libcruft-util/cruft/util/paths.hpp

/*
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 *
 * Copyright 2022, Danny Robson <danny@nerdcruft.net>
 */

#pragma once

#include "concepts/named.hpp"

#include <filesystem>
#include <optional>


///////////////////////////////////////////////////////////////////////////////
namespace cruft::paths {
    /// Return the path to the system's temporary directory.
    std::filesystem::path temp (void);


    /// Expand paths that contain platform specific variables
    ///
    /// eg, "$TMPDIR/foo" and "%HOMEPATH%/foo"
    std::filesystem::path
    expand (std::filesystem::path const&);


    /// Given a relative path, and a collection of candidate base paths,
    /// return the first path that exists.
    ///
    /// Or, if none do, return the relative path itself (if it exists).
    ///
    /// Else throw a runtime_error.
    ///
    /// Note: there's a good chance if you're using this then it's likely
    /// you'll run into TOCTOU errors.
    template <cruft::concepts::named::container ContainerT>
    std::filesystem::path
    resolve_first (std::filesystem::path const &relative, ContainerT bases)
    {
        for (auto const &base: bases) {
            auto const candidate = base / relative;
            if (std::filesystem::exists (candidate))
                return candidate;
        }

        if (exists (relative))
            return relative;

        throw std::runtime_error ("no path");
    }
}