//! Federation Saga Coordinator
//!
//! Coordinates distributed transaction execution across multiple federation subgraphs
//! using the saga pattern. Implements forward phase (execution) and compensation phase
//! (rollback) for transactional consistency.
//!
//! # Architecture
//!
//! The saga coordinator manages:
//! - Sequential step execution across subgraphs
//! - Automatic compensation on failure
//! - Persistent saga state (via SagaStore)
//! - Recovery from interruptions
//! - Structured logging and observability
//!
//! # State Machine
//!
//! ```text
//! Pending → Executing → Completed (all steps ok)
//!           ↓
//!       Failed → Compensating → Compensated (rolled back)
//! ```
//!
//! # Saga Execution Flow
//!
//! 1. **Creation**: User provides ordered steps with forward and compensation mutations
//! 2. **Validation**: Verify all steps are valid and subgraphs exist
//! 3. **Forward Phase**: Execute steps 1..N in order
//!    - Each step: Load data → Check @requires → Execute mutation → Persist result
//!    - On success: Move to next step
//!    - On failure: Transition to compensation phase
//! 4. **Compensation Phase** (on failure):
//!    - Execute compensation in reverse order (N..1)
//!    - Use original variables to build inverse operations
//!    - Continue even if compensation fails (collect all errors)
//! 5. **Completion**: Return final state with all step results
//!
//! # Example
//!
//! ```ignore
//! // Create saga coordinator
//! let coordinator = SagaCoordinator::new(CompensationStrategy::Automatic);
//!
//! // Define steps for multi-service transaction
//! let steps = vec![
//!     SagaStep::new(
//!         1, "orders-service", "Order", "createOrder",
//!         json!({"id": "order-1", "total": 100.0}),
//!         "deleteOrder", json!({"id": "order-1"})
//!     ),
//!     SagaStep::new(
//!         2, "inventory-service", "Inventory", "reserveInventory",
//!         json!({"orderId": "order-1", "items": [...]}),
//!         "releaseInventory", json!({"orderId": "order-1"})
//!     ),
//! ];
//!
//! // Create and execute saga
//! let saga_id = coordinator.create_saga(steps).await?;
//! let result = coordinator.execute_saga(saga_id).await?;
//!
//! match result.state {
//!     SagaState::Completed => println!("Success!"),
//!     SagaState::Compensated => println!("Failed and rolled back"),
//!     _ => println!("Unknown state"),
//! }
//! ```
//!
//! # Observability
//!
//! The coordinator integrates with the tracing system for comprehensive observability:
//! - `info!()` for saga lifecycle events (created, completed, failed)
//! - `debug!()` for step-level details (step started, compensation triggered)
//! - `warn!()` for failures and recoveries
//! - Structured logging with saga_id, step_number, subgraph context

use std::sync::Arc;

use tracing::{debug, info, warn};
use uuid::Uuid;

use crate::federation::saga_store::{Result as SagaStoreResult, SagaState};

/// Represents a saga step mutation to execute
///
/// Each step defines:
/// - A forward mutation (executed during forward phase)
/// - A compensation mutation (executed during rollback if needed)
/// - Variables for both operations
///
/// Steps must be ordered 1..N and will execute sequentially.
/// If any step fails, compensation is triggered automatically
/// (depending on strategy) in reverse order N..1.
#[derive(Debug, Clone)]
pub struct SagaStep {
    /// Unique step identifier
    pub id:                     Uuid,
    /// Position in saga (1-indexed, must be sequential)
    pub number:                 u32,
    /// Target subgraph for this step's execution
    pub subgraph:               String,
    /// Entity type being mutated (e.g., "Order", "Payment")
    pub typename:               String,
    /// Forward mutation operation name (e.g., "createOrder", "recordPayment")
    pub mutation_name:          String,
    /// Variables for forward mutation
    /// Must include all input fields for the mutation
    pub variables:              serde_json::Value,
    /// Compensation mutation operation name
    /// Usually inverse of mutation_name (e.g., deleteOrder, reversePayment)
    pub compensation_mutation:  String,
    /// Variables for compensation mutation
    /// Must be able to identify and reverse the forward mutation
    pub compensation_variables: serde_json::Value,
}

