// Code in this file is based on net/http/httputil/reverseproxy.go from the Go
// standard library, and covered by licenses/golang.org/x/sys/LICENSE.

package http

import (
	"net/http"
	"net/http/httputil"
	"net/url"
	"strings"
)

func newSingleHostReverseProxy(target *url.URL) *httputil.ReverseProxy {
	director := func(req *http.Request) {
		rewriteRequestURL(req, target)
	}
	return &httputil.ReverseProxy{Director: director}
}

func rewriteRequestURL(req *http.Request, target *url.URL) {
	targetQuery := target.RawQuery
	req.URL.Scheme = target.Scheme
	req.URL.Host = target.Host
	req.URL.Path, req.URL.RawPath = joinURLPath(target, req.URL)
	if targetQuery == "" || req.URL.RawQuery == "" {
		req.URL.RawQuery = targetQuery + req.URL.RawQuery
	} else {
		req.URL.RawQuery = targetQuery + "&" + req.URL.RawQuery
	}
}

// Like in httputil, but we won't add a trailing slash if the original request did
// not have one.
func joinURLPath(a, b *url.URL) (path, rawpath string) {
	if a.RawPath == "" && b.RawPath == "" {
		return singleJoiningSlash(a.Path, b.Path), ""
	}
	// Same as singleJoiningSlash, but uses EscapedPath to determine
	// whether a slash should be added
	apath := a.EscapedPath()
	bpath := b.EscapedPath()

	aslash := strings.HasSuffix(apath, "/")
	bslash := strings.HasPrefix(bpath, "/")

	switch {
	case aslash && bslash:
		return a.Path + b.Path[1:], apath + bpath[1:]
	case !aslash && !bslash && bpath != "":
		return a.Path + "/" + b.Path, apath + "/" + bpath
	}
	return a.Path + b.Path, apath + bpath
}

func singleJoiningSlash(a, b string) string {
	aslash := strings.HasSuffix(a, "/")
	bslash := strings.HasPrefix(b, "/")
	switch {
	case aslash && bslash:
		return a + b[1:]
	case !aslash && !bslash && b != "":
		return a + "/" + b
	}
	return a + b
}