package imageproxy

import (
	"bytes"
	"context"
	"image/color"
	"io"
	"io/fs"
	"testing"

	"sneak.berlin/go/pixa/internal/httpfetcher"
	"sneak.berlin/go/pixa/internal/imagerequest"
)

// TestProxy_Get_CountsStats walks Get through a miss that fetches the
// source, a hit, a miss that reuses the cached source, and two misses whose
// source cannot be used, checking every counter of the proxy and its cache
// after each.
func TestProxy_Get_CountsStats(t *testing.T) {
	t.Parallel()

	svc, fixtures := setupTestProxy(t)

	// NewTestFS builds the same files the test proxy's fetcher serves.
	testFS, _ := NewTestFS(t)

	photo, err := fs.ReadFile(testFS, fixtures.GoodHostJPEG)
	if err != nil {
		t.Fatal(err)
	}

	fake, err := fs.ReadFile(testFS, fixtures.InvalidFile)
	if err != nil {
		t.Fatal(err)
	}

	photoBytes, fakeBytes := int64(len(photo)), int64(len(fake))

	// want is hits, misses, upstream fetches, upstream bytes, transforms.
	steps := []struct {
		name    string
		path    string
		size    int
		wantErr bool
		want    counterValues
	}{
		{"miss that fetches the source", testPathPhoto, 50, false,
			counterValues{0, 1, 1, photoBytes, 1}},
		{"hit", testPathPhoto, 50, false,
			counterValues{1, 1, 1, photoBytes, 1}},
		{"miss that reuses the cached source", testPathPhoto, 25, false,
			counterValues{1, 2, 1, photoBytes, 2}},
		{"miss whose source fails the magic byte check", "/images/fake.jpg", 50, true,
			counterValues{1, 3, 2, photoBytes + fakeBytes, 2}},
		{"miss whose source is not found", "/images/nonexistent.jpg", 50, true,
			counterValues{1, 4, 2, photoBytes + fakeBytes, 2}},
	}

	for _, step := range steps {
		resp, err := svc.Get(t.Context(), &imagerequest.Request{
			Source: imagerequest.Source{
				Host: fixtures.GoodHost,
				Path: step.path,
			},
			Transform: imagerequest.Transform{
				Size:    imagerequest.Size{Width: step.size, Height: step.size},
				Format:  imagerequest.FormatJPEG,
				Quality: 85,
				FitMode: imagerequest.FitCover,
			},
		})
		if (err != nil) != step.wantErr {
			t.Fatalf("%s: Get() error = %v, want error %t", step.name, err, step.wantErr)
		}

		if err == nil {
			_ = resp.Content.Close()
		}

		got := readCounters(t, svc)
		if got != step.want {
			t.Fatalf("after the %s: counters = %+v, want %+v", step.name, got, step.want)
		}
	}
}

// fakeUpstream answers every fetch with itself as a JPEG body. The body
// serves data, then calls cancel, when set, and returns err; io.EOF ends
// the body normally.
type fakeUpstream struct {
	data   *bytes.Reader
	cancel context.CancelFunc
	err    error
}

func (u *fakeUpstream) Fetch(
	context.Context, imagerequest.Source,
) (*httpfetcher.FetchResult, error) {
	return &httpfetcher.FetchResult{
		Content:       io.NopCloser(u),
		ContentLength: -1,
		ContentType:   testContentTypeJPEG,
	}, nil
}

func (u *fakeUpstream) Read(p []byte) (int, error) {
	if u.data.Len() > 0 {
		return u.data.Read(p)
	}

	if u.cancel != nil {
		u.cancel()
	}

	return 0, u.err
}

// TestProxy_Get_CountsInterruptedMisses checks every counter of the proxy
// and its cache after a miss whose request context ends during or after the
// upstream fetch, and after a miss whose upstream body is over the size
// limit.
func TestProxy_Get_CountsInterruptedMisses(t *testing.T) {
	t.Parallel()

	photo := generateTestJPEG(t, 100, 100, color.RGBA{255, 0, 0, 255})
	half := len(photo) / 2

	// want is hits, misses, upstream fetches, upstream bytes, transforms.
	tests := []struct {
		name    string
		served  int   // bytes of the photo the upstream body serves
		cancel  bool  // whether the body then ends the request context
		readErr error // what the body then returns
		wantErr bool
		want    counterValues
	}{
		{"request context ends during the fetch", half, true, context.Canceled, true,
			counterValues{0, 1, 1, int64(half), 0}},
		{"request context ends after the fetch", len(photo), true, io.EOF, false,
			counterValues{0, 1, 1, int64(len(photo)), 1}},
		{"upstream body over the size limit", half, false,
			httpfetcher.ErrResponseTooLarge, true,
			counterValues{0, 1, 1, int64(half), 0}},
	}

	for _, tc := range tests {
		t.Run(tc.name, func(t *testing.T) {
			t.Parallel()

			svc, fixtures := setupTestProxy(t)

			ctx, cancel := context.WithCancel(t.Context())
			defer cancel()

			upstream := &fakeUpstream{
				data: bytes.NewReader(photo[:tc.served]),
				err:  tc.readErr,
			}
			if tc.cancel {
				upstream.cancel = cancel
			}

			svc.fetcher = upstream

			resp, err := svc.Get(ctx, &imagerequest.Request{
				Source: imagerequest.Source{
					Host: fixtures.GoodHost,
					Path: testPathPhoto,
				},
				Transform: imagerequest.Transform{
					Size:    imagerequest.Size{Width: 50, Height: 50},
					Format:  imagerequest.FormatJPEG,
					Quality: 85,
					FitMode: imagerequest.FitCover,
				},
			})
			t.Logf("Get() error = %v", err)

			if (err != nil) != tc.wantErr {
				t.Fatalf("Get() error = %v, want error %t", err, tc.wantErr)
			}

			if err == nil {
				_ = resp.Content.Close()
			}

			got := readCounters(t, svc)
			if got != tc.want {
				t.Errorf("counters = %+v, want %+v", got, tc.want)
			}
		})
	}
}

// TestProxy_Get_CountsHitAfterRequestEnds checks every counter of the
// proxy and its cache after a hit served with a request context that has
// already ended: only the hit count moves.
func TestProxy_Get_CountsHitAfterRequestEnds(t *testing.T) {
	t.Parallel()

	svc, fixtures := setupTestProxy(t)

	req := &imagerequest.Request{
		Source: imagerequest.Source{
			Host: fixtures.GoodHost,
			Path: testPathPhoto,
		},
		Transform: imagerequest.Transform{
			Size:    imagerequest.Size{Width: 50, Height: 50},
			Format:  imagerequest.FormatJPEG,
			Quality: 85,
			FitMode: imagerequest.FitCover,
		},
	}

	// A first request caches the variant.
	resp, err := svc.Get(t.Context(), req)
	if err != nil {
		t.Fatalf("first Get() error = %v", err)
	}

	_ = resp.Content.Close()

	want := readCounters(t, svc)
	want.hitCount++

	ctx, cancel := context.WithCancel(t.Context())
	cancel()

	resp, err = svc.Get(ctx, req)
	if err != nil {
		t.Fatalf("Get() with an ended request context: error = %v", err)
	}

	_ = resp.Content.Close()

	if resp.CacheStatus != CacheHit {
		t.Fatalf("CacheStatus = %v, want %v", resp.CacheStatus, CacheHit)
	}

	got := readCounters(t, svc)
	if got != want {
		t.Errorf("counters = %+v, want %+v", got, want)
	}
}