import { Component, ElementRef, effect, input, output, untracked, viewChild } from '@angular/core';
import { FormsModule } from '@angular/forms';
import { ButtonComponent } from '@shared/ui/button/button.component';
import { AlertComponent } from '@shared/ui/alert/alert.component';
import { SpinnerComponent } from '@shared/ui/spinner/spinner.component';
import { StepperComponent } from '@shared/ui/stepper/stepper.component';

/** A flat validation error pointing at a field: `id` matches the field's anchor. */
export interface WizardError {
  readonly id: string;
  readonly message: string;
}

export type WizardStatus = 'editing' | 'submitting' | 'submitted' | 'failed';

/**
 * Template: the canonical shell every wizard renders into, so they cannot drift.
 * It owns the consistent outline — stepper + focusable step heading + error
 * summary + the <form> + the Back/Next/Cancel action bar + the submitting/
 * submitted/failed states — and the a11y focus management.
 *
 * Presentational and unidirectional: all state stays in the wizard container
 * (the Elm-style store). Inputs flow down; the container reacts to the outputs
 * and dispatches messages. The step's own fields are projected as the default
 * slot; the success screen is projected via [wizardSuccess].
 */
@Component({
  selector: 'app-wizard-shell',
  imports: [FormsModule, ButtonComponent, AlertComponent, SpinnerComponent, StepperComponent],
  styles: [`
    .es-title{margin:0 0 var(--rhc-space-max-sm)}
    .es-list{margin:0;padding-inline-start:var(--rhc-space-max-xl)}
  `],
  template: `
    @switch (status()) {
      @case ('editing') {
        <app-stepper class="app-section" [steps]="steps()" [current]="current()" />
        <h2 #stepHeading tabindex="-1" class="rhc-heading nl-heading--level-2 app-section">{{ stepTitle() }}</h2>
        @if (errors().length) {
          <div #errorSummary tabindex="-1" role="alert" aria-labelledby="wizard-error-title" class="app-section">
            <app-alert type="error">
              <h3 id="wizard-error-title" class="rhc-heading nl-heading--level-3 es-title" i18n="@@wizard.errorTitle">Er ging iets mis met uw invoer</h3>
              <ul class="es-list">
                @for (e of errors(); track e.id) {
                  <li><a [href]="'#' + e.id" (click)="goToField($event, e.id)">{{ e.message }}</a></li>
                }
              </ul>
            </app-alert>
          </div>
        }
        <form (ngSubmit)="primary.emit()" class="app-form app-form-panel">
          <ng-content />
          <div class="app-button-row app-button-row--spaced">
            @if (canGoBack()) {
              <app-button type="button" variant="secondary" (click)="back.emit()" i18n="@@wizard.vorige">Vorige</app-button>
            }
            <app-button type="submit" variant="primary">{{ primaryLabel() }}</app-button>
            <app-button type="button" variant="subtle" (click)="cancel.emit()" i18n="@@wizard.annuleren">Annuleren</app-button>
          </div>
        </form>
      }
      @case ('submitting') {
        <app-spinner /> <span>{{ submittingLabel() }}</span>
      }
      @case ('submitted') {
        <ng-content select="[wizardSuccess]" />
      }
      @case ('failed') {
        <app-alert type="error">{{ errorMessage() }}</app-alert>
        <div class="app-section">
          <app-button variant="secondary" (click)="retry.emit()" i18n="@@wizard.opnieuwProberen">Opnieuw proberen</app-button>
        </div>
      }
    }
  `,
})
export class WizardShellComponent {
  steps = input.required<string[]>();
  current = input.required<number>();
  stepTitle = input.required<string>();
  status = input.required<WizardStatus>();
  primaryLabel = input.required<string>();
  canGoBack = input(false);
  errors = input<readonly WizardError[]>([]);
  errorMessage = input('');
  submittingLabel = input($localize`:@@wizard.submitting:Aanvraag wordt verwerkt…`);

  primary = output<void>();
  back = output<void>();
  cancel = output<void>();
  retry = output<void>();

  /** Error-summary link: focus the field instead of letting the browser navigate.
      A fragment href resolves against <base href="/">, not the current route, so
      a real navigation would reload to "/" and bounce to login. */
  protected goToField(ev: Event, id: string) {
    ev.preventDefault();
    document.getElementById(id)?.focus(); // focus() scrolls the input into view
  }

  private stepHeading = viewChild<ElementRef<HTMLElement>>('stepHeading');
  private errorSummary = viewChild<ElementRef<HTMLElement>>('errorSummary');

  constructor() {
    // A11y: move focus to the step heading when the step changes (skip first run
    // so we don't grab focus on initial load). Tracks current(), which is value-
    // stable across keystrokes, so typing never steals focus.
    let firstStep = true;
    effect(() => {
      this.current();
      if (firstStep) { firstStep = false; return; }
      untracked(() => queueMicrotask(() => this.stepHeading()?.nativeElement.focus()));
    });
    // A11y: when validation errors first appear (after a failed submit), move
    // focus to the error summary so it's announced. Only on the rising edge
    // (none → some): typing rebuilds the errors array each keystroke, and
    // re-focusing then would scroll the page up mid-edit. The summary keeps
    // role="alert", so content changes are still announced without the jump.
    let firstErr = true;
    let hadErrors = false;
    effect(() => {
      const has = this.errors().length > 0;
      if (firstErr) { firstErr = false; hadErrors = has; return; }
      if (has && !hadErrors) untracked(() => queueMicrotask(() => this.errorSummary()?.nativeElement.focus()));
      hadErrors = has;
    });
  }
}