package agent

// probe.go is the platform-neutral core of the probe collector, ported
// from monitor-probe's agent collector (collect.rs, MIT): host Facts
// (once per process) and per-heartbeat Metrics with the source's
// accounting discipline:
//   - memory "used" is free(1)'s column: total - available;
//   - disk "used" is df(1)'s: real storage only, total - free blocks
//     (not the unprivileged-available figure);
//   - network totals sum only "counted" interfaces — loopback,
//     container, tunnel and stacked devices are excluded by a filter so
//     no byte is counted twice;
//   - boot epoch = a stable boot identity + FNV-1a fingerprint of the
//     counted set, so a set change re-baselines exactly like a reboot;
//   - every source degrades independently: an unreadable source yields
//     a zero field, never a failed collection round.
//
// The samplers themselves are per-OS: probe_linux.go reads /proc and
// /sys, probe_windows.go reads the Win32 performance/registry surface.
// Both feed the shared rate/epoch machinery below and must keep the
// same accounting semantics; where a source has no equivalent on the
// platform, the field stays zero (documented at the sampler).

import (
	"hash/fnv"
	"net"
	"sort"
	"strings"
	"sync"
	"sync/atomic"
	"time"
)

// ProbeFacts mirrors monitor's Facts frame: static host identity, sampled
// once and piggybacked on the register request and (cheaply) heartbeats.
type ProbeFacts struct {
	Hostname     string `json:"hostname"`
	OS           string `json:"os"`
	Kernel       string `json:"kernel"`
	Arch         string `json:"arch"`
	Virt         string `json:"virt"`
	CPUName      string `json:"cpuName"`
	CPUCores     uint32 `json:"cpuCores"`
	MemTotal     uint64 `json:"memTotal"`
	SwapTotal    uint64 `json:"swapTotal"`
	DiskTotal    uint64 `json:"diskTotal"`
	AgentVersion string `json:"agentVersion"`
	IPv4         string `json:"ipv4"`
	IPv6         string `json:"ipv6"`
}

// ProbeMetrics mirrors monitor's Metrics frame: one sample per heartbeat.
type ProbeMetrics struct {
	BootID     string     `json:"bootId"`
	Iface      string     `json:"iface"`
	Uptime     uint64     `json:"uptime"`
	CPU        float32    `json:"cpu"`
	Load       [3]float32 `json:"load"`
	MemTotal   uint64     `json:"memTotal"`
	MemUsed    uint64     `json:"memUsed"`
	SwapTotal  uint64     `json:"swapTotal"`
	SwapUsed   uint64     `json:"swapUsed"`
	DiskTotal  uint64     `json:"diskTotal"`
	DiskUsed   uint64     `json:"diskUsed"`
	NetRxTotal uint64     `json:"netRxTotal"`
	NetTxTotal uint64     `json:"netTxTotal"`
	NetRx      uint64     `json:"netRx"`
	NetTx      uint64     `json:"netTx"`
	TCP        uint32     `json:"tcp"`
	UDP        uint32     `json:"udp"`
	Procs      uint32     `json:"procs"`
}

// probeCollector holds the cross-sample state the rates need (previous CPU
// counters and per-interface counters). Kept in memory only, like the source.
type probeCollector struct {
	mu       sync.Mutex
	prevCPU  *cpuSample
	prevNet  map[string][2]uint64
	prevNetT time.Time
}

// cpuSample is one cumulative CPU reading in whatever tick unit the
// platform reports: total covers every state, idle only the idle state.
// The differencing in cpuPercent is unit-agnostic.
type cpuSample struct{ total, idle uint64 }

var (
	probeColl  = &probeCollector{}
	factsOnce  sync.Once
	factsCache *ProbeFacts
)

// collectFacts returns the process-cached Facts, sampling on first use.
func collectFacts() *ProbeFacts {
	factsOnce.Do(func() { factsCache = sampleFacts() })
	return factsCache
}

