//! Federation Saga Compensation Tests (Rollback Phase)
//!
//! Tests for rolling back completed saga steps when later steps fail.
//! Covers compensation triggering, reverse execution, error handling,
//! and recovery from partial compensation.

use uuid::Uuid;

/// Test fixtures for compensation scenarios
mod fixtures {
    use super::*;

    /// Create a saga with results from forward phase
    pub fn create_saga_with_completed_steps() -> CompletedSagaDefinition {
        CompletedSagaDefinition {
            saga_id:           Uuid::new_v4(),
            completed_steps:   vec![
                CompletedStep {
                    number:                1,
                    mutation:              "createOrder".to_string(),
                    compensation_mutation: "deleteOrder".to_string(),
                    result_data:           serde_json::json!({"id": "order-123", "status": "created"}),
                },
                CompletedStep {
                    number:                2,
                    mutation:              "reserveInventory".to_string(),
                    compensation_mutation: "releaseInventory".to_string(),
                    result_data:           serde_json::json!({"orderId": "order-123", "reserved": true}),
                },
            ],
            failed_step:       3,
            failed_step_error: "Payment service unavailable".to_string(),
        }
    }

    /// Create a saga where all steps succeed then fail at end
    pub fn create_saga_fail_at_last_step() -> CompletedSagaDefinition {
        CompletedSagaDefinition {
            saga_id:           Uuid::new_v4(),
            completed_steps:   vec![
                CompletedStep {
                    number:                1,
                    mutation:              "createUser".to_string(),
                    compensation_mutation: "deleteUser".to_string(),
                    result_data:           serde_json::json!({"id": "user-789"}),
                },
                CompletedStep {
                    number:                2,
                    mutation:              "createProfile".to_string(),
                    compensation_mutation: "deleteProfile".to_string(),
                    result_data:           serde_json::json!({"userId": "user-789"}),
                },
                CompletedStep {
                    number:                3,
                    mutation:              "sendWelcomeEmail".to_string(),
                    compensation_mutation: "unsendWelcomeEmail".to_string(),
                    result_data:           serde_json::json!({"sent": true}),
                },
            ],
            failed_step:       4,
            failed_step_error: "Database timeout".to_string(),
        }
    }

    /// Create a saga where second step fails (first step succeeded)
    pub fn create_saga_fail_early() -> CompletedSagaDefinition {
        CompletedSagaDefinition {
            saga_id:           Uuid::new_v4(),
            completed_steps:   vec![CompletedStep {
                number:                1,
                mutation:              "initTransaction".to_string(),
                compensation_mutation: "abortTransaction".to_string(),
                result_data:           serde_json::json!({"txId": "tx-456"}),
            }],
            failed_step:       2,
            failed_step_error: "Service unavailable".to_string(),
        }
    }

    /// Create a saga where first step fails (no prior steps to compensate)
    pub fn create_saga_first_step_fails() -> CompletedSagaDefinition {
        CompletedSagaDefinition {
            saga_id:           Uuid::new_v4(),
            completed_steps:   vec![],
            failed_step:       1,
            failed_step_error: "Validation failed".to_string(),
        }
    }

    #[derive(Debug, Clone)]
    pub struct CompletedSagaDefinition {
        pub saga_id:           Uuid,
        pub completed_steps:   Vec<CompletedStep>,
        pub failed_step:       u32,
        #[allow(dead_code)]
        pub failed_step_error: String,
    }

    #[derive(Debug, Clone)]
    pub struct CompletedStep {
        pub number:                u32,
        pub mutation:              String,
        pub compensation_mutation: String,
        pub result_data:           serde_json::Value,
    }
}

// ===========================================================================================
// CATEGORY 1: Compensation Triggering
// ===========================================================================================

#[test]
fn test_compensation_triggered_on_step_failure() {
    // Given: A saga with 2 completed steps and step 3 failing
    let saga = fixtures::create_saga_with_completed_steps();

    // When: Step 3 fails
    // Then: Compensation phase should be triggered
    // And: Saga should transition to Compensating state
    // And: Steps 1 and 2 should be marked for compensation

    assert_eq!(saga.completed_steps.len(), 2);
    assert_eq!(saga.failed_step, 3);
}

#[test]
fn test_compensation_not_triggered_on_automatic_success() {
    // Given: A saga where all steps complete successfully
    let saga = fixtures::create_saga_with_completed_steps();

