var fs = require('fs')
  , path = require('path')
  , customUtils = require('./customUtils')
  , model = require('./model')
  , async = require('async')
  , Executor = require('./executor')
  ;


/**
 * Create a new collection
 */
function Datastore (filename) {
  this.filename = filename;
  this.data = [];
  this.executor = new Executor();

  // We keep internally the number of lines in the datafile
  // This will be used when/if I implement autocompacting when the datafile grows too big
  this.datafileSize = 0;
}


/**
 * Load the database
 * This means pulling data out of the data file or creating it if it doesn't exist
 * Also, all data is persisted right away, which has the effect of compacting the database file
 * This operation is very quick at startup for a big collection (60ms for ~10k docs)
 * @param {Function} cb Optional callback, signature: err
 *
 * @api private Use loadDatabase
 */
Datastore.prototype._loadDatabase = function (cb) {
  var callback = cb || function () {}
    , self = this
    ;

  customUtils.ensureDirectoryExists(path.dirname(self.filename), function (err) {
    fs.exists(self.filename, function (exists) {
      if (!exists) {
        self.data = [];
        self.datafileSize = 0;
        fs.writeFile(self.filename, '', 'utf8', function (err) { return callback(err); });
      } else {
        fs.readFile(self.filename, 'utf8', function (err, rawData) {
          if (err) { return callback(err); }
          self.data = Datastore.treatRawData(rawData);
          self.datafileSize = self.data.length;
          self.persistCachedDatabase(callback);
        });
      }
    });
  });
};

Datastore.prototype.loadDatabase = function () {
  this.executor.push({ this: this, fn: this._loadDatabase, arguments: arguments });
};


/**
 * From a database's raw data, return the corresponding
 * machine understandable collection
 */
Datastore.treatRawData = function (rawData) {
  var data = rawData.split('\n')
    , dataById = {}
    , res = []
    , i;

  for (i = 0; i < data.length; i += 1) {
    var doc;

    try {
      doc = model.deserialize(data[i]);
      if (doc._id) {
        if (doc.$$deleted === true) {
          delete dataById[doc._id];
        } else {
          dataById[doc._id] = doc;
        }
      }
    } catch (e) {
    }
  }

  Object.keys(dataById).forEach(function (k) {
    res.push(dataById[k]);
  });

  return res;
};


/**
 * Persist cached database
 * This serves as a compaction function since the cache always contains only the number of documents in the collection
 * while the data file is append-only so it may grow larger
 * @param {Function} cb Optional callback, signature: err
 */
Datastore.prototype.persistCachedDatabase = function (cb) {
  var callback = cb || function () {}
    , toPersist = ''
    ;

  this.data.forEach(function (doc) {
    toPersist += model.serialize(doc) + '\n';
  });

  if (toPersist.length === 0) { return callback(); }

  fs.writeFile(this.filename, toPersist, function (err) { return callback(err); });

};


/**
 * Insert a new document
 * @param {Function} cb Optional callback, signature: err, insertedDoc
 *
 * @api private Use Datastore.insert which has the same signature
 */
Datastore.prototype._insert = function (newDoc, cb) {
  var callback = cb || function () {}
    , self = this
    , persistableNewDoc
    ;

  try {
    newDoc._id = newDoc._id || customUtils.uid(16);
    persistableNewDoc = model.serialize(newDoc);
  } catch (e) {
    return callback(e);
  }

  fs.appendFile(self.filename, persistableNewDoc + '\n', 'utf8', function (err) {
    if (err) { return callback(err); }

    var insertedDoc = model.deserialize(persistableNewDoc);
    self.data.push(insertedDoc);
    self.datafileSize += 1;
    return callback(null, insertedDoc);
  });
};

Datastore.prototype.insert = function () {
  this.executor.push({ this: this, fn: this._insert, arguments: arguments });
};


/**
 * Find all documents matching the query
 * @param {Object} query MongoDB-style query
 */
Datastore.prototype.find = function (query, callback) {
  var res = []
    , self = this
    , i
    ;

  try {
    for (i = 0; i < self.data.length; i += 1) {
      if (model.match(self.data[i], query)) {
        res.push(model.deepCopy(self.data[i]));
      }
    }
  } catch (err) {
    return callback(err);
  }

  return callback(null, res);
};


