package main

import (
	"context"
	"fmt"
	"sort"
	"strconv"
	"strings"
)

// networkTypes are the filesystem types whose files live on another machine: a mount of one waits on a
// server that may be away, which is what makes it worth telling apart.
var networkTypes = map[string]bool{
	"nfs": true, "nfs4": true, "cifs": true, "smb3": true, "smbfs": true,
	"sshfs": true, "fuse.sshfs": true, "9p": true, "ceph": true, "glusterfs": true, "fuse.glusterfs": true,
	"davfs": true, "fuse.rclone": true,
}

// secretKeys are the mount options whose value is a credential. Their value is never answered.
var secretKeys = map[string]bool{"password": true, "pass": true, "passwd": true, "password2": true}

// Redacted stands in for a credential's value.
const Redacted = "(redacted)"

// RedactOptions answers a comma-separated option list with every credential's value replaced. The path
// of a credentials= file is kept: it names where the secret is, and the file is never read.
func RedactOptions(opts string) string {
	if opts == "" {
		return opts
	}
	parts := strings.Split(opts, ",")
	var out []string
	for i := 0; i < len(parts); i++ {
		p := parts[i]
		k, v, has := strings.Cut(p, "=")
		key := strings.ToLower(strings.TrimSpace(k))
		switch {
		case has && secretKeys[key]:
			// mount.cifs writes a comma inside a password as two, so the value runs on over every ",,": an
			// empty part, and the part after an empty one, are the password's. Read on the side of hiding:
			// a run of three commas could be either, and is taken as the password's.
			for i+1 < len(parts) && (parts[i+1] == "" || parts[i] == "") {
				i++
			}
			out = append(out, k+"="+Redacted)
		case has && (key == "user" || key == "username") && strings.Contains(v, "%"):
			// user=name%password: mount.cifs takes the password after the percent sign.
			name, _, _ := strings.Cut(v, "%")
			out = append(out, k+"="+name+"%"+Redacted)
		default:
			out = append(out, p)
		}
	}
	return strings.Join(out, ",")
}

// IsNetwork says whether a mount's files live on another machine, by its type or, for a type that
// does not say (fuse), by a source naming a host.
func IsNetwork(fstype, source string) bool {
	if networkTypes[fstype] {
		return true
	}
	return strings.HasPrefix(fstype, "fuse.") && strings.Contains(source, ":") && !strings.HasPrefix(source, "/")
}

// unescape decodes the octal escapes fstab and mountinfo use for a space, a tab, a newline and a
// backslash in a path (\040, \011, \012, \134).
func unescape(s string) string {
	if !strings.Contains(s, `\`) {
		return s
	}
	var b strings.Builder
	for i := 0; i < len(s); i++ {
		if s[i] == '\\' && i+4 <= len(s) {
			if n, err := strconv.ParseUint(s[i+1:i+4], 8, 8); err == nil {
				b.WriteByte(byte(n))
				i += 3
				continue
			}
		}
		b.WriteByte(s[i])
	}
	return b.String()
}

// FstabEntry is one line of /etc/fstab.
type FstabEntry struct {
	Line       int    `json:"line"`
	Source     string `json:"source"`
	Mountpoint string `json:"mountpoint"`
	Type       string `json:"type"`
	Options    string `json:"options"`
	Dump       string `json:"dump,omitempty"`
	Pass       string `json:"pass,omitempty"`
	Network    bool   `json:"network"`
}

// ParseFstab reads fstab text: comments and blank lines are skipped, and every credential in the
// options is redacted before it leaves this function.
func ParseFstab(text string) []FstabEntry {
	out := []FstabEntry{}
	for i, line := range strings.Split(text, "\n") {
		line = strings.TrimSpace(line)
		if line == "" || strings.HasPrefix(line, "#") {
			continue
		}
		f := strings.Fields(line)
		if len(f) < 2 {
			continue
		}
		e := FstabEntry{Line: i + 1, Source: unescape(f[0]), Mountpoint: unescape(f[1])}
		if len(f) > 2 {
			e.Type = f[2]
		}
		if len(f) > 3 {
			e.Options = RedactOptions(f[3])
		}
		if len(f) > 4 {
			e.Dump = f[4]
		}
		if len(f) > 5 {
			e.Pass = f[5]
		}
		e.Network = IsNetwork(e.Type, e.Source)
		out = append(out, e)
	}
	return out
}

