//go:build linux

package system

import (
	"bufio"
	"context"
	"fmt"
	"os"
	"os/exec"
	"path/filepath"
	"sort"
	"strconv"
	"strings"
	"syscall"
	"time"
)

// GetInfo reads system memory, disk, CPU, load, and temperature info.
// hddPath is the mount path for external HDD; if empty, HDD info is skipped.
// cpuCollector provides the latest CPU usage sample; may be nil.
func GetInfo(hddPath string, cpuCollector *CPUCollector) SystemInfo {
	start := time.Now()
	debugf("[DEBUG] [system] GetInfo starting (hddPath=%q, hasCPUCollector=%v)", hddPath, cpuCollector != nil)

	info := SystemInfo{}

	// --- Memory from /proc/meminfo ---
	readMemInfo(&info)

	// --- Root filesystem disk usage ---
	readDiskUsage("/", &info.DiskTotalGB, &info.DiskUsedGB, &info.DiskAvailGB, &info.DiskPercent)

	// --- HDD disk usage (if configured) ---
	if hddPath != "" {
		info.HDDConfigured = true
		readDiskUsage(hddPath, &info.HDDTotalGB, &info.HDDUsedGB, &info.HDDAvailGB, &info.HDDPercent)
	}

	// --- Load average ---
	readLoadAvg(&info)

	// --- Temperature ---
	readTemperature(&info)

	// --- CPU from collector ---
	if cpuCollector != nil {
		info.CPUPercent = cpuCollector.CPUPercent()
	}

	debugf("[DEBUG] [system] GetInfo done in %s — mem=%dMB/%dMB (%.1f%%), rootDisk=%.1fGB/%.1fGB (%.1f%%), load=%.2f/%.2f/%.2f, temp=%.1f°C (%s), cpu=%.1f%%",
		time.Since(start).Round(time.Millisecond),
		info.UsedMemMB, info.TotalMemMB, info.MemPercent,
		info.DiskUsedGB, info.DiskTotalGB, info.DiskPercent,
		info.LoadAvg1, info.LoadAvg5, info.LoadAvg15,
		info.TemperatureCelsius, info.TemperatureSource,
		info.CPUPercent,
	)

	return info
}

// GetTotalMemoryMB reads total system memory from /proc/meminfo.
func GetTotalMemoryMB() (int, error) {
	info := SystemInfo{}
	readMemInfo(&info)
	if info.TotalMemMB == 0 {
		return 0, fmt.Errorf("could not read MemTotal from /proc/meminfo")
	}
	return int(info.TotalMemMB), nil
}

// GetMemoryMB returns total and used system memory in MB from /proc/meminfo.
func GetMemoryMB() (totalMB, usedMB int, err error) {
	info := SystemInfo{}
	readMemInfo(&info)
	if info.TotalMemMB == 0 {
		return 0, 0, fmt.Errorf("could not read MemTotal from /proc/meminfo")
	}
	return int(info.TotalMemMB), int(info.UsedMemMB), nil
}

// cgroupRoot is the cgroup mount point. Overridable in tests.
var cgroupRoot = "/sys/fs/cgroup"

func readMemInfo(info *SystemInfo) {
	f, err := os.Open("/proc/meminfo")
	if err != nil {
		debugf("[DEBUG] [system] readMemInfo: failed to open /proc/meminfo: %v", err)
		return
	}
	defer f.Close()

	var totalKB, availKB uint64
	scanner := bufio.NewScanner(f)
	for scanner.Scan() {
		line := scanner.Text()
		switch {
		case strings.HasPrefix(line, "MemTotal:"):
			totalKB = parseMemLine(line)
		case strings.HasPrefix(line, "MemAvailable:"):
			availKB = parseMemLine(line)
		}
		if totalKB > 0 && availKB > 0 {
			break
		}
	}

	if totalKB == 0 {
		debugf("[DEBUG] [system] readMemInfo: could not parse MemTotal from /proc/meminfo")
		return
	}

	info.TotalMemMB = totalKB / 1024
	info.AvailMemMB = availKB / 1024
	info.UsedMemMB = info.TotalMemMB - info.AvailMemMB

