Refactored configuration to make sections less code intensive to add

internal/config/conf_logging.go

@@ -22,76 +22,48 @@ import (
 	"reflect"
 )
 
+const JSCKLogging string = "logging"
+
 type JobSearchConfigLogging struct {
-	Level string
-	File  string
+	Level string `cfg:"level" default:"warn"`
+	File  string `cfg:"file"`
 }
 
-// Default configuration
-func defaultConfigLogging() JobSearchConfigLogging {
-	return JobSearchConfigLogging{
-		Level: "warn",
-	}
+/*
+ * General section functions
+ * See related methods in section.go
+ */
+func (c *JobSearchConfigLogging) Keys() []string { return keysOf(c) }
+
+func (c JobSearchConfigLogging) Map() map[string]any { return mapOf(c) }
+
+func (c JobSearchConfigLogging) Flatten() map[string]any {
+	return flattenOf(JSCKLogging, c)
 }
 
-// Converts configuration to a map
-func (conf JobSearchConfigLogging) Map() map[string]any {
-	return map[string]any{
-		"level": conf.Level,
-		"file":  conf.File,
-	}
-}
-
-// Converts configuration to a flat dotted format
-func (conf JobSearchConfigLogging) Flatten() map[string]any {
-	confMap := conf.Map()
-	retMap := map[string]any{}
-	for k, v := range confMap {
-		retMap["logging."+k] = v
-	}
-	return retMap
-}
-
-// Returns the expected type of a configuration key value
 func (c JobSearchConfigLogging) TypeOf(key string) (reflect.Kind, error) {
-	switch key {
-	case "level":
-		return reflect.String, nil
-	case "file":
-		return reflect.String, nil
-	default:
-		return reflect.Invalid, errors.New("unknown configuration key")
-	}
+	return typeOf(c, key)
 }
 
-// Returns the value of a configuration key
 func (c JobSearchConfigLogging) ValueOf(key string) (any, error) {
-	switch key {
-	case "level":
-		return c.Level, nil
-	case "file":
-		return c.File, nil
-	default:
-		return "", errors.New("unknown configuration key")
-	}
+	return valueOf(c, key)
 }
 
-// Sets the value of a configuration key
 func (c *JobSearchConfigLogging) SetValue(key string, value any) error {
+	return setValue(c, key, value)
+}
+
+/* Section specific functions */
+// Checks values before they are stored (see validator)
+func (c *JobSearchConfigLogging) validate(key string, value any) error {
 	switch key {
 	case "level":
-		newLevel := value.(string)
-		switch newLevel {
+		switch value.(string) {
 		case "debug", "info", "warn", "error":
-			c.Level = value.(string)
 		default:
 			return errors.New(
 				"invalid log level. Must be one of: debug, info, warn, error")
 		}
-	case "file":
-		c.File = value.(string)
-	default:
-		return errors.New("unknown configuration key")
 	}
 	return nil
 }

internal/config/config.go

@@ -18,9 +18,8 @@ package config
 
 import (
 	"encoding/json"
-	"errors"
 	"fmt"
-	"maps"
+	"log/slog"
 	"reflect"
 	"strings"
 
@@ -31,65 +30,37 @@ import (
 const EnvPrefix string = "JOBSEARCH"
 const EtcConfigPath string = "/etc/job-search"
 
+// Each field's cfg tag must match the section's JSCK* constant.
 type JobSearchConfig struct {
-	Logging JobSearchConfigLogging
+	Logging  JobSearchConfigLogging  `cfg:"logging"`
 }
 
-// Default configuration
+// Default configuration, taken from the default struct tags
 func LoadDefaultConfig() {
-	conf := JobSearchConfig{
-		Logging: defaultConfigLogging(),
+	var conf JobSearchConfig
+	if err := applyDefaults(&conf); err != nil {
+		panic(fmt.Sprintf("config: %v", err))
 	}
 	LoadToViper(conf)
 }
 
