// Package probes collects hardware facts from a booted Linux system.
// Phase 3 only needs enough to feed the spec diff: CPU model/cores,
// total RAM, per-disk serial+size, per-NIC MAC+speed, per-GPU model.
//
// Every probe is tolerant of missing files or tools — if /sys isn't
// available the field is just left empty. The orchestrator's diff
// engine will surface missing expected fields as failures; missing
// fields that weren't expected stay silent.
package probes

import (
	"bufio"
	"fmt"
	"os"
	"os/exec"
	"path/filepath"
	"runtime"
	"strconv"
	"strings"

	"vetting/internal/spec"
)

// Collect runs every probe and returns the merged inventory. The only
// errors it surfaces are fatal ones that prevent progress — individual
// probe failures are logged to the returned Inventory's raw field and
// do not fail the whole call.
func Collect() (*spec.Inventory, error) {
	inv := &spec.Inventory{}

	inv.CPU = probeCPU()
	inv.Memory = probeMemory()
	inv.Disks = probeDisks()
	inv.NICs = probeNICs()
	inv.GPUs = probeGPUs()

	return inv, nil
}

// ----- CPU --------------------------------------------------------------

func probeCPU() spec.CPUSpec {
	// model: first "model name" in /proc/cpuinfo.
	// logical_cores: runtime.NumCPU (Linux respects cpu cgroup; agent
	// runs on bare metal so it will report every HT thread).
	c := spec.CPUSpec{LogicalCores: runtime.NumCPU()}
	f, err := os.Open("/proc/cpuinfo")
	if err != nil {
		return c
	}
	defer func() { _ = f.Close() }()
	scan := bufio.NewScanner(f)
	for scan.Scan() {
		line := scan.Text()
		if strings.HasPrefix(line, "model name") {
			if _, v, ok := strings.Cut(line, ":"); ok {
				c.Model = strings.TrimSpace(v)
				break
			}
		}
	}
	return c
}

// ----- Memory -----------------------------------------------------------

func probeMemory() spec.MemorySpec {
	// /proc/meminfo reports MemTotal in kB. Round down to the nearest
	// GiB so the diff's ±2 GiB tolerance is meaningful.
	f, err := os.Open("/proc/meminfo")
	if err != nil {
		return spec.MemorySpec{}
	}
	defer func() { _ = f.Close() }()
	scan := bufio.NewScanner(f)
	for scan.Scan() {
		fields := strings.Fields(scan.Text())
		if len(fields) >= 2 && fields[0] == "MemTotal:" {
			kb, err := strconv.ParseInt(fields[1], 10, 64)
			if err == nil {
				return spec.MemorySpec{TotalGiB: int(kb / 1024 / 1024)}
			}
		}
	}
	return spec.MemorySpec{}
}

// ----- Disks ------------------------------------------------------------

// probeDisks walks /sys/class/block and picks out real block devices
// (no partitions, no loop/ram). For each it reads size (512B sectors)
// and serial. Virtio disks in QEMU report a serial only when launched
// with `-drive serial=...`; without that the field is empty, which is
// fine — the diff skips disks with empty serials anyway.
func probeDisks() []spec.DiskSpec {
	entries, err := os.ReadDir("/sys/class/block")
	if err != nil {
		return nil
	}
	var out []spec.DiskSpec
	for _, e := range entries {
		name := e.Name()
		if !isRealDisk(name) {
			continue
		}
		base := filepath.Join("/sys/class/block", name)
		size := diskSizeGB(base)
		serial := diskSerial(name)
		// size == 0 means we couldn't read /size; skip rather than
		// emit garbage.
		if size == 0 && serial == "" {
			continue
		}
		out = append(out, spec.DiskSpec{Serial: serial, SizeGB: size})
	}
	return out
}

func isRealDisk(name string) bool {
	// Exclude partitions: they have a parent block dir and a "partition"
	// attribute. sd* disks without trailing digits are whole disks; nvme
	// disks use nvme0n1 for the namespace and nvme0n1p1 for partitions.
	if strings.HasPrefix(name, "loop") || strings.HasPrefix(name, "ram") ||
		strings.HasPrefix(name, "zram") || strings.HasPrefix(name, "dm-") {
		return false
	}
	partPath := filepath.Join("/sys/class/block", name, "partition")
	if _, err := os.Stat(partPath); err == nil {
		return false
	}
	return true
}

