package llm

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

// fakeServer mimics an OpenAI-compatible server that streams the given chunks.
func fakeServer(t *testing.T, chunks []string) *httptest.Server {
	t.Helper()
	return httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		switch r.URL.Path {
		case "/v1/models":
			fmt.Fprint(w, `{"data":[{"id":"tiny-model"},{"id":"other"}]}`)
		case "/v1/chat/completions":
			if got := r.Header.Get("Authorization"); got != "Bearer secret" {
				http.Error(w, `{"error":"bad key"}`, http.StatusUnauthorized)
				return
			}
			var req struct {
				Model  string    `json:"model"`
				Stream bool      `json:"stream"`
				Msgs   []Message `json:"messages"`
			}
			if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
				t.Errorf("decode request: %v", err)
			}
			if req.Model != "tiny-model" || !req.Stream || len(req.Msgs) != 1 {
				t.Errorf("unexpected request: %+v", req)
			}
			w.Header().Set("Content-Type", "text/event-stream")
			fmt.Fprint(w, ": keep-alive comment\n\n")
			fmt.Fprint(w, `data: {"choices":[{"delta":{"role":"assistant"}}]}`+"\n\n")
			for _, c := range chunks {
				b, _ := json.Marshal(c)
				fmt.Fprintf(w, `data: {"choices":[{"delta":{"content":%s}}]}`+"\n\n", b)
			}
			fmt.Fprint(w, "data: [DONE]\n\n")
		default:
			http.NotFound(w, r)
		}
	}))
}

func TestStream(t *testing.T) {
	srv := fakeServer(t, []string{"Hel", "lo", "\n", "world"})
	defer srv.Close()

	c := &Client{BaseURL: srv.URL + "/v1", APIKey: "secret"} // no model: auto-pick first
	var got strings.Builder
	err := c.Stream(context.Background(), []Message{{Role: "user", Content: "hi"}}, func(d string) error {
		got.WriteString(d)
		return nil
	})
	if err != nil {
		t.Fatal(err)
	}
	if got.String() != "Hello\nworld" {
		t.Fatalf("got %q", got.String())
	}
}

func TestStreamHTTPError(t *testing.T) {
	srv := fakeServer(t, nil)
	defer srv.Close()

	c := &Client{BaseURL: srv.URL + "/v1", APIKey: "wrong", Model: "tiny-model"}
	err := c.Stream(context.Background(), []Message{{Role: "user", Content: "hi"}}, func(string) error { return nil })
	if err == nil || !strings.Contains(err.Error(), "401") {
		t.Fatalf("want 401 error, got %v", err)
	}
}

func TestStreamCallbackErrorStops(t *testing.T) {
	srv := fakeServer(t, []string{"a", "b", "c"})
	defer srv.Close()

	c := &Client{BaseURL: srv.URL + "/v1", APIKey: "secret"}
	stop := fmt.Errorf("stop")
	n := 0
	err := c.Stream(context.Background(), []Message{{Role: "user", Content: "hi"}}, func(string) error {
		n++
		return stop
	})
	if err != stop || n != 1 {
		t.Fatalf("err=%v n=%d", err, n)
	}
}

func TestResolveModel(t *testing.T) {
	srv := fakeServer(t, nil)
	defer srv.Close()

	c := &Client{BaseURL: srv.URL + "/v1"}
	if m, err := c.ResolveModel(context.Background()); err != nil || m != "tiny-model" {
		t.Fatalf("auto: %q %v", m, err)
	}
	c.Model = "pinned"
	if m, _ := c.ResolveModel(context.Background()); m != "pinned" {
		t.Fatalf("pinned: %q", m)
	}
}