package profile

import (
	"context"
	"fmt"
	"os"
	"sort"
	"strconv"
	"strings"
	"sync"
	"syscall"
	"time"
)

// Machine is what this machine is made of, as it says itself (novox/hq issue 160): what somebody
// deciding where a module should go wants to know, beside what it can do.
//
// **A fact it could not determine is said, never zeroed.** Every fact below is either present or
// named in Unknown with why; a machine reporting 0 bytes of memory would be read as a machine with
// none. So a field is omitted only when Unknown says why.
type Machine struct {
	// ObservedAt is when this was read: the age every reader shows beside it.
	ObservedAt time.Time `json:"observed_at"`

	// KernelRelease is the running kernel's release, as /proc/sys/kernel/osrelease says it. (The
	// profile's own `kernel` is the kernel's family, `linux`.)
	KernelRelease string `json:"kernel_release,omitempty"`
	// Distribution and its Version, from /etc/os-release: VERSION_ID, or BUILD_ID for a rolling
	// distribution that has no version (Arch Linux says `rolling`).
	Distribution string `json:"distribution,omitempty"`
	Version      string `json:"version,omitempty"`

	// Processor is its model name; Cores the physical cores and Threads the logical processors.
	Processor string `json:"processor,omitempty"`
	Cores     int    `json:"cores,omitempty"`
	Threads   int    `json:"threads,omitempty"`

	MemoryBytes int64 `json:"memory_bytes,omitempty"`

	// Virtual is `physical`, or the kind of virtual machine or container it is (`kvm`, `lxc`), as
	// systemd-detect-virt names it.
	Virtual string `json:"virtual,omitempty"`

	// BootedAt is when it booted: its uptime is the time since, so the fact does not change between
	// two reports of the same boot.
	BootedAt *time.Time `json:"booted_at,omitempty"`

	Timezone string `json:"timezone,omitempty"`

	// Filesystems is each local filesystem mounted, by where, with its size and what is free.
	Filesystems []Filesystem `json:"filesystems,omitempty"`

	// Unknown names each fact that could not be determined, and why.
	Unknown map[string]string `json:"unknown,omitempty"`
}

// Filesystem is one mounted local filesystem.
type Filesystem struct {
	Mount  string `json:"mount"`
	Device string `json:"device"`
	Type   string `json:"type"`
	// SizeBytes and FreeBytes are what statfs says: free is what an unprivileged writer may still
	// use (f_bavail), the number a person deciding where data goes wants.
	SizeBytes int64 `json:"size_bytes"`
	FreeBytes int64 `json:"free_bytes"`
}

// The facts, by the names Unknown says them under.
const (
	FactKernelRelease = "kernel release"
	FactDistribution  = "distribution"
	FactVersion       = "version"
	FactProcessor     = "processor"
	FactCores         = "cores"
	FactThreads       = "threads"
	FactMemory        = "memory"
	FactVirtual       = "virtual or physical"
	FactUptime        = "uptime"
	FactTimezone      = "timezone"
	FactFilesystems   = "filesystems"
	FactPublicAddress = "public address"
)

// MachineFacts is every fact Unknown may name, in the order a reader shows them.
var MachineFacts = []string{FactKernelRelease, FactDistribution, FactVersion, FactProcessor, FactCores,
	FactThreads, FactMemory, FactVirtual, FactUptime, FactTimezone, FactFilesystems, FactPublicAddress}

// publicAddressUnknown is why the public uplink address is not said. A machine behind a NAT cannot see
// its public address from itself, and asking a service outside the mesh is a dependency the mesh does not
// take on unasked; how a machine learns it is not decided yet, so it is said as unknown rather than
// guessed from a private address.
const publicAddressUnknown = "a machine behind a NAT cannot see its public address from itself, and how it " +
	"learns it is not decided yet"

// Sources is where the facts are read from. Replaced in tests only for the parsing layer; the real
// sources are exercised against this machine as well (novox/hq ADR 0017).
type Sources struct {
	Read     func(path string) ([]byte, error)
	Readlink func(path string) (string, error)
	Run      Runner
	// Statfs is (size, free) in bytes of the filesystem mounted at a path.
	Statfs func(path string) (size, free int64, err error)
	Now    func() time.Time
}

