const DataLoader = require('dataloader');

const util = require('./util');

const { SEARCH_OTHER_USERS } = require('../../perms/constants');

const UsersService = require('../../services/users');
const { escapeRegExp } = require('../../services/regex');
const UserModel = require('../../models/user');

const mergeState = (query, state) => {
  const { status } = state;

  if (status) {
    const { username, banned, suspended } = status;

    if (typeof username !== 'undefined' && username && username.length > 0) {
      query.merge({
        'status.username.status': {
          $in: username,
        },
      });
    }

    if (typeof banned !== 'undefined' && banned !== null) {
      query.merge({
        'status.banned.status': banned,
      });
    }

    if (typeof suspended !== 'undefined' && suspended !== null) {
      if (suspended) {
        query.merge({
          'status.suspension.until': {
            $gte: Date.now(),
          },
        });
      } else {
        query.merge({
          $or: [
            { 'status.suspension.until': null },
            {
              'status.suspension.until': {
                $lt: Date.now(),
              },
            },
          ],
        });
      }
    }
  }
};

const genUserByIDs = async (context, ids) => {
  if (!ids || ids.length === 0) {
    return [];
  }

  if (ids.length === 1) {
    const user = await UsersService.findById(ids[0]);
    return [user];
  }

  return UsersService.findByIdArray(ids).then(util.singleJoinBy(ids, 'id'));
};

/**
 * Retrieves users based on the passed in query that is filtered by the
 * current used passed in via the context.
 * @param  {Object} context   graph context
 * @param  {Object} query     query terms to apply to the users query
 */
const getUsersByQuery = async (
  { user },
  { limit, cursor, value = '', state, action_type, sortOrder }
) => {
  let query = UserModel.find();

  if (action_type || state || value.length > 0) {
    if (!user || !user.can(SEARCH_OTHER_USERS)) {
      return null;
    }

    if (value.length > 0) {
      // Lowercase the search term and escape any regex characters.
      value = escapeRegExp(value).toLowerCase();

      // Compile the prefix search regex.
      const $regex = new RegExp(`^${value}`);

      // Merge in the regex params.
      query.merge({
        $or: [
          // Search by a prefix match on the username.
          {
            lowercaseUsername: {
              $regex,
            },
          },

          // Search by a prefix match on the email address.
          {
            profiles: {
              $elemMatch: {
                id: {
                  $regex,
                },
                provider: 'local',
              },
            },
          },
        ],
      });
    }

    if (state) {
      mergeState(query, state);
    }

    if (action_type) {
      query.merge({
        [`action_counts.${action_type.toLowerCase()}`]: {
          $gt: 0,
        },
      });
    }
  }

  if (cursor) {
    if (sortOrder === 'DESC') {
      query = query.where({
        created_at: {
          $lt: cursor,
        },
      });
    } else {
      query = query.where({
        created_at: {
          $gt: cursor,
        },
      });
    }
  }

  // Apply the limit.
  if (limit) {
    query = query.limit(limit + 1);
  }

  // Sort by created_at.
  query.sort({ created_at: sortOrder === 'DESC' ? -1 : 1 });

  // Execute the query.
  const nodes = await query.exec();

  // The hasNextPage is always handled the same (ask for one more than we need,
  // if there is one more, than there is more).
  let hasNextPage = false;
  if (limit && nodes.length > limit) {
    // There was one more than we expected! Set hasNextPage = true and remove
    // the last item from the array that we requested.
    hasNextPage = true;
    nodes.splice(limit, 1);
  }

  const startCursor = nodes.length ? nodes[0].created_at : null;
  const endCursor = nodes.length ? nodes[nodes.length - 1].created_at : null;

  return {
    startCursor,
    endCursor,
    hasNextPage,
    nodes,
  };
};

/**
 * Retrieves the count of users based on the passed in query.
 * @param  {Object} context   graph context
 * @param  {Object} query     query to execute against the users collection
 *                            to compute the counts
 * @return {Promise}          resolves to the counts of the users from the
 *                            query
 */
const getCountByQuery = async ({ user }, { action_type, state }) => {
  let query = UserModel.find();

  if (action_type || state) {
    if (!user || !user.can(SEARCH_OTHER_USERS)) {
      return null;
    }

    if (state) {
      mergeState(query, state);
    }

    if (action_type) {
      query.merge({
        [`action_counts.${action_type.toLowerCase()}`]: {
          $gt: 0,
        },
      });
    }
  }

  return UserModel.find(query).count();
};

/**
 * Creates a set of loaders based on a GraphQL context.
 * @param  {Object} context the context of the GraphQL request
 * @return {Object}         object of loaders
 */
module.exports = context => ({
  Users: {
    getByQuery: query => getUsersByQuery(context, query),
    getByID: new DataLoader(ids => genUserByIDs(context, ids)),
    getCountByQuery: query => getCountByQuery(context, query),
  },
});