Add an API for Go plugins

References: https://todo.sr.ht/~sircmpwn/koushin/39

plugin.go

@@ -22,3 +22,10 @@ type Plugin interface {
 	// Close is called when the plugin is unloaded.
 	Close() error
 }
+
+var plugins []Plugin
+
+// RegisterPlugin registers a plugin to be loaded on server startup.
+func RegisterPlugin(p Plugin) {
+	plugins = append(plugins, p)
+}

plugin_go.go

@@ -0,0 +1,97 @@
+package koushin
+
+import (
+	"html/template"
+	"net/http"
+	"path/filepath"
+
+	"github.com/labstack/echo/v4"
+)
+
+type goPlugin struct {
+	p *GoPlugin
+}
+
+func (p *goPlugin) Name() string {
+	return p.p.Name
+}
+
+func (p *goPlugin) LoadTemplate(t *template.Template) error {
+	t.Funcs(p.p.templateFuncs)
+
+	paths, err := filepath.Glob(pluginDir + "/" + p.p.Name + "/public/*.html")
+	if err != nil {
+		return err
+	}
+	if len(paths) > 0 {
+		if _, err := t.ParseFiles(paths...); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func (p *goPlugin) SetRoutes(group *echo.Group) {
+	for _, r := range p.p.routes {
+		group.Add(r.Method, r.Path, r.Handler)
+	}
+
+	group.Static("/assets", pluginDir + "/" + p.p.Name + "/public/assets")
+}
+
+func (p *goPlugin) Inject(name string, data interface{}) error {
+	return nil
+}
+
+func (p *goPlugin) Close() error {
+	return nil
+}
+
+type goPluginRoute struct {
+	Method  string
+	Path    string
+	Handler echo.HandlerFunc
+}
+
+type GoPlugin struct {
+	Name string
+
+	routes []goPluginRoute
+
+	templateFuncs template.FuncMap
+}
+
+func (p *GoPlugin) AddRoute(method, path string, handler echo.HandlerFunc) {
+	p.routes = append(p.routes, goPluginRoute{method, path, handler})
+}
+
+func (p *GoPlugin) DELETE(path string, handler echo.HandlerFunc) {
+	p.AddRoute(http.MethodDelete, path, handler)
+}
+
+func (p *GoPlugin) GET(path string, handler echo.HandlerFunc) {
+	p.AddRoute(http.MethodGet, path, handler)
+}
+
+func (p *GoPlugin) POST(path string, handler echo.HandlerFunc) {
+	p.AddRoute(http.MethodPost, path, handler)
+}
+
+func (p *GoPlugin) PUT(path string, handler echo.HandlerFunc) {
+	p.AddRoute(http.MethodPut, path, handler)
+}
+
+func (p *GoPlugin) TemplateFuncs(funcs template.FuncMap) {
+	if p.templateFuncs == nil {
+		p.templateFuncs = make(template.FuncMap, len(funcs))
+	}
+
+	for k, f := range funcs {
+		p.templateFuncs[k] = f
+	}
+}
+
+func (p *GoPlugin) Plugin() Plugin {
+	return &goPlugin{p}
+}

server.go

@@ -137,10 +137,16 @@ func New(e *echo.Echo, options *Options) error {
 		return err
 	}
 
-	s.Plugins, err = loadAllLuaPlugins(e.Logger)
+	s.Plugins = append([]Plugin(nil), plugins...)
+	for _, p := range s.Plugins {
+		e.Logger.Printf("Registered plugin '%v'", p.Name())
+	}
+
+	luaPlugins, err := loadAllLuaPlugins(e.Logger)
 	if err != nil {
 		return fmt.Errorf("failed to load plugins: %v", err)
 	}
+	s.Plugins = append(s.Plugins, luaPlugins...)
 
 	e.Renderer, err = loadTemplates(e.Logger, options.Theme, s.Plugins)
 	if err != nil {