package middleware

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

	"github.com/gin-gonic/gin"
)

func TestGzipMiddleware_CompressesLargeJSONResponses(t *testing.T) {
	gin.SetMode(gin.TestMode)

	recorder := httptest.NewRecorder()
	router := gin.New()
	router.Use(GzipMiddleware())
	router.GET("/data", func(c *gin.Context) {
		c.Header("Content-Type", "application/json")
		c.String(http.StatusOK, strings.Repeat("a", gzipMinLength+128))
	})

	req := httptest.NewRequest(http.MethodGet, "/data", nil)
	req.Header.Set("Accept-Encoding", "gzip")
	router.ServeHTTP(recorder, req)

	if got := recorder.Header().Get("Content-Encoding"); got != "gzip" {
		t.Fatalf("Content-Encoding = %q, want gzip", got)
	}

	reader, err := gzip.NewReader(bytes.NewReader(recorder.Body.Bytes()))
	if err != nil {
		t.Fatalf("gzip.NewReader() error = %v", err)
	}
	defer reader.Close()

	payload, err := io.ReadAll(reader)
	if err != nil {
		t.Fatalf("ReadAll() error = %v", err)
	}
	if got := string(payload); got != strings.Repeat("a", gzipMinLength+128) {
		t.Fatalf("decompressed payload length = %d, want %d", len(got), gzipMinLength+128)
	}
}

func TestGzipMiddleware_PassesThroughWhenCompressionNotUseful(t *testing.T) {
	gin.SetMode(gin.TestMode)

	testCases := []struct {
		name           string
		acceptEncoding string
		contentType    string
		body           string
	}{
		{
			name:           "client does not accept gzip",
			acceptEncoding: "",
			contentType:    "application/json",
			body:           strings.Repeat("b", gzipMinLength+64),
		},
		{
			name:           "body below threshold",
			acceptEncoding: "gzip",
			contentType:    "application/json",
			body:           "small-body",
		},
		{
			name:           "unsupported content type",
			acceptEncoding: "gzip",
			contentType:    "image/png",
			body:           strings.Repeat("c", gzipMinLength+64),
		},
	}

	for _, tc := range testCases {
		t.Run(tc.name, func(t *testing.T) {
			recorder := httptest.NewRecorder()
			router := gin.New()
			router.Use(GzipMiddleware())
			router.GET("/data", func(c *gin.Context) {
				c.Header("Content-Type", tc.contentType)
				c.String(http.StatusOK, tc.body)
			})

			req := httptest.NewRequest(http.MethodGet, "/data", nil)
			if tc.acceptEncoding != "" {
				req.Header.Set("Accept-Encoding", tc.acceptEncoding)
			}
			router.ServeHTTP(recorder, req)

			if got := recorder.Header().Get("Content-Encoding"); got != "" {
				t.Fatalf("Content-Encoding = %q, want empty", got)
			}
			if got := recorder.Body.String(); got != tc.body {
				t.Fatalf("body length = %d, want %d", len(got), len(tc.body))
			}
		})
	}
}