// Package telemetry collects host + Plexum-agent metrics for the
// HarborForge Monitor. Snapshot is read on demand (Monitor bridge
// queries) or pushed (Calendar heartbeat), so the collector keeps no
// background goroutine — every call re-reads /proc, sm.State, etc.
//
// Cross-platform note: Linux is the only platform Plexum t3-class
// deployments run on; we read /proc/* directly rather than pull in a
// dependency.

package telemetry

import (
	"bufio"
	"fmt"
	"os"
	"runtime"
	"strconv"
	"strings"
	"time"
)

// Snapshot is the JSON payload the Monitor bridge serves + the
// Calendar heartbeat embeds. Field names mirror what
// HarborForge.OpenclawPlugin emits so the backend doesn't need
// per-plugin parsers.
type Snapshot struct {
	Identifier   string             `json:"identifier"`
	Platform     string             `json:"platform"`
	Hostname     string             `json:"hostname"`
	UptimeSecs   uint64             `json:"uptime"`
	Memory       MemoryInfo         `json:"memory"`
	Swap         SwapInfo           `json:"swap"`
	Load         LoadInfo           `json:"load"`
	Disk         DiskInfo           `json:"disk"`
	CPU          CPUInfo            `json:"cpu"`
	Agents       []AgentInfo        `json:"agents"`
	PluginInfo   PluginInfo         `json:"plugin"`
	CapturedAt   time.Time          `json:"captured_at"`
	HostMetadata map[string]string  `json:"host_metadata,omitempty"`
}

// SwapInfo is the system swap usage. Zeroes when swap isn't configured.
type SwapInfo struct {
	Total       uint64  `json:"total"`
	Free        uint64  `json:"free"`
	Used        uint64  `json:"used"`
	UsedPercent float64 `json:"used_percent"`
}

// CPUInfo holds the most recent CPU usage estimate. UsedPercent is
// computed across one sample interval (see Collect's cpu helper).
type CPUInfo struct {
	UsedPercent float64 `json:"used_percent"`
}

// MemoryInfo mirrors OpenclawPlugin's memory shape.
type MemoryInfo struct {
	Total       uint64  `json:"total"`        // bytes
	Free        uint64  `json:"free"`         // bytes
	Used        uint64  `json:"used"`         // bytes
	UsedPercent float64 `json:"used_percent"` // 0–100
}

// LoadInfo is Linux loadavg as a flat triple.
type LoadInfo struct {
	One     float64 `json:"one"`
	Five    float64 `json:"five"`
	Fifteen float64 `json:"fifteen"`
}

// DiskInfo for the root filesystem.
type DiskInfo struct {
	Path        string  `json:"path"`
	Total       uint64  `json:"total"`
	Free        uint64  `json:"free"`
	Used        uint64  `json:"used"`
	UsedPercent float64 `json:"used_percent"`
}

// AgentInfo summarises one Plexum agent for the dashboard. Heavy
// mirror of HF's expected schema — state field maps Plexum's
// idle/working/busy/offline directly.
type AgentInfo struct {
	ID    string `json:"id"`
	Model string `json:"model"`
	State string `json:"state"`
}

// PluginInfo identifies this plugin to the dashboard so the operator
// can see what's reporting telemetry.
type PluginInfo struct {
	Name    string `json:"name"`
	Version string `json:"version"`
	Backend string `json:"backend"` // "plexum"
}

// CollectOpts wires the collector to host-side state. Hostname /
// Identifier come from the resolved config.
type CollectOpts struct {
	Identifier  string
	Version     string
	AgentLister func() []AgentInfo // resolved by the caller (plugin uses HostAPI to walk agents)

	// SampleCPU asks Collect to take a 1-second CPU sample. Off-path
	// (status endpoint, bridge serve) leave false to keep calls cheap;
	// the slow push loop sets it true.
	SampleCPU bool
}

// Collect produces a fresh snapshot from /proc + the supplied AgentLister.
// SampleCPU=true takes a 1-second CPU sample (two reads of /proc/stat
// with a sleep between); otherwise CPU usage stays zero. Set true on
// the slow push loop, false on the cheap on-demand status endpoint.
func Collect(opts CollectOpts) Snapshot {
	now := time.Now().UTC()
	host, _ := os.Hostname()
	mem, swap := readMemAndSwap()
	load := readLoadAvg()
	disk := readDiskRoot()
	cpu := CPUInfo{}
	if opts.SampleCPU {
		cpu.UsedPercent = sampleCPUPercent(time.Second)
	}
	var agents []AgentInfo
	if opts.AgentLister != nil {
		agents = opts.AgentLister()
	}
	return Snapshot{
		Identifier: opts.Identifier,
		Platform:   runtime.GOOS,
		Hostname:   host,
		UptimeSecs: readUptime(),
		Memory:     mem,
		Swap:       swap,
		Load:       load,
		Disk:       disk,
		CPU:        cpu,
		Agents:     agents,
		PluginInfo: PluginInfo{
			Name:    "harbor-forge",
			Version: opts.Version,
			Backend: "plexum",
		},
		CapturedAt: now,
	}
}

