package main

// What this machine is asked to mount (novox/hq ADR 0263, to-be 52 §2), and where the module keeps
// what it learns.
//
// The mesh renders ConfigFile from the assignment: the settings `shares` and `sources`, and the binding
// of the provision `nfs-share` (`from`, the machine that shares, and `at`, where it is reached). The
// long-running process reads it as root and writes the mount units; the bundle reads it as the operator
// account to read what the sharing machine exports from the bus. Nothing in it is secret: an SMB source's username is in its
// entry of sources, and its password the module's own secret smb-password-<source>, in a file only root reads.

import (
	"fmt"
	"net/url"
	"path/filepath"
	"regexp"
	"strings"
	"unicode"
)

// Where the module keeps its things. ConfigFile is placed by the mesh; the rest by the module's code.
const (
	ConfigFile = "/etc/mesh-mounts/mounts.conf"
	// BusDir is written by the bundle, which runs as the operator account and reaches the bus; the
	// process, which runs as root and does not, reads what the sharing machine said from it.
	BusDir      = "/var/lib/mesh-mounts/from-bus"
	ExportsFile = BusDir + "/exports.json"
	// RunDir is the process's: what it found on its last look, which the tools and the bundle read.
	RunDir     = "/run/mesh-mounts"
	StatusFile = RunDir + "/status.json"
	// UnitDir is where the process writes each unit pair, beside the operator's own units.
	UnitDir = "/etc/systemd/system"
)

// None is the value of an empty setting: a definition's default may not be empty (ADR 0262).
const None = "none"

// Config is the rendered file, read.
type Config struct {
	Shares  []Wanted `json:"shares"`
	Sources []Source `json:"sources"`
	// Server is the machine sharing the provision `nfs-share` (the binding's `from`), and At where it is
	// reached on the private network (the binding's `at`).
	Server string `json:"server,omitempty"`
	At     string `json:"at,omitempty"`
	// Passwords is the directory where the mesh places each SMB source's password,
	// `smb-password-<source>.secret` (ADR 0283); State is the module's state directory, where the
	// per-source credentials files are written.
	Passwords string `json:"passwords,omitempty"`
	State     string `json:"state,omitempty"`
	Account   string `json:"account,omitempty"`
	// Node is this machine's name: a share this machine serves itself is never mounted onto it.
	Node string `json:"node,omitempty"`
	// Problems are what in the file could not be read; each is said, and its share is left out.
	Problems []string `json:"problems,omitempty"`
	// Unreadable are the entries of shares or sources that could not be read. While there is one, no
	// pair is removed: an entry the operator mistyped names a mount point nobody can tell, so the
	// module cannot tell which of its pairs it still names (review of 2026-10-08, finding 8).
	Unreadable []string `json:"unreadable,omitempty"`
}

// Wanted is one NFS share this machine mounts: the share's name on the sharing machine, and where.
type Wanted struct {
	Name       string `json:"name"`
	Mountpoint string `json:"mountpoint"`
	ReadOnly   bool   `json:"read_only"`
}

// Source is one occasional source: a device that is not a node and is not always there.
type Source struct {
	Name  string `json:"name"`
	Kind  string `json:"kind"` // smb or disk
	Host  string `json:"host,omitempty"`
	Share string `json:"share,omitempty"`
	// User is an SMB source's username, from its entry (`smb://<user>@<host>/<share>`), percent-decoded;
	// empty when the entry names none, and the source then waits for it (ADR 0283). Not a secret.
	User       string `json:"user,omitempty"`
	UUID       string `json:"uuid,omitempty"`
	Mountpoint string `json:"mountpoint"`
	ReadOnly   bool   `json:"read_only"`
}

var (
	nameRe  = regexp.MustCompile(`^[a-z0-9][a-z0-9-]{0,62}$`)
	hostRe  = regexp.MustCompile(`^[A-Za-z0-9][A-Za-z0-9.-]{0,252}$`)
	shareRe = regexp.MustCompile(`^[A-Za-z0-9][A-Za-z0-9 ._$-]{0,79}$`)
	uuidRe  = regexp.MustCompile(`^[A-Za-z0-9-]{4,64}$`)
)

// CheckMountpoint refuses a mount point the module may not use: not absolute, not clean, the root, or
// under a directory the system owns.
func CheckMountpoint(p string) error {
	switch {
	case !strings.HasPrefix(p, "/"):
		return fmt.Errorf("the mount point %q is not an absolute path", p)
	case filepath.Clean(p) != p:
		return fmt.Errorf("the mount point %q is not written plainly (it would be %q)", p, filepath.Clean(p))
	case strings.ContainsAny(p, " \t\n\\\"'"):
		return fmt.Errorf("the mount point %q holds a space, a quote or a backslash", p)
	}
	for _, sys := range []string{"/", "/etc", "/usr", "/bin", "/sbin", "/lib", "/lib64", "/boot", "/proc", "/sys", "/dev", "/run", "/var", "/home", "/root", "/tmp"} {
		if p == sys {
			return fmt.Errorf("the mount point %q is the system's own directory", p)
		}
	}
	for _, sys := range []string{"/etc/", "/usr/", "/bin/", "/sbin/", "/lib/", "/boot/", "/proc/", "/sys/", "/dev/", "/run/"} {
		if strings.HasPrefix(p, sys) {
			return fmt.Errorf("the mount point %q is under %s, which is the system's", p, strings.TrimSuffix(sys, "/"))
		}
	}
	return nil
}

