const crypto = require('node:crypto');

const INSERT_ALERT_SQL = `
  WITH inserted AS (
    INSERT INTO alerts (route_id, alert_type, title, message, start_time, end_time, is_active, city_id)
    VALUES ($1, $2, $3, $4, $5, $6, $7, $8)
    RETURNING *
  )
  SELECT inserted.*, routes.route_number AS notification_route_number
  FROM inserted
  LEFT JOIN routes ON routes.id = inserted.route_id
`;

function createHttpError(status, message) {
  const error = new Error(message);
  error.status = status;
  return error;
}

function normalizeIdempotencyKey(value) {
  if (value === undefined || value === null) {
    return null;
  }

  const key = String(value).trim();

  if (!key) {
    throw createHttpError(400, 'Idempotency-Key must not be empty');
  }

  if (key.length > 255) {
    throw createHttpError(400, 'Idempotency-Key must not exceed 255 characters');
  }

  return key;
}

function normalizeAlertInput(payload) {
  return {
    route_id: payload.route_id || null,
    alert_type: payload.alert_type,
    title: payload.title,
    message: payload.message,
    start_time: payload.start_time,
    end_time: payload.end_time || null,
    is_active: payload.is_active !== false,
    city_id: payload.city_id || null
  };
}

function normalizeHashValue(value) {
  if (value instanceof Date) {
    return value.toISOString();
  }

  return value;
}

function createAlertRequestHash(alert) {
  const canonicalPayload = {
    route_id: normalizeHashValue(alert.route_id),
    alert_type: normalizeHashValue(alert.alert_type),
    title: normalizeHashValue(alert.title),
    message: normalizeHashValue(alert.message),
    start_time: normalizeHashValue(alert.start_time),
    end_time: normalizeHashValue(alert.end_time),
    is_active: normalizeHashValue(alert.is_active),
    city_id: normalizeHashValue(alert.city_id)
  };

  return crypto
    .createHash('sha256')
    .update(JSON.stringify(canonicalPayload))
    .digest('hex');
}

function splitNotificationRow(row) {
  const { notification_route_number: routeNumber, ...alert } = row;

  return {
    alert,
    notificationAlert: {
      ...alert,
      route_number: routeNumber ?? ''
    }
  };
}

function parseAlertSnapshot(value) {
  if (!value) {
    return null;
  }

  if (typeof value === 'string') {
    return JSON.parse(value);
  }

  return value;
}

function isAlertDue(alert, now = new Date()) {
  if (alert.is_active === false) {
    return false;
  }

  const startTime = new Date(alert.start_time);
  if (Number.isNaN(startTime.getTime()) || startTime > now) {
    return false;
  }

  if (!alert.end_time) {
    return true;
  }

  const endTime = new Date(alert.end_time);
  return !Number.isNaN(endTime.getTime()) && endTime >= now;
}

class AlertCreationService {
  constructor({ pool, notificationService, logger }) {
    this.pool = pool;
    this.notificationService = notificationService;
    this.logger = logger;
  }

  async createAlert(payload, { idempotencyKey: rawIdempotencyKey } = {}) {
    const alertInput = normalizeAlertInput(payload);
    const idempotencyKey = normalizeIdempotencyKey(rawIdempotencyKey);
    const result = idempotencyKey
      ? await this.createIdempotentAlert(alertInput, idempotencyKey)
      : await this.insertAlert(this.pool, alertInput);

    if (result.created && isAlertDue(result.alert)) {
      await this.sendNotification(result.notificationAlert);
    }

    return {
      alert: result.alert,
      created: result.created
    };
  }

  async insertAlert(queryable, alertInput) {
    const result = await queryable.query(INSERT_ALERT_SQL, [
      alertInput.route_id,
      alertInput.alert_type,
      alertInput.title,
      alertInput.message,
      alertInput.start_time,
      alertInput.end_time,
      alertInput.is_active,
      alertInput.city_id
    ]);

    const row = result.rows[0];

    if (!row) {
      throw new Error('Alert insert did not return the created row');
    }

    return {
      ...splitNotificationRow(row),
      created: true
    };
  }

  async createIdempotentAlert(alertInput, idempotencyKey) {
    const requestHash = createAlertRequestHash(alertInput);
    const client = await this.pool.connect();

    try {
      await client.query('BEGIN');

      const claimResult = await client.query(
        `INSERT INTO alert_creation_requests (idempotency_key, request_hash)
         VALUES ($1, $2)
         ON CONFLICT (idempotency_key) DO NOTHING
         RETURNING idempotency_key`,
        [idempotencyKey, requestHash]
      );

      if (claimResult.rows.length === 0) {
        const existingRequestResult = await client.query(
          `SELECT request_hash, alert_id, response_body
           FROM alert_creation_requests
           WHERE idempotency_key = $1
           FOR UPDATE`,
          [idempotencyKey]
        );
        const existingRequest = existingRequestResult.rows[0];

        if (!existingRequest) {
          throw new Error('Idempotency record disappeared during alert creation');
        }

        if (existingRequest.request_hash !== requestHash) {
          throw createHttpError(
            409,
            'Idempotency-Key was already used with a different request payload'
          );
        }

        const existingAlert = parseAlertSnapshot(existingRequest.response_body);

        if (!existingAlert) {
          throw new Error('Idempotency record is missing its alert response snapshot');
        }

        await client.query('COMMIT');

        return {
          alert: existingAlert,
          notificationAlert: null,
          created: false
        };
      }

      const created = await this.insertAlert(client, alertInput);

      await client.query(
        `UPDATE alert_creation_requests
         SET alert_id = $2,
             response_body = $3::jsonb
         WHERE idempotency_key = $1`,
        [idempotencyKey, created.alert.id, JSON.stringify(created.alert)]
      );
      await client.query('COMMIT');

      return created;
    } catch (error) {
      try {
        await client.query('ROLLBACK');
      } catch (rollbackError) {
        this.logger.error('Failed to roll back alert creation transaction', {
          reason: rollbackError.message
        });
      }

      throw error;
    } finally {
      client.release();
    }
  }

  async sendNotification(alert) {
    try {
      await this.notificationService.sendAlertCreated(alert);
    } catch (error) {
      this.logger.error('Failed to dispatch alert-created notification', {
        alertId: String(alert.id),
        reason: error.message || 'Unknown Firebase error',
        firebaseCode: error.code || 'unknown'
      });
    }
  }
}

let singleton = null;

function getAlertCreationService() {
  if (!singleton) {
    const pool = require('../config/database');
    const logger = require('../config/logger');
    const { getAlertNotificationService } = require('./alertNotificationService');

    singleton = new AlertCreationService({
      pool,
      logger,
      notificationService: getAlertNotificationService()
    });
  }

  return singleton;
}

function setAlertCreationServiceForTesting(service) {
  singleton = service;
}

module.exports = {
  AlertCreationService,
  createAlertRequestHash,
  getAlertCreationService,
  normalizeAlertInput,
  normalizeIdempotencyKey,
  parseAlertSnapshot,
  isAlertDue,
  setAlertCreationServiceForTesting
};