package middleware

import (
	"bufio"
	"bytes"
	"mime"
	"net"
	"net/http"
	"path/filepath"
	"strconv"
	"strings"

	swaggerFiles "github.com/swaggo/files"
	"github.com/gin-gonic/gin"
)

func SwaggerHandler() gin.HandlerFunc {
	return func(c *gin.Context) {
		rawPath := c.Request.URL.Path
		relPath := strings.TrimPrefix(rawPath, "/swagger")
		if relPath == "" || relPath == "/" {
			relPath = "/index.html"
		}
		c.Request.URL.Path = relPath
		defer func() { c.Request.URL.Path = rawPath }()

		isCSS := strings.HasSuffix(relPath, "swagger-ui.css")

		underlying := c.Writer
		crw := &captureResponseWriter{
			ginWriter: underlying,
			code:      200,
		}
		c.Writer = crw

		swaggerFiles.Handler.ServeHTTP(crw, c.Request)

		c.Writer = underlying

		h := underlying.Header()
		h.Set("X-Content-Type-Options", "nosniff")
		h.Set("X-Frame-Options", "DENY")
		h.Set("X-XSS-Protection", "1; mode=block")
		h.Set("Referrer-Policy", "strict-origin-when-cross-origin")
		h.Set("Content-Security-Policy", "default-src 'self'; style-src 'self' 'unsafe-inline'; img-src 'self' data:; font-src 'self' data:")

		if isCSS && crw.code == 200 && crw.buf.Len() > 0 {
			body := append(crw.buf.Bytes(), []byte(brandingCSS)...)
			h.Set("Content-Length", strconv.Itoa(len(body)))
			h.Set("Content-Type", "text/css; charset=utf-8")
			underlying.WriteHeader(crw.code)
			underlying.Write(body)
			return
		}

		if crw.buf.Len() > 0 {
			ext := filepath.Ext(relPath)
			if ct := mime.TypeByExtension(ext); ct != "" {
				h.Set("Content-Type", ct)
			}
			h.Del("Content-Length")
			underlying.WriteHeader(crw.code)
			underlying.Write(crw.buf.Bytes())
			return
		}

		underlying.WriteHeader(crw.code)
	}
}

type captureResponseWriter struct {
	ginWriter gin.ResponseWriter
	code      int
	buf       bytes.Buffer
}

func (w *captureResponseWriter) Header() http.Header         { return w.ginWriter.Header() }
func (w *captureResponseWriter) Write(b []byte) (int, error)  { return w.buf.Write(b) }
func (w *captureResponseWriter) WriteHeader(code int)         { w.code = code }
func (w *captureResponseWriter) WriteString(s string) (int, error) { return w.buf.WriteString(s) }
func (w *captureResponseWriter) Status() int                  { return w.code }
func (w *captureResponseWriter) Size() int                    { return w.buf.Len() }
func (w *captureResponseWriter) Written() bool                { return w.buf.Len() > 0 }
func (w *captureResponseWriter) WriteHeaderNow()              {}
func (w *captureResponseWriter) Pusher() http.Pusher          { return nil }
func (w *captureResponseWriter) Hijack() (net.Conn, *bufio.ReadWriter, error) {
	return w.ginWriter.Hijack()
}
func (w *captureResponseWriter) CloseNotify() <-chan bool      { return w.ginWriter.CloseNotify() }
func (w *captureResponseWriter) Flush()                       {}

const brandingCSS = `
/* MengStack API branding — replace Swagger SmartBear logo */
.topbar {
  display: flex !important;
  align-items: center !important;
  background-color: #1b1b1f !important;
  padding: 8px 20px !important;
  min-height: 50px !important;
  position: relative !important;
}
.topbar > * {
  visibility: hidden !important;
  width: 0 !important;
  height: 0 !important;
  overflow: hidden !important;
  margin: 0 !important;
  padding: 0 !important;
  flex: 0 !important;
}
.topbar::before {
  content: "MengStack API \6587\6863" !important;
  visibility: visible !important;
  width: auto !important;
  height: auto !important;
  overflow: visible !important;
  flex: 0 0 auto !important;
  color: #fff !important;
  font-size: 20px !important;
  font-weight: 700 !important;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif !important;
  letter-spacing: 1px !important;
  text-decoration: none !important;
  position: absolute !important;
  left: 20px !important;
  top: 50% !important;
  transform: translateY(-50%) !important;
}
.topbar::after {
  content: "v0.3.0" !important;
  visibility: visible !important;
  width: auto !important;
  height: auto !important;
  overflow: visible !important;
  flex: 0 0 auto !important;
  color: rgba(255,255,255,0.5) !important;
  font-size: 12px !important;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif !important;
  position: absolute !important;
  left: 230px !important;
  top: 50% !important;
  transform: translateY(-50%) !important;
}
.swagger-ui {
  margin-top: 0 !important;
}
`