package vm

import (
	"fmt"
	"os"
	"os/exec"
	"qvm/internal/config"
	"qvm/internal/logging"
	"qvm/internal/workspace"
	"strconv"
	"strings"
	"syscall"
	"time"

	"github.com/samber/mo"
)

// VMStatus represents the current state of the VM
type VMStatus struct {
	Running bool
	PID     int
	SSHPort int
}

// Mount represents a 9p filesystem mount
type Mount struct {
	Tag      string
	HostPath string
}

// Start launches the VM with all configured mounts.
// Sequence:
//  1. Check if VM is already running (via PID file and process check)
//  2. Ensure all required directories exist
//  3. Build mount list (cache mounts + workspace mounts from registry)
//  4. Find available SSH port
//  5. Build and start VM via runner script with 9p virtfs mounts
//  6. Write PID and SSH port to state files
//  7. Wait for SSH to become available (60 second timeout)
//
// Returns error if any step fails.
func Start(cfg *config.Config, reg *workspace.Registry) mo.Result[struct{}] {
	// 1. Check if already running
	if IsRunning() {
		return mo.Err[struct{}](fmt.Errorf("VM is already running"))
	}

	// 2. Ensure directories exist
	if err := config.EnsureDirs(); err != nil {
		return mo.Err[struct{}](fmt.Errorf("failed to create directories: %w", err))
	}

	// 2a. Check if base image exists
	if _, err := os.Stat(config.BaseImage); os.IsNotExist(err) {
		return mo.Err[struct{}](fmt.Errorf("base image not found at %s - run 'qvm rebuild' first", config.BaseImage))
	}

	// 2b. Create overlay if it doesn't exist (backed by base image)
	if _, err := os.Stat(config.Overlay); os.IsNotExist(err) {
		if _, err := os.Stat(config.BaseImage); os.IsNotExist(err) {
			return mo.Err[struct{}](fmt.Errorf("base image not found at %s - run 'qvm rebuild' first", config.BaseImage))
		}

		logging.Info("Creating overlay image backed by base image...")
		cmd := exec.Command("qemu-img", "create", "-f", "qcow2",
			"-F", "qcow2", "-b", config.BaseImage, config.Overlay)
		if output, err := cmd.CombinedOutput(); err != nil {
			return mo.Err[struct{}](fmt.Errorf("failed to create overlay: %s: %w", string(output), err))
		}
	}

	// 3. Build mount list (for 9p virtfs)
	mounts := []Mount{
		{Tag: "cargo_home", HostPath: config.CargoHome},
		{Tag: "cargo_target", HostPath: config.CargoTarget},
		{Tag: "pnpm_store", HostPath: config.PnpmStore},
		{Tag: "sccache", HostPath: config.Sccache},
	}

	// Add opencode config mount if directory exists
	if _, err := os.Stat(config.HostOpencodeConfig); err == nil {
		mounts = append(mounts, Mount{
			Tag:      "opencode_config",
			HostPath: config.HostOpencodeConfig,
		})
	}

	// Add workspace mounts from registry
	for _, ws := range reg.List() {
		mounts = append(mounts, Mount{
			Tag:      ws.MountTag,
			HostPath: ws.HostPath,
		})
	}

	// 4. Find available SSH port
	sshPort, err := findAvailablePort(2222)
	if err != nil {
		return mo.Err[struct{}](fmt.Errorf("failed to find available SSH port: %w", err))
	}

	// 5. Build QEMU command and start VM directly
	args := buildQEMUArgs(cfg, sshPort, mounts)
	cmd := exec.Command("qemu-system-x86_64", args...)

