package provider

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"net/http"
	"net/http/httptest"
	"os"
	"path/filepath"
	"strings"
	"sync/atomic"
	"testing"
	"time"

	"llmsproxy/internal/config"
	"llmsproxy/internal/lua"
	"llmsproxy/internal/types"
)

func newTestProvider(t *testing.T, src config.Source) *Provider {
	t.Helper()
	vm := lua.NewVM(filepath.Join(t.TempDir(), "adapters"))
	if err := vm.Start(); err != nil {
		t.Fatalf("vm: %v", err)
	}
	t.Cleanup(vm.Stop)
	return New(src, vm)
}

func src(name, url, adapter string, models ...string) config.Source {
	s := config.Source{Name: name, BaseURL: url, Adapter: adapter, MaxConcurrent: 4}
	for _, m := range models {
		s.Models = append(s.Models, config.Model{ID: m, Priority: 0})
	}
	return s
}

func TestProviderChat(t *testing.T) {
	up := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		var body map[string]interface{}
		_ = json.NewDecoder(r.Body).Decode(&body)
		if body["model"] != "mock-model" {
			t.Errorf("model = %v", body["model"])
		}
		fmt.Fprint(w, `{"choices":[{"message":{"content":"hi"},"finish_reason":"stop"}]}`)
	}))
	defer up.Close()
	p := newTestProvider(t, src("mock", up.URL, "openai", "mock-model"))
	resp, err := p.Chat(context.Background(), &types.ChatRequest{
		Model:    "mock-model",
		Messages: []types.ChatMessage{{Role: "user", Content: types.StringContent("hello")}},
	})
	if err != nil {
		t.Fatalf("chat: %v", err)
	}
	if resp.Content != "hi" {
		t.Fatalf("content = %q", resp.Content)
	}
}

func TestProviderChatStream(t *testing.T) {
	up := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Content-Type", "text/event-stream")
		fmt.Fprint(w, "data: {\"choices\":[{\"delta\":{\"content\":\"a\"}}]}\n\n")
		fmt.Fprint(w, "data: {\"choices\":[{\"delta\":{\"content\":\"b\"}}]}\n\n")
		fmt.Fprint(w, "data: {\"choices\":[{\"delta\":{},\"finish_reason\":\"stop\"}]}\n\n")
		fmt.Fprint(w, "data: [DONE]\n\n")
	}))
	defer up.Close()
	p := newTestProvider(t, src("mock", up.URL, "openai", "m"))
	ch, err := p.ChatStream(context.Background(), &types.ChatRequest{
		Model:    "m",
		Messages: []types.ChatMessage{{Role: "user", Content: types.StringContent("x")}},
	})
	if err != nil {
		t.Fatalf("stream: %v", err)
	}
	var text string
	var done bool
	for ck := range ch {
		text += ck.Content
		if ck.Done {
			done = true
		}
	}
	if text != "ab" {
		t.Fatalf("text = %q", text)
	}
	if !done {
		t.Fatal("expected done")
	}
}

// TestStreamSuccessClearsBackoff guards P6: a clean streaming end must reset
// a previously cooled (source, model) pair.
func TestStreamSuccessClearsBackoff(t *testing.T) {
	var fail atomic.Bool
	fail.Store(true)
	up := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if fail.Load() {
			w.WriteHeader(500)
			return
		}
		w.Header().Set("Content-Type", "text/event-stream")
		fmt.Fprint(w, "data: {\"choices\":[{\"delta\":{\"content\":\"a\"}}]}\n\n")
		fmt.Fprint(w, "data: [DONE]\n\n")
	}))
	defer up.Close()
	p := newTestProvider(t, src("mock", up.URL, "openai", "m"))
	if _, err := p.Chat(context.Background(), &types.ChatRequest{
		Model:    "m",
		Messages: []types.ChatMessage{{Role: "user", Content: types.StringContent("x")}},
	}); err == nil {
		t.Fatal("expected first chat to fail")
	}
	if p.ModelAvailable("m") {
		t.Fatal("m must be cooling after the failed chat")
	}
	fail.Store(false)
	ch, err := p.ChatStream(context.Background(), &types.ChatRequest{
		Model:    "m",
		Messages: []types.ChatMessage{{Role: "user", Content: types.StringContent("x")}},
	})
	if err != nil {
		t.Fatalf("stream: %v", err)
	}
	for range ch {
	}
	if !p.ModelAvailable("m") {
		t.Fatal("clean stream must clear the cooldown")
	}
	if st := p.state("m"); st.FailCount() != 0 {
		t.Fatalf("fail count after clean stream = %d", st.FailCount())
	}
}

