package middlewares

import (
	"bytes"
	"io/fs"
	"log"
	"net/http"
)

// FallbackFile serves a fallback file if the next handler returns a 404.
// fs: The file system to serve the fallback file from.
// name: The name of the fallback file.
// next: The next handler to serve.
func FallbackFile(fs fs.FS, name string, next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		bw := &buffedResponseWriter{
			w,
			0,
			bytes.NewBuffer([]byte{}),
		}
		next.ServeHTTP(bw, r)

		if bw.statusCode == http.StatusNotFound {
			bw.Clear()

			http.ServeFileFS(bw, r, fs, name)
			bw.WriteHeader(http.StatusOK)
			bw.Header().Add("Content-Type", "text/html; charset=utf-8")
		}
		bw.Apply()
	})
}

type buffedResponseWriter struct {
	http.ResponseWriter
	statusCode int
	buff       *bytes.Buffer
}

func (b *buffedResponseWriter) WriteHeader(code int) {
	b.statusCode = code
}

func (b *buffedResponseWriter) Write(p []byte) (int, error) {
	return b.buff.Write(p)
}

func (b *buffedResponseWriter) Clear() {
	b.buff.Reset()
}

func (b *buffedResponseWriter) Apply() {
	_, err := b.ResponseWriter.Write(b.buff.Bytes())
	if err != nil {
		log.Println("Error while applying buffedResponseWriter: ", err)
		b.ResponseWriter.WriteHeader(http.StatusInternalServerError)
	}
	if b.statusCode != 200 {
		b.ResponseWriter.WriteHeader(b.statusCode)
	}
}