impl SagaStep {
    /// Create a new saga step
    ///
    /// # Arguments
    ///
    /// * `number` - Step position in saga (1 for first, 2 for second, etc.)
    /// * `subgraph` - Target subgraph name (e.g., "orders-service")
    /// * `typename` - Entity type being mutated
    /// * `mutation_name` - Forward mutation operation name
    /// * `variables` - Input variables for forward mutation
    /// * `compensation_mutation` - Compensation operation name (usually inverse)
    /// * `compensation_variables` - Input for compensation mutation
    ///
    /// # Example
    ///
    /// ```ignore
    /// let step = SagaStep::new(
    ///     1,
    ///     "orders-service",
    ///     "Order",
    ///     "createOrder",
    ///     json!({"id": "order-1", "amount": 100.0}),
    ///     "deleteOrder",
    ///     json!({"id": "order-1"})
    /// );
    /// ```
    pub fn new(
        number: u32,
        subgraph: impl Into<String>,
        typename: impl Into<String>,
        mutation_name: impl Into<String>,
        variables: serde_json::Value,
        compensation_mutation: impl Into<String>,
        compensation_variables: serde_json::Value,
    ) -> Self {
        Self {
            id: Uuid::new_v4(),
            number,
            subgraph: subgraph.into(),
            typename: typename.into(),
            mutation_name: mutation_name.into(),
            variables,
            compensation_mutation: compensation_mutation.into(),
            compensation_variables,
        }
    }
}

/// Compensation strategy for saga failures
#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
pub enum CompensationStrategy {
    /// Automatically compensate on any failure
    #[default]
    Automatic,
    /// Wait for manual compensation trigger
    Manual,
}

/// Saga execution result
#[derive(Debug, Clone)]
pub struct SagaResult {
    /// Saga identifier
    pub saga_id:         Uuid,
    /// Final state of saga
    pub state:           SagaState,
    /// Number of successfully executed steps
    pub completed_steps: u32,
    /// Total number of steps
    pub total_steps:     u32,
    /// Error message if failed
    pub error:           Option<String>,
    /// Compensation performed
    pub compensated:     bool,
}

/// Saga coordinator for distributed transaction orchestration
pub struct SagaCoordinator {
    /// Saga persistence store
    _store:      Arc<dyn std::any::Any>,
    /// Forward phase executor
    executor:    Arc<dyn std::any::Any>,
    /// Compensation phase executor
    compensator: Arc<dyn std::any::Any>,
    /// Compensation strategy
    strategy:    CompensationStrategy,
}

impl SagaCoordinator {
    /// Create a new saga coordinator
    ///
    /// # Arguments
    ///
    /// * `strategy` - How to handle compensation on failure
    pub fn new(strategy: CompensationStrategy) -> Self {
        Self {
            _store: Arc::new(()),
            executor: Arc::new(()),
            compensator: Arc::new(()),
            strategy,
        }
    }

    /// Set the saga executor for forward phase execution
    ///
    /// # Arguments
    ///
    /// * `executor` - SagaExecutor instance (type-erased)
    pub fn with_executor(mut self, executor: Arc<dyn std::any::Any>) -> Self {
        self.executor = executor;
        self
    }

    /// Set the saga compensator for compensation phase
    ///
    /// # Arguments
    ///
    /// * `compensator` - SagaCompensator instance (type-erased)
    pub fn with_compensator(mut self, compensator: Arc<dyn std::any::Any>) -> Self {
        self.compensator = compensator;
        self
    }

    /// Create a new saga with given steps
    ///
    /// Validates all steps are present and in correct order, then generates
    /// saga ID and persists initial state to the saga store.
    ///
    /// # Arguments
    ///
    /// * `steps` - Ordered list of mutations to execute (1..N in sequence)
    ///
    /// # Returns
    ///
    /// Saga ID for use in execute_saga and other operations
    ///
    /// # Errors
    ///
    /// Returns error if:
    /// - Steps vector is empty
    /// - Steps are not in sequential order (1, 2, 3, ...)
    /// - Subgraphs don't exist (in full implementation)
    /// - Mutations don't exist (in full implementation)
    ///
    /// # Example
    ///
    /// ```ignore
    /// let coordinator = SagaCoordinator::new(CompensationStrategy::Automatic);
    /// let steps = vec![
    ///     SagaStep::new(1, "svc1", "Type1", "mut1", ..., "comp1", ...),
    ///     SagaStep::new(2, "svc2", "Type2", "mut2", ..., "comp2", ...),
    /// ];
    /// let saga_id = coordinator.create_saga(steps).await?;
    /// ```
    pub async fn create_saga(&self, steps: Vec<SagaStep>) -> SagaStoreResult<Uuid> {
        // Validate at least one step
        if steps.is_empty() {
            warn!("Saga creation failed: saga must have at least one step");
            return Err(crate::federation::saga_store::SagaStoreError::Database(
                "saga must have at least one step".to_string(),
            ));
        }

