a-miyashita/gulp-custom-filter

'use strict';

var assertIsFunction = require('./assertions').isFunction;
var promisenize = require('./promisenize');
var through = require('through2');

function filter(fn) {
    assertIsFunction(fn);
    return through.obj(function(file, encode, done) {
        promisenize(fn)(file, encode)
                .then(function(isTarget) {
                    if (isTarget) {
                        this.push(file);
                    }
                    done();
                }.bind(this), function(err) {
                    done(err);
                });
    });
}

module.exports = filter;