package xdrive

import (
	"context"
	"io"
	"net/http"
	"sync"
	"time"

	"github.com/xtls/xray-core/common/errors"
	"github.com/xtls/xray-core/common/net"
	"github.com/xtls/xray-core/transport/internet"
	"github.com/xtls/xray-core/transport/internet/tls"
)

var errStalled = errors.New("the request made no progress")

type serviceTransport struct {
	plain  http.RoundTripper
	secure http.RoundTripper
	stall  time.Duration
}

// RoundTrip ends a request that stands still for t.stall, with no answer that
// long after its body went out or no byte of either body, but not one that just
// runs long: a large object on a slow link takes minutes and is fine as long as
// its bytes move
func (t *serviceTransport) RoundTrip(r *http.Request) (*http.Response, error) {
	next := t.plain
	if r.URL.Scheme == "https" {
		next = t.secure
	}

	ctx, cancel := context.WithCancelCause(r.Context())
	timer := time.AfterFunc(t.stall, func() { cancel(errStalled) })
	alive := func() { timer.Reset(t.stall) }
	end := func() {
		timer.Stop()
		cancel(nil)
	}
	r = r.WithContext(ctx)
	if r.Body != nil && r.Body != http.NoBody {
		r.Body = &progressBody{ReadCloser: r.Body, alive: alive}
	}
	// a body sent again by the transport itself, after a GOAWAY or on a reused
	// connection that failed, moves just the same
	if getBody := r.GetBody; getBody != nil {
		r.GetBody = func() (io.ReadCloser, error) {
			body, err := getBody()
			if err != nil || body == http.NoBody {
				return body, err
			}
			return &progressBody{ReadCloser: body, alive: alive}, nil
		}
	}

	resp, err := next.RoundTrip(r)
	if err != nil {
		err = stalled(ctx, err)
		end()
		return nil, err
	}
	alive()
	resp.Body = &progressBody{ReadCloser: resp.Body, alive: alive, end: end, ctx: ctx}
	return resp, nil
}

// stalled returns errStalled for an error that the stall gave, which http2 reports
// as a plain cancel
func stalled(ctx context.Context, err error) error {
	if context.Cause(ctx) == errStalled {
		return errStalled
	}
	return err
}

type progressBody struct {
	io.ReadCloser
	alive func()
	end   func()
	// ctx is that of the request, for the body of its response
	ctx context.Context
}

func (b *progressBody) Read(p []byte) (int, error) {
	// http2 reads a request body up to 512 KiB at a time and sends it all before
	// the next read, which on a slow link could look like no progress
	n, err := b.ReadCloser.Read(p[:min(len(p), 16<<10)])
	if n > 0 {
		b.alive()
	}
	if err != nil && err != io.EOF && b.ctx != nil {
		err = stalled(b.ctx, err)
	}
	return n, err
}

func (b *progressBody) Close() error {
	err := b.ReadCloser.Close()
	if b.end != nil {
		b.end()
	}
	return err
}

// newServiceClient returns a client whose requests end after stall without
// progress, see serviceTransport.RoundTrip
func newServiceClient(streamSettings *internet.MemoryStreamConfig, stall time.Duration, maxConns int) *http.Client {
	var (
		tlsConfig *tls.Config
		sockopt   *internet.SocketConfig
		fronting  *net.Destination
	)
	if streamSettings != nil {
		tlsConfig = tls.ConfigFromStreamSettings(streamSettings)
		sockopt = streamSettings.SocketSettings
		fronting = streamSettings.Destination
	}
	if tlsConfig == nil {
		tlsConfig = &tls.Config{}
	}
	fingerprint := tls.GetFingerprint(tlsConfig.Fingerprint)

	dial := func(ctx context.Context, addr string) (net.Conn, net.Destination, error) {
		host, err := net.ParseDestination("tcp:" + addr)
		if err != nil {
			return nil, host, errors.New("bad address: ", addr).Base(err)
		}

		target := host
		if fronting != nil {
			target.Address = fronting.Address
			if fronting.Port != 0 {
				target.Port = fronting.Port
			}
		}

		var conn net.Conn
		if streamSettings.FinalMask != nil {
			conn, err = streamSettings.FinalMask.DialTCP(ctx, target)
		} else {
			conn, err = internet.DialSystem(ctx, target, sockopt)
		}
		if err != nil {
			return nil, host, errors.New("failed to dial to dest").Base(err)
		}
		return conn, host, nil
	}

	dialPlain := func(ctx context.Context, network, addr string) (net.Conn, error) {
		conn, _, err := dial(ctx, addr)
		return conn, err
	}

	// http.Transport picks h2 or h1 by the ALPN in the ConnectionState of the conn
	dialTLS := func(ctx context.Context, network, addr string) (net.Conn, error) {
		conn, host, err := dial(ctx, addr)
		if err != nil {
			return nil, err
		}

		gotlsConfig := tlsConfig.GetTLSConfig(tls.WithDestination(host))
		var tlsConn net.Conn
		if fingerprint == nil {
			tlsConn = tls.Client(conn, gotlsConfig)
		} else {
			tlsConn = tls.UClient(conn, gotlsConfig, fingerprint)
		}
		// the dial outlives the request that started it, and a handshake that hangs
		// would keep the one connection of the host to itself
		ctx, cancel := context.WithTimeout(ctx, stall)
		defer cancel()
		if err := tlsConn.(tls.Interface).HandshakeContext(ctx); err != nil {
			conn.Close()
			return nil, err
		}
		return tlsConn, nil
	}

	secure := func(connsPerHost int) *http.Transport {
		return &http.Transport{
			DialTLSContext:      dialTLS,
			ForceAttemptHTTP2:   true,
			IdleConnTimeout:     net.ConnIdleTimeout,
			MaxIdleConns:        maxConns,
			MaxIdleConnsPerHost: maxConns,
			MaxConnsPerHost:     connsPerHost,
			HTTP2:               &http.HTTP2Config{SendPingTimeout: net.ChromeH2KeepAlivePeriod},
		}
	}

	return &http.Client{
		Transport: &serviceTransport{
			plain: &http.Transport{
				DialContext:         dialPlain,
				IdleConnTimeout:     net.ConnIdleTimeout,
				MaxIdleConns:        maxConns,
				MaxIdleConnsPerHost: maxConns,
				MaxConnsPerHost:     maxConns,
			},
			secure: &secureTransport{h2: secure(1), h1: secure(maxConns)},
			stall:  stall,
		},
	}
}

// secureTransport keeps a host to one connection, all that h2 needs, as without
// a limit parallel requests would each dial their own. A host that answers over
// h1 moves to a transport with more, since h1 carries one request at a time
type secureTransport struct {
	h2, h1  http.RoundTripper
	h1Hosts sync.Map
}

func (t *secureTransport) RoundTrip(r *http.Request) (*http.Response, error) {
	if _, ok := t.h1Hosts.Load(r.URL.Host); ok {
		return t.h1.RoundTrip(r)
	}
	resp, err := t.h2.RoundTrip(r)
	if err == nil && resp.ProtoMajor == 1 {
		t.h1Hosts.Store(r.URL.Host, true)
	}
	return resp, err
}