Add partial config implementation

Progress on #3

application.go

@@ -6,8 +6,10 @@ import "flag"
 import "image"
 import "strings"
 import "net/url"
+import "path/filepath"
 import "git.tebibyte.media/tomo/tomo"
 import "git.tebibyte.media/tomo/objects"
+import "git.tebibyte.media/tomo/nasin/config"
 import "git.tebibyte.media/tomo/nasin/internal/registrar"
 
 // Application represents an application object.
@@ -180,6 +182,20 @@ func NewApplicationWindow (application Application, bounds image.Rectangle) (tom
 	return window, nil
 }
 
+// ApplicationConfig opens a new config for the specified application. It must
+// be closed when it is no longer needed.
+func ApplicationConfig (app ApplicationDescription) (config.ConfigCloser, error) {
+	user, err := ApplicationUserConfigDir(app)
+	if err != nil { return nil, err }
+	user = filepath.Join(user, "config.conf")
+	system, err := ApplicationSystemConfigDirs(app)
+	if err != nil { return nil, err }
+	for index, path := range system {
+		system[index] = filepath.Join(path, "config.conf")
+	}
+	return config.NewConfig(user, system...)
+}
+
 func errorPopupf (title, format string, v ...any) func (func ()) {
 	return func (callback func ()) {
 		dialog, err := objects.NewDialogOk (

config/config.go

@@ -0,0 +1,142 @@
+// Package config provides a configuration system for applications.
+package config
+
+import "fmt"
+import "math"
+import "strconv"
+import "git.tebibyte.media/tomo/tomo/event"
+
+type configError string;
+func (err configError) Error () string { return string(err) }
+
+const (
+	// ErrClosed is returned when Get/Set/Reset is called after the config
+	// has been closed.
+	ErrClosed = configError("attempt to access a closed config")
+	// ErrNonexistentEntry is returned when an entry was not found.
+	ErrNonexistentEntry = configError("nonexistent entry")
+	// ErrMalformedEntry is returned when a config entry could not be
+	// parsed.
+	ErrMalformedEntry = configError("malformed entry")
+	// ErrMalformedKey is returned when a key has invalid runes.
+	ErrMalformedKey = configError("malformed key")
+	// ErrMalformedValue is returned when a value could not be parsed.
+	ErrMalformedValue = configError("malformed value")
+	// ErrMalformedString is returned when a string value could not be
+	// parsed.
+	ErrMalformedStringValue = configError("malformed string value")
+	// ErrMalformedNumber is returned when a number value could not be
+	// parsed.
+	ErrMalformedNumberValue = configError("malformed number value")
+	// ErrMalformedBool is returned when a boolean value could not be
+	// parsed.
+	ErrMalformedBoolValue = configError("malformed bool value")
+	// ErrMalformedEscapeSequence us returned when an escape sequence could
+	// not be parsed.
+	ErrMalformedEscapeSequence = configError("malformed escape sequence")
+)
+
+// Config provides access to an application's configuration, and can notify an
+// application of changes to it.
+type Config interface {
+	// Get gets a value, first considering the user-level config file, and
+	// then falling back to system level config files. If the value could
+	// not be found anywhere, the specified fallback value is returned. If
