Configuration and Services

/**
 * Injectable service for configuring global ng-select defaults
 * Can be provided at root level or component level for different scopes
 */
@Injectable({
  providedIn: 'root'
})
export class NgSelectConfig {
  /** Default placeholder text for all selects */
  placeholder: string;
  /** Whether placeholder should remain visible when item is selected */
  fixedPlaceholder: boolean = true;
  /** Default text shown when no items match search */
  notFoundText: string = 'No items found';
  /** Default text shown when search term is required */
  typeToSearchText: string = 'Type to search';
  /** Default text for add tag functionality */
  addTagText: string = 'Add item';
  /** Default loading text */
  loadingText: string = 'Loading...';
  /** Default text for clear all action */
  clearAllText: string = 'Clear all';
  /** Disable virtual scroll globally */
  disableVirtualScroll: boolean = true;
  /** Open dropdown when Enter key is pressed */
  openOnEnter: boolean = true;
  /** Default element to append dropdown to */
  appendTo: string;
  /** Default property name for item values */
  bindValue: string;
  /** Default property name for item labels */
  bindLabel: string;
  /** Default appearance style */
  appearance: string = 'underline';
  /** Clear search term when adding items */
  clearSearchOnAdd: boolean;
  /** Deselect item when clicking on selected item */
  deselectOnClick: boolean;
  /** Move focus to tab when clearing selection */
  tabFocusOnClear: boolean = true;
}

// Configure globally in app module or main.ts
import { NgSelectConfig } from '@ng-select/ng-select';

// Method 1: Using injection token
@NgModule({
  providers: [
    {
      provide: NgSelectConfig,
      useValue: {
        placeholder: 'Choose an option...',
        notFoundText: 'No results found',
        clearAllText: 'Remove all',
        appearance: 'material'
      }
    }
  ]
})
export class AppModule {}

// Method 2: Using service configuration
@Component({
  providers: [NgSelectConfig]
})
export class CustomConfigComponent {
  constructor(private config: NgSelectConfig) {
    this.config.placeholder = 'Select from list...';
    this.config.clearable = true;
    this.config.appearance = 'outline';
  }
}

// Method 3: Per-component configuration
@Component({
  template: `
    <ng-select 
      [config]="customConfig"
      [(ngModel)]="selected">
      <!-- options -->
    </ng-select>
  `
})
export class PerComponentConfigComponent {
  customConfig = {
    placeholder: 'Pick your choice',
    clearAllText: 'Clear selection',
    notFoundText: 'Nothing matches your search'
  };
  selected: any;
}

/**
 * Injectable service for console logging and warnings
 * Used internally but can be overridden for custom logging
 */
@Injectable({
  providedIn: 'root'
})
export class ConsoleService {
  /**
   * Log warning message to console
   * @param message - Warning message to log
   */
  warn(message: string): void;
}

// Override console service for custom logging
@Injectable()
export class CustomConsoleService extends ConsoleService {
  warn(message: string): void {
    // Send warnings to external logging service
    this.loggingService.logWarning('ng-select', message);
    super.warn(message);
  }
  
  constructor(private loggingService: LoggingService) {
    super();
  }
}

@NgModule({
  providers: [
    { provide: ConsoleService, useClass: CustomConsoleService }
  ]
})
export class AppModule {}

/**
 * Injectable service for dropdown panel calculations and virtual scrolling
 * Handles viewport calculations, item positioning, and scroll optimization
 */
@Injectable({
  providedIn: 'root'
})
export class NgDropdownPanelService {
  /** Current panel dimensions and measurements */
  dimensions: PanelDimensions;
  
  /**
   * Calculate visible items range for virtual scrolling
   * @param scrollPos - Current scroll position in pixels
   * @param itemsLength - Total number of items
   * @param buffer - Number of buffer items to render outside viewport
   * @returns Object containing scroll calculations and item range
   */
  calculateItems(
    scrollPos: number, 
    itemsLength: number, 
    buffer: number
  ): ItemsRangeResult;
  
  /**
   * Get dimensions for panel sizing calculations
   * @param itemHeight - Height of individual items
   * @param panelHeight - Total height of panel
   * @returns Panel dimensions object
   */
  calculateDimensions(itemHeight: number, panelHeight: number): PanelDimensions;
  
  /**
   * Update scroll position and recalculate visible range
   * @param scrollTop - New scroll position
   * @param itemsLength - Total items count
   * @returns Updated items range
   */
  scrollTo(scrollTop: number, itemsLength: number): ItemsRangeResult;
}

/**
 * Interface for panel dimension calculations
 */
interface PanelDimensions {
  /** Height of individual items in pixels */
  itemHeight: number;
  /** Total height of the panel in pixels */
  panelHeight: number;
  /** Number of items visible in current viewport */
  itemsPerViewport: number;
}

/**
 * Interface for virtual scroll calculation results
 */
interface ItemsRangeResult {
  /** Total scroll height for scrollbar sizing */
  scrollHeight: number;
  /** Top padding to maintain scroll position */
  topPadding: number;
  /** Start index of visible range */
  start: number;
  /** End index of visible range */
  end: number;
}

