/* This file is part of DarkFi (https://dark.fi)
 *
 * Copyright (C) 2026-2026 Dyne.org foundation
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * This program 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 Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

//! Simulate the creation of a [`TreeOverlay`] on top of a [`Tree`]
//! instance, and perform checkpoints and writes to verify overlay's
//! cache checkpoint functionality.

use kvdb_overlay::{Database, Result, TreeOverlay};

const TREE: &str = "_tree";

#[test]
fn tree_overlay_checkpoint() -> Result<()> {
    // Initialize database
    let (db, _folder) = Database::open_temp()?;

    // Initialize tree and its overlay
    let tree = db.open_tree_default(TREE)?;
    let mut overlay = TreeOverlay::new(&tree);

    // Insert some values to the overlay
    overlay.insert(b"key_a", b"val_a")?;
    overlay.insert(b"key_b", b"val_b")?;
    overlay.insert(b"key_c", b"val_c")?;

    // Verify they are in the overlay
    assert_eq!(overlay.get(b"key_a")?, Some(b"val_a".into()));
    assert_eq!(overlay.get(b"key_b")?, Some(b"val_b".into()));
    assert_eq!(overlay.get(b"key_c")?, Some(b"val_c".into()));

    // Verify they are not in the database
    assert_eq!(tree.get(b"key_a")?, None);
    assert_eq!(tree.get(b"key_b")?, None);
    assert_eq!(tree.get(b"key_c")?, None);

    // Now we create an overlay checkpoint
    overlay.checkpoint();

    // We add some more values to the overlay
    overlay.insert(b"key_d", b"val_d")?;
    overlay.insert(b"key_e", b"val_e")?;
    overlay.insert(b"key_f", b"val_f")?;

    // Verify they are in the overlay
    assert_eq!(overlay.get(b"key_d")?, Some(b"val_d".into()));
    assert_eq!(overlay.get(b"key_e")?, Some(b"val_e".into()));
    assert_eq!(overlay.get(b"key_f")?, Some(b"val_f".into()));

    // Verify they are not in the database
    assert_eq!(tree.get(b"key_d")?, None);
    assert_eq!(tree.get(b"key_e")?, None);
    assert_eq!(tree.get(b"key_f")?, None);

    // We assume something went wrong, so we revert to last checkpoint
    overlay.revert_to_checkpoint();

    // Now we write it to the database
    db.write_tree_overlays_changes(&[&overlay])?;
    db.flush_default_mode()?;

    // Verify database contains pre-checkpoint keys
    assert_eq!(tree.get(b"key_a")?, Some(b"val_a".into()));
    assert_eq!(tree.get(b"key_b")?, Some(b"val_b".into()));
    assert_eq!(tree.get(b"key_c")?, Some(b"val_c".into()));

    // Verify database doesn't contains keys after checkpoint
    assert_eq!(tree.get(b"key_d")?, None);
    assert_eq!(tree.get(b"key_e")?, None);
    assert_eq!(tree.get(b"key_f")?, None);

    Ok(())
}