+	// the key is invalid, it returns nil, ErrMalformedKey.
+	Get (key string, fallback Value) (Value, error)
+	// GetString is like Get, but will only return strings. If the value is
+	// not a string, it will return fallback.
+	GetString (key string, fallback string) (string, error)
+	// GetNumber is like Get, but will only return numbers. If the value is
+	// not a number, it will return fallback.
+	GetNumber (key string, fallback float64) (float64, error)
+	// GetBool is like Get, but will only return booleans. If the value is
+	// not a boolean, it will return fallback.
+	GetBool (key string, fallback bool) (bool, error)
+	// Set sets a value in the user-level config file. If the key is
+	// invalid, it returns ErrMalformedKey.
+	Set (key string, value Value) error
+	// Reset removes the value from the user-level config file, resetting it
+	// to what is described by the system-level config files. If the key is
+	// invalid, it returns ErrMalformedKey.
+	Reset (key string) error
+	// OnChange specifies a function to be called whenever a value is
+	// changed. The callback is always run within the backend's event loop
+	// using tomo.Do. This could have been a channel but I didn't want to do
+	// that to people.
+	OnChange (func (key string)) event.Cookie
+}
+
+// ConfigCloser is a config with a Close behavior, which stops watching the
+// config file and causes any subsequent sets/gets to return errors. Anything
+// that receives a ConfigCloser must close it when done.
+type ConfigCloser interface {
+	Config
+	// Close closes the config, causing it to stop watching for changes.
+	// Reads or writes to the config after this will return an error.
+	Close () error
+}
+
+var negativeZero = math.Copysign(0, -1)
+
+// Value is a config value. Its String behavior produces a lossless and
+// syntactically valid representation of the value.
+type Value interface {
+	value ()
+	fmt.Stringer
+}
+
+// ValueString is a string value.
+type ValueString string
+var _ Value = ValueString("")
+func (ValueString) value () { }
+func (value ValueString) String () string {
+	return fmt.Sprintf("\"%s\"", escape(string(value)))
+}
+
+// ValueNumber is a number value.
+type ValueNumber float64
+var _ Value = ValueNumber(0)
+func (ValueNumber) value () { }
+func (value ValueNumber) String () string {
+	number := float64(value)
+	// the requirements I wrote said lossless in all cases. here's lossless
+	// in all cases!
+	switch {
+	case math.IsInf(number, 0):
+		if math.Signbit(number) {
+			return "-Inf"
+		} else {
+			return "Inf"
+		}
+		
+	case math.IsNaN(number):
+		return "NaN"
+		
+	case number == 0, number == negativeZero:
+		if math.Signbit(number) {
+			return "-0"
+		} else {
+			return "0"
+		}
+		
+	case math.Round(number) == number:
+		return strconv.FormatInt(int64(number), 10)
+		
+	default:
+		return strconv.FormatFloat(number, 'f', -1, 64)
+	}
+}
+
+
+// ValueBool is a boolean value.
+var _ Value = ValueBool(false)
+type ValueBool bool
+func (ValueBool) value () { }
+func (value ValueBool) String () string {
+	if value {
+		return "true"
+	} else {
+		return "false"
+	}
+}