// Mounted is one filesystem mounted now, as /proc/self/mountinfo says.
type Mounted struct {
	Mountpoint string `json:"mountpoint"`
	Source     string `json:"source"`
	Type       string `json:"type"`
	Options    string `json:"options,omitempty"`
}

// IsAutomount says whether this line is only the autofs mount an armed automount leaves at its point.
// Nothing is mounted there yet: the share is mounted over it at first use, and that line then wins in
// ParseMountinfo. Every judgement of "mounted" asks this one question, so List, the look and the checks
// before a mount cannot disagree (novox/hq issue 437).
func (mt Mounted) IsAutomount() bool {
	return mt.Type == "autofs"
}

// ParseMountinfo reads /proc/self/mountinfo: per line the mount point (field 5), and after the " - "
// separator the type, the source and the superblock options. The last mount at a point wins, as it
// is the one a path resolves to.
func ParseMountinfo(text string) map[string]Mounted {
	out := map[string]Mounted{}
	for _, line := range strings.Split(text, "\n") {
		before, after, ok := strings.Cut(line, " - ")
		if !ok {
			continue
		}
		f := strings.Fields(before)
		a := strings.Fields(after)
		if len(f) < 5 || len(a) < 2 {
			continue
		}
		mt := Mounted{Mountpoint: unescape(f[4]), Type: a[0], Source: unescape(a[1])}
		if len(a) > 2 {
			mt.Options = RedactOptions(a[2])
		}
		out[mt.Mountpoint] = mt
	}
	return out
}

// Unit is one mount or automount unit, as the service manager knows it.
type Unit struct {
	Unit         string `json:"unit"`
	Kind         string `json:"kind"`
	Where        string `json:"where"`
	What         string `json:"what,omitempty"`
	Type         string `json:"type,omitempty"`
	Options      string `json:"options,omitempty"`
	Active       string `json:"active"`
	Sub          string `json:"sub"`
	Result       string `json:"result,omitempty"`
	From         string `json:"from"`
	FragmentPath string `json:"fragment_path,omitempty"`
	SourcePath   string `json:"source_path,omitempty"`
	Timeout      string `json:"timeout,omitempty"`
	UnitFile     string `json:"unit_file_state,omitempty"`
}

// ShowProperties are what is asked of each unit.
var ShowProperties = "Id,What,Where,Type,Options,Result,ActiveState,SubState,FragmentPath,SourcePath,TimeoutUSec,UnitFileState"

// ParseListUnits reads `systemctl list-units --plain --no-legend`: the unit name is the first field.
func ParseListUnits(text string) []string {
	out := []string{}
	for _, line := range strings.Split(text, "\n") {
		f := strings.Fields(line)
		if len(f) == 0 {
			continue
		}
		name := strings.TrimLeft(f[0], "●* ")
		if strings.HasSuffix(name, ".mount") || strings.HasSuffix(name, ".automount") {
			out = append(out, name)
		}
	}
	return out
}

