decode.go

package properties

import (
	"fmt"
	"reflect"
	"strconv"
	"strings"
	"time"
)

// Decode assigns property values to exported fields of a struct or a
// map[string]interface{}.
//
// Decode traverses x recursively and returns an error if a value cannot be
// converted to the field type or a required value is missing for a field.
// If x is a map[string]interface{} the keys are traversed using dot notation.
// Values which contain semicolons are decoded as []string and all other
// values are decoded as string values.
//
// For structs the following type dependent decodings are used:
//
// String, boolean, numeric fields have the value of the property key assigned.
// The property key name is the name of the field. A different key and a default
// value can be set in the field's tag. Fields without default value are
// required. If the value cannot be converted to the field type an error is
// returned.
//
// time.Duration fields have the result of time.ParseDuration() assigned.
//
// time.Time fields have the vaule of time.Parse() assigned. The default layout
// is time.RFC3339 but can be set in the field's tag.
//
// Arrays and slices of string, boolean, numeric, time.Duration and time.Time
// fields have the value interpreted as a comma separated list of values. The
// individual values are trimmed of whitespace and empty values are ignored. A
// default value can be provided as a semicolon separated list in the field's
// tag.
//
// Struct fields are decoded recursively using the field name plus "." as
// prefix. The prefix (without dot) can be overridden in the field's tag.
// Default values are not supported in the field's tag. Specify them on the
// fields of the inner struct instead.
//
// Map fields must have a key of type string and are decoded recursively by
// using the field's name plus ".' as prefix and the next element of the key
// name as map key. The prefix (without dot) can be overridden in the field's
// tag. Default values are not supported.
//
// Examples:
//
//     // Field is ignored.
//     Field int `properties:"-"`
//
//     // Field is assigned value of 'Field'.
//     Field int
//
//     // Field is assigned value of 'myName'.
//     Field int `properties:"myName"`
//
//     // Field is assigned value of key 'myName' and has a default
//     // value 15 if the key does not exist.
//     Field int `properties:"myName,default=15"`
//
//     // Field is assigned value of key 'Field' and has a default
//     // value 15 if the key does not exist.
//     Field int `properties:",default=15"`
//
//     // Field is assigned value of key 'date' and the date
//     // is in format 2006-01-02
//     Field time.Time `properties:"date,layout=2006-01-02"`
//
//     // Field is assigned the non-empty and whitespace trimmed
//     // values of key 'Field' split by commas.
//     Field []string
//
//     // Field is assigned the non-empty and whitespace trimmed
//     // values of key 'Field' split by commas and has a default
//     // value ["a", "b", "c"] if the key does not exist.
//     Field []string `properties:",default=a;b;c"`
//
//     // Field is decoded recursively with "Field." as key prefix.
//     Field SomeStruct
//
//     // Field is decoded recursively with "myName." as key prefix.
//     Field SomeStruct `properties:"myName"`
//
//     // Field is decoded recursively with "Field." as key prefix
//     // and the next dotted element of the key as map key.
//     Field map[string]string
//
//     // Field is decoded recursively with "myName." as key prefix
//     // and the next dotted element of the key as map key.
//     Field map[string]string `properties:"myName"`
func (p *Properties) Decode(x interface{}) error {
	t, v := reflect.TypeOf(x), reflect.ValueOf(x)
	elemT := v.Elem().Type()

	switch {
	case isPtr(t) && isMap(elemT):
		m, ok := x.(*map[string]interface{})
		if !ok {
			return fmt.Errorf("not a map[string]interface{}: %s", elemT)
		}
		for key, val := range p.m {
			decMap(*m, key, val)
		}
		return nil

	case isPtr(t) && isStruct(elemT):
		if err := decStruct(p, "", nil, nil, v); err != nil {
			return err
		}
		return nil

	default:
		return fmt.Errorf("not a pointer to map or struct: %s", t)
	}
}

func decMap(m map[string]interface{}, key, val string) {
	if !strings.Contains(key, ".") {
		// TODO(cp): why support arrays and why semicolons instead of comma like decStruct?
		if strings.Contains(val, ";") {
			m[key] = split(val, ";")
		} else {
			m[key] = val
		}
		return
	}

	kk := strings.SplitN(key, ".", 2)
	prefix, rest := kk[0], kk[1]
	if _, ok := m[prefix]; !ok {
		m[prefix] = map[string]interface{}{}
	}
	decMap(m[prefix].(map[string]interface{}), rest, val)
}

func decStruct(p *Properties, key string, def *string, opts map[string]string, v reflect.Value) error {
	t := v.Type()

	// value returns the property value for key or the default if provided.
	value := func() (string, error) {
		if val, ok := p.Get(key); ok {
			return val, nil
		}
		if def != nil {
			return *def, nil
		}
		return "", fmt.Errorf("missing required key %s", key)
	}

