ParameterDecorator

ParameterDecorator.ts

class Validator {
    // Map<Class.prototype, Map<MethodName, IndexesToCheck>>
    private static notEmptyValidatorMap: Map<Object, Map<string, number[]>> = new Map();

    static registerNotEmpty(target: Object, methodName: string, paramIndex: number): void {
        let paramMap = this.notEmptyValidatorMap.get(target);
        if (!paramMap) {
            paramMap = new Map();
            this.notEmptyValidatorMap.set(target, paramMap);
        }
        let paramIndexes = paramMap.get(methodName);
        if (!paramIndexes) {
            paramIndexes = [];
            paramMap.set(methodName, paramIndexes);
        }
        paramIndexes.push(paramIndex);
    }

    static performValidation(target: Object, methodName: string, paramValues: unknown[]): boolean {
        const notEmptyMethodMap = this.notEmptyValidatorMap.get(target);
        const paramIndexes = notEmptyMethodMap?.get(methodName);

        if (!paramIndexes?.length) {
            return true;
        }

        return paramValues.every((paramValue, index) => {
            if (!paramIndexes.includes(index)) {
                return true;
            }
            return paramValue != false;
        });
    }
}

class Task {
    @Validate
    run(@NotEmpty name: string): void {
        console.log("running task, name: " + name);
    }
}

function Validate(
    target: Object,
    propertyKey: string,
    descriptor: TypedPropertyDescriptor<any>
): TypedPropertyDescriptor<any> {
    const originalMethod = descriptor.value;
    descriptor.value = function (...args) {
        if (!Validator.performValidation(target, propertyKey, args)) {
            console.error('Validation failed, method call aborted:',
                propertyKey);
            return;
        }
        return  originalMethod.apply(this, args);
    }
    return descriptor;
}

function NotEmpty(target: Object, propertyKey: string, parameterIndex: number) {
    Validator.registerNotEmpty(target, propertyKey, parameterIndex);
}


const task = new Task();
task.run('SomeTask');
task.run('');