	cmd.Stdout = nil
	cmd.Stderr = nil
	cmd.Stdin = nil

	if err := cmd.Run(); err != nil {
		return mo.Err[struct{}](fmt.Errorf("failed to start QEMU: %w", err))
	}

	logging.Info("Waiting for VM to daemonize...")
	pidFileReady := false
	for i := 0; i < 10; i++ {
		time.Sleep(500 * time.Millisecond)
		if _, err := os.Stat(config.PIDFile); err == nil {
			pidFileReady = true
			break
		}
	}

	if !pidFileReady {
		return mo.Err[struct{}](fmt.Errorf("QEMU did not create PID file after 5 seconds"))
	}

	pidBytes, err := os.ReadFile(config.PIDFile)
	if err != nil {
		return mo.Err[struct{}](fmt.Errorf("failed to read PID file: %w", err))
	}
	pid := strings.TrimSpace(string(pidBytes))

	logging.Info("VM started with PID " + pid)

	if err := os.WriteFile(config.SSHPortFile, []byte(strconv.Itoa(sshPort)), 0644); err != nil {
		if pidBytes, err := os.ReadFile(config.PIDFile); err == nil {
			if pid, err := strconv.Atoi(strings.TrimSpace(string(pidBytes))); err == nil {
				if process, err := os.FindProcess(pid); err == nil {
					_ = process.Kill()
				}
			}
		}
		_ = os.Remove(config.PIDFile)
		return mo.Err[struct{}](fmt.Errorf("failed to write SSH port file: %w", err))
	}

	// 7. Wait for SSH
	if err := waitForSSH(sshPort, 120*time.Second); err != nil {
		_ = cmd.Process.Kill()
		_ = os.Remove(config.PIDFile)
		_ = os.Remove(config.SSHPortFile)
		return mo.Err[struct{}](fmt.Errorf("VM started but SSH not available: %w", err))
	}

	return mo.Ok(struct{}{})
}

// Stop gracefully shuts down the VM.
// Sequence:
//  1. Read PID from file
//  2. Send SIGTERM to the process
//  3. Wait up to 30 seconds for graceful shutdown (poll every second)
//  4. If still running, send SIGKILL
//  5. Clean up PID and port files
//
// Returns success even if VM is not running (idempotent).
func Stop() mo.Result[struct{}] {
	// 1. Read PID file
	pidBytes, err := os.ReadFile(config.PIDFile)
	if err != nil {
		if os.IsNotExist(err) {
			// Not running
			return mo.Ok(struct{}{})
		}
		return mo.Err[struct{}](fmt.Errorf("failed to read PID file: %w", err))
	}

	pid, err := strconv.Atoi(strings.TrimSpace(string(pidBytes)))
	if err != nil {
		return mo.Err[struct{}](fmt.Errorf("invalid PID in file: %w", err))
	}

	// Check if process exists
	process, err := os.FindProcess(pid)
	if err != nil {
		// Process doesn't exist, clean up
		cleanupStateFiles()
		return mo.Ok(struct{}{})
	}

	// 2. Send SIGTERM for graceful shutdown
	if err := process.Signal(syscall.SIGTERM); err != nil {
		// Process already gone
		cleanupStateFiles()
		return mo.Ok(struct{}{})
	}

	// 3. Wait up to 30 seconds for process to exit (poll every second)
	for i := 0; i < 30; i++ {
		time.Sleep(1 * time.Second)

		// Check if process still exists by sending signal 0
		if err := process.Signal(syscall.Signal(0)); err != nil {
			// Process no longer exists
			cleanupStateFiles()
			return mo.Ok(struct{}{})
		}
	}

	// 4. Timeout, force kill
	_ = process.Signal(syscall.SIGKILL)

	// Wait a moment for SIGKILL to take effect
	time.Sleep(1 * time.Second)

	// 5. Clean up state files
	cleanupStateFiles()

	return mo.Ok(struct{}{})
}

// cleanupStateFiles removes all VM state files
func cleanupStateFiles() {
	_ = os.Remove(config.PIDFile)
	_ = os.Remove(config.SSHPortFile)
	_ = os.Remove(config.QMPSocket)
}

// Status returns the current VM status (running, PID, SSH port).
func Status() mo.Result[VMStatus] {
	status := VMStatus{
		Running: false,
		PID:     0,
		SSHPort: 0,
	}

	if !IsRunning() {
		return mo.Ok(status)
	}

	// Read PID
	pidBytes, err := os.ReadFile(config.PIDFile)
	if err != nil {
		return mo.Err[VMStatus](fmt.Errorf("failed to read PID file: %w", err))
	}

	pid, err := strconv.Atoi(strings.TrimSpace(string(pidBytes)))
	if err != nil {
		return mo.Err[VMStatus](fmt.Errorf("invalid PID in file: %w", err))
	}