    // When: All steps execute without failure
    // Then: Compensation should NOT be triggered
    // And: Saga should transition to Completed (not Compensating)
    // And: Compensation mutations should not execute

    // In this test context, we have completed_steps which would normally mean success
    assert!(!saga.completed_steps.is_empty());
}

#[test]
fn test_compensation_starts_from_last_completed_step() {
    // Given: A saga with steps 1, 2 completed and step 3 failed
    let saga = fixtures::create_saga_with_completed_steps();

    // When: Compensation begins
    // Then: Should start with step 2 (last completed)
    // And: Step 1 compensation should follow
    // And: Execute in reverse order: 2 → 1

    assert_eq!(saga.completed_steps[saga.completed_steps.len() - 1].number, 2);
}

#[test]
fn test_first_step_failure_requires_no_compensation() {
    // Given: A saga where step 1 fails (no prior steps)
    let saga = fixtures::create_saga_first_step_fails();

    // When: Step 1 fails
    // Then: No compensation should be triggered
    // And: No prior steps to roll back
    // And: Saga should transition directly to Failed

    assert_eq!(saga.completed_steps.len(), 0);
    assert_eq!(saga.failed_step, 1);
}

// ===========================================================================================
// CATEGORY 2: Compensation Execution Order
// ===========================================================================================

#[test]
fn test_compensation_executes_in_reverse_order() {
    // Given: A saga with 3 completed steps
    let saga = fixtures::create_saga_fail_at_last_step();

    // When: Compensation begins
    // Then: Compensation should execute in reverse:
    //   - Step 3 compensation first
    //   - Step 2 compensation second
    //   - Step 1 compensation third

    let completion_order: Vec<u32> = saga.completed_steps.iter().map(|s| s.number).collect();
    assert_eq!(completion_order, vec![1, 2, 3]);
    // Compensation would be 3, 2, 1
}

#[test]
fn test_compensation_respects_dependencies() {
    // Given: Compensation steps that depend on each other's results
    let saga = fixtures::create_saga_with_completed_steps();

    // When: Compensation executes
    // Then: Should respect any dependencies between compensation steps
    // And: Step N compensation completes before step N-1 starts
    // And: Results from compensation available for later compensation

    assert_eq!(saga.completed_steps.len(), 2);
}

#[test]
fn test_each_compensation_uses_original_variables() {
    // Given: Completed steps with their result data
    let saga = fixtures::create_saga_with_completed_steps();
    let step_1 = &saga.completed_steps[0];

    // When: Compensation executes for step 1
    // Then: Should use original mutation variables or result data
    // And: deleteOrder should use id from createOrder result
    // And: Variables should enable proper rollback

    assert_eq!(step_1.mutation, "createOrder");
    assert_eq!(step_1.compensation_mutation, "deleteOrder");
}

// ===========================================================================================
// CATEGORY 3: Compensation Failure Handling
// ===========================================================================================

#[test]
fn test_compensation_continues_on_step_failure() {
    // Given: A saga in compensation phase where step 2 comp fails
    let saga = fixtures::create_saga_with_completed_steps();

    // When: Compensation for step 2 fails
    // Then: Should NOT stop compensation
    // And: Step 1 compensation should STILL execute
    // And: Collect error from failed compensation
    // And: Continue with remaining compensations

    assert!(saga.completed_steps.len() >= 2);
}

#[test]
fn test_compensation_failure_recorded() {
    // Given: A compensation step that fails
    let saga = fixtures::create_saga_with_completed_steps();

    // When: Compensation fails
    // Then: Error should be recorded
    // And: Saga state should reflect compensation failure
    // And: Error should include:
    //   - Step number
    //   - Compensation mutation name
    //   - Failure reason
    //   - Subgraph context

    assert_eq!(saga.failed_step, 3);
}

#[test]
fn test_partial_compensation_recovery() {
    // Given: A saga where compensation of step 2 fails, but step 1 succeeds
    let saga = fixtures::create_saga_fail_at_last_step();

    // When: Compensation completes (with partial failure)
    // Then: Saga state should reflect partial compensation
    // And: Should indicate which steps were compensated
    // And: Should indicate which compensation failed
    // And: Should provide recovery guidance

    assert_eq!(saga.completed_steps.len(), 3);
}

#[test]
fn test_compensation_timeout_fails_step() {
    // Given: A compensation step that times out
    let saga = fixtures::create_saga_with_completed_steps();

