package client

import (
	"context"
	"fmt"
	"log"
	"net"
	"net/netip"
	"time"

	"github.com/Snawoot/dtlspipe/util"
	"github.com/pion/dtls/v2"
	"github.com/pion/transport/v2/udp"
)

const (
	MaxPktBuf = 4096
	Backlog   = 1024
)

type Client struct {
	listener    net.Listener
	dtlsConfig  *dtls.Config
	rAddr       string
	psk         func([]byte) ([]byte, error)
	timeout     time.Duration
	idleTimeout time.Duration
	baseCtx     context.Context
	cancelCtx   func()
}

func New(cfg *Config) (*Client, error) {
	cfg = cfg.populateDefaults()

	baseCtx, cancelCtx := context.WithCancel(cfg.BaseContext)

	client := &Client{
		rAddr:       cfg.RemoteAddress,
		timeout:     cfg.Timeout,
		psk:         cfg.PSKCallback,
		idleTimeout: cfg.IdleTimeout,
		baseCtx:     baseCtx,
		cancelCtx:   cancelCtx,
	}

	lAddrPort, err := netip.ParseAddrPort(cfg.BindAddress)
	if err != nil {
		cancelCtx()
		return nil, fmt.Errorf("can't parse bind address: %w", err)
	}

	client.dtlsConfig = &dtls.Config{
		CipherSuites: []dtls.CipherSuiteID{
			dtls.TLS_ECDHE_PSK_WITH_AES_128_CBC_SHA256,
			dtls.TLS_PSK_WITH_AES_128_CCM,
			dtls.TLS_PSK_WITH_AES_128_CCM_8,
			dtls.TLS_PSK_WITH_AES_256_CCM_8,
			dtls.TLS_PSK_WITH_AES_128_GCM_SHA256,
			dtls.TLS_PSK_WITH_AES_128_CBC_SHA256,
		},
		ExtendedMasterSecret: dtls.RequireExtendedMasterSecret,
		ConnectContextMaker:  client.contextMaker,
		PSK:                  client.psk,
		PSKIdentityHint:      []byte(cfg.PSKIdentity),
		MTU:                  cfg.MTU,
	}
	lc := udp.ListenConfig{
		Backlog: Backlog,
	}
	listener, err := lc.Listen("udp", net.UDPAddrFromAddrPort(lAddrPort))
	if err != nil {
		cancelCtx()
		return nil, fmt.Errorf("client listen failed: %w", err)
	}

	client.listener = listener

	go client.listen()

	return client, nil
}

func (client *Client) listen() {
	defer client.Close()
	for client.baseCtx.Err() == nil {
		conn, err := client.listener.Accept()
		if err != nil {
			log.Printf("conn accept failed: %v", err)
			continue
		}

		go func(conn net.Conn) {
			defer conn.Close()
			client.serve(conn)
		}(conn)
	}
}

func (client *Client) serve(conn net.Conn) {
	log.Printf("[+] conn %s <=> %s", conn.LocalAddr(), conn.RemoteAddr())
	defer log.Printf("[-] conn %s <=> %s", conn.LocalAddr(), conn.RemoteAddr())
	defer conn.Close()

	dialCtx, cancel := context.WithTimeout(client.baseCtx, client.timeout)
	defer cancel()
	remoteConn, err := (&net.Dialer{}).DialContext(dialCtx, "udp", client.rAddr)
	if err != nil {
		log.Printf("remote dial failed: %v", err)
		return
	}
	defer remoteConn.Close()

	remoteConn, err = dtls.ClientWithContext(dialCtx, remoteConn, client.dtlsConfig)
	if err != nil {
		log.Printf("DTL handshake with remote server failed: %v", err)
		return
	}

	util.PairConn(conn, remoteConn, client.idleTimeout)
}

func (client *Client) contextMaker() (context.Context, func()) {
	return context.WithTimeout(client.baseCtx, client.timeout)
}

func (client *Client) Close() error {
	client.cancelCtx()
	return client.listener.Close()
}