Add extended indentation function

Added a strings function to support a much more broad variety of
indentation needs.

In addition to specifying a custom indentation string, it also
inherently:

- fixes Masterminds#357
- fixes Masterminds#314 (with some careful awareness and in-template programmating addition/subtraction)
- obsoletes Masterminds#434

Author: johnnybubonic

docs/strings.md

@@ -268,6 +268,28 @@ nindent 4 $lots_of_text
 The above will indent every line of text by 4 space characters and add a new
 line to the beginning.
 
+## extindent
+
+The `extindent` function offers a much more flexible extended indenter
+at the cost of complexity.
+
+It allows for a customized indentation and indentation behavor but
+requires 5 arguments in addition to the string to be indented.
+
+```
+$levels := 1
+$skipFirst := false
+$skipEmpty := true
+$skipWs := true
+$indentString := "\t"
+
+extindent $levels $skipFirst $skipEmpty $skipWs $indentString $lots_of_text
+```
+
+The above will indent every line of `$lots_of_text` with a single (`1`) `\t` (horizontal tab),
+*unless* that line is entirely empty (only a newline) or is comprised only entirely of whitespace
+(tabs, spaces, etc.).
+
 ## replace
 
 Perform simple string replacement.

functions.go

@@ -157,6 +157,7 @@ var genericMap = map[string]interface{}{
 	"cat":        cat,
 	"indent":     indent,
 	"nindent":    nindent,
+	"extindent":  extIndent,
 	"replace":    replace,
 	"plural":     plural,
 	"sha1sum":    sha1sum,

strings.go

@@ -115,6 +115,24 @@ func nindent(spaces int, v string) string {
 	return "\n" + indent(spaces, v)
 }
 
+func extIndent(levels int, skipFirst, skipEmpty, skipWhitespace bool, indentStr, v string) string {
+	pad := strings.Repeat(indentStr, int(levels))
+	lines := strings.Split(v, "\n")
+	for idx, line := range lines {
+		if idx == 0 && skipFirst {
+			continue
+		}
+		if skipWhitespace && strings.TrimSpace(line) == "" && line != "" {
+			continue
+		}
+		if skipEmpty && (line == "" || line == "\r") {
+			continue
+		}
+		lines[idx] = pad + line
+	}
+	return strings.Join(lines, "\n")
+}
+
 func replace(old, new, src string) string {
 	return strings.Replace(src, old, new, -1)
 }

strings_test.go

@@ -280,6 +280,50 @@ func TestNindent(t *testing.T) {
 	}
 }
 
+func TestExtIndent(t *testing.T) {
+
+	cmpstr := "1\nmt\n\nws\n\t\n."
+
+	for _, tCase := range []struct{
+		indt      string
+		lvls      int
+		skipFirst bool
+		skipEmpty bool
+		skipWs    bool
+		tgt       string
+
+	}{
+		{indt: "\t", lvls: 1, skipFirst: true, skipEmpty: true, skipWs: true, tgt: "1\n\tmt\n\n\tws\n\t\n\t."},
+		{indt: "\t", lvls: 1, skipFirst: true, skipEmpty: true, skipWs: false, tgt: "1\n\tmt\n\n\tws\n\t\t\n\t."},
+		{indt: "\t", lvls: 1, skipFirst: true, skipEmpty: false, skipWs: true, tgt: "1\n\tmt\n\t\n\tws\n\t\n\t."},
+		{indt: "\t", lvls: 1, skipFirst: true, skipEmpty: false, skipWs: false, tgt: "1\n\tmt\n\t\n\tws\n\t\t\n\t."},
+		{indt: "\t", lvls: 1, skipFirst: false, skipEmpty: true, skipWs: true, tgt: "\t1\n\tmt\n\n\tws\n\t\n\t."},
+		{indt: "\t", lvls: 1, skipFirst: false, skipEmpty: true, skipWs: false, tgt: "\t1\n\tmt\n\n\tws\n\t\t\n\t."},
+		{indt: "\t", lvls: 1, skipFirst: false, skipEmpty: false, skipWs: true, tgt: "\t1\n\tmt\n\t\n\tws\n\t\n\t."},
+		{indt: "\t", lvls: 1, skipFirst: false, skipEmpty: false, skipWs: false, tgt: "\t1\n\tmt\n\t\n\tws\n\t\t\n\t."},
+	} {
+		tplStr := fmt.Sprintf(
+			"{{- $lvls := %d -}}\n"+
+			"{{- $no1st := %v -}}\n"+
+			"{{- $noMT := %v -}}\n"+
+			"{{- $noWs := %v -}}\n"+
+			"{{- $idtstr := \"%s\" -}}\n"+
+			"{{- $tstr := `%s` -}}\n"+
+			"{{ $tstr | extindent $lvls $no1st $noMT $noWs $idtstr }}",
+			tCase.lvls,
+			tCase.skipFirst,
+			tCase.skipEmpty,
+			tCase.skipWs,
+			tCase.indt,
+			cmpstr,
+		)
+		t.Log(tplStr)
+		if err := runt(tplStr, tCase.tgt); err != nil {
+			t.Error(err)
+		}
+	}
+}
+
 func TestReplace(t *testing.T) {
 	tpl := `{{"I Am Henry VIII" | replace " " "-"}}`
 	if err := runt(tpl, "I-Am-Henry-VIII"); err != nil {