func TestProviderImage(t *testing.T) {
	up := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		fmt.Fprint(w, `{"created":123,"data":[{"b64_json":"QUJD"}]}`)
	}))
	defer up.Close()
	p := newTestProvider(t, src("img", up.URL, "openai", "flux-1"))
	resp, err := p.Image(context.Background(), &types.ImageGenRequest{Model: "flux-1", Prompt: "cat"})
	if err != nil {
		t.Fatalf("image: %v", err)
	}
	if len(resp.ImageData) != 1 || resp.ImageData[0].B64JSON != "QUJD" {
		t.Fatalf("image data = %+v", resp.ImageData)
	}
}

func TestProviderBackoffPerModel(t *testing.T) {
	up := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.WriteHeader(500)
		fmt.Fprint(w, "boom")
	}))
	defer up.Close()
	// two models on one source: a failure on m1 must not blacklist m2
	p := newTestProvider(t, src("mock", up.URL, "openai", "m1", "m2"))
	_, err := p.Chat(context.Background(), &types.ChatRequest{
		Model:    "m1",
		Messages: []types.ChatMessage{{Role: "user", Content: types.StringContent("x")}},
	})
	if err == nil {
		t.Fatal("expected error")
	}
	if p.ModelAvailable("m1") {
		t.Fatal("expected m1 to be cooling down")
	}
	if !p.ModelAvailable("m2") {
		t.Fatal("m2 must stay schedulable (per-model isolation)")
	}
	if !p.Available() {
		t.Fatal("source must stay available while any model is schedulable")
	}
	if st := p.state("m1"); st.FailCount() != 1 {
		t.Fatalf("fail count = %d, want 1", st.FailCount())
	}
}

func TestProviderAuthFailureSelfHeals(t *testing.T) {
	up := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.WriteHeader(401)
		fmt.Fprint(w, `{"error":"API_KEY_DISABLED"}`)
	}))
	defer up.Close()
	p := newTestProvider(t, src("mock2", up.URL, "openai", "m2"))
	_, err := p.Chat(context.Background(), &types.ChatRequest{
		Model:    "m2",
		Messages: []types.ChatMessage{{Role: "user", Content: types.StringContent("x")}},
	})
	if err == nil {
		t.Fatal("expected error")
	}
	st := p.state("m2")
	if st.FailCount() != backoffCapN {
		t.Fatalf("auth failure must jump to capped count, got %d", st.FailCount())
	}
	if until := st.CooldownUntil(); until <= time.Now().Add(25*time.Minute).Unix() {
		t.Fatalf("auth failure must cool near the cap (until=%d)", until)
	}
	if st.Pref() != -2*int64(prefFailStep) {
		t.Fatalf("auth failure pref penalty must be doubled, got %d", st.Pref())
	}
	// not permanent: the reset channel and a later success both restore it
	st.reset()
	if !p.ModelAvailable("m2") {
		t.Fatal("reset must restore schedulability")
	}
}

