package main

import (
	"context"
	"crypto/tls"
	"fmt"
	"net"
	"strings"
	"time"

	utls "github.com/refraction-networking/utls"
)

// dialTLSChrome dials addr with a Chrome-like ClientHello so CDNs (Fastly)
// are less likely to HTTP 403 Go's default TLS fingerprint.
// Handshakes as HTTP/1.1 only so net/http can use the returned conn.
func dialTLSChrome(ctx context.Context, dialCtx func(context.Context, string, string) (net.Conn, error), network, addr string) (net.Conn, error) {
	host := serverNameFromAddr(addr)
	raw, err := dialCtx(ctx, network, addr)
	if err != nil {
		return nil, err
	}
	cfg := &utls.Config{
		ServerName:         host,
		InsecureSkipVerify: true,
		NextProtos:         []string{"http/1.1"},
	}
	spec, err := utls.UTLSIdToSpec(utls.HelloChrome_120)
	if err != nil {
		_ = raw.Close()
		return dialTLSStd(ctx, dialCtx, network, addr)
	}
	for i := range spec.Extensions {
		if alpn, ok := spec.Extensions[i].(*utls.ALPNExtension); ok {
			alpn.AlpnProtocols = []string{"http/1.1"}
		}
	}
	uConn := utls.UClient(raw, cfg, utls.HelloCustom)
	if err := uConn.ApplyPreset(&spec); err != nil {
		_ = raw.Close()
		return nil, fmt.Errorf("utls preset %s: %w", host, err)
	}
	deadline, ok := ctx.Deadline()
	if !ok {
		deadline = time.Now().Add(15 * time.Second)
	}
	_ = raw.SetDeadline(deadline)
	if err := uConn.Handshake(); err != nil {
		_ = raw.Close()
		return nil, fmt.Errorf("utls handshake %s: %w", host, err)
	}
	_ = raw.SetDeadline(time.Time{})
	return uConn, nil
}

func dialTLSStd(ctx context.Context, dialCtx func(context.Context, string, string) (net.Conn, error), network, addr string) (net.Conn, error) {
	host := serverNameFromAddr(addr)
	raw, err := dialCtx(ctx, network, addr)
	if err != nil {
		return nil, err
	}
	cfg := &tls.Config{ServerName: host, InsecureSkipVerify: true, NextProtos: []string{"http/1.1"}}
	c := tls.Client(raw, cfg)
	if err := c.HandshakeContext(ctx); err != nil {
		_ = raw.Close()
		return nil, err
	}
	return c, nil
}

func serverNameFromAddr(addr string) string {
	host, _, err := net.SplitHostPort(addr)
	if err != nil {
		return strings.TrimSpace(addr)
	}
	return host
}