const Validation = {
	types: {
		require: {
			checker(value, option) {
				return !!value;
			},
			message(option) {
				return `This field is required.`;
			}
		},

		minlength: {
			checker(value, option) {
				return !!value && value.length >= option;
			},
			message(option) {
				return `This field must has at least ${option} letters.`;
			}
		},

		nodigits: {
			checker(value, option) {
				return !/\d/.test(value);
			},
			message(option) {
				return `This field shouldn't contains digits.`;
			}
		},

		isimage: {
			checker(value, option) {
				console.log(value);
				console.log(/\.(jpe?g|png|gif|svg)$/i.test(value));
				return /\.(jpe?g|png|gif|svg)$/i.test(value);
			},
			message(option) {
				return `This file isn't an image.`
			}
		},

		email: {
			checker(value, option) {
				return /^(([^<>()\[\]\\.,;:\s@"]+(\.[^<>()\[\]\\.,;:\s@"]+)*)|(".+"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/.test(value);
			},
			message(option) {
				return `This field doesn't match with appropriate pattern`;
			}
		}
	},

	errors: {},

	validate(config, values) {
		let checker = null, 		// username, email, pass, ...
			message = null, 		// function
			checkers = null,	  	// require, minlength
			option = null;			// true, 3

		// clear existing errors
		this.errors = {};

		if (!config) throw 'You have to pass a configuration!';

		for (let key in config) {
			checkers = ( config[key] ) ? Object.keys( config[key] ) : [];

			// validation
			for (let i = 0; i < checkers.length; i++) {
				let item = checkers[i];
				checker = this.types[item].checker;
				message = this.types[item].message;
				option = config[key][item];

				// throw an error if the validation method is missed
				if (!checker) {
					throw (`You don't have a validation method for ${checker} option`);
				}

				if ( !checker(values[key], option) ) {
					// add an error into the errors object and
					this.errors[key] = message(option);

					// switch to validation of next value
					break;
				}
			}

		}

		return this.errors;
	}