<?php

namespace FluentForm\Framework\Support;

/**
 * Expands URI templates. Userland implementation of PECL uri_template.
 *
 * @see https://datatracker.ietf.org/doc/html/rfc6570
 */
final class UriTemplate
{
    /**
     * @var array<string, array{prefix:string, joiner:string, query:bool}> Hash for quick operator lookups
     */
    private static $operatorHash = [
        '' => ['prefix' => '', 'joiner' => ',', 'query' => false],
        '+' => ['prefix' => '', 'joiner' => ',', 'query' => false],
        '#' => ['prefix' => '#', 'joiner' => ',', 'query' => false],
        '.' => ['prefix' => '.', 'joiner' => '.', 'query' => false],
        '/' => ['prefix' => '/', 'joiner' => '/', 'query' => false],
        ';' => ['prefix' => ';', 'joiner' => ';', 'query' => true],
        '?' => ['prefix' => '?', 'joiner' => '&', 'query' => true],
        '&' => ['prefix' => '&', 'joiner' => '&', 'query' => true],
    ];

    /**
     * @var string[] Delimiters
     */
    private static $delims = [
        ':',
        '/',
        '?',
        '#',
        '[',
        ']',
        '@',
        '!',
        '$',
        '&',
        '\'',
        '(',
        ')',
        '*',
        '+',
        ',',
        ';',
        '=',
    ];

    /**
     * @var string[] Percent encoded delimiters
     */
    private static $delimsPct = [
        '%3A',
        '%2F',
        '%3F',
        '%23',
        '%5B',
        '%5D',
        '%40',
        '%21',
        '%24',
        '%26',
        '%27',
        '%28',
        '%29',
        '%2A',
        '%2B',
        '%2C',
        '%3B',
        '%3D',
    ];

    /**
     * @param array<string,mixed> $variables Variables to use in the template expansion
     *
     * @throws \RuntimeException
     */
    public static function expand(string $template, array $variables): string
    {
        if (false === \strpos($template, '{')) {
            return $template;
        }

        /** @var string|null */
        $result = \preg_replace_callback(
            '/\{([^\}]+)\}/',
            self::expandMatchCallback($variables),
            $template
        );

        if (null === $result) {
            throw new \RuntimeException(\sprintf(
            	'Unable to process template: %s', \preg_last_error_msg()
            ));
        }

        return $result;
    }

    /**
     * @param array<string,mixed> $variables Variables to use in the template expansion
     *
     * @return callable(string[]): string
     */
    private static function expandMatchCallback(array $variables): callable
    {
        return static function (array $matches) use ($variables): string {
            return self::expandMatch($matches, $variables);
        };
    }

    /**
     * Process an expansion
     *
     * @param array<string,mixed> $variables Variables to use in the template expansion
     * @param string[]            $matches   Matches met in the preg_replace_callback
     *
     * @return string Returns the replacement string
     */
    private static function expandMatch(array $matches, array $variables): string
    {
        $replacements = [];
        $parsed = self::parseExpression($matches[1]);
        $prefix = self::$operatorHash[$parsed['operator']]['prefix'];
        $joiner = self::$operatorHash[$parsed['operator']]['joiner'];
        $useQuery = self::$operatorHash[$parsed['operator']]['query'];
        $allUndefined = true;

        foreach ($parsed['values'] as $value) {
            if (!isset($variables[$value['value']])) {
                continue;
            }

            $variable = $variables[$value['value']];
            $actuallyUseQuery = $useQuery;
            $expanded = '';

            if (\is_array($variable)) {
                $isAssoc = self::isAssoc($variable);
                $kvp = [];
                /** @var mixed $var */
                foreach ($variable as $key => $var) {
                    if ($isAssoc) {
                        $key = \rawurlencode((string) $key);
                        $isNestedArray = \is_array($var);
                    } else {
                        $isNestedArray = false;
                    }

                    if (!$isNestedArray) {
                        $var = \rawurlencode((string) $var);
                        if ($parsed['operator'] === '+' || $parsed['operator'] === '#') {
                            $var = self::decodeReserved($var);
                        }
                    }

                    if ($value['modifier'] === '*') {
                        if ($isAssoc) {
                            if ($isNestedArray) {
                                // Nested arrays must allow for deeply nested structures.
                                $var = \http_build_query([$key => $var], '', '&', \PHP_QUERY_RFC3986);
                            } else {
                                $var = \sprintf('%s=%s', (string) $key, (string) $var);
                            }
                        } elseif ($key > 0 && $actuallyUseQuery) {
                            $var = \sprintf('%s=%s', $value['value'], (string) $var);
                        }
                    }

