clientId: string;
  proId: string;
  jobId: string;
  jobTitle: string;
  jobStatus: JobStatus;
}

/**
 * The authorization gate for everything in this file.
 *
 * Throws NOT_FOUND rather than FORBIDDEN for a match the caller is not part of —
 * same rule as `job.byId` and `request.accept`: a stranger must not be able to
 * probe whether a conversation exists.
 *
 * There is no admin bypass, unlike `job.byId`. An admin can already see the job,
 * the booking and the money; reading a private conversation is a different kind
 * of access and belongs behind a support flow that leaves an audit trail, not
 * behind the same procedure the participants use.
 */
export async function requireMatchParticipant(
  exec: Executor,
  matchId: string,
  userId: string,
): Promise<MatchContext> {
  const [row] = await exec
    .select({
      matchId: schema.matches.id,
      clientId: schema.matches.clientId,
      proId: schema.matches.proId,
      jobId: schema.jobs.id,
      jobTitle: schema.jobs.title,
      jobStatus: schema.jobs.status,
    })
    .from(schema.matches)
    .innerJoin(schema.jobs, eq(schema.jobs.id, schema.matches.jobId))
    .where(eq(schema.matches.id, matchId));

  if (!row || (row.clientId !== userId && row.proId !== userId)) {
    throw new TRPCError({ code: 'NOT_FOUND', message: 'Conversation not found' });
  }
  return row;
}

/** History is closed once the job is. See PAST_JOB_STATUSES. */
function canReply(status: JobStatus): boolean {
  return !PAST_JOB_STATUSES.includes(status);
}

/**
 * A conversation is either a MATCH or an ENQUIRY.
 *
 * A match is "a pro agreed to this job"; an enquiry is "somebody asked a
 * question before there was a job". They differ in what they hang off and what
 * closes them, and in nothing else — so they share one message table, one chat
 * screen, and the normalised context below.
 */
export const threadRefSchema = z.union([
  z.object({ matchId: z.string().uuid() }),
  z.object({ enquiryId: z.string().uuid() }),
]);
export type ThreadRef = z.infer<typeof threadRefSchema>;

export interface ThreadContext {
  kind: 'match' | 'enquiry';
  matchId: string | null;
  enquiryId: string | null;
  clientId: string;
  proId: string;
  /** Null on an enquiry — that is the whole point of one. */
  jobId: string | null;
  /** Null on an enquiry. Kept because "cancelled" and "finished" are not the
   *  same thing to say to somebody, and only the job knows which it was. */
  jobStatus: JobStatus | null;
  title: string;
  canReply: boolean;
}

/**
 * The gate for anything that reads or writes a conversation.
 *
 * NOT_FOUND rather than FORBIDDEN for a thread the caller is not part of — the
 * same rule as `job.byId` and `request.accept`: a stranger must not be able to
 * probe whether a conversation exists.
 */
export async function requireThreadParticipant(
  exec: Executor,
  ref: ThreadRef,
  userId: string,
): Promise<ThreadContext> {
  if ('matchId' in ref) {
    const match = await requireMatchParticipant(exec, ref.matchId, userId);
    return {
      kind: 'match',
      matchId: match.matchId,
      enquiryId: null,
      clientId: match.clientId,
      proId: match.proId,
      jobId: match.jobId,
      jobStatus: match.jobStatus,
      title: match.jobTitle,
      canReply: canReply(match.jobStatus),
    };
  }

  const [row] = await exec
    .select({
      id: schema.enquiries.id,
      clientId: schema.enquiries.clientId,
      proId: schema.enquiries.proId,
      closedAt: schema.enquiries.closedAt,
      headline: schema.proProfiles.headline,
    })
    .from(schema.enquiries)
    .innerJoin(schema.proProfiles, eq(schema.proProfiles.userId, schema.enquiries.proId))
    .where(eq(schema.enquiries.id, ref.enquiryId));

  if (!row || (row.clientId !== userId && row.proId !== userId)) {
    throw new TRPCError({ code: 'NOT_FOUND', message: 'Conversation not found' });
  }

  return {
    kind: 'enquiry',
    matchId: null,
    enquiryId: row.id,
    clientId: row.clientId,
    proId: row.proId,
    jobId: null,
    jobStatus: null,
    title: row.headline,
    // A pro can end an enquiry. The history stays readable; nothing more lands.
    canReply: row.closedAt === null,
  };
}

