package httpapi

import (
	"bufio"
	"bytes"
	"context"
	"encoding/json"
	"io"
	"log/slog"
	"net/http"
	"net/http/httptest"
	"strings"
	"sync/atomic"
	"testing"
	"time"

	"aigw/internal/auth"
	"aigw/internal/billing"
	"aigw/internal/catalog"
	"aigw/internal/config"
	"aigw/internal/domain"
	"aigw/internal/provider"
	"aigw/internal/routing"
	"aigw/internal/telemetry"
)

type captureUsageSink struct {
	events chan domain.UsageEvent
}

type fakeBillingMeter struct {
	authorizeErr error
	settled      chan domain.UsageEvent
}

func (m *fakeBillingMeter) Authorize(context.Context, billing.Authorization) error {
	return m.authorizeErr
}

func (m *fakeBillingMeter) Settle(_ context.Context, event domain.UsageEvent) error {
	m.settled <- event
	return nil
}

func (s *captureUsageSink) Publish(event domain.UsageEvent) {
	s.events <- event
}

func TestOpenAIProxyRewritesModelAndEmitsUsage(t *testing.T) {
	upstream := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if r.URL.Path != "/v1/chat/completions" {
			t.Errorf("unexpected path: %s", r.URL.Path)
		}
		if r.Header.Get("Authorization") != "Bearer upstream-secret" {
			t.Errorf("upstream authorization leaked or missing: %q", r.Header.Get("Authorization"))
		}
		var request map[string]any
		if err := json.NewDecoder(r.Body).Decode(&request); err != nil {
			t.Error(err)
		}
		if request["model"] != "upstream-model" {
			t.Errorf("model was not rewritten: %+v", request)
		}
		w.Header().Set("Content-Type", "application/json")
		_, _ = io.WriteString(w, `{"id":"chat-1","choices":[],"usage":{"prompt_tokens":3,"completion_tokens":2,"total_tokens":5}}`)
	}))
	defer upstream.Close()

	gateway, sink := newTestGateway(t, []config.ProviderConfig{{
		ID: "primary", Protocol: domain.ProtocolOpenAI, BaseURL: upstream.URL + "/v1", APIKey: "upstream-secret",
	}}, []config.RouteConfig{{Provider: "primary", UpstreamModel: "upstream-model", Weight: 1}})
	defer gateway.Close()

	request, _ := http.NewRequest(http.MethodPost, gateway.URL+"/v1/chat/completions", strings.NewReader(`{"model":"public/model","messages":[{"role":"user","content":"hello"}]}`))
	request.Header.Set("Authorization", "Bearer client-secret")
	response, err := http.DefaultClient.Do(request)
	if err != nil {
		t.Fatal(err)
	}
	defer response.Body.Close()
	if response.StatusCode != http.StatusOK {
		payload, _ := io.ReadAll(response.Body)
		t.Fatalf("unexpected status %d: %s", response.StatusCode, payload)
	}
	if response.Header.Get("X-AIGW-Request-ID") == "" {
		t.Fatal("missing gateway request id")
	}

	select {
	case event := <-sink.events:
		if event.PublicModel != "public/model" || event.UpstreamModel != "upstream-model" || event.Usage.TotalTokens != 5 || !event.Success {
			t.Fatalf("unexpected usage event: %+v", event)
		}
	case <-time.After(time.Second):
		t.Fatal("usage event was not emitted")
	}
}

func TestProxyFailsOverBeforeWritingResponse(t *testing.T) {
	var primaryCalls atomic.Int64
	primary := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
		primaryCalls.Add(1)
		w.WriteHeader(http.StatusServiceUnavailable)
	}))
	defer primary.Close()
	var fallbackCalls atomic.Int64
	fallback := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
		fallbackCalls.Add(1)
		w.Header().Set("Content-Type", "application/json")
		_, _ = io.WriteString(w, `{"choices":[],"usage":{"prompt_tokens":1,"completion_tokens":1,"total_tokens":2}}`)
	}))
	defer fallback.Close()

	gateway, sink := newTestGateway(t,
		[]config.ProviderConfig{
			{ID: "primary", Protocol: domain.ProtocolOpenAI, BaseURL: primary.URL + "/v1", APIKey: "one"},
			{ID: "fallback", Protocol: domain.ProtocolOpenAI, BaseURL: fallback.URL + "/v1", APIKey: "two"},
		},
		[]config.RouteConfig{
			{Provider: "primary", UpstreamModel: "model", Priority: 0, Weight: 1},
			{Provider: "fallback", UpstreamModel: "model", Priority: 10, Weight: 1},
		},
	)
	defer gateway.Close()

