package nhttp

import (
	"bufio"
	"fmt"
	"log"
	"net"
	_http "net/http"
	"path"
	"runtime"
	"strconv"
	"strings"
	"time"
)

const TrailerPrefix = "Trailer:"

func fixPragmaCacheControl(header _http.Header) {
	if hp, ok := header["Pragma"]; ok && len(hp) > 0 && hp[0] == "no-cache" {
		if _, presentcc := header["Cache-Control"]; !presentcc {
			header["Cache-Control"] = []string{"no-cache"}
		}
	}
}

func (w *response) finalTrailers() _http.Header {
	var t _http.Header
	for k, vv := range w.handlerHeader {
		if strings.HasPrefix(k, TrailerPrefix) {
			if t == nil {
				t = make(_http.Header)
			}
			t[strings.TrimPrefix(k, TrailerPrefix)] = vv
		}
	}
	for _, k := range w.trailers {
		if t == nil {
			t = make(_http.Header)
		}
		for _, v := range w.handlerHeader[k] {
			t.Add(k, v)
		}
	}
	return t
}

func (w *response) sendExpectationFailed() {
	// TODO(bradfitz): let ServeHTTP handlers handle
	// requests with non-standard expectation[s]? Seems
	// theoretical at best, and doesn't fit into the
	// current ServeHTTP model anyway. We'd need to
	// make the ResponseWriter an optional
	// "ExpectReplier" interface or something.
	//
	// For now we'll just obey RFC 7231 5.1.1 which says
	// "A server that receives an Expect field-value other
	// than 100-continue MAY respond with a 417 (Expectation
	// Failed) status code to indicate that the unexpected
	// expectation cannot be met."
	w.Header().Set("Connection", "close")
	w.WriteHeader(_http.StatusExpectationFailed)
	w.finishRequest()
}

func (w *response) finishRequest() {
	w.handlerDone.setTrue()

	if !w.wroteHeader {
		w.WriteHeader(_http.StatusOK)
	}

	w.w.Flush()
	putBufioWriter(w.w)
	w.cw.close()
	w.conn.bufw.Flush()

	w.conn.r.abortPendingRead()

	// Close the body (regardless of w.closeAfterReply) so we can
	// re-use its bufio.Reader later safely.
	w.reqBody.Close()

	if w.req.MultipartForm != nil {
		w.req.MultipartForm.RemoveAll()
	}
}

func (w *response) Header() _http.Header {
	if w.cw.header == nil && w.wroteHeader && !w.cw.wroteHeader {
		// Accessing the header between logically writing it
		// and physically writing it means we need to allocate
		// a clone to snapshot the logically written state.
		w.cw.header = w.handlerHeader.Clone()
	}
	w.calledHeader = true
	return w.handlerHeader
}

func (w *response) WriteHeader(code int) {
	if w.wroteHeader {
		caller := relevantCaller()
		log.Printf("nhttp: superfluous response.WriteHeader call from %s (%s:%d)\n", caller.Function, path.Base(caller.File), caller.Line)
		return
	}
	checkWriteHeaderCode(code)

	// Handle informational headers
	if code >= 100 && code <= 199 {
		// Prevent a potential race with an automatically-sent 100 Continue triggered by Request.Body.Read()
		if code == 100 && w.canWriteContinue.isSet() {
			w.writeContinueMu.Lock()
			w.canWriteContinue.setFalse()
			w.writeContinueMu.Unlock()
		}

		writeStatusLine(w.conn.bufw, w.req.ProtoAtLeast(1, 1), code, w.statusBuf[:])

		// Per RFC 8297 we must not clear the current header map
		w.handlerHeader.WriteSubset(w.conn.bufw, map[string]bool{"Content-Length": true, "Transfer-Encoding": true})
		w.conn.bufw.Write(crlf)
		w.conn.bufw.Flush()

		return
	}

	w.wroteHeader = true
	w.status = code

	if w.calledHeader && w.cw.header == nil {
		w.cw.header = w.handlerHeader.Clone()
	}

	if cl := w.handlerHeader.Get("Content-Length"); cl != "" {
		v, err := strconv.ParseInt(cl, 10, 64)
		if err == nil && v >= 0 {
			w.contentLength = v
		} else {
			log.Printf("nhttp: invalid Content-Length of %q\n", cl)
			w.handlerHeader.Del("Content-Length")
		}
	}
}

