feat(spaced): Support configurable spacing (#10)

README.md

@@ -14,6 +14,9 @@ space insertion (ASI).
 ```shell
 $ echo 'AESTHETIC' | spaced
 A E S T H E T I C
+
+$ echo 'AESTHETIC' | spaced 2
+A  E  S  T  H  E  T  I  C
 ```
 
 ### Go

cmd/spaced/main.go

@@ -1,17 +1,11 @@
 package main
 
 import (
-	"fmt"
 	"os"
 
-	"github.com/72636c/hyperspaced/internal/text"
-	"github.com/72636c/hyperspaced/internal/text/transform"
+	"github.com/72636c/hyperspaced/internal/cmd"
 )
 
 func main() {
-	err := text.LineFilter(transform.Spaced)
-	if err != nil {
-		fmt.Fprintln(os.Stderr, "error: ", err)
-		os.Exit(1)
-	}
+	cmd.Spaced(os.Stdin, os.Stdout, os.Args)
 }

internal/cmd/spaced.go

@@ -0,0 +1,48 @@
+package cmd
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"strconv"
+
+	"github.com/72636c/hyperspaced/internal/text"
+	"github.com/72636c/hyperspaced/internal/text/transform"
+)
+
+var usage = `spaced [n]
+  n int
+    number of spaces between each character (default 1)
+`
+
+func Spaced(reader io.Reader, writer io.Writer, args []string) {
+	n, err := spacesFromArgs(args)
+	if err != nil {
+		fmt.Fprintln(os.Stderr, usage)
+		fmt.Fprintln(os.Stderr, "error:", err)
+		os.Exit(1)
+	}
+
+	transformLine := func(str string) string {
+		return transform.SpacedN(str, n)
+	}
+
+	err = text.LineFilter(reader, writer, transformLine)
+	if err != nil {
+		fmt.Fprintln(os.Stderr, "error:", err)
+		os.Exit(1)
+	}
+}
+
+func spacesFromArgs(args []string) (int, error) {
+	if len(args) < 2 {
+		return 1, nil
+	}
+
+	n, err := strconv.Atoi(args[1])
+	if err != nil {
+		return 0, err
+	}
+
+	return n, nil
+}

internal/cmd/spaced_test.go

@@ -0,0 +1,42 @@
+package cmd
+
+import (
+	"strings"
+	"testing"
+)
+
+func Test_Spaced(t *testing.T) {
+	testCases := []struct {
+		description string
+		args        []string
+		input       string
+		expected    string
+	}{
+		{
+			description: "unspecified n",
+			args:        []string{"spaced"},
+			input:       "AESTHETIC",
+			expected:    "A E S T H E T I C\n",
+		},
+		{
+			description: "integer n",
+			args:        []string{"spaced", "2"},
+			input:       "AESTHETIC",
+			expected:    "A  E  S  T  H  E  T  I  C\n",
+		},
+	}
+
+	for _, testCase := range testCases {
+		t.Run(testCase.description, func(t *testing.T) {
+			reader := strings.NewReader(testCase.input)
+			writer := new(strings.Builder)
+
+			Spaced(reader, writer, testCase.args)
+
+			actual := writer.String()
+			if actual != testCase.expected {
+				t.Errorf("expected %s, received %s", testCase.expected, actual)
+			}
+		})
+	}
+}

internal/text/lineFilter.go

@@ -3,20 +3,24 @@ package text
 import (
 	"bufio"
 	"fmt"
-	"os"
+	"io"
 )
 
 // TransformLine is a function that transforms a line of text.
 type TransformLine func(string) string
 
-// LineFilter transforms lines of text as they pass from stdin to stdout.
-func LineFilter(transform TransformLine) error {
-	scanner := bufio.NewScanner(os.Stdin)
+// LineFilter transforms lines of text as they pass from a reader to a writer.
+func LineFilter(
+	reader io.Reader,
+	writer io.Writer,
+	transform TransformLine,
+) error {
+	scanner := bufio.NewScanner(reader)
 
 	for scanner.Scan() {
 		output := transform(scanner.Text())
 
-		_, err := fmt.Println(output)
+		_, err := fmt.Fprintln(writer, output)
 		if err != nil {
 			return err
 		}