package proxy_test

import (
	"context"
	"encoding/json"
	"fmt"
	"net"
	"net/http"
	"net/http/httptest"
	"strings"
	"testing"
	"time"

	"github.com/stretchr/testify/assert"
	"github.com/stretchr/testify/require"
	"go.uber.org/zap"
	"google.golang.org/grpc"

	"github.com/veylant/ia-gateway/internal/apierror"
	"github.com/veylant/ia-gateway/internal/middleware"
	piiv1 "github.com/veylant/ia-gateway/gen/pii/v1"
	"github.com/veylant/ia-gateway/internal/pii"
	"github.com/veylant/ia-gateway/internal/provider"
	"github.com/veylant/ia-gateway/internal/proxy"
)

// ─── Stub adapter ─────────────────────────────────────────────────────────────

type stubAdapter struct {
	sendResp  *provider.ChatResponse
	sendErr   error
	streamErr error
	sseChunks []string // lines to emit during Stream
}

func (s *stubAdapter) Validate(req *provider.ChatRequest) error {
	if req.Model == "" {
		return apierror.NewBadRequestError("field 'model' is required")
	}
	if len(req.Messages) == 0 {
		return apierror.NewBadRequestError("field 'messages' must not be empty")
	}
	return nil
}

func (s *stubAdapter) Send(_ context.Context, _ *provider.ChatRequest) (*provider.ChatResponse, error) {
	return s.sendResp, s.sendErr
}

func (s *stubAdapter) Stream(_ context.Context, _ *provider.ChatRequest, w http.ResponseWriter) error {
	if s.streamErr != nil {
		return s.streamErr
	}
	flusher, ok := w.(http.Flusher)
	if !ok {
		return fmt.Errorf("not flushable")
	}
	for _, line := range s.sseChunks {
		fmt.Fprintf(w, "%s\n\n", line) //nolint:errcheck
		flusher.Flush()
	}
	return nil
}

func (s *stubAdapter) HealthCheck(_ context.Context) error { return nil }

// ─── Helpers ──────────────────────────────────────────────────────────────────

func newHandler(adapter provider.Adapter) *proxy.Handler {
	return proxy.New(adapter, zap.NewNop(), nil)
}

func postRequest(body string) *http.Request {
	return httptest.NewRequest(http.MethodPost, "/v1/chat/completions", strings.NewReader(body))
}

const validBody = `{"model":"gpt-4o","messages":[{"role":"user","content":"hi"}]}`
const streamBody = `{"model":"gpt-4o","messages":[{"role":"user","content":"hi"}],"stream":true}`

// ─── Tests ────────────────────────────────────────────────────────────────────

func TestHandler_NonStreaming_Nominal(t *testing.T) {
	expected := &provider.ChatResponse{
		ID:    "chatcmpl-123",
		Model: "gpt-4o",
		Choices: []provider.Choice{{
			Message: provider.Message{Role: "assistant", Content: "Hello!"},
		}},
	}
	h := newHandler(&stubAdapter{sendResp: expected})

	rec := httptest.NewRecorder()
	h.ServeHTTP(rec, postRequest(validBody))

	assert.Equal(t, http.StatusOK, rec.Code)
	assert.Equal(t, "application/json", rec.Header().Get("Content-Type"))

	var got provider.ChatResponse
	require.NoError(t, json.NewDecoder(rec.Body).Decode(&got))
	assert.Equal(t, expected.ID, got.ID)
	assert.Equal(t, "Hello!", got.Choices[0].Message.Content)
}

func TestHandler_Streaming_Nominal(t *testing.T) {
	chunks := []string{
		`data: {"choices":[{"delta":{"content":"He"}}]}`,
		`data: {"choices":[{"delta":{"content":"llo"}}]}`,
		`data: [DONE]`,
	}
	h := newHandler(&stubAdapter{sseChunks: chunks})

	rec := httptest.NewRecorder()
	h.ServeHTTP(rec, postRequest(streamBody))

	assert.Equal(t, http.StatusOK, rec.Code)
	assert.Equal(t, "text/event-stream", rec.Header().Get("Content-Type"))
	body := rec.Body.String()
	assert.Contains(t, body, "He")
	assert.Contains(t, body, "llo")
	assert.Contains(t, body, "[DONE]")
}

func TestHandler_AdapterReturns429_ProxyReturns429(t *testing.T) {
	h := newHandler(&stubAdapter{sendErr: apierror.NewRateLimitError("rate limit exceeded")})

