config: load defaults

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

config/default.go

@@ -0,0 +1,218 @@
+package config
+
+import (
+	"context"
+	"reflect"
+	"strconv"
+	"strings"
+)
+
+type defaultConfig struct {
+	opts Options
+}
+
+func (c *defaultConfig) Options() Options {
+	return c.opts
+}
+
+func (c *defaultConfig) Init(opts ...Option) error {
+	for _, o := range opts {
+		o(&c.opts)
+	}
+	return nil
+}
+
+func (c *defaultConfig) Load(ctx context.Context) error {
+	valueOf := reflect.ValueOf(c.opts.Struct)
+
+	if err := c.fillValues(ctx, valueOf); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func (c *defaultConfig) fillValue(ctx context.Context, value reflect.Value, val string) error {
+	switch value.Kind() {
+	case reflect.Map:
+		t := value.Type()
+		nvals := strings.FieldsFunc(val, func(c rune) bool { return c == ',' || c == ';' })
+		if value.IsNil() {
+			value.Set(reflect.MakeMapWithSize(t, len(nvals)))
+		}
+		kt := t.Key()
+		et := t.Elem()
+		for _, nval := range nvals {
+			kv := strings.FieldsFunc(nval, func(c rune) bool { return c == '=' })
+			mkey := reflect.Indirect(reflect.New(kt))
+			mval := reflect.Indirect(reflect.New(et))
+			if err := c.fillValue(ctx, mkey, kv[0]); err != nil {
+				return err
+			}
+			if err := c.fillValue(ctx, mval, kv[1]); err != nil {
+				return err
+			}
+			value.SetMapIndex(mkey, mval)
+		}
+	case reflect.Slice, reflect.Array:
+		nvals := strings.FieldsFunc(val, func(c rune) bool { return c == ',' || c == ';' })
+		value.Set(reflect.MakeSlice(reflect.SliceOf(value.Type().Elem()), len(nvals), len(nvals)))
+		for idx, nval := range nvals {
+			nvalue := reflect.Indirect(reflect.New(value.Type().Elem()))
+			if err := c.fillValue(ctx, nvalue, nval); err != nil {
+				return err
+			}
+			value.Index(idx).Set(nvalue)
+		}
+	case reflect.Bool:
+		v, err := strconv.ParseBool(val)
+		if err != nil {
+			return err
+		}
+		value.Set(reflect.ValueOf(v))
+	case reflect.String:
+		value.Set(reflect.ValueOf(val))
+	case reflect.Float32:
+		v, err := strconv.ParseFloat(val, 32)
+		if err != nil {
+			return err
+		}
+		value.Set(reflect.ValueOf(float32(v)))
+	case reflect.Float64:
+		v, err := strconv.ParseFloat(val, 64)
+		if err != nil {
+			return err
+		}
+		value.Set(reflect.ValueOf(float64(v)))
+	case reflect.Int:
+		v, err := strconv.ParseInt(val, 10, 0)
+		if err != nil {
+			return err
+		}
+		value.Set(reflect.ValueOf(int(v)))
+	case reflect.Int8:
+		v, err := strconv.ParseInt(val, 10, 8)
+		if err != nil {
+			return err
+		}
+		value.Set(reflect.ValueOf(v))
+	case reflect.Int16:
+		v, err := strconv.ParseInt(val, 10, 16)
+		if err != nil {
+			return err
+		}
+		value.Set(reflect.ValueOf(int16(v)))
+	case reflect.Int32:
+		v, err := strconv.ParseInt(val, 10, 32)
+		if err != nil {
+			return err
+		}
+		value.Set(reflect.ValueOf(int32(v)))
+	case reflect.Int64:
+		v, err := strconv.ParseInt(val, 10, 64)
+		if err != nil {
+			return err
+		}
+		value.Set(reflect.ValueOf(int64(v)))
+	case reflect.Uint:
+		v, err := strconv.ParseUint(val, 10, 0)
+		if err != nil {
+			return err
+		}
+		value.Set(reflect.ValueOf(uint(v)))
+	case reflect.Uint8:
+		v, err := strconv.ParseUint(val, 10, 8)
+		if err != nil {
+			return err
+		}
+		value.Set(reflect.ValueOf(uint8(v)))
+	case reflect.Uint16:
+		v, err := strconv.ParseUint(val, 10, 16)
+		if err != nil {
+			return err
+		}
+		value.Set(reflect.ValueOf(uint16(v)))
+	case reflect.Uint32:
+		v, err := strconv.ParseUint(val, 10, 32)
+		if err != nil {
+			return err
+		}
+		value.Set(reflect.ValueOf(uint32(v)))
+	case reflect.Uint64:
+		v, err := strconv.ParseUint(val, 10, 64)
+		if err != nil {
+			return err
+		}
+		value.Set(reflect.ValueOf(uint64(v)))
+	}
+	return nil
+}
+
+func (c *defaultConfig) fillValues(ctx context.Context, valueOf reflect.Value) error {
+	var values reflect.Value
+
+	if valueOf.Kind() == reflect.Ptr {
+		values = valueOf.Elem()
+	} else {
+		values = valueOf
+	}
+
+	if values.Kind() == reflect.Invalid {
+		return ErrInvalidStruct
+	}
+
+	fields := values.Type()
+
+	for idx := 0; idx < fields.NumField(); idx++ {
+		field := fields.Field(idx)
+		value := values.Field(idx)
+		if !value.CanSet() {
+			continue
+		}
+		if len(field.PkgPath) != 0 {
+			continue
+		}
+		switch value.Kind() {
+		case reflect.Ptr:
+			if value.IsNil() {
+				if value.Type().Elem().Kind() != reflect.Struct {
+					// nil pointer to a non-struct: leave it alone
+					break
+				}
+				// nil pointer to struct: create a zero instance
+				value.Set(reflect.New(value.Type().Elem()))
+			}
+			value = value.Elem()
+			if err := c.fillValues(ctx, value); err != nil {
+				return err
+			}
+			continue
+		}
+		tag, ok := field.Tag.Lookup(c.opts.StructTag)
+		if !ok {
+			return nil
+		}
+
+		if err := c.fillValue(ctx, value, tag); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func (c *defaultConfig) Save(ctx context.Context) error {
+	return nil
+}
+
+func (c *defaultConfig) String() string {
+	return "default"
+}
+
+func NewConfig(opts ...Option) Config {
+	options := NewOptions(opts...)
+	if len(options.StructTag) == 0 {
+		options.StructTag = "default"
+	}
+	return &defaultConfig{opts: options}
+}