// Package agent implements a lightweight Tyto agent that collects metrics
// and reports them to a central server via gRPC.
package agent

import (
	"context"
	"encoding/json"
	"log"
	"sync"
	"time"

	"tyto/internal/collectors"
	"tyto/internal/collectors/gpu"
	"tyto/internal/config"
	"tyto/internal/models"
	pb "tyto/internal/proto"
)

// Agent collects metrics and reports to a central server.
type Agent struct {
	config *config.Config
	client *Client

	// Collectors
	system      *collectors.SystemCollector
	cpu         *collectors.CPUCollector
	memory      *collectors.MemoryCollector
	disk        *collectors.DiskCollector
	network     *collectors.NetworkCollector
	process     *collectors.ProcessCollector
	temperature *collectors.TemperatureCollector
	gpuManager  *gpu.Manager
	docker      *collectors.DockerCollector
	systemd     *collectors.SystemdCollector

	// Pooling for memory efficiency
	metricsPool sync.Pool

	// Control
	stopCh chan struct{}
	wg     sync.WaitGroup
}

// New creates a new agent with the given configuration.
func New(cfg *config.Config) *Agent {
	a := &Agent{
		config: cfg,
		stopCh: make(chan struct{}),
		metricsPool: sync.Pool{
			New: func() interface{} {
				return &models.AllMetrics{}
			},
		},
	}

	// Initialize collectors
	a.initCollectors()

	return a
}

func (a *Agent) initCollectors() {
	cfg := a.config

	a.system = collectors.NewSystemCollector(cfg.ProcPath)
	a.cpu = collectors.NewCPUCollector(cfg.ProcPath, cfg.SysPath)
	a.memory = collectors.NewMemoryCollector(cfg.ProcPath)
	a.disk = collectors.NewDiskCollector(cfg.ProcPath, cfg.MtabPath)
	a.network = collectors.NewNetworkCollector(cfg.ProcPath)
	a.process = collectors.NewProcessCollector(cfg.ProcPath)
	a.temperature = collectors.NewTemperatureCollector(cfg.SysPath)
	a.gpuManager = gpu.NewManager(cfg.SysPath)
	a.docker = collectors.NewDockerCollector(cfg.DockerSock)
	a.systemd = collectors.NewSystemdCollector()
}

// Run starts the agent's main loop.
func (a *Agent) Run(ctx context.Context) error {
	log.Printf("Agent %s starting...", a.config.Agent.ID)

	// Create gRPC client
	client, err := NewClient(a.config)
	if err != nil {
		return err
	}
	a.client = client

	// Set up reconnection callback to re-register
	a.client.SetOnReconnect(func() {
		log.Println("Reconnected to server, re-registering...")
		if err := a.register(context.Background()); err != nil {
			log.Printf("Re-registration failed: %v", err)
		}
	})

	// Connect to server with retry
	if err := a.client.ConnectWithRetry(ctx); err != nil {
		return err
	}
	defer a.client.Close()

	// Register with server
	if err := a.register(ctx); err != nil {
		log.Printf("Registration failed: %v", err)
		// Continue anyway, server might accept unregistered agents
	}

	// Start collection loop
	return a.runLoop(ctx)
}

func (a *Agent) register(ctx context.Context) error {
	info := a.collectAgentInfo()
	return a.client.Register(ctx, info)
}

func (a *Agent) collectAgentInfo() *pb.AgentInfo {
	sysInfo, _ := a.system.Collect()

	capabilities := []string{}
	if a.gpuManager.Available() {
		capabilities = append(capabilities, "gpu")
	}
	// Check docker availability
	if dockerStats, err := a.docker.Collect(); err == nil && dockerStats.Available {
		capabilities = append(capabilities, "docker")
	}
	// Check systemd availability
	if systemdStats, err := a.systemd.Collect(); err == nil && systemdStats.Available {
		capabilities = append(capabilities, "systemd")
	}

	return &pb.AgentInfo{
		AgentId:      a.config.Agent.ID,
		Hostname:     sysInfo.Hostname,
		Os:           sysInfo.OS,
		Architecture: sysInfo.Architecture,
		Version:      "1.0.0", // TODO: Use build version
		Capabilities: capabilities,
	}
}

func (a *Agent) runLoop(ctx context.Context) error {
	ticker := time.NewTicker(a.config.Agent.Interval)
	defer ticker.Stop()

	log.Printf("Starting collection loop (interval: %s)", a.config.Agent.Interval)

	for {
		select {
		case <-ctx.Done():
			log.Println("Agent stopping (context cancelled)")
			return ctx.Err()

		case <-a.stopCh:
			log.Println("Agent stopping (stop signal)")
			return nil

		case <-ticker.C:
			if err := a.collectAndSend(ctx); err != nil {
				log.Printf("Collection/send error: %v", err)
				// Don't return, keep trying
			}
		}
	}
}

func (a *Agent) collectAndSend(ctx context.Context) error {
	// Get metrics struct from pool
	metrics := a.metricsPool.Get().(*models.AllMetrics)
	defer a.metricsPool.Put(metrics)

	// Reset metrics
	*metrics = models.AllMetrics{
		Timestamp: time.Now(),
	}

	// Collect all metrics
	a.collect(metrics)

	// Send to server
	err := a.client.SendMetrics(ctx, a.config.Agent.ID, metrics)
	if err != nil {
		// Check if we need to reconnect
		if !a.client.IsConnected() {
			log.Println("Connection lost, attempting reconnection...")
			a.wg.Add(1)
			go func() {
				defer a.wg.Done()
				if reconnErr := a.client.Reconnect(ctx); reconnErr != nil {
					log.Printf("Reconnection failed: %v", reconnErr)
				}
			}()
		}
		return err
	}

	return nil
}

func (a *Agent) collect(m *models.AllMetrics) {
	// System info
	if sys, err := a.system.Collect(); err == nil {
		m.System = sys
	}

	// CPU
	if cpu, err := a.cpu.Collect(); err == nil {
		m.CPU = cpu
	}

	// Memory
	if mem, err := a.memory.Collect(); err == nil {
		m.Memory = mem
	}

	// Disk
	if disk, err := a.disk.Collect(); err == nil {
		m.Disk = disk
	}

	// Network
	if net, err := a.network.Collect(); err == nil {
		m.Network = net
	}

	// Processes
	if proc, err := a.process.Collect(); err == nil {
		m.Processes = proc
	}

	// Temperature
	if temp, err := a.temperature.Collect(); err == nil {
		m.Temperature = temp
	}

	// GPU
	if gpuStats, err := a.gpuManager.Collect(); err == nil {
		m.GPU = models.AMDGPUStatsFromGPUInfo(gpuStats)
	}

	// Docker
	if docker, err := a.docker.Collect(); err == nil {
		m.Docker = docker
	}

	// Systemd
	if systemd, err := a.systemd.Collect(); err == nil {
		m.Systemd = systemd
	}
}

// Stop signals the agent to stop and waits for cleanup.
func (a *Agent) Stop() {
	close(a.stopCh)
	a.wg.Wait()
}

// SerializeMetrics converts metrics to JSON bytes.
func SerializeMetrics(m *models.AllMetrics) ([]byte, error) {
	return json.Marshal(m)
}