package appview

import (
	"compress/gzip"
	"io"
	"net/http"
	"net/http/httptest"
	"strings"
	"testing"
)

// handlerWriting returns a handler that writes n bytes of compressible body
// under the given content type.
func handlerWriting(contentType string, n int) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Content-Type", contentType)
		_, _ = w.Write([]byte(strings.Repeat("a", n)))
	})
}

func TestCompressUIResponses(t *testing.T) {
	tests := []struct {
		name        string
		path        string
		contentType string
		size        int
		wantGzip    bool
	}{
		{"html is compressed", "/", "text/html; charset=utf-8", 4096, true},
		{"css is compressed", "/css/style.css", "text/css; charset=utf-8", 4096, true},
		{"js is compressed", "/js/bundle.min.js", "application/javascript", 4096, true},
		{"svg is compressed", "/icons.svg", "image/svg+xml", 4096, true},
		{"ui json is compressed", "/api/thing", "application/json", 4096, true},

		// The registry must stay out of the compression path entirely: OCI
		// layers are already gzipped tarballs.
		{"registry blob untouched", "/v2/u/i/blobs/sha256:abc", "application/octet-stream", 4096, false},
		{"registry json untouched", "/v2/u/i/tags/list", "application/json", 4096, false},
		{"registry root untouched", "/v2/", "application/json", 4096, false},
		{"registry bare untouched", "/v2", "application/json", 4096, false},

		{"binary not compressed", "/static/img.png", "image/png", 4096, false},
		{"tiny body not compressed", "/", "text/html; charset=utf-8", 16, false},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			h := compressUIResponses(handlerWriting(tt.contentType, tt.size))

			req := httptest.NewRequest(http.MethodGet, tt.path, nil)
			req.Header.Set("Accept-Encoding", "gzip")
			rec := httptest.NewRecorder()
			h.ServeHTTP(rec, req)

			gotGzip := rec.Header().Get("Content-Encoding") == "gzip"
			if gotGzip != tt.wantGzip {
				t.Fatalf("Content-Encoding gzip = %v, want %v (header %q)",
					gotGzip, tt.wantGzip, rec.Header().Get("Content-Encoding"))
			}

			body := rec.Body.Bytes()
			if gotGzip {
				zr, err := gzip.NewReader(rec.Body)
				if err != nil {
					t.Fatalf("response not valid gzip: %v", err)
				}
				defer func() { _ = zr.Close() }()
				body, err = io.ReadAll(zr)
				if err != nil {
					t.Fatalf("gzip decode: %v", err)
				}
				if len(rec.Body.Bytes()) >= tt.size {
					t.Errorf("compressed body %d bytes, not smaller than raw %d",
						len(rec.Body.Bytes()), tt.size)
				}
			}
			if len(body) != tt.size {
				t.Errorf("decoded body = %d bytes, want %d", len(body), tt.size)
			}
		})
	}
}

// A client that does not advertise gzip must still get a usable response.
func TestCompressUIResponsesWithoutAcceptEncoding(t *testing.T) {
	h := compressUIResponses(handlerWriting("text/html", 4096))
	req := httptest.NewRequest(http.MethodGet, "/", nil)
	rec := httptest.NewRecorder()
	h.ServeHTTP(rec, req)

	if enc := rec.Header().Get("Content-Encoding"); enc != "" {
		t.Fatalf("Content-Encoding = %q, want empty for a client that did not ask", enc)
	}
	if rec.Body.Len() != 4096 {
		t.Errorf("body = %d bytes, want 4096", rec.Body.Len())
	}
}