package main

// The setting prefs, one entry per preference (novox/hq issue 586, ADR 0329; ADR 0316 §11 for the user.js).
//
// Until issue 586 the setting was one line of user_pref(…) statements, so a node's layer replaced it whole and
// the operator's own choices were shipped in the catalogue as the module's defaults file. Now the setting is a
// map from a preference's name to its value, and reaches the machine as ~/.config/betterbird/prefs.json, a
// file the node-engine merges from the module's layers key by key: the mesh-wide layer holds the operator's
// setup, and a node's layer overrides one preference, or takes one out with null. The module itself ships only
// its policy's locks and Betterbird's own defaults (mesh-defaults.js names the preferences it manages there).
//
// The tools turn the setting into the head of the user.js they place in the profile, where Betterbird reads it
// at its start and lets it win over what it saved itself. A preference that can hold a credential, or that
// another setting owns (an account's, an identity's, a calendar's, an address book's, a tag's), is refused, so
// each value has one owner (ADR 0316 §11, ADR 0329 §6).

import (
	"bytes"
	"encoding/json"
	"errors"
	"fmt"
	"math"
	"os"
	"regexp"
	"sort"
	"strconv"
	"strings"
)

// prefsFile is the setting prefs on the machine, written by the node-engine.
const prefsFile = ".config/betterbird/prefs.json"

// configurationOwned are the preferences the settings of ADR 0329 own: the setting prefs refuses them (§6).
var configurationOwned = []string{"calendar.registry.", "calendar.list.", "ldap_2.servers.", "mailnews.tags."}

// prefName is a preference's name as the setting may give it.
var prefName = regexp.MustCompile(`^[A-Za-z0-9_][A-Za-z0-9_.\-\[\]@{}]{0,199}$`)

// prefOwner says why the setting prefs may not set a preference, or "" when it may.
func prefOwner(name string) string {
	if passwordSecret.MatchString(name) {
		return "a preference that can hold a credential: not through the mesh"
	}
	for _, p := range accountOwned {
		if strings.HasPrefix(name, p) {
			return "an account's preference: an account is declared in the setting accounts, never in prefs (novox/hq ADR 0316 §11)"
		}
	}
	for _, p := range configurationOwned {
		if strings.HasPrefix(name, p) {
			return "owned by the setting calendars, address-books or tags, never by prefs (novox/hq ADR 0329 §6)"
		}
	}
	return ""
}

// readDeclaredPrefs reads the setting prefs on the machine: each preference's value as user.js writes it. A
// missing file says the module is not pushed here in this form; a file that names a preference another setting
// owns, or holds a value user.js cannot carry, is refused whole, naming the preference.
func (m *Machine) readDeclaredPrefs() (map[string]string, bool, error) {
	raw, err := readBounded(m.home(prefsFile))
	if errors.Is(err, os.ErrNotExist) {
		return map[string]string{}, false, nil
	}
	if err != nil {
		return nil, false, err
	}
	prefs, err := parseDeclaredPrefs(raw)
	return prefs, true, err
}

func parseDeclaredPrefs(raw []byte) (map[string]string, error) {
	var top map[string]json.RawMessage
	if err := json.Unmarshal(raw, &top); err != nil {
		return nil, fmt.Errorf("~/%s is not a JSON object: %v", prefsFile, err)
	}
	out := map[string]string{}
	body, ok := top["prefs"]
	if !ok || string(body) == "null" {
		return out, nil
	}
	var values map[string]any
	dec := json.NewDecoder(bytes.NewReader(body))
	dec.UseNumber()
	if err := dec.Decode(&values); err != nil {
		return nil, fmt.Errorf("the setting prefs is a map from a preference's name to its value: %v", err)
	}
	var problems []string
	for _, name := range sortedKeys(values) {
		if !prefName.MatchString(name) {
			problems = append(problems, fmt.Sprintf("%q is not a preference's name", name))
			continue
		}
		if why := prefOwner(name); why != "" {
			problems = append(problems, name+": "+why)
			continue
		}
		lit, err := prefLiteral(values[name])
		if err != nil {
			problems = append(problems, name+": "+err.Error())
			continue
		}
		if lit != "" {
			out[name] = lit
		}
	}
	if len(problems) > 0 {
		return nil, fmt.Errorf("the setting prefs is refused: %s", strings.Join(problems, "; "))
	}
	return out, nil
}

