Better event handling via DiscordGo's handlers

tools/cmd/eventhandlers.go

@@ -0,0 +1,101 @@
+package main
+
+import (
+	"bytes"
+	"go/format"
+	"go/parser"
+	"go/token"
+	"io/ioutil"
+	"log"
+	"path/filepath"
+	"sort"
+	"strings"
+	"text/template"
+)
+
+var eventHandlerTmpl = template.Must(template.New("eventHandler").Funcs(template.FuncMap{
+	"constName":   constName,
+	"privateName": privateName,
+}).Parse(`// Code generated by "eventhandlers"; DO NOT EDIT
+// See events.go
+
+package gavalink
+
+// Following are all the event types.
+// Event type values are used to match the events returned by Lavalink.
+const ({{range .}}
+  {{privateName .}}EventType = "{{constName .}}"{{end}}
+)
+{{range .}}
+// {{privateName .}}EventHandler is an event handler for {{.}} events.
+type {{privateName .}}EventHandler func(*Player, *{{.}})
+
+// Type returns the event type for {{.}} events.
+func (eh {{privateName .}}EventHandler) Type() string {
+  return {{privateName .}}EventType
+}
+// New returns a new instance of {{.}}.
+func (eh {{privateName .}}EventHandler) New() interface{} {
+  return &{{.}}{}
+}
+// Handle is the handler for {{.}} events.
+func (eh {{privateName .}}EventHandler) Handle(p *Player, i interface{}) {
+  if t, ok := i.(*{{.}}); ok {
+    eh(p, t)
+  }
+}
+
+{{end}}
+func handlerForInterface(handler interface{}) EventHandler {
+  switch v := handler.(type) {
+  case func(*Player, interface{}):
+    return interfaceEventHandler(v){{range .}}
+  case func(*Player, *{{.}}):
+    return {{privateName .}}EventHandler(v){{end}}
+  }
+
+  return nil
+}
+
+func init() { {{range .}}
+  registerInterfaceProvider({{privateName .}}EventHandler(nil)){{end}}
+}
+`))
+
+func main() {
+	var buf bytes.Buffer
+	dir := filepath.Dir(".")
+
+	fs := token.NewFileSet()
+	parsedFile, err := parser.ParseFile(fs, "events.go", nil, 0)
+	if err != nil {
+		log.Fatalf("warning: internal error: could not parse events.go: %s", err)
+		return
+	}
+
+	names := []string{}
+	for object := range parsedFile.Scope.Objects {
+		names = append(names, object)
+	}
+	sort.Strings(names)
+	eventHandlerTmpl.Execute(&buf, names)
+
+	src, err := format.Source(buf.Bytes())
+	if err != nil {
+		log.Println("warning: internal error: invalid Go generated:", err)
+		src = buf.Bytes()
+	}
+
+	err = ioutil.WriteFile(filepath.Join(dir, strings.ToLower("eventhandlers.go")), src, 0644)
+	if err != nil {
+		log.Fatal(buf, "writing output: %s", err)
+	}
+}
+
+func constName(name string) string {
+	return name + "Event"
+}
+
+func privateName(name string) string {
+	return strings.ToLower(string(name[0])) + name[1:]
+}