Improve peek and add input tests (#9)

core/input.go

@@ -41,11 +41,11 @@ func NewInput(s string) Input {
 }
 
 func (i *input) Peek(n int) (s string, ok bool) {
-	if i.index+n > len(i.s) {
+	if i.index+n > len(i.s) || i.index+n < 0 {
 		return
 	}
 	if n < 0 {
-		return i.s[i.index:], true
+		return i.s[i.index+n : i.index], true
 	}
 	return i.s[i.index : i.index+n], true
 }

core/input_test.go

@@ -0,0 +1,99 @@
+// Copyright 2024 Liam White
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package core_test
+
+import (
+	"testing"
+
+	. "github.com/liamawhite/parse/core"
+	"github.com/stretchr/testify/assert"
+)
+
+const input = `Some words
+and some more words
+and even more words`
+
+func TestInput(t *testing.T) {
+	i := NewInput(input)
+	start := i.Checkpoint()
+
+	t.Run("Peek forward", func(t *testing.T) {
+		s, ok := i.Peek(10)
+		assert.True(t, ok)
+		assert.Equal(t, "Some words", s)
+	})
+	t.Run("Peek forward single", func(t *testing.T) {
+		s, ok := i.Peek(1)
+		assert.True(t, ok)
+		assert.Equal(t, "S", s)
+	})
+	t.Run("Peek zero", func(t *testing.T) {
+		s, ok := i.Peek(0)
+		assert.True(t, ok)
+		assert.Equal(t, "", s)
+	})
+	t.Run("Peek backward single", func(t *testing.T) {
+		i.Take(1)
+		s, ok := i.Peek(-1)
+		assert.True(t, ok)
+		assert.Equal(t, "S", s)
+		i.Restore(start)
+	})
+	t.Run("Peek backward", func(t *testing.T) {
+		i.Take(10) // need to move the index so we can peek backwards
+		s, ok := i.Peek(-10)
+		assert.True(t, ok)
+		assert.Equal(t, "Some words", s)
+		i.Restore(start)
+	})
+	t.Run("Peek backward beyond start", func(t *testing.T) {
+		s, ok := i.Peek(-5)
+		assert.False(t, ok)
+		assert.Equal(t, "", s)
+	})
+	t.Run("Peek forward beyond end", func(t *testing.T) {
+		s, ok := i.Peek(100)
+		assert.False(t, ok)
+		assert.Equal(t, "", s)
+	})
+	t.Run("Take forward", func(t *testing.T) {
+		s, ok := i.Take(10)
+		assert.True(t, ok)
+		assert.Equal(t, "Some words", s)
+		i.Restore(start)
+	})
+	t.Run("Take forward single", func(t *testing.T) {
+		s, ok := i.Take(1)
+		assert.True(t, ok)
+		assert.Equal(t, "S", s)
+		i.Restore(start)
+	})
+	t.Run("Take forward zero", func(t *testing.T) {
+		s, ok := i.Take(0)
+		assert.True(t, ok)
+		assert.Equal(t, "", s)
+	})
+	t.Run("Take forward beyond end", func(t *testing.T) {
+		s, ok := i.Take(100)
+		assert.False(t, ok)
+		assert.Equal(t, "", s)
+	})
+	t.Run("Take backward fails", func(t *testing.T) {
+		s, ok := i.Take(-1)
+		assert.False(t, ok)
+		assert.Equal(t, "", s)
+	})
+
+}