// fleet-hostapi — read-only workstation host-info agent for the kiosk.
//
// Implements the contract in HOST-API.md: a tiny HTTP service on the diskless
// workstation that reports facts about the machine the kiosk renders on. The
// kiosk SPA (served from the boot server, a different origin) fetches
//
//	GET http://localhost:9099/v1/host  ->  application/json
//
// Design constraints (see CLAUDE.md invariants):
//   - LOOPBACK ONLY. Never bind a routable address — this leaks host facts and
//     must never reach the boot LAN.
//   - READ ONLY. No endpoint mutates anything; the agent only reads /proc, /sys,
//     /etc/os-release, and a build-time facts file.
//   - NO PER-HOST STATE baked into the image. Everything host-specific (kernel,
//     hostname, IP, MAC, board, uptime) is read at RUNTIME. The only baked facts
//     are image-generic (image version + weston/chromium versions), written to a
//     facts file by the build provisioner — same for every host of a release.
//   - Stdlib only -> reproducible build (the verity hash is a security property).
//
// CORS + Private Network Access: the SPA is cross-origin AND the fetch is a
// Chromium "private network" request, so every response (incl. the OPTIONS
// preflight) carries Access-Control-Allow-Private-Network: true.
package main

import (
	"bufio"
	"encoding/json"
	"flag"
	"log"
	"math"
	"net"
	"net/http"
	"os"
	"runtime"
	"strconv"
	"strings"
	"syscall"
	"time"
)

// agentVersion is overridable at build time via -ldflags "-X main.agentVersion=…".
var agentVersion = "1.0.0"

// ---- response shape (HOST-API.md) — all fields optional, omit what's unknown --

type osInfo struct {
	Name    string `json:"name,omitempty"`
	Version string `json:"version,omitempty"`
	Kernel  string `json:"kernel,omitempty"`
	Image   string `json:"image,omitempty"`
}

type hwInfo struct {
	CPU   string `json:"cpu,omitempty"`
	Cores int    `json:"cores,omitempty"`
	MemGB int    `json:"memGB,omitempty"`
	GPU   string `json:"gpu,omitempty"`
	Board string `json:"board,omitempty"`
}

type netInfo struct {
	Hostname string `json:"hostname,omitempty"`
	IP       string `json:"ip,omitempty"`
	MAC      string `json:"mac,omitempty"`
}

type kioskInfo struct {
	Uptime   string `json:"uptime,omitempty"`
	Weston   string `json:"weston,omitempty"`
	Chromium string `json:"chromium,omitempty"`
}

type agentInfo struct {
	Version string `json:"version,omitempty"`
}

type hostResponse struct {
	OS       osInfo    `json:"os"`
	Hardware hwInfo    `json:"hardware"`
	Net      netInfo   `json:"net"`
	Kiosk    kioskInfo `json:"kiosk"`
	Agent    agentInfo `json:"agent"`
}

// buildFacts is the image-generic, build-time facts file (written by the Packer
// provisioner). Distinct from anything per-host.
type buildFacts struct {
	Image    string `json:"image"`
	Weston   string `json:"weston"`
	Chromium string `json:"chromium"`
}

func main() {
	addr := flag.String("addr", env("FLEET_HOSTAPI_ADDR", "127.0.0.1:9099"), "listen address (MUST be loopback)")
	origin := flag.String("allow-origin", env("FLEET_HOSTAPI_ALLOW_ORIGIN", "*"), "Access-Control-Allow-Origin value")
	factsPath := flag.String("facts", env("FLEET_HOSTAPI_FACTS", "/etc/fleet-hostinfo.json"), "build-time facts file")
	flag.Parse()

	// Refuse to bind anything that isn't loopback — a hard guardrail against a
	// misconfiguration exposing host facts on the boot LAN.
	if host, _, err := net.SplitHostPort(*addr); err != nil || !isLoopback(host) {
		log.Fatalf("refusing to listen on %q: bind address must be loopback (127.0.0.1/::1)", *addr)
	}

	facts := loadFacts(*factsPath)

	mux := http.NewServeMux()
	mux.HandleFunc("/v1/host", func(w http.ResponseWriter, r *http.Request) {
		cors(w, *origin)
		if r.Method == http.MethodOptions {
			w.WriteHeader(http.StatusNoContent)
			return
		}
		if r.Method != http.MethodGet {
			http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
			return
		}
		w.Header().Set("Content-Type", "application/json")
		w.Header().Set("Cache-Control", "no-store")
		enc := json.NewEncoder(w)
		enc.SetIndent("", "  ")
		_ = enc.Encode(collect(facts))
	})
	// Liveness for the unit / debugging (no host facts).
	mux.HandleFunc("/healthz", func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Content-Type", "text/plain")
		_, _ = w.Write([]byte("ok\n"))
	})