func TestModelStateCooldownAndRecovery(t *testing.T) {
	up := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.WriteHeader(500)
	}))
	defer up.Close()
	p := newTestProvider(t, src("mock", up.URL, "openai", "m"))
	_, err := p.Chat(context.Background(), &types.ChatRequest{
		Model:    "m",
		Messages: []types.ChatMessage{{Role: "user", Content: types.StringContent("x")}},
	})
	if err == nil {
		t.Fatal("expected error")
	}
	st := p.state("m")
	if st.FailCount() != 1 {
		t.Fatalf("fail count = %d", st.FailCount())
	}
	// one failure -> 5s cooldown from now
	until := st.CooldownUntil()
	want := time.Now().Add(backoffBase).Unix()
	if until < want-2 || until > want+2 {
		t.Fatalf("cooldown = %d, want ~%d", until, want)
	}
	// success resets everything and bumps the preference
	st.RecordSuccess()
	if !p.ModelAvailable("m") {
		t.Fatal("success must clear cooldown")
	}
	if st.FailCount() != 0 {
		t.Fatalf("fail count after success = %d", st.FailCount())
	}
	if st.Pref() != 1-int64(prefFailStep) {
		t.Fatalf("pref after one failure (-5) then success (+1) = %d, want %d", st.Pref(), 1-int64(prefFailStep))
	}
}

func TestModelStateRateLimitShortCooldown(t *testing.T) {
	// 429 must NOT use the exponential backoff schedule: a rate-limited but
	// quota-rich source has to re-enter rotation after the short fixed window.
	p := newTestProvider(t, src("mock", "http://127.0.0.1:1", "openai", "m"))
	st := p.state("m")

	// repeated 429s must stay at the fixed short cooldown, never escalate
	for i := 0; i < 15; i++ {
		p.ReportStatus("m", 429)
	}
	until := st.CooldownUntil()
	want := time.Now().Add(rateLimitCooldown).Unix()
	if until < want-2 || until > want+2 {
		t.Fatalf("429 cooldown = %d, want ~%d (fixed %v, not exponential)", until, want, rateLimitCooldown)
	}
	if st.FailCount() != 15 {
		t.Fatalf("fail count = %d, want 15 (counted but not escalating)", st.FailCount())
	}
	if st.Pref() != -15*int64(prefFailStep) && st.Pref() > int64(prefMin) {
		t.Fatalf("pref = %d", st.Pref())
	}
	if p.ModelAvailable("m") {
		t.Fatal("model must be cooling right after a 429")
	}
}

func TestThrottleSpacingAndCancel(t *testing.T) {
	p := newTestProvider(t, src("mock", "http://127.0.0.1:1", "openai", "m"))
	p.cfg.RPM = 120 // gap = 500ms
	p.rpmGap = time.Minute / time.Duration(p.cfg.RPM)

	start := time.Now()
	for i := 0; i < 3; i++ {
		if err := p.Throttle(context.Background()); err != nil {
			t.Fatalf("throttle %d: %v", i, err)
		}
	}
	elapsed := time.Since(start)
	// first call passes immediately, the next two wait one gap each
	want := 2 * time.Minute / time.Duration(p.cfg.RPM)
	if elapsed < want-time.Duration(100*time.Millisecond) || elapsed > want+time.Second {
		t.Fatalf("3 throttled calls took %v, want ~%v", elapsed, want)
	}

	// unlimited source: Throttle is a no-op
	p2 := newTestProvider(t, src("free", "http://127.0.0.1:1", "openai", "m"))
	if err := p2.Throttle(context.Background()); err != nil {
		t.Fatalf("unlimited throttle: %v", err)
	}

	// cancelled context aborts a pending window reservation
	p3 := newTestProvider(t, src("slow", "http://127.0.0.1:1", "openai", "m"))
	p3.cfg.RPM = 6 // 10s gap
	p3.rpmGap = time.Minute / time.Duration(p3.cfg.RPM)
	// first call passes immediately (fresh provider) and reserves the next window
	if err := p3.Throttle(context.Background()); err != nil {
		t.Fatalf("first throttle: %v", err)
	}
	ctx, cancel := context.WithTimeout(context.Background(), 50*time.Millisecond)
	defer cancel()
	// second call must wait ~10s for the reserved window; the short deadline aborts it
	start = time.Now()
	err := p3.Throttle(ctx)
	if !errors.Is(err, context.DeadlineExceeded) {
		t.Fatalf("cancelled throttle = %v, want DeadlineExceeded", err)
	}
	if time.Since(start) > time.Second {
		t.Fatalf("cancel took %v, want fast abort", time.Since(start))
	}
}

