adds the ability to set a custom writer (#5)

cursor.go

@@ -4,17 +4,27 @@ package cursor
 
 import (
 	"fmt"
+	"io"
+	"os"
 )
 
+var target io.Writer = os.Stdout
+
+// SetTarget allows for any arbitrary io.Writer to be used
+// for cursor movement (will not work on Windows).
+func SetTarget(w io.Writer) {
+	target = w
+}
+
 // Up moves the cursor n lines up relative to the current position.
 func Up(n int) {
-	fmt.Printf("\x1b[%dA", n)
+	fmt.Fprintf(target, "\x1b[%dA", n)
 	height += n
 }
 
 // Down moves the cursor n lines down relative to the current position.
 func Down(n int) {
-	fmt.Printf("\x1b[%dB", n)
+	fmt.Fprintf(target, "\x1b[%dB", n)
 	if height-n <= 0 {
 		height = 0
 	} else {
@@ -24,36 +34,36 @@ func Down(n int) {
 
 // Right moves the cursor n characters to the right relative to the current position.
 func Right(n int) {
-	fmt.Printf("\x1b[%dC", n)
+	fmt.Fprintf(target, "\x1b[%dC", n)
 }
 
 // Left moves the cursor n characters to the left relative to the current position.
 func Left(n int) {
-	fmt.Printf("\x1b[%dD", n)
+	fmt.Fprintf(target, "\x1b[%dD", n)
 }
 
 // HorizontalAbsolute moves the cursor to n horizontally.
 // The position n is absolute to the start of the line.
 func HorizontalAbsolute(n int) {
 	n += 1 // Moves the line to the character after n
-	fmt.Printf("\x1b[%dG", n)
+	fmt.Fprintf(target, "\x1b[%dG", n)
 }
 
 // Show the cursor if it was hidden previously.
 // Don't forget to show the cursor at least at the end of your application.
 // Otherwise the user might have a terminal with a permanently hidden cursor, until they reopen the terminal.
 func Show() {
-	fmt.Print("\x1b[?25h")
+	fmt.Fprint(target, "\x1b[?25h")
 }
 
 // Hide the cursor.
 // Don't forget to show the cursor at least at the end of your application with Show.
 // Otherwise the user might have a terminal with a permanently hidden cursor, until they reopen the terminal.
 func Hide() {
-	fmt.Print("\x1b[?25l")
+	fmt.Fprintf(target, "\x1b[?25l")
 }
 
 // ClearLine clears the current line and moves the cursor to it's start position.
 func ClearLine() {
-	fmt.Print("\x1b[2K")
+	fmt.Fprintf(target, "\x1b[2K")
 }

cursor_test.go

@@ -1,7 +1,9 @@
 package cursor
 
 import (
+	"bytes"
 	"fmt"
+	"runtime"
 	"testing"
 )
 
@@ -25,3 +27,75 @@ func TestHeightCannotBeNegative(t *testing.T) {
 		t.Errorf("height is negative: %d", height)
 	}
 }
+
+func TestCustomIOWriter(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("skipping these tests on windows")
+	}
+
+	var w bytes.Buffer
+	SetTarget(&w)
+
+	Up(2)
+	expected := "\x1b[2A"
+	actual := w.String()
+	if expected != actual {
+		t.Errorf("wanted: %v, got %v", expected, actual)
+	}
+
+	w.Reset()
+	Down(2)
+	expected = "\x1b[2B"
+	actual = w.String()
+	if expected != actual {
+		t.Errorf("wanted: %v, got %v", expected, actual)
+	}
+
+	w.Reset()
+	Right(2)
+	expected = "\x1b[2C"
+	actual = w.String()
+	if expected != actual {
+		t.Errorf("wanted: %v, got %v", expected, actual)
+	}
+
+	w.Reset()
+	Left(2)
+	expected = "\x1b[2D"
+	actual = w.String()
+	if expected != actual {
+		t.Errorf("wanted: %v, got %v", expected, actual)
+	}
+
+	w.Reset()
+	Hide()
+	expected = "\x1b[?25l"
+	actual = w.String()
+	if expected != actual {
+		t.Errorf("wanted: %v, got %v", expected, actual)
+	}
+
+	w.Reset()
+	Show()
+	expected = "\x1b[?25h"
+	actual = w.String()
+	if expected != actual {
+		t.Errorf("wanted: %v, got %v", expected, actual)
+	}
+
+	w.Reset()
+	ClearLine()
+	expected = "\x1b[2K"
+	actual = w.String()
+	if expected != actual {
+		t.Errorf("wanted: %v, got %v", expected, actual)
+	}
+
+	w.Reset()
+	HorizontalAbsolute(3)
+	expected = "\x1b[4G"
+	actual = w.String()
+	if expected != actual {
+		t.Errorf("wanted: %v, got %v", expected, actual)
+	}
+}

cursor_windows.go

@@ -1,11 +1,17 @@
 package cursor
 
 import (
+	"io"
 	"os"
 	"syscall"
 	"unsafe"
 )
 
+// SetTarget allows for any arbitrary io.Writer to be used
+// for cursor movement (will not work on Windows).
+func SetTarget(w io.Writer) {
+}
+
 // Up moves the cursor n lines up relative to the current position.
 func Up(n int) {
 	move(0, -n)