package agent

import (
	"context"
	"fmt"
	"sync"
	"testing"

	"github.com/Tencent/WeKnora/internal/event"
	"github.com/Tencent/WeKnora/internal/models/chat"
	"github.com/Tencent/WeKnora/internal/types"
	"github.com/stretchr/testify/assert"
	"github.com/stretchr/testify/require"
)

// ---------------------------------------------------------------------------
// Mock: chat.Chat
// ---------------------------------------------------------------------------

type mockResponse struct {
	chunks []types.StreamResponse
}

type mockChat struct {
	mu        sync.Mutex
	responses []mockResponse
	callCount int
}

func (m *mockChat) ChatStream(_ context.Context, _ []chat.Message, _ *chat.ChatOptions) (<-chan types.StreamResponse, error) {
	m.mu.Lock()
	defer m.mu.Unlock()
	if m.callCount >= len(m.responses) {
		return nil, fmt.Errorf("unexpected ChatStream call #%d (only %d responses prepared)", m.callCount, len(m.responses))
	}
	resp := m.responses[m.callCount]
	m.callCount++

	ch := make(chan types.StreamResponse, len(resp.chunks))
	for _, chunk := range resp.chunks {
		ch <- chunk
	}
	close(ch)
	return ch, nil
}

func (m *mockChat) Chat(_ context.Context, _ []chat.Message, _ *chat.ChatOptions) (*types.ChatResponse, error) {
	return nil, fmt.Errorf("not implemented")
}

func (m *mockChat) GetModelName() string { return "mock-model" }
func (m *mockChat) GetModelID() string   { return "mock-id" }

// ---------------------------------------------------------------------------
// Test helpers
// ---------------------------------------------------------------------------

type testEngineOption func(*types.AgentConfig)

func withMaxIterations(n int) testEngineOption {
	return func(cfg *types.AgentConfig) {
		cfg.MaxIterations = n
	}
}

func newTestEngine(t *testing.T, chatModel chat.Chat, opts ...testEngineOption) *AgentEngine {
	t.Helper()
	cfg := &types.AgentConfig{
		MaxIterations: 10,
		Temperature:   0.7,
	}
	for _, opt := range opts {
		opt(cfg)
	}
	engine := NewAgentEngine(
		cfg,
		chatModel,
		nil,
		event.NewEventBus(),
		nil,
		nil,
		"test-session",
		"",
	)
	require.NotNil(t, engine, "NewAgentEngine returned nil (agenttoken.NewEstimator failed?)")
	return engine
}

func emptyMessages() []chat.Message {
	return []chat.Message{
		{Role: "system", Content: "You are a test agent."},
		{Role: "user", Content: "test query"},
	}
}

func emptyTools() []chat.Tool {
	return nil
}

// ---------------------------------------------------------------------------
// TC1: Empty content + stop → should NOT complete with empty FinalAnswer
// ---------------------------------------------------------------------------

func TestExecuteLoop_EmptyContentWithStop_ShouldNotCompleteWithEmpty(t *testing.T) {
	// Simulate: LLM returns empty content with no tool calls (natural stop).
	// The stream closes with no content chunks → streamLLMToEventBus returns fullContent="".
	// streamThinkingToEventBus wraps it as ChatResponse{Content:"", FinishReason:"stop"}.
	// analyzeResponse() returns verdict{isDone:true, finalAnswer:""} → BUG: empty answer.
	//
	// Prepare 3 responses for initial attempt + 2 retries (after fix).
	mock := &mockChat{
		responses: []mockResponse{
			{chunks: []types.StreamResponse{{Done: true}}},
			{chunks: []types.StreamResponse{{Done: true}}},
			{chunks: []types.StreamResponse{{Done: true}}},
		},
	}

	engine := newTestEngine(t, mock)
	state := &types.AgentState{}
	ctx := context.Background()

	_, err := engine.executeLoop(ctx, state, "test query", emptyMessages(), emptyTools(), "sess-1", "msg-1")

	assert.NoError(t, err)
	assert.True(t, state.IsComplete)
	assert.NotEmpty(t, state.FinalAnswer,
		"BUG: FinalAnswer is empty when LLM returns empty content with stop. "+
			"analyzeResponse() should not allow empty content to be accepted as final answer.")
}

