package models

import (
	"fmt"
	"strings"
	"time"

	"github.com/lib/pq"
	"github.com/robfig/cron/v3"
	"gorm.io/gorm"

	"rocketgit.ru/rsmon/worker/app/models/concerns"
)

const (
	MaintenanceManual              = "manual"
	MaintenanceSingle              = "single"
	MaintenanceCron                = "cron"
	MaintenanceRecurringInterval   = "recurring-interval"
	MaintenanceRecurringWeekday    = "recurring-weekday"
	MaintenanceRecurringDayOfMonth = "recurring-day-of-month"
)

// Maintenance is account-owned planned downtime. Times are stored as UTC;
// Timezone only defines how recurring wall-clock fields are interpreted.
type Maintenance struct {
	concerns.Model
	AccountID                     int64          `gorm:"type:bigint REFERENCES accounts(id) ON DELETE CASCADE;not null;index" json:"account_id"`
	Account                       *Account       `json:"-"`
	Title                         string         `gorm:"size:200;not null" json:"title"`
	Description                   string         `gorm:"type:text;not null;default:''" json:"description"`
	Strategy                      string         `gorm:"size:32;not null" json:"strategy"`
	Cron                          string         `gorm:"type:text;not null;default:''" json:"cron"`
	DurationSec                   int            `gorm:"not null;default:0" json:"duration_sec"`
	StartDate                     *time.Time     `json:"start_date,omitempty"`
	EndDate                       *time.Time     `json:"end_date,omitempty"`
	StartTime                     string         `gorm:"size:5;not null;default:''" json:"start_time"`
	EndTime                       string         `gorm:"size:5;not null;default:''" json:"end_time"`
	Weekdays                      pq.Int64Array  `gorm:"type:bigint[];not null;default:'{}'" json:"weekdays"`
	DaysOfMonth                   pq.StringArray `gorm:"type:text[];not null;default:'{}'" json:"days_of_month"`
	IntervalDay                   int            `gorm:"not null;default:1" json:"interval_day"`
	Timezone                      string         `gorm:"size:64;not null;default:'UTC'" json:"timezone"`
	Active                        bool           `gorm:"not null;default:true" json:"active"`
	LastStartDate                 *time.Time     `json:"last_start_date,omitempty"`
	LegacyStatusPageMaintenanceID *int64         `gorm:"uniqueIndex" json:"-"`
	ShowOnAllStatusPages          bool           `gorm:"not null;default:true" json:"show_on_all_status_pages"`
	Monitors                      []Monitor      `gorm:"many2many:maintenance_monitors;constraint:OnDelete:CASCADE" json:"monitors,omitempty"`
	StatusPages                   []StatusPage   `gorm:"many2many:maintenance_status_pages;constraint:OnDelete:CASCADE" json:"status_pages,omitempty"`
	concerns.Timestamped
	Audited
	DeletedAt gorm.DeletedAt `gorm:"index" json:"-"`
}

func (Maintenance) TableName() string { return "maintenances" }

func (m *Maintenance) location() (*time.Location, error) {
	if m.Timezone == "" || m.Timezone == "SAME_AS_SERVER" {
		return time.UTC, nil
	}
	return time.LoadLocation(m.Timezone)
}

func (m *Maintenance) generatedCron() (string, error) {
	if m.Strategy == MaintenanceCron {
		return m.Cron, nil
	}
	if m.Strategy == MaintenanceManual || m.Strategy == MaintenanceSingle {
		return "", nil
	}
	parts := strings.Split(m.StartTime, ":")
	if len(parts) != 2 {
		return "", fmt.Errorf("start_time must be HH:MM")
	}
	base := parts[1] + " " + parts[0]
	switch m.Strategy {
	case MaintenanceRecurringInterval:
		return "", nil
	case MaintenanceRecurringWeekday:
		if len(m.Weekdays) == 0 {
			return "", fmt.Errorf("at least one weekday is required")
		}
		values := make([]string, len(m.Weekdays))
		for i, day := range m.Weekdays {
			if day < 0 || day > 6 {
				return "", fmt.Errorf("weekday must be 0 through 6")
			}
			values[i] = fmt.Sprint(day)
		}
		return base + " * * " + strings.Join(values, ","), nil
	case MaintenanceRecurringDayOfMonth:
		if len(m.DaysOfMonth) == 0 {
			return "", fmt.Errorf("at least one day of month is required")
		}
		values := make([]string, 0, len(m.DaysOfMonth))
		for _, day := range m.DaysOfMonth {
			if day == "lastDay1" {
				values = append(values, "28-31")
			} else {
				values = append(values, day)
			}
		}
		return base + " " + strings.Join(values, ",") + " * *", nil
	default:
		return "", fmt.Errorf("unknown maintenance strategy %q", m.Strategy)
	}
}