/** Scopes a message query to one thread, whichever kind it is. */
function inThread(ctx: ThreadContext) {
  return ctx.kind === 'match'
    ? eq(schema.messages.matchId, ctx.matchId!)
    : eq(schema.messages.enquiryId, ctx.enquiryId!);
}

/**
 * Keyset pagination, oldest-ward.
 *
 * The cursor is the id of the oldest message on the page, and the comparison
 * resolves that row's `created_at` inside the query. Two reasons it is not a
 * timestamp the caller carries:
 *
 *  - Postgres stores microseconds and a JS `Date` holds milliseconds, so a
 *    round-tripped timestamp is truncated — and every message that landed later
 *    in the same millisecond then falls the wrong side of `<` and is skipped.
 *  - A cursor from another conversation resolves to NULL here, which yields an
 *    empty page rather than a row from a thread the caller cannot see.
 *
 * `(created_at, id)` rather than `created_at` alone because a tie on the
 * timestamp would otherwise drop a message or repeat one.
 */
const cursorSchema = z.string().uuid();

export const messageRouter = router({
  /**
   * One thread: the header the screen needs, plus a page of messages oldest-first.
   *
   * Header and page come back together because the first render needs both, and
   * a second round trip to learn whose conversation this is would leave the
   * screen titleless for a beat.
   */
  thread: protectedProcedure
    .input(z.object({ ref: threadRefSchema, cursor: cursorSchema.optional() }))
    .query(async ({ ctx, input }) => {
      const uid = ctx.session.userId;
      const thread = await requireThreadParticipant(ctx.db, input.ref, uid);

      const peerId = thread.clientId === uid ? thread.proId : thread.clientId;
      const [peer] = await ctx.db
        .select({
          id: schema.users.id,
          name: schema.users.name,
          image: schema.users.image,
          role: schema.users.role,
        })
        .from(schema.users)
        .where(eq(schema.users.id, peerId));

      const rows = await ctx.db
        .select({
          id: schema.messages.id,
          senderId: schema.messages.senderId,
          body: schema.messages.body,
          attachments: schema.messages.attachments,
          readAt: schema.messages.readAt,
          createdAt: schema.messages.createdAt,
        })
        .from(schema.messages)
        .where(
          and(
            inThread(thread),
            input.cursor
              ? sql`(${schema.messages.createdAt}, ${schema.messages.id}) < (
                  SELECT anchor.created_at, anchor.id FROM messages anchor
                   WHERE anchor.id = ${input.cursor}::uuid
                )`
              : undefined,
          ),
        )
        .orderBy(desc(schema.messages.createdAt), desc(schema.messages.id))
        .limit(PAGE_SIZE + 1);

      const hasMore = rows.length > PAGE_SIZE;
      const page = hasMore ? rows.slice(0, PAGE_SIZE) : rows;
      const oldest = page[page.length - 1];

      return {
        match: {
          kind: thread.kind,
          id: thread.matchId ?? thread.enquiryId!,
          matchId: thread.matchId,
          enquiryId: thread.enquiryId,
          jobId: thread.jobId,
          jobStatus: thread.jobStatus,
          jobTitle: thread.title,
          canReply: thread.canReply,
          peer: peer ?? null,
        },
        // Newest last, the way a chat reads.
        messages: page.reverse().map((m) => ({ ...m, isMine: m.senderId === uid })),
        nextCursor: hasMore && oldest ? oldest.id : null,
      };
    }),

