velesdb-core 1.7.1

#![allow(
    clippy::cast_precision_loss,
    clippy::cast_possible_truncation,
    clippy::cast_sign_loss,
    clippy::float_cmp
)]
//! Tests for `ConcurrentEdgeStore` - thread-safety and performance.

use super::edge::GraphEdge;
use super::edge_concurrent::ConcurrentEdgeStore;
use std::sync::Arc;
use std::thread;

// =============================================================================
// Basic functionality tests
// =============================================================================

#[test]
fn test_concurrent_store_add_and_get() {
    let store = ConcurrentEdgeStore::new();
    store
        .add_edge(GraphEdge::new(1, 100, 200, "KNOWS").expect("valid"))
        .expect("add");

    let outgoing = store.get_outgoing(100);
    assert_eq!(outgoing.len(), 1);
    assert_eq!(outgoing[0].target(), 200);
}

#[test]
fn test_concurrent_store_get_neighbors() {
    let store = ConcurrentEdgeStore::new();
    store
        .add_edge(GraphEdge::new(1, 100, 200, "A").expect("valid"))
        .expect("add");
    store
        .add_edge(GraphEdge::new(2, 100, 300, "B").expect("valid"))
        .expect("add");

    let neighbors = store.get_neighbors(100);
    assert_eq!(neighbors.len(), 2);
    assert!(neighbors.contains(&200));
    assert!(neighbors.contains(&300));
}

#[test]
fn test_concurrent_store_cascade_delete() {
    let store = ConcurrentEdgeStore::new();
    store
        .add_edge(GraphEdge::new(1, 100, 200, "A").expect("valid"))
        .expect("add");
    store
        .add_edge(GraphEdge::new(2, 100, 300, "B").expect("valid"))
        .expect("add");
    store
        .add_edge(GraphEdge::new(3, 400, 100, "C").expect("valid"))
        .expect("add");

    store.remove_node_edges(100);

    // Note: cascade delete in sharded store only cleans the source shard
    // Full cross-shard cleanup would require more complex logic
    assert!(store.get_outgoing(100).is_empty());
}

// =============================================================================
// BFS Traversal tests (AC-2: Multi-hop traversal)
// =============================================================================

#[test]
fn test_traverse_bfs_single_hop() {
    let store = ConcurrentEdgeStore::new();
    store
        .add_edge(GraphEdge::new(1, 1, 2, "LINK").expect("valid"))
        .expect("add");
    store
        .add_edge(GraphEdge::new(2, 1, 3, "LINK").expect("valid"))
        .expect("add");

    let reachable = store.traverse_bfs(1, 1);
    assert!(reachable.contains(&1));
    assert!(reachable.contains(&2));
    assert!(reachable.contains(&3));
}

#[test]
fn test_traverse_bfs_multi_hop() {
    let store = ConcurrentEdgeStore::new();
    // Chain: 1 -> 2 -> 3 -> 4 -> 5
    store
        .add_edge(GraphEdge::new(1, 1, 2, "NEXT").expect("valid"))
        .expect("add");
    store
        .add_edge(GraphEdge::new(2, 2, 3, "NEXT").expect("valid"))
        .expect("add");
    store
        .add_edge(GraphEdge::new(3, 3, 4, "NEXT").expect("valid"))
        .expect("add");
    store
        .add_edge(GraphEdge::new(4, 4, 5, "NEXT").expect("valid"))
        .expect("add");

    // Depth 2: should reach 1, 2, 3
    let depth2 = store.traverse_bfs(1, 2);
    assert!(depth2.contains(&1));
    assert!(depth2.contains(&2));
    assert!(depth2.contains(&3));
    assert!(!depth2.contains(&4));

    // Depth 4: should reach all
    let depth4 = store.traverse_bfs(1, 4);
    assert_eq!(depth4.len(), 5);
}

#[test]
fn test_traverse_bfs_with_cycle() {
    let store = ConcurrentEdgeStore::new();
    // Cycle: 1 -> 2 -> 3 -> 1
    store
        .add_edge(GraphEdge::new(1, 1, 2, "NEXT").expect("valid"))
        .expect("add");
    store
        .add_edge(GraphEdge::new(2, 2, 3, "NEXT").expect("valid"))
        .expect("add");
    store
        .add_edge(GraphEdge::new(3, 3, 1, "NEXT").expect("valid"))
        .expect("add");

