//! Local data export/import (Phase M — sync transparency).
//!
//! Bundles every player-owned JSON save (settings, stats, achievements,
//! progress) into one versioned backup file so a player can move their
//! data between devices without an account, or keep a manual backup.
//!
//! The bundle deliberately excludes the in-progress game and the replay
//! history: the former is transient, the latter can be large and is
//! shareable through the replay upload path instead.

use std::fs;
use std::io;
use std::path::{Path, PathBuf};

use chrono::{DateTime, Utc};
use serde::{Deserialize, Serialize};

use crate::settings::Settings;
use solitaire_sync::{AchievementRecord, PlayerProgress, StatsSnapshot};

/// Bundle format version. Bump on any breaking shape change; the loader
/// rejects newer versions rather than misreading them.
pub const DATA_BUNDLE_SCHEMA_VERSION: u32 = 1;

/// File name of the default backup location (next to the other saves).
pub const DATA_BUNDLE_FILE_NAME: &str = "ferrous-solitaire-backup.json";

/// One-file backup of every player-owned JSON save.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct DataBundle {
    /// Format version — see [`DATA_BUNDLE_SCHEMA_VERSION`].
    pub schema_version: u32,
    /// When the bundle was written.
    pub exported_at: DateTime<Utc>,
    pub settings: Settings,
    pub stats: StatsSnapshot,
    pub achievements: Vec<AchievementRecord>,
    pub progress: PlayerProgress,
}

/// Why a bundle could not be loaded.
#[derive(Debug, thiserror::Error)]
pub enum BundleError {
    #[error("could not read backup file: {0}")]
    Io(#[from] io::Error),
    #[error("backup file is not valid JSON: {0}")]
    Parse(#[from] serde_json::Error),
    #[error("backup was written by a newer app version (schema {found} > {supported})")]
    UnsupportedVersion { found: u32, supported: u32 },
}

/// Default backup path: `<data dir>/<app dir>/ferrous-solitaire-backup.json`,
/// or `None` when no data directory is available on this platform.
pub fn data_bundle_path() -> Option<PathBuf> {
    crate::data_dir().map(|d| d.join(crate::APP_DIR_NAME).join(DATA_BUNDLE_FILE_NAME))
}

/// Write `bundle` to `path` atomically (`.tmp` → rename), creating parent
/// directories as needed. Mirrors the other save-file writers.
pub fn save_bundle_to(path: &Path, bundle: &DataBundle) -> io::Result<()> {
    if let Some(parent) = path.parent() {
        fs::create_dir_all(parent)?;
    }
    let json = serde_json::to_string_pretty(bundle).map_err(io::Error::other)?;
    let tmp = path.with_extension("json.tmp");
    fs::write(&tmp, json.as_bytes())?;
    fs::rename(&tmp, path)?;
    Ok(())
}

/// Read and validate a bundle from `path`. Unlike the per-file loaders this
/// does NOT default-on-error — an import silently replacing player data
/// with defaults would be destructive, so every failure is surfaced.
pub fn load_bundle_from(path: &Path) -> Result<DataBundle, BundleError> {
    let data = fs::read(path)?;
    let bundle: DataBundle = serde_json::from_slice(&data)?;
    if bundle.schema_version > DATA_BUNDLE_SCHEMA_VERSION {
        return Err(BundleError::UnsupportedVersion {
            found: bundle.schema_version,
            supported: DATA_BUNDLE_SCHEMA_VERSION,
        });
    }
    Ok(bundle)
}

#[cfg(test)]
mod tests {
    use super::*;

    fn sample_bundle() -> DataBundle {
        DataBundle {
            schema_version: DATA_BUNDLE_SCHEMA_VERSION,
            exported_at: Utc::now(),
            settings: Settings::default(),
            stats: StatsSnapshot {
                games_played: 7,
                ..Default::default()
            },
            achievements: vec![],
            progress: PlayerProgress::default(),
        }
    }

    #[test]
    fn round_trips_through_disk() {
        let dir = std::env::temp_dir().join(format!("bundle_test_{}", std::process::id()));
        let path = dir.join(DATA_BUNDLE_FILE_NAME);
        let bundle = sample_bundle();
        save_bundle_to(&path, &bundle).expect("save should succeed");
        let loaded = load_bundle_from(&path).expect("load should succeed");
        assert_eq!(loaded.schema_version, DATA_BUNDLE_SCHEMA_VERSION);
        assert_eq!(loaded.stats.games_played, 7);
        let _ = fs::remove_dir_all(&dir);
    }

    #[test]
    fn rejects_newer_schema() {
        let dir = std::env::temp_dir().join(format!("bundle_test_v_{}", std::process::id()));
        let path = dir.join(DATA_BUNDLE_FILE_NAME);
        let mut bundle = sample_bundle();
        bundle.schema_version = DATA_BUNDLE_SCHEMA_VERSION + 1;
        save_bundle_to(&path, &bundle).expect("save should succeed");
        assert!(matches!(
            load_bundle_from(&path),
            Err(BundleError::UnsupportedVersion { .. })
        ));
        let _ = fs::remove_dir_all(&dir);
    }

    #[test]
    fn missing_file_is_an_io_error() {
        assert!(matches!(
            load_bundle_from(Path::new("/nonexistent/backup.json")),
            Err(BundleError::Io(_))
        ));
    }
}