-// Converts configuration to a map
-func (conf JobSearchConfig) Map() map[string]any {
-	confMap := map[string]any{}
-	confMap["logging"] = conf.Logging.Map()
-	return confMap
-}
+func (c JobSearchConfig) Map() map[string]any { return mapOf(c) }
 
-// Converts configuration to a flat dotted format
-func (conf JobSearchConfig) Flatten() map[string]any {
-	confFlat := map[string]any{}
-	maps.Copy(confFlat, conf.Logging.Flatten())
-	return confFlat
-}
+func (c JobSearchConfig) Flatten() map[string]any { return flattenOf("", c) }
 
-// Returns the expected type of a configuration key value
 func (c JobSearchConfig) TypeOf(key string) (reflect.Kind, error) {
-	keyParts := strings.Split(key, ".")
-	switch keyParts[0] {
-	case "logging":
-		return c.Logging.TypeOf(strings.Join(keyParts[1:], "."))
-	default:
-		return reflect.Invalid, errors.New("unknown configuration key")
-	}
+	return typeOf(c, key)
 }
 
-// Returns the expected type of a configuration value
 func (c JobSearchConfig) ValueOf(key string) (any, error) {
-	keyParts := strings.Split(key, ".")
-	switch keyParts[0] {
-	case "logging":
-		return c.Logging.ValueOf(strings.Join(keyParts[1:], "."))
-	default:
-		return nil, errors.New("unknown configuration key")
-	}
+	return valueOf(c, key)
 }
 
-// Returns the expected type of a configuration value
 func (c *JobSearchConfig) SetValue(key string, value any) error {
-	keyParts := strings.Split(key, ".")
-	switch keyParts[0] {
-	case "logging":
-		return c.Logging.SetValue(strings.Join(keyParts[1:], "."), value)
-	default:
-		return errors.New("unknown configuration key")
-	}
+	return setValue(c, key, value)
 }
 
+// Utility method for loading a configuration from Viper
 func LoadFromViper(conf *JobSearchConfig) {
 	keys := viper.AllKeys()
 	for idx := range keys {
@@ -105,10 +76,13 @@ func LoadFromViper(conf *JobSearchConfig) {
 			conf.SetValue(key, viper.GetInt(key))
 		case reflect.Bool:
 			conf.SetValue(key, viper.GetBool(key))
+		default:
+			slog.Error(fmt.Sprintf("unknown key type: %s", keyType))
 		}
 	}
 }
 
+// Utility method for loading a configuration into Viper as defaults
 func LoadToViper(conf JobSearchConfig) {
 	flatMap := conf.Flatten()
 	for key := range flatMap {
@@ -121,7 +95,7 @@ func (conf JobSearchConfig) String() string {
 	var sb strings.Builder
 	for k, v := range conf.Flatten() {
 		typ, _ := conf.TypeOf(k)
-		sb.WriteString(fmt.Sprint(k, " = ", v, " <", typ, ">"))
+		sb.WriteString(fmt.Sprint(k, " = ", v, " <", typ, ">\n"))
 	}
 	return sb.String()
 }