    // Should not infinite loop
    let reachable = store.traverse_bfs(1, 10);
    assert_eq!(reachable.len(), 3);
}

#[test]
fn test_traverse_bfs_disconnected() {
    let store = ConcurrentEdgeStore::new();
    store
        .add_edge(GraphEdge::new(1, 1, 2, "LINK").expect("valid"))
        .expect("add");
    store
        .add_edge(GraphEdge::new(2, 100, 200, "OTHER").expect("valid")) // Disconnected
        .expect("add");

    let reachable = store.traverse_bfs(1, 10);
    assert!(reachable.contains(&1));
    assert!(reachable.contains(&2));
    assert!(!reachable.contains(&100));
    assert!(!reachable.contains(&200));
}

// =============================================================================
// Concurrency tests
// =============================================================================

#[test]
fn test_concurrent_reads_no_block() {
    let store = Arc::new(ConcurrentEdgeStore::new());

    // Add some edges
    for i in 0..100 {
        store
            .add_edge(GraphEdge::new(i, i, i + 1, "LINK").expect("valid"))
            .expect("add");
    }

    // Spawn many readers
    let mut handles = vec![];
    for _ in 0..10 {
        let store_clone = Arc::clone(&store);
        handles.push(thread::spawn(move || {
            for i in 0..100 {
                let _ = store_clone.get_outgoing(i);
            }
        }));
    }

    for h in handles {
        h.join().expect("Thread panicked");
    }
}

#[test]
fn test_concurrent_write_different_shards() {
    let store = Arc::new(ConcurrentEdgeStore::with_shards(64));

    let mut handles = vec![];
    for t in 0..8 {
        let store_clone = Arc::clone(&store);
        handles.push(thread::spawn(move || {
            for i in 0..100 {
                let id = (t * 1000 + i) as u64;
                let source = t as u64 * 1000 + i as u64;
                let target = source + 1;
                store_clone
                    .add_edge(GraphEdge::new(id, source, target, "LINK").expect("valid"))
                    .expect("add");
            }
        }));
    }

    for h in handles {
        h.join().expect("Thread panicked");
    }

    assert_eq!(store.edge_count(), 800);
}

#[test]
fn test_concurrent_read_write_same_shard() {
    let store = Arc::new(ConcurrentEdgeStore::with_shards(1)); // Single shard

    let store_writer = Arc::clone(&store);
    let store_reader = Arc::clone(&store);

    let writer = thread::spawn(move || {
        for i in 0..100 {
            store_writer
                .add_edge(GraphEdge::new(i, 1, i + 100, "LINK").expect("valid"))
                .expect("add");
        }
    });

    let reader = thread::spawn(move || {
        for _ in 0..100 {
            let _ = store_reader.get_outgoing(1);
        }
    });

    writer.join().expect("Writer panicked");
    reader.join().expect("Reader panicked");
}

#[test]
fn test_sharded_lock_ordering_no_deadlock() {
    let store = Arc::new(ConcurrentEdgeStore::with_shards(4));

    // Create edges that cross shards in different orders
    let mut handles = vec![];
    for t in 0..4 {
        let store_clone = Arc::clone(&store);
        handles.push(thread::spawn(move || {
            for i in 0..50 {
                let source = (t * 100 + i) as u64;
                let target = ((t + 1) % 4 * 100 + i) as u64;
                store_clone
                    .add_edge(
                        GraphEdge::new((t * 1000 + i) as u64, source, target, "CROSS")
                            .expect("valid"),
                    )
                    .expect("add");
            }
        }));
    }

    // If there's a deadlock, this will hang
    for h in handles {
        h.join().expect("Thread panicked - possible deadlock");
    }
}

// =============================================================================
// Cross-shard incoming edges test (Bug fix verification)
// =============================================================================

#[test]
fn test_get_incoming_cross_shard() {
    // Use 64 shards to ensure source and target are in different shards
    let store = ConcurrentEdgeStore::with_shards(64);