config/escape.go

@@ -0,0 +1,97 @@
+package config
+
+import "fmt"
+import "strings"
+// import "unicode"
+
+var escapeCodeToRune = map[rune] rune {
+	'\\': '\\',
+	'a':  '\a',
+	'b':  '\b',
+	't':  '\t',
+	'n':  '\n',
+	'v':  '\v',
+	'f':  '\f',
+	'r':  '\r',
+	'"':  '"',
+}
+
+var runeToEscapeCode = map[rune] rune { }
+func init () {
+	for code, char := range escapeCodeToRune {
+		runeToEscapeCode[char] = code
+	}
+}
+
+func escape (str string) string {
+	builder := strings.Builder { }
+	for _, char := range str {
+		code, escaped := runeToEscapeCode[char]
+		switch {
+		case escaped:
+			fmt.Fprintf(&builder, "\\%c", code)
+		// case !unicode.IsPrint(char):
+			// fmt.Fprintf(&builder, "\\%o", char)
+		default:
+			builder.WriteRune(char)
+		}
+	}
+	return builder.String()
+}
+
+func unescape (str string) (string, bool) {
+	runes := []rune(str)
+	builder := strings.Builder { }
+
+	end := func () bool {
+		return len(runes) < 1
+	}
+	next := func () {
+		if !end() { runes = runes[1:] }
+	}
+	
+	for !end() {
+		if runes[0] == '\\' {
+			if end() { return "", false }
+			next()
+			char, isEscape := escapeCodeToRune[runes[0]]
+			switch {
+			case isEscape:
+				builder.WriteRune(char)
+				next()
+			// case isOctalDigit(runes[0]):
+				// char = 0
+				// for !end() && isOctalDigit(runes[0]) {
+					// char *= 8
+					// char += runes[0] - '0'
+					// next()
+				// }
+				// builder.WriteRune(char)
+			default:
+				return "", false
+			}
+		} else {
+			builder.WriteRune(runes[0])
+			next()
+		}
+	}
+	return builder.String(), true
+}
+
+func unquote (str string) (string, bool) {
+	if len(str) < 2             { return "", false }
+	if firstRune(str)    != '"' { return "", false }
+	if str[len(str) - 1] != '"' { return "", false }
+	return str[1:len(str) - 1], true
+}
+
+func isOctalDigit (char rune) bool {
+	return char >= '0' && char <= '7'
+}
+
+func firstRune (str string) rune {
+	for _, char := range str {
+		return char
+	}
+	return 0
+}

