package core

import (
	"context"
	"fmt"
	"net"
	"os"
	"os/exec"
	"path/filepath"
	"strings"
	"sync"
	"time"
)

// StateChangedHandler is called when VPN connection state changes.
type StateChangedHandler func(state ConnectionState)

// LogHandler is called when a log message is produced. (source, message)
type LogHandler func(source, message string)

// CoreManager manages the lifecycle of xray (proxy backend) and sing-box (TUN frontend).
//
// Connection flow:
//  1. Parse VPN link
//  2. Generate configs for xray and sing-box
//  3. Start xray (SOCKS5 inbound -> proxy outbound)
//  4. Wait for SOCKS5 port readiness
//  5. Start sing-box (TUN -> SOCKS5)
type CoreManager struct {
	mu sync.Mutex

	xrayProcess   *exec.Cmd
	singBoxProcess *exec.Cmd
	xrayConfigPath    string
	singBoxConfigPath string
	cancel            context.CancelFunc

	coresPath   string
	configsPath string

	State         ConnectionState
	CurrentServer *ProxyLink

	OnStateChanged StateChangedHandler
	OnLog          LogHandler
}

// NewCoreManager creates a new CoreManager with paths under %APPDATA%/kettuRay.
func NewCoreManager() (*CoreManager, error) {
	appData, err := os.UserConfigDir()
	if err != nil {
		return nil, fmt.Errorf("failed to get app data dir: %w", err)
	}

	appDir := filepath.Join(appData, "kettuRay")
	coresPath := filepath.Join(appDir, "cores")
	configsPath := filepath.Join(appDir, "configs")

	if err := os.MkdirAll(coresPath, 0o755); err != nil {
		return nil, fmt.Errorf("failed to create cores dir: %w", err)
	}
	if err := os.MkdirAll(configsPath, 0o755); err != nil {
		return nil, fmt.Errorf("failed to create configs dir: %w", err)
	}

	cm := &CoreManager{
		coresPath:   coresPath,
		configsPath: configsPath,
		State:       Disconnected,
	}
	// Kill any leftover xray/sing-box processes from a previous crash
	cm.killStaleProcesses()
	return cm, nil
}

// Connect starts the VPN connection using the provided link.
func (cm *CoreManager) Connect(link string) error {
	cm.mu.Lock()
	if cm.State == Connected || cm.State == Connecting {
		cm.mu.Unlock()
		cm.log("Core", "Already connected or connecting. Disconnect first.")
		return nil
	}
	cm.mu.Unlock()

	ctx, cancel := context.WithCancel(context.Background())
	cm.mu.Lock()
	cm.cancel = cancel
	cm.mu.Unlock()

	defer func() {
		if cm.State != Connected {
			cancel()
		}
	}()

	cm.setState(Connecting)

	// 0. Kill stale processes
	cm.killStaleProcesses()
	if err := sleepCtx(ctx, 1*time.Second); err != nil {
		cm.log("Core", "Connection cancelled.")
		cm.cleanup()
		cm.setState(Disconnected)
		return nil
	}

	// 1. Parse link
	cm.log("Core", "Parsing link...")
	proxyLink, err := ParseLink(link)
	if err != nil {
		cm.log("Core", fmt.Sprintf("Failed to parse link: %v", err))
		cm.cleanup()
		cm.setState(Error)
		return err
	}
	cm.mu.Lock()
	cm.CurrentServer = proxyLink
	cm.mu.Unlock()
	cm.log("Core", fmt.Sprintf("Server: %s", proxyLink))

	// 2. Generate configs
	cm.log("Core", "Generating configurations...")
	xrayConfig, err := GenerateXrayConfig(proxyLink, DefaultSocksPort)
	if err != nil {
		cm.log("Core", fmt.Sprintf("Failed to generate xray config: %v", err))
		cm.cleanup()
		cm.setState(Error)
		return err
	}
	singBoxConfig, err := GenerateSingBoxConfig(proxyLink.Address, DefaultSocksPort, "kettuTun")
	if err != nil {
		cm.log("Core", fmt.Sprintf("Failed to generate sing-box config: %v", err))
		cm.cleanup()
		cm.setState(Error)
		return err
	}

