entity-core 0.3.0

// SPDX-FileCopyrightText: 2025-2026 RAprogramm <andrey.rozanov.vl@gmail.com>
// SPDX-License-Identifier: MIT

//! Transaction support for entity-derive.
//!
//! This module provides type-safe transaction management with automatic
//! commit/rollback semantics. It uses a fluent builder pattern for composing
//! multiple entity operations into a single transaction.
//!
//! # Overview
//!
//! - [`Transaction`] — Entry point for creating transactions
//! - [`TransactionContext`] — Holds active transaction, provides repo access
//! - [`TransactionError`] — Error wrapper for transaction operations
//!
//! # Example
//!
//! ```rust,ignore
//! use entity_derive::prelude::*;
//!
//! async fn transfer(pool: &PgPool, from: Uuid, to: Uuid, amount: i64) -> Result<(), AppError> {
//!     Transaction::new(pool)
//!         .with_accounts()
//!         .with_transfers()
//!         .run(|mut ctx| async move {
//!             let from_acc = ctx.accounts().find_by_id(from).await?.ok_or(AppError::NotFound)?;
//!
//!             ctx.accounts().update(from, UpdateAccount {
//!                 balance: Some(from_acc.balance - amount),
//!                 ..Default::default()
//!             }).await?;
//!
//!             ctx.transfers().create(CreateTransfer { from, to, amount }).await?;
//!             Ok(())
//!         })
//!         .await
//! }
//! ```

#[cfg(feature = "postgres")]
use std::future::Future;
use std::{error::Error as StdError, fmt};

/// Transaction builder for composing multi-entity operations.
///
/// Use [`Transaction::new`] to create a builder, chain `.with_*()` methods
/// to declare which entities you'll use, then call `.run()` to execute.
///
/// # Type Parameters
///
/// - `'p` — Pool lifetime
/// - `DB` — Database pool type (e.g., `PgPool`)
///
/// # Example
///
/// ```rust,ignore
/// Transaction::new(&pool)
///     .with_users()
///     .with_orders()
///     .run(|mut ctx| async move {
///         let user = ctx.users().find_by_id(id).await?;
///         ctx.orders().create(order).await?;
///         Ok(())
///     })
///     .await?;
/// ```
pub struct Transaction<'p, DB> {
    pool: &'p DB
}

impl<'p, DB> Transaction<'p, DB> {
    /// Create a new transaction builder.
    ///
    /// # Arguments
    ///
    /// * `pool` — Database connection pool
    ///
    /// # Example
    ///
    /// ```rust,ignore
    /// let tx = Transaction::new(&pool);
    /// ```
    pub const fn new(pool: &'p DB) -> Self {
        Self {
            pool
        }
    }

    /// Get reference to the underlying pool.
    pub const fn pool(&self) -> &'p DB {
        self.pool
    }
}

/// Active transaction context with repository access.
///
/// This struct holds the database transaction and provides access to
/// entity repositories via extension traits generated by the macro.
///
/// # Automatic Rollback
///
/// If dropped without explicit commit, the transaction is automatically
/// rolled back via the underlying database transaction's Drop impl.
///
/// # Accessing Repositories
///
/// Each entity with `#[entity(transactions)]` generates an extension trait
/// that adds an accessor method:
///
/// ```rust,ignore
/// // For entity BankAccount, use:
/// ctx.bank_accounts().find_by_id(id).await?;
/// ctx.bank_accounts().create(dto).await?;
/// ctx.bank_accounts().update(id, dto).await?;
/// ```
#[cfg(feature = "postgres")]
pub struct TransactionContext {
    tx: sqlx::Transaction<'static, sqlx::Postgres>
}

#[cfg(feature = "postgres")]
impl TransactionContext {
    /// Create a new transaction context.
    ///
    /// # Arguments
    ///
    /// * `tx` — Active database transaction
    #[doc(hidden)]
    pub fn new(tx: sqlx::Transaction<'static, sqlx::Postgres>) -> Self {
        Self {
            tx
        }
    }

    /// Get mutable reference to the underlying transaction.
    ///
    /// Use this for custom queries within the transaction or
    /// for repository adapters to execute queries.
    pub fn transaction(&mut self) -> &mut sqlx::Transaction<'static, sqlx::Postgres> {
        &mut self.tx
    }

    /// Commit the transaction.
    ///
    /// Consumes self and commits all changes.
    pub async fn commit(self) -> Result<(), sqlx::Error> {
        self.tx.commit().await
    }

