footnotes/includes/plugin-settings.php

<?php
/**
 * Created by Stefan Herndler.
 * User: Stefan
 * Date: 15.05.14
 * Time: 16:21
 * Version: 1.0-beta
 * Since: 1.0
 */


/**
 * add short links to the plugin main page
 * @since 1.0
 * @param array $links
 * @param mixed $file
 * @return array
 */
function footnotes_plugin_settings_link($links, $file)
{
    /* add link to the footnotes plugin settings page */
    $l_str_SettingsLink = '<a href="' . admin_url('options-general.php?page=' . FOOTNOTES_SETTINGS_PAGE_ID) . '">' . __('Settings', FOOTNOTES_PLUGIN_NAME) . '</a>';
	/* add link to the footnotes plugin support page on wordpress.org */
	$l_str_SupportLink = '<a href="http://wordpress.org/support/plugin/footnotes" target="_blank">' . __('Support', FOOTNOTES_PLUGIN_NAME) . '</a>';

	/* add defined links to the plugin main page */
	$links[] = $l_str_SupportLink;
	$links[] = $l_str_SettingsLink;

    /* return new links */
    return $links;
}


/**
 * reads a option field, filters the values and returns the filtered option array
 * fallback to default value since 1.0-gamma
 * @since 1.0
 * @param string $p_str_OptionsField
 * @param array $p_arr_DefaultValues
 * @param bool $p_bool_ConvertHtmlChars
 * @return array
 */
function footnotes_filter_options($p_str_OptionsField, $p_arr_DefaultValues, $p_bool_ConvertHtmlChars = true)
{
    $l_arr_Options = get_option($p_str_OptionsField);
	/* if no settings set yet return default values */
	if (empty($l_arr_Options)) {
		return $p_arr_DefaultValues;
	}
    /* loop through all keys in the array and filters them */
    foreach ($l_arr_Options as $l_str_Key => $l_str_Value) {
        /* removes special chars from the settings value */
        $l_str_Value = stripcslashes($l_str_Value);
        /* if set, convert html special chars */
        if ($p_bool_ConvertHtmlChars) {
            $l_str_Value = htmlspecialchars($l_str_Value);
        }
        /* check if settings value is not empty, otherwise load the default value, or empty string if no default is defined */
        if (!empty($l_str_Value)) {
            $l_arr_Options[$l_str_Key] = stripcslashes($l_str_Value);
            /* check if default value is defined */
        } else if (array_key_exists($l_str_Key, $p_arr_DefaultValues)) {
            $l_arr_Options[$l_str_Key] = $p_arr_DefaultValues[$l_str_Key];
        } else {
            $l_arr_Options[$l_str_Key] = "";
        }
    }

	// check if each key from the default values exist in return array
	foreach($p_arr_DefaultValues as $l_str_Key => $l_str_Value) {
		// if key not exists, add it with its default value
		if (!array_key_exists($l_str_Key, $l_arr_Options)) {
			$l_arr_Options[$l_str_Key] = $l_str_Value;
		}
	}
    /* returns the filtered array */
    return $l_arr_Options;
}

/**
 * converts a string depending on its value to a boolean
 * @since 1.0-beta
 * @param string $p_str_Value
 * @return bool
 */
function footnotes_ConvertToBool($p_str_Value)
{
    /* convert string to lower-case to make it easier */
    $p_str_Value = strtolower($p_str_Value);
    /* check if string seems to contain a "true" value */
    switch ($p_str_Value) {
        case "checked":
        case "yes":
        case "true":
        case "on":
        case "1":
            return true;
    }
    /* nothing found that says "true", so we return false */
    return false;
}