package state

import (
	"encoding/json"
	"errors"
	"fmt"
	"math"
	"os"
	"path/filepath"
	"sort"
	"strconv"
	"strings"
	"sync"
	"syscall"
	"time"
)

type RunRecord struct {
	ID              string    `json:"id"`
	Action          string    `json:"action"`
	Reason          string    `json:"reason,omitempty"`
	StartedAt       time.Time `json:"started_at"`
	EndedAt         time.Time `json:"ended_at"`
	DurationSeconds int       `json:"duration_seconds"`
	Success         bool      `json:"success"`
	Error           string    `json:"error,omitempty"`
}

type Store struct {
	path string
	mu   sync.Mutex
}

func New(path string) *Store {
	return &Store{path: path}
}

func EnsureDir(dir string) error {
	if dir == "" {
		return fmt.Errorf("state dir must not be empty")
	}
	return os.MkdirAll(dir, 0o750)
}

func AcquireLock(path string) (func(), error) {
	if err := os.MkdirAll(filepath.Dir(path), 0o750); err != nil {
		return nil, err
	}

	create := func() (func(), error) {
		f, err := os.OpenFile(path, os.O_CREATE|os.O_EXCL|os.O_WRONLY, 0o600)
		if err != nil {
			return nil, err
		}
		_, _ = f.WriteString(fmt.Sprintf("pid=%d started=%s\n", os.Getpid(), time.Now().Format(time.RFC3339)))
		_ = f.Close()
		return func() {
			_ = os.Remove(path)
		}, nil
	}

	unlock, err := create()
	if err == nil {
		return unlock, nil
	}
	if !errors.Is(err, os.ErrExist) {
		return nil, fmt.Errorf("acquire lock %s: %w", path, err)
	}

	stale, staleErr := staleLock(path)
	if staleErr != nil {
		return nil, fmt.Errorf("acquire lock %s: existing lock check failed: %w", path, staleErr)
	}
	if !stale {
		return nil, fmt.Errorf("acquire lock %s: lock is held by active process", path)
	}
	if rmErr := os.Remove(path); rmErr != nil {
		return nil, fmt.Errorf("acquire lock %s: remove stale lock: %w", path, rmErr)
	}
	unlock, err = create()
	if err != nil {
		return nil, fmt.Errorf("acquire lock %s: recreate after stale lock removal: %w", path, err)
	}
	return unlock, nil
}

func staleLock(path string) (bool, error) {
	b, err := os.ReadFile(path)
	if err != nil {
		if os.IsNotExist(err) {
			return true, nil
		}
		return false, err
	}
	lines := strings.Split(string(b), "\n")
	var pid int
	for _, line := range lines {
		line = strings.TrimSpace(line)
		if strings.HasPrefix(line, "pid=") {
			v := strings.TrimPrefix(line, "pid=")
			parsed, parseErr := strconv.Atoi(v)
			if parseErr != nil {
				return true, nil
			}
			pid = parsed
			break
		}
	}
	if pid <= 0 {
		return true, nil
	}
	if err := syscall.Kill(pid, 0); err != nil {
		if errors.Is(err, syscall.ESRCH) {
			return true, nil
		}
	}
	return false, nil
}

func (s *Store) Append(record RunRecord) error {
	s.mu.Lock()
	defer s.mu.Unlock()

	records, err := s.loadUnlocked()
	if err != nil {
		return err
	}
	records = append(records, record)
	if len(records) > 200 {
		records = records[len(records)-200:]
	}
	if err := os.MkdirAll(filepath.Dir(s.path), 0o750); err != nil {
		return err
	}
	b, err := json.MarshalIndent(records, "", "  ")
	if err != nil {
		return err
	}
	return os.WriteFile(s.path, b, 0o640)
}

func (s *Store) Load() ([]RunRecord, error) {
	s.mu.Lock()
	defer s.mu.Unlock()
	return s.loadUnlocked()
}

func (s *Store) loadUnlocked() ([]RunRecord, error) {
	b, err := os.ReadFile(s.path)
	if err != nil {
		if os.IsNotExist(err) {
			return nil, nil
		}
		return nil, err
	}
	if len(b) == 0 {
		return nil, nil
	}
	var records []RunRecord
	if err := json.Unmarshal(b, &records); err != nil {
		if healErr := quarantineCorruptFile(s.path, b, []byte("[]\n"), 0o640); healErr != nil {
			return nil, fmt.Errorf("decode run history: %w (auto-heal failed: %v)", err, healErr)
		}
		return nil, nil
	}
	return records, nil
}

func (s *Store) ShutdownP95(defaultSeconds int) int {
	records, err := s.Load()
	if err != nil {
		return defaultSeconds
	}
	var d []int
	for _, r := range records {
		if r.Action == "shutdown" && r.Success && r.DurationSeconds > 0 {
			d = append(d, r.DurationSeconds)
		}
	}
	if len(d) == 0 {
		return defaultSeconds
	}
	sort.Ints(d)
	idx := int(math.Ceil(0.95*float64(len(d)))) - 1
	if idx < 0 {
		idx = 0
	}
	if idx >= len(d) {
		idx = len(d) - 1
	}
	if d[idx] <= 0 {
		return defaultSeconds
	}
	return d[idx]
}