//go:build linux

package storage

import (
	"fmt"
	"os"
	"path/filepath"
	"strings"
	"syscall"
	"time"
)

// IsSystemDisk checks if the given device path overlaps with the root filesystem device.
// Returns true if the device is (or is the parent of) the system disk.
func IsSystemDisk(devicePath string) (bool, error) {
	// Get the block device major number of the root filesystem
	var rootStat syscall.Stat_t
	if err := syscall.Stat("/", &rootStat); err != nil {
		return false, fmt.Errorf("cannot stat /: %w", err)
	}

	// Get block device info of the target device
	var devStat syscall.Stat_t
	if err := syscall.Stat(devicePath, &devStat); err != nil {
		return false, fmt.Errorf("cannot stat %s: %w", devicePath, err)
	}

	// Compare major device numbers
	rootMajor := rootStat.Dev >> 8 & 0xff
	devMajor := devStat.Rdev >> 8 & 0xff
	if rootMajor == devMajor {
		return true, nil
	}

	return false, nil
}

// IsDeviceMounted checks if a device or any of its partitions is currently mounted.
func IsDeviceMounted(devicePath string) (bool, error) {
	data, err := os.ReadFile("/proc/mounts")
	if err != nil {
		return false, fmt.Errorf("cannot read /proc/mounts: %w", err)
	}

	base := filepath.Base(devicePath)
	for _, line := range strings.Split(string(data), "\n") {
		fields := strings.Fields(line)
		if len(fields) < 2 {
			continue
		}
		dev := fields[0]
		devBase := filepath.Base(dev)
		if devBase == base || strings.HasPrefix(devBase, base) {
			return true, nil
		}
	}
	return false, nil
}

// IsMountPathInUse checks if a path is already used as a mount point.
func IsMountPathInUse(mountPath string) (bool, error) {
	data, err := os.ReadFile("/proc/mounts")
	if err != nil {
		return false, fmt.Errorf("cannot read /proc/mounts: %w", err)
	}
	mountPath = filepath.Clean(mountPath)
	for _, line := range strings.Split(string(data), "\n") {
		fields := strings.Fields(line)
		if len(fields) < 2 {
			continue
		}
		if filepath.Clean(fields[1]) == mountPath {
			return true, nil
		}
	}
	return false, nil
}

// BackupFstab creates a dated backup of the fstab file.
func BackupFstab(fstabPath string) error {
	data, err := os.ReadFile(fstabPath)
	if err != nil {
		return fmt.Errorf("cannot read %s: %w", fstabPath, err)
	}
	backupPath := fstabPath + ".bak." + time.Now().Format("20060102")
	return os.WriteFile(backupPath, data, 0644)
}

// AppendFstabEntry appends a UUID-based fstab entry.
func AppendFstabEntry(fstabPath, uuid, mountPoint, fsType, options string) error {
	entry := fmt.Sprintf("\nUUID=%s\t%s\t%s\t%s\t0 2\n", uuid, mountPoint, fsType, options)
	f, err := os.OpenFile(fstabPath, os.O_APPEND|os.O_WRONLY, 0644)
	if err != nil {
		return fmt.Errorf("cannot open fstab for writing: %w", err)
	}
	defer f.Close()
	if _, err := f.WriteString(entry); err != nil {
		return fmt.Errorf("cannot write fstab entry: %w", err)
	}
	return nil
}