	// 3. Save configs
	cm.xrayConfigPath = filepath.Join(cm.configsPath, "xray-config.json")
	cm.singBoxConfigPath = filepath.Join(cm.configsPath, "singbox-config.json")

	if err := os.WriteFile(cm.xrayConfigPath, []byte(xrayConfig), 0o644); err != nil {
		cm.log("Core", fmt.Sprintf("Failed to save xray config: %v", err))
		cm.cleanup()
		cm.setState(Error)
		return err
	}
	if err := os.WriteFile(cm.singBoxConfigPath, []byte(singBoxConfig), 0o644); err != nil {
		cm.log("Core", fmt.Sprintf("Failed to save sing-box config: %v", err))
		cm.cleanup()
		cm.setState(Error)
		return err
	}

	cm.log("Core", fmt.Sprintf("Xray config saved: %s", cm.xrayConfigPath))
	cm.log("Core", fmt.Sprintf("Sing-box config saved: %s", cm.singBoxConfigPath))

	// 4. Start xray
	cm.log("Xray", "Starting xray-core...")
	xrayPath := filepath.Join(cm.coresPath, "xray.exe")
	xrayCmd, err := cm.startProcess(xrayPath, []string{"run", "-config", cm.xrayConfigPath}, "Xray")
	if err != nil {
		cm.log("Core", fmt.Sprintf("Failed to start xray: %v", err))
		cm.cleanup()
		cm.setState(Error)
		return err
	}
	cm.mu.Lock()
	cm.xrayProcess = xrayCmd
	cm.mu.Unlock()

	// 5. Wait for SOCKS5 port
	cm.log("Core", fmt.Sprintf("Waiting for SOCKS5 port %d...", DefaultSocksPort))
	if err := waitForPort(ctx, DefaultSocksPort, 10*time.Second); err != nil {
		cm.log("Core", fmt.Sprintf("Xray failed to open port %d: %v", DefaultSocksPort, err))
		cm.cleanup()
		cm.setState(Error)
		return fmt.Errorf("xray failed to open port %d within timeout", DefaultSocksPort)
	}
	cm.log("Core", "SOCKS5 port ready.")

	if ctx.Err() != nil {
		cm.log("Core", "Connection cancelled.")
		cm.cleanup()
		cm.setState(Disconnected)
		return nil
	}

	// 6. Start sing-box
	cm.log("SingBox", "Starting sing-box (TUN)...")
	singBoxPath := filepath.Join(cm.coresPath, "sing-box.exe")
	singBoxCmd, err := cm.startProcess(singBoxPath, []string{"run", "-c", cm.singBoxConfigPath}, "SingBox")
	if err != nil {
		cm.log("Core", fmt.Sprintf("Failed to start sing-box: %v", err))
		cm.cleanup()
		cm.setState(Error)
		return err
	}
	cm.mu.Lock()
	cm.singBoxProcess = singBoxCmd
	cm.mu.Unlock()

	// 7. Wait for TUN setup
	if err := sleepCtx(ctx, 2*time.Second); err != nil {
		cm.log("Core", "Connection cancelled.")
		cm.cleanup()
		cm.setState(Disconnected)
		return nil
	}

	// Check both processes are alive
	if cm.xrayProcess.ProcessState != nil {
		err := fmt.Errorf("xray exited with code %d", cm.xrayProcess.ProcessState.ExitCode())
		cm.log("Core", err.Error())
		cm.cleanup()
		cm.setState(Error)
		return err
	}
	if cm.singBoxProcess.ProcessState != nil {
		err := fmt.Errorf("sing-box exited with code %d", cm.singBoxProcess.ProcessState.ExitCode())
		cm.log("Core", err.Error())
		cm.cleanup()
		cm.setState(Error)
		return err
	}

	cm.setState(Connected)
	cm.log("Core", fmt.Sprintf("Connected to %s (%s:%d)", proxyLink.Remark, proxyLink.Address, proxyLink.Port))
	return nil
}

// Disconnect stops the VPN connection.
func (cm *CoreManager) Disconnect() {
	cm.mu.Lock()
	if cm.State == Disconnected || cm.State == Disconnecting {
		cm.mu.Unlock()
		return
	}
	cm.mu.Unlock()

	cm.setState(Disconnecting)
	cm.log("Core", "Disconnecting...")

	cm.mu.Lock()
	if cm.cancel != nil {
		cm.cancel()
	}
	cm.mu.Unlock()

	cm.cleanup()

	cm.mu.Lock()
	cm.CurrentServer = nil
	cm.mu.Unlock()

	cm.setState(Disconnected)
	cm.log("Core", "Disconnected.")
}

func (cm *CoreManager) startProcess(path string, args []string, source string) (*exec.Cmd, error) {
	if _, err := os.Stat(path); err != nil {
		return nil, fmt.Errorf("binary not found: %s", path)
	}

	cmd := exec.Command(path, args...)
	cmd.Dir = filepath.Dir(path)
	cmd.SysProcAttr = procAttr() // platform-specific: hide window on Windows

	stdout, _ := cmd.StdoutPipe()
	stderr, _ := cmd.StderrPipe()

	if err := cmd.Start(); err != nil {
		return nil, fmt.Errorf("failed to start %s: %w", source, err)
	}

	cm.log(source, fmt.Sprintf("Process started (PID: %d)", cmd.Process.Pid))