// statIfacePin (V2.0.1) names the single interface to count when
// the operator pinned one on the master (its probe_meta.stat_iface,
// delivered on the config poll). "" keeps the automatic counted-set
// selection. The pin bypasses the filter on purpose: the operator
// named this exact device, including when it is one the filter would
// skip (a tunnel the node actually bills on). A pinned name absent
// from the interface table counts nothing — the boot epoch changes
// with the counted set, so the master re-baselines instead of booking
// a phantom delta.
var statIfacePin atomic.Value // string

// SetStatIfacePin records the master's counted-interface pin.
func SetStatIfacePin(name string) { statIfacePin.Store(name) }

func statIfacePinValue() string {
	if v := statIfacePin.Load(); v != nil {
		return v.(string)
	}
	return ""
}

// netCounters is one interface's cumulative byte totals.
type netCounters struct {
	name   string
	rx, tx uint64
}

func pinnedInterfaces(all []netCounters, pin string) []netCounters {
	for _, c := range all {
		if c.name == pin {
			return []netCounters{c}
		}
	}
	return nil
}

// cpuPercent diffs two cumulative samples into a busy percentage. A
// missing or non-advancing previous sample reports 0 (the round only
// re-baselines) — the source's discipline on both platforms.
func (c *probeCollector) cpuPercent(now *cpuSample) float32 {
	if now == nil {
		return 0
	}
	prev := c.prevCPU
	c.prevCPU = now
	if prev == nil || now.total <= prev.total {
		return 0
	}
	dt := float32(now.total - prev.total)
	di := float32(0)
	if now.idle > prev.idle {
		di = float32(now.idle - prev.idle)
	}
	pct := (dt - di) / dt * 100
	if pct < 0 {
		pct = 0
	}
	if pct > 100 {
		pct = 100
	}
	return pct
}

// bootEpoch = "{boot identity}/{FNV-1a-64 of the sorted counted names}".
// The master only tests it for equality: any change re-baselines.
func bootEpoch(bootID string, names []string) string {
	sorted := append([]string(nil), names...)
	sort.Strings(sorted)
	h := fnv.New64a()
	_, _ = h.Write([]byte(strings.Join(sorted, "\n")))
	return bootID + "/" + hex16(h.Sum64())
}

func hex16(v uint64) string {
	const digits = "0123456789abcdef"
	var buf [16]byte
	for i := 15; i >= 0; i-- {
		buf[i] = digits[v&0xf]
		v >>= 4
	}
	return string(buf[:])
}

// netRate diffs per interface over those present in both samples
// (saturating), divided by the elapsed wall time.
func (c *probeCollector) netRate(counted []netCounters, now time.Time) (uint64, uint64) {
	prev, prevT := c.prevNet, c.prevNetT
	next := make(map[string][2]uint64, len(counted))
	for _, ct := range counted {
		next[ct.name] = [2]uint64{ct.rx, ct.tx}
	}
	c.prevNet, c.prevNetT = next, now
	if prev == nil {
		return 0, 0
	}
	secs := now.Sub(prevT).Seconds()
	if secs <= 0 {
		return 0, 0
	}
	var rx, tx uint64
	for _, ct := range counted {
		p, ok := prev[ct.name]
		if !ok {
			continue
		}
		if ct.rx > p[0] {
			rx += ct.rx - p[0]
		}
		if ct.tx > p[1] {
			tx += ct.tx - p[1]
		}
	}
	return uint64(float64(rx) / secs), uint64(float64(tx) / secs)
}

// isPublicIP mirrors monitor's is_public: v4 excludes RFC1918, CGNAT
// 100.64/10, loopback, link-local, 0/8, >=224, 192.0.0/24, 198.18/15;
// v6 is only 2000::/3.
func isPublicIP(ip net.IP) bool {
	if ip4 := ip.To4(); ip4 != nil {
		a, b, c := ip4[0], ip4[1], ip4[2]
		switch {
		case ip4.IsPrivate(), ip4.IsLoopback(), ip4.IsLinkLocalUnicast():
			return false
		case a == 0 || a >= 224:
			return false
		case a == 100 && b&0xc0 == 64:
			return false
		case a == 192 && b == 0 && c == 0:
			return false
		case a == 198 && b&0xfe == 18:
			return false
		}
		return true
	}
	ip16 := ip.To16()
	if ip16 == nil {
		return false
	}
	return ip16[0]&0xe0 == 0x20
}