	srv := &http.Server{
		Addr:              *addr,
		Handler:           mux,
		ReadHeaderTimeout: 5 * time.Second,
		ReadTimeout:       10 * time.Second,
		WriteTimeout:      10 * time.Second,
		IdleTimeout:       60 * time.Second,
	}
	log.Printf("fleet-hostapi %s listening on %s (loopback, read-only)", agentVersion, *addr)
	log.Fatal(srv.ListenAndServe())
}

func cors(w http.ResponseWriter, origin string) {
	// Private Network Access: the kiosk page (boot-server origin, an insecure/
	// public context) fetching localhost is a "private network" request — the
	// preflight needs this header or Chromium blocks it. See HOST-API.md.
	w.Header().Set("Access-Control-Allow-Origin", origin)
	w.Header().Set("Access-Control-Allow-Private-Network", "true")
	w.Header().Set("Access-Control-Allow-Methods", "GET, OPTIONS")
	w.Header().Set("Vary", "Origin")
}

// collect gathers all host facts. Each source is best-effort: a failed read
// leaves its field empty (the SPA renders "—" for missing fields).
func collect(f buildFacts) hostResponse {
	var resp hostResponse

	// os
	rel := parseKV("/etc/os-release")
	resp.OS.Name = firstNonEmpty(rel["NAME"], rel["ID"])
	resp.OS.Version = firstNonEmpty(rel["VERSION_ID"], rel["VERSION"])
	resp.OS.Kernel = kernelRelease()
	resp.OS.Image = f.Image

	// hardware
	resp.Hardware.CPU = cpuModel()
	resp.Hardware.Cores = runtime.NumCPU()
	resp.Hardware.MemGB = memGB()
	resp.Hardware.GPU = gpuModel()
	resp.Hardware.Board = boardModel()

	// net
	resp.Net.Hostname, _ = os.Hostname()
	resp.Net.IP, resp.Net.MAC = primaryIfaceAddr()

	// kiosk
	resp.Kiosk.Uptime = uptimeHuman()
	resp.Kiosk.Weston = f.Weston
	resp.Kiosk.Chromium = f.Chromium

	resp.Agent.Version = agentVersion
	return resp
}

// ---- collectors -----------------------------------------------------------

func kernelRelease() string {
	var u syscall.Utsname
	if err := syscall.Uname(&u); err != nil {
		return ""
	}
	return charsToString(u.Release[:])
}

func cpuModel() string {
	f, err := os.Open("/proc/cpuinfo")
	if err != nil {
		return ""
	}
	defer f.Close()
	sc := bufio.NewScanner(f)
	for sc.Scan() {
		line := sc.Text()
		// x86: "model name". arm64: "Hardware"/"Processor" if present.
		for _, key := range []string{"model name", "Hardware", "Processor"} {
			if strings.HasPrefix(line, key) {
				if _, v, ok := strings.Cut(line, ":"); ok {
					return strings.TrimSpace(v)
				}
			}
		}
	}
	_ = sc.Err() // best-effort read; empty result on any error
	return ""
}

func memGB() int {
	for _, line := range readLines("/proc/meminfo") {
		if strings.HasPrefix(line, "MemTotal:") {
			fields := strings.Fields(line) // MemTotal: <kB> kB
			if len(fields) >= 2 {
				if kb, err := strconv.ParseFloat(fields[1], 64); err == nil {
					return int(math.Round(kb / 1024.0 / 1024.0))
				}
			}
		}
	}
	return 0
}

// boardModel: vendor + product from DMI (world-readable sysfs — NOT product_serial,
// which is root-only and per-host; we never read it).
func boardModel() string {
	vendor := strings.TrimSpace(readFile("/sys/class/dmi/id/sys_vendor"))
	product := strings.TrimSpace(readFile("/sys/class/dmi/id/product_name"))
	if vendor == "" && product == "" {
		vendor = strings.TrimSpace(readFile("/sys/class/dmi/id/board_vendor"))
		product = strings.TrimSpace(readFile("/sys/class/dmi/id/board_name"))
	}
	return strings.TrimSpace(strings.TrimSpace(vendor + " " + product))
}

