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

use lanspread_db::content_manifest::validate_portable_component;

const PEER_IDENTITY_FILE: &str = "peer-identity-v1.json";
const LOCAL_LIBRARY_DIR: &str = "local_library";
const LOCAL_LIBRARY_INDEX_FILE: &str = "index.json";
const GAMES_DIR: &str = "games";
const SETUP_DONE_FILE: &str = "setup_done";
const LAUNCH_SETTINGS_APPLIED_FILE: &str = "launch_settings_applied";
pub(crate) const DOWNLOAD_OWNERSHIP_DIR: &str = "download_ownership";
pub(crate) const DOWNLOAD_OWNERSHIP_RECORD_FILE: &str = "record.json";
pub(crate) const DOWNLOAD_OWNERSHIP_TMP_FILE: &str = "record.json.tmp";
pub(crate) const DOWNLOAD_OWNERSHIP_RECOVERY_REQUIRED_FILE: &str = "recovery-required";
pub(crate) const LEGACY_DOWNLOAD_OWNERSHIP_FILE: &str = "download_ownership.json";
pub(crate) const LEGACY_DOWNLOAD_OWNERSHIP_TMP_FILE: &str = "download_ownership.json.tmp";
pub(crate) const LEGACY_DOWNLOAD_OWNERSHIP_RECOVERY_REQUIRED_FILE: &str =
    "download_ownership.recovery-required";

/// Resolves the directory that holds the peer identity, ownership journals and
/// other durable state.
///
/// Precedence: an explicit path from the embedding application (the Tauri
/// app passes its app-data directory, the CLI its `--state-dir`), then
/// `LANSPREAD_STATE_DIR`, then `$HOME`/`%USERPROFILE%/.lanspread`.
///
/// # Errors
///
/// Returns an error when none of these sources is available. State holds the
/// private identity key, so it is never placed in a shared, world-writable
/// temporary directory where another local user could pre-create it.
pub(crate) fn resolve_state_dir(explicit: Option<&Path>) -> eyre::Result<PathBuf> {
    if let Some(dir) = explicit {
        return Ok(dir.to_path_buf());
    }

    if let Some(dir) = std::env::var_os("LANSPREAD_STATE_DIR") {
        return Ok(PathBuf::from(dir));
    }

    if let Some(home) = std::env::var_os("HOME").or_else(|| std::env::var_os("USERPROFILE")) {
        return Ok(PathBuf::from(home).join(".lanspread"));
    }

    eyre::bail!(
        "no state directory: pass one explicitly or set LANSPREAD_STATE_DIR, HOME, or USERPROFILE"
    )
}

pub(crate) fn peer_identity_path(state_dir: &Path) -> PathBuf {
    state_dir.join(PEER_IDENTITY_FILE)
}

pub(crate) fn local_library_index_path(state_dir: &Path) -> PathBuf {
    state_dir
        .join(LOCAL_LIBRARY_DIR)
        .join(LOCAL_LIBRARY_INDEX_FILE)
}

/// Joins a per-game state directory below `<state_dir>/games`.
///
/// Callers inside this crate pass IDs that come from the catalog or have
/// already passed [`validate_game_state_id`]; the debug assertion documents
/// that contract without turning a bad ID into a release-build panic.
pub(crate) fn game_state_dir(state_dir: &Path, game_id: &str) -> PathBuf {
    debug_assert!(
        validate_game_state_id(game_id).is_ok(),
        "game_state_dir called with an unvalidated game ID: {game_id:?}"
    );
    games_state_dir(state_dir).join(game_id)
}

/// Rejects a game ID that could escape or alias its per-game state
/// directory: separators, NUL, `.`/`..`, trailing dots or spaces, control or
/// Windows-reserved characters and Windows device names.
///
/// The rules are the catalog's own portable component rules, so every ID a
/// catalog can publish is accepted and the check cannot drift from the
/// validator that admits game IDs in the first place.
///
/// # Errors
///
/// Returns the first violated rule.
pub(crate) fn validate_game_state_id(game_id: &str) -> eyre::Result<()> {
    if game_id.contains(['/', '\\', '\0']) {
        eyre::bail!("game ID must be one path component: {game_id:?}");
    }
    validate_portable_component(game_id)
}

pub(crate) fn games_state_dir(state_dir: &Path) -> PathBuf {
    state_dir.join(GAMES_DIR)
}

/// Path of the marker that records a completed one-time `game_setup` run.
///
/// This is the only state path exposed to embedding applications, whose game
/// IDs may originate from UI input rather than the catalog, so it validates
/// the ID before joining it below the state directory.
///
/// # Errors
///
/// Returns an error when `game_id` is not a single portable path component.
pub fn setup_done_path(state_dir: &Path, game_id: &str) -> eyre::Result<PathBuf> {
    validate_game_state_id(game_id)?;
    Ok(game_state_dir(state_dir, game_id).join(SETUP_DONE_FILE))
}

pub(crate) fn launch_settings_applied_path(state_dir: &Path, game_id: &str) -> PathBuf {
    game_state_dir(state_dir, game_id).join(LAUNCH_SETTINGS_APPLIED_FILE)
}