func entries(v string) []string {
	v = strings.TrimSpace(v)
	if v == "" || v == None {
		return nil
	}
	return strings.FieldsFunc(v, func(r rune) bool { return r == ' ' || r == ',' || r == '\n' || r == '\t' })
}

func readOnly(s string) (string, bool) {
	if strings.HasSuffix(s, ":ro") {
		return strings.TrimSuffix(s, ":ro"), true
	}
	return strings.TrimSuffix(s, ":rw"), false
}

// ParseShares reads the setting `shares`: space-separated `name=mountpoint`, each optionally `:ro`.
// What cannot be read is said, and only that entry is left out.
func ParseShares(v string) ([]Wanted, []string) {
	var out []Wanted
	var problems []string
	seen := map[string]bool{}
	for _, e := range entries(v) {
		name, rest, ok := strings.Cut(e, "=")
		if !ok {
			problems = append(problems, fmt.Sprintf("the share %q is not name=mountpoint", e))
			continue
		}
		point, ro := readOnly(rest)
		if !nameRe.MatchString(name) {
			problems = append(problems, fmt.Sprintf("the share name %q is not lower-case letters, digits and dashes", name))
			continue
		}
		if err := CheckMountpoint(point); err != nil {
			problems = append(problems, fmt.Sprintf("the share %s: %v", name, err))
			continue
		}
		if seen[name] || seen["@"+point] {
			problems = append(problems, fmt.Sprintf("the share %s or its mount point %s is named twice", name, point))
			continue
		}
		seen[name], seen["@"+point] = true, true
		out = append(out, Wanted{Name: name, Mountpoint: point, ReadOnly: ro})
	}
	return out, problems
}

// ParseSources reads the setting `sources`: space-separated `name=smb://<host>/<share>@<mountpoint>` or
// `name=disk:<uuid>@<mountpoint>`, each optionally `:ro`.
func ParseSources(v string) ([]Source, []string) {
	var out []Source
	var problems []string
	seen := map[string]bool{}
	// **Nothing an entry holds is said back until the whole entry has read**: an entry may carry a password
	// where the user goes, in any scheme, and a password with a space or a comma splits it in two, whose
	// tail may itself look like name=…. A malformed entry is named by its position alone.
	for i, e := range entries(v) {
		name, rest, ok := strings.Cut(e, "=")
		if !ok || !nameRe.MatchString(name) {
			problems = append(problems, malformed(i, "it is not name=<where>@<mountpoint>, its name lower-case letters, digits and dashes"))
			continue
		}
		at := strings.LastIndex(rest, "@")
		if at < 0 {
			problems = append(problems, malformed(i, "it names no mount point (…@<mountpoint>)"))
			continue
		}
		where, pointRO := rest[:at], rest[at+1:]
		point, ro := readOnly(pointRO)
		if CheckMountpoint(point) != nil {
			problems = append(problems, malformed(i, "its mount point is not an absolute, plainly written path outside the system's own directories"))
			continue
		}
		s := Source{Name: name, Mountpoint: point, ReadOnly: ro}
		switch {
		case strings.HasPrefix(where, "smb://"):
			user, host, share, problem := parseSMB(strings.TrimPrefix(where, "smb://"))
			if problem != "" {
				problems = append(problems, malformed(i, problem))
				continue
			}
			s.Kind, s.User, s.Host, s.Share = "smb", user, host, share
		case strings.HasPrefix(where, "disk:"):
			uuid := strings.TrimPrefix(where, "disk:")
			if !uuidRe.MatchString(uuid) {
				problems = append(problems, malformed(i, "it is not disk:<filesystem uuid>"))
				continue
			}
			s.Kind, s.UUID = "disk", uuid
		default:
			problems = append(problems, malformed(i, "it is neither smb://[<user>@]<host>/<share> nor disk:<uuid>"))
			continue
		}
		if seen[name] || seen["@"+point] {
			problems = append(problems, fmt.Sprintf("the source %s or its mount point is named twice", name))
			continue
		}
		seen[name], seen["@"+point] = true, true
		out = append(out, s)
	}
	return out, problems
}

// malformed is a problem with the i-th entry of sources, by its position alone: nothing it holds is said.
func malformed(i int, why string) string {
	return fmt.Sprintf("entry %d of sources is malformed: %s", i+1, why)
}

