package daemon

import (
	"crypto/sha256"
	"encoding/hex"
	"fmt"
	"os"
	"path/filepath"
	"strconv"
	"strings"
	"syscall"
)

const (
	sockName = "daemon.sock"
	pidName  = "daemon.pid"
	logName  = "daemon.log"
)

// Paths holds filesystem locations for one DataDir's daemon instance.
type Paths struct {
	RuntimeDir string
	Socket     string
	PIDFile    string
	LogFile    string
}

// PathsForDataDir returns runtime paths unique to dataDir.
func PathsForDataDir(dataDir string) (Paths, error) {
	dataDir = filepath.Clean(dataDir)
	sum := sha256.Sum256([]byte(dataDir))
	id := hex.EncodeToString(sum[:8])

	dir, err := mkdirRuntime(id, dataDir)
	if err != nil {
		return Paths{}, err
	}
	return Paths{
		RuntimeDir: dir,
		Socket:     filepath.Join(dir, sockName),
		PIDFile:    filepath.Join(dir, pidName),
		LogFile:    filepath.Join(dir, logName),
	}, nil
}

func mkdirRuntime(id, dataDir string) (string, error) {
	candidates := []string{}
	if r := strings.TrimSpace(os.Getenv("XDG_RUNTIME_DIR")); r != "" {
		candidates = append(candidates, filepath.Join(r, "task-master-"+id))
	}
	candidates = append(candidates,
		filepath.Join(os.TempDir(), fmt.Sprintf("task-master-%d-%s", os.Getuid(), id)),
		filepath.Join(dataDir, ".runtime"),
	)
	var last error
	for _, dir := range candidates {
		if err := os.MkdirAll(dir, 0o700); err != nil {
			last = err
			continue
		}
		return dir, nil
	}
	if last == nil {
		last = fmt.Errorf("no runtime dir candidate")
	}
	return "", fmt.Errorf("create runtime dir: %w", last)
}

func writePID(path string, pid int) error {
	return os.WriteFile(path, []byte(strconv.Itoa(pid)+"\n"), 0o600)
}

func readPID(path string) (int, error) {
	data, err := os.ReadFile(path)
	if err != nil {
		return 0, err
	}
	s := strings.TrimSpace(string(data))
	if s == "" {
		return 0, fmt.Errorf("empty pid file")
	}
	return strconv.Atoi(s)
}

func processAlive(pid int) bool {
	if pid <= 0 {
		return false
	}
	err := syscall.Kill(pid, 0)
	return err == nil
}