func TestTryAcquire(t *testing.T) {
	p := newTestProvider(t, src("mock", "http://127.0.0.1:1", "openai", "m"))
	p.cfg.MaxConcurrent = 1
	p.sem = make(chan struct{}, 1)
	if err := p.TryAcquire(context.Background()); err != nil {
		t.Fatalf("first acquire: %v", err)
	}
	if err := p.TryAcquire(context.Background()); !errors.Is(err, ErrBusy) {
		t.Fatalf("second acquire = %v, want ErrBusy", err)
	}
	p.Release()
	if err := p.TryAcquire(context.Background()); err != nil {
		t.Fatalf("acquire after release: %v", err)
	}
	p.Release()
}

func TestChatBusyFailsFast(t *testing.T) {
	release := make(chan struct{})
	started := make(chan struct{}, 10)
	up := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		started <- struct{}{}
		<-release
		fmt.Fprint(w, `{"choices":[{"message":{"content":"ok"}}]}`)
	}))
	defer up.Close()
	p := newTestProvider(t, src("mock", up.URL, "openai", "m"))
	p.cfg.MaxConcurrent = 1
	p.sem = make(chan struct{}, 1)

	done := make(chan error, 1)
	go func() {
		_, err := p.Chat(context.Background(), &types.ChatRequest{
			Model:    "m",
			Messages: []types.ChatMessage{{Role: "user", Content: types.StringContent("x")}},
		})
		done <- err
	}()
	<-started // first request holds the only slot

	// second request must fail fast with ErrBusy instead of queueing
	_, err2 := p.Chat(context.Background(), &types.ChatRequest{
		Model:    "m",
		Messages: []types.ChatMessage{{Role: "user", Content: types.StringContent("x")}},
	})
	if !errors.Is(err2, ErrBusy) {
		t.Fatalf("second chat err = %v, want ErrBusy", err2)
	}
	close(release)
	if err := <-done; err != nil {
		t.Fatalf("first chat: %v", err)
	}
}

func eventually(t *testing.T, timeout time.Duration, cond func() bool, msg string) {
	t.Helper()
	deadline := time.Now().Add(timeout)
	for time.Now().Before(deadline) {
		if cond() {
			return
		}
		time.Sleep(10 * time.Millisecond)
	}
	t.Fatalf("timed out: %s", msg)
}

// TestChatClientCancelNotRecorded: a client disconnect before the response is
// neither success nor failure — the (source, model) state must stay clean.
func TestChatClientCancelNotRecorded(t *testing.T) {
	started := make(chan struct{})
	release := make(chan struct{})
	up := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		close(started)
		<-release // hold the upstream open; release at cleanup
		fmt.Fprint(w, `{"choices":[{"message":{"content":"late"}}]}`)
	}))
	defer up.Close()
	p := newTestProvider(t, src("mock", up.URL, "openai", "m"))
	ctx, cancel := context.WithCancel(context.Background())
	errCh := make(chan error, 1)
	go func() {
		_, err := p.Chat(ctx, &types.ChatRequest{
			Model:    "m",
			Messages: []types.ChatMessage{{Role: "user", Content: types.StringContent("x")}},
		})
		errCh <- err
	}()
	<-started
	cancel() // client disconnects mid-request
	if err := <-errCh; err == nil {
		t.Fatal("cancelled request must return an error")
	}
	close(release)
	eventually(t, 2*time.Second, func() bool {
		_, fc, _ := p.ModelHealthInfo("m")
		return fc == 0
	}, "client cancel must not record a scheduling failure")
}

