//! Integration tests for Leader Election (P1) and Log Replication (P2)
//!
//! Tests cover:
//! - Single-node auto-election
//! - 3-node majority election
//! - Role transitions
//! - Term management
//! - Heartbeat mechanism
//! - Log replication
//! - Leader failure recovery

#![cfg(all(test, feature = "custom-raft"))]

use std::sync::Arc;
use std::time::Duration;
use tokio::time;
use tokio::sync::mpsc;

use chainfire_raft::core::{
    RaftCore, RaftConfig, RaftRole, NodeId,
};
use chainfire_raft::network::custom_test_client::{InMemoryRpcClient, RpcMessage};
use chainfire_storage::{LogStorage, StateMachine, RocksStore};

/// Helper to create a test node
async fn create_test_node(node_id: NodeId, peers: Vec<NodeId>) -> (Arc<RaftCore>, tempfile::TempDir) {
    let temp_dir = tempfile::TempDir::new().unwrap();
    let rocks = RocksStore::new(temp_dir.path()).unwrap();
    let storage = Arc::new(LogStorage::new(rocks.clone()));
    let state_machine = Arc::new(StateMachine::new(rocks).unwrap());
    let network = Arc::new(InMemoryRpcClient::new());

    let config = RaftConfig {
        election_timeout_min: 150,
        election_timeout_max: 300,
        heartbeat_interval: 50,
    };

    let node = Arc::new(RaftCore::new(
        node_id,
        peers,
        storage,
        state_machine,
        network,
        config,
    ));

    node.initialize().await.unwrap();

    (node, temp_dir)
}

/// Helper to create a 3-node cluster with RPC wiring
async fn create_3node_cluster() -> (
    Vec<Arc<RaftCore>>,
    Vec<tempfile::TempDir>,
    Arc<InMemoryRpcClient>,
) {
    let network = Arc::new(InMemoryRpcClient::new());
    let mut nodes = Vec::new();
    let mut temp_dirs = Vec::new();

    // Create 3 nodes
    for node_id in 1..=3 {
        let peers: Vec<NodeId> = (1..=3).filter(|&id| id != node_id).collect();

        let temp_dir = tempfile::TempDir::new().unwrap();
        let rocks = RocksStore::new(temp_dir.path()).unwrap();
        let storage = Arc::new(LogStorage::new(rocks.clone()));
        let state_machine = Arc::new(StateMachine::new(rocks).unwrap());

        let config = RaftConfig {
            election_timeout_min: 150,  // 150ms - matches single-node test
            election_timeout_max: 300,  // 300ms
            heartbeat_interval: 50,     // 50ms - matches single-node test
        };

        let node = Arc::new(RaftCore::new(
            node_id,
            peers,
            storage,
            state_machine,
            Arc::clone(&network) as Arc<dyn chainfire_raft::network::RaftRpcClient>,
            config,
        ));

        node.initialize().await.unwrap();
        nodes.push(node);
        temp_dirs.push(temp_dir);
    }

    // Wire up RPC channels for each node
    for node in &nodes {
        let node_id = node.node_id();
        let (tx, mut rx) = mpsc::unbounded_channel::<RpcMessage>();
        network.register(node_id, tx).await;

        // Spawn handler for this node's RPC messages
        let node_clone = Arc::clone(node);
        tokio::spawn(async move {
            eprintln!("[RPC Handler {}] Started", node_clone.node_id());
            while let Some(msg) = rx.recv().await {
                match msg {
                    RpcMessage::Vote(req, resp_tx) => {
                        eprintln!("[RPC Handler {}] Processing Vote from {}",
                            node_clone.node_id(), req.candidate_id);
                        node_clone.request_vote_rpc(req, resp_tx).await;
                    }
                    RpcMessage::AppendEntries(req, resp_tx) => {
                        eprintln!("[RPC Handler {}] Processing AppendEntries from {} term={}",
                            node_clone.node_id(), req.leader_id, req.term);
                        node_clone.append_entries_rpc(req, resp_tx).await;
                    }
                }
            }
            eprintln!("[RPC Handler {}] Stopped (channel closed)", node_clone.node_id());
        });
    }

    // Give all RPC handler tasks time to start
    tokio::time::sleep(tokio::time::Duration::from_millis(10)).await;

    (nodes, temp_dirs, network)
}

// ============================================================================
// Test Cases
// ============================================================================