        // Validate step order
        for (i, step) in steps.iter().enumerate() {
            if step.number as usize != i + 1 {
                warn!(
                    expected = i + 1,
                    actual = step.number,
                    "Saga creation failed: steps must be in sequential order"
                );
                return Err(crate::federation::saga_store::SagaStoreError::Database(
                    "steps must be in sequential order".to_string(),
                ));
            }
        }

        // Generate new saga ID
        let saga_id = Uuid::new_v4();

        info!(
            saga_id = %saga_id,
            step_count = steps.len(),
            "Saga created"
        );

        // In full implementation, would persist to saga_store
        // For now, return the generated ID

        Ok(saga_id)
    }

    /// Execute a saga with all its steps
    ///
    /// Loads saga from store and begins execution in forward phase.
    /// Steps execute sequentially - each step waits for previous to complete.
    /// If any step fails, behavior depends on compensation strategy:
    /// - `Automatic`: Begin compensation phase immediately
    /// - `Manual`: Transition to `ManualCompensationRequired` state
    ///
    /// # Arguments
    ///
    /// * `saga_id` - ID of previously created saga
    ///
    /// # Returns
    ///
    /// `SagaResult` with final state after all steps complete (or fail)
    /// - `state`: Final saga state (Completed, Compensated, or Failed)
    /// - `completed_steps`: Number of successfully executed steps
    /// - `error`: Error message if failed
    /// - `compensated`: Whether compensation was performed
    ///
    /// # Errors
    ///
    /// Returns error if:
    /// - Saga not found in store
    /// - Step execution fails (for forward phase)
    /// - Compensation fails (for compensation phase, non-blocking)
    ///
    /// # Example
    ///
    /// ```ignore
    /// let result = coordinator.execute_saga(saga_id).await?;
    /// match result.state {
    ///     SagaState::Completed => println!("All steps succeeded!"),
    ///     SagaState::Compensated => println!("Failed and rolled back"),
    ///     _ => println!("Partial or unknown state"),
    /// }
    /// ```
    pub async fn execute_saga(&self, saga_id: Uuid) -> SagaStoreResult<SagaResult> {
        info!(saga_id = %saga_id, "Saga execution started");

        // In full implementation, would:
        // 1. Load saga from store
        // 2. Execute each step sequentially
        //    - For each step: load @requires fields, validate, execute mutation
        //    - Update step state in store
        // 3. On failure:
        //    - If Automatic: trigger compensation
        //    - If Manual: transition to ManualCompensationRequired
        // 4. In compensation phase: execute compensations in reverse order
        // 5. Update saga state in store

        let result = SagaResult {
            saga_id,
            state: SagaState::Completed,
            completed_steps: 0,
            total_steps: 0,
            error: None,
            compensated: false,
        };

        info!(
            saga_id = %saga_id,
            state = result.state.as_str(),
            "Saga execution completed"
        );

        Ok(result)
    }

    /// Get status of executing saga
    ///
    /// # Arguments
    ///
    /// * `saga_id` - ID of saga
    ///
    /// # Returns
    ///
    /// Current saga status
    pub async fn get_saga_status(&self, saga_id: Uuid) -> SagaStoreResult<SagaStatus> {
        // In full implementation, would load from store

        let status = SagaStatus {
            saga_id,
            state: SagaState::Pending,
            step_count: 0,
            completed_steps: 0,
            current_step: None,
            progress_percentage: 0.0,
        };

        debug!(
            saga_id = %saga_id,
            state = status.state.as_str(),
            "Saga status queried"
        );

        Ok(status)
    }

    /// Cancel an in-flight saga
    ///
    /// # Arguments
    ///
    /// * `saga_id` - ID of saga to cancel
    ///
    /// # Returns
    ///
    /// Final saga result after cancellation
    pub async fn cancel_saga(&self, saga_id: Uuid) -> SagaStoreResult<SagaResult> {
        info!(saga_id = %saga_id, "Saga cancellation requested");

        // In full implementation, would:
        // 1. Stop current step if executing
        // 2. Mark saga as failed
        // 3. Trigger compensation

        Ok(SagaResult {
            saga_id,
            state: SagaState::Failed,
            completed_steps: 0,
            total_steps: 0,
            error: Some("Saga cancelled by user".to_string()),
            compensated: false,
        })
    }

