go-gst/cmd/gst-plugin-gen/main.go

package main

import (
	"bufio"
	"io"
	"os"
	"path"
	"path/filepath"
	"reflect"
	"strings"
	"text/template"
)

func main() {
	var wd string
	var err error
	if len(os.Args) == 1 {
		wd, err = os.Getwd()
		if err != nil {
			panic(err)
		}
	} else {
		wd = os.Args[1]
	}

	cfg := buildCfgFromDir(wd)

	outfile := path.Join(wd, "zzgenerated_plugin.go")
	out, err := os.Create(outfile)
	if err != nil {
		panic(err)
	}
	defer out.Close()

	pluginTmpl.Execute(out, map[string]interface{}{
		"Config": cfg,
	})
}

type libraryConfig struct {
	Plugin  *pluginConfig
	Element *elementConfig
}

type pluginConfig struct {
	Name, Description, Version, License, Source, Package, Origin, ReleaseDate string
}

type elementConfig struct {
	Name, Rank, Impl, Subclass, Interfaces string
}

func buildCfgFromDir(dir string) *libraryConfig {
	cfg := &libraryConfig{
		Plugin:  &pluginConfig{},
		Element: &elementConfig{},
	}
	err := filepath.Walk(dir, func(path string, info os.FileInfo, err error) error {
		if err != nil {
			return err
		}
		if info.IsDir() {
			return nil
		}
		if !strings.HasSuffix(path, ".go") {
			return nil
		}
		parseFileIntoCfg(path, cfg)
		return nil
	})
	if err != nil {
		panic(err)
	}
	return cfg
}

func parseFileIntoCfg(path string, cfg *libraryConfig) {
	f, err := os.Open(path)
	if err != nil {
		panic(err)
	}
	scanner := bufio.NewScanner(f)
	for scanner.Scan() {
		line := scanner.Text()
		if !strings.HasPrefix(line, "// +") {
			continue
		}
		line = strings.TrimPrefix(line, "// +")
		if strings.HasPrefix(line, "plugin:") {
			parseLineToConfig("plugin", line, cfg.Plugin)
			continue
		}
		if strings.HasPrefix(line, "element:") {
			parseLineToConfig("element", line, cfg.Element)
		}
	}
	if err := scanner.Err(); err != nil && err != io.EOF {
		panic(err)
	}
}

func parseLineToConfig(prefix, line string, cfg interface{}) {
	trimmed := strings.TrimPrefix(line, prefix+":")
	arg, val := parseArgAndValue(trimmed)
	v := reflect.ValueOf(cfg).Elem()
	for i := 0; i < v.NumField(); i++ {
		if v.Type().Field(i).Name == arg {
			v.FieldByName(arg).SetString(val)
		}
	}
}

func parseArgAndValue(line string) (arg, val string) {
	spl := strings.Split(line, "=")
	return spl[0], spl[1]
}

var pluginTmpl = template.Must(template.New("").Funcs(template.FuncMap{
	"adjustedName": func(name string) string {
		return strings.ToLower(strings.Replace(name, "-", "_", -1))
	},
	"splitInterfaces": func(ifacesString string) []string {
		return strings.Split(ifacesString, ",")
	},
	"extendsFromBase": func(subclass string) bool {
		return strings.HasPrefix(subclass, "base.")
	},
}).Parse(`// !WARNING!    THIS FILE WAS GENERATED BY GST-PLUGIN-GEN    !WARNING! //
package main

import "C"

import (
	"unsafe"

	"github.com/go-gst/go-gst/gst"
	{{- if (.Config.Element.Subclass | extendsFromBase) }}
	"github.com/go-gst/go-gst/gst/base"
	{{- end }}
)

// The metadata for this plugin
var pluginMeta = &gst.PluginMetadata{
	MajorVersion: gst.VersionMajor,
	MinorVersion: gst.VersionMinor,
	Name:         "{{ .Config.Plugin.Name }}",
	Description:  "{{ .Config.Plugin.Description }}",
	Version:      "{{ .Config.Plugin.Version }}",
	License:      {{ .Config.Plugin.License }},
	Source:       "{{ .Config.Plugin.Source }}",
	Package:      "{{ .Config.Plugin.Package }}",
	Origin:       "{{ .Config.Plugin.Origin }}",
	ReleaseDate:  "{{ .Config.Plugin.ReleaseDate }}",
	// The init function is called to register elements provided by the plugin.
	Init: func(plugin *gst.Plugin) bool {
		return gst.RegisterElement(
			plugin,
			// The name of the element
			"{{ .Config.Element.Name }}",
			// The rank of the element
			{{ .Config.Element.Rank }},
			// The GoElement implementation for the element
			&{{ .Config.Element.Impl }}{},
			// The base subclass this element extends
			{{ .Config.Element.Subclass }},
			{{- if .Config.Element.Interfaces }}
			// The interfaces this element implements
			{{- range $index, $interface := .Config.Element.Interfaces | splitInterfaces }}
			{{ $interface }},
			{{- end }}
			{{- end }}
		)
	},
}

// A single method must be exported from the compiled library that provides for GStreamer
// to fetch the description and init function for this plugin. The name of the method
// must match the format gst_plugin_NAME_get_desc, where NAME is the name of the compiled
// artifact with or without the "libgst" prefix and hyphens are replaced with underscores.

//export gst_plugin_{{ .Config.Plugin.Name | adjustedName }}_get_desc
func gst_plugin_{{ .Config.Plugin.Name | adjustedName }}_get_desc() unsafe.Pointer { return pluginMeta.Export() }
`))