	// F1: the controller runs as a Docker container inside an LXC. /proc/meminfo reports the HOST's RAM
	// (no lxcfs in the container) and the container's OWN cgroup is unlimited (the 2GB cap lives on the
	// LXC, an ancestor hidden from the container), so the reported total massively overstates the guest's
	// real ceiling and defeats the deploy memory-headroom guard. Determine the true guest cap from, in
	// order: the container's cgroup limit (correct when Docker sets -m, e.g. non-nested deploys), else
	// `docker info` MemTotal (dockerd runs IN the LXC and reports the guest's lxcfs-backed RAM — the
	// accurate cap in the nested-LXC case). The instantaneous guest-wide RSS is NOT observable from the
	// container, so when we override the cap we scale the host's used-fraction onto it as an estimate for
	// display; the CAP itself (what the headroom math depends on) is accurate. The deploy guard uses the
	// controller's own committed-memory accounting for "used", so safety does not rely on this estimate.
	capMB := uint64(0)
	if v, ok := readCgroupMemLimitMB(cgroupRoot); ok && v > 0 && v < info.TotalMemMB {
		capMB = v
	}
	if capMB == 0 {
		if v, ok := guestMemTotalMB(); ok && v > 0 && v < info.TotalMemMB {
			capMB = v
		}
	}
	if capMB > 0 && capMB < info.TotalMemMB {
		frac := 0.0
		if info.TotalMemMB > 0 {
			frac = float64(info.UsedMemMB) / float64(info.TotalMemMB)
		}
		info.TotalMemMB = capMB
		// Scaled host-pressure estimate (the container can't read guest-wide RSS). The /api/system/info
		// handler overrides this with the controller's committed-app memory for an accurate figure; this
		// estimate covers the other GetInfo callers (monitoring) without alarming at ~100%.
		info.UsedMemMB = uint64(float64(capMB) * frac)
		info.AvailMemMB = info.TotalMemMB - info.UsedMemMB
		debugf("[DEBUG] [system] readMemInfo: guest cap=%dMB (host total was %dKB) → used≈%dMB avail≈%dMB",
			capMB, totalKB, info.UsedMemMB, info.AvailMemMB)
	}

	if info.TotalMemMB > 0 {
		info.MemPercent = float64(info.UsedMemMB) / float64(info.TotalMemMB) * 100
	}
	debugf("[DEBUG] [system] readMemInfo: totalKB=%d availKB=%d → total=%dMB avail=%dMB used=%dMB (%.1f%%)",
		totalKB, availKB, info.TotalMemMB, info.AvailMemMB, info.UsedMemMB, info.MemPercent)
}

// guestMemTotalMB returns the guest's total RAM (MB) as reported by the Docker daemon. The daemon runs
// inside the LXC, so `docker info` MemTotal reflects the guest's lxcfs-backed /proc/meminfo (the real
// cap) — unlike the container's own /proc/meminfo, which shows the Proxmox host's RAM. Overridable in
// tests via dockerMemTotalFn.
func guestMemTotalMB() (uint64, bool) {
	if dockerMemTotalFn != nil {
		return dockerMemTotalFn()
	}
	ctx, cancel := context.WithTimeout(context.Background(), 4*time.Second)
	defer cancel()
	out, err := exec.CommandContext(ctx, "docker", "info", "--format", "{{.MemTotal}}").Output()
	if err != nil {
		return 0, false
	}
	bytesVal, err := strconv.ParseUint(strings.TrimSpace(string(out)), 10, 64)
	if err != nil || bytesVal == 0 {
		return 0, false
	}
	return bytesVal / (1024 * 1024), true
}

// dockerMemTotalFn lets tests stub the docker-info read.
var dockerMemTotalFn func() (uint64, bool)