    // source=100 → shard 36 (100 % 64)
    // target=200 → shard 8 (200 % 64)
    // These are in DIFFERENT shards
    store
        .add_edge(GraphEdge::new(1, 100, 200, "WROTE").expect("valid"))
        .expect("add");

    // get_outgoing should work (looks in source shard)
    let outgoing = store.get_outgoing(100);
    assert_eq!(outgoing.len(), 1, "get_outgoing should find the edge");
    assert_eq!(outgoing[0].target(), 200);

    // get_incoming MUST also work (must look in correct shard)
    let incoming = store.get_incoming(200);
    assert_eq!(
        incoming.len(),
        1,
        "get_incoming must find cross-shard edges"
    );
    assert_eq!(incoming[0].source(), 100);
}

#[test]
fn test_bidirectional_traversal_cross_shard() {
    let store = ConcurrentEdgeStore::with_shards(64);

    // Create edges that definitely cross shards
    // Node IDs chosen to be in different shards
    store
        .add_edge(GraphEdge::new(1, 0, 64, "A").expect("valid")) // shard 0 -> shard 0
        .expect("add");
    store
        .add_edge(GraphEdge::new(2, 1, 65, "B").expect("valid")) // shard 1 -> shard 1
        .expect("add");
    store
        .add_edge(GraphEdge::new(3, 2, 100, "C").expect("valid")) // shard 2 -> shard 36
        .expect("add");

    // All incoming lookups must work
    assert_eq!(store.get_incoming(64).len(), 1);
    assert_eq!(store.get_incoming(65).len(), 1);
    assert_eq!(store.get_incoming(100).len(), 1);
}

// =============================================================================
// Edge count
// =============================================================================

#[test]
#[should_panic(expected = "num_shards must be at least 1")]
fn test_with_shards_zero_panics() {
    let _ = ConcurrentEdgeStore::with_shards(0);
}

// =============================================================================
// Cross-shard remove_node_edges cleanup test (Bug fix verification)
// =============================================================================

#[test]
fn test_remove_node_edges_cross_shard_cleanup() {
    // Use 64 shards to ensure source and target are in different shards
    let store = ConcurrentEdgeStore::with_shards(64);

    // source=100 → shard 36 (100 % 64)
    // target=200 → shard 8 (200 % 64)
    store
        .add_edge(GraphEdge::new(1, 100, 200, "WROTE").expect("valid"))
        .expect("add");

    // Verify edge exists in both directions
    assert_eq!(store.get_outgoing(100).len(), 1);
    assert_eq!(store.get_incoming(200).len(), 1);
    assert_eq!(store.edge_count(), 1);

    // Remove edges for node 100 (source node)
    store.remove_node_edges(100);

    // Edge should be completely removed from both shards
    assert_eq!(
        store.get_outgoing(100).len(),
        0,
        "Outgoing edges should be removed"
    );
    assert_eq!(
        store.get_incoming(200).len(),
        0,
        "Incoming edges in other shard should also be cleaned up"
    );
    assert_eq!(
        store.edge_count(),
        0,
        "Edge count should be 0 after cleanup"
    );
}

#[test]
fn test_remove_node_edges_incoming_cross_shard() {
    let store = ConcurrentEdgeStore::with_shards(64);

    // source=200 → shard 8
    // target=100 → shard 36
    store
        .add_edge(GraphEdge::new(1, 200, 100, "POINTS_TO").expect("valid"))
        .expect("add");

    // Remove edges for node 100 (target node)
    store.remove_node_edges(100);

    // Edge should be completely removed from both shards
    assert_eq!(store.get_outgoing(200).len(), 0);
    assert_eq!(store.get_incoming(100).len(), 0);
    assert_eq!(store.edge_count(), 0);
}

#[test]
fn test_edge_count_across_shards() {
    let store = ConcurrentEdgeStore::with_shards(4);

    for i in 0..100 {
        store
            .add_edge(GraphEdge::new(i, i, i + 1, "LINK").expect("valid"))
            .expect("add");
    }

    assert_eq!(store.edge_count(), 100);
}

// =============================================================================
// Bug fix tests: Duplicate ID handling in ConcurrentEdgeStore
// =============================================================================

