use rusqlite::{Connection, OptionalExtension, Transaction, TransactionBehavior};

#[derive(Clone, Copy, PartialEq, Eq)]
pub(crate) struct HeaderSync {
    generation: u64,
}

impl HeaderSync {
    pub(crate) fn capture(conn: &Connection) -> Result<Self, String> {
        let generation = conn
            .query_row(
                crate::queries::sqlite::queries::db_header_sync::Q_001,
                [],
                |row| row.get::<_, String>(0),
            )
            .optional()
            .map_err(|e| e.to_string())?
            .map(|value| value.parse::<u64>().map_err(|e| e.to_string()))
            .transpose()?
            .unwrap_or(0);
        Ok(Self { generation })
    }

    pub(crate) fn begin_write(self, conn: &Connection) -> Result<Transaction<'_>, String> {
        let transaction = Transaction::new_unchecked(conn, TransactionBehavior::Immediate)
            .map_err(|e| e.to_string())?;
        if Self::capture(conn)?.generation != self.generation {
            return Err("Header sync superseded by cache removal; retry on next sync".into());
        }
        Ok(transaction)
    }
}

pub(crate) fn invalidate(conn: &Transaction<'_>) -> Result<(), String> {
    conn.execute(crate::queries::sqlite::queries::db_header_sync::Q_002, [])
        .map_err(|e| e.to_string())?;
    Ok(())
}