Add format functions

Add functions to go templates such as truncating a field.  Also add
the table keyword, which, if placed at the beginning of a format string,
adds headers to the output

Signed-off-by: Ryan Cole <rcyoalne@gmail.com>

cmd/kpod/formats/formats.go

@@ -3,9 +3,11 @@ package formats
 import (
 	"encoding/json"
 	"fmt"
-	"github.com/pkg/errors"
 	"os"
+	"strings"
 	"text/template"
+
+	"github.com/pkg/errors"
 )
 
 // Writer interface for outputs
@@ -22,6 +24,7 @@ type JSONstruct struct {
 type StdoutTemplate struct {
 	Output   []interface{}
 	Template string
+	Fields   map[string]string
 }
 
 // Out method for JSON
@@ -36,14 +39,23 @@ func (j JSONstruct) Out() error {
 
 // Out method for Go templates
 func (t StdoutTemplate) Out() error {
-
-	tmpl, err := template.New("image").Parse(t.Template)
+	if strings.HasPrefix(t.Template, "table") {
+		t.Template = strings.TrimSpace(t.Template[5:])
+		headerTmpl, err := template.New("header").Funcs(headerFunctions).Parse(t.Template)
+		if err != nil {
+			errors.Wrapf(err, "Template parsing error")
+		}
+		err = headerTmpl.Execute(os.Stdout, t.Fields)
+		fmt.Println()
+	}
+	tmpl, err := template.New("image").Funcs(basicFunctions).Parse(t.Template)
 	if err != nil {
 		return errors.Wrapf(err, "Template parsing error")
 	}
 
 	for _, img := range t.Output {
-		err = tmpl.Execute(os.Stdout, img)
+		basicTmpl := tmpl.Funcs(basicFunctions)
+		err = basicTmpl.Execute(os.Stdout, img)
 		if err != nil {
 			return err
 		}

cmd/kpod/formats/templates.go

@@ -0,0 +1,78 @@
+package formats
+
+import (
+	"bytes"
+	"encoding/json"
+	"strings"
+	"text/template"
+)
+
+// basicFunctions are the set of initial
+// functions provided to every template.
+var basicFunctions = template.FuncMap{
+	"json": func(v interface{}) string {
+		buf := &bytes.Buffer{}
+		enc := json.NewEncoder(buf)
+		enc.SetEscapeHTML(false)
+		enc.Encode(v)
+		// Remove the trailing new line added by the encoder
+		return strings.TrimSpace(buf.String())
+	},
+	"split":    strings.Split,
+	"join":     strings.Join,
+	"title":    strings.Title,
+	"lower":    strings.ToLower,
+	"upper":    strings.ToUpper,
+	"pad":      padWithSpace,
+	"truncate": truncateWithLength,
+}
+
+// HeaderFunctions are used to created headers of a table.
+// This is a replacement of basicFunctions for header generation
+// because we want the header to remain intact.
+// Some functions like `split` are irrevelant so not added.
+var headerFunctions = template.FuncMap{
+	"json": func(v string) string {
+		return v
+	},
+	"title": func(v string) string {
+		return v
+	},
+	"lower": func(v string) string {
+		return v
+	},
+	"upper": func(v string) string {
+		return v
+	},
+	"truncate": func(v string, l int) string {
+		return v
+	},
+}
+
+// Parse creates a new anonymous template with the basic functions
+// and parses the given format.
+func Parse(format string) (*template.Template, error) {
+	return NewParse("", format)
+}
+
+// NewParse creates a new tagged template with the basic functions
+// and parses the given format.
+func NewParse(tag, format string) (*template.Template, error) {
+	return template.New(tag).Funcs(basicFunctions).Parse(format)
+}
+
+// padWithSpace adds whitespace to the input if the input is non-empty
+func padWithSpace(source string, prefix, suffix int) string {
+	if source == "" {
+		return source
+	}
+	return strings.Repeat(" ", prefix) + source + strings.Repeat(" ", suffix)
+}
+
+// truncateWithLength truncates the source string up to the length provided by the input
+func truncateWithLength(source string, length int) string {
+	if len(source) < length {
+		return source
+	}
+	return source[:length]
+}