#[test]
fn test_concurrent_store_duplicate_id_rejected() {
    let store = ConcurrentEdgeStore::new();
    store
        .add_edge(GraphEdge::new(1, 100, 200, "FIRST").expect("valid"))
        .expect("add first");

    // Adding edge with same ID should fail
    let result = store.add_edge(GraphEdge::new(1, 300, 400, "SECOND").expect("valid"));
    assert!(result.is_err());

    // Original edge should still be intact
    assert_eq!(store.edge_count(), 1);
    let edges = store.get_outgoing(100);
    assert_eq!(edges.len(), 1);
    assert_eq!(edges[0].label(), "FIRST");
}

#[test]
fn test_concurrent_store_duplicate_id_cross_shard() {
    // Use 64 shards to ensure edges are in different shards
    let store = ConcurrentEdgeStore::with_shards(64);

    // First edge: source=100 (shard 36), target=200 (shard 8)
    store
        .add_edge(GraphEdge::new(1, 100, 200, "FIRST").expect("valid"))
        .expect("add first");

    // Second edge with same ID but different shards: source=1 (shard 1), target=2 (shard 2)
    let result = store.add_edge(GraphEdge::new(1, 1, 2, "SECOND").expect("valid"));
    assert!(
        result.is_err(),
        "duplicate ID should be rejected even in different shards"
    );

    // Verify original edge is intact
    assert_eq!(store.edge_count(), 1);
}

#[test]
fn test_remove_node_edges_allows_id_reuse() {
    // Bug #8: After remove_node_edges, the edge IDs should be available for reuse
    let store = ConcurrentEdgeStore::new();

    // Add edge with ID 1
    store
        .add_edge(GraphEdge::new(1, 100, 200, "FIRST").expect("valid"))
        .expect("add first");
    assert_eq!(store.edge_count(), 1);

    // Remove all edges for node 100
    store.remove_node_edges(100);
    assert_eq!(store.edge_count(), 0);

    // Now we should be able to reuse ID 1
    let result = store.add_edge(GraphEdge::new(1, 300, 400, "REUSED").expect("valid"));
    assert!(
        result.is_ok(),
        "should be able to reuse ID after remove_node_edges"
    );
    assert_eq!(store.edge_count(), 1);
}

#[test]
fn test_remove_edge_allows_id_reuse() {
    // Verify remove_edge also cleans up the ID registry
    let store = ConcurrentEdgeStore::new();

    store
        .add_edge(GraphEdge::new(42, 1, 2, "TEST").expect("valid"))
        .expect("add");
    assert_eq!(store.edge_count(), 1);

    store.remove_edge(42);
    assert_eq!(store.edge_count(), 0);

    // Should be able to reuse ID 42
    let result = store.add_edge(GraphEdge::new(42, 3, 4, "REUSED").expect("valid"));
    assert!(
        result.is_ok(),
        "should be able to reuse ID after remove_edge"
    );
}

#[test]
fn test_concurrent_remove_and_add_same_id() {
    // Regression test for race condition: remove_edge must clean shards
    // BEFORE removing from registry to prevent duplicate ID insertion
    use std::sync::Arc;
    use std::thread;

    let store = Arc::new(ConcurrentEdgeStore::new());

    // Add initial edge
    store
        .add_edge(GraphEdge::new(100, 1, 2, "INITIAL").expect("valid"))
        .expect("add initial");

    // Spawn multiple threads that try to remove and re-add the same ID
    let mut handles = vec![];
    for i in 0..10 {
        let store_clone = Arc::clone(&store);
        handles.push(thread::spawn(move || {
            // Remove and immediately try to re-add
            store_clone.remove_edge(100);
            // Small delay to increase chance of race
            std::thread::yield_now();
            let _ = store_clone.add_edge(
                GraphEdge::new(100, (i * 10) as u64, (i * 10 + 1) as u64, "RETRY").expect("valid"),
            );
        }));
    }

    for handle in handles {
        handle.join().unwrap();
    }

    // After all operations, we should have at most 1 edge with ID 100
    // The key invariant: no duplicate IDs should exist
    assert!(
        store.edge_count() <= 1,
        "should have at most 1 edge, got {}",
        store.edge_count()
    );
}

