//! SQLite persistence layer for Jetstream events.

use bevy::prelude::*;
use crossbeam_channel::{Receiver, Sender};
use jacquard::types::string::{Did, Nsid};
use rusqlite::{Connection, params};

pub enum DbWriteRequest {
    WriteEvents(Vec<DbEvent>),
}

pub enum DbReadRequest {
    QueryTimeRange {
        start_us: i64,
        end_us: i64,
        response_tx: Sender<Vec<Vec<rusqlite::types::Value>>>,
    },
    GetLatestCursor {
        response_tx: Sender<Option<i64>>,
    },
}

/// Event data for SQLite insertion.
pub struct DbEvent {
    pub kind: String,
    pub did: Did,
    pub time_us: i64,
    pub collection: Option<Nsid>,
    pub message_json: String,
}

#[derive(Resource, Clone)]
pub struct DbChannel {
    pub writer: Sender<DbWriteRequest>,
    pub reader: Sender<DbReadRequest>,
}

const CREATE_EVENTS_TABLE: &str = "
CREATE TABLE IF NOT EXISTS events (
    id           INTEGER PRIMARY KEY,
    kind         TEXT    NOT NULL,
    did          TEXT    NOT NULL,
    time_us      INTEGER NOT NULL,
    collection   TEXT,
    message_json TEXT    NOT NULL
);
";

const CREATE_IDX_TIME_US: &str =
    "CREATE INDEX IF NOT EXISTS idx_events_time_us ON events(time_us);";
const CREATE_IDX_COLLECTION: &str =
    "CREATE INDEX IF NOT EXISTS idx_events_collection ON events(collection);";
const CREATE_IDX_DID: &str = "CREATE INDEX IF NOT EXISTS idx_events_did ON events(did);";

pub fn spawn_db_thread(mut commands: Commands) {
    let (write_tx, write_rx) = crossbeam_channel::bounded::<DbWriteRequest>(256);
    let (read_tx, read_rx) = crossbeam_channel::bounded::<DbReadRequest>(64);

    std::thread::spawn(move || {
        run_writer(write_rx);
    });

    std::thread::spawn(move || {
        run_reader(read_rx);
    });

    commands.insert_resource(DbChannel {
        writer: write_tx,
        reader: read_tx,
    });
    info!("SQLite writer + reader threads started");
}

fn run_writer(rx: Receiver<DbWriteRequest>) {
    let conn = match open_and_init() {
        Some(c) => c,
        None => return,
    };

    loop {
        match rx.recv() {
            Ok(DbWriteRequest::WriteEvents(events)) => {
                if let Err(e) = write_events(&conn, &events) {
                    error!("failed to write events to SQLite: {e}");
                }
            }
            Err(_) => {
                info!("SQLite writer shutting down");
                break;
            }
        }
    }
}

fn run_reader(rx: Receiver<DbReadRequest>) {
    let conn = match open_and_init() {
        Some(c) => c,
        None => return,
    };

    loop {
        match rx.recv() {
            Ok(DbReadRequest::QueryTimeRange {
                start_us,
                end_us,
                response_tx,
            }) => {
                let result = query_time_range(&conn, start_us, end_us);
                match result {
                    Ok(rows) => {
                        let _ = response_tx.send(rows);
                    }
                    Err(e) => {
                        error!("failed to query time range: {e}");
                        let _ = response_tx.send(vec![]);
                    }
                }
            }
            Ok(DbReadRequest::GetLatestCursor { response_tx }) => match get_latest_cursor(&conn) {
                Ok(cursor) => {
                    let _ = response_tx.send(cursor);
                }
                Err(e) => {
                    error!("failed to get latest cursor: {e}");
                    let _ = response_tx.send(None);
                }
            },
            Err(_) => {
                info!("SQLite reader shutting down");
                break;
            }
        }
    }
}

fn open_and_init() -> Option<Connection> {
    let conn = match Connection::open("jetstream_events.db") {
        Ok(c) => c,
        Err(e) => {
            error!("failed to open SQLite database: {e}");
            return None;
        }
    };

    if let Err(e) = apply_schema(&conn) {
        error!("failed to apply SQLite schema: {e}");
        return None;
    }

    if let Err(e) = conn.execute_batch("PRAGMA journal_mode = WAL; PRAGMA synchronous = NORMAL;") {
        error!("failed to set SQLite pragmas: {e}");
        return None;
    }

    Some(conn)
}

fn apply_schema(conn: &Connection) -> rusqlite::Result<()> {
    let has_message_json: bool = conn
        .prepare("PRAGMA table_info(events)")?
        .query_map([], |row| row.get::<_, String>(1))?
        .filter_map(Result::ok)
        .any(|col| col == "message_json");

    let table_exists: bool = conn
        .prepare("SELECT count(*) FROM sqlite_master WHERE type='table' AND name='events'")?
        .query_row([], |row| row.get::<_, i64>(0))
        .unwrap_or(0)
        > 0;

    if table_exists && !has_message_json {
        warn!("existing events table has incompatible schema — recreating");
        conn.execute_batch("DROP TABLE events")?;
    }

    conn.execute_batch(CREATE_EVENTS_TABLE)?;
    conn.execute_batch(CREATE_IDX_TIME_US)?;
    conn.execute_batch(CREATE_IDX_COLLECTION)?;
    conn.execute_batch(CREATE_IDX_DID)?;
    Ok(())
}

fn write_events(conn: &Connection, events: &[DbEvent]) -> rusqlite::Result<()> {
    if events.is_empty() {
        return Ok(());
    }

    let tx = conn.unchecked_transaction()?;

    {
        let mut stmt = tx.prepare_cached(
            "INSERT INTO events (kind, did, time_us, collection, message_json)
             VALUES (?1, ?2, ?3, ?4, ?5)",
        )?;

        for event in events {
            let collection_str = event.collection.as_ref().map(|n| n.as_str().to_owned());
            stmt.execute(params![
                event.kind,
                event.did.as_str(),
                event.time_us,
                collection_str,
                event.message_json,
            ])?;
        }
    }

    tx.commit()?;
    Ok(())
}

fn query_time_range(
    conn: &Connection,
    start_us: i64,
    end_us: i64,
) -> rusqlite::Result<Vec<Vec<rusqlite::types::Value>>> {
    let mut stmt = conn.prepare_cached(
        "SELECT id, kind, did, time_us, collection, message_json
         FROM events
         WHERE time_us >= ?1 AND time_us <= ?2
         ORDER BY time_us ASC",
    )?;

    let rows = stmt.query_map(params![start_us, end_us], |row| {
        let col_count = row.as_ref().column_count();
        let mut values = Vec::with_capacity(col_count);
        for i in 0..col_count {
            values.push(row.get::<_, rusqlite::types::Value>(i)?);
        }
        Ok(values)
    })?;

    rows.collect()
}

fn get_latest_cursor(conn: &Connection) -> rusqlite::Result<Option<i64>> {
    conn.query_row("SELECT MAX(time_us) FROM events", [], |row| {
        row.get::<_, Option<i64>>(0)
    })
}