package proxy

import (
	"bufio"
	"bytes"
	"errors"
	"net"
	"net/http"
	"sync"
)

// captureWriter 包装 http.ResponseWriter，边转发边缓冲响应体。
// 实现 http.Flusher 与 http.Hijacker 以支持 SSE/chunked/WebSocket。
type captureWriter struct {
	http.ResponseWriter
	buf         bytes.Buffer
	max         int64
	written     int64
	truncated   bool
	status      int
	wroteHeader bool
	hijacked    bool
	writeFailed bool
	onHijack    func(net.Conn) net.Conn
	sse         sseEventTracker
}

func newCaptureWriter(w http.ResponseWriter, max int64) *captureWriter {
	return &captureWriter{ResponseWriter: w, max: max, status: http.StatusOK}
}

func (c *captureWriter) WriteHeader(code int) {
	if c.wroteHeader {
		return
	}
	c.status = code
	c.wroteHeader = true
	c.ResponseWriter.WriteHeader(code)
}

func (c *captureWriter) Write(p []byte) (int, error) {
	if !c.wroteHeader {
		c.wroteHeader = true
	}
	n, err := c.ResponseWriter.Write(p)
	if err != nil || n != len(p) {
		c.writeFailed = true
	}
	if n > len(p) {
		n = len(p)
	}
	if n > 0 {
		// 仅缓冲 max 字节以内的内容。
		remaining := c.max - c.written
		if remaining > 0 {
			toBuf := n
			if int64(toBuf) > remaining {
				toBuf = int(remaining)
				c.truncated = true
			}
			c.buf.Write(p[:toBuf])
		} else if c.max > 0 {
			c.truncated = true
		}
		c.written += int64(n)
		if isStreamResponse(c.Header()) {
			c.sse.Write(p[:n])
		}
		c.flush()
	}
	return n, err
}

func (c *captureWriter) Flush() {
	c.flush()
}

func (c *captureWriter) flush() {
	if _, ok := c.ResponseWriter.(http.Flusher); !ok {
		return
	}
	if err := http.NewResponseController(c.ResponseWriter).Flush(); err != nil {
		c.writeFailed = true
	}
}

func (c *captureWriter) Hijack() (net.Conn, *bufio.ReadWriter, error) {
	h, ok := c.ResponseWriter.(http.Hijacker)
	if !ok {
		return nil, nil, errors.New("hijack not supported")
	}
	conn, rw, err := h.Hijack()
	if err != nil {
		c.writeFailed = true
		return nil, nil, err
	}
	c.hijacked = true
	if c.onHijack != nil {
		conn = c.onHijack(conn)
		rw = bufio.NewReadWriter(rw.Reader, bufio.NewWriter(conn))
	}
	return conn, rw, nil
}

func (c *captureWriter) Body() []byte      { return c.buf.Bytes() }
func (c *captureWriter) Truncated() bool   { return c.truncated }
func (c *captureWriter) Status() int       { return c.status }
func (c *captureWriter) Hijacked() bool    { return c.hijacked }
func (c *captureWriter) Complete() bool    { return !c.writeFailed }
func (c *captureWriter) SSEComplete() bool { return c.sse.Complete() }

func (c *captureWriter) OnHijack(fn func(net.Conn) net.Conn) { c.onHijack = fn }

func (c *captureWriter) SetHijackedResponse(status int, header http.Header) {
	c.status = status
	for key := range c.Header() {
		c.Header().Del(key)
	}
	for key, values := range header {
		c.Header()[key] = append([]string(nil), values...)
	}
}

type trackedConn struct {
	net.Conn
	closeOnce sync.Once
	onClose   func()
}

func (c *trackedConn) Close() error {
	err := c.Conn.Close()
	c.closeOnce.Do(c.onClose)
	return err
}

type headerDeliveryConn struct {
	net.Conn
	tail        []byte
	onDelivered func()
	delivered   bool
}

func (c *headerDeliveryConn) Write(p []byte) (int, error) {
	n, err := c.Conn.Write(p)
	if c.delivered || err != nil || n == 0 {
		return n, err
	}
	c.tail = append(c.tail, p[:n]...)
	if bytes.Contains(c.tail, []byte("\r\n\r\n")) {
		c.delivered = true
		c.tail = nil
		c.onDelivered()
	} else if len(c.tail) > 3 {
		c.tail = append(c.tail[:0], c.tail[len(c.tail)-3:]...)
	}
	return n, err
}