#[test]
fn test_concurrent_remove_node_edges_and_add() {
    // Regression test for race condition: remove_node_edges must clean shards
    // BEFORE removing IDs from registry
    use std::sync::Arc;
    use std::thread;

    let store = Arc::new(ConcurrentEdgeStore::new());

    // Add multiple edges from node 1
    for i in 1..=5 {
        store
            .add_edge(GraphEdge::new(i, 1, i + 100, "LINK").expect("valid"))
            .expect("add");
    }
    assert_eq!(store.edge_count(), 5);

    // Thread 1: remove all edges from node 1
    let store1 = Arc::clone(&store);
    let h1 = thread::spawn(move || {
        store1.remove_node_edges(1);
    });

    // Thread 2: try to add edge with ID that might be getting removed
    let store2 = Arc::clone(&store);
    let h2 = thread::spawn(move || {
        std::thread::yield_now();
        // Try to reuse ID 3 (one of the IDs being removed)
        let _ = store2.add_edge(GraphEdge::new(3, 50, 51, "NEW").expect("valid"));
    });

    h1.join().unwrap();
    h2.join().unwrap();

    // Key invariant: no corruption, edge_count should be consistent
    let count = store.edge_count();
    // After remove_node_edges(1), we should have 0 or 1 edge
    // (1 if thread 2 managed to add after removal completed)
    assert!(
        count <= 1,
        "edge count should be <= 1 after remove_node_edges, got {}",
        count
    );
}

#[test]
fn test_cross_shard_add_edge_consistency() {
    // Regression test: cross-shard add_edge should maintain consistency
    // If we add an edge spanning shards, both indices must be populated
    let store = ConcurrentEdgeStore::with_shards(64);

    // Add cross-shard edge: source=100 and target=200 should be in different shards
    store
        .add_edge(GraphEdge::new(1, 100, 200, "CROSS").expect("valid"))
        .expect("add cross-shard");

    // Verify outgoing index is populated
    let outgoing = store.get_outgoing(100);
    assert_eq!(outgoing.len(), 1, "outgoing index should have 1 edge");
    assert_eq!(outgoing[0].id(), 1);

    // Verify incoming index is populated
    let incoming = store.get_incoming(200);
    assert_eq!(incoming.len(), 1, "incoming index should have 1 edge");
    assert_eq!(incoming[0].id(), 1);

    // Verify both point to same edge data
    assert_eq!(outgoing[0].source(), incoming[0].source());
    assert_eq!(outgoing[0].target(), incoming[0].target());
}

#[test]
fn test_get_outgoing_by_label() {
    let store = ConcurrentEdgeStore::new();

    store
        .add_edge(GraphEdge::new(1, 100, 200, "KNOWS").expect("valid"))
        .expect("add");
    store
        .add_edge(GraphEdge::new(2, 100, 300, "LIKES").expect("valid"))
        .expect("add");
    store
        .add_edge(GraphEdge::new(3, 100, 400, "KNOWS").expect("valid"))
        .expect("add");

    let knows = store.get_outgoing_by_label(100, "KNOWS");
    assert_eq!(knows.len(), 2);

    let likes = store.get_outgoing_by_label(100, "LIKES");
    assert_eq!(likes.len(), 1);
    assert_eq!(likes[0].target(), 300);

    let none = store.get_outgoing_by_label(100, "HATES");
    assert!(none.is_empty());
}

#[test]
fn test_get_incoming_by_label() {
    let store = ConcurrentEdgeStore::new();

    store
        .add_edge(GraphEdge::new(1, 100, 500, "FOLLOWS").expect("valid"))
        .expect("add");
    store
        .add_edge(GraphEdge::new(2, 200, 500, "FOLLOWS").expect("valid"))
        .expect("add");
    store
        .add_edge(GraphEdge::new(3, 300, 500, "BLOCKS").expect("valid"))
        .expect("add");

    let follows = store.get_incoming_by_label(500, "FOLLOWS");
    assert_eq!(follows.len(), 2);

    let blocks = store.get_incoming_by_label(500, "BLOCKS");
    assert_eq!(blocks.len(), 1);
}