// prefLiteral is a setting's value as user.js writes it: true or false, a whole number, or a string. null is
// no value: a node's layer takes the mesh-wide one out with it, and Betterbird's own default holds there.
func prefLiteral(v any) (string, error) {
	switch x := v.(type) {
	case nil:
		return "", nil
	case bool:
		return strconv.FormatBool(x), nil
	case json.Number:
		n, err := x.Int64()
		if err != nil || n > math.MaxInt32 || n < math.MinInt32 {
			return "", fmt.Errorf("%s is not a whole number Betterbird keeps", x)
		}
		return strconv.FormatInt(n, 10), nil
	case float64:
		if x != math.Trunc(x) || x > math.MaxInt32 || x < math.MinInt32 {
			return "", fmt.Errorf("%v is not a whole number Betterbird keeps", x)
		}
		return strconv.FormatInt(int64(x), 10), nil
	case string:
		if strings.ContainsAny(x, lineEnds) {
			return "", errors.New("a string preference is one line")
		}
		return jsQuoted(x), nil
	}
	return "", fmt.Errorf("a value is true, false, a whole number or a string, not %T", v)
}

// prefValue is a preference's literal as the setting holds it: the reverse of prefLiteral.
func prefValue(lit string) (any, bool) {
	switch {
	case lit == "true":
		return true, true
	case lit == "false":
		return false, true
	}
	if n, err := strconv.ParseInt(lit, 10, 32); err == nil {
		return n, true
	}
	if strings.HasPrefix(lit, `"`) {
		if s, err := strconv.Unquote(lit); err == nil {
			return s, true
		}
	}
	return nil, false
}

// lineEnds are the characters a reader may take as a line's end: a setting holds none (novox/hq issue 339).
const lineEnds = "\n\r\v\f\x00\u0085

"

// jsQuoted is a string as a preference file writes it: quote, backslash and the control characters escaped the
// way Gecko's preference parser reads them.
func jsQuoted(s string) string {
	var b strings.Builder
	b.WriteByte('"')
	for _, r := range s {
		switch {
		case r == '"':
			b.WriteString(`\"`)
		case r == '\\':
			b.WriteString(`\\`)
		case r == '\n':
			b.WriteString(`\n`)
		case r == '\r':
			b.WriteString(`\r`)
		case r == '\t':
			b.WriteString(`\t`)
		case r < 0x20 || r == 0x7f || r == 0x2028 || r == 0x2029 || r == 0x85:
			fmt.Fprintf(&b, `\u%04x`, r)
		default:
			b.WriteRune(r)
		}
	}
	b.WriteByte('"')
	return b.String()
}

// declaredText is the head of the user.js the module places: its mark and the setting prefs, one statement a
// line, by name. present says the setting is on this machine; err says why it is refused.
func (m *Machine) declaredText() (string, bool, error) {
	prefs, present, err := m.readDeclaredPrefs()
	if err != nil || !present {
		return "", present, err
	}
	return composeDeclared(prefs), true, nil
}

// composeDeclared is the user.js head for a set of declared preferences.
func composeDeclared(prefs map[string]string) string {
	var b strings.Builder
	b.WriteString(mark + ", novox/hq issue 345). Owned by the mesh: the tools write it into the profile from the\n" +
		"// module's settings at Betterbird's start (betterbird_user_js with apply, betterbird_restart, the launcher), and\n" +
		"// Betterbird reads it at its start, where it wins over what Betterbird saved. Change the settings, never this file.\n" +
		"//\n// The setting prefs (novox/hq issue 586): the operator's setup, mesh-wide with a node's own layer over it.\n")
	names := make([]string, 0, len(prefs))
	for n := range prefs {
		names = append(names, n)
	}
	sort.Strings(names)
	for _, n := range names {
		fmt.Fprintf(&b, "user_pref(%s, %s);\n", quoted(n), prefs[n])
	}
	if len(names) == 0 {
		b.WriteString("// none\n")
	}
	return b.String()
}

func sortedKeys[V any](m map[string]V) []string {
	out := make([]string, 0, len(m))
	for k := range m {
		out = append(out, k)
	}
	sort.Strings(out)
	return out
}