import QRCode from 'qrcode';
import { resolveRpcAuthority } from '../../rpc-authority.mjs';

export const WEIXIN_RPC_CHANNEL = '/weixin';
export const WEIXIN_ENDPOINTS = Object.freeze({
  status: 'connection.status',
  beginProvisioning: 'provision.begin',
  pollProvisioning: 'provision.poll',
  submitVerification: 'provision.verify',
  cancelProvisioning: 'provision.cancel',
  reconnectBot: 'bot.reconnect',
  deleteBot: 'bot.delete',
});
export const WEIXIN_RPC_ENDPOINTS = Object.freeze(Object.values(WEIXIN_ENDPOINTS));

function isRecord(value) {
  return value !== null && typeof value === 'object' && !Array.isArray(value);
}

function exactKeys(value, allowed) {
  return isRecord(value) && Object.keys(value).every((key) => allowed.includes(key));
}

function validId(value) {
  return typeof value === 'string' && /^[A-Za-z0-9_-]{1,128}$/.test(value);
}

function payloadFailure(endpoint, payload) {
  if (!isRecord(payload)) return 'Payload must be an object.';
  if (endpoint === WEIXIN_ENDPOINTS.status) {
    return exactKeys(payload, []) ? null : 'connection.status does not accept fields.';
  }
  if (endpoint === WEIXIN_ENDPOINTS.beginProvisioning) {
    return exactKeys(payload, ['locale']) && (payload.locale === undefined || payload.locale === 'zh-CN')
      ? null
      : 'provision.begin received unsupported fields.';
  }
  if ([WEIXIN_ENDPOINTS.pollProvisioning, WEIXIN_ENDPOINTS.cancelProvisioning].includes(endpoint)) {
    return exactKeys(payload, ['attemptId']) && validId(payload.attemptId)
      ? null
      : `${endpoint} requires an attemptId.`;
  }
  if (endpoint === WEIXIN_ENDPOINTS.submitVerification) {
    return exactKeys(payload, ['attemptId', 'verifyCode'])
      && validId(payload.attemptId)
      && typeof payload.verifyCode === 'string'
      && /^\d{4,8}$/.test(payload.verifyCode)
      ? null
      : 'provision.verify requires an attemptId and a 4-to-8-digit code.';
  }
  if (endpoint === WEIXIN_ENDPOINTS.reconnectBot) {
    return exactKeys(payload, ['botId']) && validId(payload.botId)
      ? null
      : 'bot.reconnect requires a botId.';
  }
  if (endpoint === WEIXIN_ENDPOINTS.deleteBot) {
    return exactKeys(payload, ['botId', 'confirm']) && validId(payload.botId) && payload.confirm === true
      ? null
      : 'bot.delete requires a botId and confirm=true.';
  }
  return 'Unknown Weixin endpoint.';
}

function badRequest(message) {
  return { ok: false, error: { code: 'bad-request', message } };
}

function cancelled() {
  return { ok: false, error: { code: 'cancelled', message: 'The request was cancelled.' } };
}

function internalFailure() {
  return {
    ok: false,
    error: { code: 'weixin-operation-failed', message: '微信操作失败，请稍后重试。' },
  };
}

async function qrDataUrl(value) {
  return QRCode.toDataURL(value, {
    type: 'image/png',
    errorCorrectionLevel: 'M',
    margin: 2,
    width: 320,
  });
}

async function withEncodedQr(value, encodeQr) {
  if (!value || !value.verificationUrl) return value;
  return {
    ...value,
    qrCodeDataUrl: await encodeQr(value.verificationUrl),
  };
}

async function publicStatus(status, encodeQr) {
  const safe = structuredClone(status);
  if (safe.provisioning) safe.provisioning = await withEncodedQr(safe.provisioning, encodeQr);
  return safe;
}

function assertController(controller) {
  if (!controller
    || typeof controller.status !== 'function'
    || typeof controller.startProvisioning !== 'function'
    || typeof controller.registrationStatus !== 'function'
    || typeof controller.submitVerification !== 'function'
    || typeof controller.cancelProvisioning !== 'function'
    || typeof controller.reconnectBot !== 'function'
    || typeof controller.deleteBot !== 'function') {
    throw new TypeError('A complete Weixin controller is required');
  }
}

export function createWeixinRpcHandler(controller, { encodeQr = qrDataUrl } = {}) {
  assertController(controller);
  const qrCache = new Map();
  const cachedEncode = (url) => {
    let encoded = qrCache.get(url);
    if (!encoded) {
      if (qrCache.size >= 16) qrCache.delete(qrCache.keys().next().value);
      encoded = Promise.resolve().then(() => encodeQr(url));
      qrCache.set(url, encoded);
    }
    return encoded;
  };

  return async (endpoint, payload, signal) => {
    if (signal?.aborted) return cancelled();
    if (!WEIXIN_RPC_ENDPOINTS.includes(endpoint)) return badRequest('Unknown Weixin endpoint.');
    const invalid = payloadFailure(endpoint, payload);
    if (invalid) return badRequest(invalid);

    try {
      let value;
      if (endpoint === WEIXIN_ENDPOINTS.status) {
        value = await publicStatus(await controller.status(), cachedEncode);
      } else if (endpoint === WEIXIN_ENDPOINTS.beginProvisioning) {
        const started = await controller.startProvisioning();
        if (signal?.aborted) {
          await controller.cancelProvisioning(started.attemptId);
          return cancelled();
        }
        value = await withEncodedQr(started, cachedEncode);
      } else if (endpoint === WEIXIN_ENDPOINTS.pollProvisioning) {
        const current = await controller.registrationStatus(payload.attemptId);
        if (!current) return badRequest('The provisioning attempt no longer exists.');
        value = await withEncodedQr(current, cachedEncode);
      } else if (endpoint === WEIXIN_ENDPOINTS.submitVerification) {
        value = await withEncodedQr(
          await controller.submitVerification(payload.attemptId, payload.verifyCode),
          cachedEncode,
        );
      } else if (endpoint === WEIXIN_ENDPOINTS.cancelProvisioning) {
        value = await controller.cancelProvisioning(payload.attemptId);
        if (!value) return badRequest('The provisioning attempt no longer exists.');
      } else if (endpoint === WEIXIN_ENDPOINTS.reconnectBot) {
        value = await publicStatus(await controller.reconnectBot(payload.botId), cachedEncode);
      } else {
        value = await publicStatus(await controller.deleteBot(payload.botId), cachedEncode);
      }
      return signal?.aborted ? cancelled() : { ok: true, value };
    } catch {
      return signal?.aborted ? cancelled() : internalFailure();
    }
  };
}

export function installWeixinRpc(ctx, controller, options, authority) {
  if (!ctx?.connection?.rpc || typeof ctx.connection.rpc.handle !== 'function') {
    throw new TypeError('DSH Host Connection RPC is required');
  }
  return ctx.connection.rpc.handle(
    WEIXIN_RPC_CHANNEL,
    createWeixinRpcHandler(controller, options),
    { authority: resolveRpcAuthority(authority) },
  );
}