//go:build linux

package system

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

// IsMountPoint checks if a path is on a different device than its parent.
// Returns true if the path is a mount point (different device ID from parent).
func IsMountPoint(path string) bool {
	var pathStat, parentStat syscall.Stat_t
	if err := syscall.Stat(path, &pathStat); err != nil {
		return false
	}
	parent := filepath.Dir(path)
	if err := syscall.Stat(parent, &parentStat); err != nil {
		return false
	}
	return pathStat.Dev != parentStat.Dev
}

// IsWritable checks if the given path is writable by attempting to create+remove a temp file.
func IsWritable(path string) bool {
	testFile := filepath.Join(path, ".felhom-write-test")
	f, err := os.Create(testFile)
	if err != nil {
		return false
	}
	f.Close()
	os.Remove(testFile)
	return true
}

// PathsOverlap returns true if one path is a parent or child of the other.
func PathsOverlap(a, b string) bool {
	a = filepath.Clean(a)
	b = filepath.Clean(b)
	if a == b {
		return true
	}
	aSep := a + string(os.PathSeparator)
	bSep := b + string(os.PathSeparator)
	return strings.HasPrefix(aSep, bSep) || strings.HasPrefix(bSep, aSep)
}

// DiskUsageInfo holds disk usage statistics for a path.
type DiskUsageInfo struct {
	TotalGB     float64
	UsedGB      float64
	AvailGB     float64
	UsedPercent float64
	TotalHuman  string
	UsedHuman   string
}

// GetDiskUsage returns disk usage info for a path, or nil on error.
func GetDiskUsage(path string) *DiskUsageInfo {
	var stat syscall.Statfs_t
	if err := syscall.Statfs(path, &stat); err != nil {
		return nil
	}

	bsize := uint64(stat.Bsize)
	total := stat.Blocks * bsize
	avail := stat.Bavail * bsize
	used := total - (stat.Bfree * bsize)

	const gb = 1024 * 1024 * 1024
	info := &DiskUsageInfo{
		TotalGB: float64(total) / float64(gb),
		UsedGB:  float64(used) / float64(gb),
		AvailGB: float64(avail) / float64(gb),
	}
	if total > 0 {
		info.UsedPercent = float64(used) / float64(total) * 100
	}
	info.TotalHuman = formatGB(info.TotalGB)
	info.UsedHuman = formatGB(info.UsedGB)
	return info
}

func formatGB(gb float64) string {
	if gb >= 1000 {
		return fmt.Sprintf("%.1f TB", gb/1024)
	}
	return fmt.Sprintf("%.1f GB", gb)
}

// FSInfo holds filesystem type, device, and disk model info.
type FSInfo struct {
	FSType string // "ext4", "btrfs"
	Device string // "/dev/sda1"
	Model  string // "WD Elements 25A2" (best-effort from sysfs)
}

// GetFSInfo returns filesystem info for a path using findmnt, or nil on error.
func GetFSInfo(path string) *FSInfo {
	out, err := exec.Command("findmnt", "-n", "-o", "SOURCE,FSTYPE", "--target", path).Output()
	if err != nil {
		return nil
	}
	fields := strings.Fields(strings.TrimSpace(string(out)))
	if len(fields) < 2 {
		return nil
	}
	info := &FSInfo{
		Device: fields[0],
		FSType: fields[1],
	}
	// Try to get disk model from sysfs
	info.Model = diskModel(info.Device)
	return info
}

// diskModel reads the disk model from /sys/block/<dev>/device/model.
func diskModel(device string) string {
	// /dev/sda1 → sda, /dev/nvme0n1p1 → nvme0n1
	base := filepath.Base(device)
	// Strip partition number: sda1 → sda, nvme0n1p1 → nvme0n1
	disk := base
	if strings.HasPrefix(base, "nvme") {
		// nvme0n1p1 → find last 'p' followed by digits
		if idx := strings.LastIndex(base, "p"); idx > 4 {
			disk = base[:idx]
		}
	} else {
		// sda1 → sda: strip trailing digits
		disk = strings.TrimRight(base, "0123456789")
	}
	modelPath := "/sys/block/" + disk + "/device/model"
	data, err := os.ReadFile(modelPath)
	if err != nil {
		return ""
	}
	return strings.TrimSpace(string(data))
}