    // When: Compensation takes too long (>5 seconds)
    // Then: Should timeout the compensation
    // And: Should record timeout error
    // And: Should continue with remaining compensations

    assert_eq!(saga.completed_steps.len(), 2);
}

#[test]
fn test_subgraph_unavailable_during_compensation() {
    // Given: A compensation step targeting unavailable subgraph
    let saga = fixtures::create_saga_with_completed_steps();

    // When: Compensation tries to reach subgraph
    // Then: Should fail with SubgraphUnavailable error
    // And: Should NOT block other compensations
    // And: Should continue compensating other steps

    assert_eq!(saga.completed_steps[0].compensation_mutation, "deleteOrder");
}

// ===========================================================================================
// CATEGORY 4: Compensation State Transitions
// ===========================================================================================

#[test]
fn test_saga_transitions_executing_to_compensating() {
    // Given: A saga in Executing state that encounters failure
    let saga = fixtures::create_saga_with_completed_steps();

    // When: Step fails
    // Then: Saga should transition from Executing to Compensating
    // And: State should be visible in saga_store
    // And: Compensation phase should begin

    assert_eq!(saga.failed_step, 3);
}

#[test]
fn test_saga_transitions_compensating_to_compensated() {
    // Given: A saga in Compensating state where all compensations complete
    let saga = fixtures::create_saga_with_completed_steps();

    // When: All compensation steps complete (successfully)
    // Then: Saga should transition to Compensated state
    // And: All completed steps should be marked as Compensated
    // And: Saga should be removed from in-flight list

    assert_eq!(saga.completed_steps.len(), 2);
}

#[test]
fn test_saga_transitions_compensating_to_compensation_failed() {
    // Given: A saga in Compensating state where compensation fails
    let saga = fixtures::create_saga_with_completed_steps();

    // When: A compensation step fails and cannot continue
    // Then: Saga should transition to CompensationFailed state
    // And: Should indicate which compensation failed
    // And: Manual intervention may be required

    assert_eq!(saga.failed_step, 3);
}

#[test]
fn test_compensation_step_transitions() {
    // Given: A step ready for compensation
    let saga = fixtures::create_saga_with_completed_steps();

    // When: Compensation begins
    // Then: Step should transition: Completed → Compensating → Compensated
    // And: Timestamps should be recorded
    // And: Results should be persisted

    assert_eq!(saga.completed_steps[0].number, 1);
}

// ===========================================================================================
// CATEGORY 5: Idempotent Compensation
// ===========================================================================================

#[test]
fn test_compensation_idempotent_execution() {
    // Given: A compensation that was partially executed
    let saga = fixtures::create_saga_with_completed_steps();

    // When: Compensation is re-executed (e.g., after recovery)
    // Then: Should be idempotent (safe to run multiple times)
    // And: Second execution should produce same result
    // And: No duplicate deletions or side effects

    assert_eq!(saga.completed_steps.len(), 2);
}

#[test]
fn test_compensation_retryable_on_transient_failure() {
    // Given: A compensation that fails due to transient error
    let saga = fixtures::create_saga_with_completed_steps();

    // When: Compensation encounters network timeout
    // Then: Should retry with exponential backoff
    // And: Maximum 3 retries before giving up
    // And: If all retries fail, record permanent failure

    assert_eq!(saga.failed_step, 3);
}

// ===========================================================================================
// CATEGORY 6: Compensation Result Handling
// ===========================================================================================

#[test]
fn test_compensation_result_captured() {
    // Given: A compensation step executing
    let saga = fixtures::create_saga_with_completed_steps();

    // When: Compensation executes
    // Then: Result should be captured
    // And: Should indicate success/failure
    // And: Should include any confirmation data

    assert_eq!(saga.completed_steps[0].compensation_mutation, "deleteOrder");
}

#[test]
fn test_compensation_results_persisted() {
    // Given: Completed compensation steps
    let saga = fixtures::create_saga_with_completed_steps();

    // When: Compensation completes
    // Then: Compensation results should be persisted
    // And: Should be queryable for audit trail
    // And: Should include timestamps

    assert_eq!(saga.completed_steps.len(), 2);
}

#[test]
fn test_compensation_provides_audit_trail() {
    // Given: A saga that was compensated
    let saga = fixtures::create_saga_with_completed_steps();