                    /** @var string $var */
                    $kvp[$key] = $var;
                }

                if (0 === \count($variable)) {
                    $actuallyUseQuery = false;
                } elseif ($value['modifier'] === '*') {
                    $expanded = \implode($joiner, $kvp);
                    if ($isAssoc) {
                        // Don't prepend the value name when using the explode
                        // modifier with an associative array.
                        $actuallyUseQuery = false;
                    }
                } else {
                    if ($isAssoc) {
                        // When an associative array is encountered and the
                        // explode modifier is not set, then the result must be
                        // a comma separated list of keys followed by their
                        // respective values.
                        foreach ($kvp as $k => &$v) {
                            $v = \sprintf('%s,%s', $k, $v);
                        }
                    }
                    $expanded = \implode(',', $kvp);
                }
            } else {
                $allUndefined = false;
                if ($value['modifier'] === ':' && isset($value['position'])) {
                    $variable = \substr((string) $variable, 0, $value['position']);
                }
                $expanded = \rawurlencode((string) $variable);
                if ($parsed['operator'] === '+' || $parsed['operator'] === '#') {
                    $expanded = self::decodeReserved($expanded);
                }
            }

            if ($actuallyUseQuery) {
                if ($expanded === '' && $joiner !== '&') {
                    $expanded = $value['value'];
                } else {
                    $expanded = \sprintf('%s=%s', $value['value'], $expanded);
                }
            }

            $replacements[] = $expanded;
        }

        $ret = \implode($joiner, $replacements);

        if ('' === $ret) {
            // Spec section 3.2.4 and 3.2.5
            if (false === $allUndefined && ('#' === $prefix || '.' === $prefix)) {
                return $prefix;
            }
        } else {
            if ('' !== $prefix) {
                return \sprintf('%s%s', $prefix, $ret);
            }
        }

        return $ret;
    }

    /**
     * Parse an expression into parts
     *
     * @param string $expression Expression to parse
     *
     * @return array{operator:string, values:array<array{value:string, modifier:(''|'*'|':'), position?:int}>}
     */
    private static function parseExpression(string $expression): array
    {
        $result = [];

        if (isset(self::$operatorHash[$expression[0]])) {
            $result['operator'] = $expression[0];
            /** @var string */
            $expression = \substr($expression, 1);
        } else {
            $result['operator'] = '';
        }

        $result['values'] = [];
        foreach (\explode(',', $expression) as $value) {
            $value = \trim($value);
            $varspec = [];
            if ($colonPos = \strpos($value, ':')) {
                $varspec['value'] = (string) \substr($value, 0, $colonPos);
                $varspec['modifier'] = ':';
                $varspec['position'] = (int) \substr($value, $colonPos + 1);
            } elseif (\substr($value, -1) === '*') {
                $varspec['modifier'] = '*';
                $varspec['value'] = (string) \substr($value, 0, -1);
            } else {
                $varspec['value'] = $value;
                $varspec['modifier'] = '';
            }
            $result['values'][] = $varspec;
        }

        return $result;
    }

    /**
     * Determines if an array is associative.
     *
     * This makes the assumption that input arrays are sequences or hashes.
     * This assumption is a tradeoff for accuracy in favor of speed, but it
     * should work in almost every case where input is supplied for a URI
     * template.
     */
    private static function isAssoc(array $array): bool
    {
        return $array && \array_keys($array)[0] !== 0;
    }

    /**
     * Removes percent encoding on reserved characters (used with + and #
     * modifiers).
     */
    private static function decodeReserved(string $string): string
    {
        return \str_replace(self::$delimsPct, self::$delims, $string);
    }
}
