//! Location → culture resolution (D-128).
//!
//! Single canonical lookup: `location_id → CultureTag`.
//! Culture is implicit in the starting location — Van Maanen's Star start =
//! Van Maanen's Star culture. All downstream pipelines (voice, NPC blueprint,
//! apartment generator, visual grammar) call through here, not ad-hoc queries.

use std::{
    path::Path,
    sync::{Arc, Mutex},
};

use bevy_ecs::prelude::*;
use rusqlite::{Connection, OpenFlags};
use serde::{Deserialize, Serialize};

/// Canonical culture identifier (D-128).
///
/// String-backed — cultures expand with content, not code.
/// Value space matches `star_systems.cultural_corridor` in systems.db:
///   `"core"`, `"sol-gateway-axis"`, `"north_reach"`, `"south_reach"`,
///   `"east_reach"`, `"west_reach"`, `"deep_frontier"`.
///
/// Wire format: plain `String` over IPC.
#[derive(Debug, Clone, Eq, PartialEq, Hash, Ord, PartialOrd, Serialize, Deserialize)]
pub struct CultureTag(pub String);

impl CultureTag {
    pub fn as_str(&self) -> &str {
        &self.0
    }
}

impl std::fmt::Display for CultureTag {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        self.0.fmt(f)
    }
}

/// Error from culture resolution.
#[derive(Debug, thiserror::Error)]
pub enum CultureError {
    /// `location_id` does not resolve to any known row in systems.db.
    #[error("unknown location: `{0}`")]
    UnknownLocation(String),

    /// Location row found but `cultural_corridor` is NULL — this is a data bug.
    #[error("no culture assigned to location `{0}` in systems.db")]
    NoCulture(String),

    /// Underlying SQLite error.
    #[error("database error: {0}")]
    Db(String),
}

/// Handle that owns the DB connection.
///
/// Constructed once at startup against `server/data/systems.db`.
/// `Mutex<Connection>` mirrors `SettingsStoreResource` — rusqlite `Connection`
/// is `!Sync`. All queries are indexed primary-key lookups: sub-microsecond.
pub struct CultureResolver {
    conn: Arc<Mutex<Connection>>,
}

impl CultureResolver {
    /// Open a resolver. `SQLITE_OPEN_READ_ONLY` — purely query-side.
    pub fn open(path: &Path) -> Result<Self, CultureError> {
        let conn = Connection::open_with_flags(path, OpenFlags::SQLITE_OPEN_READ_ONLY)
            .map_err(|e| CultureError::Db(e.to_string()))?;
        Ok(CultureResolver {
            conn: Arc::new(Mutex::new(conn)),
        })
    }
}

/// Bevy `Resource` wrapper — `Res<CultureResolverResource>` in systems.
#[derive(Resource)]
pub struct CultureResolverResource(pub CultureResolver);

/// Resolve a `location_id` to the `CultureTag` it implies (D-128).
///
/// Accepted forms:
/// - `system_id`  — e.g. `"GJ 35"` (matched against `star_systems.system_id`)
/// - `body_id`    — e.g. `"GJ 35-2"` (body override wins; falls to parent system)
/// - `station_id` — e.g. `"sova-transit"` (always falls through to parent system)
///
/// Tries each table in order, returns the first match.
/// For v0.2 bookmark selection, callers pass `system_id`, but the function is
/// body/station-aware so downstream systems don't need a second lookup path.
///
/// # Errors
/// - `CultureError::UnknownLocation` — not found in any table.
/// - `CultureError::NoCulture`       — found but culture column is NULL (data bug).
/// - `CultureError::Db`              — SQLite I/O failure.
pub fn resolve_culture(
    resolver: &CultureResolver,
    location_id: &str,
) -> Result<CultureTag, CultureError> {
    let conn = resolver
        .conn
        .lock()
        .map_err(|e| CultureError::Db(format!("mutex poisoned: {}", e)))?;

    if let Some(culture) = query_system_culture(&conn, location_id)? {
        return Ok(CultureTag(culture));
    }
    if let Some(culture) = query_body_culture(&conn, location_id)? {
        return Ok(CultureTag(culture));
    }
    if let Some(culture) = query_station_culture(&conn, location_id)? {
        return Ok(CultureTag(culture));
    }

    Err(CultureError::UnknownLocation(location_id.to_string()))
}

/// Try `star_systems` by `system_id`.
/// Returns `Ok(None)` if no row. `Ok(Some(culture))` or `Err(NoCulture)` if found.
fn query_system_culture(conn: &Connection, loc: &str) -> Result<Option<String>, CultureError> {
    let result: rusqlite::Result<Option<Option<String>>> = conn
        .query_row(
            "SELECT cultural_corridor FROM star_systems WHERE system_id = ?1",
            [loc],
            |row| row.get(0),
        )
        .map(Some)
        .or_else(|e| match e {
            rusqlite::Error::QueryReturnedNoRows => Ok(None),
            other => Err(other),
        });

    match result.map_err(|e| CultureError::Db(e.to_string()))? {
        None => Ok(None),
        Some(Some(c)) => Ok(Some(c)),
        Some(None) => Err(CultureError::NoCulture(loc.to_string())),
    }
}

