change.go

package osm

import (
	"encoding/xml"
)

// Change is the structure of a changeset to be
// uploaded or downloaded from the osm api server.
// See: http://wiki.openstreetmap.org/wiki/OsmChange
type Change struct {
	Version   string `xml:"version,attr,omitempty" json:"version,omitempty"`
	Generator string `xml:"generator,attr,omitempty" json:"generator,omitempty"`

	// to indicate the origin of the data
	Copyright   string `xml:"copyright,attr,omitempty" json:"copyright,omitempty"`
	Attribution string `xml:"attribution,attr,omitempty" json:"attribution,omitempty"`
	License     string `xml:"license,attr,omitempty" json:"license,omitempty"`

	Create *OSM `xml:"create" json:"create,omitempty"`
	Modify *OSM `xml:"modify" json:"modify,omitempty"`
	Delete *OSM `xml:"delete" json:"delete,omitempty"`
}

// AppendCreate will append the object to the Create OSM object.
func (c *Change) AppendCreate(o Object) {
	if c.Create == nil {
		c.Create = &OSM{}
	}

	c.Create.Append(o)
}

// AppendModify will append the object to the Modify OSM object.
func (c *Change) AppendModify(o Object) {
	if c.Modify == nil {
		c.Modify = &OSM{}
	}

	c.Modify.Append(o)
}

// AppendDelete will append the object to the Delete OSM object.
func (c *Change) AppendDelete(o Object) {
	if c.Delete == nil {
		c.Delete = &OSM{}
	}

	c.Delete.Append(o)
}

// HistoryDatasource converts the change object to a datasource accessible
// by feature id. All the creates, modifies and deletes will be added
// in that order.
func (c *Change) HistoryDatasource() *HistoryDatasource {
	ds := &HistoryDatasource{}

	ds.add(c.Create, true)
	ds.add(c.Modify, true)
	ds.add(c.Delete, false)

	return ds
}

// MarshalXML implements the xml.Marshaller method to allow for the
// correct wrapper/start element case and attr data.
func (c Change) MarshalXML(e *xml.Encoder, start xml.StartElement) error {
	start.Name.Local = "osmChange"
	start.Attr = []xml.Attr{}

	if c.Version != "" {
		start.Attr = append(start.Attr, xml.Attr{Name: xml.Name{Local: "version"}, Value: c.Version})
	}

	if c.Generator != "" {
		start.Attr = append(start.Attr, xml.Attr{Name: xml.Name{Local: "generator"}, Value: c.Generator})
	}

	if c.Copyright != "" {
		start.Attr = append(start.Attr, xml.Attr{Name: xml.Name{Local: "copyright"}, Value: c.Copyright})
	}

	if c.Attribution != "" {
		start.Attr = append(start.Attr, xml.Attr{Name: xml.Name{Local: "attribution"}, Value: c.Attribution})
	}

	if c.License != "" {
		start.Attr = append(start.Attr, xml.Attr{Name: xml.Name{Local: "license"}, Value: c.License})
	}

	if err := e.EncodeToken(start); err != nil {
		return err
	}

	if err := marshalInnerChange(e, "create", c.Create); err != nil {
		return err
	}

	if err := marshalInnerChange(e, "modify", c.Modify); err != nil {
		return err
	}

	if err := marshalInnerChange(e, "delete", c.Delete); err != nil {
		return err
	}

	return e.EncodeToken(start.End())
}

func marshalInnerChange(e *xml.Encoder, name string, o *OSM) error {
	if o == nil {
		return nil
	}

	t := xml.StartElement{Name: xml.Name{Local: name}}
	if err := e.EncodeToken(t); err != nil {
		return err
	}

	if err := o.marshalInnerXML(e); err != nil {
		return err
	}

	return e.EncodeToken(t.End())
}