'use strict';
var utils = require('./utils');
var merge = require('./merge');
var errors = require('./deps/errors');
var EE = require('events').EventEmitter;
var evalFilter = require('./evalFilter');
var evalView = require('./evalView');
module.exports = Changes;
utils.inherits(Changes, EE);

function Changes(db, opts, callback) {
  EE.call(this);
  var self = this;
  this.db = db;
  opts = opts ? utils.clone(opts) : {};
  var oldComplete = callback || opts.complete || function () {};
  var complete = opts.complete = utils.once(function (err, resp) {
    if (err) {
      self.emit('error', err);
    } else {
      self.emit('complete', resp);
    }
    self.removeAllListeners();
    db.removeListener('destroyed', onDestroy);
  });
  if (oldComplete) {
    self.on('complete', function (resp) {
      oldComplete(null, resp);
    });
    self.on('error', function (err) {
      oldComplete(err);
    });
  }
  var oldOnChange = opts.onChange;
  if (oldOnChange) {
    self.on('change', oldOnChange);
  }
  function onDestroy() {
    self.cancel();
  }
  db.once('destroyed', onDestroy);

  opts.onChange = function (change) {
    if (opts.isCancelled) {
      return;
    }
    self.emit('change', change);
    if (self.startSeq && self.startSeq <= change.seq) {
      self.emit('uptodate');
      self.startSeq = false;
    }
    if (change.deleted) {
      self.emit('delete', change);
    } else if (change.changes.length === 1 &&
      change.changes[0].rev.slice(0, 2) === '1-') {
      self.emit('create', change);
    } else {
      self.emit('update', change);
    }
  };

  var promise = new utils.Promise(function (fulfill, reject) {
    opts.complete = function (err, res) {
      if (err) {
        reject(err);
      } else {
        fulfill(res);
      }
    };
  });
  self.once('cancel', function () {
    if (oldOnChange) {
      self.removeListener('change', oldOnChange);
    }
    opts.complete(null, {status: 'cancelled'});
  });
  this.then = promise.then.bind(promise);
  this['catch'] = promise['catch'].bind(promise);
  this.then(function (result) {
    complete(null, result);
  }, complete);


  if (!db.taskqueue.isReady) {
    db.taskqueue.addTask(function () {
      if (self.isCancelled) {
        self.emit('cancel');
      } else {
        self.doChanges(opts);
      }
    });
  } else {
    self.doChanges(opts);
  }
}
Changes.prototype.cancel = function () {
  this.isCancelled = true;
  if (this.db.taskqueue.isReady) {
    this.emit('cancel');
  }
};
function processChange(doc, metadata, opts) {
  var changeList = [{rev: doc._rev}];
  if (opts.style === 'all_docs') {
    changeList = merge.collectLeaves(metadata.rev_tree)
    .map(function (x) { return {rev: x.rev}; });
  }
  var change = {
    id: metadata.id,
    changes: changeList,
    doc: doc
  };

  if (utils.isDeleted(metadata, doc._rev)) {
    change.deleted = true;
  }
  if (opts.conflicts) {
    change.doc._conflicts = merge.collectConflicts(metadata);
    if (!change.doc._conflicts.length) {
      delete change.doc._conflicts;
    }
  }
  return change;
}

Changes.prototype.doChanges = function (opts) {
  var self = this;
  var callback = opts.complete;

  opts = utils.clone(opts);
  if ('live' in opts && !('continuous' in opts)) {
    opts.continuous = opts.live;
  }
  opts.processChange = processChange;

  if (opts.since === 'latest') {
    opts.since = 'now';
  }
  if (!opts.since) {
    opts.since = 0;
  }
  if (opts.since === 'now') {
    this.db.info().then(function (info) {
      if (self.isCancelled) {
        callback(null, {status: 'cancelled'});
        return;
      }
      opts.since = info.update_seq;
      self.doChanges(opts);
    }, callback);
    return;
  }

  if (opts.continuous && opts.since !== 'now') {
    this.db.info().then(function (info) {
      self.startSeq = info.update_seq;
    }, function (err) {
      if (err.id === 'idbNull') {
        //db closed before this returned
        //thats ok
        return;
      }
      throw err;
    });
  }

  if (this.db.type() !== 'http' &&
      opts.filter && typeof opts.filter === 'string' &&
      !opts.doc_ids) {
    return this.filterChanges(opts);
  }

  if (!('descending' in opts)) {
    opts.descending = false;
  }

  // 0 and 1 should return 1 document
  opts.limit = opts.limit === 0 ? 1 : opts.limit;
  opts.complete = callback;
  var newPromise = this.db._changes(opts);
  if (newPromise && typeof newPromise.cancel === 'function') {
    var cancel = self.cancel;
    self.cancel = utils.getArguments(function (args) {
      newPromise.cancel();
      cancel.apply(this, args);
    });
  }
};

Changes.prototype.filterChanges = function (opts) {
  var self = this;
  var callback = opts.complete;
  if (opts.filter === '_view') {
    if (!opts.view || typeof opts.view !== 'string') {
      var err = errors.error(errors.BAD_REQUEST,
                             '`view` filter parameter is not provided.');
      callback(err);
      return;
    }
    // fetch a view from a design doc, make it behave like a filter
    var viewName = opts.view.split('/');
    this.db.get('_design/' + viewName[0], function (err, ddoc) {
      if (self.isCancelled) {
        callback(null, {status: 'cancelled'});
        return;
      }
      if (err) {
        callback(errors.generateErrorFromResponse(err));
        return;
      }
      if (ddoc && ddoc.views && ddoc.views[viewName[1]]) {
        
        var filter = evalView(ddoc.views[viewName[1]].map);
        opts.filter = filter;
        self.doChanges(opts);
        return;
      }
      var msg = ddoc.views ? 'missing json key: ' + viewName[1] :
        'missing json key: views';
      if (!err) {
        err = errors.error(errors.MISSING_DOC, msg);
      }
      callback(err);
      return;
    });
  } else {
    // fetch a filter from a design doc
    var filterName = opts.filter.split('/');
    this.db.get('_design/' + filterName[0], function (err, ddoc) {
      if (self.isCancelled) {
        callback(null, {status: 'cancelled'});
        return;
      }
      if (err) {
        callback(errors.generateErrorFromResponse(err));
        return;
      }
      if (ddoc && ddoc.filters && ddoc.filters[filterName[1]]) {
        var filter = evalFilter(ddoc.filters[filterName[1]]);
        opts.filter = filter;
        self.doChanges(opts);
        return;
      } else {
        var msg = (ddoc && ddoc.filters) ? 'missing json key: ' + filterName[1]
          : 'missing json key: filters';
        if (!err) {
          err = errors.error(errors.MISSING_DOC, msg);
        }
        callback(err);
        return;
      }
    });
  }
};