// RealSources reads this machine.
func RealSources() Sources {
	return Sources{Read: os.ReadFile, Readlink: os.Readlink, Run: ExecRunner, Statfs: statfs, Now: time.Now}
}

func statfs(path string) (int64, int64, error) {
	var s syscall.Statfs_t
	if err := syscall.Statfs(path, &s); err != nil {
		return 0, 0, err
	}
	return int64(s.Blocks) * int64(s.Bsize), int64(s.Bavail) * int64(s.Bsize), nil
}

// DescribeMachine reads what this machine is made of. It never fails: a fact that cannot be read is
// named in Unknown with why, and the rest are still said.
func DescribeMachine(ctx context.Context, src Sources) Machine {
	if src.Now == nil {
		src.Now = time.Now
	}
	m := Machine{ObservedAt: src.Now().UTC(), Unknown: map[string]string{}}
	unknown := func(fact string, why string) { m.Unknown[fact] = why }

	if b, err := src.Read("/proc/sys/kernel/osrelease"); err != nil {
		unknown(FactKernelRelease, err.Error())
	} else if r := strings.TrimSpace(string(b)); r == "" {
		unknown(FactKernelRelease, "/proc/sys/kernel/osrelease is empty")
	} else {
		m.KernelRelease = r
	}

	if b, err := src.Read("/etc/os-release"); err != nil {
		unknown(FactDistribution, err.Error())
		unknown(FactVersion, err.Error())
	} else {
		name, version, whyName, whyVersion := distributionOf(string(b))
		m.Distribution, m.Version = name, version
		if whyName != "" {
			unknown(FactDistribution, whyName)
		}
		if whyVersion != "" {
			unknown(FactVersion, whyVersion)
		}
	}

	if b, err := src.Read("/proc/cpuinfo"); err != nil {
		unknown(FactProcessor, err.Error())
		unknown(FactCores, err.Error())
		unknown(FactThreads, err.Error())
	} else {
		c := processorOf(string(b))
		m.Processor, m.Cores, m.Threads = c.model, c.cores, c.threads
		for fact, why := range c.unknown {
			unknown(fact, why)
		}
	}

	if b, err := src.Read("/proc/meminfo"); err != nil {
		unknown(FactMemory, err.Error())
	} else if kb, ok := memTotalKB(string(b)); !ok {
		unknown(FactMemory, "MemTotal not found in /proc/meminfo")
	} else {
		m.MemoryBytes = kb * 1024
	}

	m.Virtual, _ = virtualOf(ctx, src.Run, unknown)

	if b, err := src.Read("/proc/stat"); err != nil {
		unknown(FactUptime, err.Error())
	} else if booted, ok := bootedAt(string(b)); !ok {
		unknown(FactUptime, "btime not found in /proc/stat")
	} else {
		m.BootedAt = &booted
	}

	if tz, why := timezoneOf(src); why != "" {
		unknown(FactTimezone, why)
	} else {
		m.Timezone = tz
	}

	if b, err := src.Read("/proc/self/mounts"); err != nil {
		unknown(FactFilesystems, err.Error())
	} else {
		fs, why := filesystemsOf(ctx, string(b), src.Statfs)
		m.Filesystems = fs
		if why != "" {
			unknown(FactFilesystems, why)
		}
	}

	unknown(FactPublicAddress, publicAddressUnknown)
	return m
}

// distributionOf is the distribution's name and version from an os-release file, with why either is
// not said. NAME first, then ID; VERSION_ID first, then BUILD_ID.
func distributionOf(osRelease string) (name, version, whyName, whyVersion string) {
	fields := map[string]string{}
	for _, line := range strings.Split(osRelease, "\n") {
		line = strings.TrimSpace(line)
		if line == "" || strings.HasPrefix(line, "#") {
			continue
		}
		key, value, found := strings.Cut(line, "=")
		if !found {
			continue
		}
		fields[strings.TrimSpace(key)] = strings.Trim(strings.TrimSpace(value), `"'`)
	}
	name = firstOf(fields["NAME"], fields["ID"])
	version = firstOf(fields["VERSION_ID"], fields["BUILD_ID"])
	if name == "" {
		whyName = "/etc/os-release names neither NAME nor ID"
	}
	if version == "" {
		whyVersion = "/etc/os-release names neither VERSION_ID nor BUILD_ID"
	}
	return name, version, whyName, whyVersion
}

