package storage

import (
	"fmt"
	"os"
	"regexp"
	"strconv"
	"strings"
	"time"

	"github.com/Fuwn/kaze/internal/config"
)

type MaintenanceState struct {
	lastCheck    time.Time
	lastDaily    time.Time
	nextCronTime time.Time
	totalChecks  int64
	cfg          config.MaintenanceConfig
	dbPath       string
	sizeBytes    int64
	cronFields   []cronField
}

type cronField struct {
	values map[int]bool
	any    bool
}

func NewMaintenanceState(dbPath string, cfg config.MaintenanceConfig) (*MaintenanceState, error) {
	m := &MaintenanceState{
		cfg:       cfg,
		dbPath:    dbPath,
		lastCheck: time.Now(),
		lastDaily: time.Now(),
	}

	if cfg.Triggers.Size != "" {
		bytes, err := parseSize(cfg.Triggers.Size)
		if err != nil {
			return nil, fmt.Errorf("invalid size %q: %w", cfg.Triggers.Size, err)
		}
		m.sizeBytes = bytes
	}

	if cfg.Triggers.Cron != "" {
		fields, err := parseCron(cfg.Triggers.Cron)
		if err != nil {
			return nil, fmt.Errorf("invalid cron %q: %w", cfg.Triggers.Cron, err)
		}
		m.cronFields = fields
		m.nextCronTime = m.calculateNextCron(time.Now())
	}

	return m, nil
}

func (m *MaintenanceState) IncrementChecks() {
	m.totalChecks++
}

func (m *MaintenanceState) ShouldRun() bool {
	if m.cfg.Mode == "" || m.cfg.Mode == "never" {
		return false
	}

	if m.checkSizeTrigger() {
		return true
	}

	if m.checkChecksTrigger() {
		return true
	}

	if m.checkCronTrigger() {
		return true
	}

	if m.checkDailyTrigger() {
		return true
	}

	return false
}

func (m *MaintenanceState) checkSizeTrigger() bool {
	if m.sizeBytes == 0 {
		return false
	}

	info, err := os.Stat(m.dbPath)
	if err != nil {
		return false
	}

	return info.Size() >= m.sizeBytes
}

func (m *MaintenanceState) checkChecksTrigger() bool {
	if m.cfg.Triggers.Checks == 0 {
		return false
	}
	return m.totalChecks >= m.cfg.Triggers.Checks
}

func (m *MaintenanceState) checkCronTrigger() bool {
	if len(m.cronFields) == 0 {
		return false
	}

	now := time.Now()
	if now.After(m.nextCronTime) || now.Equal(m.nextCronTime) {
		return true
	}
	return false
}

func (m *MaintenanceState) checkDailyTrigger() bool {
	if m.cfg.Triggers.Daily == "" {
		return false
	}

	parts := strings.Split(m.cfg.Triggers.Daily, ":")
	if len(parts) != 2 {
		return false
	}

	hour, err1 := strconv.Atoi(parts[0])
	minute, err2 := strconv.Atoi(parts[1])
	if err1 != nil || err2 != nil {
		return false
	}

	now := time.Now()
	today := time.Date(now.Year(), now.Month(), now.Day(), hour, minute, 0, 0, now.Location())

	if now.After(today) && m.lastDaily.Before(today) {
		return true
	}
	return false
}

func (m *MaintenanceState) Execute() error {
	switch m.cfg.Mode {
	case "backup":
		return m.executeBackup()
	case "reset":
		return m.executeReset()
	default:
		return nil
	}
}

func (m *MaintenanceState) executeBackup() error {
	epoch := time.Now().Unix()
	backupPath := fmt.Sprintf("%s.%d", m.dbPath, epoch)

	if err := os.Rename(m.dbPath, backupPath); err != nil {
		return fmt.Errorf("failed to backup database: %w", err)
	}

	m.resetState()
	return nil
}

func (m *MaintenanceState) executeReset() error {
	if err := os.Remove(m.dbPath); err != nil && !os.IsNotExist(err) {
		return fmt.Errorf("failed to remove database: %w", err)
	}

	walPath := m.dbPath + "-wal"
	if err := os.Remove(walPath); err != nil && !os.IsNotExist(err) {
		return fmt.Errorf("failed to remove WAL file: %w", err)
	}

	shmPath := m.dbPath + "-shm"
	if err := os.Remove(shmPath); err != nil && !os.IsNotExist(err) {
		return fmt.Errorf("failed to remove SHM file: %w", err)
	}

