import { Component, OnInit, Input, ChangeDetectionStrategy } from '@angular/core';
import { FormGroup, ValidationErrors } from '@angular/forms';

@Component({
  selector: 'validation-errors',
  templateUrl: './validation-errors.component.html',
  styleUrls: ['./validation-errors.component.css'],
  changeDetection: ChangeDetectionStrategy.OnPush
})
export class ValidationErrorsComponent implements OnInit {
  @Input() errors: ValidationErrors;

  constructor() {}

  ngOnInit() {}

}

<ng-container *ngIf="errors && errors['required']"> Required</ng-container>
<ng-container *ngIf="errors && errors['notUnique']">Already exists</ng-container>
<ng-container *ngIf="errors && errors['email']">Please enter a valid email</ng-container>

const nameControl = this.userForm.get('name');
nameControl.setErrors({
  "notUnique": true
});

<form [formGroup]="userForm" (ngSubmit)="submit()">
      <mat-form-field>
        <input matInput placeholder="name" formControlName="name" required>
        <mat-error *ngIf="userForm.get('name').status === 'INVALID'">
          <validation-errors [errors]="userForm.get('name').errors"></validation-errors>
        </mat-error>
      </mat-form-field>
      <mat-form-field>
        <input matInput placeholder="email" formControlName="email" required>
        <mat-error *ngIf="userForm.get('email').status === 'INVALID'">
          <validation-errors [errors]="userForm.get('email').errors"></validation-errors>
        </mat-error>
      </mat-form-field>
      <button mat-raised-button class="mat-raised-button" color="accent">SUBMIT</button>
    </form>

@Component({
  selector: '[validator]',
  template: `
    <ng-content></ng-content>
    <div *ngIf="formControl.invalid">
        <div *ngIf="formControl.errors.required && (form.submitted || formControl.dirty)">
             Please provide {{ formControl.name }}
        </div>
        <div *ngIf="formControl.errors.email && (form.submitted || formControl.dirty)">
             Please provide a valid email
        </div>
        <div *ngIf="formControl.errors.notstring && (form.submitted || formControl.dirty)">
             Invalid name
        </div>

    </div>
`})

export class ValidatorComponent implements OnInit {
   @ContentChild(FormControlName) formControl;
   constructor(private form: NgForm) {

   }

   ngOnInit() { }

}

<form #f="ngForm" (ngSubmit)="onSubmit(f)" novalidate>
<div [formGroup]="myForm">
     <label>Name</label>
     <div validator>
         <input type="text" formControlName="name">
     </div>
     <label>Lastname</label>
     <div validator>
         <input type="text" formControlName="lastname">
     </div>
     <label>Email</label>
     <div validator>
         <input type="text" formControlName="email">
     </div>
</div>
<button type="submit">Submit</button>
</form>

[{
  "nameType" : {
   maxLength : 5 ,
   minLength : 1 ,
   pattern  :  xxxxxx,
   etc
   etc

   }
}
]

<p class="error_message" *ngIf="form.get(controlName).hasError('required') && (form.submitted || form.get(controlName).dirty)">Please provide {{controlName}}</p>
<p class="error_message" *ngIf="form.get(controlName).hasError('email') && (form.submitted || form.get(controlName).dirty)">Please provide valid {{controlName}}</p>
...other errors

@Input() controlName;
@Input() form;

<validation-messages [form]="myForm" controlName="email"></validation-messages>

<div *ngIf="this.formControl.errors">
    <p>this.formControl.errors?.message</p>
</div>

<form [formGroup]="editorForm" novalidate>
    <label>First Name</label>
    <input formControlName="firstName" type="text">
    <ng2-mdf-validation-message [control]="firstName" *ngIf="!firstName.pristine"></ng2-mdf-validation-message>
</form>