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

type processor struct {
	model          string
	cores, threads int
	unknown        map[string]string
}

// processorOf reads /proc/cpuinfo: the model from `model name` (or `Model`, `Hardware`, `cpu model`,
// which other architectures use), threads from its `processor` entries, and cores from the distinct
// (physical id, core id) pairs — which an architecture that does not say them leaves unknown rather than
// guessed equal to the threads.
func processorOf(cpuinfo string) processor {
	p := processor{unknown: map[string]string{}}
	pairs := map[string]bool{}
	physical := "0"
	var models = map[string]string{}
	for _, line := range strings.Split(cpuinfo, "\n") {
		key, value, found := strings.Cut(line, ":")
		if !found {
			continue
		}
		key, value = strings.TrimSpace(key), strings.TrimSpace(value)
		switch key {
		case "processor":
			p.threads++
		case "physical id":
			physical = value
		case "core id":
			pairs[physical+"/"+value] = true
		case "model name", "Model", "Hardware", "cpu model":
			if _, had := models[key]; !had {
				models[key] = value
			}
		}
	}
	p.model = firstOf(models["model name"], models["cpu model"], models["Model"], models["Hardware"])
	p.cores = len(pairs)
	if p.model == "" {
		p.unknown[FactProcessor] = "/proc/cpuinfo names no model"
	}
	if p.threads == 0 {
		p.unknown[FactThreads] = "/proc/cpuinfo lists no processor"
	}
	if p.cores == 0 {
		p.unknown[FactCores] = "/proc/cpuinfo says no core id"
	}
	return p
}

func memTotalKB(meminfo string) (int64, bool) {
	for _, line := range strings.Split(meminfo, "\n") {
		if !strings.HasPrefix(line, "MemTotal:") {
			continue
		}
		parts := strings.Fields(line)
		if len(parts) < 2 {
			return 0, false
		}
		kb, err := strconv.ParseInt(parts[1], 10, 64)
		if err != nil || kb <= 0 {
			return 0, false
		}
		return kb, true
	}
	return 0, false
}

// virtualOf asks systemd-detect-virt. It says `none` on a physical machine, and exits 1 doing so.
func virtualOf(ctx context.Context, run Runner, unknown func(string, string)) (string, bool) {
	if run == nil {
		unknown(FactVirtual, "nothing here runs commands")
		return "", false
	}
	out, err := run(ctx, "systemd-detect-virt")
	switch said := strings.TrimSpace(out); {
	case said == "none":
		return "physical", true
	case said != "" && err == nil:
		return said, true
	case err != nil:
		unknown(FactVirtual, "systemd-detect-virt: "+err.Error())
	default:
		unknown(FactVirtual, "systemd-detect-virt said nothing")
	}
	return "", false
}

func bootedAt(stat string) (time.Time, bool) {
	for _, line := range strings.Split(stat, "\n") {
		parts := strings.Fields(line)
		if len(parts) == 2 && parts[0] == "btime" {
			secs, err := strconv.ParseInt(parts[1], 10, 64)
			if err != nil || secs <= 0 {
				return time.Time{}, false
			}
			return time.Unix(secs, 0).UTC(), true
		}
	}
	return time.Time{}, false
}