#[test]
fn test_contains_edge() {
    let store = ConcurrentEdgeStore::new();

    assert!(!store.contains_edge(1));

    store
        .add_edge(GraphEdge::new(1, 100, 200, "TEST").expect("valid"))
        .expect("add");

    assert!(store.contains_edge(1));
    assert!(!store.contains_edge(2));

    store.remove_edge(1);
    assert!(!store.contains_edge(1));
}

#[test]
fn test_get_edge() {
    let store = ConcurrentEdgeStore::new();

    assert!(store.get_edge(1).is_none());

    store
        .add_edge(GraphEdge::new(1, 100, 200, "TEST").expect("valid"))
        .expect("add");

    let edge = store.get_edge(1);
    assert!(edge.is_some());
    let edge = edge.unwrap();
    assert_eq!(edge.id(), 1);
    assert_eq!(edge.source(), 100);
    assert_eq!(edge.target(), 200);
    assert_eq!(edge.label(), "TEST");

    assert!(store.get_edge(999).is_none());
}

#[test]
fn test_self_loop_remove_node_edges() {
    // Test that self-loops are handled correctly in remove_node_edges
    let store = ConcurrentEdgeStore::new();

    // Add a self-loop (source == target)
    store
        .add_edge(GraphEdge::new(1, 100, 100, "SELF").expect("valid"))
        .expect("add self-loop");

    // Add another regular edge
    store
        .add_edge(GraphEdge::new(2, 100, 200, "OTHER").expect("valid"))
        .expect("add");

    assert_eq!(store.edge_count(), 2);

    // Remove all edges for node 100
    store.remove_node_edges(100);

    assert_eq!(store.edge_count(), 0);

    // Should be able to reuse both IDs
    assert!(store
        .add_edge(GraphEdge::new(1, 1, 2, "REUSED").expect("valid"))
        .is_ok());
    assert!(store
        .add_edge(GraphEdge::new(2, 3, 4, "REUSED").expect("valid"))
        .is_ok());
}

/// Regression test for Devin R74-157: Race between add_edge and remove_edge
/// Scenario: remove_edge must not free an ID while add_edge is inserting it.
/// Fix: edge_ids lock is held throughout add_edge/remove_edge operations.
#[test]
fn test_add_remove_race_registry_consistency() {
    use std::sync::Arc;
    use std::thread;

    let store = Arc::new(ConcurrentEdgeStore::with_shards(4));

    // Pre-populate with edge ID 1
    store
        .add_edge(GraphEdge::new(1, 100, 200, "INITIAL").expect("valid"))
        .expect("initial add");

    // Spawn threads that concurrently add and remove
    let mut handles = vec![];

    for i in 0..10 {
        let store_clone = Arc::clone(&store);
        handles.push(thread::spawn(move || {
            // Thread alternates between remove and re-add of same ID
            store_clone.remove_edge(1);
            // Try to re-add with same ID - should succeed if remove completed
            let _ =
                store_clone.add_edge(GraphEdge::new(1, 100 + i, 200 + i, "RETRY").expect("valid"));
        }));
    }

    for handle in handles {
        handle.join().expect("thread join");
    }

    // After all operations, registry and shards must be consistent:
    // If ID 1 exists in registry, it must exist in a shard
    // If ID 1 doesn't exist in registry, it must not exist in any shard
    let in_registry = store.contains_edge(1);
    let in_shard = store.get_edge(1).is_some();

    assert_eq!(
        in_registry, in_shard,
        "Registry and shard must be consistent: registry={}, shard={}",
        in_registry, in_shard
    );
}

/// Test that edge_ids lock ordering prevents deadlock between add and remove
#[test]
fn test_lock_ordering_no_deadlock_add_remove() {
    use std::sync::Arc;
    use std::thread;

    let store = Arc::new(ConcurrentEdgeStore::with_shards(4));

    // Many threads doing concurrent add/remove operations
    let mut handles = vec![];

    for i in 0..20 {
        let store_clone = Arc::clone(&store);
        handles.push(thread::spawn(move || {
            let edge_id = (i % 5) as u64; // Only 5 unique IDs to force contention
            for _ in 0..50 {
                let _ = store_clone.add_edge(
                    GraphEdge::new(edge_id, i as u64 * 100, i as u64 * 100 + 1, "CONTEND")
                        .expect("valid"),
                );
                store_clone.remove_edge(edge_id);
            }
        }));
    }

