feat: string-unpack

string-unpack/unpack.go

@@ -0,0 +1,54 @@
+package stringunpack
+
+import (
+	"errors"
+	"strconv"
+	"strings"
+)
+
+var ErrIncorrectString = errors.New("incorrect string")
+
+func Unpack(s string) (string, error) {
+	if s == "" {
+		return "", nil
+	}
+
+	var sb strings.Builder
+	sb.Grow(len(s))
+
+	var curSymbol rune
+	for _, r := range s {
+		isNumber := false
+		number := 0
+		if n, err := strconv.Atoi(string(r)); err == nil {
+			number = n
+			isNumber = true
+		}
+
+		if curSymbol == rune(0) {
+			switch {
+			case isNumber:
+				return "", ErrIncorrectString
+			case !isNumber:
+				curSymbol = r
+			}
+		} else {
+			switch {
+			case !isNumber:
+				sb.WriteRune(curSymbol)
+				curSymbol = r
+			case isNumber:
+				for i := 0; i < number; i++ {
+					sb.WriteRune(curSymbol)
+				}
+				curSymbol = rune(0)
+			}
+		}
+	}
+
+	if curSymbol != rune(0) {
+		sb.WriteRune(curSymbol)
+	}
+
+	return sb.String(), nil
+}

string-unpack/unpack_test.go

@@ -0,0 +1,44 @@
+package stringunpack_test
+
+import (
+	"testing"
+
+	stringunpack "git.grachevko.ru/grachevko/h/string-unpack"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestUnpack(t *testing.T) {
+	testcases := []struct {
+		input    string
+		expected string
+	}{
+		{input: "a4bc2d5e", expected: "aaaabccddddde"},
+		{input: "abcd", expected: "abcd"},
+		{input: "aaa0b", expected: "aab"},
+		{input: "", expected: ""},
+		{input: "d\n5abc", expected: "d\n\n\n\n\nabc"},
+	}
+
+	for _, tc := range testcases {
+		t.Run(tc.input, func(t *testing.T) {
+			result, err := stringunpack.Unpack(tc.input)
+			assert.NoError(t, err)
+			assert.Equal(t, tc.expected, result)
+		})
+	}
+}
+
+func TestUnpackIncorrectString(t *testing.T) {
+	testcases := []string{
+		"3abc",
+		"45",
+		"aaa10b",
+	}
+
+	for _, input := range testcases {
+		t.Run(input, func(t *testing.T) {
+			_, err := stringunpack.Unpack(input)
+			assert.Equal(t, stringunpack.ErrIncorrectString, err)
+		})
+	}
+}