From 5c4e66d1443593b1446cd0b9d82be58cdd824cf3 Mon Sep 17 00:00:00 2001
From: Dan Jones <danjones@goodevilgenius.org>
Date: Mon, 10 Mar 2025 14:25:00 -0500
Subject: [PATCH] =?UTF-8?q?=E2=9C=A8=20Add=20MultiGenerator?=
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---
 generators.go      | 27 +++++++++++++++++++++++++++
 generators_test.go | 45 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 72 insertions(+)

diff --git a/generators.go b/generators.go
index 01242fe..c409988 100644
--- a/generators.go
+++ b/generators.go
@@ -1,6 +1,7 @@
 package nomino
 
 import (
+	"errors"
 	"time"
 
 	"github.com/google/uuid"
@@ -18,6 +19,32 @@ func WithGenerator(g Generator) Option {
 	}
 }
 
+// ErrMissingGenerators is returned by a multi-generator if no generators are supplied.
+var ErrMissingGenerators = errors.New("no generators supplied")
+
+func missingGen() (string, error) {
+	return "", ErrMissingGenerators
+}
+
+// MultiGeneratorInOrder allows the use of multiple generators. Each new invokation will use the next generator in turn.
+// If none are passed, the generator will always return ErrMissingGenerators.
+func MultiGeneratorInOrder(gens ...Generator) Generator {
+	if len(gens) == 0 {
+		return missingGen
+	}
+
+	if len(gens) == 1 {
+		return gens[0]
+	}
+
+	var idx int
+	return func() (string, error) {
+		st, err := gens[idx]()
+		idx = (idx + 1) % len(gens)
+		return st, err
+	}
+}
+
 func uuidGen() (string, error) {
 	u, err := uuid.NewRandom()
 	if err != nil {
diff --git a/generators_test.go b/generators_test.go
index 96759ff..210181f 100644
--- a/generators_test.go
+++ b/generators_test.go
@@ -18,6 +18,51 @@ func TestWithGenerator(t *testing.T) {
 	assert.Equal(t, "abc", st)
 }
 
+func TestMultiGeneratorInOrder(t *testing.T) {
+	st1 := "abc"
+	st2 := "def"
+	er1 := errors.New("oops")
+	g1 := func() (string, error) { return st1, nil }
+	g2 := func() (string, error) { return st2, nil }
+	g3 := func() (string, error) { return "", er1 }
+	g := MultiGeneratorInOrder(g1, g2, g3)
+	st, err := g()
+	assert.NoError(t, err)
+	assert.Equal(t, st1, st)
+	st, err = g()
+	assert.NoError(t, err)
+	assert.Equal(t, st2, st)
+	st, err = g()
+	assert.Zero(t, st)
+	assert.ErrorIs(t, err, er1)
+	st, err = g()
+	assert.NoError(t, err)
+	assert.Equal(t, st1, st)
+}
+
+func TestMultiGeneratorInOrderOne(t *testing.T) {
+	st1 := "abc"
+	g1 := func() (string, error) { return st1, nil }
+	g := MultiGeneratorInOrder(g1)
+
+	st, err := g()
+	assert.NoError(t, err)
+	assert.Equal(t, st1, st)
+	st, err = g()
+	assert.NoError(t, err)
+	assert.Equal(t, st1, st)
+}
+
+func TestMultiGeneratorInOrderMissing(t *testing.T) {
+	g := MultiGeneratorInOrder()
+	st, err := g()
+	assert.Zero(t, st)
+	assert.ErrorIs(t, err, ErrMissingGenerators)
+	st, err = g()
+	assert.Zero(t, st)
+	assert.ErrorIs(t, err, ErrMissingGenerators)
+}
+
 func TestUUID(t *testing.T) {
 	st, err := UUID()()
 	assert.NoError(t, err)