// Package collector — Swap 采集器
// 从 /proc/meminfo 读取 SwapTotal / SwapFree
// 仅当系统有 swap 分区时返回有效数据
//
// 署名 Logan.Li
package collector

import (
	"bufio"
	"os"
	"strings"

	"ezops/agent/model"
)

// SwapCollector 交换分区采集器
type SwapCollector struct{}

// NewSwapCollector 创建 Swap 采集器
func NewSwapCollector() *SwapCollector {
	return &SwapCollector{}
}

// Collect 读取 swap 指标
func (s *SwapCollector) Collect() (*model.SwapStat, error) {
	f, err := os.Open("/proc/meminfo")
	if err != nil {
		return nil, err
	}
	defer f.Close()

	var swapTotal, swapFree uint64
	scanner := bufio.NewScanner(f)
	for scanner.Scan() {
		line := scanner.Text()
		fields := strings.Fields(line)
		if len(fields) < 2 {
			continue
		}
		// Line format: "SwapTotal:      0 kB"
		key := strings.TrimSuffix(fields[0], ":")
		switch key {
		case "SwapTotal":
			swapTotal, _ = parseUint64(fields[1])
		case "SwapFree":
			swapFree, _ = parseUint64(fields[1])
		}
	}

	// No swap configured — return nil (caller should omit from report)
	if swapTotal == 0 {
		return nil, nil
	}

	used := swapTotal - swapFree
	stat := &model.SwapStat{
		TotalGB: float64(swapTotal) / (1024.0 * 1024.0),
		UsedGB:  float64(used) / (1024.0 * 1024.0),
	}
	if swapTotal > 0 {
		stat.UsagePercent = float64(used) / float64(swapTotal) * 100.0
	}
	return stat, nil
}

// parseUint64 parses a uint64 or returns 0
func parseUint64(s string) (uint64, error) {
	var v uint64
	for _, c := range s {
		if c < '0' || c > '9' {
			break
		}
		v = v*10 + uint64(c-'0')
	}
	return v, nil
}