    /// Rollback the transaction.
    ///
    /// Consumes self and rolls back all changes.
    pub async fn rollback(self) -> Result<(), sqlx::Error> {
        self.tx.rollback().await
    }
}

/// Error type for transaction operations.
///
/// Wraps database errors and provides context about the transaction state.
#[derive(Debug)]
pub enum TransactionError<E> {
    /// Failed to begin transaction.
    Begin(E),

    /// Failed to commit transaction.
    Commit(E),

    /// Failed to rollback transaction.
    Rollback(E),

    /// Operation within transaction failed.
    Operation(E)
}

impl<E: fmt::Display> fmt::Display for TransactionError<E> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::Begin(e) => write!(f, "failed to begin transaction: {e}"),
            Self::Commit(e) => write!(f, "failed to commit transaction: {e}"),
            Self::Rollback(e) => write!(f, "failed to rollback transaction: {e}"),
            Self::Operation(e) => write!(f, "transaction operation failed: {e}")
        }
    }
}

impl<E: StdError + 'static> StdError for TransactionError<E> {
    fn source(&self) -> Option<&(dyn StdError + 'static)> {
        match self {
            Self::Begin(e) | Self::Commit(e) | Self::Rollback(e) | Self::Operation(e) => Some(e)
        }
    }
}

impl<E> TransactionError<E> {
    /// Check if this is a begin error.
    pub const fn is_begin(&self) -> bool {
        matches!(self, Self::Begin(_))
    }

    /// Check if this is a commit error.
    pub const fn is_commit(&self) -> bool {
        matches!(self, Self::Commit(_))
    }

    /// Check if this is a rollback error.
    pub const fn is_rollback(&self) -> bool {
        matches!(self, Self::Rollback(_))
    }

    /// Check if this is an operation error.
    pub const fn is_operation(&self) -> bool {
        matches!(self, Self::Operation(_))
    }

    /// Get the inner error.
    pub fn into_inner(self) -> E {
        match self {
            Self::Begin(e) | Self::Commit(e) | Self::Rollback(e) | Self::Operation(e) => e
        }
    }
}

#[cfg(feature = "postgres")]
impl From<TransactionError<sqlx::Error>> for sqlx::Error {
    fn from(err: TransactionError<sqlx::Error>) -> Self {
        err.into_inner()
    }
}

// PostgreSQL implementation
#[cfg(feature = "postgres")]
impl<'p> Transaction<'p, sqlx::PgPool> {
    /// Execute a closure within a PostgreSQL transaction.
    ///
    /// Automatically commits on `Ok`, rolls back on `Err` or drop.
    ///
    /// # Type Parameters
    ///
    /// - `F` — Closure type
    /// - `Fut` — Future returned by closure
    /// - `T` — Success type
    /// - `E` — Error type (must be convertible from sqlx::Error)
    ///
    /// # Example
    ///
    /// ```rust,ignore
    /// Transaction::new(&pool)
    ///     .with_users()
    ///     .run(|mut ctx| async move {
    ///         let user = ctx.users().create(dto).await?;
    ///         Ok(user)
    ///     })
    ///     .await?;
    /// ```
    pub async fn run<F, Fut, T, E>(self, f: F) -> Result<T, E>
    where
        F: FnOnce(TransactionContext) -> Fut + Send,
        Fut: Future<Output = Result<T, E>> + Send,
        E: From<sqlx::Error>
    {
        let tx = self.pool.begin().await.map_err(E::from)?;
        let ctx = TransactionContext::new(tx);

        match f(ctx).await {
            Ok(result) => Ok(result),
            Err(e) => Err(e)
        }
    }

    /// Execute a closure within a transaction with explicit commit.
    ///
    /// Unlike `run`, this method requires the closure to explicitly
    /// commit the transaction by calling `ctx.commit()`.
    ///
    /// # Example
    ///
    /// ```rust,ignore
    /// Transaction::new(&pool)
    ///     .run_with_commit(|mut ctx| async move {
    ///         let user = ctx.users().create(dto).await?;
    ///         ctx.commit().await?;
    ///         Ok(user)
    ///     })
    ///     .await?;
    /// ```
    pub async fn run_with_commit<F, Fut, T, E>(self, f: F) -> Result<T, E>
    where
        F: FnOnce(TransactionContext) -> Fut + Send,
        Fut: Future<Output = Result<T, E>> + Send,
        E: From<sqlx::Error>
    {
        let tx = self.pool.begin().await.map_err(E::from)?;
        let ctx = TransactionContext::new(tx);
        f(ctx).await
    }
}

