loader

func (*Loader) Load(ctx context.Context, target any) error
{
	val := reflect.ValueOf(target)
	if val.Kind() != reflect.Ptr || val.Elem().Kind() != reflect.Struct {
		return errors.New("target must be a pointer to a struct")
	}

	finalMap := make(map[string]any)

	for _, src := range l.sources {
		data, err := src.Load(ctx)
		if err != nil {
			return fmt.Errorf("source '%s' failed: %w", src.Name(), err)
		}
		for k, v := range data {
			finalMap[strings.ToLower(k)] = v
		}
	}

	fields := parser.Parse(val.Elem().Type())

	elem := val.Elem()
	for i := 0; i < elem.NumField(); i++ {
		field := elem.Type().Field(i)
		fieldVal := elem.Field(i)
		fieldNameLower := strings.ToLower(field.Name)

		fi, hasTag := fields[fieldNameLower]

		var valueToSet any
		found := false

		if hasTag && fi.EnvKey != "" {
			if v, ok := finalMap[strings.ToLower(fi.EnvKey)]; ok {
				valueToSet = v
				found = true
			}
		}

		if !found && hasTag && fi.FlagKey != "" {
			look := strings.ReplaceAll(strings.ToLower(fi.FlagKey), "-", "_")
			if v, ok := finalMap[look]; ok {
				valueToSet = v
				found = true
			}
		}

		if !found && hasTag && fi.Default != "" {
			valueToSet = fi.Default
			found = true
		}

		if !found {
			continue
		}

		if err := setField(fieldVal, fmt.Sprintf("%v", valueToSet)); err != nil {
			return fmt.Errorf("failed to set field %s: %w", field.Name, err)
		}
	}

	return nil
}