// TestChatStreamEmptyBodyNotSuccess: a 200 that yields zero chunks and no
// [DONE] must fail the candidate (error return, no delivered chunks) so the
// scheduler falls through to the next source, and record the failure.
func TestChatStreamEmptyBodyNotSuccess(t *testing.T) {
	up := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Content-Type", "text/event-stream")
		// 200 with an empty body: no chunks, no [DONE]
	}))
	defer up.Close()
	p := newTestProvider(t, src("mock", up.URL, "openai", "m"))
	ch, err := p.ChatStream(context.Background(), &types.ChatRequest{
		Model:    "m",
		Messages: []types.ChatMessage{{Role: "user", Content: types.StringContent("x")}},
	})
	if err == nil {
		if ch != nil {
			for range ch {
			}
		}
		t.Fatal("empty stream must fail the candidate for scheduler fallback")
	}
	eventually(t, 2*time.Second, func() bool {
		_, fc, _ := p.ModelHealthInfo("m")
		return fc >= 1
	}, "empty stream must record a failure")
}

// TestChatStreamErrorFinishFailsCandidate: zen free pool answers HTTP 200
// with a single-chunk stream whose only payload is finish_reason:"network_error"
// and an empty delta. That must fail the candidate (not deliver a laundered
// empty reply), so the scheduler can fall through to the next source.
func TestChatStreamErrorFinishFailsCandidate(t *testing.T) {
	up := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Content-Type", "text/event-stream")
		fmt.Fprint(w, `data: {"choices":[{"index":0,"finish_reason":"network_error","delta":{"role":"assistant","content":""}}]}`+"\n\n")
		fmt.Fprint(w, "data: [DONE]\n\n")
	}))
	defer up.Close()
	p := newTestProvider(t, src("mock", up.URL, "opencode", "m"))
	_, err := p.ChatStream(context.Background(), &types.ChatRequest{
		Model:    "m",
		Messages: []types.ChatMessage{{Role: "user", Content: types.StringContent("x")}},
	})
	if err == nil {
		t.Fatal("network_error-only stream must fail the candidate")
	}
	eventually(t, 2*time.Second, func() bool {
		_, fc, _ := p.ModelHealthInfo("m")
		return fc >= 1
	}, "error-only stream must record a failure")
}

// TestChatStreamInstantEmptyStopStillDelivered: a legitimate completion that
// ends immediately with the standard finish_reason:"stop" and zero content is
// NOT an upstream error and must still reach the client.
func TestChatStreamInstantEmptyStopStillDelivered(t *testing.T) {
	up := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Content-Type", "text/event-stream")
		fmt.Fprint(w, `data: {"choices":[{"index":0,"finish_reason":"stop","delta":{}}]}`+"\n\n")
		fmt.Fprint(w, "data: [DONE]\n\n")
	}))
	defer up.Close()
	p := newTestProvider(t, src("mock", up.URL, "openai", "m"))
	ch, err := p.ChatStream(context.Background(), &types.ChatRequest{
		Model:    "m",
		Messages: []types.ChatMessage{{Role: "user", Content: types.StringContent("x")}},
	})
	if err != nil {
		t.Fatalf("standard stop stream must be delivered: %v", err)
	}
	n := 0
	for range ch {
		n++
	}
	if n == 0 {
		t.Fatal("expected at least the terminating chunk")
	}
	eventually(t, 2*time.Second, func() bool {
		_, fc, _ := p.ModelHealthInfo("m")
		return fc == 0
	}, "standard stop must count as success")
}