@Component({
  template: `
    <ng-select 
      [items]="largeItemList"
      [virtualScroll]="true"
      [bufferAmount]="customBuffer"
      (scroll)="onScroll($event)">
    </ng-select>
  `
})
export class VirtualScrollComponent {
  largeItemList = Array.from({length: 50000}, (_, i) => ({
    id: i,
    name: `Item ${i + 1}`,
    category: `Category ${Math.floor(i / 100)}`
  }));
  
  customBuffer = 10;
  
  constructor(private panelService: NgDropdownPanelService) {}
  
  onScroll(event: {start: number, end: number}) {
    console.log(`Visible items: ${event.start} to ${event.end}`);
    
    // Access panel dimensions
    const dimensions = this.panelService.dimensions;
    console.log(`Item height: ${dimensions.itemHeight}px`);
    console.log(`Items per viewport: ${dimensions.itemsPerViewport}`);
  }
}

/**
 * Angular module providing all ng-select functionality
 * Exports all components and directives for use in templates
 */
@NgModule({
  declarations: [
    NgSelectComponent,
    NgOptionComponent,
    NgDropdownPanelComponent,
    // All template directives...
  ],
  imports: [CommonModule, FormsModule],
  exports: [
    NgSelectComponent,
    NgOptionComponent,
    NgDropdownPanelComponent,
    // All template directives...
  ],
  providers: [
    NgSelectConfig,
    ConsoleService,
    NgDropdownPanelService,
    { provide: SELECTION_MODEL_FACTORY, useValue: DefaultSelectionModelFactory }
  ]
})
export class NgSelectModule {
  /**
   * Configure the module with custom settings
   * @param config - Configuration options for the module
   * @returns ModuleWithProviders for use in app module imports
   */
  static forRoot(config?: Partial<NgSelectConfig>): ModuleWithProviders<NgSelectModule>;
}

// Basic module import
@NgModule({
  imports: [NgSelectModule],
  // ...
})
export class FeatureModule {}

// Module with global configuration
@NgModule({
  imports: [
    NgSelectModule.forRoot({
      placeholder: 'Select an option...',
      notFoundText: 'No matches found',
      appearance: 'material',
      clearAllText: 'Clear all selections'
    })
  ],
  // ...
})
export class AppModule {}

// Standalone component imports
@Component({
  selector: 'app-standalone',
  standalone: true,
  imports: [
    NgSelectComponent, 
    NgOptionComponent,
    NgLabelTemplateDirective,
    NgOptionTemplateDirective
  ],
  template: `
    <ng-select [(ngModel)]="selected">
      <ng-option *ngFor="let item of items" [value]="item">
        {{ item.name }}
      </ng-option>
    </ng-select>
  `
})
export class StandaloneSelectComponent {}

/**
 * Injection token for providing custom selection model factory
 */
export const SELECTION_MODEL_FACTORY: InjectionToken<SelectionModelFactory>;

/**
 * Function type for creating selection model instances  
 */
type SelectionModelFactory = () => SelectionModel;

/**
 * Interface defining selection model behavior
 */
interface SelectionModel {
  /** Currently selected items */
  value: NgOption[];
  
  /**
   * Select an item
   * @param item - Item to select
   * @param multiple - Whether multiple selection is enabled
   * @param selectableGroupAsModel - Whether groups should be part of model
   */
  select(item: NgOption, multiple: boolean, selectableGroupAsModel: boolean): void;
  
  /**
   * Unselect an item
   * @param item - Item to unselect  
   * @param multiple - Whether multiple selection is enabled
   */
  unselect(item: NgOption, multiple: boolean): void;
  
  /**
   * Clear all selections
   * @param keepDisabled - Whether to keep disabled items selected
   */
  clear(keepDisabled: boolean): void;
}

/**
 * Default selection model implementation
 */
export class DefaultSelectionModel implements SelectionModel {
  value: NgOption[] = [];
  
  select(item: NgOption, multiple: boolean, selectableGroupAsModel: boolean): void;
  unselect(item: NgOption, multiple: boolean): void;
  clear(keepDisabled: boolean): void;
}

/**
 * Default factory function for creating selection models
 */
export function DefaultSelectionModelFactory(): SelectionModel;

// Custom selection model with additional behavior
class AuditedSelectionModel extends DefaultSelectionModel {
  private auditLog: Array<{action: string, item: any, timestamp: Date}> = [];
  
  select(item: NgOption, multiple: boolean, selectableGroupAsModel: boolean): void {
    super.select(item, multiple, selectableGroupAsModel);
    this.auditLog.push({
      action: 'select',
      item: item.value,
      timestamp: new Date()
    });
  }
  
  unselect(item: NgOption, multiple: boolean): void {
    super.unselect(item, multiple);
    this.auditLog.push({
      action: 'unselect', 
      item: item.value,
      timestamp: new Date()
    });
  }
  
  getAuditLog() {
    return this.auditLog;
  }
}

// Provide custom selection model factory
@NgModule({
  providers: [
    {
      provide: SELECTION_MODEL_FACTORY,
      useValue: () => new AuditedSelectionModel()
    }
  ]
})
export class AppModule {}