/// Try `bodies` by `body_id`. Body's own `cultural_corridor` wins; NULL falls
/// through to parent system's corridor via COALESCE.
fn query_body_culture(conn: &Connection, loc: &str) -> Result<Option<String>, CultureError> {
    let result: rusqlite::Result<Option<Option<String>>> = conn
        .query_row(
            "SELECT COALESCE(b.cultural_corridor, s.cultural_corridor) \
             FROM bodies b \
             JOIN star_systems s ON s.system_id = b.system_id \
             WHERE b.body_id = ?1",
            [loc],
            |row| row.get(0),
        )
        .map(Some)
        .or_else(|e| match e {
            rusqlite::Error::QueryReturnedNoRows => Ok(None),
            other => Err(other),
        });

    match result.map_err(|e| CultureError::Db(e.to_string()))? {
        None => Ok(None),
        Some(Some(c)) => Ok(Some(c)),
        Some(None) => Err(CultureError::NoCulture(loc.to_string())),
    }
}

/// Try `stations` by `station_id`. Always falls through to parent system's corridor.
fn query_station_culture(conn: &Connection, loc: &str) -> Result<Option<String>, CultureError> {
    let result: rusqlite::Result<Option<Option<String>>> = conn
        .query_row(
            "SELECT s.cultural_corridor \
             FROM stations st \
             JOIN star_systems s ON s.system_id = st.system_id \
             WHERE st.station_id = ?1",
            [loc],
            |row| row.get(0),
        )
        .map(Some)
        .or_else(|e| match e {
            rusqlite::Error::QueryReturnedNoRows => Ok(None),
            other => Err(other),
        });

    match result.map_err(|e| CultureError::Db(e.to_string()))? {
        None => Ok(None),
        Some(Some(c)) => Ok(Some(c)),
        Some(None) => Err(CultureError::NoCulture(loc.to_string())),
    }
}

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

    fn fixture_db() -> CultureResolver {
        let path =
            Path::new(env!("CARGO_MANIFEST_DIR")).join("src/knowledge/fixtures/culture_test.db");
        CultureResolver::open(&path).expect("open fixture DB")
    }

    #[test]
    fn resolves_known_system() {
        let r = fixture_db();
        let tag = resolve_culture(&r, "GJ 35").expect("resolve");
        assert_eq!(tag.as_str(), "south_reach");
    }

    #[test]
    fn resolves_known_system_gateway() {
        let r = fixture_db();
        let tag = resolve_culture(&r, "GJ 244A").expect("resolve");
        assert_eq!(tag.as_str(), "sol-gateway-axis");
    }

    #[test]
    fn resolves_known_body_override() {
        let r = fixture_db();
        // GJ 35-2 has body-level override "core" despite parent being "south_reach"
        let tag = resolve_culture(&r, "GJ 35-2").expect("resolve body");
        assert_eq!(tag.as_str(), "core");
    }

    #[test]
    fn resolves_body_inherits_parent_system() {
        let r = fixture_db();
        // GJ 35-3 has NULL cultural_corridor — falls through to parent GJ 35 = "south_reach"
        let tag = resolve_culture(&r, "GJ 35-3").expect("resolve body inheritance");
        assert_eq!(tag.as_str(), "south_reach");
    }

    #[test]
    fn resolves_station_to_parent_system() {
        let r = fixture_db();
        let tag = resolve_culture(&r, "sova-transit").expect("resolve station");
        assert_eq!(tag.as_str(), "south_reach");
    }

    #[test]
    fn unknown_location_returns_err() {
        let r = fixture_db();
        let err = resolve_culture(&r, "BOGUS-SYSTEM-XYZ").unwrap_err();
        assert!(
            matches!(err, CultureError::UnknownLocation(_)),
            "expected UnknownLocation, got {:?}",
            err
        );
    }

    #[test]
    fn null_culture_returns_err() {
        let r = fixture_db();
        // GJ 999-null exists in fixture but has NULL cultural_corridor
        let err = resolve_culture(&r, "GJ 999-null").unwrap_err();
        assert!(
            matches!(err, CultureError::NoCulture(_)),
            "expected NoCulture, got {:?}",
            err
        );
    }

    #[test]
    fn concurrent_reads_are_safe() {
        use std::sync::Arc;
        use std::thread;

        let path =
            Path::new(env!("CARGO_MANIFEST_DIR")).join("src/knowledge/fixtures/culture_test.db");
        let r = Arc::new(CultureResolver::open(&path).expect("open"));

        let handles: Vec<_> = (0..4)
            .map(|_| {
                let r2 = Arc::clone(&r);
                thread::spawn(move || {
                    for _ in 0..250 {
                        let tag = resolve_culture(&r2, "GJ 35").expect("resolve in thread");
                        assert_eq!(tag.as_str(), "south_reach");
                    }
                })
            })
            .collect();

        for h in handles {
            h.join().expect("thread panic");
        }
    }
}