// TestImageAutoUsesImageModel: AUTO image generation on a mixed source must
// send the image-kind model id, never the best chat model.
func TestImageAutoUsesImageModel(t *testing.T) {
	var gotModel string
	up := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		var body map[string]interface{}
		_ = json.NewDecoder(r.Body).Decode(&body)
		gotModel, _ = body["model"].(string)
		fmt.Fprint(w, `{"created":1,"data":[{"url":"http://x/1.png"}]}`)
	}))
	defer up.Close()
	s := config.Source{Name: "mix", BaseURL: up.URL, Adapter: "openai", MaxConcurrent: 4}
	s.Models = []config.Model{
		{ID: "chat-m", Kind: "chat", Priority: 100},
		{ID: "img-m", Kind: "image", Priority: 50},
	}
	p := newTestProvider(t, s)
	resp, err := p.Image(context.Background(), &types.ImageGenRequest{Prompt: "cat", Model: "AUTO"})
	if err != nil {
		t.Fatalf("image: %v", err)
	}
	if len(resp.ImageData) == 0 {
		t.Fatal("no image data returned")
	}
	if gotModel != "img-m" {
		t.Fatalf("AUTO image must use the image-kind model, got %q", gotModel)
	}
}

func TestStandardSSEChunkFinishReason(t *testing.T) {
	out := standardSSEChunk(`{"choices":[{"index":0,"finish_reason":"tool_calls","delta":{}}]}`)
	if !strings.Contains(out, `"done":true`) || !strings.Contains(out, `"finish_reason":"tool_calls"`) {
		t.Fatalf("real finish reason must pass through: %s", out)
	}
	out = standardSSEChunk(`{"choices":[{"index":0,"finish_reason":"","delta":{"content":"hi"}}]}`)
	if strings.Contains(out, `"Done":true`) {
		t.Fatalf("empty-string finish reason is not a finish signal: %s", out)
	}
}

// TestAdapterHookCondensesError: the adapter transform_error hook owns the
// per-source error format; its reason must reach the client verbatim.
func TestAdapterHookCondensesError(t *testing.T) {
	up := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Content-Type", "application/json")
		w.WriteHeader(503)
		fmt.Fprint(w, `{"error":{"type":"FreeUsageLimitError","message":"Rate limit exceeded. Please try again later."}}`)
	}))
	defer up.Close()
	p := newTestProvider(t, src("mock", up.URL, "opencode", "m"))
	_, err := p.Chat(context.Background(), &types.ChatRequest{
		Model:    "m",
		Messages: []types.ChatMessage{{Role: "user", Content: types.StringContent("x")}},
	})
	if err == nil || !strings.Contains(err.Error(), "zen free pool quota exhausted") {
		t.Fatalf("adapter hook reason must surface, got %v", err)
	}
	if strings.Contains(err.Error(), "Rate limit exceeded") {
		t.Fatalf("raw upstream body must not leak past the hook: %v", err)
	}
}

// TestUnknownErrorFallbackWithoutHook: an adapter without transform_error
// gets the uniform core fallback; the raw body must not leak to clients.
func TestUnknownErrorFallbackWithoutHook(t *testing.T) {
	dir := filepath.Join(t.TempDir(), "adapters")
	if err := os.MkdirAll(dir, 0o755); err != nil {
		t.Fatal(err)
	}
	minimal := `return { name="custom", endpoint="/chat/completions",
	transform_request=function(raw) return raw end,
	transform_response=function(raw) return raw end }
`
	if err := os.WriteFile(filepath.Join(dir, "custom.lua"), []byte(minimal), 0o644); err != nil {
		t.Fatal(err)
	}
	vm := lua.NewVM(dir)
	if err := vm.Start(); err != nil {
		t.Fatalf("vm: %v", err)
	}
	defer vm.Stop()
	up := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.WriteHeader(500)
		fmt.Fprint(w, `{"weird":{"shape":["no","message"]}}`)
	}))
	defer up.Close()
	p := New(src("mock", up.URL, "custom", "m"), vm)
	_, err := p.Chat(context.Background(), &types.ChatRequest{
		Model:    "m",
		Messages: []types.ChatMessage{{Role: "user", Content: types.StringContent("x")}},
	})
	if err == nil || !strings.Contains(err.Error(), "unknown error") {
		t.Fatalf("hook-less adapter must fall back to unknown error, got %v", err)
	}
	if strings.Contains(err.Error(), "shape") {
		t.Fatalf("raw body must not leak: %v", err)
	}
}