decode.go

package qstring

import (
	"net/url"
	"reflect"
	"strconv"
	"strings"
	"time"
)

// Unmarshaller defines the interface for performing custom unmarshalling of
// query strings into struct values
type Unmarshaller interface {
	UnmarshalQuery(url.Values) error
}

// Unmarshal unmarshalls the provided url.Values (query string) into the
// interface provided
func Unmarshal(data url.Values, v interface{}) error {
	var d decoder
	d.init(data)
	return d.unmarshal(v)
}

// An InvalidUnmarshalError describes an invalid argument passed to Unmarshal.
// (The argument to Unmarshal must be a non-nil pointer.)
type InvalidUnmarshalError struct {
	Type reflect.Type
}

func (e InvalidUnmarshalError) Error() string {
	if e.Type == nil {
		return "qstring: Unmarshal(nil)"
	}

	if e.Type.Kind() != reflect.Ptr {
		return "qstring: Unmarshal(non-pointer " + e.Type.String() + ")"
	}
	return "qstring: Unmarshal(nil " + e.Type.String() + ")"
}

type decoder struct {
	data url.Values
}

func (d *decoder) init(data url.Values) *decoder {
	d.data = data
	return d
}

func (d *decoder) unmarshal(v interface{}) error {
	rv := reflect.ValueOf(v)
	if rv.Kind() != reflect.Ptr || rv.IsNil() {
		return &InvalidUnmarshalError{reflect.TypeOf(v)}
	}

	switch val := v.(type) {
	case Unmarshaller:
		return val.UnmarshalQuery(d.data)
	default:
		return d.value(rv)
	}
}

func (d *decoder) value(val reflect.Value) error {
	var err error
	elem := val.Elem()
	typ := elem.Type()

	for i := 0; i < elem.NumField(); i++ {
		// pull out the qstring struct tag
		elemField := elem.Field(i)
		typField := typ.Field(i)
		qstring, _ := parseTag(typField.Tag.Get(Tag))
		if qstring == "" {
			// resolvable fields must have at least the `flag` struct tag
			qstring = strings.ToLower(typField.Name)
		}

		// determine if this is an unsettable field or was explicitly set to be
		// ignored
		if !elemField.CanSet() || qstring == "-" {
			continue
		}

		// only do work if the current fields query string parameter was provided
		if query, ok := d.data[qstring]; ok {
			switch k := typField.Type.Kind(); k {
			case reflect.Slice:
				err = d.coerceSlice(query, k, elemField)
			default:
				err = d.coerce(query[0], k, elemField)
			}
		} else if typField.Type.Kind() == reflect.Struct {
			if elemField.CanAddr() {
				err = d.value(elemField.Addr())
			}
		}
		if err != nil {
			return err
		}
	}
	return nil
}

// coerce converts the provided query parameter slice into the proper type for
// the target field. this coerced value is then assigned to the current field
func (d *decoder) coerce(query string, target reflect.Kind, field reflect.Value) error {
	var err error
	var c interface{}

	switch target {
	case reflect.String:
		field.SetString(query)
	case reflect.Bool:
		c, err = strconv.ParseBool(query)
		if err == nil {
			field.SetBool(c.(bool))
		}
	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		c, err = strconv.ParseInt(query, 10, 64)
		if err == nil {
			field.SetInt(c.(int64))
		}
	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
		c, err = strconv.ParseUint(query, 10, 64)
		if err == nil {
			field.SetUint(c.(uint64))
		}
	case reflect.Float32, reflect.Float64:
		c, err = strconv.ParseFloat(query, 64)
		if err == nil {
			field.SetFloat(c.(float64))
		}
	case reflect.Struct:
		// unescape the query parameter before attempting to parse it
		query, err = url.QueryUnescape(query)
		if err != nil {
			return err
		}

		switch field.Interface().(type) {
		case time.Time:
			var t time.Time
			t, err = time.Parse(time.RFC3339, query)
			if err == nil {
				field.Set(reflect.ValueOf(t))
			}
		case ComparativeTime:
			t := *NewComparativeTime()
			err = t.Parse(query)
			if err == nil {
				field.Set(reflect.ValueOf(t))
			}
		default:
			d.value(field)
		}
	}

	return err
}

// coerceSlice creates a new slice of the appropriate type for the target field
// and coerces each of the query parameter values into the destination type.
// Should any of the provided query parameters fail to be coerced, an error is
// returned and the entire slice will not be applied
func (d *decoder) coerceSlice(query []string, target reflect.Kind, field reflect.Value) error {
	var err error
	sliceType := field.Type().Elem()
	coerceKind := sliceType.Kind()
	sl := reflect.MakeSlice(reflect.SliceOf(sliceType), 0, 0)
	// Create a pointer to a slice value and set it to the slice
	slice := reflect.New(sl.Type())
	slice.Elem().Set(sl)
	for _, q := range query {
		val := reflect.New(sliceType).Elem()
		err = d.coerce(q, coerceKind, val)
		if err != nil {
			return err
		}
		slice.Elem().Set(reflect.Append(slice.Elem(), val))
	}
	field.Set(slice.Elem())
	return nil
}