Abstract class for handling selected items

checkboxes-single-page.ts

export interface ICheckBoxModel {
    checked: boolean;
}

export class CheckboxesSinglePageModel<T extends ICheckBoxModel> {
    items: T[];
    isSelectAll: boolean;
    isIndeterminate: boolean;

    constructor(items: T[], initialState = false) {
        this.items = items;
        this.updateSelectAllState();
        if (initialState) {
            this.setAllItemState(initialState);
        }
    }

    get itemCount(): number {
        return this.items.length;
    }
    
    get hasItems(): boolean {
        return !!this.itemCount
    }

    get selectedItems() {
        return this.items.filter(x => x.checked);
    }

    get selectItemsCount(): number {
        return this.selectedItems.length;
    }

    onCheckboxClick(e: MouseEvent) {
        e.stopPropagation();
    }

    onItemChange() {
        this.updateSelectAllState();
    }

    selectAll(toggleSelectAll = false) {
        if (toggleSelectAll) {
            this.isSelectAll = !this.isSelectAll;
        }
        this.setAllItemState(this.isSelectAll);
    }

    setAllItemState(isCheck: boolean) {
        this.items.forEach(item => item.checked = isCheck);
        this.updateSelectAllState();
    }
    
    updateSelectAllState() {
        this.isSelectAll = this.items.length === this.selectedItems.length;
        this.isIndeterminate = !this.isSelectAll && !!this.selectedItems.length;
    }    
}