database.rs

//! Database-specific traits.
//!
//! The main traits for implementing a database within Telephone. Backends for the bot should implement [`Database`], along with all the relevant
//! database operation traits in this module for the types they wish to use with the backend.
use serenity::futures::future::BoxFuture as BoxedFuture;
use serenity::futures::FutureExt;
use sqlx::Acquire;

#[cfg(any(
    feature = "with-postgres",
    feature = "with-mysql",
    feature = "with-sqlite"
))]
impl<'c, A: 'c> Database<'c> for A
    where
        A: Acquire<'c> + Send,
        for<'e> &'e mut <A::Database as sqlx::Database>::Connection: sqlx::Executor<'e>,
{
    type Error = sqlx::Error;
    type Backend = &'c mut sqlx::Transaction<'c, <A as Acquire<'c>>::Database>;

    fn create<T: Create<'c, Self>>(self, key: T::Key) -> BoxedFuture<'c, Result<(), Self::Error>> {
        async move {
            let tx = self.begin().await?;
            match T::create(key, &mut tx).await {
                Ok(v) => {
                    tx.commit().await;
                    Ok(())
                }
                Err(e) => {
                    tx.rollback().await;
                    Err(e)
                }
            }
        }.boxed()
      /*
      error[E0308]: mismatched types
  --> src/util/database.rs:36:11
   |
36 |         }.boxed()
   |           ^^^^^ one type is more general than the other
   |
   = note: expected type `sqlx::Acquire<'_>`
              found type `sqlx::Acquire<'c>`
      */
    }

    fn read<T: Read<'c, Self>>(self, key: T::Key) -> BoxedFuture<'c, Result<Option<T>, Self::Error>> {
        todo!()
    }

    fn update<T: Update<'c, Self>>(self, target: T) -> BoxedFuture<'c, Result<(), Self::Error>> {
        todo!()
    }

    fn delete<T: Delete<'c, Self>>(self, target: T) -> BoxedFuture<'c, Result<(), Self::Error>> {
        todo!()
    }
}

/// The main trait for backends.
///
/// This is the main trait for backends to implement in order to be used with the bot, and allows for a generic interface between the discord frontend and
/// database backend.
pub trait Database<'c>: Send + Sized {
    type Error: std::error::Error;
    type Backend;

    fn create<T: Create<'c, Self>>(self, key: T::Key) -> BoxedFuture<'c, Result<(), Self::Error>>; 
    fn read<T: Read<'c, Self>>(self, key: T::Key) -> BoxedFuture<'c, Result<Option<T>, Self::Error>>; 
    fn update<T: Update<'c, Self>>(self, target: T) -> BoxedFuture<'c, Result<(), Self::Error>>;
    fn delete<T: Delete<'c, Self>>(self, target: T) -> BoxedFuture<'c, Result<(), Self::Error>>;
}

/// Trait for creating a database object.
pub trait Create<'c, T: Database<'c>>: Sized {
    type Key: Send + Sync;
    fn create(key: Self::Key, db: T::Backend) -> BoxedFuture<'c, Result<(), T::Error>>;
}

/// Trait for reading an object from the database.
pub trait Read<'c, T: Database<'c>>: Sized {
    type Key: Send + Sync;
    fn read(key: Self::Key, db: T::Backend) -> BoxedFuture<'c, Result<Option<Self>, T::Error>>;
}

/// Trait for updating a database object.
pub trait Update<'c, T: Database<'c>>: Sized + Send {
    fn update(self, db: T::Backend) -> BoxedFuture<'c, Result<(), T::Error>>;
}

/// Trait for deleting a database object.
pub trait Delete<'c, T: Database<'c>>: Sized + Send {
    fn delete(self, db: T::Backend) -> BoxedFuture<'c, Result<(), T::Error>>;
}