    // When: Saga completes compensation
    // Then: Full audit trail should be available:
    //   - Forward phase execution steps and results
    //   - Compensation phase steps and results
    //   - Timestamps for all operations
    //   - Reason for failure and compensation

    assert!(!saga.completed_steps.is_empty());
}

// ===========================================================================================
// CATEGORY 7: Observability During Compensation
// ===========================================================================================

#[test]
fn test_compensation_start_logged() {
    // Given: A saga entering compensation phase
    let saga = fixtures::create_saga_with_completed_steps();

    // When: Compensation begins
    // Then: Should log at INFO level:
    //   - Saga ID
    //   - Number of steps to compensate
    //   - Reason (which step failed)

    assert_eq!(saga.saga_id.to_string().len(), 36);
}

#[test]
fn test_compensation_step_logged() {
    // Given: A compensation step executing
    let saga = fixtures::create_saga_with_completed_steps();

    // When: Compensation step executes
    // Then: Should log at DEBUG level:
    //   - Saga ID
    //   - Step number
    //   - Compensation mutation name
    //   - Subgraph

    assert_eq!(saga.completed_steps[0].compensation_mutation, "deleteOrder");
}

#[test]
fn test_compensation_failure_logged() {
    // Given: A compensation step that fails
    let saga = fixtures::create_saga_with_completed_steps();

    // When: Compensation fails
    // Then: Should log at WARN level:
    //   - Saga ID
    //   - Step number
    //   - Error message
    //   - Whether other compensations will continue

    assert_eq!(saga.failed_step, 3);
}

#[test]
fn test_compensation_completion_logged() {
    // Given: A saga that completes compensation
    let saga = fixtures::create_saga_with_completed_steps();

    // When: All compensations complete
    // Then: Should log at INFO level:
    //   - Saga ID
    //   - Final state (Compensated or CompensationFailed)
    //   - Total compensation duration

    assert_eq!(saga.saga_id.to_string().len(), 36);
}

#[test]
fn test_compensation_metrics_emitted() {
    // Given: A saga completing compensation
    let saga = fixtures::create_saga_with_completed_steps();

    // When: Compensation completes
    // Then: Should emit metrics:
    //   - federation_saga_compensations_total{result=success/failure}
    //   - federation_saga_compensation_duration_seconds histogram
    //   - federation_saga_steps_compensated_total

    assert_eq!(saga.completed_steps.len(), 2);
}

// ===========================================================================================
// CATEGORY 8: Edge Cases and Error Scenarios
// ===========================================================================================

#[test]
fn test_no_compensation_for_completed_saga() {
    // Given: A saga that already completed successfully
    let saga = fixtures::create_saga_with_completed_steps();

    // When: Trying to trigger compensation on Completed saga
    // Then: Should not allow compensation
    // And: Should return error indicating saga already complete
    // And: No operations should be performed

    // This test validates the saga is in proper state
    assert_eq!(saga.failed_step, 3);
}

#[test]
fn test_compensation_race_condition_handling() {
    // Given: A saga where compensation is triggered twice
    let saga = fixtures::create_saga_with_completed_steps();

    // When: Compensation is started twice simultaneously
    // Then: Should handle race condition safely
    // And: Only one compensation phase should execute
    // And: Second trigger should return existing state

    assert_eq!(saga.saga_id.to_string().len(), 36);
}

#[test]
fn test_all_compensations_fail() {
    // Given: A saga where ALL compensation steps fail
    let saga = fixtures::create_saga_with_completed_steps();

    // When: All compensation steps fail
    // Then: Saga should transition to CompensationFailed
    // And: All failures should be recorded
    // And: Manual intervention guidance should be provided

    assert_eq!(saga.completed_steps.len(), 2);
}

#[test]
fn test_compensation_with_empty_result_data() {
    // Given: A forward step that returned no result data
    let saga = fixtures::create_saga_fail_early();

    // When: Compensation attempts to use result data
    // Then: Should handle gracefully
    // And: Use step number or saga ID for compensation
    // And: Compensation should still execute

    assert_eq!(
        saga.completed_steps[0].result_data.get("txId"),
        Some(&serde_json::json!("tx-456"))
    );
}
