<?php

/** Load only named top-level functions, never the application's startup code. */
final class LegacyFunctions
{
    public static function load(string $root, array $selection): array
    {
        $manifest = [];
        foreach ($selection as $relative => $names) {
            $file = $root . '/' . $relative;
            if (!is_file($file) || !is_readable($file)) {
                throw new RuntimeException('Missing readable source: ' . $file);
            }
            $source = file_get_contents($file);
            $functions = self::extract($source, $names);
            foreach ($functions as $name => $definition) {
                if (function_exists($name)) {
                    throw new RuntimeException('Function already defined: ' . $name);
                }
                // Preserve the source bytes and weak scalar coercion of the legacy code.
                eval($definition['code']);
                $manifest[$relative]['functions'][$name] = [
                    'line' => $definition['line'],
                    'sha256' => hash('sha256', $definition['code']),
                ];
            }
            $manifest[$relative]['sha256'] = hash('sha256', $source);
        }
        return $manifest;
    }

    public static function extract(string $source, array $names): array
    {
        $tokens = token_get_all($source);
        $found = [];
        $depth = 0;
        for ($i = 0, $count = count($tokens); $i < $count; $i++) {
            $token = $tokens[$i];
            if ($depth === 0 && is_array($token) && $token[0] === T_FUNCTION) {
                $j = $i + 1;
                while (isset($tokens[$j]) && is_array($tokens[$j]) &&
                    in_array($tokens[$j][0], [T_WHITESPACE, T_COMMENT, T_DOC_COMMENT,
                        T_AMPERSAND_NOT_FOLLOWED_BY_VAR_OR_VARARG, T_AMPERSAND_FOLLOWED_BY_VAR_OR_VARARG], true)) {
                    $j++;
                }
                $name = is_array($tokens[$j] ?? null) && $tokens[$j][0] === T_STRING
                    ? $tokens[$j][1] : null;
                if ($name !== null && in_array($name, $names, true)) {
                    if (isset($found[$name])) {
                        throw new RuntimeException('Duplicate function: ' . $name);
                    }
                    $code = '';
                    $bodyDepth = 0;
                    $started = false;
                    for ($j = $i; $j < $count; $j++) {
                        $part = $tokens[$j];
                        $code .= is_array($part) ? $part[1] : $part;
                        if (is_array($part) && in_array($part[0], [T_INCLUDE, T_INCLUDE_ONCE,
                            T_REQUIRE, T_REQUIRE_ONCE, T_EVAL, T_EXIT], true)) {
                            throw new RuntimeException('Unsafe startup/exit operation in ' . $name);
                        }
                        if ($part === '{' || (is_array($part) && in_array($part[0],
                            [T_CURLY_OPEN, T_DOLLAR_OPEN_CURLY_BRACES], true))) {
                            $bodyDepth++;
                            $started = true;
                        } elseif ($part === '}') {
                            $bodyDepth--;
                            if ($started && $bodyDepth === 0) {
                                $found[$name] = ['code' => $code, 'line' => $token[2]];
                                $i = $j;
                                break;
                            }
                        }
                    }
                    if (!isset($found[$name])) {
                        throw new RuntimeException('Incomplete function: ' . $name);
                    }
                    continue;
                }
            }
            if ($token === '{' || (is_array($token) && in_array($token[0],
                [T_CURLY_OPEN, T_DOLLAR_OPEN_CURLY_BRACES], true))) {
                $depth++;
            } elseif ($token === '}') {
                $depth--;
            }
        }
        $missing = array_diff($names, array_keys($found));
        if ($missing) {
            throw new RuntimeException('Missing top-level function(s): ' . implode(', ', $missing));
        }
        return $found;
    }
}