<?php
namespace Blyzer;

defined('ABSPATH') || exit;

class TemplateEngine
{
    private const SECTION = '/{{\s*([#^])\s*([a-zA-Z0-9_.@]+)\s*}}(.*?){{\s*\/\s*\2\s*}}/s';
    private const VARIABLE = '/{{\s*([a-zA-Z0-9_.@]+)\s*}}/';

    public static function render(string $template, array $context): string
    {
        return self::renderStack($template, [$context]);
    }

    public static function isList(array $arr): bool
    {
        if ($arr === []) return true;
        return array_keys($arr) === range(0, count($arr) - 1);
    }

    private static function renderStack(string $template, array $stack): string
    {
        $parts = preg_split(self::SECTION, $template, -1, PREG_SPLIT_DELIM_CAPTURE);
        if (!is_array($parts)) return '';

        $out = '';
        $count = count($parts);

        for ($i = 0; $i < $count; $i += 4) {
            $out .= self::renderVariables($parts[$i], $stack);
            if (!isset($parts[$i + 3])) break;
            $out .= self::renderSection($parts[$i + 1], $parts[$i + 2], $parts[$i + 3], $stack);
        }

        return $out;
    }

    private static function renderSection(string $kind, string $name, string $body, array $stack): string
    {
        $value = self::lookup($name, $stack);
        $empty = self::isEmpty($value);

        if ($kind === '^') {
            return $empty ? self::renderStack($body, $stack) : '';
        }

        if ($empty) return '';

        if (is_array($value) && self::isList($value)) {
            $out = '';
            $total = count($value);
            foreach ($value as $index => $row) {
                $frame = is_array($row) ? $row : ['.' => $row];
                $frame['@index'] = $index + 1;
                $frame['@first'] = $index === 0;
                $frame['@last'] = $index === $total - 1;
                $out .= self::renderStack($body, array_merge($stack, [$frame]));
            }
            return $out;
        }

        if (is_array($value)) {
            return self::renderStack($body, array_merge($stack, [$value]));
        }

        return self::renderStack($body, $stack);
    }

    private static function renderVariables(string $template, array $stack): string
    {
        return (string) preg_replace_callback(self::VARIABLE, function (array $m) use ($stack): string {
            $value = self::lookup($m[1], $stack);
            if (is_bool($value)) return $value ? '1' : '';
            if (is_scalar($value)) return esc_html((string) $value);
            return '';
        }, $template);
    }

    private static function lookup(string $name, array $stack)
    {
        if ($name === '.') {
            $top = end($stack);
            return (is_array($top) && array_key_exists('.', $top)) ? $top['.'] : $top;
        }

        $segments = explode('.', $name);
        $first = array_shift($segments);
        $value = null;
        $found = false;

        for ($i = count($stack) - 1; $i >= 0; $i--) {
            if (is_array($stack[$i]) && array_key_exists($first, $stack[$i])) {
                $value = $stack[$i][$first];
                $found = true;
                break;
            }
        }

        if (!$found) return null;

        foreach ($segments as $segment) {
            if (!is_array($value) || !array_key_exists($segment, $value)) return null;
            $value = $value[$segment];
        }

        return $value;
    }

    private static function isEmpty($value): bool
    {
        return $value === null || $value === false || $value === '' || $value === [];
    }
}