stash.cpp

// Copyright 2021 Chris Spiegel.
//
// This file is part of Bocfel.
//
// Bocfel is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License, version
// 2 or 3, as published by the Free Software Foundation.
//
// Bocfel is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Bocfel. If not, see <http://www.gnu.org/licenses/>.

#include <algorithm>
#include <functional>
#include <utility>
#include <vector>

#include "stash.h"
#include "types.h"

// Restoring (as in @restore) is done in-place, meaning that data
// structures used by the interpreter are updated during the restore. If
// any error is encountered during restore, the system could thus be in
// a state of partial update, preventing things from working properly.
// To avoid this, any structures which are updated in-place are first
// backed up. On restore failure, these will be restored. Anything can
// register functions to back up, restore, and free any particular piece
// of state that needs to be protected. The restore code will ensure
// these are all called appropriately.
//
// Required functions:
//
// void backup()  - Stash away the current state for future restore
// bool restore() - Restore the stashed state, returning true if it
//                  could successfully be restored, false otherwise.
// void free()    - Free any resources that were allocated by
//                  backup(). This can be called at any time,
//                  including before any calls to backup(), and
//                  including multiple times in a row without any
//                  intervening call to backup().

struct PrivateStash {
    std::function<void()> backup;
    std::function<bool()> restore;
    std::function<void()> free;
};

static std::vector<PrivateStash> stashes;

void stash_register(std::function<void()> backup, std::function<bool()> restore, std::function<void()> free)
{
    PrivateStash stash = {
        std::move(backup),
        std::move(restore),
        std::move(free),
    };

    stashes.push_back(stash);
}

Stash::~Stash()
{
    free();
}

void Stash::backup()
{
    for (const auto &stash : stashes) {
        stash.backup();
    }

    m_have_stash = true;
}

bool Stash::restore()
{
    bool success = std::all_of(stashes.begin(), stashes.end(), [](const PrivateStash &stash) { return stash.restore(); });

    free();

    return success;
}

void Stash::free()
{
    for (const auto &stash : stashes) {
        stash.free();
    }

    m_have_stash = false;
}

bool Stash::exists() const
{
    return m_have_stash;
}