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dot.go
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/
dot.go
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// Package dot provides an encoder for DOT format (graphviz).
package dot
import (
"fmt"
"io"
"strings"
"github.com/cayleygraph/cayley/quad"
)
func init() {
quad.RegisterFormat(quad.Format{
Name: "graphviz",
Ext: []string{".gv", ".dot"},
Writer: func(w io.Writer) quad.WriteCloser { return NewWriter(w) },
})
}
func NewWriter(w io.Writer) *Writer {
return &Writer{w: w}
}
type Writer struct {
w io.Writer
written bool
err error
}
var escaper = strings.NewReplacer(
`\`, `\\`,
`"`, `\"`,
)
func escape(s string) string {
return `"` + escaper.Replace(s) + `"`
}
func (w *Writer) writeString(s string) {
if w.err != nil {
return
}
_, w.err = w.w.Write([]byte(s))
}
func (w *Writer) WriteQuad(q quad.Quad) error {
if w.err != nil {
return w.err
}
if !w.written {
if _, err := w.w.Write([]byte(header)); err != nil {
return err
}
w.written = true
}
// TODO: use label
w.writeString("\t")
w.writeString(escape(q.Subject.String()))
w.writeString(" -> ")
w.writeString(escape(q.Object.String()))
w.writeString(" [ label = ")
w.writeString(escape(q.Predicate.String()))
w.writeString(" ];\n")
return w.err
}
func (w *Writer) Close() error {
if w.err != nil {
return w.err
}
if !w.written {
if _, w.err = w.w.Write([]byte(header)); w.err != nil {
return w.err
}
}
if _, w.err = w.w.Write([]byte(footer)); w.err != nil {
return w.err
}
w.err = fmt.Errorf("closed")
return nil
}
const header = `digraph cayley_graph {
`
const footer = "}\n"