config/escape_test.go

@@ -0,0 +1,22 @@
+package config
+
+import "testing"
+
+func TestEscape (test *testing.T) {
+	expected := `\\\a\bhello\t\n\vworld!\f\r\"`
+	got      := escape("\\\a\bhello\t\n\vworld!\f\r\"")
+	if got != expected {
+		test.Fatalf("expected: [%s]\ngot:[%s]", expected, got)
+	}
+}
+
+func TestUnescape (test *testing.T) {
+	expected := "\\\a\bhello\t\n\vworld!\f\r\""
+	got, ok  := unescape(`\\\a\bhello\t\n\vworld!\f\r\"`)
+	if !ok {
+		test.Fatalf("text could not be unescaped")
+	}
+	if got != expected {
+		test.Fatalf("expected: [%s]\ngot:[%s]", expected, got)
+	}
+}

config/file.go

@@ -0,0 +1,231 @@
+package config
+
+import "io"
+import "fmt"
+import "math"
+import "bufio"
+import "errors"
+import "strconv"
+import "strings"
+import "unicode"
+
+type line any
+type comment string
+type entry struct { key string; value Value }
+
+// File represents a config file. It preserves the order of the lines, as well
+// as blank lines and comments.
+type File struct {
+	lines []line
+	keys  map[string] int
+}
+
+// NewFile creates a blank file with nothing in it.
+func NewFile () *File {
+	return &File {
+		 keys: make(map[string] int),
+	}
+}
+
+// Parse parses a config file from a reader. This function operates on a
+// best-effort basis: A file will always be returned, and any errors encountered
+// will be joined together.
+//
+// The general format of the file is as follows:
+//   - Encoded in UTF-8
+//   - Consists of lines, separated by \n, or \r\n
+//   - Lines can be any of these:
+//     - Blank line: has only whitespace
+//     - Comment: begins with a '#'
+//     - Entry: a key/value pair separated by an '=' sign
+//
+// For entries, all whitespace on either side of the '=' sign, the key, or the
+// value is ignored. The key may contain any letter or digit, as well as '-'
+// and '.'. The value is always identified by its first rune (after the
+// preliminary whitespace of course) and can be one of:
+//   - String: either a double-quoted string, or any string of runes not
+//     identifiable as any other kind of value. The quoted string is always
+//     unquoted when it is read. Either way, these escape sequences are
+//     supported, and resolved when they are read:
+//     - '\\': a literal backslash
+//     - '\a': alert, bell
+//     - '\b': backspace
+//     - '\t': horizontal tab
+//     - '\n': line feed
+//     - '\v': vertical tab
+//     - '\f': form feed
+//     - '\r': carriage return
+//     - '\"': double quote
+//   - Number: a floating point value. It can be of the form:
+//     - Inf
+//     - -Inf
+//     - NaN
+//     - [0-9]+
+//     - [0-9]+\.[0-9]*
+//   - Bool: a boolean value. It can be one of:
+//     - true
+//     - false
+//
+// Be aware that some unquoted strings, within reason, are subject to being read
+// as some other value in the future. For example, if there were suddenly a
+// third boolean value called glorble, the unquoted string glorble would be read
+// as a boolean value instead of a string.
+func Parse (reader io.Reader) (*File, error) {
+	file := &File {
+		keys: make(map[string] int),
+	}
+	errs    := []error { }
+	scanner := bufio.NewScanner(reader)
+	
+	for scanner.Scan() {
+		text := strings.TrimSpace(scanner.Text())
+		switch {
+		case text == "",  strings.HasPrefix(text, "#"):
+			file.lines = append(file.lines, comment(text))
+		default:
+			entry, err := parseEntry(text)
+			if err == nil {
+				file.keys[entry.key] = len(file.lines)
+				file.lines = append(file.lines, entry)
+			} else {
+				errs = append (errs, err )
+			}
+		}
+	}
+	errs = append(errs, scanner.Err())
+	return file, errors.Join(errs...)
+}
+
+func parseEntry (str string) (entry, error) {
+	key, value, ok := strings.Cut(str, "=")
+	if !ok { return entry { }, ErrMalformedEntry }
+	