// ---------------------------------------------------------------------------
// TC2: Non-empty content + stop → normal completion (regression guard)
// ---------------------------------------------------------------------------

func TestExecuteLoop_NonEmptyContentWithStop_ShouldComplete(t *testing.T) {
	mock := &mockChat{
		responses: []mockResponse{
			{chunks: []types.StreamResponse{
				{Content: "Here is my answer", Done: true},
			}},
		},
	}

	engine := newTestEngine(t, mock)
	state := &types.AgentState{}
	ctx := context.Background()

	_, err := engine.executeLoop(ctx, state, "test query", emptyMessages(), emptyTools(), "sess-1", "msg-1")

	assert.NoError(t, err)
	assert.True(t, state.IsComplete)
	assert.Equal(t, "Here is my answer", state.FinalAnswer)
}

// ---------------------------------------------------------------------------
// TC4: Empty → retry with nudge → non-empty → success
// ---------------------------------------------------------------------------

func TestExecuteLoop_EmptyThenNonEmpty_ShouldRetryAndComplete(t *testing.T) {
	mock := &mockChat{
		responses: []mockResponse{
			// Round 1: empty content → triggers retry + nudge
			{chunks: []types.StreamResponse{{Done: true}}},
			// Round 2: after nudge, LLM produces answer
			{chunks: []types.StreamResponse{
				{Content: "Here is the answer.", Done: true},
			}},
		},
	}

	engine := newTestEngine(t, mock)
	state := &types.AgentState{}
	ctx := context.Background()

	_, err := engine.executeLoop(ctx, state, "test query", emptyMessages(), emptyTools(), "sess-1", "msg-1")

	assert.NoError(t, err)
	assert.True(t, state.IsComplete)
	assert.Equal(t, "Here is the answer.", state.FinalAnswer)
}

// ---------------------------------------------------------------------------
// TC5: FinishReason propagation through streamThinkingToEventBus
// ---------------------------------------------------------------------------

func TestStreamThinkingToEventBus_PropagatesFinishReason(t *testing.T) {
	tests := []struct {
		name         string
		finishReason string
		wantReason   string
	}{
		{"stop", "stop", "stop"},
		{"tool_calls", "tool_calls", "tool_calls"},
		{"length", "length", "length"},
		{"empty_fallback", "", "stop"}, // empty FinishReason → fallback to "stop"
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			mock := &mockChat{
				responses: []mockResponse{
					{chunks: []types.StreamResponse{
						{Content: "test content", Done: true, FinishReason: tt.finishReason},
					}},
				},
			}

			engine := newTestEngine(t, mock)
			ctx := context.Background()
			msgs := []chat.Message{{Role: "user", Content: "test"}}
			tools := []chat.Tool{}

			resp, err := engine.streamThinkingToEventBus(ctx, msgs, tools, 0, "sess-1")

			assert.NoError(t, err)
			assert.Equal(t, tt.wantReason, resp.FinishReason)
		})
	}
}

func TestStreamFinalAnswerToEventBus_EmitsDoneWhenProviderEndsWithEmptyChunk(t *testing.T) {
	mock := &mockChat{
		responses: []mockResponse{
			{chunks: []types.StreamResponse{
				{ResponseType: types.ResponseTypeAnswer, Content: "final answer", Done: false},
				{ResponseType: types.ResponseTypeAnswer, Done: true, FinishReason: "stop"},
			}},
		},
	}

	engine := newTestEngine(t, mock)
	var finalAnswerEvents []event.AgentFinalAnswerData
	engine.eventBus.On(event.EventAgentFinalAnswer, func(_ context.Context, evt event.Event) error {
		data, ok := evt.Data.(event.AgentFinalAnswerData)
		require.True(t, ok)
		finalAnswerEvents = append(finalAnswerEvents, data)
		return nil
	})

	state := &types.AgentState{}
	err := engine.streamFinalAnswerToEventBus(context.Background(), "test query", state, "sess-1")

	require.NoError(t, err)
	require.Len(t, finalAnswerEvents, 2)
	assert.Equal(t, "final answer", finalAnswerEvents[0].Content)
	assert.False(t, finalAnswerEvents[0].Done)
	assert.Empty(t, finalAnswerEvents[1].Content)
	assert.True(t, finalAnswerEvents[1].Done)
	assert.Equal(t, "final answer", state.FinalAnswer)
}