/**
 * Bridge routes — V3.7.
 *
 * Three transports, one delivery semantic. Each one streams the same
 * not-yet-acked inbox blobs for an authenticated address:
 *
 *   GET /v1/bridge/stream  — SSE feed, one envelope per `event: envelope`
 *   GET /v1/bridge/poll    — long-poll, returns at most one batch then closes
 *   GET /v1/bridge/ws      — WebSocket, JSON frame per envelope
 *
 * Auth: signed query string (`address`, `kind`, `since`, `signedAt`,
 * `signature`). The signature is verified against the address's owner key
 * registered via `/v1/inbox/register`. The `kind` field is bound into the
 * canonical signed payload to prevent cross-endpoint replay.
 *
 * Cursor semantics: `since` is the highest `receivedAt` the client already
 * processed. The server returns blobs strictly greater than that cursor and
 * advances the client's cursor by emitting a fresh `id:` (SSE) or by
 * including the highest seen `receivedAt` in the JSON response (poll/ws).
 *
 * The implementations subscribe to {@link InboxServerEvents} so that newly
 * stored blobs land on connected clients without polling the store. The
 * fallback path (no events configured) relies on a small in-process polling
 * timer with a configurable interval.
 */

import { Hono, type Context } from 'hono';
import { streamSSE } from 'hono/streaming';
import { createBunWebSocket } from 'hono/bun';
import type { CryptoProvider } from '@shade/core';
import {
  errorToHttpStatus,
  ShadeError,
  ValidationError,
  UnauthorizedError,
  toBase64,
} from '@shade/core';
import { verifyPayload, validateAddress } from '@shade/server';
import type { InboxStore } from './store.js';
import type { InboxServerEvents } from './events.js';

export type BridgeKind = 'stream' | 'poll' | 'ws';

export interface BridgeRoutesOptions {
  store: InboxStore;
  crypto: CryptoProvider;
  /** Optional events emitter — enables push-style delivery. */
  events?: InboxServerEvents;
  /** Maximum blobs returned per fetch page. Default 50. */
  pageLimit?: number;
  /** Default long-poll hold (ms). Default 25_000 (under typical proxy cutoffs). */
  longPollTimeoutMs?: number;
  /** Maximum long-poll hold (ms). Hard cap. Default 55_000. */
  longPollMaxTimeoutMs?: number;
  /** SSE heartbeat interval (ms). Default 15_000. */
  heartbeatIntervalMs?: number;
  /**
   * Fallback poll interval (ms) used when no `events` emitter is wired in.
   * The bridge will re-check the store at this cadence to detect new blobs.
   * Default 1_000.
   */
  fallbackPollIntervalMs?: number;
}

interface VerifiedBridgeRequest {
  address: string;
  kind: BridgeKind;
  since: number;
}

/**
 * Build the bridge Hono router and a paired Bun-WebSocket handler.
 *
 * The HTTP routes (`/v1/bridge/stream`, `/v1/bridge/poll`) work on every
 * Hono runtime. The `/v1/bridge/ws` route requires `hono/adapter/bun` to be
 * available — we lazy-require it so that non-Bun deployments aren't
 * forced to ship the import.
 */
export function createBridgeRoutes(opts: BridgeRoutesOptions): {
  app: Hono;
  /** Pass to `Bun.serve({ websocket })`. Undefined if Bun adapter is missing. */
  websocket: unknown;
} {
  const app = new Hono();
  const pageLimit = opts.pageLimit ?? 50;
  const heartbeatIntervalMs = opts.heartbeatIntervalMs ?? 15_000;
  const longPollDefault = opts.longPollTimeoutMs ?? 25_000;
  const longPollMax = opts.longPollMaxTimeoutMs ?? 55_000;
  const fallbackPollIntervalMs = opts.fallbackPollIntervalMs ?? 1_000;

  app.onError((err, c) => {
    if (err instanceof ShadeError) {
      const status = errorToHttpStatus(err);
      return c.json(err.toJSON(), status as any);
    }
    console.error('[Shade] Unhandled bridge error:', err);
    return c.json({ error: 'Internal server error' }, 500);
  });

