/*
 * @Author: hongyu guo
 * @Description:
 * @Version: 1.0.0
 * @Date: 11:34 2021/06/15
 * @Copyright: MIN-Group；国家重大科技基础设施——未来网络北大实验室；深圳市信息论与未来网络重点实验室
 */

package minhttp

import (
	"net"
	"net/url"
	"path"
	"sort"
	"strings"
	"sync"
)

type ServeMux struct {
	mu    sync.RWMutex
	m     map[string]muxEntry
	es    []muxEntry // slice of entries sorted from longest to shortest.
	hosts bool       // whether any patterns contain hostnames
}
type muxEntry struct {
	h       Handler
	pattern string
}

// A Handler responds to an HTTP request.
//
// ServeHTTP should write reply headers and data to the ResponseWriter
// and then return. Returning signals that the request is finished; it
// is not valid to use the ResponseWriter or read from the
// Request.Body after or concurrently with the completion of the
// ServeHTTP call.
type Handler interface {
	ServeHTTP(ResponseWriter, *Request)
}

// 函数适配器， 简化开发流程
// 传入的handler不需要重新生成类
// The HandlerFunc type is an adapter to allow the use of
// ordinary functions as HTTP handlers. If f is a function
// with the appropriate signature, HandlerFunc(f) is a
// Handler that calls f.
type HandlerFunc func(ResponseWriter, *Request)

// ServeHTTP calls f(w, r).
func (f HandlerFunc) ServeHTTP(w ResponseWriter, r *Request) {
	f(w, r)
}

// DefaultServeMux is the default ServeMux used by Serve.
var DefaultServeMux = &defaultServeMux
var defaultServeMux ServeMux


func HandleFunc(pattern string, handler func(ResponseWriter, *Request)) {
	DefaultServeMux.HandleFunc(pattern, handler)
}

func (mux *ServeMux) HandleFunc(pattern string, handler func(ResponseWriter, *Request)) {
	if handler == nil {
		panic("minhttp: nil handler")
	}
	mux.Handle(pattern, HandlerFunc(handler))
}

// pattern -> function注册
// Handle registers the handler for the given pattern.
// If a handler already exists for pattern, Handle panics.
func (mux *ServeMux) Handle(pattern string, handler Handler) {
	mux.mu.Lock()
	defer mux.mu.Unlock()

	if pattern == "" {
		panic("minhttp: invalid pattern")
	}
	if handler == nil {
		panic("minhttp: nil handler")
	}
	if _, exist := mux.m[pattern]; exist {
		panic("minhttp: multiple registrations for " + pattern)
	}

	if mux.m == nil {
		mux.m = make(map[string]muxEntry)
	}
	e := muxEntry{h: handler, pattern: pattern}
	mux.m[pattern] = e
	if pattern[len(pattern)-1] == '/' {
		mux.es = appendSorted(mux.es, e)
	}

	if pattern[0] != '/' {
		mux.hosts = true
	}
}

// ServeHTTP dispatches the request to the handler whose
// pattern most closely matches the request URL.
func (mux *ServeMux) ServeHTTP(w ResponseWriter, r *Request) {
	// if r.RequestURI == "*" {
	// 	if r.ProtoAtLeast(1, 1) {
	// 		w.Header().Set("Connection", "close")
	// 	}
	// 	w.WriteHeader(StatusBadRequest)
	// 	return
	// }
	h, _ := mux.Handler(r)
	h.ServeHTTP(w, r)
}

// Handler returns the handler to use for the given request,
// consulting r.Method, r.Host, and r.URL.Path. It always returns
// a non-nil handler. If the path is not in its canonical form, the
// handler will be an internally-generated handler that redirects
// to the canonical path. If the host contains a port, it is ignored
// when matching handlers.
//
// The path and host are used unchanged for CONNECT requests.
//
// Handler also returns the registered pattern that matches the
// request or, in the case of internally-generated redirects,
// the pattern that will match after following the redirect.
//
// If there is no registered handler that applies to the request,
// Handler returns a ``page not found'' handler and an empty pattern.
func (mux *ServeMux) Handler(r *Request) (h Handler, pattern string) {