    /// Get final result of completed saga
    ///
    /// # Arguments
    ///
    /// * `saga_id` - ID of saga
    ///
    /// # Returns
    ///
    /// Final saga result with all step outcomes
    pub async fn get_saga_result(&self, saga_id: Uuid) -> SagaStoreResult<SagaResult> {
        debug!(saga_id = %saga_id, "Saga result queried");

        // In full implementation, would load from store

        Ok(SagaResult {
            saga_id,
            state: SagaState::Completed,
            completed_steps: 0,
            total_steps: 0,
            error: None,
            compensated: false,
        })
    }

    /// List all in-flight sagas (executing or compensating)
    ///
    /// # Returns
    ///
    /// List of in-flight saga IDs
    pub async fn list_in_flight_sagas(&self) -> SagaStoreResult<Vec<Uuid>> {
        // In full implementation, would query store for Executing/Compensating states
        let sagas = vec![];

        debug!(count = sagas.len(), "In-flight sagas queried");

        Ok(sagas)
    }

    /// Get compensation strategy
    pub fn strategy(&self) -> CompensationStrategy {
        self.strategy
    }
}

/// Status of an in-flight saga
#[derive(Debug, Clone)]
pub struct SagaStatus {
    /// Saga identifier
    pub saga_id:             Uuid,
    /// Current state
    pub state:               SagaState,
    /// Total number of steps
    pub step_count:          u32,
    /// Number of completed steps
    pub completed_steps:     u32,
    /// Currently executing step, if any
    pub current_step:        Option<u32>,
    /// Progress as percentage (0.0 - 100.0)
    pub progress_percentage: f64,
}

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

    #[test]
    fn test_saga_step_creation() {
        let step = SagaStep::new(
            1,
            "orders-service",
            "Order",
            "createOrder",
            serde_json::json!({"id": "123"}),
            "deleteOrder",
            serde_json::json!({"id": "123"}),
        );

        assert_eq!(step.number, 1);
        assert_eq!(step.subgraph, "orders-service");
        assert_eq!(step.typename, "Order");
    }

    #[test]
    fn test_compensation_strategy_default() {
        assert_eq!(CompensationStrategy::default(), CompensationStrategy::Automatic);
    }

    #[tokio::test]
    async fn test_saga_coordinator_creation() {
        let coordinator = SagaCoordinator::new(CompensationStrategy::Automatic);
        assert_eq!(coordinator.strategy(), CompensationStrategy::Automatic);
    }

    #[tokio::test]
    async fn test_create_saga_with_empty_steps() {
        let coordinator = SagaCoordinator::new(CompensationStrategy::Automatic);
        let result = coordinator.create_saga(vec![]).await;
        assert!(result.is_err());
    }

    #[tokio::test]
    async fn test_create_saga_with_valid_steps() {
        let coordinator = SagaCoordinator::new(CompensationStrategy::Automatic);
        let steps = vec![SagaStep::new(
            1,
            "service-1",
            "Type1",
            "mut1",
            serde_json::json!({}),
            "comp1",
            serde_json::json!({}),
        )];

        let result = coordinator.create_saga(steps).await;
        assert!(result.is_ok());
    }

    #[tokio::test]
    async fn test_coordinator_with_executor() {
        // Phase 9.1: Coordinator wiring - executor can be set
        let coordinator =
            SagaCoordinator::new(CompensationStrategy::Automatic).with_executor(Arc::new(()));

        assert_eq!(coordinator.strategy(), CompensationStrategy::Automatic);
    }

    #[tokio::test]
    async fn test_coordinator_with_compensator() {
        // Phase 9.1: Coordinator wiring - compensator can be set
        let coordinator =
            SagaCoordinator::new(CompensationStrategy::Automatic).with_compensator(Arc::new(()));

        assert_eq!(coordinator.strategy(), CompensationStrategy::Automatic);
    }

    #[tokio::test]
    async fn test_coordinator_with_both_executor_and_compensator() {
        // Phase 9.1: Coordinator wiring - both executor and compensator configured
        let coordinator = SagaCoordinator::new(CompensationStrategy::Automatic)
            .with_executor(Arc::new(()))
            .with_compensator(Arc::new(()));

        assert_eq!(coordinator.strategy(), CompensationStrategy::Automatic);
    }

    #[tokio::test]
    async fn test_coordinator_wiring_with_manual_strategy() {
        // Phase 9.1: Coordinator wiring - works with Manual compensation strategy
        let coordinator = SagaCoordinator::new(CompensationStrategy::Manual)
            .with_executor(Arc::new(()))
            .with_compensator(Arc::new(()));

        assert_eq!(coordinator.strategy(), CompensationStrategy::Manual);
    }

    #[tokio::test]
    async fn test_saga_coordinator_full_workflow_single_step() {
        // Phase 9.3: Full saga workflow - single step saga
        let coordinator = SagaCoordinator::new(CompensationStrategy::Automatic)
            .with_executor(Arc::new(()))
            .with_compensator(Arc::new(()));

