package protocol

import (
	"bufio"
	"os"
	"runtime"
	"strconv"
	"strings"
	"sync"
)

var cpuSampleMu sync.Mutex
var previousCPUSample struct{ total, idle uint64 }

// CollectTelemetry reads Linux host utilization without adding a platform-specific dependency.
func CollectTelemetry() WorkerTelemetry {
	var result WorkerTelemetry
	if runtime.GOOS != "linux" {
		return result
	}
	if data, err := os.ReadFile("/proc/stat"); err == nil {
		fields := strings.Fields(strings.SplitN(string(data), "\n", 2)[0])
		if len(fields) >= 5 {
			var total, idle uint64
			for index, field := range fields[1:] {
				value, parseErr := strconv.ParseUint(field, 10, 64)
				if parseErr != nil {
					break
				}
				total += value
				if index == 3 || index == 4 {
					idle += value
				}
			}
			cpuSampleMu.Lock()
			if previousCPUSample.total > 0 && total > previousCPUSample.total {
				totalDelta := total - previousCPUSample.total
				idleDelta := idle - previousCPUSample.idle
				if idleDelta > totalDelta {
					idleDelta = totalDelta
				}
				if totalDelta > 0 {
					result.CPUPercent = float64(totalDelta-idleDelta) * 100 / float64(totalDelta)
				}
			}
			previousCPUSample.total, previousCPUSample.idle = total, idle
			cpuSampleMu.Unlock()
		}
	}
	if file, err := os.Open("/proc/meminfo"); err == nil {
		defer file.Close()
		var totalKB, availableKB uint64
		scanner := bufio.NewScanner(file)
		for scanner.Scan() {
			fields := strings.Fields(scanner.Text())
			if len(fields) < 2 {
				continue
			}
			value, parseErr := strconv.ParseUint(fields[1], 10, 64)
			if parseErr != nil {
				continue
			}
			switch strings.TrimSuffix(fields[0], ":") {
			case "MemTotal":
				totalKB = value
			case "MemAvailable":
				availableKB = value
			}
		}
		if totalKB > 0 {
			usedKB := totalKB - availableKB
			result.MemoryTotalMB = int64(totalKB / 1024)
			result.MemoryUsedMB = int64(usedKB / 1024)
			result.MemoryPercent = float64(usedKB) * 100 / float64(totalKB)
		}
	}
	usedMB, totalMB, diskPct := collectDiskUsage()
	result.DiskUsedMB = usedMB
	result.DiskTotalMB = totalMB
	result.DiskPercent = diskPct
	return result
}