package systemmetrics

import (
	"context"
	"math"
	"os"
	"path/filepath"
	"strconv"
	"strings"
	"sync"
	"time"

	"tera-clone/services/tera-api/internal/domain"
)

type Reader interface {
	Read(context.Context, []domain.NetworkInterface) domain.SystemRuntimeMetrics
}

type UnavailableReader struct{}

func (UnavailableReader) Read(context.Context, []domain.NetworkInterface) domain.SystemRuntimeMetrics {
	return domain.SystemRuntimeMetrics{}
}

type LinuxReaderOptions struct {
	ProcRoot      string
	SysRoot       string
	EtcRoot       string
	Clock         func() time.Time
	StoragePath   string
	StorageReader func(string) (*domain.StorageMetrics, error)
}

type LinuxReader struct {
	procRoot      string
	sysRoot       string
	etcRoot       string
	clock         func() time.Time
	mu            sync.Mutex
	previous      cpuCounters
	storagePath   string
	storageReader func(string) (*domain.StorageMetrics, error)
}

type cpuCounters struct {
	total uint64
	idle  uint64
	valid bool
}

func NewLinuxReader(options LinuxReaderOptions) *LinuxReader {
	procRoot := options.ProcRoot
	if procRoot == "" {
		procRoot = "/proc"
	}
	sysRoot := options.SysRoot
	if sysRoot == "" {
		sysRoot = "/sys"
	}
	etcRoot := options.EtcRoot
	if etcRoot == "" {
		etcRoot = "/etc"
	}
	clock := options.Clock
	if clock == nil {
		clock = time.Now
	}
	storagePath := options.StoragePath
	if storagePath == "" {
		storagePath = "/userdata"
	}
	storageReader := options.StorageReader
	if storageReader == nil {
		storageReader = readStorage
	}
	return &LinuxReader{procRoot: procRoot, sysRoot: sysRoot, etcRoot: etcRoot, clock: clock, storagePath: storagePath, storageReader: storageReader}
}

func (r *LinuxReader) Read(ctx context.Context, interfaces []domain.NetworkInterface) domain.SystemRuntimeMetrics {
	metrics := domain.SystemRuntimeMetrics{SystemTime: r.clock().UTC(), LoadAverages: []float64{}, NetworkInterfaces: []domain.SystemNetworkInterface{}}
	if ctx.Err() != nil {
		return metrics
	}
	metrics.BuildNumber = firstNonEmptyFile(filepath.Join(r.etcRoot, "tera", "build-number"), filepath.Join(r.etcRoot, "tera-release"))
	metrics.DeviceID = firstNonEmptyFile(filepath.Join(r.etcRoot, "machine-id"))
	metrics.UptimeSeconds = readUptime(filepath.Join(r.procRoot, "uptime"))
	metrics.LoadAverages = readLoadAverages(filepath.Join(r.procRoot, "loadavg"))
	metrics.TemperatureCelsius = readTemperature(r.sysRoot)
	metrics.CPUUsagePercent = r.readCPUUsage(filepath.Join(r.procRoot, "stat"))
	metrics.MemoryTotalBytes, metrics.MemoryAvailableBytes, metrics.MemoryUsedBytes, metrics.MemoryUsagePercent = readMemory(filepath.Join(r.procRoot, "meminfo"))
	if storage, err := r.storageReader(r.storagePath); err == nil {
		metrics.Storage = storage
	}
	for _, item := range interfaces {
		if ctx.Err() != nil {
			break
		}
		metrics.NetworkInterfaces = append(metrics.NetworkInterfaces, r.readInterface(item))
	}
	return metrics
}

func (r *LinuxReader) readInterface(item domain.NetworkInterface) domain.SystemNetworkInterface {
	result := domain.SystemNetworkInterface{Name: item.Name, Device: item.Device, Link: strings.ToLower(strings.TrimSpace(item.Link)), Addresses: []string{}}
	if item.Address != "" {
		result.Addresses = append(result.Addresses, item.Address)
	}
	if item.IPv6Address != "" {
		result.Addresses = append(result.Addresses, item.IPv6Address)
	}
	if !validDeviceName(item.Device) {
		return result
	}
	root := filepath.Join(r.sysRoot, "class", "net", item.Device)
	result.MACAddress = readTrimmed(filepath.Join(root, "address"))
	if link := readTrimmed(filepath.Join(root, "operstate")); link != "" {
		result.Link = strings.ToLower(link)
	}
	if speed, err := strconv.Atoi(readTrimmed(filepath.Join(root, "speed"))); err == nil && speed > 0 {
		result.SpeedMbps = speed
	}
	result.RXBytes = readUint(filepath.Join(root, "statistics", "rx_bytes"))
	result.TXBytes = readUint(filepath.Join(root, "statistics", "tx_bytes"))
	return result
}

