<?php
/** SFTP paths use POSIX separators, regardless of the OS running PHP. */
function normalizePath(string $path): string {
    $parts = array_filter(explode('/', $path), fn($part) => $part !== '' && $part !== '.');
    $stack = [];
    foreach ($parts as $part) {
        if ($part === '..') {
            array_pop($stack);
        } else {
            $stack[] = $part;
        }
    }
    return '/' . implode('/', $stack);
}

/** Like dirname(), but only '/' is a separator and the root stays '/'. */
function remoteDirname(string $path): string {
    $path = rtrim($path, '/');
    if ($path === '') return '/';
    $separator = strrpos($path, '/');
    if ($separator === false) return '.';
    $parent = rtrim(substr($path, 0, $separator), '/');
    return $parent === '' ? '/' : $parent;
}

/** Compare directory boundaries, so /data-other is not considered part of /data. */
function isRemotePathWithin(string $path, string $basePath): bool {
    $path = normalizePath($path);
    $basePath = normalizePath($basePath);
    return $path === $basePath || strpos($path, rtrim($basePath, '/') . '/') === 0;
}

/** Validate a single POSIX filename before joining it to a directory. */
function isRemoteNameValid(string $name): bool {
    return $name !== '' && $name !== '.' && $name !== '..'
        && strpos($name, '/') === false && strpos($name, "\0") === false;
}

/** Resolve a request path inside the user's configured workspace. */
function requireRemotePath(string $path, string $basePath): string {
    if (strpos($path, "\0") !== false || !isRemotePathWithin($path, $basePath)) {
        http_response_code(403);
        exit('Path is outside your workspace.');
    }
    return normalizePath($path);
}