// timezoneOf is the zone /etc/localtime links into the zoneinfo tree, or /etc/timezone's.
func timezoneOf(src Sources) (string, string) {
	var whys []string
	if src.Readlink != nil {
		target, err := src.Readlink("/etc/localtime")
		if err == nil {
			if _, zone, found := strings.Cut(target, "zoneinfo/"); found && zone != "" {
				return zone, ""
			}
			whys = append(whys, "/etc/localtime links to "+target+", outside a zoneinfo tree")
		} else {
			whys = append(whys, "/etc/localtime: "+err.Error())
		}
	}
	if b, err := src.Read("/etc/timezone"); err == nil {
		if zone := strings.TrimSpace(string(b)); zone != "" {
			return zone, ""
		}
		whys = append(whys, "/etc/timezone is empty")
	} else {
		whys = append(whys, err.Error())
	}
	return "", strings.Join(whys, "; ")
}

// localTypes are the filesystem types said: those on a local device. A network filesystem is left out on
// purpose — statfs on a server that stopped answering blocks, and this runs on every apply.
var localTypes = map[string]bool{"ext2": true, "ext3": true, "ext4": true, "xfs": true, "btrfs": true,
	"zfs": true, "f2fs": true, "vfat": true, "exfat": true, "ntfs": true, "ntfs3": true, "fuseblk": true,
	"jfs": true, "reiserfs": true, "bcachefs": true}

// sizing is held while a check of the filesystems' sizes runs.
var sizing sync.Mutex

// filesystemsOf lists each local filesystem once — a device mounted at several places (a btrfs
// subvolume, a bind mount) under its shortest mount — with its size and what is free. Bounded by the
// context, so a filesystem whose statfs hangs cannot hang the apply that reports it.
func filesystemsOf(ctx context.Context, mounts string, stat func(string) (int64, int64, error)) ([]Filesystem, string) {
	if stat == nil {
		return nil, "nothing here can ask a filesystem its size"
	}
	byDevice := map[string]Filesystem{}
	for _, line := range strings.Split(mounts, "\n") {
		f := strings.Fields(line)
		if len(f) < 3 || !localTypes[f[2]] {
			continue
		}
		mount := unescapeMount(f[1])
		if had, ok := byDevice[f[0]]; ok && len(had.Mount) <= len(mount) {
			continue
		}
		byDevice[f[0]] = Filesystem{Mount: mount, Device: f[0], Type: f[2]}
	}
	if len(byDevice) == 0 {
		return nil, "/proc/self/mounts lists no local filesystem"
	}

	// One check at a time, across every report: a filesystem whose statfs hangs keeps the one check that
	// asked it, and every report after it says the sizes unknown until it finishes, rather than leaving
	// another goroutine and thread blocked behind it on every apply.
	if !sizing.TryLock() {
		return nil, "the last check of the filesystems' sizes has not finished yet"
	}

	type answer struct {
		fs  []Filesystem
		why []string
	}
	done := make(chan answer, 1)
	go func() {
		defer sizing.Unlock()
		var a answer
		for _, fs := range byDevice {
			size, free, err := stat(fs.Mount)
			if err != nil {
				a.why = append(a.why, fmt.Sprintf("%s: %v", fs.Mount, err))
				continue
			}
			fs.SizeBytes, fs.FreeBytes = size, free
			a.fs = append(a.fs, fs)
		}
		done <- a
	}()
	select {
	case a := <-done:
		sort.Slice(a.fs, func(i, j int) bool { return a.fs[i].Mount < a.fs[j].Mount })
		sort.Strings(a.why)
		return a.fs, strings.Join(a.why, "; ")
	case <-ctx.Done():
		return nil, "asking the filesystems their size did not finish: " + ctx.Err().Error()
	}
}

// unescapeMount undoes the octal escapes /proc/self/mounts writes a space or tab in a path as.
func unescapeMount(path string) string {
	if !strings.Contains(path, `\`) {
		return path
	}
	var b strings.Builder
	for i := 0; i < len(path); i++ {
		if path[i] == '\\' && i+3 < len(path) {
			if n, err := strconv.ParseUint(path[i+1:i+4], 8, 8); err == nil {
				b.WriteByte(byte(n))
				i += 3
				continue
			}
		}
		b.WriteByte(path[i])
	}
	return b.String()
}