  /**
   * Say something.
   *
   * Insert and `lastMessageAt` move together in one transaction: the jobs list
   * sorts and previews on that column, so a message that lands without it is a
   * conversation that silently stops surfacing.
   */
  send: protectedProcedure.input(sendMessageSchema).mutation(async ({ ctx, input }) => {
    const uid = ctx.session.userId;
    assertSendRate(uid);

    return await ctx.db.transaction(async (tx) => {
      const thread = await requireThreadParticipant(tx, input.ref, uid);

      if (!thread.canReply) {
        throw new TRPCError({
          code: 'PRECONDITION_FAILED',
          message:
            thread.kind === 'enquiry'
              ? 'This enquiry was closed.'
              : thread.jobStatus === 'cancelled'
                ? 'This job was cancelled. The conversation is closed.'
                : 'This job is finished. The conversation is closed.',
        });
      }

      const [message] = await tx
        .insert(schema.messages)
        .values({
          matchId: thread.matchId,
          enquiryId: thread.enquiryId,
          senderId: uid,
          body: input.body,
          attachments: input.attachments,
        })
        .returning();

      if (!message) {
        throw new TRPCError({ code: 'INTERNAL_SERVER_ERROR', message: 'Could not send' });
      }

      // Both parents carry lastMessageAt: the jobs list and the pro's enquiry
      // inbox both sort on it, so a message that lands without it is a
      // conversation that silently stops surfacing.
      if (thread.kind === 'match') {
        await tx
          .update(schema.matches)
          .set({ lastMessageAt: message.createdAt })
          .where(eq(schema.matches.id, thread.matchId!));
      } else {
        await tx
          .update(schema.enquiries)
          .set({
            lastMessageAt: message.createdAt,
            // The pro answering is what takes this off the client's open cap.
            ...(uid === thread.proId ? { respondedAt: message.createdAt } : {}),
          })
          .where(eq(schema.enquiries.id, thread.enquiryId!));
      }

      return { ...message, isMine: true as const };
    });
  }),

  /**
   * Mark everything the other side sent as read.
   *
   * Idempotent by construction — the `read_at IS NULL` predicate is also the
   * partial index (`messages_unread_idx`), so a second call touches no rows.
   */
  markRead: protectedProcedure
    .input(z.object({ ref: threadRefSchema }))
    .mutation(async ({ ctx, input }) => {
      const uid = ctx.session.userId;
      const thread = await requireThreadParticipant(ctx.db, input.ref, uid);

      const updated = await ctx.db
        .update(schema.messages)
        .set({ readAt: new Date() })
        .where(
          and(
            inThread(thread),
            ne(schema.messages.senderId, uid),
            isNull(schema.messages.readAt),
          ),
        )
        .returning({ id: schema.messages.id });

      return { read: updated.length };
    }),

  /**
   * One number for the tab badge: everything unread across every conversation
   * this person is part of, on either side of the market.
   */
  unreadTotal: protectedProcedure.query(async ({ ctx }) => {
    const uid = ctx.session.userId;

    // Both kinds of thread, in one scan. Written as a single predicate rather
    // than two queries because the badge is one number and reading it twice
    // would let the halves disagree.
    const [row] = await ctx.db
      .select({ n: sql<number>`count(*)::int` })
      .from(schema.messages)
      .where(
        and(
          ne(schema.messages.senderId, uid),
          isNull(schema.messages.readAt),
          or(
            sql`EXISTS (
              SELECT 1 FROM matches m
               WHERE m.id = ${schema.messages.matchId}
                 AND (m.client_id = ${uid} OR m.pro_id = ${uid})
            )`,
            sql`EXISTS (
              SELECT 1 FROM enquiries e
               WHERE e.id = ${schema.messages.enquiryId}
                 AND (e.client_id = ${uid} OR e.pro_id = ${uid})
            )`,
          ),
        ),
      );

    return { unread: row?.n ?? 0 };
  }),
});