#[tokio::test]
async fn test_node_creation_and_initialization() {
    // Test that we can create a node and initialize it
    let (node, _temp_dir) = create_test_node(1, vec![2, 3]).await;

    // Node should start as follower
    assert_eq!(node.role().await, RaftRole::Follower);

    // Node ID should be correct
    assert_eq!(node.node_id(), 1);

    // Term should start at 0
    assert_eq!(node.current_term().await, 0);
}

#[tokio::test]
async fn test_role_transitions() {
    // Test basic role enumeration
    assert_ne!(RaftRole::Follower, RaftRole::Candidate);
    assert_ne!(RaftRole::Candidate, RaftRole::Leader);
    assert_ne!(RaftRole::Leader, RaftRole::Follower);
}

#[tokio::test]
async fn test_term_persistence() {
    // Test that term can be persisted and loaded
    let temp_dir = tempfile::TempDir::new().unwrap();
    let path = temp_dir.path().to_str().unwrap().to_string();

    {
        // Create first node and let it initialize
        let rocks = RocksStore::new(&path).unwrap();
        let storage = Arc::new(LogStorage::new(rocks.clone()));
        let state_machine = Arc::new(StateMachine::new(rocks).unwrap());
        let network = Arc::new(InMemoryRpcClient::new());

        let node = Arc::new(RaftCore::new(
            1,
            vec![2, 3],
            storage,
            state_machine,
            network,
            RaftConfig::default(),
        ));

        node.initialize().await.unwrap();

        // Initial term should be 0
        assert_eq!(node.current_term().await, 0);
    }

    {
        // Create second node with same storage path
        let rocks = RocksStore::new(&path).unwrap();
        let storage = Arc::new(LogStorage::new(rocks.clone()));
        let state_machine = Arc::new(StateMachine::new(rocks).unwrap());
        let network = Arc::new(InMemoryRpcClient::new());

        let node = Arc::new(RaftCore::new(
            1,
            vec![2, 3],
            storage,
            state_machine,
            network,
            RaftConfig::default(),
        ));

        node.initialize().await.unwrap();

        // Term should still be 0 (loaded from storage)
        assert_eq!(node.current_term().await, 0);
    }
}

#[tokio::test]
async fn test_config_defaults() {
    // Test that default config has reasonable values
    let config = RaftConfig::default();

    assert!(config.election_timeout_min > 0);
    assert!(config.election_timeout_max > config.election_timeout_min);
    assert!(config.heartbeat_interval > 0);
    assert!(config.heartbeat_interval < config.election_timeout_min);
}

// ============================================================================
// P2: Log Replication Integration Tests
// ============================================================================

#[tokio::test]
async fn test_3node_cluster_formation() {
    // Test 1: 3-Node Cluster Formation Test
    // - 3 nodes start → Leader elected
    // - All followers receive heartbeat
    // - No election timeout occurs

    let (nodes, _temp_dirs, _network) = create_3node_cluster().await;

    // Start event loops for all nodes
    let mut handles = Vec::new();
    for node in &nodes {
        let node_clone = Arc::clone(node);
        let handle = tokio::spawn(async move {
            let _ = node_clone.run().await;
        });
        handles.push(handle);
    }

    // Wait for leader election (should happen within ~500ms)
    time::sleep(Duration::from_millis(500)).await;

    // Check that exactly one leader was elected
    let mut leader_count = 0;
    let mut follower_count = 0;
    let mut leader_id = None;

    for node in &nodes {
        match node.role().await {
            RaftRole::Leader => {
                leader_count += 1;
                leader_id = Some(node.node_id());
            }
            RaftRole::Follower => {
                follower_count += 1;
            }
            RaftRole::Candidate => {
                // Should not have candidates after election
                panic!("Node {} is still candidate after election", node.node_id());
            }
        }
    }

    assert_eq!(leader_count, 1, "Expected exactly one leader");
    assert_eq!(follower_count, 2, "Expected exactly two followers");
    assert!(leader_id.is_some(), "Leader should be identified");

    println!("✓ Leader elected: node {}", leader_id.unwrap());

    // Wait a bit more to ensure heartbeats prevent election timeout
    // Heartbeat interval is 50ms, election timeout is 150-300ms
    // So after 400ms, no new election should occur
    time::sleep(Duration::from_millis(400)).await;

