Validators.ts

import { Todo, TodoState } from './Model';

@validatable
export class ValidatableTodo implements Todo {

    id: number;

    @required
    @regex(`^[a-zA-Z ]*$`)
    name: string;

    state: TodoState;
}

export interface ValidatableTodo extends IValidatable {
}


export interface IValidatable {
    validate(): IValidationResult[];
}

export interface IValidationResult {
    isValid: boolean;
    message: string;
    property?: string;
}

export interface IValidator {
    (instance: Object): IValidationResult;
}

export function validate(): IValidationResult[] {
    let validators: IValidator[] = [].concat(this._validators),
        errors: IValidationResult[] = [];

    for (let validator of validators) {

        let result = validator(this);

        if (!result.isValid) {
            errors.push(result);
        }

    }

    return errors;
}

export function validatable(target: Function) {

    target.prototype.validate = validate;

}

export function required(target: Object, propertyName: string) {

    let validatable = <{ _validators: IValidator[] }>target,
        validators = (validatable._validators || (validatable._validators = []));

    validators.push(function(instance) {

        let propertyValue = instance[propertyName],
            isValid = propertyValue != undefined;

        if (typeof propertyValue === 'string') {
            isValid = propertyValue && propertyValue.length > 0;
        }

        return {
            isValid,
            message: `${propertyName} is required`,
            property: propertyName
        }

    })

}

export function regex(pattern: string) {
    
    let expression = new RegExp(pattern);

    return function regex(target: Object, propertyName: string) {

        let validatable = <{ _validators: IValidator[] }>target,
            validators = (validatable._validators || (validatable._validators = []));

        validators.push(function(instance) {

            let propertyValue = instance[propertyName],
                isValid = expression.test(propertyValue);

            return {
                isValid,
                message: `${propertyName} does not match ${expression}`,
                property: propertyName
            }

        })
        
    };

}