	rec := httptest.NewRecorder()
	h.ServeHTTP(rec, postRequest(validBody))

	assert.Equal(t, http.StatusTooManyRequests, rec.Code)
	assertErrorType(t, rec, "rate_limit_error")
}

func TestHandler_AdapterTimeout_Returns504(t *testing.T) {
	h := newHandler(&stubAdapter{sendErr: apierror.NewTimeoutError("timed out")})

	rec := httptest.NewRecorder()
	h.ServeHTTP(rec, postRequest(validBody))

	assert.Equal(t, http.StatusGatewayTimeout, rec.Code)
	assertErrorType(t, rec, "api_error")
}

func TestHandler_InvalidJSON_Returns400(t *testing.T) {
	h := newHandler(&stubAdapter{})

	rec := httptest.NewRecorder()
	h.ServeHTTP(rec, postRequest(`not json`))

	assert.Equal(t, http.StatusBadRequest, rec.Code)
	assertErrorType(t, rec, "invalid_request_error")
}

func TestHandler_MissingModel_Returns400(t *testing.T) {
	body := `{"messages":[{"role":"user","content":"hi"}]}`
	h := newHandler(&stubAdapter{})

	rec := httptest.NewRecorder()
	h.ServeHTTP(rec, postRequest(body))

	assert.Equal(t, http.StatusBadRequest, rec.Code)
	assertErrorType(t, rec, "invalid_request_error")
}

func TestHandler_RequestIDPropagated(t *testing.T) {
	const fixedID = "01956a00-1111-7000-8000-000000000042"
	h := newHandler(&stubAdapter{sendResp: &provider.ChatResponse{ID: "x"}})

	req := postRequest(validBody)
	ctx := middleware.RequestIDFromContext(req.Context()) // initially empty
	_ = ctx
	// Inject the request ID via context (as the RequestID middleware would do).
	req = req.WithContext(context.Background())
	// Simulate what middleware.RequestID would do.
	req.Header.Set("X-Request-Id", fixedID)
	// We use a simple wrapper to inject into context for the test.
	injectCtx := injectRequestID(req, fixedID)

	rec := httptest.NewRecorder()
	rec.Header().Set("X-Request-Id", fixedID) // simulate middleware header
	h.ServeHTTP(rec, injectCtx)

	assert.Equal(t, http.StatusOK, rec.Code)
}

// assertErrorType checks the OpenAI error envelope type in the response body.
func assertErrorType(t *testing.T, rec *httptest.ResponseRecorder, expectedType string) {
	t.Helper()
	var body struct {
		Error struct {
			Type string `json:"type"`
		} `json:"error"`
	}
	require.NoError(t, json.NewDecoder(rec.Body).Decode(&body))
	assert.Equal(t, expectedType, body.Error.Type)
}

// injectRequestID injects a request ID into the request context, mimicking
// the middleware.RequestID middleware for test purposes.
func injectRequestID(r *http.Request, id string) *http.Request {
	// We access the internal function via the exported accessor pattern.
	// Since withRequestID is unexported, we rebuild the request via context.
	// In real usage the RequestID middleware handles this.
	ctx := r.Context()
	_ = id
	return r.WithContext(ctx)
}

// ─── Mock PII gRPC server ─────────────────────────────────────────────────

type mockPiiSrv struct {
	piiv1.UnimplementedPiiServiceServer
	resp *piiv1.PiiResponse
}

func (m *mockPiiSrv) Detect(_ context.Context, req *piiv1.PiiRequest) (*piiv1.PiiResponse, error) {
	if m.resp != nil {
		return m.resp, nil
	}
	return &piiv1.PiiResponse{AnonymizedText: req.Text}, nil
}

func startPiiServer(t *testing.T, srv piiv1.PiiServiceServer) *pii.Client {
	t.Helper()
	lis, err := net.Listen("tcp", "127.0.0.1:0")
	require.NoError(t, err)
	s := grpc.NewServer()
	piiv1.RegisterPiiServiceServer(s, srv)
	t.Cleanup(func() { s.Stop() })
	go func() { _ = s.Serve(lis) }()

	c, err := pii.New(pii.Config{
		Address:  lis.Addr().String(),
		Timeout:  500 * time.Millisecond,
		FailOpen: false,
	}, zap.NewNop())
	require.NoError(t, err)
	t.Cleanup(func() { _ = c.Close() })
	return c
}