    // Verify leader is still the same
    for node in &nodes {
        if node.node_id() == leader_id.unwrap() {
            assert_eq!(node.role().await, RaftRole::Leader, "Leader should remain leader");
        } else {
            assert_eq!(
                node.role().await,
                RaftRole::Follower,
                "Followers should remain followers due to heartbeats"
            );
        }
    }

    println!("✓ Heartbeats prevent election timeout");
}

#[tokio::test]
#[ignore] // Requires client write API implementation
async fn test_log_replication() {
    // Test 2: Log Replication Test
    // - Leader adds entries
    // - Replicated to all followers
    // - commit_index synchronized

    // TODO: Implement once client write API is ready
    // This requires handle_client_write to be fully implemented
}

#[tokio::test]
#[ignore] // Requires graceful node shutdown
async fn test_leader_failure_recovery() {
    // Test 3: Leader Failure Test
    // - Leader stops → New leader elected
    // - Log consistency maintained

    // TODO: Implement once we have graceful shutdown mechanism
    // Currently, aborting the event loop doesn't cleanly stop the node
}

// ============================================================================
// Deferred complex tests
// ============================================================================

#[tokio::test]
#[ignore] // Requires full cluster setup
async fn test_split_vote_recovery() {
    // Test that cluster recovers from split vote
    // Deferred: Requires complex timing control
}

#[tokio::test]
#[ignore] // Requires node restart mechanism
async fn test_vote_persistence_across_restart() {
    // Test that votes persist across node restarts
    // Deferred: Requires proper shutdown/startup sequencing
}

// ============================================================================
// P3: Commitment & State Machine Integration Tests
// ============================================================================

#[tokio::test]
async fn test_write_replicate_commit() {
    // Test: Client write on leader → replication → commit → state machine apply
    // Verifies the complete write→replicate→commit→apply flow

    use chainfire_types::command::RaftCommand;

    let (nodes, _temp_dirs, _network) = create_3node_cluster().await;

    // Start event loops for all nodes
    let mut handles = Vec::new();
    for node in &nodes {
        let node_clone = Arc::clone(node);
        let handle = tokio::spawn(async move {
            let _ = node_clone.run().await;
        });
        handles.push(handle);
    }

    // Wait for leader election (election timeout is 2-4s)
    time::sleep(Duration::from_millis(5000)).await;

    // Find the leader
    let mut leader = None;
    for node in &nodes {
        if matches!(node.role().await, RaftRole::Leader) {
            leader = Some(node);
            break;
        }
    }
    let leader = leader.expect("Leader should be elected");

    println!("✓ Leader elected: node {}", leader.node_id());

    // Submit a write command to the leader
    let cmd = RaftCommand::Put {
        key: b"test_key_1".to_vec(),
        value: b"test_value_1".to_vec(),
        lease_id: None,
        prev_kv: false,
    };

    leader
        .client_write(cmd)
        .await
        .expect("Client write should succeed");

    println!("✓ Client write submitted to leader");

    // Wait for replication and commit (heartbeat + replication + commit)
    // Heartbeat interval is 50ms, need multiple rounds:
    // 1. First heartbeat sends entries
    // 2. Followers ack, leader updates match_index and commit_index
    // 3. Second heartbeat propagates new leader_commit to followers
    // 4. Followers update their commit_index and apply entries
    // Give extra time to avoid re-election issues
    time::sleep(Duration::from_millis(1500)).await;

    // Debug: Check all nodes' roles and states
    println!("\nDEBUG: All nodes after write:");
    for node in &nodes {
        println!("  Node {} role={:?} term={} commit_index={} last_applied={}",
                 node.node_id(), node.role().await, node.current_term().await,
                 node.commit_index().await, node.last_applied().await);
    }
    println!();

    // Verify that the value is committed and applied on all nodes
    for node in &nodes {
        let commit_index = node.commit_index().await;
        let last_applied = node.last_applied().await;

        assert!(
            commit_index >= 1,
            "Node {} should have commit_index >= 1, got {}",
            node.node_id(),
            commit_index
        );
        assert!(
            last_applied >= 1,
            "Node {} should have last_applied >= 1, got {}",
            node.node_id(),
            last_applied
        );

        // Verify the value exists in the state machine
        let state_machine = node.state_machine();
        let result = state_machine.kv().get(b"test_key_1").expect("Get should succeed");

        assert!(
            result.is_some(),
            "Node {} should have test_key_1 in state machine",
            node.node_id()
        );

        let entry = result.unwrap();
        assert_eq!(
            entry.value,
            b"test_value_1",
            "Node {} has wrong value for test_key_1",
            node.node_id()
        );

        println!(
            "✓ Node {} has test_key_1=test_value_1 (commit_index={}, last_applied={})",
            node.node_id(),
            commit_index,
            last_applied
        );
    }

    println!("✓ All nodes have committed and applied the write");
}

#[tokio::test]
async fn test_commit_consistency() {
    // Test: Multiple writes preserve order across all nodes
    // Verifies that the commit mechanism maintains consistency

    use chainfire_types::command::RaftCommand;

    let (nodes, _temp_dirs, _network) = create_3node_cluster().await;