+	key   = strings.TrimSpace(key)
+	if !KeyValid(key) { return entry { }, ErrMalformedKey }
+
+	value = strings.TrimSpace(value)
+	parsedValue, err := ParseValue(value)
+	if err != nil { return entry { }, err }
+	
+	return entry { key: key, value: parsedValue }, nil
+}
+
+// ParseValue parses a value from a string. For any Value v,
+// ParseValue(v.String()) should hold data exactly equal to v. This function
+// does not trim whitespace.
+func ParseValue (str string) (Value, error) {
+	first := firstRune(str)
+	switch {
+	case str == "":
+		return ValueString(""), nil
+	case first == '"':
+		value, ok := unescape(str)
+		if !ok { return nil, ErrMalformedEscapeSequence }
+		value, ok = unquote(value)
+		if !ok { return nil, ErrMalformedStringValue }
+		return ValueString(value), nil
+	case first == '-' || (first >= '0' && first <= '9'):
+		value, err := strconv.ParseFloat(str, 64)
+		if err != nil { return nil, ErrMalformedNumberValue }
+		return ValueNumber(value), nil
+	case str == "false":
+		return ValueBool(false), nil
+	case str == "true":
+		return ValueBool(true), nil
+	case str == "Inf":
+		return ValueNumber(math.Inf(1)), nil
+	case str == "NaN":
+		return ValueNumber(math.NaN()), nil
+	default:
+		value, ok := unescape(str)
+		if !ok { return nil, ErrMalformedEscapeSequence }
+		return ValueString(value), nil
+	}
+}
+
+// Get gets the keyed value. If the value is unspecified, it returns nil,
+// ErrNonexistentEntry. If the key is invalid, it returns nil, ErrMalformedKey.
+func (this *File) Get (key string) (Value, error) {
+	if !KeyValid(key) { return nil, ErrMalformedKey }
+	if index, ok := this.keys[key]; ok {
+		if lin := this.lines[index].(entry); ok {
+			return lin.value, nil
+		}
+	}
+	return nil, ErrNonexistentEntry
+}
+
+// Set sets a value. If the key is invalid, it returns ErrMalformedKey.
+func (this *File) Set (key string, value Value) error {
+	if !KeyValid(key) { return ErrMalformedKey }
+	if index, ok := this.keys[key]; ok {
+		ent := this.lines[index].(entry)
+		ent.value = value
+		this.lines[index] = ent
+		return nil
+	}
+	this.keys[key] = len(this.lines)
+	this.lines     = append(this.lines, value)
+	return nil
+}
+
+// Reset removes the value from the file. If the value is set again, it will be
+// added back at the same location. Note that because of this, the positions of
+// lines are not forgotten until the file is written and reloaded. This is why
+// the method is called Reset and not Remove. If the key is invalid, it returns
+// ErrMalformedKey.
+func (this *File) Reset (key string) error {
+	if !KeyValid(key) { return ErrMalformedKey }
+	for index, lin := range this.lines {
+		if lin, ok := lin.(entry); ok {
+			if lin.key == key {
+				this.lines[index] = nil
+			}
+		}
+	}
+	return nil
+}
+
+// Map returns a map of keys to values.
+func (this *File) Map () map[string] Value {
+	mp := make(map[string] Value)
+	for key, index := range this.keys {
+		if lin, ok := this.lines[index].(entry); ok {
+			mp[key] = lin.value
+		}
+	}
+	return mp
+}
+
+// WriteTo writes the data in this file to an io.Writer.
+func (file *File) WriteTo (writer io.Writer) (n int64, err error) {
+	for _, lin := range file.lines {
+		nint := 0
+		switch lin := lin.(type) {
+		case comment:
+			nint, err = fmt.Fprintln(writer, string(lin))
+		case entry:
+			nint, err = fmt.Fprintf(writer, "%s=%v\n", lin.key, lin.value)
+		}
+		n += int64(nint)
+		if err != nil { return n, err }
+	}
+	return n, nil
+}
+
+// KeyValid returns whether a key contains only valid runes. They are:
+//   - Letters
+//   - Digits
+//   - '-'
+//   - '.'
+func KeyValid (key string) bool {
+	for _, char := range key {
+		valid :=
+			char == '.' ||
+			char == '-' ||
+			unicode.IsLetter(char) ||
+			unicode.IsDigit(char)
+		if !valid { return false }
+	}
+	return true
+}