#[cfg(test)]
mod tests {
    use std::error::Error;

    use super::*;

    #[test]
    fn transaction_error_display_begin() {
        let err: TransactionError<std::io::Error> =
            TransactionError::Begin(std::io::Error::other("test"));
        assert!(err.to_string().contains("begin"));
        assert!(err.to_string().contains("test"));
    }

    #[test]
    fn transaction_error_display_commit() {
        let err: TransactionError<std::io::Error> =
            TransactionError::Commit(std::io::Error::other("test"));
        assert!(err.to_string().contains("commit"));
    }

    #[test]
    fn transaction_error_display_rollback() {
        let err: TransactionError<std::io::Error> =
            TransactionError::Rollback(std::io::Error::other("test"));
        assert!(err.to_string().contains("rollback"));
    }

    #[test]
    fn transaction_error_display_operation() {
        let err: TransactionError<std::io::Error> =
            TransactionError::Operation(std::io::Error::other("test"));
        assert!(err.to_string().contains("operation"));
    }

    #[test]
    fn transaction_error_is_methods() {
        let begin: TransactionError<&str> = TransactionError::Begin("e");
        let commit: TransactionError<&str> = TransactionError::Commit("e");
        let rollback: TransactionError<&str> = TransactionError::Rollback("e");
        let operation: TransactionError<&str> = TransactionError::Operation("e");

        assert!(begin.is_begin());
        assert!(!begin.is_commit());
        assert!(!begin.is_rollback());
        assert!(!begin.is_operation());

        assert!(!commit.is_begin());
        assert!(commit.is_commit());
        assert!(!commit.is_rollback());
        assert!(!commit.is_operation());

        assert!(!rollback.is_begin());
        assert!(!rollback.is_commit());
        assert!(rollback.is_rollback());
        assert!(!rollback.is_operation());

        assert!(!operation.is_begin());
        assert!(!operation.is_commit());
        assert!(!operation.is_rollback());
        assert!(operation.is_operation());
    }

    #[test]
    fn transaction_error_into_inner() {
        let err: TransactionError<&str> = TransactionError::Operation("test");
        assert_eq!(err.into_inner(), "test");
    }

    #[test]
    fn transaction_error_into_inner_begin() {
        let err: TransactionError<&str> = TransactionError::Begin("begin_err");
        assert_eq!(err.into_inner(), "begin_err");
    }

    #[test]
    fn transaction_error_into_inner_commit() {
        let err: TransactionError<&str> = TransactionError::Commit("commit_err");
        assert_eq!(err.into_inner(), "commit_err");
    }

    #[test]
    fn transaction_error_into_inner_rollback() {
        let err: TransactionError<&str> = TransactionError::Rollback("rollback_err");
        assert_eq!(err.into_inner(), "rollback_err");
    }

    #[test]
    fn transaction_error_source_begin() {
        let err: TransactionError<std::io::Error> =
            TransactionError::Begin(std::io::Error::other("src"));
        assert!(err.source().is_some());
    }

    #[test]
    fn transaction_error_source_commit() {
        let err: TransactionError<std::io::Error> =
            TransactionError::Commit(std::io::Error::other("src"));
        assert!(err.source().is_some());
    }

    #[test]
    fn transaction_error_source_rollback() {
        let err: TransactionError<std::io::Error> =
            TransactionError::Rollback(std::io::Error::other("src"));
        assert!(err.source().is_some());
    }

    #[test]
    fn transaction_error_source_operation() {
        let err: TransactionError<std::io::Error> =
            TransactionError::Operation(std::io::Error::other("src"));
        assert!(err.source().is_some());
    }

    #[test]
    fn transaction_builder_new() {
        struct MockPool;
        let pool = MockPool;
        let tx = Transaction::new(&pool);
        let _ = tx.pool();
    }

    #[test]
    fn transaction_builder_pool_accessor() {
        struct MockPool {
            id: u32
        }
        let pool = MockPool {
            id: 42
        };
        let tx = Transaction::new(&pool);
        assert_eq!(tx.pool().id, 42);
    }

    #[test]
    fn transaction_error_debug() {
        let err: TransactionError<&str> = TransactionError::Begin("test");
        let debug_str = format!("{:?}", err);
        assert!(debug_str.contains("Begin"));
        assert!(debug_str.contains("test"));
    }
}