// ParseShow reads `systemctl show -p ... a b c`: one block of Key=Value lines per unit, blocks
// separated by a blank line.
func ParseShow(text string) []Unit {
	out := []Unit{}
	for _, block := range strings.Split(strings.ReplaceAll(text, "\r", ""), "\n\n") {
		kv := map[string]string{}
		for _, line := range strings.Split(block, "\n") {
			k, v, ok := strings.Cut(line, "=")
			if ok {
				kv[k] = v
			}
		}
		if kv["Id"] == "" {
			continue
		}
		u := Unit{
			Unit: kv["Id"], Where: kv["Where"], What: kv["What"], Type: kv["Type"],
			Options: RedactOptions(kv["Options"]), Active: kv["ActiveState"], Sub: kv["SubState"],
			Result: kv["Result"], FragmentPath: kv["FragmentPath"], SourcePath: kv["SourcePath"],
			Timeout: kv["TimeoutUSec"], UnitFile: kv["UnitFileState"],
		}
		u.Kind = "mount"
		if strings.HasSuffix(u.Unit, ".automount") {
			u.Kind = "automount"
		}
		switch {
		case strings.HasPrefix(u.FragmentPath, "/run/systemd/generator"):
			u.From = "generated from " + orDefault(u.SourcePath, "/etc/fstab")
		case u.FragmentPath != "":
			u.From = "unit file " + u.FragmentPath
		default:
			u.From = "made by the service manager at runtime (no unit file)"
		}
		out = append(out, u)
	}
	return out
}

func orDefault(s, d string) string {
	if s == "" {
		return d
	}
	return s
}

// Mount is one mount point, everything the machine knows of it joined: its fstab line, its mount and
// automount units, and what is mounted there now.
type Mount struct {
	Mountpoint string      `json:"mountpoint"`
	Network    bool        `json:"network"`
	Fstab      *FstabEntry `json:"fstab,omitempty"`
	MountUnit  *Unit       `json:"mount_unit,omitempty"`
	Automount  *Unit       `json:"automount_unit,omitempty"`
	MountedNow *Mounted    `json:"mounted_now,omitempty"`
}

// MountsReport is what mounts_list answers.
type MountsReport struct {
	Said   []string `json:"said"`
	Mounts []Mount  `json:"mounts"`
	Notes  []string `json:"notes,omitempty"`
}

// virtualTypes are the kernel's own filesystems; a unit for one is never a storage question.
var virtualTypes = map[string]bool{
	"proc": true, "sysfs": true, "devtmpfs": true, "devpts": true, "tmpfs": true, "cgroup": true, "cgroup2": true,
	"securityfs": true, "pstore": true, "efivarfs": true, "bpf": true, "debugfs": true, "tracefs": true,
	"configfs": true, "fusectl": true, "mqueue": true, "hugetlbfs": true, "binfmt_misc": true, "autofs": true,
	"nsfs": true, "overlay": true, "ramfs": true, "rpc_pipefs": true, "nfsd": true,
}

// List joins fstab, the service manager's units and mountinfo, narrowed as asked.
func (m *Machine) List(onlyNetwork bool, match string) MountsReport {
	r := MountsReport{Said: []string{}, Mounts: []Mount{}}
	byPoint := map[string]*Mount{}
	get := func(p string) *Mount {
		if mt, ok := byPoint[p]; ok {
			return mt
		}
		mt := &Mount{Mountpoint: p}
		byPoint[p] = mt
		return mt
	}

	fstab, err := m.read("/etc/fstab")
	if err != nil {
		r.Notes = append(r.Notes, unreadable("/etc/fstab", err))
	}
	for _, e := range ParseFstab(fstab) {
		if e.Type == "swap" || e.Mountpoint == "none" {
			continue
		}
		e := e
		get(e.Mountpoint).Fstab = &e
	}

	info, err := m.read("/proc/self/mountinfo")
	if err != nil {
		r.Notes = append(r.Notes, unreadable("/proc/self/mountinfo", err))
	}
	now := ParseMountinfo(info)

	ctx := context.Background()
	listed, err := m.Run(ctx, "systemctl", "list-units", "--type=mount,automount", "--all", "--no-legend", "--plain", "--no-pager")
	if err != nil {
		r.Notes = append(r.Notes, fmt.Sprintf("the service manager's units were not read: %v", err))
	}
	if names := ParseListUnits(listed); len(names) > 0 {
		// The names go after "--": the root mount's unit is -.mount, and systemctl reads an argument
		// that starts with a dash as an option and refuses the whole call, so every mount lost its
		// unit state (novox/hq issue 374).
		args := append([]string{"show", "-p", ShowProperties, "--no-pager", "--"}, names...)
		shown, err := m.Run(ctx, "systemctl", args...)
		if err != nil && shown == "" {
			r.Notes = append(r.Notes, fmt.Sprintf("the units' properties were not read: %v", err))
		}
		for _, u := range ParseShow(shown) {
			if u.Where == "" || virtualTypes[u.Type] {
				continue
			}
			u := u
			mt := get(u.Where)
			if u.Kind == "automount" {
				mt.Automount = &u
			} else {
				mt.MountUnit = &u
			}
		}
	}