	// CONNECT requests are not canonicalized.
	// if r.Method == "CONNECT" {
	// 	// If r.URL.Path is /tree and its handler is not registered,
	// 	// the /tree -> /tree/ redirect applies to CONNECT requests
	// 	// but the path canonicalization does not.
	// 	if u, ok := mux.redirectToPathSlash(r.URL.Host, r.URL.Path, r.URL); ok {
	// 		return RedirectHandler(u.String(), StatusMovedPermanently), u.Path
	// 	}
	//
	// 	return mux.handler(r.Host, r.URL.Path)
	// }

	// All other requests have any port stripped and path cleaned
	// before passing to mux.handler.
	host := stripHostPort(r.Host)
	path := cleanPath(r.URL.Path)

	// If the given path is /tree and its handler is not registered,
	// redirect for /tree/.
	if u, ok := mux.redirectToPathSlash(host, path, r.URL); ok {
		return RedirectHandler(u.String(), StatusMovedPermanently), u.Path
	}

	if path != r.URL.Path {
		_, pattern = mux.handler(host, path)
		url := *r.URL
		url.Path = path
		return RedirectHandler(url.String(), StatusMovedPermanently), pattern
	}

	return mux.handler(host, r.URL.Path)
}

// handler is the main implementation of Handler.
// The path is known to be in canonical form, except for CONNECT methods.
func (mux *ServeMux) handler(host, path string) (h Handler, pattern string) {
	mux.mu.RLock()
	defer mux.mu.RUnlock()

	// Host-specific pattern takes precedence over generic ones
	if mux.hosts {
		h, pattern = mux.match(host + path)
	}
	if h == nil {
		h, pattern = mux.match(path)
	}
	if h == nil {
		h, pattern = NotFoundHandler(), ""
	}
	return
}


// Find a handler on a handler map given a path string.
// Most-specific (longest) pattern wins.
func (mux *ServeMux) match(path string) (h Handler, pattern string) {
	// Check for exact match first.
	v, ok := mux.m[path]
	if ok {
		return v.h, v.pattern
	}

	// Check for longest valid match.  mux.es contains all patterns
	// that end in / sorted from longest to shortest.
	for _, e := range mux.es {
		if strings.HasPrefix(path, e.pattern) {
			return e.h, e.pattern
		}
	}
	return nil, ""
}

// redirectToPathSlash determines if the given path needs appending "/" to it.
// This occurs when a handler for path + "/" was already registered, but
// not for path itself. If the path needs appending to, it creates a new
// URL, setting the path to u.Path + "/" and returning true to indicate so.
func (mux *ServeMux) redirectToPathSlash(host, path string, u *url.URL) (*url.URL, bool) {
	mux.mu.RLock()
	shouldRedirect := mux.shouldRedirectRLocked(host, path)
	mux.mu.RUnlock()
	if !shouldRedirect {
		return u, false
	}
	path = path + "/"
	u = &url.URL{Path: path, RawQuery: u.RawQuery}
	return u, true
}

// shouldRedirectRLocked reports whether the given path and host should be redirected to
// path+"/". This should happen if a handler is registered for path+"/" but
// not path -- see comments at ServeMux.
func (mux *ServeMux) shouldRedirectRLocked(host, path string) bool {
	p := []string{path, host + path}

	for _, c := range p {
		if _, exist := mux.m[c]; exist {
			return false
		}
	}

	n := len(path)
	if n == 0 {
		return false
	}
	for _, c := range p {
		if _, exist := mux.m[c+"/"]; exist {
			return path[n-1] != '/'
		}
	}

	return false
}

// Redirect to a fixed URL
type redirectHandler struct {
	url  string
	code int
}

func (rh *redirectHandler) ServeHTTP(w ResponseWriter, r *Request) {
	Redirect(w, r, rh.url, rh.code)
}