config/file_test.go

@@ -0,0 +1,146 @@
+package config
+
+import "math"
+import "strings"
+import "testing"
+
+func TestParseEntryUnquotedString (test *testing.T) {
+	testParseEntry(test, "stringValue = Unquoted\\nString", "stringValue", ValueString("Unquoted\nString"))
+}
+
+func TestParseEntryQuotedString (test *testing.T) {
+	testParseEntry(test, "stringValue = \"Quoted\\nString\"", "stringValue", ValueString("Quoted\nString"))
+}
+
+func TestParseEntryNumber (test *testing.T) {
+	testParseEntry(test, "numberValue = -349.29034", "numberValue", ValueNumber(-349.29034))
+}
+
+func TestParseEntryNumberInf (test *testing.T) {
+	testParseEntry(test, "numberValue = Inf", "numberValue", ValueNumber(math.Inf(1)))
+}
+
+func TestParseEntryNumberNegativeInf (test *testing.T) {
+	testParseEntry(test, "numberValue = -Inf", "numberValue", ValueNumber(math.Inf(-1)))
+}
+
+func TestParseEntryNumberNaN (test *testing.T) {
+	testParseEntry(test, "numberValue = NaN", "numberValue", ValueNumber(math.NaN()))
+}
+
+func TestParseEntryBoolTrue (test *testing.T) {
+	testParseEntry(test, "boolValue = true", "boolValue", ValueBool(true))
+}
+
+func TestParseEntryBoolFalse (test *testing.T) {
+	testParseEntry(test, "boolValue = false", "boolValue", ValueBool(false))
+}
+
+func TestParseEntryComplexKey (test *testing.T) {
+	testParseEntry (
+		test, "--Something.OtherThing...another-Thing-=value",
+		"--Something.OtherThing...another-Thing-", ValueString("value"))
+}
+
+func TestParse (test *testing.T) {
+testParse(test,
+`  thing  =something
+# comment
+
+   otherThing   = otherValue
+   otherThing = otherValue1
+   otherThing = otherValue2 # not a comment
+`,
+`thing="something"
+# comment
+
+otherThing="otherValue"
+otherThing="otherValue1"
+otherThing="otherValue2 # not a comment"
+`)
+}
+
+func TestGetValue (test *testing.T) {
+	file := parseFileString(test,
+`key=askdhj
+# some comment
+key = value
+key1 = 7`)
+	got, err := file.Get("key")
+	if err != nil { test.Fatal(err) }
+	testValueString(test, got, `"value"`)
+}
+
+func TestModifyValue (test *testing.T) {
+	file := parseFileString(test,
+`key=askdhj
+# some comment
+key = value
+key1 = 7`)
+	err := file.Set("key", ValueNumber(324980.2349))
+	if err != nil { test.Fatal(err) }
+	testFileString(test, file,
+`key="askdhj"
+# some comment
+key=324980.2349
+key1=7
+`)
+}
+
+func TestResetValue (test *testing.T) {
+	file := parseFileString(test,
+`key=askdhj
+# some comment
+key = value
+
+key1 = 7`)
+	err := file.Reset("key")
+	if err != nil { test.Fatal(err) }
+	testFileString(test, file,
+`# some comment
+
+key1=7
+`)
+}
+
+func testParseEntry (test *testing.T, str string, key string, value Value) {
+	ent, err := parseEntry(str)
+	if err != nil { test.Fatal(err) }
+	if ent.key != key {
+		test.Fatalf("expected key: [%s]\ngot key: [%s]", key, ent.key)
+	}
+	if ent.value.String() != value.String() {
+		test.Fatalf("expected value: [%s]\ngot value: [%s]", value.String(), ent.value.String())
+	}
+}
+
+func testParse (test *testing.T, str, correct string) {
+	if correct == "" { correct = str }
+	testFileString(test, parseFileString(test, str), correct)
+}
+
+func parseFileString (test *testing.T, str string) *File {
+	file, err := Parse(strings.NewReader(str))
+	if err != nil { test.Fatal(err) }
+	return file
+}
+
+func testFileString (test *testing.T, file *File, correct string) {
+	got := strings.Builder { }
+	file.WriteTo(&got)
+	if got.String() != correct {
+		test.Error("strings do not match")
+		test.Errorf("EXPECTED:\n%s", correct)
+		test.Errorf("GOT:\n%s", got.String())
+		test.Fail()
+	}
+}
+
+func testValueString (test *testing.T, got Value, correct string) {
+	if got.String() != correct {
+		test.Error("strings do not match")
+		test.Errorf("EXPECTED:\n%s", correct)
+		test.Errorf("GOT:\n%s", got.String())
+		test.Fail()
+	}
+}