	for p, mt := range byPoint {
		if cur, ok := now[p]; ok {
			cur := cur
			mt.MountedNow = &cur
		}
		mt.Network = mt.Fstab != nil && mt.Fstab.Network ||
			mt.MountUnit != nil && IsNetwork(mt.MountUnit.Type, mt.MountUnit.What) ||
			mt.MountedNow != nil && IsNetwork(mt.MountedNow.Type, mt.MountedNow.Source)
	}

	points := make([]string, 0, len(byPoint))
	for p := range byPoint {
		points = append(points, p)
	}
	sort.Strings(points)
	for _, p := range points {
		mt := byPoint[p]
		if onlyNetwork && !mt.Network {
			continue
		}
		if match != "" && !strings.Contains(p, match) && !strings.Contains(mt.source(), match) {
			continue
		}
		r.Mounts = append(r.Mounts, *mt)
		r.Said = append(r.Said, mt.say())
	}
	return r
}

func (mt *Mount) source() string {
	switch {
	case mt.Fstab != nil:
		return mt.Fstab.Source
	case mt.MountUnit != nil:
		return mt.MountUnit.What
	case mt.MountedNow != nil:
		return mt.MountedNow.Source
	}
	return ""
}

func (mt *Mount) fstype() string {
	switch {
	case mt.Fstab != nil && mt.Fstab.Type != "":
		return mt.Fstab.Type
	case mt.MountUnit != nil && mt.MountUnit.Type != "":
		return mt.MountUnit.Type
	case mt.MountedNow != nil:
		return mt.MountedNow.Type
	}
	return "?"
}

func (mt *Mount) options() string {
	if mt.Fstab != nil {
		return mt.Fstab.Options
	}
	if mt.MountUnit != nil {
		return mt.MountUnit.Options
	}
	return ""
}

// say is the mount in one line: what it is, its state, where it is declared, and for a network
// mount whether it can hold up a boot.
func (mt *Mount) say() string {
	head := fmt.Sprintf("%s (%s from %s)", mt.Mountpoint, mt.fstype(), mt.source())
	var state string
	switch {
	case mt.MountUnit != nil && mt.MountUnit.Active == "failed":
		state = "failed"
		if mt.MountUnit.Result != "" && mt.MountUnit.Result != "success" {
			state += ", " + mt.MountUnit.Result
		}
	case mt.MountedNow != nil && !mt.MountedNow.IsAutomount():
		state = "mounted"
	case mt.Automount != nil && mt.Automount.Active == "active":
		state = "not mounted, waits for its first use (automount " + mt.Automount.Sub + ")"
	case mt.MountUnit != nil:
		state = "not mounted (" + mt.MountUnit.Active + ", " + mt.MountUnit.Sub + ")"
	default:
		state = "not mounted"
	}
	var from []string
	switch {
	case mt.Fstab != nil:
		from = append(from, fmt.Sprintf("from /etc/fstab line %d", mt.Fstab.Line))
	case mt.MountUnit != nil:
		from = append(from, mt.MountUnit.From)
	}
	if mt.Network {
		opts := "," + mt.options() + ","
		if mt.Automount == nil && !strings.Contains(opts, ",x-systemd.automount,") {
			from = append(from, "no automount")
		}
		if !strings.Contains(opts, ",nofail,") {
			from = append(from, "no nofail")
		}
	}
	line := head + ": " + state
	if len(from) > 0 {
		line += "; " + strings.Join(from, ", ")
	}
	return line
}