passit: add generic Transform and case transforming generators

Author: tmthrgd

README.md

@@ -79,13 +79,17 @@ The package also provides a number of generators that produce output based on us
 
 There are also a number of 'helper' generators that interact with the output of other generators:
 
-| Generator         | Description                                                            |
-| ----------------- | ---------------------------------------------------------------------- |
-| `Alternate`       | Select a generator at random                                           |
-| `Join`            | Concatenate the output of multiple generators                          |
-| `Repeat`          | Invoke a generator multiple times and concatenate the output           |
-| `RandomRepeat`    | Invoke a generator a random number of times and concatenate the output |
-| `RejectionSample` | Continually invoke a generator until the output passes a test          |
+| Generator         | Description                                                                     |
+| ----------------- | ------------------------------------------------------------------------------- |
+| `Alternate`       | Select a generator at random                                                    |
+| `Join`            | Concatenate the output of multiple generators                                   |
+| `Repeat`          | Invoke a generator multiple times and concatenate the output                    |
+| `RandomRepeat`    | Invoke a generator a random number of times and concatenate the output          |
+| `RejectionSample` | Continually invoke a generator until the output passes a test                   |
+| `Transform`       | Invoke a generator and convert the output according to a user supplied function |
+| `LowerCase`       | Invoke a generator and convert the output to lower case                         |
+| `UpperCase`       | Invoke a generator and convert the output to upper case                         |
+| `TitleCase`       | Invoke a generator and convert the output to language-specific title case       |
 
 Most generators only generate a single of something, be it a rune, ASCII character
 or word. For generating longer passwords use `Repeat` or `RandomRepeat`, possibly

transform.go

@@ -0,0 +1,43 @@
+package passit
+
+import (
+	"io"
+	"strings"
+
+	"golang.org/x/text/cases"
+	"golang.org/x/text/language"
+)
+
+type transformGenerator struct {
+	gen Generator
+	fn  func(string) string
+}
+
+// Transform returns a Generator that converts the generated password according to
+// the user supplied function fn.
+func Transform(gen Generator, fn func(string) string) Generator {
+	return &transformGenerator{gen, fn}
+}
+
+func (tg *transformGenerator) Password(r io.Reader) (string, error) {
+	pass, err := tg.gen.Password(r)
+	return tg.fn(pass), err
+}
+
+// LowerCase returns a Generator that uses [strings.ToLower] to map all Unicode
+// letters in the generated password to their lower case.
+func LowerCase(gen Generator) Generator {
+	return Transform(gen, strings.ToLower)
+}
+
+// UpperCase returns a Generator that uses [strings.ToUpper] to map all Unicode
+// letters in the generated password to their upper case.
+func UpperCase(gen Generator) Generator {
+	return Transform(gen, strings.ToUpper)
+}
+
+// TitleCase returns a Generator that uses [golang.org/x/text/cases.Title] to
+// convert the generated password to language-specific title case.
+func TitleCase(gen Generator, t language.Tag) Generator {
+	return Transform(gen, cases.Title(t).String)
+}

transform_test.go

@@ -0,0 +1,41 @@
+package passit
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"golang.org/x/text/language"
+)
+
+func TestLowerCase(t *testing.T) {
+	tr := newTestRand()
+
+	pass, err := LowerCase(Repeat(LatinMixed, "", 25)).Password(tr)
+	require.NoError(t, err)
+	assert.Equal(t, "yxishgyluarukywwtcxdjirmd", pass)
+}
+
+func TestUpperCase(t *testing.T) {
+	tr := newTestRand()
+
+	pass, err := UpperCase(Repeat(LatinMixed, "", 25)).Password(tr)
+	require.NoError(t, err)
+	assert.Equal(t, "YXISHGYLUARUKYWWTCXDJIRMD", pass)
+}
+
+func TestTitleCase(t *testing.T) {
+	tr := newTestRand()
+
+	pass, err := TitleCase(Repeat(OrchardStreetLong, " ", 10), language.English).Password(tr)
+	require.NoError(t, err)
+	assert.Equal(t, "Agreed Stopping Brilliant Elongated Richness Populous Sprung Grassland Stamens Dined", pass)
+
+	pass, err = TitleCase(Repeat(OrchardStreetLong, "-", 10), language.English).Password(tr)
+	require.NoError(t, err)
+	assert.Equal(t, "Emphasizes-Weaving-Pickup-Cascades-Newborn-Provider-Noisy-Retailer-Compromise-Inventors", pass)
+
+	pass, err = TitleCase(Repeat(OrchardStreetLong, "_", 10), language.English).Password(tr)
+	require.NoError(t, err)
+	assert.Equal(t, "Biplane_kingship_ambient_altered_injustices_precedes_yearning_kitten_chop_carefully", pass)
+}