var Q = require('q');
var format = require('util').format;
var low = require('lowdb');
low.mixin(low.mixin(require('underscore-db')));

/**
 * OKDB!
 * Minimal interface over a database of named collections of documents.
 */
function OKDB(options) {
  if (!(this instanceof OKDB)) return new OKDB(options);
  options = options || {};
  var type;
  if (typeof options === 'string')
    type = options;
  else
    type = options.type;
  if (!type)
    throw new Error('No DB type provided');
  switch (type) {
    case 'fs':
      return FSDB(options);
    default:
      throw new Error('Invalid DB type');
  }
}

/**
 * DB implementation backed by a JSON file.
 * TODO Incomplete
 */
function FSDB(options) {
  if (!(this instanceof FSDB)) return new FSDB(options);
  options = options || {};
  var name = options.name || 'db';
  var filename = name + '.json';
  this._db = low(filename);
}

FSDB.prototype._resolve = function(data, error) {
  return Q.Promise(function resolvePromise(resolve, reject) {
    if (error) {
      reject(error);
    } else {
      resolve(data);
    }
  });
};

FSDB.prototype.get = function(collection, query) {
  var data = this._db(collection).find(query);
  if (!query) {
    return this._resolve(null, new Error('No query given'));
  } else {
    return this._resolve(data);
  }
};

FSDB.prototype.put = function(collection, query, data) {
  data = data || {};
  if (!query) {
    return this._resolve(null, new Error('No query given'));
  } else if (this._db(collection).find(query)) {
    var updated = this._db(collection)
        .chain()
        .find(query)
        .assign(data)
        .value();
    return this._resolve(updated);
  } else {
    return this._resolve(null, new Error('Cannot update nonexistent entry'));
  }
};

FSDB.prototype.create = function(collection, id, data) {
  throw new Error('Not implemented!');
};

FSDB.prototype.remove = function(collection, id, data) {
  throw new Error('Not implemented!');
};

FSDB.prototype.find = function(collection, id, data) {
  throw new Error('Not implemented!');
};

FSDB.prototype.getMeta = function() {
  var data = this._db('meta').first();
  return this._resolve(data || {});
};

FSDB.prototype.getAll = function(collection) {
  var data = this._db(collection).toArray();
  return this._resolve(data || []);
};

module.exports = OKDB;