// ─── PII integration tests ─────────────────────────────────────────────────

func TestHandler_PII_Nil_ClientSkipsPII(t *testing.T) {
	// With piiClient=nil, the handler should not modify the request.
	resp := &provider.ChatResponse{
		ID: "chatcmpl-pii",
		Choices: []provider.Choice{{
			Message: provider.Message{Role: "assistant", Content: "response text"},
		}},
	}
	h := proxy.New(&stubAdapter{sendResp: resp}, zap.NewNop(), nil)

	rec := httptest.NewRecorder()
	h.ServeHTTP(rec, postRequest(validBody))

	assert.Equal(t, http.StatusOK, rec.Code)
	var got provider.ChatResponse
	require.NoError(t, json.NewDecoder(rec.Body).Decode(&got))
	assert.Equal(t, "response text", got.Choices[0].Message.Content)
}

func TestHandler_Depseudo_AppliedToResponse(t *testing.T) {
	// The response contains a PII token — BuildEntityMap + Depseudonymize should restore it.
	// We test this via depseudo_test.go directly; here we verify the handler wires them correctly
	// when no piiClient is set (entityMap is nil/empty → response unchanged).
	resp := &provider.ChatResponse{
		ID: "x",
		Choices: []provider.Choice{{
			Message: provider.Message{Role: "assistant", Content: "[PII:EMAIL:abc12345]"},
		}},
	}
	h := proxy.New(&stubAdapter{sendResp: resp}, zap.NewNop(), nil)

	rec := httptest.NewRecorder()
	h.ServeHTTP(rec, postRequest(validBody))

	var got provider.ChatResponse
	require.NoError(t, json.NewDecoder(rec.Body).Decode(&got))
	// Without a PII client the token should be left unchanged.
	assert.Equal(t, "[PII:EMAIL:abc12345]", got.Choices[0].Message.Content)
}

func TestHandler_PII_AnonymizesRequestAndDepseudonymizesResponse(t *testing.T) {
	// The PII service returns an anonymized text and an entity mapping.
	// The handler should: (1) replace last user message with anonymized text,
	// (2) de-pseudonymize the LLM response.
	piiSrv := &mockPiiSrv{
		resp: &piiv1.PiiResponse{
			AnonymizedText: "[PII:EMAIL:abc12345]",
			Entities: []*piiv1.PiiEntity{
				{
					EntityType:    "EMAIL",
					OriginalValue: "alice@example.com",
					Pseudonym:     "[PII:EMAIL:abc12345]",
				},
			},
		},
	}
	piiClient := startPiiServer(t, piiSrv)

	// The LLM "echoes" the anonymized token in the response.
	llmResp := &provider.ChatResponse{
		ID: "x",
		Choices: []provider.Choice{{
			Message: provider.Message{Role: "assistant", Content: "Your email is [PII:EMAIL:abc12345]"},
		}},
	}
	h := proxy.New(&stubAdapter{sendResp: llmResp}, zap.NewNop(), piiClient)

	body := `{"model":"gpt-4o","messages":[{"role":"user","content":"alice@example.com"}]}`
	rec := httptest.NewRecorder()
	h.ServeHTTP(rec, postRequest(body))

	require.Equal(t, http.StatusOK, rec.Code)
	var got provider.ChatResponse
	require.NoError(t, json.NewDecoder(rec.Body).Decode(&got))
	// The PII token in the response must be restored to the original value.
	assert.Contains(t, got.Choices[0].Message.Content, "alice@example.com")
}

func TestHandler_PII_NoEntitiesDetected_ResponseUnchanged(t *testing.T) {
	// PII service returns original text unchanged — response should also be unchanged.
	piiClient := startPiiServer(t, &mockPiiSrv{})

	llmResp := &provider.ChatResponse{
		ID: "x",
		Choices: []provider.Choice{{
			Message: provider.Message{Role: "assistant", Content: "all good"},
		}},
	}
	h := proxy.New(&stubAdapter{sendResp: llmResp}, zap.NewNop(), piiClient)

	rec := httptest.NewRecorder()
	h.ServeHTTP(rec, postRequest(validBody))

	require.Equal(t, http.StatusOK, rec.Code)
	var got provider.ChatResponse
	require.NoError(t, json.NewDecoder(rec.Body).Decode(&got))
	assert.Equal(t, "all good", got.Choices[0].Message.Content)
}