// ---- /proc helpers ----

func readMemAndSwap() (MemoryInfo, SwapInfo) {
	f, err := os.Open("/proc/meminfo")
	if err != nil {
		return MemoryInfo{}, SwapInfo{}
	}
	defer f.Close()
	fields := map[string]uint64{}
	sc := bufio.NewScanner(f)
	for sc.Scan() {
		line := sc.Text()
		i := strings.IndexByte(line, ':')
		if i < 0 {
			continue
		}
		key := strings.TrimSpace(line[:i])
		rest := strings.TrimSpace(line[i+1:])
		// rest format: "1234 kB"
		parts := strings.Fields(rest)
		if len(parts) == 0 {
			continue
		}
		v, err := strconv.ParseUint(parts[0], 10, 64)
		if err != nil {
			continue
		}
		// All MemInfo values are in KB; convert to bytes.
		fields[key] = v * 1024
	}
	mem := buildMemInfo(fields)
	swap := buildSwapInfo(fields)
	return mem, swap
}

func buildMemInfo(fields map[string]uint64) MemoryInfo {
	total := fields["MemTotal"]
	free := fields["MemAvailable"]
	if free == 0 {
		free = fields["MemFree"] + fields["Buffers"] + fields["Cached"]
	}
	used := total - free
	var pct float64
	if total > 0 {
		pct = float64(used) / float64(total) * 100
	}
	return MemoryInfo{Total: total, Free: free, Used: used, UsedPercent: pct}
}

func buildSwapInfo(fields map[string]uint64) SwapInfo {
	total := fields["SwapTotal"]
	free := fields["SwapFree"]
	if total == 0 {
		return SwapInfo{}
	}
	used := total - free
	pct := float64(used) / float64(total) * 100
	return SwapInfo{Total: total, Free: free, Used: used, UsedPercent: pct}
}

// sampleCPUPercent computes overall CPU usage across one sample
// interval. Two reads of /proc/stat's aggregate "cpu" line, derive
// busy-time delta as (1 - idle/total). Returns 0 on read failure.
func sampleCPUPercent(interval time.Duration) float64 {
	total1, idle1, ok := readCPUStat()
	if !ok {
		return 0
	}
	time.Sleep(interval)
	total2, idle2, ok := readCPUStat()
	if !ok || total2 <= total1 {
		return 0
	}
	totalDelta := total2 - total1
	idleDelta := idle2 - idle1
	if idleDelta > totalDelta {
		return 0
	}
	return float64(totalDelta-idleDelta) / float64(totalDelta) * 100
}

func readCPUStat() (total, idle uint64, ok bool) {
	f, err := os.Open("/proc/stat")
	if err != nil {
		return 0, 0, false
	}
	defer f.Close()
	sc := bufio.NewScanner(f)
	if !sc.Scan() {
		return 0, 0, false
	}
	parts := strings.Fields(sc.Text())
	if len(parts) < 5 || parts[0] != "cpu" {
		return 0, 0, false
	}
	for i := 1; i < len(parts); i++ {
		v, err := strconv.ParseUint(parts[i], 10, 64)
		if err != nil {
			return 0, 0, false
		}
		total += v
		// idle is the 4th column (parts[4]); iowait (parts[5]) is also
		// idle-ish but we count it as busy to match gopsutil's default.
		if i == 4 {
			idle = v
		}
	}
	return total, idle, true
}

func readLoadAvg() LoadInfo {
	raw, err := os.ReadFile("/proc/loadavg")
	if err != nil {
		return LoadInfo{}
	}
	parts := strings.Fields(string(raw))
	if len(parts) < 3 {
		return LoadInfo{}
	}
	one, _ := strconv.ParseFloat(parts[0], 64)
	five, _ := strconv.ParseFloat(parts[1], 64)
	fifteen, _ := strconv.ParseFloat(parts[2], 64)
	return LoadInfo{One: one, Five: five, Fifteen: fifteen}
}

func readUptime() uint64 {
	raw, err := os.ReadFile("/proc/uptime")
	if err != nil {
		return 0
	}
	parts := strings.Fields(string(raw))
	if len(parts) == 0 {
		return 0
	}
	f, _ := strconv.ParseFloat(parts[0], 64)
	return uint64(f)
}

// readDiskRoot uses syscall.Statfs on "/" — we keep it inline to
// avoid pulling in another package.
func readDiskRoot() DiskInfo {
	var st diskStat
	if err := statfs("/", &st); err != nil {
		return DiskInfo{Path: "/"}
	}
	total := st.blockSize * st.blocks
	free := st.blockSize * st.bavail
	used := total - free
	var pct float64
	if total > 0 {
		pct = float64(used) / float64(total) * 100
	}
	return DiskInfo{
		Path:        "/",
		Total:       total,
		Free:        free,
		Used:        used,
		UsedPercent: pct,
	}
}

// FormatBytes is a small helper for human-readable Status output.
func FormatBytes(b uint64) string {
	switch {
	case b >= 1<<40:
		return fmt.Sprintf("%.2fTiB", float64(b)/(1<<40))
	case b >= 1<<30:
		return fmt.Sprintf("%.2fGiB", float64(b)/(1<<30))
	case b >= 1<<20:
		return fmt.Sprintf("%.2fMiB", float64(b)/(1<<20))
	case b >= 1<<10:
		return fmt.Sprintf("%.2fKiB", float64(b)/(1<<10))
	default:
		return fmt.Sprintf("%dB", b)
	}
}