    // If there's a deadlock, this will hang
    for handle in handles {
        handle.join().expect("thread should not deadlock");
    }
}

// =============================================================================
// EPIC-019 US-001: Scalability - Increase shards from 64 to 256
// =============================================================================

/// AC-1: Default shard count should be 256 for better scalability
#[test]
fn test_default_shard_count_is_256() {
    let store = ConcurrentEdgeStore::new();
    // Verify by checking edge distribution - add 256 edges with sequential IDs
    // Each should go to a different shard if we have 256 shards
    for i in 0..256u64 {
        store
            .add_edge(GraphEdge::new(i, i, i + 1000, "TEST").expect("valid"))
            .expect("add");
    }
    // All 256 edges should be distributed (proves we have at least 256 shards)
    assert_eq!(store.edge_count(), 256);

    // Add edge with source=256, should go to shard 0 (256 % 256 = 0)
    // If we only had 64 shards, source=256 would go to shard 0 (256 % 64 = 0)
    // and source=0 also goes to shard 0, so they'd be in same shard
    // With 256 shards, source=256 goes to shard 0, same as source=0
    // Test that shard selection is deterministic based on 256 shards
    store
        .add_edge(GraphEdge::new(1000, 256, 1256, "TEST").expect("valid"))
        .expect("add");
    assert_eq!(store.edge_count(), 257);
}

/// AC-2: Edge distribution should be uniform across 256 shards
#[test]
fn test_edge_distribution_across_256_shards() {
    let store = ConcurrentEdgeStore::new();

    // Add 2560 edges (10 per shard if evenly distributed across 256 shards)
    for i in 0..2560u64 {
        store
            .add_edge(GraphEdge::new(i, i, i + 10000, "DIST").expect("valid"))
            .expect("add");
    }

    assert_eq!(store.edge_count(), 2560);
}

/// AC-3: Shard selection must be deterministic
#[test]
fn test_shard_selection_deterministic() {
    let store1 = ConcurrentEdgeStore::new();
    let store2 = ConcurrentEdgeStore::new();

    // Same edge added to two stores should behave identically
    store1
        .add_edge(GraphEdge::new(1, 12345, 67890, "DET").expect("valid"))
        .expect("add");
    store2
        .add_edge(GraphEdge::new(1, 12345, 67890, "DET").expect("valid"))
        .expect("add");

    // Both should have same outgoing edges for same source
    let out1 = store1.get_outgoing(12345);
    let out2 = store2.get_outgoing(12345);
    assert_eq!(out1.len(), out2.len());
    assert_eq!(out1[0].target(), out2[0].target());
}

/// AC-4: Concurrent insert with 16 threads should not deadlock
#[test]
fn test_concurrent_insert_16_threads_256_shards() {
    let store = Arc::new(ConcurrentEdgeStore::new()); // Uses 256 shards

    let mut handles = vec![];
    for t in 0..16 {
        let store_clone = Arc::clone(&store);
        handles.push(thread::spawn(move || {
            for i in 0..1000 {
                let id = (t * 10000 + i) as u64;
                let source = (t * 10000 + i) as u64;
                let target = source + 1;
                store_clone
                    .add_edge(GraphEdge::new(id, source, target, "CONCURRENT").expect("valid"))
                    .expect("add");
            }
        }));
    }

    for h in handles {
        h.join()
            .expect("Thread panicked - possible deadlock with 256 shards");
    }

    // 16 threads x 1000 edges = 16000 edges
    assert_eq!(store.edge_count(), 16000);
}

// =============================================================================
// Concurrency hardening tests (Issue #330)
// =============================================================================