config/impl.go

@@ -0,0 +1,210 @@
+package config
+
+import "os"
+import "log"
+import "sync"
+import "slices"
+import "path/filepath"
+import "github.com/fsnotify/fsnotify"
+import "git.tebibyte.media/tomo/tomo/event"
+
+type config struct {
+	open    bool
+	watcher *fsnotify.Watcher
+
+	paths struct {
+		user     string
+		system   []string
+		watching map[string] struct { }
+	}
+
+	data struct {
+		user *File
+		system []map[string] Value
+	}
+	
+	on struct {
+		lock   sync.RWMutex
+		change event.Broadcaster[func (string)]
+	}
+}
+
+// NewConfig creates a new Config using paths to the user-level config file, and
+// a set of system config files. These files need not exist: the user-level file
+// will be created when Set is called for the first time if it does not exist
+// already, and nonexistent system files are simply ignored (unless the Config
+// finds them at any point to have been spontaneously created).
+//
+// The user file is written to when Set is called, and the system files are only
+// read from. Values in the user file override those in the system files, and
+// system files specified nearer to the start of the vararg list will override
+// those farther down.
+func NewConfig (user string, system ...string) (ConfigCloser, error) {
+	conf := new(config)
+	conf.paths.user   = user
+	conf.paths.system = system
+	err := conf.init()
+	if err != nil { return nil, err }
+	go conf.run()
+	return conf, nil
+}
+
+func (this *config) init () error {
+	watcher, err := fsnotify.NewWatcher()
+	if err != nil { return err }
+	this.watcher = watcher
+	
+	this.paths.watching = make(map[string] struct { })
+	this.watcher.Add(filepath.Dir(this.paths.user))
+	this.paths.watching[this.paths.user] = struct { } { }
+	this.reloadUser()
+	for index, path := range this.paths.system {
+		this.watcher.Add(filepath.Dir(path))
+		this.paths.watching[path] = struct { } { }
+		this.reloadSystem(index)
+	}
+
+	return nil
+}
+
+func (this *config) run () {
+	for event := range this.watcher.Events {
+		if !(event.Has(fsnotify.Write))                  { continue }
+		if _, ok := this.paths.watching[event.Name]; !ok { continue }
+
+		if event.Name == this.paths.user {
+			this.reloadUser()
+		} else {
+			index := slices.Index(this.paths.system, event.Name)
+			if index > 0 {
+				this.reloadSystem(index)
+			}
+		}
+
+		// TODO diff and call event handler if changed
+	}
+}
+
+func (this *config) Close () error {
+	this.open = false
+	return this.watcher.Close()
+}
+
+func (this *config) errIfClosed () error {
+	if this.open {
+		return nil
+	} else {
+		return ErrClosed
+	}
+}
+
+func (this *config) reloadUser () {
+	file, err := os.Open(this.paths.user)
+	if err != nil { return }
+	defer file.Close()
+	
+	userFile, err := Parse(file)
+	if err != nil {
+		log.Printf("nasin: problems loading user config file %s: %v", this.paths.user, err)
+		return
+	}
+	this.data.user = userFile
+}
+
+func (this *config) reloadSystem (index int) {
+	path := this.paths.system[index]
+	file, err := os.Open(path)
+	if err != nil { return }
+	defer file.Close()
+	
+	systemFile, err := Parse(file)
+	if err != nil {
+		log.Printf("nasin: problems loading system config file %s: %v", path, err)
+		return
+	}
+	this.data.system[index] = systemFile.Map()
+}
+
+func (this *config) saveUser () error {
+	// TODO set some sort of flag to ignore the next inotify event for the
+	// user file so we dont reload it immediately after. also need to
+	// broadacast Changed event.
+	enclosingDir := filepath.Dir(this.paths.user)
+	err := os.MkdirAll(enclosingDir, 755)
+	if err != nil { return err }
+	file, err := os.Create(this.paths.user)
+	if err != nil { return err }
+	defer file.Close()
+	_, err = this.data.user.WriteTo(file)
+	if err != nil { return err }
+	return nil
+}
+
+func (this *config) Get (key string, fallback Value) (Value, error) {
+	// try user config
+	if !KeyValid(key) { return nil, ErrMalformedKey }
+
+	if this.data.user != nil {
+		value, err := this.data.user.Get(key)
+		if err == nil && err != ErrNonexistentEntry {
+			return value, nil
+		}
+	}
+
+	// try system configs
+	for _, config := range this.data.system {
+		if value, ok := config[key]; ok {
+			return value, nil
+		}
+	}
+
+	// use fallback
+	return fallback, nil
+}
+
+func (this *config) GetString (key string, fallback string) (string, error) {
+	value, err := this.Get(key, ValueString(fallback))
+	if err != nil { return "", err }
+	if value, ok := value.(ValueString); ok {
+		return string(value), nil
+	}
+	return fallback, nil
+}
+
+func (this *config) GetNumber (key string, fallback float64) (float64, error) {
+	value, err := this.Get(key, ValueNumber(fallback))
+	if err != nil { return 0, err }
+	if value, ok := value.(ValueNumber); ok {
+		return float64(value), nil
+	}
+	return fallback, nil
+}
+
+func (this *config) GetBool (key string, fallback bool) (bool, error) {
+	value, err := this.Get(key, ValueBool(fallback))
+	if err != nil { return false, err }
+	if value, ok := value.(ValueBool); ok {
+		return bool(value), nil
+	}
+	return fallback, nil
+}
+
+func (this *config) Set (key string, value Value) error {
+	if this.data.user == nil { this.data.user = NewFile() }
+	err := this.data.user.Set(key, value)
+	if err != nil { return err }
+	return this.saveUser()
+}
+
+func (this *config) Reset (key string) error {
+	if this.data.user == nil { this.data.user = NewFile() }
+	err := this.data.user.Reset(key)
+	if err != nil { return err }
+	return this.saveUser()
+}
+
+func (this *config) OnChange (callback func (string)) event.Cookie {
+	this.on.lock.Lock()
+	defer this.on.lock.Unlock()
+	return this.on.change.Connect(callback)
+}