	response := postOpenAI(t, gateway.URL, false)
	defer response.Body.Close()
	if response.StatusCode != http.StatusOK || primaryCalls.Load() != 1 || fallbackCalls.Load() != 1 {
		t.Fatalf("failover did not complete: status=%d primary=%d fallback=%d", response.StatusCode, primaryCalls.Load(), fallbackCalls.Load())
	}
	event := <-sink.events
	if event.Attempts != 2 || event.ProviderID != "fallback" {
		t.Fatalf("unexpected failover event: %+v", event)
	}
}

func TestSSEIsFlushedBeforeUpstreamCompletes(t *testing.T) {
	release := make(chan struct{})
	upstream := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
		w.Header().Set("Content-Type", "text/event-stream")
		_, _ = io.WriteString(w, "data: {\"id\":\"chunk-1\",\"choices\":[]}\n\n")
		w.(http.Flusher).Flush()
		<-release
		_, _ = io.WriteString(w, "data: [DONE]\n\n")
	}))
	defer upstream.Close()
	gateway, _ := newTestGateway(t, []config.ProviderConfig{{
		ID: "primary", Protocol: domain.ProtocolOpenAI, BaseURL: upstream.URL + "/v1", APIKey: "secret",
	}}, []config.RouteConfig{{Provider: "primary", UpstreamModel: "model", Weight: 1}})
	defer gateway.Close()

	response := postOpenAI(t, gateway.URL, true)
	defer response.Body.Close()
	reader := bufio.NewReader(response.Body)
	line, err := reader.ReadString('\n')
	if err != nil {
		close(release)
		t.Fatal(err)
	}
	if !strings.Contains(line, "chunk-1") {
		close(release)
		t.Fatalf("unexpected first SSE line: %q", line)
	}
	close(release)
}

func TestAnthropicHeadersAndPath(t *testing.T) {
	upstream := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if r.URL.Path != "/v1/messages" || r.Header.Get("x-api-key") != "anthropic-upstream" || r.Header.Get("anthropic-version") != "2023-06-01" {
			t.Errorf("unexpected anthropic request: path=%s key=%q version=%q", r.URL.Path, r.Header.Get("x-api-key"), r.Header.Get("anthropic-version"))
		}
		_, _ = io.WriteString(w, `{"type":"message","content":[],"usage":{"input_tokens":4,"output_tokens":6}}`)
	}))
	defer upstream.Close()
	gateway, sink := newTestGateway(t, []config.ProviderConfig{{
		ID: "anthropic", Protocol: domain.ProtocolAnthropic, BaseURL: upstream.URL + "/v1", APIKey: "anthropic-upstream",
	}}, []config.RouteConfig{{Provider: "anthropic", UpstreamModel: "claude-upstream", Weight: 1}})
	defer gateway.Close()

	request, _ := http.NewRequest(http.MethodPost, gateway.URL+"/anthropic/v1/messages", strings.NewReader(`{"model":"public/model","max_tokens":10,"messages":[{"role":"user","content":"hello"}]}`))
	request.Header.Set("x-api-key", "client-secret")
	request.Header.Set("anthropic-version", "2023-06-01")
	response, err := http.DefaultClient.Do(request)
	if err != nil {
		t.Fatal(err)
	}
	defer response.Body.Close()
	if response.StatusCode != http.StatusOK {
		t.Fatalf("unexpected status: %d", response.StatusCode)
	}
	event := <-sink.events
	if event.Usage.InputTokens != 4 || event.Usage.OutputTokens != 6 {
		t.Fatalf("unexpected anthropic usage: %+v", event.Usage)
	}
}

func TestInsufficientBalanceRejectsBeforeCallingUpstream(t *testing.T) {
	var calls atomic.Int64
	upstream := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
		calls.Add(1)
		w.WriteHeader(http.StatusOK)
	}))
	defer upstream.Close()
	meter := &fakeBillingMeter{authorizeErr: billing.ErrInsufficientBalance, settled: make(chan domain.UsageEvent, 1)}
	gateway, sink := newTestGatewayWithBilling(t, []config.ProviderConfig{{
		ID: "primary", Protocol: domain.ProtocolOpenAI, BaseURL: upstream.URL + "/v1", APIKey: "secret",
	}}, []config.RouteConfig{{Provider: "primary", UpstreamModel: "model", Weight: 1}}, meter)
	defer gateway.Close()

