<?php
/*
Template Name: Tag Index
*/

get_header();

$valid_characters = range( 'a' , 'z' );
$valid_numbers = array(1,2,3,4,5,6,7,8,9,0);

// -----> This fixes the previous issue <----- //
$ent = ( strpos( get_permalink( $post->ID ) , '?' ) != false ) ? '&' : '?' ;

$nav = array();
// Build nav array
foreach( $valid_characters as $key => $character ) {
    $nav[] = '<a href="' . get_permalink( $post->ID ) . $ent.'tags=' . $character . '">' . strtoupper( $character ) . '</a>';
}
foreach( $valid_numbers as $key => $number ) {
    $nav[] = '<a href="' . get_permalink( $post->ID ) . $ent.'tags=' . $number . '">' . $number . '</a>';
}
// Array to hold tags, needs to be set, so the empty check works when none of the switch cases hit a match (for whatever reason)
$tags = array();
// Array that will hold arrays of tags based on their first letter
$tag_array = array();

// Main switch
switch( true ) {
    // If request for tag with particular letter
    case ( isset( $_GET['tags'] ) ):
        // If it's in the arrays created earlier, get tafs and sort into array
        case ( in_array( $_GET['tags'] , $valid_characters ) || in_array( $_GET['tags'] , $valid_numbers ) ):
            $tags = get_terms( 'post_tag' , "hide_empty=0&name__like=$_GET[tags]" );

            if( !empty( $tags ) ) {
                foreach( $tags as $tag ) {
                    $tag_array[$tag->name{0}][] = '<li><a href="'.get_tag_link( $tag->term_id ).'">'.$tag->name.'</a></li>';
                }
            }
        break;
    break;
    case ( !isset( $_GET['tags'] ) ):
    default:
        $tags = get_terms( 'post_tag' , 'hide_empty=0' );

        if( !empty( $tags ) ) {
            foreach( $tags as $tag ) {
                $tag_array[$tag->name{0}][] = '<li><a href="'.get_tag_link( $tag->term_id ).'">'.$tag->name.'</a></li>';
            }
        }
    break;
}
// If theres only one item in the array ( well one key ) , then it's a requested tag letter, so add a "Show all" link at the start of the nav
if( count( $tag_array ) == 1 ) array_unshift( $nav , '<a href="' . get_permalink( $post->ID ) . '">Show all</a>' );
?>

<div id="content" class="widecolumn">
    <!-- Feel free to add regular stuff you want here, like the_content() etc. -->
    <div class="nav">
        <?php
            // Imploding an array is an easy and reliable way to create a string with seperators
            echo implode( ' | ' , $nav );
        ?>
    </div>
<?php
    // If there's tags in the array
    if( !empty( $tag_array ) ) {
        foreach( $tag_array as $character => $character_tags ) {
        ?>
            <div class="tagindex">
                <h4><?php echo $character; ?></h4>
                <ul class="links">
                    <?php foreach( $character_tags as $key => $tag ) { echo $tag; } ?>
                </ul>
            </div>
        <?php
        }
    }
    else {
        ?>
        <h4>No tags found</h4>
        <?php
    }
    ?>
</div>
</div>
<?php get_footer(); ?>