internal/config/config_test.go

@@ -0,0 +1,84 @@
+/*
+Copyright © 2026 Craig Williams <craig@avsdev.uk>
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU Lesser General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU Lesser General Public License for more details.
+
+You should have received a copy of the GNU Lesser General Public License
+along with this program. If not, see <http://www.gnu.org/licenses/>.
+*/
+package config
+
+import (
+	"reflect"
+	"testing"
+)
+
+// Kinds that LoadFromViper knows how to read.
+var viperKinds = map[reflect.Kind]bool{
+	reflect.String: true, reflect.Int: true, reflect.Bool: true,
+}
+
+// Every key round-trips through TypeOf/ValueOf/SetValue and has a type that
+// LoadFromViper can read.
+func TestKeysRoundTrip(t *testing.T) {
+	var conf JobSearchConfig
+	if err := applyDefaults(&conf); err != nil {
+		t.Fatalf("defaults: %v", err)
+	}
+	for key, want := range conf.Flatten() {
+		kind, err := conf.TypeOf(key)
+		if err != nil {
+			t.Errorf("TypeOf(%q): %v", key, err)
+		} else if !viperKinds[kind] {
+			t.Errorf("TypeOf(%q) = %v, which LoadFromViper does not handle", key, kind)
+		}
+		got, err := conf.ValueOf(key)
+		if err != nil || !reflect.DeepEqual(got, want) {
+			t.Errorf("ValueOf(%q) = %#v, %v; want %#v", key, got, err, want)
+		}
+		if err := conf.SetValue(key, got); err != nil {
+			t.Errorf("SetValue(%q, %#v): %v", key, got, err)
+		}
+	}
+}
+
+// Every section has the full method set, and its Flatten keys (which use the
+// section's JSCK* constant) line up with its cfg tag in the parent.
+func TestSections(t *testing.T) {
+	var conf JobSearchConfig
+	all := conf.Flatten()
+	checkSections(t, all, "", reflect.ValueOf(&conf).Elem())
+}
+
+func checkSections(t *testing.T, all map[string]any, prefix string, section reflect.Value) {
+	for _, f := range fieldsOf(section.Type()) {
+		if !f.section {
+			continue
+		}
+		fv := section.FieldByIndex(f.index)
+		name := fv.Type().Name()
+		for _, m := range []string{"Map", "Flatten", "TypeOf", "ValueOf", "SetValue"} {
+			if !fv.Addr().MethodByName(m).IsValid() {
+				t.Errorf("%s is missing method %s", name, m)
+			}
+		}
+		if flatten := fv.MethodByName("Flatten"); flatten.IsValid() {
+			keys := flatten.Call(nil)[0].Interface().(map[string]any)
+			for k := range keys {
+				if _, ok := all[joinKey(prefix, k)]; !ok {
+					t.Errorf("%s.Flatten() key %q does not match its cfg tag %q",
+						name, k, joinKey(prefix, f.key))
+				}
+			}
+		}
+		checkSections(t, all, joinKey(prefix, f.key), fv)
+	}
+}