	// conv converts a string to a value of the given type.
	conv := func(s string, t reflect.Type) (val reflect.Value, err error) {
		var v interface{}

		switch {
		case isDuration(t):
			v, err = time.ParseDuration(s)

		case isTime(t):
			layout := opts["layout"]
			if layout == "" {
				layout = time.RFC3339
			}
			v, err = time.Parse(layout, s)

		case isBool(t):
			v, err = boolVal(s), nil

		case isString(t):
			v, err = s, nil

		case isFloat(t):
			v, err = strconv.ParseFloat(s, 64)

		case isInt(t):
			v, err = strconv.ParseInt(s, 10, 64)

		case isUint(t):
			v, err = strconv.ParseUint(s, 10, 64)

		default:
			return reflect.Zero(t), fmt.Errorf("unsupported type %s", t)
		}
		if err != nil {
			return reflect.Zero(t), err
		}
		return reflect.ValueOf(v).Convert(t), nil
	}

	// keydef returns the property key and the default value based on the
	// name of the struct field and the options in the tag.
	keydef := func(f reflect.StructField) (string, *string, map[string]string) {
		key, opts := parseTag(f.Tag.Get("properties"))

		var def *string
		if d, ok := opts["default"]; ok {
			def = &d
		}
		if key != "" {
			return key, def, opts
		}
		return f.Name, def, opts
	}

	switch {
	case isDuration(t) || isTime(t) || isBool(t) || isString(t) || isFloat(t) || isInt(t) || isUint(t):
		s, err := value()
		if err != nil {
			return err
		}
		val, err := conv(s, t)
		if err != nil {
			return err
		}
		v.Set(val)

	case isPtr(t):
		return decStruct(p, key, def, opts, v.Elem())

	case isStruct(t):
		for i := 0; i < v.NumField(); i++ {
			fv := v.Field(i)
			fk, def, opts := keydef(t.Field(i))
			if !fv.CanSet() {
				return fmt.Errorf("cannot set ", t.Field(i).Name)
			}
			if fk == "-" {
				continue
			}
			if key != "" {
				fk = key + "." + fk
			}
			if err := decStruct(p, fk, def, opts, fv); err != nil {
				return err
			}
		}
		return nil

	case isArray(t):
		val, err := value()
		if err != nil {
			return err
		}
		vals := split(val, ";")
		a := reflect.MakeSlice(t, 0, len(vals))
		for _, s := range vals {
			val, err := conv(s, t.Elem())
			if err != nil {
				return err
			}
			a = reflect.Append(a, val)
		}
		v.Set(a)

	case isMap(t):
		valT := t.Elem()
		m := reflect.MakeMap(t)
		for postfix, _ := range p.FilterStripPrefix(key + ".").m {
			pp := strings.SplitN(postfix, ".", 2)
			mk, mv := pp[0], reflect.New(valT)
			if err := decStruct(p, key+"."+mk, nil, nil, mv); err != nil {
				return err
			}
			m.SetMapIndex(reflect.ValueOf(mk), mv.Elem())
		}
		v.Set(m)

	default:
		return fmt.Errorf("unsupported type %s", t)
	}
	return nil
}

// split splits a string on sep, trims whitespace of elements
// and omits empty elements
func split(s string, sep string) []string {
	var a []string
	for _, v := range strings.Split(s, sep) {
		if v = strings.TrimSpace(v); v != "" {
			a = append(a, v)
		}
	}
	return a
}

// parseTag parses a "key,k=v,k=v,..."
func parseTag(tag string) (key string, opts map[string]string) {
	opts = map[string]string{}
	for i, s := range strings.Split(tag, ",") {
		if i == 0 {
			key = s
			continue
		}

		pp := strings.SplitN(s, "=", 2)
		if len(pp) == 1 {
			opts[pp[0]] = ""
		} else {
			opts[pp[0]] = pp[1]
		}
	}
	return key, opts
}

func isArray(t reflect.Type) bool    { return t.Kind() == reflect.Array || t.Kind() == reflect.Slice }
func isBool(t reflect.Type) bool     { return t.Kind() == reflect.Bool }
func isDuration(t reflect.Type) bool { return t == reflect.TypeOf(time.Second) }
func isMap(t reflect.Type) bool      { return t.Kind() == reflect.Map }
func isNumeric(t reflect.Type) bool  { return isInt(t) || isUint(t) || isFloat(t) }
func isPtr(t reflect.Type) bool      { return t.Kind() == reflect.Ptr }
func isString(t reflect.Type) bool   { return t.Kind() == reflect.String }
func isStruct(t reflect.Type) bool   { return t.Kind() == reflect.Struct }
func isTime(t reflect.Type) bool     { return t == reflect.TypeOf(time.Time{}) }
func isFloat(t reflect.Type) bool {
	return t.Kind() == reflect.Float32 || t.Kind() == reflect.Float64
}
func isInt(t reflect.Type) bool {
	return t.Kind() == reflect.Int || t.Kind() == reflect.Int8 || t.Kind() == reflect.Int16 || t.Kind() == reflect.Int32 || t.Kind() == reflect.Int64
}
func isUint(t reflect.Type) bool {
	return t.Kind() == reflect.Uint || t.Kind() == reflect.Uint8 || t.Kind() == reflect.Uint16 || t.Kind() == reflect.Uint32 || t.Kind() == reflect.Uint64
}