package util

import (
	"bytes"
	"fmt"
	"log"
	"net/http"
	"runtime"
	"strconv"
)

type httpResponseBuffer struct {
	inner  http.ResponseWriter
	buf    bytes.Buffer
	status int
}

func (o *httpResponseBuffer) Header() http.Header {
	return o.inner.Header()
}

func (o *httpResponseBuffer) Write(data []byte) (int, error) {
	return o.buf.Write(data)
}

func (o *httpResponseBuffer) WriteHeader(status int) {
	o.status = status
}

type SaneHTTPHandler struct {
	Inner http.Handler
}

func (h SaneHTTPHandler) ServeHTTP(out http.ResponseWriter, in *http.Request) {
	HTTPHandlerFuncWrapper(out, in, h.Inner.ServeHTTP)
}

func HTTPHandlerFuncWrapper(out http.ResponseWriter, in *http.Request, fn http.HandlerFunc) {
	buf := httpResponseBuffer{
		inner:  out,
		status: http.StatusOK,
	}
	ok := true
	func() {
		defer func() {
			if r := recover(); r != nil {
				const size = 64 << 10
				buf := make([]byte, size)
				buf = buf[:runtime.Stack(buf, false)]
				st := fmt.Sprintf("%[1]T(%#[1]v) => %[1]v\n\n%[2]s", r, string(buf))
				log.Printf("panic serving %v\n\n%s", in.URL, st)
				http.Error(out, fmt.Sprintf("500 Internal Server Error:\n\n%s", st), 500)
				ok = false
			}
		}()
		fn(&buf, in)
	}()
	if ok {
		out.Header().Set("Content-Length", strconv.Itoa(buf.buf.Len()))
		out.WriteHeader(buf.status)
		buf.buf.WriteTo(out)
	}
}