//go:build windows

package starssh

import (
	"bytes"
	"context"
	"encoding/binary"
	"errors"
	"fmt"
	"io"
	"net"
	"os"
	"path/filepath"
	"strconv"
	"strings"
	"time"

	"github.com/Microsoft/go-winio"
	"golang.org/x/sys/windows"
)

const defaultWindowsSSHAgentPipe = `\\.\pipe\openssh-ssh-agent`

var errInvalidGPGSocketInfo = errors.New("invalid gpg agent socket file")

type gpgSocketInfo struct {
	port   uint16
	nonce  []byte
	cygwin bool
}

func defaultSSHAgentEndpoint() (resolvedSSHAgentEndpoint, error) {
	return resolvedSSHAgentEndpoint{
		Endpoint: defaultWindowsSSHAgentPipe,
		Source:   "platform-default",
		Network:  "windows-pipe",
	}, nil
}

func defaultSSHAgentNetwork(endpoint string) string {
	if _, ok := normalizeWindowsSSHAgentPipe(endpoint); ok {
		return "windows-pipe"
	}
	if isAgentSSHSocketPath(endpoint) {
		return "gpg-socket"
	}
	return "unix"
}

func dialResolvedSSHAgent(resolved resolvedSSHAgentEndpoint, timeout time.Duration) (net.Conn, error) {
	if pipePath, ok := normalizeWindowsSSHAgentPipe(resolved.Endpoint); ok {
		return dialWindowsNamedPipe(pipePath, timeout, resolved.Source == "platform-default")
	}
	if isAgentSSHSocketPath(resolved.Endpoint) {
		return dialWindowsGPGSocketFile(resolved.Endpoint, timeout)
	}
	return dialWindowsUnixAgent(resolved.Endpoint, timeout)
}

func dialWindowsNamedPipe(path string, timeout time.Duration, unavailableOnNotFound bool) (net.Conn, error) {
	ctx := context.Background()
	cancel := func() {}
	if timeout > 0 {
		ctx, cancel = context.WithTimeout(ctx, timeout)
	}
	defer cancel()

	return dialWindowsNamedPipeContext(ctx, path, unavailableOnNotFound)
}

func normalizeWindowsSSHAgentPipe(endpoint string) (string, bool) {
	trimmed := strings.TrimSpace(endpoint)
	if trimmed == "" {
		return "", false
	}

	normalized := trimmed
	if strings.HasPrefix(normalized, "//./pipe/") {
		normalized = `\\.\pipe\` + strings.TrimPrefix(normalized, "//./pipe/")
	}
	if strings.HasPrefix(normalized, `\\.\pipe\`) {
		return normalized, true
	}
	return "", false
}

func isWindowsPipeUnavailable(err error) bool {
	return errors.Is(err, windows.ERROR_FILE_NOT_FOUND) || errors.Is(err, windows.ERROR_PATH_NOT_FOUND)
}

func dialWindowsUnixAgent(endpoint string, timeout time.Duration) (net.Conn, error) {
	if timeout > 0 {
		return net.DialTimeout("unix", endpoint, timeout)
	}
	return net.Dial("unix", endpoint)
}

func dialWindowsGPGSocketFile(path string, timeout time.Duration) (net.Conn, error) {
	ctx := context.Background()
	cancel := func() {}
	if timeout > 0 {
		ctx, cancel = context.WithTimeout(ctx, timeout)
	}
	defer cancel()
	return dialWindowsGPGSocketFileDepth(ctx, strings.TrimSpace(path), 0)
}

func dialWindowsGPGSocketFileDepth(ctx context.Context, path string, depth int) (net.Conn, error) {
	if path == "" {
		return nil, fmt.Errorf("gpg agent endpoint is empty")
	}
	if depth > 8 {
		return nil, fmt.Errorf("gpg agent socket redirect loop at %s", path)
	}

	data, err := os.ReadFile(path)
	if err != nil {
		return nil, err
	}
	if target, ok := parseGPGAssuanSocketRedirect(data); ok {
		target = resolveGPGSocketRedirectTarget(path, target)
		if pipePath, ok := normalizeWindowsSSHAgentPipe(target); ok {
			return dialWindowsNamedPipeContext(ctx, pipePath, false)
		}
		return dialWindowsGPGSocketFileDepth(ctx, target, depth+1)
	}

	info, err := parseGPGSocketInfo(path, data)
	if err != nil {
		return nil, err
	}
	return dialWindowsGPGSocketInfo(ctx, info)
}

