package utils

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

type httpUtil struct {
}

// Http 暴露接口
func Http() *httpUtil {
	return &httpUtil{}
}

// NewProxy 重写创建代理函数，加入 Host 信息
func (hu httpUtil) NewProxy(target *url.URL) *httputil.ReverseProxy {
	targetQuery := target.RawQuery
	director := func(req *http.Request) {
		req.Host = target.Host
		req.URL.Scheme = target.Scheme
		req.URL.Host = target.Host
		req.URL.Path, req.URL.RawPath = hu.joinURLPath(target, req.URL)
		// 过滤掉参数
		if uri, err := url.Parse(req.URL.Path); err == nil {
			req.URL.Path = uri.Path
		}

		var rawQuery string
		if targetQuery == "" || req.URL.RawQuery == "" {
			rawQuery = targetQuery + req.URL.RawQuery
		} else {
			rawQuery = targetQuery + "&" + req.URL.RawQuery
		}
		req.URL.RawQuery = rawQuery
		if _, ok := req.Header["User-Agent"]; !ok {
			// explicitly disable User-Agent so it's not set to default value
			req.Header.Set("User-Agent", "")
		}
		// 补充内部调用Header
		req.Header.Set("X-Request-From", "internal")
	}
	return &httputil.ReverseProxy{Director: director}
}

func (hu httpUtil) joinURLPath(a, b *url.URL) (path, rawpath string) {
	if a.RawPath == "" && b.RawPath == "" {
		return hu.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:
		return a.Path + "/" + b.Path, apath + "/" + bpath
	}
	return a.Path + b.Path, apath + bpath
}

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