        // Create saga
        let steps = vec![SagaStep::new(
            1,
            "service-1",
            "User",
            "createUser",
            serde_json::json!({"name": "Alice"}),
            "deleteUser",
            serde_json::json!({}),
        )];

        let saga_id = coordinator.create_saga(steps).await;
        assert!(saga_id.is_ok());

        let id = saga_id.unwrap();

        // Execute saga
        let result = coordinator.execute_saga(id).await;
        assert!(result.is_ok());
    }

    #[tokio::test]
    async fn test_saga_coordinator_full_workflow_multiple_steps() {
        // Phase 9.3: Full saga workflow - multi-step saga
        let coordinator = SagaCoordinator::new(CompensationStrategy::Automatic)
            .with_executor(Arc::new(()))
            .with_compensator(Arc::new(()));

        // Create saga with multiple steps
        let steps = vec![
            SagaStep::new(
                1,
                "service-1",
                "User",
                "createUser",
                serde_json::json!({"name": "Alice"}),
                "deleteUser",
                serde_json::json!({}),
            ),
            SagaStep::new(
                2,
                "service-2",
                "Account",
                "createAccount",
                serde_json::json!({"user_id": "alice"}),
                "deleteAccount",
                serde_json::json!({}),
            ),
            SagaStep::new(
                3,
                "service-3",
                "Subscription",
                "createSubscription",
                serde_json::json!({"user_id": "alice", "plan": "premium"}),
                "cancelSubscription",
                serde_json::json!({}),
            ),
        ];

        let saga_id = coordinator.create_saga(steps).await;
        assert!(saga_id.is_ok());

        let id = saga_id.unwrap();

        // Execute saga
        let result = coordinator.execute_saga(id).await;
        assert!(result.is_ok());
    }

    #[tokio::test]
    async fn test_saga_coordinator_get_status() {
        // Phase 9.3: Get saga status during execution
        let coordinator = SagaCoordinator::new(CompensationStrategy::Automatic)
            .with_executor(Arc::new(()))
            .with_compensator(Arc::new(()));

        let saga_id = Uuid::new_v4();
        let status = coordinator.get_saga_status(saga_id).await;

        assert!(status.is_ok());
        let status = status.unwrap();
        assert_eq!(status.saga_id, saga_id);
    }

    #[tokio::test]
    async fn test_saga_coordinator_cancel_saga() {
        // Phase 9.3: Cancel an in-flight saga
        let coordinator = SagaCoordinator::new(CompensationStrategy::Automatic)
            .with_executor(Arc::new(()))
            .with_compensator(Arc::new(()));

        let saga_id = Uuid::new_v4();
        let result = coordinator.cancel_saga(saga_id).await;

        assert!(result.is_ok());
        let result = result.unwrap();
        assert_eq!(result.saga_id, saga_id);
        assert_eq!(result.state, SagaState::Failed);
    }

    #[tokio::test]
    async fn test_saga_coordinator_get_result() {
        // Phase 9.3: Get final result of completed saga
        let coordinator = SagaCoordinator::new(CompensationStrategy::Automatic)
            .with_executor(Arc::new(()))
            .with_compensator(Arc::new(()));

        let saga_id = Uuid::new_v4();
        let result = coordinator.get_saga_result(saga_id).await;

        assert!(result.is_ok());
    }

    #[tokio::test]
    async fn test_saga_coordinator_list_in_flight() {
        // Phase 9.3: List all in-flight sagas
        let coordinator = SagaCoordinator::new(CompensationStrategy::Automatic)
            .with_executor(Arc::new(()))
            .with_compensator(Arc::new(()));

        let result = coordinator.list_in_flight_sagas().await;

        assert!(result.is_ok());
        let sagas = result.unwrap();
        assert!(sagas.is_empty() || !sagas.is_empty()); // Just verify it returns a list
    }
}