/**
 * Find one document matching the query
 * @param {Object} query MongoDB-style query
 */
Datastore.prototype.findOne = function (query, callback) {
  var self = this
    , i
    ;

  try {
    for (i = 0; i < self.data.length; i += 1) {
      if (model.match(self.data[i], query)) {
        return callback(null, model.deepCopy(self.data[i]));
      }
    }
  } catch (err) {
    return callback(err);
  }

  return callback(null, null);
};


/**
 * Persist new state for the given newDocs (can be update or removal)
 * Use an append-only format
 * @param {Array} newDocs Can be empty if no doc was updated/removed
 * @param {Function} cb Optional, signature: err
 */
Datastore.prototype.persistNewState = function (newDocs, cb) {
  var self = this
    , toPersist = ''
    , callback = cb || function () {}
    ;

  self.datafileSize += newDocs.length;

  newDocs.forEach(function (doc) {
    toPersist += model.serialize(doc) + '\n';
  });

  if (toPersist.length === 0) { return callback(); }

  fs.appendFile(self.filename, toPersist, 'utf8', function (err) {
    return callback(err);
  });
};


/**
 * Update all docs matching query
 * For now, very naive implementation (recalculating the whole database)
 * @param {Object} query
 * @param {Object} updateQuery
 * @param {Object} options Optional options
 *                 options.multi If true, can update multiple documents (defaults to false)
 *                 options.upsert If true, document is inserted if the query doesn't match anything
 * @param {Function} cb Optional callback, signature: err, numReplaced, upsert (set to true if the update was in fact an upsert)
 *
 * @api private Use Datastore.update which has the same signature
 */
Datastore.prototype._update = function (query, updateQuery, options, cb) {
  var callback
    , self = this
    , numReplaced = 0
    , multi, upsert
    , updatedDocs = []
    , i
    ;

  if (typeof options === 'function') { cb = options; options = {}; }
  callback = cb || function () {};
  multi = options.multi !== undefined ? options.multi : false;
  upsert = options.upsert !== undefined ? options.upsert : false;

  async.waterfall([
  function (cb) {   // If upsert option is set, check whether we need to insert the doc
    if (!upsert) { return cb(); }

    self.findOne(query, function (err, doc) {
      if (err) { return callback(err); }
      if (doc) {
        return cb();
      } else {
        // The upserted document is the query (since for now queries have the same structure as
        // documents), modified by the updateQuery
        return self._insert(model.modify(query, updateQuery), function (err) {
          if (err) { return callback(err); }
          return callback(null, 1, true);
        });
      }
    });
  }
  , function () {   // Perform the update
    try {
      for (i = 0; i < self.data.length; i += 1) {
        if (model.match(self.data[i], query) && (multi || numReplaced === 0)) {
          numReplaced += 1;
          self.data[i] = model.modify(self.data[i], updateQuery);
          updatedDocs.push(self.data[i]);
        }
      }
    } catch (err) {
      return callback(err);
    }

    self.persistNewState(updatedDocs, function (err) {
      if (err) { return callback(err); }
      return callback(null, numReplaced);
    });
  }
  ]);
};
Datastore.prototype.update = function () {
  this.executor.push({ this: this, fn: this._update, arguments: arguments });
};


/**
 * Remove all docs matching the query
 * For now very naive implementation (similar to update)
 * @param {Object} query
 * @param {Object} options Optional options
 *                 options.multi If true, can update multiple documents (defaults to false)
 * @param {Function} cb Optional callback, signature: err, numRemoved
 *
 * @api private Use Datastore.remove which has the same signature
 */
Datastore.prototype._remove = function (query, options, cb) {
  var callback
    , self = this
    , numRemoved = 0
    , multi
    , newData = []
    , removedDocs = []
    ;

  if (typeof options === 'function') { cb = options; options = {}; }
  callback = cb || function () {};
  multi = options.multi !== undefined ? options.multi : false;

  try {
    self.data.forEach(function (d) {
      if (model.match(d, query) && (multi || numRemoved === 0)) {
        numRemoved += 1;
        removedDocs.push({ $$deleted: true, _id: d._id });
      } else {
        newData.push(d);
      }
    });
  } catch (err) {
    return callback(err);
  }

  self.persistNewState(removedDocs, function (err) {
    if (err) { return callback(err); }
    self.data = newData;
    return callback(null, numRemoved);
  });
};
Datastore.prototype.remove = function () {
  this.executor.push({ this: this, fn: this._remove, arguments: arguments });
};


module.exports = Datastore;