  // ─── SSE ──────────────────────────────────────────────────────
  app.get('/v1/bridge/stream', async (c) => {
    const verified = await verifyBridgeAuth(c, opts, 'stream');
    return streamSSE(c, async (stream) => {
      const address = verified.address;
      let cursor = verified.since;
      const writer = makeBlobWriter(opts.store, pageLimit);

      // Initial backlog drain.
      const flushed = await flushTo(writer, address, cursor, async (blob) => {
        await stream.writeSSE({
          id: String(blob.receivedAt),
          event: 'envelope',
          data: JSON.stringify(serializeBlob(blob)),
        });
      });
      cursor = Math.max(cursor, flushed);

      // Hook up event-driven push if available, else fall back to a poll
      // timer that does the same scan.
      let cleanupSubscription: (() => void) | null = null;
      let signalled = false;
      let pendingFlushPromise: Promise<void> = Promise.resolve();

      const triggerFlush = (): void => {
        signalled = true;
        // Serialize fan-in so concurrent triggers don't double-fetch.
        pendingFlushPromise = pendingFlushPromise.then(async () => {
          while (signalled) {
            signalled = false;
            const drained = await flushTo(writer, address, cursor, async (blob) => {
              await stream.writeSSE({
                id: String(blob.receivedAt),
                event: 'envelope',
                data: JSON.stringify(serializeBlob(blob)),
              });
            });
            if (drained > cursor) cursor = drained;
          }
        });
      };

      if (opts.events) {
        cleanupSubscription = opts.events.on((e) => {
          if (e.name === 'inbox.blob_stored' && e.data.address === address) {
            triggerFlush();
          }
        });
      }
      const fallbackTimer = setInterval(() => triggerFlush(), fallbackPollIntervalMs);
      const heartbeat = setInterval(() => {
        // Comment lines are valid SSE keepalives.
        stream.write(`: ping ${Date.now()}\n\n`).catch(() => {});
      }, heartbeatIntervalMs);

      // Wait for the request to abort (client disconnect).
      await new Promise<void>((resolve) => {
        const sig = c.req.raw.signal;
        if (sig.aborted) return resolve();
        sig.addEventListener('abort', () => resolve(), { once: true });
      });

      cleanupSubscription?.();
      clearInterval(fallbackTimer);
      clearInterval(heartbeat);
      await pendingFlushPromise.catch(() => {});
    });
  });

  // ─── Long-poll ────────────────────────────────────────────────
  app.get('/v1/bridge/poll', async (c) => {
    const verified = await verifyBridgeAuth(c, opts, 'poll');
    const requestedTimeout = Number(c.req.query('timeoutMs') ?? longPollDefault);
    const timeoutMs = Math.min(
      Math.max(0, Number.isFinite(requestedTimeout) ? requestedTimeout : longPollDefault),
      longPollMax,
    );

    // Try immediate fetch first.
    let blobs = await opts.store.fetchBlobs({
      address: verified.address,
      sinceCursor: verified.since,
      now: Date.now(),
      limit: pageLimit,
    });
    if (blobs.length > 0) {
      return c.json(buildPollResponse(blobs, verified.since));
    }

    // Otherwise, wait for either a new event or the timeout.
    blobs = await waitForBlobs({
      events: opts.events ?? null,
      store: opts.store,
      address: verified.address,
      since: verified.since,
      timeoutMs,
      pageLimit,
      fallbackPollIntervalMs,
      abortSignal: c.req.raw.signal,
    });
    return c.json(buildPollResponse(blobs, verified.since));
  });