	response := postOpenAI(t, gateway.URL, false)
	defer response.Body.Close()
	if response.StatusCode != http.StatusPaymentRequired {
		t.Fatalf("status = %d, want 402", response.StatusCode)
	}
	if calls.Load() != 0 {
		t.Fatalf("upstream calls = %d, want 0", calls.Load())
	}
	select {
	case <-meter.settled:
		t.Fatal("rejected request was settled")
	default:
	}
	select {
	case event := <-sink.events:
		if event.StatusCode != http.StatusPaymentRequired || event.ErrorType != "insufficient_balance" {
			t.Fatalf("unexpected rejection usage: %+v", event)
		}
	case <-time.After(time.Second):
		t.Fatal("rejected request did not emit usage")
	}
}

func TestSuccessfulRequestIsSettled(t *testing.T) {
	upstream := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
		_, _ = io.WriteString(w, `{"choices":[],"usage":{"prompt_tokens":2,"completion_tokens":3,"total_tokens":5}}`)
	}))
	defer upstream.Close()
	meter := &fakeBillingMeter{settled: make(chan domain.UsageEvent, 1)}
	gateway, _ := newTestGatewayWithBilling(t, []config.ProviderConfig{{
		ID: "primary", Protocol: domain.ProtocolOpenAI, BaseURL: upstream.URL + "/v1", APIKey: "secret",
	}}, []config.RouteConfig{{Provider: "primary", UpstreamModel: "model", Weight: 1}}, meter)
	defer gateway.Close()

	response := postOpenAI(t, gateway.URL, false)
	defer response.Body.Close()
	if response.StatusCode != http.StatusOK {
		t.Fatalf("status = %d, want 200", response.StatusCode)
	}
	select {
	case event := <-meter.settled:
		if event.Usage.TotalTokens != 5 {
			t.Fatalf("settled usage = %+v", event.Usage)
		}
	case <-time.After(time.Second):
		t.Fatal("request was not settled")
	}
}

func newTestGateway(t *testing.T, providers []config.ProviderConfig, routes []config.RouteConfig) (*httptest.Server, *captureUsageSink) {
	return newTestGatewayWithBilling(t, providers, routes, nil)
}

func newTestGatewayWithBilling(t *testing.T, providers []config.ProviderConfig, routes []config.RouteConfig, meter billing.Meter) (*httptest.Server, *captureUsageSink) {
	t.Helper()
	authenticator, err := auth.NewStatic(`[{"key":"client-secret","key_id":"key-1","tenant_id":"tenant-1","project_id":"project-1","scopes":["inference"]}]`, false)
	if err != nil {
		t.Fatal(err)
	}
	cfg := config.Config{
		Providers: providers,
		Models:    []config.ModelConfig{{ID: "public/model", OwnedBy: "test", Routes: routes}},
		UpstreamHTTP: config.UpstreamHTTPConfig{
			MaxIdleConnections: 100, MaxIdleConnectionsPerHost: 20,
			IdleConnectionTimeoutSecs: 10, ResponseHeaderTimeoutSecs: 2,
		},
	}
	metrics := &telemetry.Metrics{}
	modelCatalog := catalog.New(cfg)
	sink := &captureUsageSink{events: make(chan domain.UsageEvent, 10)}
	api := New(Options{
		Authenticator: authenticator,
		Catalog:       modelCatalog,
		Router:        routing.New(modelCatalog),
		Forwarder:     provider.New(cfg.UpstreamHTTP, metrics),
		UsageSink:     sink,
		BillingMeter:  meter,
		Metrics:       metrics,
		Logger:        slog.New(slog.NewTextHandler(io.Discard, nil)),
		MaxBodyBytes:  1 << 20,
	})
	return httptest.NewServer(api.Handler()), sink
}

func postOpenAI(t *testing.T, gatewayURL string, stream bool) *http.Response {
	t.Helper()
	payload := []byte(`{"model":"public/model","messages":[{"role":"user","content":"hello"}],"stream":false}`)
	if stream {
		payload = []byte(`{"model":"public/model","messages":[{"role":"user","content":"hello"}],"stream":true}`)
	}
	request, _ := http.NewRequest(http.MethodPost, gatewayURL+"/v1/chat/completions", bytes.NewReader(payload))
	request.Header.Set("Authorization", "Bearer client-secret")
	response, err := http.DefaultClient.Do(request)
	if err != nil {
		t.Fatal(err)
	}
	return response
}