	// Read SSH port
	portBytes, err := os.ReadFile(config.SSHPortFile)
	if err != nil {
		return mo.Err[VMStatus](fmt.Errorf("failed to read SSH port file: %w", err))
	}

	sshPort, err := strconv.Atoi(strings.TrimSpace(string(portBytes)))
	if err != nil {
		return mo.Err[VMStatus](fmt.Errorf("invalid SSH port in file: %w", err))
	}

	status.Running = true
	status.PID = pid
	status.SSHPort = sshPort

	return mo.Ok(status)
}

// Reset stops the VM and deletes the overlay image.
// This returns the VM to a fresh state based on the base image.
func Reset() mo.Result[struct{}] {
	// Stop VM if running
	stopResult := Stop()
	if stopResult.IsError() {
		return mo.Err[struct{}](fmt.Errorf("failed to stop VM: %w", stopResult.Error()))
	}

	// Delete overlay image
	if err := os.Remove(config.Overlay); err != nil && !os.IsNotExist(err) {
		return mo.Err[struct{}](fmt.Errorf("failed to delete overlay: %w", err))
	}

	return mo.Ok(struct{}{})
}

// IsRunning performs a quick check if the VM is running by checking
// the PID file and verifying the process exists.
func IsRunning() bool {
	pidBytes, err := os.ReadFile(config.PIDFile)
	if err != nil {
		return false
	}

	pid, err := strconv.Atoi(strings.TrimSpace(string(pidBytes)))
	if err != nil {
		return false
	}

	// Check if process exists by sending signal 0
	process, err := os.FindProcess(pid)
	if err != nil {
		return false
	}

	err = process.Signal(syscall.Signal(0))
	return err == nil
}

func buildQEMUArgs(cfg *config.Config, sshPort int, mounts []Mount) []string {
	// Boot directly from the qcow2 disk image (has GRUB installed)
	// Do NOT use -kernel/-initrd - that's for NixOS VM runner which requires special 9p mounts
	args := []string{
		"-machine", "q35",
		"-accel", "kvm",
		"-cpu", "host",
		"-m", cfg.VM.Memory,
		"-smp", strconv.Itoa(cfg.VM.CPUs),
		"-display", "none",
		"-daemonize",
		"-pidfile", config.PIDFile,
		"-drive", fmt.Sprintf("file=%s,if=virtio,format=qcow2", config.Overlay),
		"-netdev", fmt.Sprintf("user,id=n0,hostfwd=tcp::%d-:22", sshPort),
		"-device", "virtio-net-pci,netdev=n0",
		"-serial", fmt.Sprintf("file:%s", config.SerialLog),
	}

	// Add 9p mounts for cache directories and workspaces
	for _, mount := range mounts {
		args = append(args,
			"-virtfs", fmt.Sprintf("local,path=%s,mount_tag=%s,security_model=mapped-xattr,id=%s",
				mount.HostPath, mount.Tag, mount.Tag),
		)
	}

	return args
}

// findAvailablePort finds an available TCP port starting from the given base port.
func findAvailablePort(basePort int) (int, error) {
	const maxAttempts = 100

	for i := 0; i < maxAttempts; i++ {
		port := basePort + i

		cmd := exec.Command("nc", "-z", "localhost", strconv.Itoa(port))
		if err := cmd.Run(); err != nil {
			return port, nil
		}
	}

	return 0, fmt.Errorf("could not find available port after %d attempts", maxAttempts)
}

// waitForSSH waits for SSH to become available on the given port.
// Uses sshpass with password 'root' to test connection.
func waitForSSH(port int, timeout time.Duration) error {
	deadline := time.Now().Add(timeout)

	for time.Now().Before(deadline) {
		cmd := exec.Command("sshpass", "-p", "root",
			"ssh",
			"-o", "StrictHostKeyChecking=no",
			"-o", "UserKnownHostsFile=/dev/null",
			"-o", "ConnectTimeout=1",
			"-p", strconv.Itoa(port),
			"root@localhost",
			"exit 0")

		if err := cmd.Run(); err == nil {
			return nil
		}

		time.Sleep(1 * time.Second)
	}

	return fmt.Errorf("SSH did not become available within %v", timeout)
}