func dialWindowsGPGSocketInfo(ctx context.Context, info gpgSocketInfo) (net.Conn, error) {
	var dialer net.Dialer
	conn, err := dialer.DialContext(ctx, "tcp", net.JoinHostPort("127.0.0.1", strconv.Itoa(int(info.port))))
	if err != nil {
		return nil, err
	}
	if deadline, ok := ctx.Deadline(); ok {
		if err := conn.SetDeadline(deadline); err != nil {
			_ = conn.Close()
			return nil, err
		}
	}
	if _, err := conn.Write(info.nonce); err != nil {
		_ = conn.Close()
		return nil, err
	}
	if info.cygwin {
		var nonce [16]byte
		if _, err := io.ReadFull(conn, nonce[:]); err != nil {
			_ = conn.Close()
			return nil, err
		}
		var credential [8]byte
		binary.LittleEndian.PutUint32(credential[:4], uint32(os.Getpid()))
		if _, err := conn.Write(credential[:]); err != nil {
			_ = conn.Close()
			return nil, err
		}
		if _, err := io.ReadFull(conn, credential[:]); err != nil {
			_ = conn.Close()
			return nil, err
		}
	}
	_ = conn.SetDeadline(time.Time{})
	return conn, nil
}

func resolveGPGSocketRedirectTarget(source string, target string) string {
	target = strings.TrimSpace(target)
	if target == "" || filepath.IsAbs(target) {
		return target
	}
	if _, ok := normalizeWindowsSSHAgentPipe(target); ok {
		return target
	}
	return filepath.Join(filepath.Dir(source), target)
}

func parseGPGSocketInfo(path string, data []byte) (gpgSocketInfo, error) {
	if info, ok := parseGPGAssuanSocketInfo(data); ok {
		return info, nil
	}
	if info, ok := parseGPGCygwinSocketInfo(data); ok {
		return info, nil
	}
	return gpgSocketInfo{}, fmt.Errorf("%w %s: expected GnuPG port/nonce socket file; if SSH_AUTH_SOCK was set to this file, restart gpg-agent to recreate it", errInvalidGPGSocketInfo, path)
}

func parseGPGAssuanSocketRedirect(data []byte) (string, bool) {
	text := strings.ReplaceAll(string(data), "\r\n", "\n")
	text = strings.TrimSuffix(text, "\n")
	lines := strings.Split(text, "\n")
	if len(lines) != 2 || lines[0] != "%Assuan%" {
		return "", false
	}
	target, ok := strings.CutPrefix(lines[1], "socket=")
	if !ok || strings.TrimSpace(target) == "" {
		return "", false
	}
	return os.ExpandEnv(target), true
}

func parseGPGAssuanSocketInfo(data []byte) (gpgSocketInfo, bool) {
	newline := bytes.IndexByte(data, '\n')
	if newline <= 0 || len(data)-newline-1 != 16 {
		return gpgSocketInfo{}, false
	}
	port64, err := strconv.ParseUint(strings.TrimSpace(string(data[:newline])), 10, 16)
	if err != nil || port64 == 0 {
		return gpgSocketInfo{}, false
	}
	nonce := make([]byte, 16)
	copy(nonce, data[newline+1:])
	return gpgSocketInfo{port: uint16(port64), nonce: nonce}, true
}

func parseGPGCygwinSocketInfo(data []byte) (gpgSocketInfo, bool) {
	if !bytes.HasPrefix(data, []byte("!<socket >")) {
		return gpgSocketInfo{}, false
	}
	fields := strings.Fields(strings.TrimRight(string(data[10:]), "\x00"))
	if len(fields) != 3 || fields[1] != "s" {
		return gpgSocketInfo{}, false
	}
	port64, err := strconv.ParseUint(fields[0], 10, 16)
	if err != nil || port64 == 0 {
		return gpgSocketInfo{}, false
	}
	hexParts := strings.Split(fields[2], "-")
	if len(hexParts) != 4 {
		return gpgSocketInfo{}, false
	}
	nonce := make([]byte, 0, 16)
	for _, part := range hexParts {
		if len(part) != 8 {
			return gpgSocketInfo{}, false
		}
		value, err := strconv.ParseUint(part, 16, 32)
		if err != nil {
			return gpgSocketInfo{}, false
		}
		var chunk [4]byte
		binary.LittleEndian.PutUint32(chunk[:], uint32(value))
		nonce = append(nonce, chunk[:]...)
	}
	return gpgSocketInfo{port: uint16(port64), nonce: nonce, cygwin: true}, true
}

func isAgentSSHSocketPath(endpoint string) bool {
	normalized := strings.ToLower(strings.TrimSpace(endpoint))
	return strings.HasSuffix(normalized, "s.gpg-agent.ssh")
}

func dialWindowsNamedPipeContext(ctx context.Context, path string, unavailableOnNotFound bool) (net.Conn, error) {
	if ctx == nil {
		ctx = context.Background()
	}
	conn, err := winio.DialPipeContext(ctx, path)
	if err != nil && unavailableOnNotFound && isWindowsPipeUnavailable(err) {
		return nil, errSSHAgentUnavailable
	}
	if err != nil {
		return nil, err
	}
	return conn, nil
}