// ParseConfig reads the rendered file: `key=value` lines.
func ParseConfig(text string) Config {
	kv := map[string]string{}
	for _, line := range strings.Split(text, "\n") {
		line = strings.TrimSpace(line)
		if line == "" || strings.HasPrefix(line, "#") {
			continue
		}
		k, v, ok := strings.Cut(line, "=")
		if ok {
			kv[strings.TrimSpace(k)] = strings.TrimSpace(v)
		}
	}
	var c Config
	var p []string
	c.Shares, p = ParseShares(kv["shares"])
	c.Problems = append(c.Problems, p...)
	c.Unreadable = append(c.Unreadable, p...)
	c.Sources, p = ParseSources(kv["sources"])
	c.Problems = append(c.Problems, p...)
	c.Unreadable = append(c.Unreadable, p...)
	c.Server, c.At, c.Passwords, c.State, c.Account = kv["server"], kv["at"], kv["passwords"], kv["state"], kv["account"]
	if c.Passwords == "" {
		c.Passwords = c.State
	}
	c.Node = kv["node"]
	if c.At != "" && !hostRe.MatchString(c.At) {
		c.Problems = append(c.Problems, fmt.Sprintf("the sharing machine's address %q is not a name or an address", c.At))
		c.At = ""
	}
	points := map[string]string{}
	for _, w := range c.Shares {
		points[w.Mountpoint] = w.Name
	}
	kept := c.Sources[:0]
	for _, s := range c.Sources {
		if other, dup := points[s.Mountpoint]; dup {
			c.Problems = append(c.Problems, fmt.Sprintf("the source %s mounts where the share %s already does", s.Name, other))
			continue
		}
		kept = append(kept, s)
	}
	c.Sources = kept
	return c
}

// ServerNode is the sharing machine, the key of its exports on the bus: the binding's `from`, else the first label of `at`.
func (c Config) ServerNode() string {
	if c.Server != "" {
		return c.Server
	}
	if c.At == "" {
		return ""
	}
	first, _, _ := strings.Cut(c.At, ".")
	return first
}

// SMBCredential is one source's login: the username from its entry of `sources`, the password from the
// source's own secret `smb-password-<source>` (novox/hq ADR 0283).
type SMBCredential struct {
	Username string
	Password string
}

// PasswordSecret is the name of a source's password: a member of the module's secret family
// `smb-password-*`, given by that full name (`secret ask <node> mounts smb-password-<source>`).
func PasswordSecret(source string) string { return "smb-password-" + source }

// PasswordFile is where the mesh places a source's password, in the directory the config names.
func PasswordFile(dir, source string) string {
	return filepath.Join(dir, PasswordSecret(source)+".secret")
}

// userRe is a username mount.cifs takes on its own line: no space, no `=`, no line break, nothing that
// would end the line early.
var userRe = regexp.MustCompile(`^[^\s=,]{1,64}$`)

// parseSMB reads what follows smb:// in a source's entry: `[<user>@]<host>/<share>`. The user is
// percent-decoded, so `DOMAIN%5Cuser` or a user holding `@` can be written; a password in its place
// (`user:pass@`) is refused, and no problem says anything of what was written.
func parseSMB(body string) (user, host, share, problem string) {
	const form = "is not smb://[<user>@]<host>/<share>, the host a name or an IPv4 address"
	if at := strings.LastIndex(body, "@"); at >= 0 {
		raw := body[:at]
		body = body[at+1:]
		switch {
		case strings.Contains(raw, ":"):
			return "", "", "", "it carries a password in the URL; a password is given as the secret smb-password-<source>, never in a setting"
		case strings.Contains(raw, "@"):
			return "", "", "", "its user holds an @; write it %40"
		}
		decoded, err := url.PathUnescape(raw)
		if err != nil || !userRe.MatchString(decoded) || strings.IndexFunc(decoded, unicode.IsControl) >= 0 {
			return "", "", "", "its user is not a username without spaces, commas, = or control characters (percent-encode a \\ or an @ in it)"
		}
		user = decoded
	}
	host, share, ok := strings.Cut(body, "/")
	if !ok || !hostRe.MatchString(host) || !shareRe.MatchString(share) {
		return "", "", "", form
	}
	return user, host, share, ""
}

// ReadPassword reads a source's password secret as one line, as typed at the desk's hidden prompt (ADR
// 0277): one trailing line break is dropped, everything else is kept as typed, so a password may hold
// spaces and `=`. Empty is not given. A second line is refused: it is said, never what it holds.
func ReadPassword(text string) (password string, given bool, err error) {
	text = strings.TrimSuffix(text, "\n")
	text = strings.TrimSuffix(text, "\r")
	if text == "" {
		return "", false, nil
	}
	if strings.ContainsAny(text, "\n\r") {
		return "", true, fmt.Errorf("holds more than one line; a password is one line")
	}
	return text, true, nil
}

// CredentialsFile is a source's credentials in mount.cifs's format.
func (c SMBCredential) CredentialsFile() string {
	return "username=" + c.Username + "\npassword=" + c.Password + "\n"
}