From f66770a9e458a78bfce1536380cb7434a532a44e Mon Sep 17 00:00:00 2001
From: Skip Baney <twelvelabs@gmail.com>
Date: Sat, 10 Jun 2023 15:51:05 -0500
Subject: [PATCH] feat: additional template render methods

---
 render/render.go        |  2 +-
 render/template.go      | 56 +++++++++++++++++++++++++++--
 render/template_test.go | 78 +++++++++++++++++++++++++++++++++++++++++
 3 files changed, 133 insertions(+), 3 deletions(-)

diff --git a/render/render.go b/render/render.go
index c6a8e53..9598160 100644
--- a/render/render.go
+++ b/render/render.go
@@ -108,7 +108,7 @@ func String(s string, data any) (string, error) {
 
 func execute(t *template.Template, data any) (string, error) {
 	if t == nil {
-		return "", nil
+		return strEmpty, nil
 	}
 	buf := bytes.Buffer{}
 	err := t.Execute(&buf, data)
diff --git a/render/template.go b/render/template.go
index a01c925..c9544b2 100644
--- a/render/template.go
+++ b/render/template.go
@@ -1,7 +1,15 @@
 package render
 
 import (
+	"fmt"
 	"text/template"
+
+	"github.com/spf13/cast"
+)
+
+const (
+	strEmpty   string = ""
+	strNoValue string = "<no value>"
 )
 
 // Compile parses a template string and returns, if successful,
@@ -45,7 +53,51 @@ func (ts *Template) UnmarshalText(text []byte) error {
 	return err
 }
 
-// Render renders the template using data.
+// Render renders the template as a string.
 func (ts *Template) Render(data any) (string, error) {
-	return execute(ts.t, data)
+	rendered, err := execute(ts.t, data)
+	if err != nil {
+		return strEmpty, err
+	}
+	if rendered == strEmpty || rendered == strNoValue {
+		return strEmpty, nil
+	}
+	return rendered, nil
+}
+
+// Render renders the template as a bool.
+func (ts *Template) RenderBool(data any) (bool, error) {
+	rendered, err := ts.Render(data)
+	if err != nil {
+		return false, err
+	}
+	if rendered == strEmpty {
+		return false, nil
+	}
+	return cast.ToBoolE(rendered)
+}
+
+// Render renders the template as an int.
+func (ts *Template) RenderInt(data any) (int, error) {
+	rendered, err := ts.Render(data)
+	if err != nil {
+		return 0, err
+	}
+	if rendered == strEmpty {
+		return 0, nil
+	}
+	return cast.ToIntE(rendered)
+}
+
+// RenderRequired renders the template as a string,
+// but returns an error if the result is empty.
+func (ts *Template) RenderRequired(data any) (string, error) {
+	rendered, err := ts.Render(data)
+	if err != nil {
+		return strEmpty, err
+	}
+	if rendered == strEmpty {
+		return strEmpty, fmt.Errorf("evaluated to an empty string")
+	}
+	return rendered, nil
 }
diff --git a/render/template_test.go b/render/template_test.go
index 632e2e2..09e466c 100644
--- a/render/template_test.go
+++ b/render/template_test.go
@@ -31,12 +31,90 @@ func TestTemplate_Render(t *testing.T) {
 	assert.NoError(t, err)
 	assert.Equal(t, "Hello, World", rendered)
 
+	ts, _ = Compile(`{{ .Something }}`)
+	rendered, err = ts.Render(nil)
+	assert.NoError(t, err)
+	assert.Equal(t, "", rendered)
+
 	ts, _ = Compile(`Hello, {{ fail "boom" }}`)
 	rendered, err = ts.Render(nil)
 	assert.ErrorContains(t, err, "fail: boom")
 	assert.Equal(t, "", rendered)
 }
 
+func TestTemplate_RenderBool(t *testing.T) {
+	ts, _ := Compile(`{{ .Value }}`)
+	rendered, err := ts.RenderBool(map[string]any{
+		"Value": "true",
+	})
+	assert.NoError(t, err)
+	assert.Equal(t, true, rendered)
+
+	ts, _ = Compile(`{{ .Value }}`)
+	rendered, err = ts.RenderBool(nil)
+	assert.NoError(t, err)
+	assert.Equal(t, false, rendered)
+
+	ts, _ = Compile(`{{ .Value }}`)
+	rendered, err = ts.RenderBool(map[string]any{
+		"Value": "not-a-bool",
+	})
+	assert.ErrorContains(t, err, "invalid syntax")
+	assert.Equal(t, false, rendered)
+
+	ts, _ = Compile(`{{ fail "boom" }}`)
+	rendered, err = ts.RenderBool(nil)
+	assert.ErrorContains(t, err, "fail: boom")
+	assert.Equal(t, false, rendered)
+}
+
+func TestTemplate_RenderInt(t *testing.T) {
+	ts, _ := Compile(`{{ .Value }}`)
+	rendered, err := ts.RenderInt(map[string]any{
+		"Value": "12",
+	})
+	assert.NoError(t, err)
+	assert.Equal(t, 12, rendered)
+
+	ts, _ = Compile(`{{ .Value }}`)
+	rendered, err = ts.RenderInt(nil)
+	assert.NoError(t, err)
+	assert.Equal(t, 0, rendered)
+
+	ts, _ = Compile(`{{ .Value }}`)
+	rendered, err = ts.RenderInt(map[string]any{
+		"Value": "not-a-number",
+	})
+	assert.ErrorContains(t, err, "unable to cast")
+	assert.Equal(t, 0, rendered)
+
+	ts, _ = Compile(`{{ fail "boom" }}`)
+	rendered, err = ts.RenderInt(nil)
+	assert.ErrorContains(t, err, "fail: boom")
+	assert.Equal(t, 0, rendered)
+}
+
+func TestTemplate_RenderRequired(t *testing.T) {
+	ts, _ := Compile(`{{ .Value }}`)
+	rendered, err := ts.RenderRequired(map[string]any{
+		"Value": "Howdy",
+	})
+	assert.NoError(t, err)
+	assert.Equal(t, "Howdy", rendered)
+
+	ts, _ = Compile(`{{ fail "boom" }}`)
+	rendered, err = ts.RenderRequired(nil)
+	assert.ErrorContains(t, err, "fail: boom")
+	assert.Equal(t, "", rendered)
+
+	ts, _ = Compile(`{{ .Value }}`)
+	rendered, err = ts.RenderRequired(map[string]any{
+		"Value": "",
+	})
+	assert.ErrorContains(t, err, "empty string")
+	assert.Equal(t, "", rendered)
+}
+
 func TestTemplate_MarshalText(t *testing.T) {
 	ts, err := Compile(`Hello, {{ .Name }}`)
 	assert.NoError(t, err)