  // ─── WebSocket ────────────────────────────────────────────────
  // Hono's Bun adapter resolves `getBunServer` from the request's `env`
  // (the second argument of Bun.serve's fetch). On non-Bun runtimes the
  // upgrade simply fails at runtime; the SSE/long-poll routes still work.
  const { upgradeWebSocket, websocket } = createBunWebSocket();

  app.get(
    '/v1/bridge/ws',
    upgradeWebSocket(async (c: Context) => {
      let verified: VerifiedBridgeRequest | null = null;
      let upgradeError: Error | null = null;
      try {
        verified = await verifyBridgeAuth(c, opts, 'ws');
      } catch (err) {
        upgradeError = err as Error;
      }
      if (!verified) {
        // Hono's API doesn't let us reject the upgrade with a status code
        // before opening the socket; close immediately on open with a 4xxx
        // policy code so the client can fall back to a different bridge.
        return {
          onOpen(_evt: unknown, ws: { close: (code?: number, reason?: string) => void }) {
            const status =
              upgradeError instanceof ShadeError ? errorToHttpStatus(upgradeError) : 500;
            ws.close(4000 + (status % 1000), upgradeError?.message ?? 'unauthorized');
          },
        };
      }

      const address = verified.address;
      let cursor = verified.since;
      const writer = makeBlobWriter(opts.store, pageLimit);
      let unsubscribe: (() => void) | null = null;
      let fallbackTimer: ReturnType<typeof setInterval> | null = null;
      let pendingFlushPromise: Promise<void> = Promise.resolve();
      let signalled = false;
      let connected = true;

      return {
        onOpen(_evt: unknown, ws: {
          send: (data: string) => void;
          close: (code?: number, reason?: string) => void;
        }) {
          const triggerFlush = (): void => {
            signalled = true;
            pendingFlushPromise = pendingFlushPromise.then(async () => {
              while (signalled && connected) {
                signalled = false;
                const drained = await flushTo(writer, address, cursor, async (blob) => {
                  ws.send(JSON.stringify(serializeBlob(blob)));
                });
                if (drained > cursor) cursor = drained;
              }
            });
          };
          if (opts.events) {
            unsubscribe = opts.events.on((e) => {
              if (e.name === 'inbox.blob_stored' && e.data.address === address) {
                triggerFlush();
              }
            });
          }
          fallbackTimer = setInterval(() => triggerFlush(), fallbackPollIntervalMs);
          triggerFlush();
        },
        onClose() {
          connected = false;
          unsubscribe?.();
          if (fallbackTimer) clearInterval(fallbackTimer);
        },
      };
    }),
  );

  return { app, websocket };
}

// ─── helpers ──────────────────────────────────────────────────

async function verifyBridgeAuth(
  c: Context,
  opts: BridgeRoutesOptions,
  expectedKind: BridgeKind,
): Promise<VerifiedBridgeRequest> {
  const url = new URL(c.req.url);
  const qs = url.searchParams;
  const address = validateAddress(qs.get('address'));
  const kind = qs.get('kind');
  if (kind !== expectedKind) {
    throw new ValidationError(`bridge kind mismatch: expected ${expectedKind}`, 'kind');
  }
  const sinceStr = qs.get('since');
  const signedAtStr = qs.get('signedAt');
  const signature = qs.get('signature');
  if (sinceStr === null) throw new ValidationError('missing since', 'since');
  if (signedAtStr === null) throw new ValidationError('missing signedAt', 'signedAt');
  if (!signature) throw new ValidationError('missing signature', 'signature');
  const since = Number(sinceStr);
  const signedAt = Number(signedAtStr);
  if (!Number.isFinite(since) || since < 0) {
    throw new ValidationError('since must be a non-negative number', 'since');
  }
  if (!Number.isFinite(signedAt)) {
    throw new ValidationError('signedAt must be a number', 'signedAt');
  }

  const owner = await opts.store.getAddressOwner(address);
  if (!owner) {
    throw new UnauthorizedError(`address ${address} is not registered`);
  }

  await verifyPayload(opts.crypto, owner, {
    address,
    kind,
    since,
    signedAt,
    signature,
  });
  return { address, kind: kind as BridgeKind, since };
}

