package memory

import (
	"runtime"
	"sync"
	"sync/atomic"
	"time"
)

// MemoryMonitor tracks system memory usage and provides dynamic sizing recommendations
type MemoryMonitor struct {
	targetMemoryUsage   uint64 // Target total memory usage in bytes
	currentMemoryUsage  uint64 // Current total memory usage in bytes
	monitoringInterval  time.Duration
	adjustmentThreshold float64 // Threshold for cache size adjustments (e.g., 0.1 = 10%)
	mu                  sync.RWMutex
	ctx                 chan struct{}
	stopChan            chan struct{}
	isMonitoring        int32
}

// NewMemoryMonitor creates a new memory monitor
func NewMemoryMonitor(targetMemoryUsage uint64, monitoringInterval time.Duration, adjustmentThreshold float64) *MemoryMonitor {
	return &MemoryMonitor{
		targetMemoryUsage:   targetMemoryUsage,
		monitoringInterval:  monitoringInterval,
		adjustmentThreshold: adjustmentThreshold,
		ctx:                 make(chan struct{}),
		stopChan:            make(chan struct{}),
	}
}

// Start begins monitoring memory usage
func (mm *MemoryMonitor) Start() {
	if atomic.CompareAndSwapInt32(&mm.isMonitoring, 0, 1) {
		go mm.monitor()
	}
}

// Stop stops monitoring memory usage
func (mm *MemoryMonitor) Stop() {
	if atomic.CompareAndSwapInt32(&mm.isMonitoring, 1, 0) {
		close(mm.stopChan)
	}
}

// GetCurrentMemoryUsage returns the current total memory usage
func (mm *MemoryMonitor) GetCurrentMemoryUsage() uint64 {
	mm.mu.RLock()
	defer mm.mu.RUnlock()
	return atomic.LoadUint64(&mm.currentMemoryUsage)
}

// GetTargetMemoryUsage returns the target memory usage
func (mm *MemoryMonitor) GetTargetMemoryUsage() uint64 {
	mm.mu.RLock()
	defer mm.mu.RUnlock()
	return mm.targetMemoryUsage
}

// GetMemoryUtilization returns the current memory utilization as a percentage
func (mm *MemoryMonitor) GetMemoryUtilization() float64 {
	mm.mu.RLock()
	defer mm.mu.RUnlock()
	current := atomic.LoadUint64(&mm.currentMemoryUsage)
	return float64(current) / float64(mm.targetMemoryUsage)
}

// GetRecommendedCacheSize calculates the recommended cache size based on current memory usage
func (mm *MemoryMonitor) GetRecommendedCacheSize(originalCacheSize uint64) uint64 {
	mm.mu.RLock()
	defer mm.mu.RUnlock()

	current := atomic.LoadUint64(&mm.currentMemoryUsage)
	target := mm.targetMemoryUsage

	// If we're under target, we can use the full cache size
	if current <= target {
		return originalCacheSize
	}

	// Calculate how much we're over target
	overage := current - target

	// If overage is significant, reduce cache size
	if overage > uint64(float64(target)*mm.adjustmentThreshold) {
		// Reduce cache size by the overage amount, but don't go below 10% of original
		minCacheSize := uint64(float64(originalCacheSize) * 0.1)
		recommendedSize := originalCacheSize - overage

		if recommendedSize < minCacheSize {
			recommendedSize = minCacheSize
		}

		return recommendedSize
	}

	return originalCacheSize
}

// monitor runs the memory monitoring loop
func (mm *MemoryMonitor) monitor() {
	ticker := time.NewTicker(mm.monitoringInterval)
	defer ticker.Stop()

	for {
		select {
		case <-mm.stopChan:
			return
		case <-ticker.C:
			mm.updateMemoryUsage()
		}
	}
}

// updateMemoryUsage updates the current memory usage
func (mm *MemoryMonitor) updateMemoryUsage() {
	var m runtime.MemStats
	runtime.ReadMemStats(&m)

	// Use Alloc (currently allocated memory) as our metric
	atomic.StoreUint64(&mm.currentMemoryUsage, m.Alloc)
}

// SetTargetMemoryUsage updates the target memory usage
func (mm *MemoryMonitor) SetTargetMemoryUsage(target uint64) {
	mm.mu.Lock()
	defer mm.mu.Unlock()
	mm.targetMemoryUsage = target
}

// GetMemoryStats returns detailed memory statistics
func (mm *MemoryMonitor) GetMemoryStats() map[string]interface{} {
	var m runtime.MemStats
	runtime.ReadMemStats(&m)

	mm.mu.RLock()
	defer mm.mu.RUnlock()

	return map[string]interface{}{
		"current_usage":  atomic.LoadUint64(&mm.currentMemoryUsage),
		"target_usage":   mm.targetMemoryUsage,
		"utilization":    mm.GetMemoryUtilization(),
		"heap_alloc":     m.HeapAlloc,
		"heap_sys":       m.HeapSys,
		"heap_idle":      m.HeapIdle,
		"heap_inuse":     m.HeapInuse,
		"stack_inuse":    m.StackInuse,
		"stack_sys":      m.StackSys,
		"gc_cycles":      m.NumGC,
		"gc_pause_total": m.PauseTotalNs,
	}
}