// Validate normalizes generated schedules and rejects ambiguous or invalid
// input before it can reach the scheduler.
func (m *Maintenance) Validate() error {
	m.Title = strings.TrimSpace(m.Title)
	if m.Title == "" || len(m.Title) > 200 {
		return fmt.Errorf("title is required and must be at most 200 characters")
	}
	if _, err := m.location(); err != nil {
		return fmt.Errorf("invalid timezone: %w", err)
	}
	switch m.Strategy {
	case MaintenanceManual:
		return nil
	case MaintenanceSingle:
		if m.StartDate == nil || m.EndDate == nil || !m.EndDate.After(*m.StartDate) {
			return fmt.Errorf("single maintenance requires end_date after start_date")
		}
		m.DurationSec = int(m.EndDate.Sub(*m.StartDate).Seconds())
		return nil
	case MaintenanceRecurringInterval:
		if m.DurationSec <= 0 || m.IntervalDay <= 0 || (m.IntervalDay > 1 && m.StartDate == nil) {
			return fmt.Errorf("recurring interval requires positive duration_sec and interval_day; intervals over one day require start_date")
		}
		if _, _, err := parseMaintenanceTime(m.StartTime); err != nil {
			return err
		}
		m.Cron = ""
		return nil
	case MaintenanceCron, MaintenanceRecurringWeekday, MaintenanceRecurringDayOfMonth:
		if m.DurationSec <= 0 {
			return fmt.Errorf("duration_sec must be positive")
		}
		cronText, err := m.generatedCron()
		if err != nil {
			return err
		}
		if _, err := cron.ParseStandard(cronText); err != nil {
			return fmt.Errorf("invalid cron: %w", err)
		}
		m.Cron = cronText
		return nil
	default:
		return fmt.Errorf("unknown maintenance strategy %q", m.Strategy)
	}
}

func (m *Maintenance) BeforeSave(_ *gorm.DB) error { return m.Validate() }

// IsUnderMaintenance evaluates durable data only. This intentionally avoids
// scheduler-owned state so a process restart and multiple web pods agree.
func (m *Maintenance) IsUnderMaintenance(now time.Time) bool {
	if !m.Active {
		return false
	}
	if m.Strategy == MaintenanceManual {
		return true
	}
	if m.Strategy == MaintenanceSingle {
		return m.StartDate != nil && m.EndDate != nil && !now.Before(*m.StartDate) && now.Before(*m.EndDate)
	}
	if m.Strategy == MaintenanceRecurringInterval {
		return m.isUnderInterval(now)
	}
	if m.DurationSec <= 0 {
		return false
	}
	loc, err := m.location()
	if err != nil {
		return false
	}
	schedule, err := cron.ParseStandard(m.Cron)
	if err != nil {
		return false
	}
	// Ask cron for each candidate since the earliest possible active start.
	// Cron is minute-granular, hence the extra minute catches exact boundaries.
	from := now.In(loc).Add(-time.Duration(m.DurationSec)*time.Second - time.Minute)
	to := now.In(loc)
	for candidate := schedule.Next(from); !candidate.After(to); candidate = schedule.Next(candidate) {
		if !m.allowsRecurringCandidate(candidate.In(loc)) {
			continue
		}
		start := candidate.UTC()
		if !now.Before(start) && now.Before(start.Add(time.Duration(m.DurationSec)*time.Second)) {
			return true
		}
	}
	return false
}

func parseMaintenanceTime(value string) (int, int, error) {
	parsed, err := time.Parse("15:04", value)
	if err != nil {
		return 0, 0, fmt.Errorf("start_time must be HH:MM")
	}
	return parsed.Hour(), parsed.Minute(), nil
}

