package main

import (
	"database/sql"
	"fmt"
	"sync"
	"time"
)

type TripState struct {
	StartDate            string         `json:"start_date"`              // YYYY-MM-DD
	StartTime            time.Time      `json:"start_time"`              // Exact start time
	StartDayInitialSteps int            `json:"start_day_initial_steps"` // Steps on the tracker when trip started
	DailyCache           map[string]int `json:"daily_cache"`             // Cache of steps for past days
}

type StepManager struct {
	mu        sync.Mutex
	userID    string // Fitbit user ID
	tripState TripState

	// Smoothing State
	previousTotalSteps int // What we last told the client (or where we started smoothing from)
	targetTotalSteps   int // The actual total steps we just fetched/calculated
	lastSyncTime       time.Time
	nextSyncTime       time.Time
	syncInterval       time.Duration
}

func NewStepManager(userID string) *StepManager {
	now := time.Now()
	sm := &StepManager{
		userID:       userID,
		syncInterval: 15 * time.Minute,
		lastSyncTime: now.Add(-15 * time.Minute),
		nextSyncTime: now.Add(24 * time.Hour), // Don't sync unless a trip is started or loaded
	}
	sm.LoadTripState()
	return sm
}

func (sm *StepManager) LoadTripState() error {
	sm.mu.Lock()
	defer sm.mu.Unlock()
	return sm.loadTripStateLocked()
}

func (sm *StepManager) loadTripStateLocked() error {
	var startTime time.Time
	err := db.QueryRow(`
		SELECT start_date, start_time, start_day_initial_steps, previous_total_steps, target_total_steps, last_sync_time, next_sync_time
		FROM trips WHERE user_id = ?
	`, sm.userID).Scan(
		&sm.tripState.StartDate, &startTime, &sm.tripState.StartDayInitialSteps,
		&sm.previousTotalSteps, &sm.targetTotalSteps, &sm.lastSyncTime, &sm.nextSyncTime,
	)
	if err != nil {
		if err == sql.ErrNoRows {
			// Initialize with defaults if no trip exists
			now := time.Now()
			sm.tripState.StartDate = "" // No active trip
			sm.nextSyncTime = now.Add(24 * time.Hour)
			return nil
		}
		return err
	}
	sm.tripState.StartTime = startTime

	// Load daily cache from DB
	rows, err := db.Query("SELECT date, steps FROM daily_steps WHERE user_id = ?", sm.userID)
	if err != nil {
		return err
	}
	defer rows.Close()

	sm.tripState.DailyCache = make(map[string]int)
	for rows.Next() {
		var date string
		var steps int
		if err := rows.Scan(&date, &steps); err != nil {
			return err
		}
		sm.tripState.DailyCache[date] = steps
	}

	return nil
}

func (sm *StepManager) SaveTripState() {
	sm.mu.Lock()
	defer sm.mu.Unlock()
	sm.saveTripStateLocked()
}

func (sm *StepManager) saveTripStateLocked() {
	_, err := db.Exec(`
		INSERT INTO trips (user_id, start_date, start_time, start_day_initial_steps, previous_total_steps, target_total_steps, last_sync_time, next_sync_time)
		VALUES (?, ?, ?, ?, ?, ?, ?, ?)
		ON DUPLICATE KEY UPDATE
			start_date = VALUES(start_date),
			start_time = VALUES(start_time),
			start_day_initial_steps = VALUES(start_day_initial_steps),
			previous_total_steps = VALUES(previous_total_steps),
			target_total_steps = VALUES(target_total_steps),
			last_sync_time = VALUES(last_sync_time),
			next_sync_time = VALUES(next_sync_time)
	`, sm.userID, sm.tripState.StartDate, sm.tripState.StartTime, sm.tripState.StartDayInitialSteps,
		sm.previousTotalSteps, sm.targetTotalSteps, sm.lastSyncTime, sm.nextSyncTime)
	if err != nil {
		fmt.Printf("Error saving trip state: %v\n", err)
	}

	// Save daily cache
	for date, steps := range sm.tripState.DailyCache {
		_, err := db.Exec(`
			INSERT INTO daily_steps (user_id, date, steps)
			VALUES (?, ?, ?)
			ON DUPLICATE KEY UPDATE steps = VALUES(steps)
		`, sm.userID, date, steps)
		if err != nil {
			fmt.Printf("Error saving daily steps for %s: %v\n", date, err)
		}
	}
}

func (sm *StepManager) StartNewTrip() {
	sm.mu.Lock()
	defer sm.mu.Unlock()
	now := time.Now()
	initialSteps, err := GetDailySteps(sm.userID, now.Format("2006-01-02"))
	if err != nil {
		initialSteps = 0
		fmt.Printf("Error fetching initial steps: %v\n", err)
	}
	sm.tripState = TripState{
		StartDate:            now.Format("2006-01-02"),
		StartTime:            now,
		StartDayInitialSteps: initialSteps,
		DailyCache:           make(map[string]int),
	}
	// On new trip, previous total is 0
	sm.previousTotalSteps = 0
	sm.targetTotalSteps = 0
	sm.saveTripStateLocked()

	// Trigger immediate sync to set baseline
	go sm.Sync()
}

// Sync fetches data for all days in the trip using the default interval
func (sm *StepManager) Sync() {
	sm.performSync(sm.syncInterval)
}