internal/config/section.go

@@ -0,0 +1,314 @@
+/*
+Copyright © 2026 Craig Williams <craig@avsdev.uk>
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU Lesser General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU Lesser General Public License for more details.
+
+You should have received a copy of the GNU Lesser General Public License
+along with this program. If not, see <http://www.gnu.org/licenses/>.
+*/
+package config
+
+import (
+	"errors"
+	"fmt"
+	"reflect"
+	"strconv"
+	"strings"
+	"time"
+)
+
+// Configuration sections are plain structs described with struct tags:
+//
+//	cfg:"key"        the field's configuration key. Fields without it are
+//	                 not part of the configuration.
+//	default:"value"  the field's default, parsed the same way as a string
+//	                 passed to SetValue (e.g. "10m", "true", "42").
+//
+// A tagged field whose type is a struct (other than time.Time) is a nested
+// section, addressed as "section.key". An embedded struct has its tagged
+// fields promoted into the enclosing section, just as Go promotes fields.
+//
+// time.Duration fields report reflect.String from TypeOf and accept either a
+// time.Duration or a duration string such as "90s" in SetValue.
+//
+// A section can check values before they are stored by implementing
+// validator on its pointer type.
+const (
+	keyTag     = "cfg"
+	defaultTag = "default"
+)
+
+var (
+	errUnknownKey = errors.New("unknown configuration key")
+	durationType  = reflect.TypeOf(time.Duration(0))
+	timeType      = reflect.TypeOf(time.Time{})
+)
+
+// validator is implemented by sections that need to reject some values.
+// key is the field's own key within the section; value has already been
+// converted to the field's type.
+type validator interface {
+	validate(key string, value any) error
+}
+
+type field struct {
+	key        string
+	index      []int // path for reflect.Value.FieldByIndex
+	typ        reflect.Type
+	section    bool
+	def        string
+	hasDefault bool
+}
+
+// fieldsOf lists the configuration fields of a section type in declaration
+// order, with the fields of embedded structs promoted into it.
+func fieldsOf(t reflect.Type) []field {
+	var fields []field
+	for i := 0; i < t.NumField(); i++ {
+		sf := t.Field(i)
+		if sf.Anonymous && sf.Type.Kind() == reflect.Struct {
+			for _, f := range fieldsOf(sf.Type) {
+				f.index = append([]int{i}, f.index...)
+				fields = append(fields, f)
+			}
+			continue
+		}
+		key, ok := sf.Tag.Lookup(keyTag)
+		if !ok || key == "" || key == "-" || !sf.IsExported() {
+			continue
+		}
+		def, hasDefault := sf.Tag.Lookup(defaultTag)
+		fields = append(fields, field{
+			key:        key,
+			index:      []int{i},
+			typ:        sf.Type,
+			section:    sf.Type.Kind() == reflect.Struct && sf.Type != timeType,
+			def:        def,
+			hasDefault: hasDefault,
+		})
+	}
+	return fields
+}
+
+// structValue dereferences v down to the section struct it holds.
+func structValue(v any) reflect.Value {
+	rv := reflect.ValueOf(v)
+	for rv.Kind() == reflect.Pointer {
+		rv = rv.Elem()
+	}
+	if rv.Kind() != reflect.Struct {
+		panic(fmt.Sprintf("config: %T is not a configuration section", v))
+	}
+	return rv
+}
+
+// lookup resolves a dotted key to the leaf field and the section holding it.
+func lookup(section reflect.Value, key string) (reflect.Value, field, error) {
+	head, rest, nested := strings.Cut(key, ".")
+	for _, f := range fieldsOf(section.Type()) {
+		if f.key != head {
+			continue
+		}
+		switch {
+		case f.section && nested:
+			return lookup(section.FieldByIndex(f.index), rest)
+		case !f.section && !nested:
+			return section, f, nil
+		}
+		// Key matched but the shape didn't: a section with no sub-key, or a
+		// value with one.
+		return reflect.Value{}, field{}, errUnknownKey
+	}
+	return reflect.Value{}, field{}, errUnknownKey
+}
+
+func joinKey(prefix, key string) string {
+	if prefix == "" {
+		return key
+	}
+	return prefix + "." + key
+}
+
+// keysOf returns the keys directly in a section.
+func keysOf(v any) []string {
+	fields := fieldsOf(structValue(v).Type())
+	keys := make([]string, 0, len(fields))
+	for _, f := range fields {
+		keys = append(keys, f.key)
+	}
+	return keys
+}
+
+// mapOf converts a section to a map, with nested sections as nested maps.