interface BlobRow {
  msgId: string;
  ciphertext: Uint8Array;
  receivedAt: number;
  expiresAt: number;
}

interface BlobWriter {
  fetchPage(address: string, cursor: number): Promise<BlobRow[]>;
}

function makeBlobWriter(store: InboxStore, pageLimit: number): BlobWriter {
  return {
    async fetchPage(address, cursor) {
      return store.fetchBlobs({
        address,
        sinceCursor: cursor,
        now: Date.now(),
        limit: pageLimit,
      });
    },
  };
}

async function flushTo(
  writer: BlobWriter,
  address: string,
  startCursor: number,
  emit: (blob: BlobRow) => Promise<void>,
): Promise<number> {
  let cursor = startCursor;
  // Drain page-by-page so a backlog larger than `pageLimit` still flushes.
  // eslint-disable-next-line no-constant-condition
  while (true) {
    const page = await writer.fetchPage(address, cursor);
    if (page.length === 0) break;
    for (const row of page) {
      await emit(row);
      if (row.receivedAt > cursor) cursor = row.receivedAt;
    }
    if (page.length === 0) break;
  }
  return cursor;
}

function serializeBlob(blob: BlobRow): {
  msgId: string;
  ciphertext: string;
  receivedAt: number;
  expiresAt: number;
} {
  return {
    msgId: blob.msgId,
    ciphertext: toBase64(blob.ciphertext),
    receivedAt: blob.receivedAt,
    expiresAt: blob.expiresAt,
  };
}

function buildPollResponse(blobs: BlobRow[], sinceFallback: number): {
  blobs: ReturnType<typeof serializeBlob>[];
  cursor: number;
  hasMore: boolean;
} {
  const out = blobs.map(serializeBlob);
  const cursor = blobs.length > 0 ? blobs[blobs.length - 1]!.receivedAt : sinceFallback;
  return { blobs: out, cursor, hasMore: false };
}

interface WaitForBlobsArgs {
  events: InboxServerEvents | null;
  store: InboxStore;
  address: string;
  since: number;
  timeoutMs: number;
  pageLimit: number;
  fallbackPollIntervalMs: number;
  abortSignal?: AbortSignal;
}

async function waitForBlobs(args: WaitForBlobsArgs): Promise<BlobRow[]> {
  if (args.timeoutMs === 0) return [];

  return new Promise<BlobRow[]>((resolve) => {
    let resolved = false;
    let unsubscribe: (() => void) | null = null;
    let timer: ReturnType<typeof setTimeout> | null = null;
    let fallback: ReturnType<typeof setInterval> | null = null;
    let abortHandler: (() => void) | null = null;

    const finish = (blobs: BlobRow[]) => {
      if (resolved) return;
      resolved = true;
      if (timer) clearTimeout(timer);
      if (fallback) clearInterval(fallback);
      if (unsubscribe) unsubscribe();
      if (abortHandler && args.abortSignal) {
        args.abortSignal.removeEventListener('abort', abortHandler);
      }
      resolve(blobs);
    };

    const tryFetch = async (): Promise<void> => {
      try {
        const rows = await args.store.fetchBlobs({
          address: args.address,
          sinceCursor: args.since,
          now: Date.now(),
          limit: args.pageLimit,
        });
        if (rows.length > 0) finish(rows);
      } catch {
        // swallow — let timeout handle it
      }
    };

    if (args.events) {
      unsubscribe = args.events.on((e) => {
        if (e.name === 'inbox.blob_stored' && e.data.address === args.address) {
          void tryFetch();
        }
      });
    }
    fallback = setInterval(tryFetch, args.fallbackPollIntervalMs);

    timer = setTimeout(() => finish([]), args.timeoutMs);

    if (args.abortSignal) {
      if (args.abortSignal.aborted) {
        finish([]);
        return;
      }
      abortHandler = () => finish([]);
      args.abortSignal.addEventListener('abort', abortHandler, { once: true });
    }
  });
}