private _calculatePageStartEnd()

in components/RuiPagination/src/RuiPagination.ts [256:313]
46 lines of code
8 McCabe index (conditional complexity)

	private _calculatePageStartEnd(): number[] {
		let pageStart = 1;
		let pageEnd = this.numberOfPages;

		// if the number of pages to show is greater or equal to the number of pages
		// then we should just display every page as a pagination item
		if (
			this.pagesToShow === undefined ||
			this.pagesToShow >= this.numberOfPages
		) {
			return [pageStart, pageEnd];
		}

		// the number of items that should show to the left of the current page
		const leftShown = Math.floor(this.pagesToShow / 2);

		// the render logic is slightly different when we are in the
		// part of the app where ellipses are not shown
		const leftSideThreshold = leftShown + 2;

		if (this.currentPage <= leftSideThreshold) {
			// the number of pagination items that should show is
			// defined by pages to show + 4 where
			// the 4 comes from the start and end item which are always present,
			// and the two ellipses slots which may or may not be actual ellipses
			// e.g | 1 | ... | pages-to-show items | ... | n |
			const MAX_ITEMS = Math.min(this.pagesToShow + 4, this.numberOfPages);
			pageEnd = this.currentPage + (MAX_ITEMS - 2 - this.currentPage);
		} else {
			const rightShown = this.pagesToShow - leftShown - 1;
			const rightSideThreshold = this.numberOfPages - rightShown - 1;

			let rightTruncate = 0;
			if (this.currentPage >= rightSideThreshold) {
				rightTruncate = rightShown - (this.numberOfPages - this.currentPage) + 2
			}

			pageStart = Math.max(this.currentPage - leftShown - rightTruncate, 1);
			pageEnd =  Math.min(this.currentPage + rightShown, this.numberOfPages);
		}

		// if page start is at 3, then to the left will be 1 and ...
		// rather than spend a space on ..., may as well render the 2 instead
		// | 1 | ... | 3 |  => | 1 | 2 | 3 |
		if (pageStart === 3) {
			pageStart = 2;
		}

		// same principal as above but | n - 2 | ... | n |  => | n - 2 | n - 1 | n |
		if (pageEnd === this.numberOfPages - 2) {
			pageEnd = this.numberOfPages - 1;
		}

		return [
			pageStart,
			pageEnd
		];
	}