// GuestMemTotalMB returns the guest's memory cap in MB (docker-info MemTotal), preferring the cgroup
// limit when finite. ok=false if neither is determinable. The deploy memory guard uses this as the
// accurate denominator (the controller container cannot read the guest cap from /proc — no lxcfs).
func GuestMemTotalMB() (int, bool) {
	if v, ok := readCgroupMemLimitMB(cgroupRoot); ok && v > 0 {
		return int(v), true
	}
	if v, ok := guestMemTotalMB(); ok && v > 0 {
		return int(v), true
	}
	return 0, false
}

// readCgroupMemLimitMB returns the cgroup memory limit in MB. It tries cgroup v2 (memory.max) first,
// then v1 (memory/memory.limit_in_bytes). A sentinel ("max" on v2, or a near-uint64-max value on v1)
// means "unlimited" → ok=false so the caller keeps the /proc/meminfo value.
func readCgroupMemLimitMB(root string) (mb uint64, ok bool) {
	// cgroup v2
	if b, err := os.ReadFile(filepath.Join(root, "memory.max")); err == nil {
		s := strings.TrimSpace(string(b))
		if s == "max" {
			return 0, false
		}
		if v, err := strconv.ParseUint(s, 10, 64); err == nil && v > 0 {
			return v / (1024 * 1024), true
		}
	}
	// cgroup v1
	if b, err := os.ReadFile(filepath.Join(root, "memory", "memory.limit_in_bytes")); err == nil {
		s := strings.TrimSpace(string(b))
		if v, err := strconv.ParseUint(s, 10, 64); err == nil && v > 0 {
			// v1 "unlimited" is a huge page-aligned value near uint64 max; treat >= 1 PiB as unlimited.
			if v >= (1 << 50) {
				return 0, false
			}
			return v / (1024 * 1024), true
		}
	}
	return 0, false
}

// readCgroupMemCurrentMB returns the cgroup current memory usage in MB (v2 memory.current, v1
// memory/memory.usage_in_bytes). ok=false if unreadable.
func readCgroupMemCurrentMB(root string) (mb uint64, ok bool) {
	for _, p := range []string{
		filepath.Join(root, "memory.current"),
		filepath.Join(root, "memory", "memory.usage_in_bytes"),
	} {
		if b, err := os.ReadFile(p); err == nil {
			if v, err := strconv.ParseUint(strings.TrimSpace(string(b)), 10, 64); err == nil {
				return v / (1024 * 1024), true
			}
		}
	}
	return 0, false
}

// parseMemLine extracts the kB value from a /proc/meminfo line like "MemTotal:       16384000 kB"
func parseMemLine(line string) uint64 {
	parts := strings.SplitN(line, ":", 2)
	if len(parts) < 2 {
		return 0
	}
	valStr := strings.TrimSpace(parts[1])
	valStr = strings.TrimSuffix(valStr, " kB")
	valStr = strings.TrimSpace(valStr)

	var val uint64
	for _, c := range valStr {
		if c >= '0' && c <= '9' {
			val = val*10 + uint64(c-'0')
		}
	}
	return val
}

func readDiskUsage(path string, totalGB, usedGB, availGB *float64, percent *float64) {
	var stat syscall.Statfs_t
	if err := syscall.Statfs(path, &stat); err != nil {
		debugf("[DEBUG] [system] readDiskUsage: statfs(%q) failed: %v", path, err)
		return
	}

	bsize := uint64(stat.Bsize)
	total := stat.Blocks * bsize
	avail := stat.Bavail * bsize
	used := total - (stat.Bfree * bsize)

	const gb = 1024 * 1024 * 1024
	*totalGB = float64(total) / gb
	*usedGB = float64(used) / gb
	*availGB = float64(avail) / gb
	if total > 0 {
		*percent = float64(used) / float64(total) * 100
	}
	debugf("[DEBUG] [system] readDiskUsage: path=%q bsize=%d total=%.1fGB used=%.1fGB avail=%.1fGB (%.1f%%)",
		path, bsize, *totalGB, *usedGB, *availGB, *percent)
}

