package driver

import (
	"bufio"
	"context"
	"fmt"
	"io"
	"net"
	"net/url"
	"strconv"
	"strings"

	"git.unkin.net/unkin/waitfordb/internal/config"
)

func init() { register(valkey{}) }

type valkey struct{}

func (valkey) Name() string { return "valkey" }

func (valkey) Open(cfg config.Config) (Pinger, error) {
	p := &valkeyPinger{
		addr:     net.JoinHostPort(cfg.Host, cfg.Port),
		user:     cfg.User,
		password: cfg.Password,
	}
	if cfg.DSN != "" {
		u, err := url.Parse(cfg.DSN)
		if err != nil {
			return nil, fmt.Errorf("invalid valkey DSN: %w", err)
		}
		if u.Scheme != "redis" && u.Scheme != "valkey" {
			return nil, fmt.Errorf("unsupported valkey DSN scheme %q (use redis:// or valkey://)", u.Scheme)
		}
		port := u.Port()
		if port == "" {
			port = "6379"
		}
		p.addr = net.JoinHostPort(u.Hostname(), port)
		if u.User != nil {
			p.user = u.User.Username()
			if pw, ok := u.User.Password(); ok {
				p.password = pw
			}
		}
	}
	return p, nil
}

// valkeyPinger speaks just enough RESP to AUTH and PING. Each Ping uses a
// fresh connection so a half-open socket from a failed attempt cannot linger.
type valkeyPinger struct {
	addr     string
	user     string
	password string
}

func (p *valkeyPinger) Ping(ctx context.Context) error {
	var d net.Dialer
	conn, err := d.DialContext(ctx, "tcp", p.addr)
	if err != nil {
		return err
	}
	defer conn.Close()
	if dl, ok := ctx.Deadline(); ok {
		_ = conn.SetDeadline(dl)
	}

	r := bufio.NewReader(conn)
	if p.password != "" {
		args := []string{"AUTH"}
		if p.user != "" && p.user != "default" {
			args = append(args, p.user)
		}
		args = append(args, p.password)
		if _, err := roundTrip(conn, r, args...); err != nil {
			return fmt.Errorf("AUTH %s: %w", p.user, err)
		}
	}

	reply, err := roundTrip(conn, r, "PING")
	if err != nil {
		return fmt.Errorf("PING: %w", err)
	}
	if reply != "PONG" {
		return fmt.Errorf("PING: unexpected reply %q", reply)
	}
	return nil
}

func (p *valkeyPinger) Close() error { return nil }

func roundTrip(w io.Writer, r *bufio.Reader, args ...string) (string, error) {
	var b strings.Builder
	fmt.Fprintf(&b, "*%d\r\n", len(args))
	for _, a := range args {
		fmt.Fprintf(&b, "$%d\r\n%s\r\n", len(a), a)
	}
	if _, err := io.WriteString(w, b.String()); err != nil {
		return "", err
	}
	return readReply(r)
}

func readReply(r *bufio.Reader) (string, error) {
	line, err := r.ReadString('\n')
	if err != nil {
		return "", err
	}
	line = strings.TrimRight(line, "\r\n")
	if line == "" {
		return "", fmt.Errorf("empty reply")
	}
	switch line[0] {
	case '+':
		return line[1:], nil
	case '-':
		return "", fmt.Errorf("server error: %s", line[1:])
	case '$':
		n, err := strconv.Atoi(line[1:])
		if err != nil || n < 0 {
			return "", fmt.Errorf("unexpected reply %q", line)
		}
		buf := make([]byte, n+2) // payload + trailing CRLF
		if _, err := io.ReadFull(r, buf); err != nil {
			return "", err
		}
		return string(buf[:n]), nil
	default:
		return "", fmt.Errorf("unexpected reply %q", line)
	}
}