Pagination Sequence Generator

paginationsequence.php

<?php

/**
 * Generate a sequence of numbers for use in a pagination system, the clever way.
 * @author Bramus Van Damme <[email protected]>
 *
 * The algorithm always returns the same amount of items in the sequence,
 * indepdendent of the position of the current page.
 *
 * Example rows generated:
 * (adjusted to indicate the current page between [] + leading 0s added)
 *
 * [01]-02-03-04-05-06-07-08-..-73-74
 * 01-[02]-03-04-05-06-07-08-..-73-74
 * 01-02-[03]-04-05-06-07-08-..-73-74
 * 01-02-03-[04]-05-06-07-08-..-73-74
 * 01-02-03-04-[05]-06-07-08-..-73-74
 * 01-02-03-04-05-[06]-07-08-..-73-74
 * 01-02-..-05-06-[07]-08-09-..-73-74
 * 01-02-..-06-07-[08]-09-10-..-73-74
 * 01-02-..-07-08-[09]-10-11-..-73-74
 * ...
 * 01-02-..-65-66-[67]-68-69-..-73-74
 * 01-02-..-66-67-[68]-69-70-..-73-74
 * 01-02-..-67-68-[69]-70-71-72-73-74
 * 01-02-..-67-68-69-[70]-71-72-73-74
 * 01-02-..-67-68-69-70-[71]-72-73-74
 * 01-02-..-67-68-69-70-71-[72]-73-74
 * 01-02-..-67-68-69-70-71-72-[73]-74
 * 01-02-..-67-68-69-70-71-72-73-[74]
 *
 */
function generatePaginationSequence($curPage, $numPages, $numberOfPagesAtEdges = 2, $numberOfPagesAroundCurrent = 2, $glue = '..', $indicateActive = false) {
	
	// Define the number of items we would generate in a normal scenario
	// (viz. lots of pages, current page in the middle):
	//
	// numItemsInSequence = the current page + the number of items surrounding
	// the current page (left and right) + the number of items at the edges
	// of the generated sequence (left and right) + the glue in between the
	// different parts generated
	//
	// The goal is to enforce all sequences generated to have this amount
	// of items. By default this magic number would be 11, as seen/counted
	// in this sequence: 1-02-..-11-12-[13]-14-15-..-88-74
	$numItemsInSequence = 1 + ($numberOfPagesAroundCurrent * 2) + ($numberOfPagesAtEdges * 2) + 2;
	
	// Fix: curPage cannot be greater than numPages.
	$curPage = min($curPage, $numPages);
	
	// If we have less than $numItemsInSequence pages in total, there is no need to
	// start calculating but just return the full sequence, starting at 1
	if ($numPages <= $numItemsInSequence) {
		$finalSequence = range(1, $numPages);
	}
	
	// We have more pages than $numItemsInSequence, start calculating
	else {
	
		// If we have no forced amount of items on the edges, then the 
		// sequence must start from the current page number instead of 1
		$start = ($numberOfPagesAtEdges > 0) ? 1 : $curPage;
		
		// Parts of the sequence we'll be generating
		$sequence = array(
			'leftEdge' => null,
			'glueLeftCenter' => null,
			'centerPiece' => null,
			'glueCenterRight' => null,
			'rightEdge' => null
		);
		
		// If the current page is nearby the left edge (viz. curPage is
		// less than half of $numItemsInSequence away from left edge):
		// Don't generate a Center Piece, but extend the left part as
		// the left part would otherwise overlap the center piece.
		if ($curPage < ($numItemsInSequence/2)) {
			$sequence['leftEdge'] = range(1, ceil($numItemsInSequence/2) + $numberOfPagesAroundCurrent);
			$sequence['centerPiece'] = array($glue);
			if ($numberOfPagesAtEdges > 0) $sequence['rightEdge'] = range($numPages-($numberOfPagesAtEdges-1), $numPages);
		}

		// If the current page is nearby the right edge (viz. curPage is
		// less than half of $numItemsInSequence away from right edge):
		// Don't generate a center piece but extend the right part as
		// the right part would otherwise overlap the center piece.
		else if ($curPage > $numPages - ($numItemsInSequence/2)) {
			if ($numberOfPagesAtEdges > 0) $sequence['leftEdge'] = range($start, $numberOfPagesAtEdges);
			$sequence['centerPiece'] = array($glue);
			$sequence['rightEdge'] = range(min($numPages - floor($numItemsInSequence/2) - $numberOfPagesAroundCurrent, $curPage - $numberOfPagesAroundCurrent), $numPages);
		} 
		
		// The current page falls somewhere in the middle:
		// Generate ranges normally
		else {
			
			// Center Piece
			$sequence['centerPiece'] = range($curPage - $numberOfPagesAroundCurrent, $curPage + $numberOfPagesAroundCurrent);
			
			// Left/Right Edges (only if we requested)
			if ($numberOfPagesAtEdges > 0) $sequence['leftEdge'] = range($start,$numberOfPagesAtEdges);
			if ($numberOfPagesAtEdges > 0) $sequence['rightEdge'] = range($numPages-($numberOfPagesAtEdges-1), $numPages);
			
			// The glue we'll use to stick left, center, and right together
			// Special case: If the gap between left and center is only one
			// unit, don't add '...' but add that number instead
			$sequence['glueLeftCenter'] = ($sequence['centerPiece'][0] == ($numberOfPagesAtEdges+2)) ? array($numberOfPagesAtEdges+1) : array($glue);
			$sequence['glueCenterRight'] = array($glue);
			
		}
		
		// Join all (non-empty) parts of sequence into the final sequence
		$finalSequence = array();
		foreach($sequence as $k => $v) {
			if ($v !== null) {
				$finalSequence = array_merge($finalSequence, $v);
			}
		}

	}
	
	// Return the final sequence
	if ($indicateActive) {
		return array_replace($finalSequence, array(array_search($curPage, $finalSequence) => '[' . $curPage. ']'));
	} else {
		return $finalSequence;
	}

}

// EOF