//go:build linux
// +build linux

package persistence

import (
	"fmt"
	"io"
	"os"
	"os/user"
	"path/filepath"
	"text/template"
)

var currentUserHomeDir = func() (string, error) {
	usr, err := user.Current()
	if err != nil {
		return "", err
	}
	if usr.HomeDir == "" {
		return "", fmt.Errorf("current user home directory is empty")
	}
	return usr.HomeDir, nil
}

const systemdService = `[Unit]
Description=Overlord Agent
After=network.target

[Service]
Type=simple
ExecStart={{.ExePath}}
Restart=always
RestartSec=10

[Install]
WantedBy=default.target
`

const desktopEntry = `[Desktop Entry]
Type=Application
Name=Overlord Agent
Exec={{.ExePath}}
Hidden=false
NoDisplay=false
X-GNOME-Autostart-enabled=true
`

func binaryName() string {
	if DefaultStartupName != "" {
		return DefaultStartupName
	}
	return "agent"
}

func getSystemdPath() (string, error) {
	homeDir, err := currentUserHomeDir()
	if err != nil {
		return "", err
	}
	return filepath.Join(homeDir, ".config", "systemd", "user", binaryName()+".service"), nil
}

func getAutostartPath() (string, error) {
	homeDir, err := currentUserHomeDir()
	if err != nil {
		return "", err
	}
	return filepath.Join(homeDir, ".config", "autostart", binaryName()+".desktop"), nil
}

func getTargetPath() (string, error) {
	homeDir, err := currentUserHomeDir()
	if err != nil {
		return "", err
	}
	return filepath.Join(homeDir, ".local", "share", "overlord", binaryName()), nil
}

func install(exePath string) error {

	targetPath, err := getTargetPath()
	if err != nil {
		return fmt.Errorf("failed to get target path: %w", err)
	}

	dir := filepath.Dir(targetPath)
	if err := os.MkdirAll(dir, 0755); err != nil {
		return fmt.Errorf("failed to create overlord directory: %w", err)
	}

	if err := replaceExecutable(exePath, targetPath); err != nil {
		return err
	}

	if err := installSystemd(targetPath); err == nil {
		return nil
	}

	return installAutostart(targetPath)
}

func replaceExecutable(exePath, targetPath string) error {
	srcFile, err := os.Open(exePath)
	if err != nil {
		return fmt.Errorf("failed to open source executable: %w", err)
	}
	defer srcFile.Close()

	dir := filepath.Dir(targetPath)
	tmpFile, err := os.CreateTemp(dir, "agent-*.tmp")
	if err != nil {
		return fmt.Errorf("failed to create temp executable: %w", err)
	}
	tmpPath := tmpFile.Name()
	defer func() {
		_ = tmpFile.Close()
		_ = os.Remove(tmpPath)
	}()

	if _, err := io.Copy(tmpFile, srcFile); err != nil {
		return fmt.Errorf("failed to copy executable: %w", err)
	}
	if err := tmpFile.Sync(); err != nil {
		return fmt.Errorf("failed to sync temp file: %w", err)
	}
	if err := tmpFile.Close(); err != nil {
		return fmt.Errorf("failed to close temp file: %w", err)
	}

	if err := os.Rename(tmpPath, targetPath); err != nil {
		if removeErr := os.Remove(targetPath); removeErr == nil {
			err = os.Rename(tmpPath, targetPath)
		}
		if err != nil {
			return fmt.Errorf("failed to replace executable at %s: %w", targetPath, err)
		}
	}

	if err := os.Chmod(targetPath, 0755); err != nil {
		return fmt.Errorf("failed to set executable permissions: %w", err)
	}

	return nil
}

func installSystemd(exePath string) error {
	servicePath, err := getSystemdPath()
	if err != nil {
		return err
	}

	dir := filepath.Dir(servicePath)
	if err := os.MkdirAll(dir, 0755); err != nil {
		return fmt.Errorf("failed to create systemd directory: %w", err)
	}

	file, err := os.Create(servicePath)
	if err != nil {
		return fmt.Errorf("failed to create service file: %w", err)
	}
	defer file.Close()

	tmpl, err := template.New("service").Parse(systemdService)
	if err != nil {
		return fmt.Errorf("failed to parse template: %w", err)
	}

	data := struct {
		ExePath string
	}{
		ExePath: exePath,
	}

	if err := tmpl.Execute(file, data); err != nil {
		return fmt.Errorf("failed to write service file: %w", err)
	}

	return nil
}

func configure(exePath string) error {
	if err := installSystemd(exePath); err == nil {
		return nil
	}
	return installAutostart(exePath)
}

func installAutostart(exePath string) error {
	autostartPath, err := getAutostartPath()
	if err != nil {
		return err
	}

	dir := filepath.Dir(autostartPath)
	if err := os.MkdirAll(dir, 0755); err != nil {
		return fmt.Errorf("failed to create autostart directory: %w", err)
	}

	file, err := os.Create(autostartPath)
	if err != nil {
		return fmt.Errorf("failed to create desktop entry: %w", err)
	}
	defer file.Close()

	tmpl, err := template.New("desktop").Parse(desktopEntry)
	if err != nil {
		return fmt.Errorf("failed to parse template: %w", err)
	}

	data := struct {
		ExePath string
	}{
		ExePath: exePath,
	}

	if err := tmpl.Execute(file, data); err != nil {
		return fmt.Errorf("failed to write desktop entry: %w", err)
	}

	return nil
}

func uninstall() error {

	var lastErr error

	if servicePath, err := getSystemdPath(); err == nil {
		if err := os.Remove(servicePath); err != nil && !os.IsNotExist(err) {
			lastErr = fmt.Errorf("failed to remove systemd service: %w", err)
		}
	}

	if autostartPath, err := getAutostartPath(); err == nil {
		if err := os.Remove(autostartPath); err != nil && !os.IsNotExist(err) {
			lastErr = fmt.Errorf("failed to remove autostart entry: %w", err)
		}
	}

	if targetPath, err := getTargetPath(); err == nil {
		os.Remove(targetPath)
	}

	return lastErr
}