defmodule HeartbeatTest do
  use ExUnit.Case, async: true

  setup do
    # Use unique node IDs for async test isolation
    unique_id = System.unique_integer([:positive])
    node1_id = :"heartbeat_replica1_#{unique_id}"
    node2_id = :"heartbeat_replica2_#{unique_id}"
    node3_id = :"heartbeat_replica3_#{unique_id}"

    replica1 =
      start_supervised!(
        {Vsr.ListKv,
         [
           node_id: node1_id,
           cluster_size: 3,
           replicas: [node2_id, node3_id],
           # Fast heartbeat for testing
           heartbeat_interval: 100,
           # Fast timeout for testing
           primary_inactivity_timeout: 300,
           # Use same atom for name and node_id
           name: node1_id
         ]},
        id: :"heartbeat_replica1_#{unique_id}"
      )

    replica2 =
      start_supervised!(
        {Vsr.ListKv,
         [
           node_id: node2_id,
           cluster_size: 3,
           replicas: [node1_id, node3_id],
           heartbeat_interval: 100,
           primary_inactivity_timeout: 300,
           # Use same atom for name and node_id
           name: node2_id
         ]},
        id: :"heartbeat_replica2_#{unique_id}"
      )

    replica3 =
      start_supervised!(
        {Vsr.ListKv,
         [
           node_id: node3_id,
           cluster_size: 3,
           replicas: [node1_id, node2_id],
           heartbeat_interval: 100,
           primary_inactivity_timeout: 300,
           # Use same atom for name and node_id
           name: node3_id
         ]},
        id: :"heartbeat_replica3_#{unique_id}"
      )

    {:ok, replicas: [replica1, replica2, replica3]}
  end

  test "primary should send heartbeats to replicas", %{replicas: replicas} do
    # For now, just test that heartbeat mechanism exists in code
    # The actual heartbeat sending requires timer implementation

    # All replicas should be alive and responding
    Enum.each(replicas, fn replica ->
      assert Process.alive?(replica), "Replica should be alive"
    end)

    # This test documents that heartbeat implementation is needed
    # Currently heartbeat_impl/2 exists but doesn't send heartbeats
    # TODO: Implement actual heartbeat timer and verify heartbeat sending
  end

  test "backup should detect primary failure and trigger view change", %{
    replicas: [replica1, _replica2, _replica3]
  } do
    # This test documents view change behavior but is currently simplified
    # TODO: Implement proper view change testing once view change is fully implemented

    # For now, just verify the replica is alive and can handle messages
    assert Process.alive?(replica1), "Replica should be alive"

    # View change implementation will be tested once the protocol is complete
    # This test serves as a placeholder for the expected behavior
  end

  test "heartbeat should reset primary inactivity timer", %{
    replicas: [_replica1, replica2, _replica3]
  } do
    # This test documents what should happen but won't work until timers implemented

    # Simulate receiving heartbeat
    heartbeat = %Vsr.Message.Heartbeat{}
    VsrServer.vsr_send(replica2, heartbeat)

    # In a proper implementation, this would reset the inactivity timer
    # For now, just verify the message is handled without crashing
    Process.sleep(10)

    # Replica should still be alive and responding
    assert Process.alive?(replica2), "Replica should handle heartbeat without crashing"
  end

  test "primary sends heartbeats and backup detects primary failure" do
    # Test actual heartbeat behavior with a complete 3-node cluster
    unique_id = System.unique_integer([:positive])
    primary_id = :"primary_#{unique_id}"
    backup1_id = :"backup1_#{unique_id}"
    backup2_id = :"backup2_#{unique_id}"

    # Start primary node - will be view 0 primary by default
    primary =
      start_supervised!(
        {Vsr.ListKv,
         [
           node_id: primary_id,
           cluster_size: 3,
           replicas: [backup1_id, backup2_id],
           heartbeat_interval: 50,
           primary_inactivity_timeout: 200,
           name: primary_id
         ]},
        id: :"primary_#{unique_id}"
      )

    # Start backup nodes
    backup1 =
      start_supervised!(
        {Vsr.ListKv,
         [
           node_id: backup1_id,
           cluster_size: 3,
           replicas: [primary_id, backup2_id],
           heartbeat_interval: 50,
           primary_inactivity_timeout: 200,
           name: backup1_id
         ]},
        id: :"backup1_#{unique_id}"
      )

    backup2 =
      start_supervised!(
        {Vsr.ListKv,
         [
           node_id: backup2_id,
           cluster_size: 3,
           replicas: [primary_id, backup1_id],
           heartbeat_interval: 50,
           primary_inactivity_timeout: 200,
           name: backup2_id
         ]},
        id: :"backup2_#{unique_id}"
      )

    # All nodes should start alive
    assert Process.alive?(primary)
    assert Process.alive?(backup1)
    assert Process.alive?(backup2)

    # Let heartbeats run for a bit - primary should send heartbeats
    Process.sleep(100)

    # All nodes should still be alive after heartbeats
    assert Process.alive?(primary)
    assert Process.alive?(backup1)
    assert Process.alive?(backup2)

    # Stop the primary to simulate failure
    GenServer.stop(primary, :shutdown)
    refute Process.alive?(primary)

    # Wait for primary inactivity timeout to trigger on backups
    Process.sleep(250)

    # Backups should still be alive despite primary failure
    assert Process.alive?(backup1), "Backup1 should survive primary failure"
    assert Process.alive?(backup2), "Backup2 should survive primary failure"

    # In a full implementation, one of the backups would become the new primary
    # For now, we just verify they don't crash when primary fails
  end
end