@Directive(...)
export class ValidatorMessageDirective implements OnInit {

  constructor(
    private container: ControlContainer,
    private elem: ElementRef,          // host dom element
    private control: NgControl         // host form control
  ) { }

  ngOnInit() {
    const control = this.control.control;

    control.valueChanges.pipe(distinctUntilChanged()).subscribe(() => {
      this.option.forEach(validate => {
        if (control.hasError(validate.type)) {
          const validateMessageElem = document.getElementById(validate.id);
          if (!validateMessageElem) {
            const divElem = document.createElement('div');
            divElem.innerHTML = validate.message;
            divElem.id = validate.id;
            this.elem.nativeElement.parentNode.insertBefore(divElem, this.elem.nativeElement.nextSibling);
          }
        } else {
          const validateMessageElem = document.getElementById(validate.id);
          if (validateMessageElem) {
             this.elem.nativeElement.parentNode.removeChild(validateMessageElem);
          }
        }
      })
    });
  }
}

<form [formGroup]="form">
  <input type="text" formControlName="test" [validate-message]="testValidateOption"><br/>
  <input type="number" formControlName="test2" [validate-message]="test2ValidateOption">
</form>

<div class="input" [caption]="'SSN: '" name="ssn" type="text" [(ngModel)]="item.ssn" [async]="memberSsnValidatorFn" required></div>

import { AbstractControl } from "@angular/forms";

type ErrorFunction = (errorName: string, error: object) => string;
export type ErrorGetter =
    string | { [key2: string]: string } | ErrorFunction;

export class FormError {
    constructor(private errorGetter?: ErrorGetter) { }
    hasError(abstractControl: AbstractControl) {
        return abstractControl.errors && (abstractControl.dirty || abstractControl.touched);
    }
    getErrorMsgs(abstractControl: AbstractControl): string[] {
        if (!this.hasError(abstractControl))
            return null;
        let errors = abstractControl.errors;
        return Object.keys(errors).map(anyError => this.getErrorValue(anyError, errors[anyError]));
    }
    getErrorValue(errorName: string, error: object): string {
        let errorGetter = this.errorGetter;
        if (!errorGetter)
            return predictError(errorName, error);
        if (isString(errorGetter))
            return errorGetter;
        else if (isErrorFunction(errorGetter)) {
            let errorString = errorGetter(errorName, error);
            return this.predictedErrorIfEmpty(errorString, errorName, error)
        }
        else {
            let errorString = this.errorGetter[errorName];
            return this.predictedErrorIfEmpty(errorString, errorName, error)
        }
    }
    predictedErrorIfEmpty(errorString: string, errorName: string, error: object) {
        if (errorString == null || errorString == undefined)
            return predictError(errorName, error);
        return errorString;
    }


}
function predictError(errorName: string, error: object): string {
    if (errorName === 'required')
        return 'Cannot be blank';
    if (errorName === 'min')
        return `Should not be less than ${error['min']}`;
    if (errorName === 'max')
        return `Should not be more than ${error['max']}`;
    if (errorName === 'minlength')
        return `Alteast ${error['requiredLength']} characters`;
    if (errorName === 'maxlength')
        return `Atmost ${error['requiredLength']} characters`;
    // console.warn(`Error for ${errorName} not found. Error object = ${error}`);
    return 'Error';
}
export function isString(s: any): s is string {
    return typeof s === 'string' || s instanceof String;
}
export function isErrorFunction(f: any): f is ErrorFunction {
    return typeof f === "function";
}

class FormError {
    constructor(private errorGetter?: ErrorGetter) { }
    }

type ErrorFunction = (errorName: string, error: object) => string;
type ErrorGetter =
    string | { [key2: string]: string } | ErrorFunction;

<ng-container *ngIf="formError.hasError(control)">
  <div class='form-error-message' *ngFor='let error of  formError.getErrorMsgs(control)'>{{error}}</div>
</ng-container>

form-error {
    .form-error-message {
        color: red;
        font-size: .75em;
        padding-left: 16px;
    }
}

@Component({
  selector: 'form-error',
  templateUrl: 'form-error.html'
})
export class FormErrorComponent {
  @Input() formError: FromError;
  @Input() control: AbstractControl;
}

<form-error [control]='thatControl' ></form-error>