pub(crate) fn download_ownership_namespaces_dir(state_dir: &Path, game_id: &str) -> PathBuf {
    game_state_dir(state_dir, game_id).join(DOWNLOAD_OWNERSHIP_DIR)
}

pub(crate) fn download_ownership_namespace_component(games_folder_key: &str) -> String {
    let key = games_folder_key.as_bytes();
    let mut hasher = blake3::Hasher::new();
    hasher.update(b"lanspread-download-ownership-root\0");
    hasher.update(&u64::try_from(key.len()).unwrap_or(u64::MAX).to_le_bytes());
    hasher.update(key);
    format!("v1-{}", hasher.finalize().to_hex())
}

pub(crate) fn download_ownership_namespace_dir(
    state_dir: &Path,
    game_id: &str,
    games_folder_key: &str,
) -> PathBuf {
    download_ownership_namespaces_dir(state_dir, game_id)
        .join(download_ownership_namespace_component(games_folder_key))
}

pub(crate) fn download_ownership_path(
    state_dir: &Path,
    game_id: &str,
    games_folder_key: &str,
) -> PathBuf {
    download_ownership_namespace_dir(state_dir, game_id, games_folder_key)
        .join(DOWNLOAD_OWNERSHIP_RECORD_FILE)
}

pub(crate) fn download_ownership_tmp_path(
    state_dir: &Path,
    game_id: &str,
    games_folder_key: &str,
) -> PathBuf {
    download_ownership_namespace_dir(state_dir, game_id, games_folder_key)
        .join(DOWNLOAD_OWNERSHIP_TMP_FILE)
}

pub(crate) fn download_ownership_recovery_required_path(
    state_dir: &Path,
    game_id: &str,
    games_folder_key: &str,
) -> PathBuf {
    download_ownership_namespace_dir(state_dir, game_id, games_folder_key)
        .join(DOWNLOAD_OWNERSHIP_RECOVERY_REQUIRED_FILE)
}

pub(crate) fn legacy_download_ownership_path(state_dir: &Path, game_id: &str) -> PathBuf {
    game_state_dir(state_dir, game_id).join(LEGACY_DOWNLOAD_OWNERSHIP_FILE)
}

pub(crate) fn legacy_download_ownership_tmp_path(state_dir: &Path, game_id: &str) -> PathBuf {
    game_state_dir(state_dir, game_id).join(LEGACY_DOWNLOAD_OWNERSHIP_TMP_FILE)
}

pub(crate) fn legacy_download_ownership_recovery_required_path(
    state_dir: &Path,
    game_id: &str,
) -> PathBuf {
    game_state_dir(state_dir, game_id).join(LEGACY_DOWNLOAD_OWNERSHIP_RECOVERY_REQUIRED_FILE)
}

/// Stable, lossless platform-native identity for a canonical games directory.
///
/// Callers must canonicalize and validate the directory before deriving its
/// key. Persistent state uses this value to prevent records from one configured
/// games directory from authorizing mutations in another.
#[cfg(unix)]
pub(crate) fn games_folder_key(path: &Path) -> String {
    use std::os::unix::ffi::OsStrExt as _;

    format!("unix:{}", hex_encode(path.as_os_str().as_bytes()))
}

#[cfg(windows)]
pub(crate) fn games_folder_key(path: &Path) -> String {
    use std::{fmt::Write as _, os::windows::ffi::OsStrExt as _};

    let mut encoded = String::from("windows:");
    for unit in path.as_os_str().encode_wide() {
        let _ = write!(encoded, "{unit:04x}");
    }
    encoded
}

#[cfg(not(any(unix, windows)))]
pub(crate) fn games_folder_key(path: &Path) -> String {
    format!("native:{}", hex_encode(path.as_os_str().as_encoded_bytes()))
}

#[cfg(not(windows))]
fn hex_encode(bytes: &[u8]) -> String {
    use std::fmt::Write as _;

    let mut encoded = String::with_capacity(bytes.len() * 2);
    for byte in bytes {
        let _ = write!(encoded, "{byte:02x}");
    }
    encoded
}

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

    #[test]
    fn explicit_state_dir_takes_precedence() {
        let explicit = Path::new("/explicit/state");
        assert_eq!(
            resolve_state_dir(Some(explicit)).expect("explicit path resolves"),
            explicit
        );
    }

    #[test]
    fn setup_done_path_accepts_catalog_style_game_ids() {
        let state_dir = Path::new("/state");
        assert_eq!(
            setup_done_path(state_dir, "game").expect("plain ID should be accepted"),
            Path::new("/state/games/game/setup_done")
        );
        for game_id in ["game..v1 (final)", "console.txt", "com10", "Jörg"] {
            assert!(
                setup_done_path(state_dir, game_id).is_ok(),
                "rejected catalog-valid game ID {game_id:?}"
            );
        }
    }

    #[test]
    fn setup_done_path_rejects_escaping_game_ids() {
        let state_dir = Path::new("/state");
        for game_id in [
            "",
            ".",
            "..",
            "../outside",
            "/outside",
            r"nested\game",
            "game/child",
            "game\0",
            "game.",
            "game ",
            "NUL",
            "con.txt",
            "a:b",
        ] {
            assert!(
                setup_done_path(state_dir, game_id).is_err(),
                "accepted unsafe game ID {game_id:?}"
            );
        }
    }
}