// gpuModel: best-effort from the first DRM card's PCI ids. No PCI-ID database —
// we map the few known vendors and otherwise emit the raw ids. Often empty on a
// headless/virtio build VM; that's fine (optional field).
func gpuModel() string {
	for _, card := range []string{"card0", "card1"} {
		base := "/sys/class/drm/" + card + "/device/"
		vid := strings.TrimSpace(readFile(base + "vendor"))
		did := strings.TrimSpace(readFile(base + "device"))
		if vid == "" {
			continue
		}
		name := map[string]string{
			"0x8086": "Intel",
			"0x1002": "AMD",
			"0x10de": "NVIDIA",
			"0x1af4": "Red Hat (virtio-gpu)",
			"0x1234": "QEMU",
			"0x1a03": "ASPEED",
		}[strings.ToLower(vid)]
		ids := strings.TrimPrefix(strings.ToLower(vid), "0x")
		if did != "" {
			ids += ":" + strings.TrimPrefix(strings.ToLower(did), "0x")
		}
		if name != "" {
			return name + " [" + ids + "]"
		}
		return "[" + ids + "]"
	}
	return ""
}

// primaryIfaceAddr returns the preferred outbound IPv4 + the MAC of the
// interface that owns it. Uses a UDP "connect" (no packet is sent) to let the
// kernel pick the route's source address.
func primaryIfaceAddr() (ip string, mac string) {
	c, err := net.Dial("udp", "192.0.2.1:9") // TEST-NET-1, never reachable; no traffic on UDP connect
	if err != nil {
		return "", ""
	}
	defer c.Close()
	la, ok := c.LocalAddr().(*net.UDPAddr)
	if !ok || la.IP == nil {
		return "", ""
	}
	ip = la.IP.String()
	// find the interface carrying this IP -> its MAC
	ifaces, err := net.Interfaces()
	if err != nil {
		return ip, ""
	}
	for _, ifc := range ifaces {
		addrs, _ := ifc.Addrs()
		for _, a := range addrs {
			if n, ok := a.(*net.IPNet); ok && n.IP.Equal(la.IP) {
				return ip, ifc.HardwareAddr.String()
			}
		}
	}
	return ip, ""
}

// uptimeHuman formats system uptime as "3h 12m". On a kiosk appliance the system
// boots straight into the kiosk, so system uptime ≈ kiosk-session uptime —
// reported here to avoid coupling to (and exec'ing) systemd for the unit time.
func uptimeHuman() string {
	var si syscall.Sysinfo_t
	if err := syscall.Sysinfo(&si); err != nil {
		return ""
	}
	d := time.Duration(si.Uptime) * time.Second
	days := int(d.Hours()) / 24
	hours := int(d.Hours()) % 24
	mins := int(d.Minutes()) % 60
	switch {
	case days > 0:
		return strconv.Itoa(days) + "d " + strconv.Itoa(hours) + "h " + strconv.Itoa(mins) + "m"
	case hours > 0:
		return strconv.Itoa(hours) + "h " + strconv.Itoa(mins) + "m"
	default:
		return strconv.Itoa(mins) + "m"
	}
}

// ---- helpers --------------------------------------------------------------

func loadFacts(path string) buildFacts {
	var f buildFacts
	b, err := os.ReadFile(path)
	if err != nil {
		return f // file absent at runtime -> image/weston/chromium just omitted
	}
	_ = json.Unmarshal(b, &f)
	return f
}

func env(k, def string) string {
	if v := os.Getenv(k); v != "" {
		return v
	}
	return def
}

func isLoopback(host string) bool {
	if host == "localhost" {
		return true
	}
	ip := net.ParseIP(host)
	return ip != nil && ip.IsLoopback()
}

func parseKV(path string) map[string]string {
	m := map[string]string{}
	for _, line := range readLines(path) {
		k, v, ok := strings.Cut(line, "=")
		if !ok {
			continue
		}
		m[strings.TrimSpace(k)] = strings.Trim(strings.TrimSpace(v), `"`)
	}
	return m
}

func readLines(path string) []string {
	b := readFile(path)
	if b == "" {
		return nil
	}
	return strings.Split(strings.TrimRight(b, "\n"), "\n")
}

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

func firstNonEmpty(vals ...string) string {
	for _, v := range vals {
		if v != "" {
			return v
		}
	}
	return ""
}

// charsToString converts a NUL-terminated Utsname field (int8 or uint8 across
// arches) to a Go string.
func charsToString(ca []int8) string {
	b := make([]byte, 0, len(ca))
	for _, c := range ca {
		if c == 0 {
			break
		}
		b = append(b, byte(c))
	}
	return string(b)
}