// TODO: redirect

// Redirect replies to the request with a redirect to url,
// which may be a path relative to the request path.
//
// The provided code should be in the 3xx range and is usually
// StatusMovedPermanently, StatusFound or StatusSeeOther.
//
// If the Content-Type header has not been set, Redirect sets it
// to "text/html; charset=utf-8" and writes a small HTML body.
// Setting the Content-Type header to any value, including nil,
// disables that behavior.
func Redirect(w ResponseWriter, r *Request, url string, code int) {
	// if u, err := urlpkg.Parse(url); err == nil {
	// 	// If url was relative, make its path absolute by
	// 	// combining with request path.
	// 	// The client would probably do this for us,
	// 	// but doing it ourselves is more reliable.
	// 	// See RFC 7231, section 7.1.2
	// 	if u.Scheme == "" && u.Host == "" {
	// 		oldpath := r.URL.Path
	// 		if oldpath == "" { // should not happen, but avoid a crash if it does
	// 			oldpath = "/"
	// 		}
	//
	// 		// no leading http://server
	// 		if url == "" || url[0] != '/' {
	// 			// make relative path absolute
	// 			olddir, _ := path.Split(oldpath)
	// 			url = olddir + url
	// 		}
	//
	// 		var query string
	// 		if i := strings.Index(url, "?"); i != -1 {
	// 			url, query = url[:i], url[i:]
	// 		}
	//
	// 		// clean up but preserve trailing slash
	// 		trailing := strings.HasSuffix(url, "/")
	// 		url = path.Clean(url)
	// 		if trailing && !strings.HasSuffix(url, "/") {
	// 			url += "/"
	// 		}
	// 		url += query
	// 	}
	// }
	//
	// h := w.Header()
	//
	// // RFC 7231 notes that a short HTML body is usually included in
	// // the response because older user agents may not understand 301/307.
	// // Do it only if the request didn't already have a Content-Type header.
	// _, hadCT := h["Content-Type"]
	//
	// h.Set("Location", hexEscapeNonASCII(url))
	// if !hadCT && (r.Method == "GET" || r.Method == "HEAD") {
	// 	h.Set("Content-Type", "text/html; charset=utf-8")
	// }
	// w.WriteHeader(code)
	//
	// // Shouldn't send the body for POST or HEAD; that leaves GET.
	// if !hadCT && r.Method == "GET" {
	// 	body := "<a href=\"" + htmlEscape(url) + "\">" + statusText[code] + "</a>.\n"
	// 	fmt.Fprintln(w, body)
	// }
}

// RedirectHandler returns a request handler that redirects
// each request it receives to the given url using the given
// status code.
//
// The provided code should be in the 3xx range and is usually
// StatusMovedPermanently, StatusFound or StatusSeeOther.
func RedirectHandler(url string, code int) Handler {
	return &redirectHandler{url, code}
}


// 添加并排序
func appendSorted(es []muxEntry, e muxEntry) []muxEntry {
	n := len(es)
	i := sort.Search(n, func(i int) bool {
		return len(es[i].pattern) < len(e.pattern)
	})
	if i == n {
		return append(es, e)
	}
	// we now know that i points at where we want to insert
	es = append(es, muxEntry{}) // try to grow the slice in place, any entry works.
	copy(es[i+1:], es[i:])      // Move shorter entries down
	es[i] = e
	return es
}

// stripHostPort returns h without any trailing ":<port>".
func stripHostPort(h string) string {
	// If no port on host, return unchanged
	if strings.IndexByte(h, ':') == -1 {
		return h
	}
	host, _, err := net.SplitHostPort(h)
	if err != nil {
		return h // on error, return unchanged
	}
	return host
}

// cleanPath returns the canonical path for p, eliminating . and .. elements.
func cleanPath(p string) string {
	if p == "" {
		return "/"
	}
	if p[0] != '/' {
		p = "/" + p
	}
	np := path.Clean(p)
	// path.Clean removes trailing slash except for root;
	// put the trailing slash back if necessary.
	if p[len(p)-1] == '/' && np != "/" {
		// Fast path for common case of p being the string we want:
		if len(p) == len(np)+1 && strings.HasPrefix(p, np) {
			np = p
		} else {
			np += "/"
		}
	}
	return np
}