	m.resetState()
	return nil
}

func (m *MaintenanceState) resetState() {
	m.totalChecks = 0
	m.lastDaily = time.Now()
	if len(m.cronFields) > 0 {
		m.nextCronTime = m.calculateNextCron(time.Now())
	}
}

func (m *MaintenanceState) calculateNextCron(from time.Time) time.Time {
	t := from.Add(time.Minute).Truncate(time.Minute)

	for i := 0; i < 366*24*60; i++ {
		if m.cronMatches(t) {
			return t
		}
		t = t.Add(time.Minute)
	}

	return from.Add(24 * time.Hour)
}

func (m *MaintenanceState) cronMatches(t time.Time) bool {
	if len(m.cronFields) != 5 {
		return false
	}

	minute := t.Minute()
	hour := t.Hour()
	dayOfMonth := t.Day()
	month := int(t.Month())
	dayOfWeek := int(t.Weekday())

	return (m.cronFields[0].any || m.cronFields[0].values[minute]) &&
		(m.cronFields[1].any || m.cronFields[1].values[hour]) &&
		(m.cronFields[2].any || m.cronFields[2].values[dayOfMonth]) &&
		(m.cronFields[3].any || m.cronFields[3].values[month]) &&
		(m.cronFields[4].any || m.cronFields[4].values[dayOfWeek])
}

func parseSize(s string) (int64, error) {
	s = strings.TrimSpace(strings.ToUpper(s))

	re := regexp.MustCompile(`^(\d+(?:\.\d+)?)\s*(B|KB|MB|GB|TB)?$`)
	matches := re.FindStringSubmatch(s)
	if matches == nil {
		return 0, fmt.Errorf("invalid size format")
	}

	value, err := strconv.ParseFloat(matches[1], 64)
	if err != nil {
		return 0, err
	}

	unit := matches[2]
	if unit == "" {
		unit = "B"
	}

	multipliers := map[string]float64{
		"B":  1,
		"KB": 1024,
		"MB": 1024 * 1024,
		"GB": 1024 * 1024 * 1024,
		"TB": 1024 * 1024 * 1024 * 1024,
	}

	return int64(value * multipliers[unit]), nil
}

func parseCron(expr string) ([]cronField, error) {
	parts := strings.Fields(expr)
	if len(parts) != 5 {
		return nil, fmt.Errorf("cron must have 5 fields (minute hour day month weekday)")
	}

	limits := []struct{ min, max int }{
		{0, 59},
		{0, 23},
		{1, 31},
		{1, 12},
		{0, 6},
	}

	fields := make([]cronField, 5)
	for i, part := range parts {
		f, err := parseCronField(part, limits[i].min, limits[i].max)
		if err != nil {
			return nil, fmt.Errorf("field %d: %w", i+1, err)
		}
		fields[i] = f
	}

	return fields, nil
}

func parseCronField(field string, min, max int) (cronField, error) {
	cf := cronField{values: make(map[int]bool)}

	if field == "*" {
		cf.any = true
		return cf, nil
	}

	for _, part := range strings.Split(field, ",") {
		if strings.Contains(part, "/") {
			stepParts := strings.Split(part, "/")
			if len(stepParts) != 2 {
				return cf, fmt.Errorf("invalid step %q", part)
			}

			step, err := strconv.Atoi(stepParts[1])
			if err != nil || step <= 0 {
				return cf, fmt.Errorf("invalid step value %q", stepParts[1])
			}

			start := min
			end := max
			if stepParts[0] != "*" {
				rangeParts := strings.Split(stepParts[0], "-")
				start, _ = strconv.Atoi(rangeParts[0])
				if len(rangeParts) == 2 {
					end, _ = strconv.Atoi(rangeParts[1])
				} else {
					end = max
				}
			}

			for i := start; i <= end; i += step {
				cf.values[i] = true
			}
		} else if strings.Contains(part, "-") {
			rangeParts := strings.Split(part, "-")
			if len(rangeParts) != 2 {
				return cf, fmt.Errorf("invalid range %q", part)
			}
			start, err1 := strconv.Atoi(rangeParts[0])
			end, err2 := strconv.Atoi(rangeParts[1])
			if err1 != nil || err2 != nil {
				return cf, fmt.Errorf("invalid range values")
			}
			for i := start; i <= end; i++ {
				cf.values[i] = true
			}
		} else {
			val, err := strconv.Atoi(part)
			if err != nil {
				return cf, fmt.Errorf("invalid value %q", part)
			}
			cf.values[val] = true
		}
	}

	return cf, nil
}