+func mapOf(v any) map[string]any {
+	return mapOfValue(structValue(v))
+}
+
+func mapOfValue(section reflect.Value) map[string]any {
+	m := map[string]any{}
+	for _, f := range fieldsOf(section.Type()) {
+		fv := section.FieldByIndex(f.index)
+		if f.section {
+			m[f.key] = mapOfValue(fv)
+		} else {
+			m[f.key] = fv.Interface()
+		}
+	}
+	return m
+}
+
+// flattenOf converts a section to a flat map of dotted keys, each prefixed
+// with prefix (if non-empty).
+func flattenOf(prefix string, v any) map[string]any {
+	m := map[string]any{}
+	flattenInto(m, prefix, structValue(v))
+	return m
+}
+
+func flattenInto(m map[string]any, prefix string, section reflect.Value) {
+	for _, f := range fieldsOf(section.Type()) {
+		fv := section.FieldByIndex(f.index)
+		key := joinKey(prefix, f.key)
+		if f.section {
+			flattenInto(m, key, fv)
+		} else {
+			m[key] = fv.Interface()
+		}
+	}
+}
+
+// kindOf is the kind reported by TypeOf, i.e. how the value is read from
+// Viper. Durations are read as strings and parsed by SetValue.
+func kindOf(t reflect.Type) reflect.Kind {
+	if t == durationType {
+		return reflect.String
+	}
+	return t.Kind()
+}
+
+func typeOf(v any, key string) (reflect.Kind, error) {
+	_, f, err := lookup(structValue(v), key)
+	if err != nil {
+		return reflect.Invalid, err
+	}
+	return kindOf(f.typ), nil
+}
+
+func valueOf(v any, key string) (any, error) {
+	section, f, err := lookup(structValue(v), key)
+	if err != nil {
+		return nil, err
+	}
+	return section.FieldByIndex(f.index).Interface(), nil
+}
+
+// setValue sets a dotted key on the section that ptr points to.
+func setValue(ptr any, key string, value any) error {
+	section, f, err := lookup(structValue(ptr), key)
+	if err != nil {
+		return err
+	}
+	return setField(section, f, value)
+}
+
+func setField(section reflect.Value, f field, value any) error {
+	newValue, err := convert(value, f.typ)
+	if err != nil {
+		return err
+	}
+	if v, ok := section.Addr().Interface().(validator); ok {
+		if err := v.validate(f.key, newValue.Interface()); err != nil {
+			return err
+		}
+	}
+	section.FieldByIndex(f.index).Set(newValue)
+	return nil
+}
+
+// convert turns value into a value of type t. Values already of the right
+// type are used as-is; strings are parsed.
+func convert(value any, t reflect.Type) (reflect.Value, error) {
+	if value != nil {
+		rv := reflect.ValueOf(value)
+		if rv.Type().AssignableTo(t) {
+			return rv, nil
+		}
+		if s, ok := value.(string); ok {
+			return parseString(s, t)
+		}
+	}
+	return reflect.Value{}, fmt.Errorf("unsupported type %T", value)
+}
+
+func parseString(s string, t reflect.Type) (reflect.Value, error) {
+	v := reflect.New(t).Elem()
+	if t == durationType {
+		d, err := time.ParseDuration(s)
+		if err != nil {
+			return reflect.Value{}, fmt.Errorf("unable to convert to duration: %w", err)
+		}
+		v.SetInt(int64(d))
+		return v, nil
+	}
+
+	var err error
+	switch t.Kind() {
+	case reflect.String:
+		v.SetString(s)
+	case reflect.Bool:
+		var b bool
+		b, err = strconv.ParseBool(s)
+		v.SetBool(b)
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		var n int64
+		n, err = strconv.ParseInt(s, 10, t.Bits())
+		v.SetInt(n)
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
+		var n uint64
+		n, err = strconv.ParseUint(s, 10, t.Bits())
+		v.SetUint(n)
+	case reflect.Float32, reflect.Float64:
+		var n float64
+		n, err = strconv.ParseFloat(s, t.Bits())
+		v.SetFloat(n)
+	default:
+		return reflect.Value{}, fmt.Errorf("unsupported type string for %s", t)
+	}
+	if err != nil {
+		return reflect.Value{}, fmt.Errorf("unable to convert %q to %s: %w", s, t, err)
+	}
+	return v, nil
+}
+
+// applyDefaults sets every field that has a default tag, recursing into
+// nested sections. ptr must point to a section struct.
+func applyDefaults(ptr any) error {
+	return applyDefaultsTo("", structValue(ptr))
+}
+
+func applyDefaultsTo(prefix string, section reflect.Value) error {
+	for _, f := range fieldsOf(section.Type()) {
+		key := joinKey(prefix, f.key)
+		if f.section {
+			if err := applyDefaultsTo(key, section.FieldByIndex(f.index)); err != nil {
+				return err
+			}
+			continue
+		}
+		if !f.hasDefault {
+			continue
+		}
+		if err := setField(section, f, f.def); err != nil {
+			return fmt.Errorf("invalid default for %s: %w", key, err)
+		}
+	}
+	return nil
+}