From 481fd9c7a3418076aaa536f7ce29f9c757d219fc Mon Sep 17 00:00:00 2001
From: Vito Sartori <hey@vito.io>
Date: Mon, 2 Nov 2020 21:36:02 -0300
Subject: [PATCH] Add support to cached templates

---
 engine.go                | 16 ++++++++++++++++
 engine_test.go           | 16 ++++++++++++++++
 render/config.go         |  3 ++-
 render/context.go        | 10 +++++++++-
 tags/include_tag_test.go | 15 +++++++++++++++
 5 files changed, 58 insertions(+), 2 deletions(-)

diff --git a/engine.go b/engine.go
index d143364..bcc1295 100644
--- a/engine.go
+++ b/engine.go
@@ -110,3 +110,19 @@ func (e *Engine) Delims(objectLeft, objectRight, tagLeft, tagRight string) *Engi
 	e.cfg.Delims = []string{objectLeft, objectRight, tagLeft, tagRight}
 	return e
 }
+
+// ParseTemplateAndCache is the same as ParseTemplateLocation, except that the
+// source location is used for error reporting and for the {% include %} tag.
+// If parsing is successful, provided source is then cached, and can be retrieved
+// by {% include %} tags, as long as there is not a real file in the provided path.
+//
+// The path and line number are used for error reporting.
+// The path is also the reference for relative pathnames in the {% include %} tag.
+func (e *Engine) ParseTemplateAndCache(source []byte, path string, line int) (*Template, SourceError) {
+	t, err := e.ParseTemplateLocation(source, path, line)
+	if err != nil {
+		return t, err
+	}
+	e.cfg.Cache[path] = source
+	return t, err
+}
diff --git a/engine_test.go b/engine_test.go
index 4a56258..c3a6971 100644
--- a/engine_test.go
+++ b/engine_test.go
@@ -92,3 +92,19 @@ func BenchmarkEngine_Parse(b *testing.B) {
 		engine.ParseTemplate(s)
 	}
 }
+
+func TestEngine_ParseTemplateAndCache(t *testing.T) {
+	// Given two templates...
+	templateA := []byte("Foo")
+	templateB := []byte(`{% include "template_a.html" %}, Bar`)
+
+	// Cache the first
+	eng := NewEngine()
+	_, err := eng.ParseTemplateAndCache(templateA, "template_a.html", 1)
+	require.NoError(t, err)
+
+	// ...and execute the second.
+	result, err := eng.ParseAndRender(templateB, Bindings{})
+	require.NoError(t, err)
+	require.Equal(t, string(result), "Foo, Bar")
+}
diff --git a/render/config.go b/render/config.go
index ab66bf2..65ec55b 100644
--- a/render/config.go
+++ b/render/config.go
@@ -8,6 +8,7 @@ import (
 type Config struct {
 	parser.Config
 	grammar
+	Cache map[string][]byte
 }
 
 type grammar struct {
@@ -21,5 +22,5 @@ func NewConfig() Config {
 		tags:      map[string]TagCompiler{},
 		blockDefs: map[string]*blockSyntax{},
 	}
-	return Config{parser.NewConfig(g), g}
+	return Config{Config: parser.NewConfig(g), grammar: g, Cache: map[string][]byte{}}
 }
diff --git a/render/context.go b/render/context.go
index 0931924..bae220a 100644
--- a/render/context.go
+++ b/render/context.go
@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"io"
 	"io/ioutil"
+	"os"
 	"strings"
 
 	"github.com/osteele/liquid/expressions"
@@ -111,7 +112,14 @@ func (c rendererContext) RenderChildren(w io.Writer) Error {
 
 func (c rendererContext) RenderFile(filename string, b map[string]interface{}) (string, error) {
 	source, err := ioutil.ReadFile(filename)
-	if err != nil {
+	if err != nil && os.IsNotExist(err) {
+		// Is it cached?
+		if cval, ok := c.ctx.config.Cache[filename]; ok {
+			source = cval
+		} else {
+			return "", err
+		}
+	} else if err != nil {
 		return "", err
 	}
 	root, err := c.ctx.config.Compile(string(source), c.node.SourceLoc)
diff --git a/tags/include_tag_test.go b/tags/include_tag_test.go
index 52647ab..cb329e8 100644
--- a/tags/include_tag_test.go
+++ b/tags/include_tag_test.go
@@ -58,3 +58,18 @@ func TestIncludeTag_file_not_found_error(t *testing.T) {
 	require.Error(t, err)
 	require.True(t, os.IsNotExist(err.Cause()))
 }
+
+func TestIncludeTag_cached_value_handling(t *testing.T) {
+	config := render.NewConfig()
+	// foo.html does not exist on testdata.
+	config.Cache["testdata/foo.html"] = []byte("bar")
+	loc := parser.SourceLoc{Pathname: "testdata/include_source.html", LineNo: 1}
+	AddStandardTags(config)
+
+	root, err := config.Compile(`{% include "foo.html" %}`, loc)
+	require.NoError(t, err)
+	buf := new(bytes.Buffer)
+	err = render.Render(root, buf, includeTestBindings, config)
+	require.NoError(t, err)
+	require.Equal(t, "bar", strings.TrimSpace(buf.String()))
+}