/// Multiple writer threads insert disjoint edges, then we verify every single
/// edge is individually retrievable via `get_edge`. This catches any silent
/// data loss from lock contention (not just count mismatches).
#[test]
fn test_concurrent_insertions_all_edges_retrievable() {
    let store = Arc::new(ConcurrentEdgeStore::with_shards(16));
    let threads = 8;
    let edges_per_thread = 200;

    let mut handles = vec![];
    for t in 0..threads {
        let s = Arc::clone(&store);
        handles.push(thread::spawn(move || {
            for i in 0..edges_per_thread {
                let id = (t * edges_per_thread + i) as u64;
                let source = id * 7; // spread across shards
                let target = source + 1;
                s.add_edge(GraphEdge::new(id, source, target, "LINK").expect("valid"))
                    .expect("add");
            }
        }));
    }

    for h in handles {
        h.join().expect("writer panicked");
    }

    let expected_total = threads * edges_per_thread;
    assert_eq!(store.edge_count(), expected_total);

    // Every edge must be individually retrievable with correct endpoints.
    for t in 0..threads {
        for i in 0..edges_per_thread {
            let id = (t * edges_per_thread + i) as u64;
            let edge = store
                .get_edge(id)
                .unwrap_or_else(|| panic!("edge {id} missing after concurrent insert"));
            assert_eq!(edge.source(), id * 7);
            assert_eq!(edge.target(), id * 7 + 1);
        }
    }
}

/// One writer thread continuously inserts edges while a reader thread
/// continuously reads. The reader must observe a monotonically
/// non-decreasing edge count (no transient drops from partial state).
#[test]
fn test_concurrent_read_write_monotonic_count() {
    use std::sync::atomic::{AtomicBool, Ordering};

    let store = Arc::new(ConcurrentEdgeStore::with_shards(16));
    let done = Arc::new(AtomicBool::new(false));

    let store_w = Arc::clone(&store);
    let done_w = Arc::clone(&done);
    let writer = thread::spawn(move || {
        for i in 0..500u64 {
            store_w
                .add_edge(GraphEdge::new(i, i * 3, i * 3 + 1, "W").expect("valid"))
                .expect("add");
        }
        done_w.store(true, Ordering::Release);
    });

    let store_r = Arc::clone(&store);
    let done_r = Arc::clone(&done);
    let reader = thread::spawn(move || {
        let mut max_seen = 0usize;
        loop {
            let count = store_r.edge_count();
            assert!(
                count >= max_seen,
                "edge_count went backwards: was {max_seen}, now {count}"
            );
            max_seen = count;

            // Also exercise per-edge reads to verify no panics.
            for id in 0..max_seen as u64 {
                let _ = store_r.get_edge(id);
            }

            if done_r.load(Ordering::Acquire) {
                break;
            }
            thread::yield_now();
        }
    });

    writer.join().expect("writer panicked");
    reader.join().expect("reader panicked");
    assert_eq!(store.edge_count(), 500);
}

/// Explicit verification that `shard_index()` is deterministic and consistent
/// with the modulo formula. The same node ID must always map to the same shard.
#[test]
fn test_shard_index_deterministic_and_consistent() {
    for num_shards in [1, 4, 16, 64, 256] {
        let store = ConcurrentEdgeStore::with_shards(num_shards);

        for node_id in [0u64, 1, 255, 256, 1000, u64::MAX] {
            let expected = (node_id as usize) % num_shards;
            let actual = store.shard_index(node_id);
            assert_eq!(
                actual, expected,
                "shard_index({node_id}) with {num_shards} shards: expected {expected}, got {actual}"
            );

            // Calling twice must yield the same result (determinism).
            assert_eq!(
                store.shard_index(node_id),
                actual,
                "shard_index must be deterministic"
            );
        }
    }
}

/// Edges with the same source always land in the same shard regardless of
/// insertion order or concurrency. Verified by checking that outgoing edges
/// are always retrievable from the expected shard's perspective.
#[test]
fn test_same_source_always_same_shard() {
    let store = ConcurrentEdgeStore::with_shards(8);
    let source_id = 42u64;
    let expected_shard = (source_id as usize) % 8;

    // Insert multiple edges from the same source.
    for i in 0..20u64 {
        store
            .add_edge(GraphEdge::new(i, source_id, i + 1000, "REL").expect("valid"))
            .expect("add");
    }

    // All 20 must be retrievable via get_outgoing (which reads from the
    // source's shard).
    let outgoing = store.get_outgoing(source_id);
    assert_eq!(outgoing.len(), 20);

    // Verify the shard index is what we expect.
    assert_eq!(store.shard_index(source_id), expected_shard);
}