From 76599232dc8f652e04dfc62258c8707c00f8b7fc Mon Sep 17 00:00:00 2001
From: Simon Ser <contact@emersion.fr>
Date: Mon, 9 Dec 2019 17:54:24 +0100
Subject: [PATCH] Add a Lua API to set template filters

---
 plugin.go   | 40 +++++++++++++++++++++++++++++++++++++---
 server.go   |  8 ++++----
 template.go | 11 ++++++++---
 3 files changed, 49 insertions(+), 10 deletions(-)

diff --git a/plugin.go b/plugin.go
index d2737d0..26473b1 100644
--- a/plugin.go
+++ b/plugin.go
@@ -2,6 +2,7 @@ package koushin
 
 import (
 	"fmt"
+	"html/template"
 	"path/filepath"
 
 	"github.com/labstack/echo/v4"
@@ -11,6 +12,7 @@ import (
 
 type Plugin interface {
 	Name() string
+	Filters() template.FuncMap
 	Render(name string, data interface{}) error
 	Close() error
 }
@@ -19,6 +21,7 @@ type luaPlugin struct {
 	filename        string
 	state           *lua.LState
 	renderCallbacks map[string]*lua.LFunction
+	filters         template.FuncMap
 }
 
 func (p *luaPlugin) Name() string {
@@ -32,23 +35,53 @@ func (p *luaPlugin) onRender(l *lua.LState) int {
 	return 0
 }
 
+func (p *luaPlugin) setFilter(l *lua.LState) int {
+	name := l.CheckString(1)
+	f := l.CheckFunction(2)
+	p.filters[name] = func(args... interface{}) string {
+		luaArgs := make([]lua.LValue, len(args))
+		for i, v := range args {
+			luaArgs[i] = luar.New(l, v)
+		}
+
+		err := l.CallByParam(lua.P{
+			Fn: f,
+			NRet: 1,
+			Protect: true,
+		}, luaArgs...)
+		if err != nil {
+			panic(err) // TODO: better error handling?
+		}
+
+		ret := l.CheckString(-1)
+		l.Pop(1)
+		return ret
+	}
+	return 0
+}
+
 func (p *luaPlugin) Render(name string, data interface{}) error {
 	f, ok := p.renderCallbacks[name]
 	if !ok {
 		return nil
 	}
 
-	if err := p.state.CallByParam(lua.P{
+	err := p.state.CallByParam(lua.P{
 		Fn:      f,
 		NRet:    0,
 		Protect: true,
-	}, luar.New(p.state, data)); err != nil {
+	}, luar.New(p.state, data))
+	if err != nil {
 		return err
 	}
 
 	return nil
 }
 
+func (p *luaPlugin) Filters() template.FuncMap {
+	return p.filters
+}
+
 func (p *luaPlugin) Close() error {
 	p.state.Close()
 	return nil
@@ -60,12 +93,13 @@ func loadLuaPlugin(filename string) (*luaPlugin, error) {
 		filename:        filename,
 		state:           l,
 		renderCallbacks: make(map[string]*lua.LFunction),
+		filters:         make(template.FuncMap),
 	}
 
 	mt := l.NewTypeMetatable("koushin")
 	l.SetGlobal("koushin", mt)
 	l.SetField(mt, "on_render", l.NewFunction(p.onRender))
-	// TODO: set_filter
+	l.SetField(mt, "set_filter", l.NewFunction(p.setFilter))
 
 	if err := l.DoFile(filename); err != nil {
 		l.Close()
diff --git a/server.go b/server.go
index 0845628..501f503 100644
--- a/server.go
+++ b/server.go
@@ -128,14 +128,14 @@ func New(e *echo.Echo, options *Options) error {
 		return err
 	}
 
-	e.Renderer, err = loadTemplates(e.Logger, options.Theme)
+	s.plugins, err = loadAllLuaPlugins(e.Logger)
 	if err != nil {
-		return fmt.Errorf("failed to load templates: %v", err)
+		return fmt.Errorf("failed to load plugins: %v", err)
 	}
 
-	s.plugins, err = loadAllLuaPlugins(e.Logger)
+	e.Renderer, err = loadTemplates(e.Logger, options.Theme, s.plugins)
 	if err != nil {
-		return fmt.Errorf("failed to load plugins: %v", err)
+		return fmt.Errorf("failed to load templates: %v", err)
 	}
 
 	e.HTTPErrorHandler = func(err error, c echo.Context) {
diff --git a/template.go b/template.go
index a4c3ee0..2cce5a3 100644
--- a/template.go
+++ b/template.go
@@ -27,15 +27,20 @@ func (t *tmpl) Render(w io.Writer, name string, data interface{}, ectx echo.Cont
 	return t.t.ExecuteTemplate(w, name, data)
 }
 
-func loadTemplates(logger echo.Logger, themeName string) (*tmpl, error) {
-	base, err := template.New("").Funcs(template.FuncMap{
+func loadTemplates(logger echo.Logger, themeName string, plugins []Plugin) (*tmpl, error) {
+	base := template.New("").Funcs(template.FuncMap{
 		"tuple": func(values ...interface{}) []interface{} {
 			return values
 		},
 		"pathescape": func(s string) string {
 			return url.PathEscape(s)
 		},
-	}).ParseGlob("public/*.html")
+	})
+	for _, p := range plugins {
+		base = base.Funcs(p.Filters())
+	}
+
+	base, err := base.ParseGlob("public/*.html")
 	if err != nil {
 		return nil, err
 	}