package middleware

import (
	"compress/gzip"
	"io"
	"net/http"
	"strconv"
	"strings"
	"time"
)

type gzipResponseWriter struct {
	http.ResponseWriter
	io.Writer
}

func (w *gzipResponseWriter) Write(b []byte) (int, error) {
	return w.Writer.Write(b)
}

// Gzip compresses responses when the client accepts it.
func Gzip(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if !strings.Contains(r.Header.Get("Accept-Encoding"), "gzip") {
			next.ServeHTTP(w, r)
			return
		}
		w.Header().Set("Vary", "Accept-Encoding")
		w.Header().Set("Content-Encoding", "gzip")
		gz := gzip.NewWriter(w)
		defer gz.Close()
		next.ServeHTTP(&gzipResponseWriter{ResponseWriter: w, Writer: gz}, r)
	})
}

// CacheStatic wraps a file server with long-lived cache headers.
func CacheStatic(dir string, maxAge time.Duration) http.Handler {
	fs := http.FileServer(http.Dir(dir))
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Cache-Control", "public, max-age="+formatMaxAge(maxAge)+", immutable")
		fs.ServeHTTP(w, r)
	})
}

// CacheImages wraps image serving; thumbs cache longer than originals.
func CacheImages(dir string) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		rel := strings.TrimPrefix(r.URL.Path, "/")
		if strings.HasPrefix(rel, "thumbs/") || strings.HasPrefix(rel, "hero/") {
			w.Header().Set("Cache-Control", "public, max-age=604800, immutable")
		} else {
			w.Header().Set("Cache-Control", "public, max-age=86400")
		}
		http.FileServer(http.Dir(dir)).ServeHTTP(w, r)
	})
}

func formatMaxAge(d time.Duration) string {
	return strconv.Itoa(int(d.Seconds()))
}