// relevantCaller searches the call stack for the first function outside of net/nhttp.
// The purpose of this function is to provide more helpful error messages.
func relevantCaller() runtime.Frame {
	pc := make([]uintptr, 16)
	n := runtime.Callers(1, pc)
	frames := runtime.CallersFrames(pc[:n])
	var frame runtime.Frame
	for {
		frame, more := frames.Next()
		if !strings.HasPrefix(frame.Function, "net/nhttp.") {
			return frame
		}
		if !more {
			break
		}
	}
	return frame
}

func checkWriteHeaderCode(code int) {
	// Issue 22880: require valid WriteHeader status codes.
	// For now we only enforce that it's three digits.
	// In the future we might block things over 599 (600 and above aren't defined
	// at https://httpwg.org/specs/rfc7231.html#status.codes).
	// But for now any three digits.
	//
	// We used to send "HTTP/1.1 000 0" on the wire in responses but there's
	// no equivalent bogus thing we can realistically send in HTTP/2,
	// so we'll consistently panic instead and help people find their bugs
	// early. (We can't return an error from WriteHeader even if we wanted to.)
	if code < 100 || code > 999 {
		panic(fmt.Sprintf("invalid WriteHeader code %v", code))
	}
}

// writeStatusLine writes an HTTP/1.x Status-Line (RFC 7230 Section 3.1.2)
// to bw. is11 is whether the HTTP request is HTTP/1.1. false means HTTP/1.0.
// code is the response status code.
// scratch is an optional scratch buffer. If it has at least capacity 3, it's used.
func writeStatusLine(bw *bufio.Writer, is11 bool, code int, scratch []byte) {
	if is11 {
		bw.WriteString("HTTP/1.1 ")
	} else {
		bw.WriteString("HTTP/1.0 ")
	}
	if text := _http.StatusText(code); text != "" {
		bw.Write(strconv.AppendInt(scratch[:0], int64(code), 10))
		bw.WriteByte(' ')
		bw.WriteString(text)
		bw.WriteString("\r\n")
	} else {
		// don't worry about performance
		fmt.Fprintf(bw, "%03d status code %d\r\n", code, code)
	}
}

func (w *response) Write(data []byte) (n int, err error) {
	return w.write(len(data), data, "")
}

func (w *response) WriteString(data string) (n int, err error) {
	return w.write(len(data), nil, data)
}

// either dataB or dataS is non-zero.
func (w *response) write(lenData int, dataB []byte, dataS string) (n int, err error) {
	if w.canWriteContinue.isSet() {
		// Body reader wants to write 100 Continue but hasn't yet.
		// Tell it not to. The store must be done while holding the lock
		// because the lock makes sure that there is not an active write
		// this very moment.
		w.writeContinueMu.Lock()
		w.canWriteContinue.setFalse()
		w.writeContinueMu.Unlock()
	}

	if !w.wroteHeader {
		w.WriteHeader(_http.StatusOK)
	}
	if lenData == 0 {
		return 0, nil
	}
	/*if !w.bodyAllowed() {
		return 0, _http.ErrBodyNotAllowed
	}*/

	w.written += int64(lenData) // ignoring errors, for errorKludge
	if w.contentLength != -1 && w.written > w.contentLength {
		return 0, _http.ErrContentLength
	}
	if dataB != nil {
		return w.w.Write(dataB)
	} else {
		return w.w.WriteString(dataS)
	}
}

// shouldReuseConnection reports whether the underlying TCP connection can be reused.
// It must only be called after the handler is done executing.
func (w *response) shouldReuseConnection() bool {
	if w.closeAfterReply {
		// The request or something set while executing the
		// handler indicated we shouldn't reuse this
		// connection.
		return false
	}

	if w.req.Method != "HEAD" && w.contentLength != -1 && w.contentLength != w.written {
		// Did not write enough. Avoid getting out of sync.
		return false
	}

	// There was some error writing to the underlying connection
	// during the request, so don't re-use this conn.
	if w.conn.werr != nil {
		return false
	}

	if w.closedRequestBodyEarly() {
		return false
	}

	return true
}

func (w *response) closedRequestBodyEarly() bool {
	body, ok := w.req.Body.(*body)
	return ok && body.didEarlyClose()
}

// rstAvoidanceDelay is the amount of time we sleep after closing the
// write side of a TCP connection before closing the entire socket.
// By sleeping, we increase the chances that the client sees our FIN
// and processes its final data before they process the subsequent RST
// from closing a connection with known unread data.
// This RST seems to occur mostly on BSD systems. (And Windows?)
// This timeout is somewhat arbitrary (~latency around the planet).
const rstAvoidanceDelay = 500 * time.Millisecond

type closeWriter interface {
	CloseWrite() error
}

var _ closeWriter = (*net.TCPConn)(nil)

// closeWrite flushes any outstanding data and sends a FIN packet (if
// client is connected via TCP), signaling that we're done. We then
// pause for a bit, hoping the client processes it before any
// subsequent RST.
//
// See https://golang.org/issue/3595
func (c *conn) closeWriteAndWait() {
	c.finalFlush()
	if tcp, ok := c.rwc.(closeWriter); ok {
		tcp.CloseWrite()
	}
	time.Sleep(rstAvoidanceDelay)
}