import { Component, EventEmitter, Input, OnChanges, OnInit, Output, SimpleChanges } from '@angular/core';

type Page = {
  startPage: number;
  currentPage: number;
  endPage: number;
  totalPages: number;
  pages: number[];
};

@Component({
  selector: 'app-paginator',
  templateUrl: './paginator.component.html',
  styleUrls: ['./paginator.component.scss']
})
export class PaginatorComponent implements OnChanges {

  @Input()
  totalItems: number;

  @Input()
  pageSize: number;

  @Input()
  maxPages: number;

  @Output()
  pageChange: EventEmitter<number> = new EventEmitter();

  currentPage: number = 1;
  pages: Page;

  ngOnChanges(_: SimpleChanges): void {
    this.#paginate();
  }

  setPage(page: number) {
    if(page === this.currentPage)
      return;

    this.pageChange.emit(page);
    this.currentPage = page;
    this.#paginate();
  }

  #paginate() {
    const totalPages = Math.ceil(this.totalItems / this.pageSize);

    let startPage: number;
    let endPage: number;
    if (totalPages <= this.maxPages) {
      // total pages less than max so show all pages
      startPage = 1;
      endPage = totalPages;
    } else {
      // total pages more than max so calculate start and end pages
      const maxPagesBeforeCurrentPage = Math.floor(this.maxPages / 2);
      const maxPagesAfterCurrentPage = Math.ceil(this.maxPages / 2) - 1;
      if (this.currentPage <= maxPagesBeforeCurrentPage) {
        // current page near the start
        startPage = 1;
        endPage = this.maxPages;
      } else if (this.currentPage + maxPagesAfterCurrentPage >= totalPages) {
        // current page near the end
        startPage = totalPages - this.maxPages + 1;
        endPage = totalPages;
      } else {
        // current page somewhere in the middle
        startPage = this.currentPage - maxPagesBeforeCurrentPage;
        endPage = this.currentPage + maxPagesAfterCurrentPage;
      }
    }

    const pages = Array.from(Array((endPage + 1) - startPage).keys()).map(i => startPage + i);
    // return object with all pager properties required by the view
    this.pages = {
      currentPage: this.currentPage,
      startPage: startPage,
      endPage: endPage,
      totalPages: totalPages,
      pages: pages
    };
  }

}