func (r *LinuxReader) readCPUUsage(path string) *float64 {
	content, err := os.ReadFile(path)
	if err != nil {
		return nil
	}
	line := strings.SplitN(string(content), "\n", 2)[0]
	fields := strings.Fields(line)
	if len(fields) < 5 || fields[0] != "cpu" {
		return nil
	}
	values := make([]uint64, 0, len(fields)-1)
	for _, field := range fields[1:] {
		value, err := strconv.ParseUint(field, 10, 64)
		if err != nil {
			return nil
		}
		values = append(values, value)
	}
	var total uint64
	for _, value := range values {
		total += value
	}
	idle := values[3]
	if len(values) > 4 {
		idle += values[4]
	}
	r.mu.Lock()
	previous := r.previous
	r.previous = cpuCounters{total: total, idle: idle, valid: true}
	r.mu.Unlock()
	if !previous.valid || total <= previous.total {
		return nil
	}
	deltaTotal := total - previous.total
	deltaIdle := idle - previous.idle
	value := 100 * (1 - float64(deltaIdle)/float64(deltaTotal))
	value = math.Round(math.Max(0, math.Min(100, value))*10) / 10
	return &value
}

func readUptime(path string) int64 {
	fields := strings.Fields(readTrimmed(path))
	if len(fields) == 0 {
		return 0
	}
	value, err := strconv.ParseFloat(fields[0], 64)
	if err != nil || value < 0 {
		return 0
	}
	return int64(value)
}

func readLoadAverages(path string) []float64 {
	fields := strings.Fields(readTrimmed(path))
	if len(fields) < 3 {
		return []float64{}
	}
	result := make([]float64, 0, 3)
	for _, field := range fields[:3] {
		value, err := strconv.ParseFloat(field, 64)
		if err != nil {
			return []float64{}
		}
		result = append(result, value)
	}
	return result
}

func readTemperature(sysRoot string) *float64 {
	paths, _ := filepath.Glob(filepath.Join(sysRoot, "class", "thermal", "thermal_zone*", "temp"))
	for _, path := range paths {
		value, err := strconv.ParseFloat(readTrimmed(path), 64)
		if err != nil {
			continue
		}
		if math.Abs(value) > 1000 {
			value /= 1000
		}
		if value >= -50 && value <= 200 {
			return &value
		}
	}
	return nil
}

func readMemory(path string) (totalBytes, availableBytes, usedBytes uint64, usagePercent *float64) {
	values := make(map[string]uint64)
	for _, line := range strings.Split(readTrimmed(path), "\n") {
		fields := strings.Fields(line)
		if len(fields) < 2 {
			continue
		}
		key := strings.TrimSuffix(fields[0], ":")
		value, err := strconv.ParseUint(fields[1], 10, 64)
		if err != nil {
			continue
		}
		if len(fields) >= 3 && !strings.EqualFold(fields[2], "kB") {
			continue
		}
		if value > ^uint64(0)/1024 {
			continue
		}
		values[key] = value * 1024
	}

	totalBytes = values["MemTotal"]
	if totalBytes == 0 {
		return 0, 0, 0, nil
	}
	var availableKnown bool
	availableBytes, availableKnown = values["MemAvailable"]
	if !availableKnown {
		availableBytes = values["MemFree"] + values["Buffers"] + values["Cached"] + values["SReclaimable"]
		if shmem := values["Shmem"]; shmem < availableBytes {
			availableBytes -= shmem
		}
	}
	if availableBytes > totalBytes {
		availableBytes = totalBytes
	}
	usedBytes = totalBytes - availableBytes
	percent := math.Round((float64(usedBytes)/float64(totalBytes))*1000) / 10
	return totalBytes, availableBytes, usedBytes, &percent
}

func firstNonEmptyFile(paths ...string) string {
	for _, path := range paths {
		if value := readTrimmed(path); value != "" {
			if newline := strings.IndexByte(value, '\n'); newline >= 0 {
				value = strings.TrimSpace(value[:newline])
			}
			if len(value) > 128 {
				value = value[:128]
			}
			return value
		}
	}
	return ""
}

func readTrimmed(path string) string {
	content, err := os.ReadFile(path)
	if err != nil || len(content) > 4096 {
		return ""
	}
	return strings.TrimSpace(strings.ToValidUTF8(string(content), ""))
}

func readUint(path string) uint64 {
	value, _ := strconv.ParseUint(readTrimmed(path), 10, 64)
	return value
}

func validDeviceName(value string) bool {
	if value == "" || len(value) > 32 {
		return false
	}
	for _, char := range value {
		if (char >= 'a' && char <= 'z') || (char >= 'A' && char <= 'Z') || (char >= '0' && char <= '9') || char == '-' || char == '_' || char == '.' {
			continue
		}
		return false
	}
	return true
}