func (m *Maintenance) intervalStartOn(date time.Time, loc *time.Location) (time.Time, bool) {
	if m.IntervalDay <= 0 {
		return time.Time{}, false
	}
	hour, minute, err := parseMaintenanceTime(m.StartTime)
	if err != nil {
		return time.Time{}, false
	}
	if m.IntervalDay == 1 && m.StartDate == nil {
		return time.Date(date.Year(), date.Month(), date.Day(), hour, minute, 0, 0, loc), true
	}
	if m.StartDate == nil {
		return time.Time{}, false
	}
	anchor := m.StartDate.In(loc)
	anchorDay := time.Date(anchor.Year(), anchor.Month(), anchor.Day(), 0, 0, 0, 0, loc)
	candidateDay := time.Date(date.Year(), date.Month(), date.Day(), 0, 0, 0, 0, loc)
	// Compare civil dates rather than elapsed hours: a local day can be 23 or
	// 25 hours when the maintenance timezone crosses a DST boundary.
	days := civilDaysBetween(anchorDay, candidateDay)
	if days < 0 || days%m.IntervalDay != 0 {
		return time.Time{}, false
	}
	return time.Date(date.Year(), date.Month(), date.Day(), hour, minute, 0, 0, loc), true
}

func civilDaysBetween(from, to time.Time) int {
	fromDay := time.Date(from.Year(), from.Month(), from.Day(), 0, 0, 0, 0, time.UTC)
	toDay := time.Date(to.Year(), to.Month(), to.Day(), 0, 0, 0, 0, time.UTC)
	return int(toDay.Sub(fromDay) / (24 * time.Hour))
}

func (m *Maintenance) isUnderInterval(now time.Time) bool {
	loc, err := m.location()
	if err != nil || m.DurationSec <= 0 {
		return false
	}
	localNow := now.In(loc)
	for day := 0; day <= int(time.Duration(m.DurationSec)/24/time.Hour)+1; day++ {
		start, ok := m.intervalStartOn(localNow.AddDate(0, 0, -day), loc)
		if ok && !now.Before(start.UTC()) && now.Before(start.UTC().Add(time.Duration(m.DurationSec)*time.Second)) {
			return true
		}
	}
	return false
}

// robfig/cron cannot express "last day". The generated 28-31 range is only
// a candidate generator; this final predicate makes lastDay1 exact.
func (m *Maintenance) allowsRecurringCandidate(candidate time.Time) bool {
	if m.Strategy != MaintenanceRecurringDayOfMonth {
		return true
	}
	lastDay := candidate.AddDate(0, 0, 1).Month() != candidate.Month()
	for _, value := range m.DaysOfMonth {
		if value == "lastDay1" && lastDay {
			return true
		}
		if value == fmt.Sprint(candidate.Day()) {
			return true
		}
	}
	return false
}

func (m *Maintenance) NextRun(now time.Time) *time.Time {
	if !m.Active || m.Strategy == MaintenanceManual {
		return nil
	}
	if m.Strategy == MaintenanceSingle {
		if m.StartDate != nil && m.StartDate.After(now) {
			return m.StartDate
		}
		return nil
	}
	if m.Strategy == MaintenanceRecurringInterval {
		loc, err := m.location()
		if err != nil {
			return nil
		}
		localNow := now.In(loc)
		for day := 0; day <= m.IntervalDay; day++ {
			if next, ok := m.intervalStartOn(localNow.AddDate(0, 0, day), loc); ok && next.After(localNow) {
				result := next.UTC()
				return &result
			}
		}
		return nil
	}
	loc, err := m.location()
	if err != nil {
		return nil
	}
	s, err := cron.ParseStandard(m.Cron)
	if err != nil {
		return nil
	}
	for candidate := s.Next(now.In(loc)); ; candidate = s.Next(candidate) {
		if m.allowsRecurringCandidate(candidate.In(loc)) {
			next := candidate.UTC()
			return &next
		}
	}
}

// MonitorUnderMaintenance is the notifier/public-page lookup.
func MonitorUnderMaintenance(monitorID int64, now time.Time) (bool, error) {
	var rows []Maintenance
	err := DB().Joins("JOIN maintenance_monitors mm ON mm.maintenance_id = maintenances.id").Where("mm.monitor_id = ? AND maintenances.active = TRUE", monitorID).Find(&rows).Error
	if err != nil {
		return false, err
	}
	for i := range rows {
		if rows[i].IsUnderMaintenance(now) {
			return true, nil
		}
	}
	return false, nil
}