// Drain fetches data and sets a short sync interval to fast-forward interpolation
func (sm *StepManager) Drain() {
	sm.performSync(30 * time.Second)
}

// performSync implementation
func (sm *StepManager) performSync(interval time.Duration) {
	sm.mu.Lock()
	tripStateCopy := sm.tripState
	// Deep copy the map to avoid data races during async network calls
	newDailyCache := make(map[string]int)
	for k, v := range tripStateCopy.DailyCache {
		newDailyCache[k] = v
	}
	sm.mu.Unlock()

	totalSteps := 0
	today := time.Now().Format("2006-01-02")

	// Parse start date in local time
	if tripStateCopy.StartDate == "" {
		fmt.Println("[StepManager] Skipping sync: No active trip start date")
		sm.mu.Lock()
		sm.nextSyncTime = time.Now().Add(1 * time.Hour) // Check again in an hour
		sm.mu.Unlock()
		return
	}

	start, err := time.ParseInLocation("2006-01-02", tripStateCopy.StartDate, time.Local)
	if err != nil {
		fmt.Printf("[StepManager] ERROR: Invalid start date '%s': %v\n", tripStateCopy.StartDate, err)
		return
	}
	end, _ := time.ParseInLocation("2006-01-02", today, time.Local)

	// Iterate from Start Date to Today
	for d := start; !d.After(end); d = d.AddDate(0, 0, 1) {
		dateStr := d.Format("2006-01-02")

		var steps int
		var err error

		// Check cache first for past days
		// For today, we always fetch.
		// Ideally we might trust cache for past days, but re-checking isn't bad if we want to catch up.
		// The current logic trusts cache for past days.
		shouldFetch := (dateStr == today)
		if !shouldFetch {
			if cached, ok := newDailyCache[dateStr]; ok {
				steps = cached
			} else {
				shouldFetch = true
			}
		}

		if shouldFetch {
			steps, err = GetDailySteps(sm.userID, dateStr)
			if err != nil {
				fmt.Printf("Error fetching steps for %s: %v\n", dateStr, err)
				return // Don't proceed with sync if fetch fails
			}
			// Update the local cache
			newDailyCache[dateStr] = steps
		}

		// Calculate contribution to total
		if dateStr == tripStateCopy.StartDate {
			// Substract the steps that were already there when we started
			contribution := steps - tripStateCopy.StartDayInitialSteps
			if contribution < 0 {
				contribution = 0
			}
			totalSteps += contribution
		} else {
			totalSteps += steps
		}
	}

	sm.mu.Lock()
	defer sm.mu.Unlock()

	// Update State
	sm.tripState.DailyCache = newDailyCache
	sm.saveTripStateLocked()

	// Update Smoothing Targets
	sm.previousTotalSteps = sm.calculateSmoothedTokenAt(time.Now()) // Snapshot current interpolated value as new start
	sm.targetTotalSteps = totalSteps

	sm.lastSyncTime = time.Now()
	sm.nextSyncTime = time.Now().Add(interval)

	fmt.Printf("Sync Complete. Total Trip Steps: %d\n", sm.targetTotalSteps)
}

// calculateSmoothedTokenAt returns the interpolated step count at a given time
func (sm *StepManager) calculateSmoothedTokenAt(t time.Time) int {
	totalDuration := sm.nextSyncTime.Sub(sm.lastSyncTime)
	elapsed := t.Sub(sm.lastSyncTime)

	if totalDuration <= 0 {
		return sm.targetTotalSteps
	}

	progress := float64(elapsed) / float64(totalDuration)
	if progress < 0 {
		progress = 0
	}
	if progress > 1 {
		progress = 1
	}

	// Linear interpolation from Previous -> Target
	delta := sm.targetTotalSteps - sm.previousTotalSteps
	return sm.previousTotalSteps + int(float64(delta)*progress)
}

func (sm *StepManager) GetStatus() map[string]interface{} {
	// Reload from DB to get latest sync results from other instances
	sm.LoadTripState()

	sm.mu.Lock()
	shouldSync := time.Now().After(sm.nextSyncTime)
	nextSyncMilli := sm.nextSyncTime.UnixMilli()
	currentSmoothed := sm.calculateSmoothedTokenAt(time.Now())
	sm.mu.Unlock()

	// Auto-trigger sync if needed (out of initial lock to avoid deadlock)
	if shouldSync {
		go sm.Sync() // Async sync
	}

	return map[string]interface{}{
		"tripSteps":    currentSmoothed,
		"nextSyncTime": nextSyncMilli,
	}
}

// RecalculateTotalFromState sums up the steps from the DailyCache without making external API calls
func (sm *StepManager) RecalculateTotalFromState() int {
	total := 0
	for dateStr, steps := range sm.tripState.DailyCache {
		// YYYY-MM-DD string comparison works for chronological order
		if dateStr < sm.tripState.StartDate {
			continue
		}

		if dateStr == sm.tripState.StartDate {
			contribution := steps - sm.tripState.StartDayInitialSteps
			if contribution < 0 {
				contribution = 0
			}
			total += contribution
		} else {
			total += steps
		}
	}
	return total
}