// readLoadAvg reads 1/5/15 minute load averages from /proc/loadavg.
func readLoadAvg(info *SystemInfo) {
	data, err := os.ReadFile("/proc/loadavg")
	if err != nil {
		debugf("[DEBUG] [system] readLoadAvg: failed to read /proc/loadavg: %v", err)
		return
	}
	fmt.Sscanf(string(data), "%f %f %f", &info.LoadAvg1, &info.LoadAvg5, &info.LoadAvg15)
	debugf("[DEBUG] [system] readLoadAvg: raw=%q → 1m=%.2f 5m=%.2f 15m=%.2f",
		strings.TrimSpace(string(data)), info.LoadAvg1, info.LoadAvg5, info.LoadAvg15)
}

// readTemperature reads CPU/SoC temperature from thermal zones.
// Tries /host/sys first (Docker mount), then /sys (native).
func readTemperature(info *SystemInfo) {
	prefixes := []string{"/host/sys", "/sys"}

	for _, prefix := range prefixes {
		if readThermalZones(prefix, info) {
			debugf("[DEBUG] [system] readTemperature: found via thermal_zone at %s — %.1f°C (%s)", prefix, info.TemperatureCelsius, info.TemperatureSource)
			return
		}
	}

	// Fallback: try hwmon
	for _, prefix := range prefixes {
		if readHwmon(prefix, info) {
			debugf("[DEBUG] [system] readTemperature: found via hwmon at %s — %.1f°C (%s)", prefix, info.TemperatureCelsius, info.TemperatureSource)
			return
		}
	}

	debugf("[DEBUG] [system] readTemperature: no temperature source found")
}

func readThermalZones(sysPrefix string, info *SystemInfo) bool {
	pattern := filepath.Join(sysPrefix, "class", "thermal", "thermal_zone*", "temp")
	matches, err := filepath.Glob(pattern)
	if err != nil || len(matches) == 0 {
		return false
	}

	sort.Strings(matches)
	debugf("[DEBUG] [system] readThermalZones: %s — found %d zones", sysPrefix, len(matches))

	var maxTemp float64
	var maxSource string

	for _, tempPath := range matches {
		data, err := os.ReadFile(tempPath)
		if err != nil {
			continue
		}

		var milliDeg int64
		if _, err := fmt.Sscanf(strings.TrimSpace(string(data)), "%d", &milliDeg); err != nil {
			continue
		}

		temp := float64(milliDeg) / 1000.0

		// Read the type file for the label
		zoneDir := filepath.Dir(tempPath)
		typePath := filepath.Join(zoneDir, "type")
		typeData, err := os.ReadFile(typePath)
		source := strings.TrimSpace(string(typeData))
		if err != nil || source == "" {
			source = filepath.Base(zoneDir)
		}

		if temp > maxTemp {
			maxTemp = temp
			maxSource = source
		}
	}

	if maxTemp > 0 {
		info.TemperatureCelsius = maxTemp
		info.TemperatureSource = maxSource
		return true
	}
	return false
}

func readHwmon(sysPrefix string, info *SystemInfo) bool {
	pattern := filepath.Join(sysPrefix, "class", "hwmon", "hwmon*", "temp1_input")
	matches, err := filepath.Glob(pattern)
	if err != nil || len(matches) == 0 {
		return false
	}

	var maxTemp float64
	var maxSource string

	for _, tempPath := range matches {
		data, err := os.ReadFile(tempPath)
		if err != nil {
			continue
		}

		var milliDeg int64
		if _, err := fmt.Sscanf(strings.TrimSpace(string(data)), "%d", &milliDeg); err != nil {
			continue
		}

		temp := float64(milliDeg) / 1000.0
		source := filepath.Base(filepath.Dir(tempPath))

		if temp > maxTemp {
			maxTemp = temp
			maxSource = source
		}
	}

	if maxTemp > 0 {
		info.TemperatureCelsius = maxTemp
		info.TemperatureSource = maxSource
		return true
	}
	return false
}
