<?php

/**
 * pjdietz\WellRESTed\TemplateRoute
 *
 * @author PJ Dietz <pj@pjdietz.com>
 * @copyright Copyright 2014 by PJ Dietz
 * @license MIT
 */

namespace pjdietz\WellRESTed\Routes;

/**
 * Maps a URI template to a Handler
 */
class TemplateRoute extends RegexRoute
{
    /**
     * Regular expression matching URL friendly characters (i.e., letters,
     * digits, hyphen and underscore)
     */
    const RE_SLUG = '[0-9a-zA-Z\-_]+';
    /** Regular expression matching digitis */
    const RE_NUM = '[0-9]+';
    /** Regular expression matching letters */
    const RE_ALPHA = '[a-zA-Z]+';
    /** Regular expression matching letters and digits */
    const RE_ALPHANUM = '[0-9a-zA-Z]+';
    /** Regular expression matching a URI template variable (e.g., {id}) */
    const URI_TEMPLATE_EXPRESSION_RE = '/{([a-zA-Z]+)}/';

    /**
     * Create a new route that matches a URI template to a Handler.
     *
     * Optionally provide patterns for the variables in the template.
     *
     * @param string $template URI template the path must match
     * @param string $targetClassName Fully qualified name to an autoloadable handler class
     * @param string $defaultPattern Regular expression for variables
     * @param array|null $variablePatterns Map of variable names and regular expression
     */
    public function __construct(
        $template,
        $targetClassName,
        $defaultPattern = self::RE_SLUG,
        $variablePatterns = null
    ) {
        $pattern = $this->buildPattern($template, $defaultPattern, $variablePatterns);
        parent::__construct($pattern, $targetClassName);
    }

    /**
     * Translate the URI template into a regular expression.
     *
     * @param string $template URI template the path must match
     * @param string $defaultPattern Regular expression for variables
     * @param array $variablePatterns Map of variable names and regular expression
     * @return string
     */
    private function buildPattern($template, $defaultPattern, $variablePatterns)
    {
        if (is_null($variablePatterns)) {
            $variablePatterns = array();
        } elseif (is_object($variablePatterns)) {
            $variablePatterns = (array) $variablePatterns;
        }

        if (!$defaultPattern) {
            $defaultPattern = self::RE_SLUG;
        }

        $pattern = '';

        // Explode the template into an array of path segments.
        if ($template[0] === '/') {
            $parts = explode('/', substr($template, 1));
        } else {
            $parts = explode('/', $template);
        }

        foreach ($parts as $part) {

            $pattern .= '\/';

            // Is this part an expression or a literal?
            if (preg_match(self::URI_TEMPLATE_EXPRESSION_RE, $part, $matches)) {

                // Locate the name for the variable from the template.
                $variableName = $matches[1];

                // If the caller passed an array with this variable name
                // as a key, use its value for the pattern here.
                // Otherwise, use the class's current default.
                if (isset($variablePatterns[$variableName])) {
                    $variablePattern = $variablePatterns[$variableName];
                } else {
                    $variablePattern = $defaultPattern;
                }

                $pattern .= sprintf(
                    '(?<%s>%s)',
                    $variableName,
                    $variablePattern
                );

            } else {
                // This part is a literal.
                $pattern .= $part;
            }

        }

        $pattern = '/^' . $pattern . '$/';
        return $pattern;
    }

}