go.mod

@@ -8,6 +8,7 @@ require (
 	git.tebibyte.media/tomo/objects v0.22.0
 	git.tebibyte.media/tomo/tomo v0.46.1
 	git.tebibyte.media/tomo/xdg v0.1.0
+	github.com/fsnotify/fsnotify v1.7.0
 	golang.org/x/image v0.11.0
 )
 
@@ -18,4 +19,5 @@ require (
 	github.com/BurntSushi/graphics-go v0.0.0-20160129215708-b43f31a4a966 // indirect
 	github.com/jezek/xgb v1.1.1 // indirect
 	github.com/jezek/xgbutil v0.0.0-20231116234834-47f30c120111 // indirect
+	golang.org/x/sys v0.5.0 // indirect
 )

go.sum

@@ -17,6 +17,8 @@ github.com/BurntSushi/freetype-go v0.0.0-20160129220410-b763ddbfe298 h1:1qlsVAQJ
 github.com/BurntSushi/freetype-go v0.0.0-20160129220410-b763ddbfe298/go.mod h1:D+QujdIlUNfa0igpNMk6UIvlb6C252URs4yupRUV4lQ=
 github.com/BurntSushi/graphics-go v0.0.0-20160129215708-b43f31a4a966 h1:lTG4HQym5oPKjL7nGs+csTgiDna685ZXjxijkne828g=
 github.com/BurntSushi/graphics-go v0.0.0-20160129215708-b43f31a4a966/go.mod h1:Mid70uvE93zn9wgF92A/r5ixgnvX8Lh68fxp9KQBaI0=
+github.com/fsnotify/fsnotify v1.7.0 h1:8JEhPFa5W2WU7YfeZzPNqzMP6Lwt7L2715Ggo0nosvA=
+github.com/fsnotify/fsnotify v1.7.0/go.mod h1:40Bi/Hjc2AVfZrqy+aj+yEI+/bRxZnMJyTJwOpGvigM=
 github.com/jezek/xgb v1.1.0/go.mod h1:nrhwO0FX/enq75I7Y7G8iN1ubpSGZEiA3v9e9GyRFlk=
 github.com/jezek/xgb v1.1.1 h1:bE/r8ZZtSv7l9gk6nU0mYx51aXrvnyb44892TwSaqS4=
 github.com/jezek/xgb v1.1.1/go.mod h1:nrhwO0FX/enq75I7Y7G8iN1ubpSGZEiA3v9e9GyRFlk=
@@ -42,6 +44,7 @@ golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7w
 golang.org/x/sys v0.0.0-20210615035016-665e8c7367d1/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20220520151302-bc2c85ada10a/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20220722155257-8c9f86f7a55f/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.5.0 h1:MUK/U/4lj1t1oPg0HfuXDN/Z1wv31ZJ/YcPiGccS4DU=
 golang.org/x/sys v0.5.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
 golang.org/x/term v0.0.0-20210927222741-03fcf44c2211/go.mod h1:jbD1KX2456YbFQfuXm/mYQcufACuNUgVhRMnK/tPxf8=