func diskSizeGB(base string) int {
	b, err := os.ReadFile(filepath.Join(base, "size"))
	if err != nil {
		return 0
	}
	sectors, err := strconv.ParseInt(strings.TrimSpace(string(b)), 10, 64)
	if err != nil {
		return 0
	}
	// /sys reports sectors of 512B regardless of physical sector size.
	return int(sectors * 512 / 1_000_000_000)
}

func diskSerial(name string) string {
	// Try a few known paths; the kernel exposes serials differently for
	// ATA/SCSI vs NVMe.
	for _, rel := range []string{
		filepath.Join("/sys/block", name, "device", "serial"),
		filepath.Join("/sys/block", name, "device", "vpd_pg80"),
		filepath.Join("/sys/block", name, "serial"),
	} {
		if b, err := os.ReadFile(rel); err == nil {
			s := strings.TrimSpace(string(b))
			if s != "" {
				return s
			}
		}
	}
	// Fallback: udevadm often knows the wwid / serial. Best-effort.
	cmd := exec.Command("udevadm", "info", "--query=property", "--name="+name)
	out, err := cmd.Output()
	if err != nil {
		return ""
	}
	for _, line := range strings.Split(string(out), "\n") {
		if v, ok := strings.CutPrefix(line, "ID_SERIAL_SHORT="); ok {
			return strings.TrimSpace(v)
		}
	}
	return ""
}

// ----- NICs -------------------------------------------------------------

func probeNICs() []spec.NICSpec {
	root := "/sys/class/net"
	entries, err := os.ReadDir(root)
	if err != nil {
		return nil
	}
	var out []spec.NICSpec
	for _, e := range entries {
		name := e.Name()
		if name == "lo" {
			continue
		}
		base := filepath.Join(root, name)
		mac := readLine(filepath.Join(base, "address"))
		if mac == "" || mac == "00:00:00:00:00:00" {
			continue
		}
		// /sys/class/net/*/speed reports Mbps or -1 if link down.
		speed := 0
		if b, err := os.ReadFile(filepath.Join(base, "speed")); err == nil {
			if mbps, err := strconv.Atoi(strings.TrimSpace(string(b))); err == nil && mbps > 0 {
				speed = mbps / 1000
			}
		}
		out = append(out, spec.NICSpec{MAC: strings.ToLower(mac), SpeedGbps: speed})
	}
	return out
}

// ----- GPUs -------------------------------------------------------------

// probeGPUs leans on lspci; if lspci is missing, returns nothing and
// the diff engine just won't match any GPU expectations. Phase 4 will
// add nvidia-smi for VRAM and firmware.
func probeGPUs() []spec.GPUSpec {
	cmd := exec.Command("lspci", "-mm", "-nnk")
	out, err := cmd.Output()
	if err != nil {
		return nil
	}
	var gpus []spec.GPUSpec
	for _, line := range strings.Split(string(out), "\n") {
		low := strings.ToLower(line)
		if !strings.Contains(low, "vga compatible controller") &&
			!strings.Contains(low, "3d controller") {
			continue
		}
		// `lspci -mm` quotes fields; device name is usually field 3.
		fields := splitQuoted(line)
		if len(fields) >= 4 {
			gpus = append(gpus, spec.GPUSpec{Model: fmt.Sprintf("%s %s", fields[2], fields[3])})
		}
	}
	return gpus
}

func splitQuoted(line string) []string {
	var out []string
	var cur strings.Builder
	inQ := false
	for _, r := range line {
		switch {
		case r == '"':
			inQ = !inQ
			if !inQ {
				out = append(out, cur.String())
				cur.Reset()
			}
		case r == ' ' && !inQ:
			continue
		default:
			cur.WriteRune(r)
		}
	}
	return out
}

// ----- shared helpers ---------------------------------------------------

func readLine(path string) string {
	b, err := os.ReadFile(path)
	if err != nil {
		return ""
	}
	return strings.TrimSpace(string(b))
}