// Credits:
// - http://stackoverflow.com/questions/5409831/mysql-stored-function-to-create-a-slug
// - https://gist.github.com/jareis/847e7e1523e4ea8f8676

DELIMITER ;;

DROP FUNCTION IF EXISTS `slugify`;;
CREATE FUNCTION `slugify`(dirty_string varchar(255)) RETURNS varchar(255) CHARSET utf8
    DETERMINISTIC
BEGIN
    DECLARE x, y , z , k INT;
    DECLARE temp_string, new_string, accents, noAccents VARCHAR(255);
    DECLARE is_allowed BOOL;
    DECLARE c, check_char VARCHAR(1);

    -- IF NULL DO NOT PROCEED
    If dirty_string IS NULL Then
        return dirty_string;
    End If;

    set temp_string = LOWER(dirty_string);

    -- REPLACE ACCENTS
    -- WITH CAPS
    -- set accents = 'ŠšŽžÀÁÂÃÄÅÆÇÈÉÊËÌÍÎÏÑÒÓÔÕÖØÙÚÛÜÝŸÞàáâãäåæçèéêëìíîïñòóôõöøùúûüýÿþƒ';
    -- set noAccents = 'SsZzAAAAAAACEEEEIIIINOOOOOOUUUUYYBaaaaaaaceeeeiiiinoooooouuuuyybf';
    -- ONLY SMALL CAPS
    set accents = 'šžàáâãäåæçèéêëìíîïñòóôõöøùúûüýÿþƒ';
    set noAccents = 'szaaaaaaaceeeeiiiinoooooouuuuyybf';
    set k = CHAR_LENGTH(accents);

    while k > 0 do
        set temp_string = REPLACE(temp_string, SUBSTRING(accents, k, 1), SUBSTRING(noAccents, k, 1));
        set k = k - 1;
    end while;

    -- CONVERT & TO EMPTY SPACE
    Set temp_string = REPLACE(temp_string, '&', '');

    -- REPLACE ALL UNWANTED CHARS
    Select temp_string REGEXP('[^a-z0-9\-]+') into x;
    If x = 1 then
        set z = 1;
        set k = CHAR_LENGTH(temp_string);
        While z <= k Do
            Set c = SUBSTRING(temp_string, z, 1);
            Set is_allowed = FALSE;
            If !((ascii(c) = 45) or (ascii(c) >= 48 and ascii(c) <= 57) or (ascii(c) >= 97 and ascii(c) <= 122)) Then
                Set temp_string = REPLACE(temp_string, c, '-');
            End If;
            set z = z + 1;
        End While;
    End If;

    Select temp_string REGEXP("^-|-$|'") into x;
    If x = 1 Then
        Set temp_string = Replace(temp_string, "'", '');
        Set z = CHAR_LENGTH(temp_string);
        Set y = CHAR_LENGTH(temp_string);
        Dash_check: While z > 1 Do
            If STRCMP(SUBSTRING(temp_string, -1, 1), '-') = 0 Then
                Set temp_string = SUBSTRING(temp_string,1, y-1);
                Set y = y - 1;
            Else
                Leave Dash_check;
            End If;
            Set z = z - 1;
        End While;
    End If;

    Repeat
        Select temp_string REGEXP("--") into x;
        If x = 1 Then
            Set temp_string = REPLACE(temp_string, "--", "-");
        End If;
    Until x <> 1 End Repeat;

    If LOCATE('-', temp_string) = 1 Then
        Set temp_string = SUBSTRING(temp_string, 2);
    End If;

    Return temp_string;
END;;

DELIMITER ;