Fix edgecases for lineinfile module (home-assistant#221)

Edgecases where the file contains only a single line and no before/after
regexp was given were not handled correctly. Also the Find method should
accept empty string for searching from the beginning of the file.

Moreover, it's useful if the file can be created by Present (it's also
what Ansible does), so handle this case too.

utils/lineinfile/lineinfile.go

@@ -47,16 +47,23 @@ func NewAbsentParams() Params {
 }
 
 func (l LineInFile) Present(params Params) error {
-	if _, err := os.Stat(l.FilePath); err != nil {
+	createFile := false
+	if _, err := os.Stat(l.FilePath); os.IsNotExist(err) {
+		// will be created by atomic.WriteFile
+		createFile = true
+	} else if err != nil {
 		return err
 	}
 
-	content, err := os.ReadFile(l.FilePath)
-	if err != nil {
-		return err
-	}
+	var lines []string
+	if !createFile {
+		content, err := os.ReadFile(l.FilePath)
+		if err != nil {
+			return err
+		}
 
-	lines := strings.Split(string(content), "\n")
+		lines = strings.Split(string(content), "\n")
+	}
 
 	outLines, err := processPresent(lines, params)
 	if err != nil {
@@ -132,7 +139,7 @@ func processPresent(inLines []string, params Params) ([]string, error) {
 			afterIndex = idx
 			continue
 		}
-		if (needsAfter && afterIndex >= 0 || needsBefore && beforeIndex >= 0) && foundIndex < 0 && params.Regexp.MatchString(curr) {
+		if ((!needsAfter && !needsBefore) || needsAfter && afterIndex >= 0 || needsBefore && beforeIndex >= 0) && foundIndex < 0 && params.Regexp.MatchString(curr) {
 			foundIndex = idx
 		}
 	}
@@ -186,7 +193,7 @@ func processAbsent(inLines []string, params Params) ([]string, error) {
 			afterIndex = idx
 			continue
 		}
-		if (needsAfter && afterIndex >= 0 || needsBefore && beforeIndex >= 0) && foundIndex < 0 && params.Regexp.MatchString(curr) {
+		if ((!needsAfter && !needsBefore) || needsAfter && afterIndex >= 0 || needsBefore && beforeIndex >= 0) && foundIndex < 0 && params.Regexp.MatchString(curr) {
 			foundIndex = idx
 		}
 	}
@@ -227,7 +234,7 @@ func processFind(regexp string, after string, inLines []string) *string {
 	lineRegexp, _ := re.Compile(regexp)
 	afterRegexp, _ := re.Compile(after)
 
-	var foundAfter = false
+	var foundAfter = after == ""
 
 	for _, curr := range inLines {
 		if !foundAfter && afterRegexp.MatchString(curr) {

utils/lineinfile/lineinfile_test.go

@@ -61,6 +61,16 @@ func TestFindMissingNotAfter(t *testing.T) {
 	}
 }
 
+func TestFindEmptyAfter(t *testing.T) {
+	content := "KEY=value\nKEY2=value2"
+	lines := strings.Split(content, "\n")
+	result := processFind(`^KEY=`, "", lines)
+	if *result != "KEY=value" {
+		t.Errorf("Expected a result, got nil")
+		return
+	}
+}
+
 func TestPresentSimple(t *testing.T) {
 	params := NewPresentParams("NTP=ntp2.example.com")
 	params.Regexp, _ = regexp.Compile(`^\s*#?\s*(NTP=).*$`)
@@ -130,6 +140,31 @@ func TestPresentAppendedEOF(t *testing.T) {
 	}
 }
 
+func TestPresentEmptyContent(t *testing.T) {
+	params := NewPresentParams("NTP=ntp.example.com")
+	params.Regexp, _ = regexp.Compile(`^\s*#?\s*(NTP=).*$`)
+	params.After = `EOF`
+	var lines []string
+	processed, _ := processPresent(lines, params)
+	result := strings.Join(processed, "\n")
+	expected := "NTP=ntp.example.com"
+	if result != expected {
+		t.Errorf("Expected %s, got %s", expected, result)
+	}
+}
+
+func TestPresentNoBeforeAfterRegex(t *testing.T) {
+	params := NewPresentParams("NTP=ntp.example.com")
+	params.Regexp, _ = regexp.Compile(`^\s*#?\s*(NTP=).*$`)
+	content := "NTP=ntp.example.com"
+	lines := strings.Split(content, "\n")
+	processed, _ := processPresent(lines, params)
+	result := strings.Join(processed, "\n")
+	if result != content {
+		t.Errorf("Expected %s, got %s", content, result)
+	}
+}
+
 func TestPresentNoRegexp(t *testing.T) {
 	params := NewPresentParams("NTP=ntp.example.com")
 	params.After = `\[Time\]`
@@ -179,3 +214,16 @@ func TestAbsentNoRegexp(t *testing.T) {
 		t.Errorf("Expected an error, got nil")
 	}
 }
+
+func TestAbsentNoBeforeAfterRegex(t *testing.T) {
+	params := NewAbsentParams()
+	params.Regexp, _ = regexp.Compile(`^\s*#?\s*(NTP=).*$`)
+	content := "NTP=ntp.example.com"
+	lines := strings.Split(content, "\n")
+	processed, _ := processAbsent(lines, params)
+	result := strings.Join(processed, "\n")
+	expected := ""
+	if result != expected {
+		t.Errorf("Expected %s, got %s", expected, result)
+	}
+}