package httpfetcher

import (
	"errors"
	"io"
	"net/http"
	"net/http/httptest"
	"sync"
	"testing"
)

// TestFetch_SendsConditionalHeadersAndHandlesNotModified checks that Fetch
// sends a non-empty ifNoneMatch and ifModifiedSince as request headers, that
// upstream's 304 to such a request is a result with status 304 and no
// content, and that a 304 to a request with neither is ErrUpstreamError.
func TestFetch_SendsConditionalHeadersAndHandlesNotModified(t *testing.T) {
	t.Parallel()

	const (
		etag         = `"abc"`
		lastModified = "Mon, 02 Nov 2026 10:00:00 GMT"
	)

	var (
		mu       sync.Mutex
		received http.Header
	)

	srv := httptest.NewServer(http.HandlerFunc(
		func(w http.ResponseWriter, r *http.Request) {
			mu.Lock()
			received = r.Header.Clone()
			mu.Unlock()

			w.WriteHeader(http.StatusNotModified)
		}))
	t.Cleanup(srv.Close)

	f, _ := newServerFetcher(t, srv, nil)

	res, err := f.Fetch(testContext(t), upstreamSource("/image"), etag, lastModified)
	if err != nil {
		t.Fatalf("conditional Fetch() error = %v", err)
	}

	body, err := io.ReadAll(res.Content)
	_ = res.Content.Close()

	mu.Lock()
	t.Logf("status = %d, body = %q, request headers = %v", res.StatusCode, body, received)
	gotIfNoneMatch := received.Get("If-None-Match")
	gotIfModifiedSince := received.Get("If-Modified-Since")
	mu.Unlock()

	if err != nil || len(body) != 0 {
		t.Errorf("304 content = %q, error = %v; want empty", body, err)
	}

	if res.StatusCode != http.StatusNotModified {
		t.Errorf("StatusCode = %d, want 304", res.StatusCode)
	}

	if gotIfNoneMatch != etag || gotIfModifiedSince != lastModified {
		t.Errorf("If-None-Match = %q, If-Modified-Since = %q; want %q and %q",
			gotIfNoneMatch, gotIfModifiedSince, etag, lastModified)
	}

	if held := len(f.allHostsSemaphore); held != 0 {
		t.Errorf("connection still held after the 304: %d held", held)
	}

	_, err = f.Fetch(testContext(t), upstreamSource("/image"), "", "")
	if !errors.Is(err, ErrUpstreamError) {
		t.Errorf("unconditional Fetch() answered 304: error = %v, want ErrUpstreamError", err)
	}
}