	// Read stdout/stderr in background
	go scanPipe(stdout, func(line string) { cm.log(source, line) })
	go scanPipe(stderr, func(line string) { cm.log(source, markIfError(line)) })

	// Monitor process exit
	go func() {
		_ = cmd.Wait()
		cm.log(source, fmt.Sprintf("Process exited (code: %d)", cmd.ProcessState.ExitCode()))

		cm.mu.Lock()
		state := cm.State
		isOurs := cmd == cm.xrayProcess || cmd == cm.singBoxProcess
		cm.mu.Unlock()

		if isOurs && (state == Connected || state == Connecting) {
			cm.log(source, fmt.Sprintf("CRITICAL: Process %s crashed! Cleaning up...", source))
			cm.setState(Error)
			cm.mu.Lock()
			if cm.cancel != nil {
				cm.cancel()
			}
			cm.mu.Unlock()
		}
	}()

	return cmd, nil
}

func waitForPort(ctx context.Context, port int, timeout time.Duration) error {
	ctx, cancel := context.WithTimeout(ctx, timeout)
	defer cancel()

	addr := fmt.Sprintf("127.0.0.1:%d", port)
	for {
		select {
		case <-ctx.Done():
			return ctx.Err()
		default:
			conn, err := net.DialTimeout("tcp", addr, 1*time.Second)
			if err == nil {
				conn.Close()
				return nil
			}
			time.Sleep(300 * time.Millisecond)
		}
	}
}

func (cm *CoreManager) cleanup() {
	// Stop sing-box first (TUN), then xray
	cm.mu.Lock()
	singBox := cm.singBoxProcess
	xray := cm.xrayProcess
	cm.singBoxProcess = nil
	cm.xrayProcess = nil
	xrayConfig := cm.xrayConfigPath
	singBoxConfig := cm.singBoxConfigPath
	cm.xrayConfigPath = ""
	cm.singBoxConfigPath = ""
	cm.mu.Unlock()

	stopProcess(singBox, "SingBox", cm.log)
	stopProcess(xray, "Xray", cm.log)

	tryDeleteFile(xrayConfig)
	tryDeleteFile(singBoxConfig)
}

func stopProcess(cmd *exec.Cmd, source string, logFn func(string, string)) {
	if cmd == nil || cmd.Process == nil {
		return
	}
	if cmd.ProcessState != nil {
		return // already exited
	}

	logFn(source, fmt.Sprintf("Terminating process (PID: %d)...", cmd.Process.Pid))
	if err := cmd.Process.Kill(); err != nil {
		logFn(source, fmt.Sprintf("Error terminating process: %v", err))
		return
	}
	logFn(source, "Process terminated.")
}

func tryDeleteFile(path string) {
	if path == "" {
		return
	}
	_ = os.Remove(path)
}

func (cm *CoreManager) killStaleProcesses() {
	for _, name := range []string{"xray", "sing-box"} {
		killProcessByName(name, func(pid int) {
			cm.log("Core", fmt.Sprintf("Killing stale %s process (PID: %d)", name, pid))
		})
	}
}

func (cm *CoreManager) setState(state ConnectionState) {
	cm.mu.Lock()
	if cm.State == state {
		cm.mu.Unlock()
		return
	}
	cm.State = state
	handler := cm.OnStateChanged
	cm.mu.Unlock()

	if handler != nil {
		handler(state)
	}
}

func (cm *CoreManager) log(source, message string) {
	cm.mu.Lock()
	handler := cm.OnLog
	cm.mu.Unlock()

	if handler != nil {
		handler(source, message)
	}
}

// markIfError prefixes a line with [ERR] only if it actually contains an error/fatal level.
// sing-box and xray write INFO/WARN/ERROR to stderr, so we can't blindly mark all stderr as errors.
func markIfError(line string) string {
	upper := strings.ToUpper(line)
	if strings.Contains(upper, "ERROR") || strings.Contains(upper, "FATAL") || strings.Contains(upper, "PANIC") {
		return "[ERR] " + line
	}
	return line
}

func sleepCtx(ctx context.Context, d time.Duration) error {
	select {
	case <-ctx.Done():
		return ctx.Err()
	case <-time.After(d):
		return nil
	}
}

// Close stops all processes and cleans up.
func (cm *CoreManager) Close() {
	cm.mu.Lock()
	if cm.cancel != nil {
		cm.cancel()
	}
	cm.mu.Unlock()

	cm.cleanup()
}