    // Start event loops
    let mut handles = Vec::new();
    for node in &nodes {
        let node_clone = Arc::clone(node);
        let handle = tokio::spawn(async move {
            let _ = node_clone.run().await;
        });
        handles.push(handle);
    }

    // Wait for leader election (election timeout is 2-4s)
    time::sleep(Duration::from_millis(5000)).await;

    // Find the leader
    let mut leader = None;
    for node in &nodes {
        if matches!(node.role().await, RaftRole::Leader) {
            leader = Some(node);
            break;
        }
    }
    let leader = leader.expect("Leader should be elected");

    println!("✓ Leader elected: node {}", leader.node_id());

    // Submit multiple writes in sequence
    for i in 1..=5 {
        let cmd = RaftCommand::Put {
            key: format!("key_{}", i).into_bytes(),
            value: format!("value_{}", i).into_bytes(),
            lease_id: None,
            prev_kv: false,
        };

        leader
            .client_write(cmd)
            .await
            .expect("Client write should succeed");
    }

    println!("✓ Submitted 5 writes to leader");

    // Wait for all writes to commit and apply
    time::sleep(Duration::from_millis(500)).await;

    // Verify all nodes have all 5 keys in correct order
    for node in &nodes {
        let commit_index = node.commit_index().await;
        let last_applied = node.last_applied().await;

        assert!(
            commit_index >= 5,
            "Node {} should have commit_index >= 5, got {}",
            node.node_id(),
            commit_index
        );
        assert!(
            last_applied >= 5,
            "Node {} should have last_applied >= 5, got {}",
            node.node_id(),
            last_applied
        );

        let state_machine = node.state_machine();

        for i in 1..=5 {
            let key = format!("key_{}", i).into_bytes();
            let expected_value = format!("value_{}", i).into_bytes();

            let result = state_machine.kv().get(&key).expect("Get should succeed");

            assert!(
                result.is_some(),
                "Node {} missing key_{}",
                node.node_id(),
                i
            );

            let entry = result.unwrap();
            assert_eq!(
                entry.value, expected_value,
                "Node {} has wrong value for key_{}",
                node.node_id(), i
            );
        }

        println!(
            "✓ Node {} has all 5 keys in correct order (commit_index={}, last_applied={})",
            node.node_id(),
            commit_index,
            last_applied
        );
    }

    println!("✓ All nodes maintain consistent order");
}

#[tokio::test]
async fn test_leader_only_write() {
    // Test: Follower should reject client writes
    // Verifies that only the leader can accept writes (Raft safety)

    use chainfire_types::command::RaftCommand;
    use chainfire_raft::core::RaftError;

    let (nodes, _temp_dirs, _network) = create_3node_cluster().await;

    // Start event loops
    let mut handles = Vec::new();
    for node in &nodes {
        let node_clone = Arc::clone(node);
        let handle = tokio::spawn(async move {
            let _ = node_clone.run().await;
        });
        handles.push(handle);
    }

    // Wait for leader election (election timeout is 2-4s)
    time::sleep(Duration::from_millis(5000)).await;

    // Find a follower
    let mut follower = None;
    for node in &nodes {
        if matches!(node.role().await, RaftRole::Follower) {
            follower = Some(node);
            break;
        }
    }
    let follower = follower.expect("Follower should exist");

    println!("✓ Found follower: node {}", follower.node_id());

    // Try to write to the follower
    let cmd = RaftCommand::Put {
        key: b"follower_write".to_vec(),
        value: b"should_fail".to_vec(),
        lease_id: None,
        prev_kv: false,
    };

    let result = follower.client_write(cmd).await;

    // Should return NotLeader error
    assert!(
        result.is_err(),
        "Follower write should fail with NotLeader error"
    );

    if let Err(RaftError::NotLeader { .. }) = result {
        println!("✓ Follower correctly rejected write with NotLeader error");
    } else {
        panic!(
            "Expected NotLeader error, got: {:?}",
            result.err().unwrap()
        );
    }
}