feat(platform): add textblock helper for idempotent config-file blocks

internal/platform/textblock.go

@@ -0,0 +1,78 @@
+package platform
+
+import (
+	"fmt"
+	"os"
+	"strings"
+)
+
+func blockMarkers(marker string) (string, string) {
+	return fmt.Sprintf("# >>> %s >>>", marker), fmt.Sprintf("# <<< %s <<<", marker)
+}
+
+// EnsureBlock writes a marker-delimited block into path. If the file does
+// not exist it is created. If a block with the same marker already exists
+// it is replaced in place. Surrounding content is preserved.
+func EnsureBlock(path, marker, content string) error {
+	start, end := blockMarkers(marker)
+	existing, err := os.ReadFile(path)
+	if err != nil && !os.IsNotExist(err) {
+		return err
+	}
+	block := start + "\n" + strings.TrimRight(content, "\n") + "\n" + end + "\n"
+
+	text := string(existing)
+	si := strings.Index(text, start)
+	ei := strings.Index(text, end)
+	if si >= 0 && ei > si {
+		endPos := ei + len(end)
+		if endPos < len(text) && text[endPos] == '\n' {
+			endPos++
+		}
+		text = text[:si] + block + text[endPos:]
+	} else {
+		if text != "" && !strings.HasSuffix(text, "\n") {
+			text += "\n"
+		}
+		text += block
+	}
+	return os.WriteFile(path, []byte(text), 0o644)
+}
+
+// HasBlock reports whether path contains a block with the given marker.
+// A missing file yields (false, nil).
+func HasBlock(path, marker string) (bool, error) {
+	start, _ := blockMarkers(marker)
+	data, err := os.ReadFile(path)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return false, nil
+		}
+		return false, err
+	}
+	return strings.Contains(string(data), start), nil
+}
+
+// RemoveBlock deletes a marker-delimited block if present.
+func RemoveBlock(path, marker string) error {
+	start, end := blockMarkers(marker)
+	data, err := os.ReadFile(path)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil
+		}
+		return err
+	}
+	text := string(data)
+	si := strings.Index(text, start)
+	ei := strings.Index(text, end)
+	if si < 0 || ei <= si {
+		return nil
+	}
+	endPos := ei + len(end)
+	if endPos < len(text) && text[endPos] == '\n' {
+		endPos++
+	}
+	text = text[:si] + text[endPos:]
+	return os.WriteFile(path, []byte(text), 0o644)
+}

internal/platform/textblock_test.go

@@ -0,0 +1,88 @@
+package platform
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func TestEnsureBlockInsertsIntoMissingFile(t *testing.T) {
+	dir := t.TempDir()
+	p := filepath.Join(dir, "rc")
+	if err := EnsureBlock(p, "archduino", "export FOO=1"); err != nil {
+		t.Fatal(err)
+	}
+	got, _ := os.ReadFile(p)
+	want := "# >>> archduino >>>\nexport FOO=1\n# <<< archduino <<<\n"
+	if string(got) != want {
+		t.Fatalf("got %q want %q", got, want)
+	}
+}
+
+func TestEnsureBlockReplacesExisting(t *testing.T) {
+	dir := t.TempDir()
+	p := filepath.Join(dir, "rc")
+	initial := "alias ll='ls -l'\n# >>> archduino >>>\nold content\n# <<< archduino <<<\necho tail\n"
+	if err := os.WriteFile(p, []byte(initial), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	if err := EnsureBlock(p, "archduino", "new content"); err != nil {
+		t.Fatal(err)
+	}
+	got, _ := os.ReadFile(p)
+	want := "alias ll='ls -l'\n# >>> archduino >>>\nnew content\n# <<< archduino <<<\necho tail\n"
+	if string(got) != want {
+		t.Fatalf("got %q want %q", got, want)
+	}
+}
+
+func TestEnsureBlockIdempotent(t *testing.T) {
+	dir := t.TempDir()
+	p := filepath.Join(dir, "rc")
+	_ = EnsureBlock(p, "a", "x")
+	before, _ := os.ReadFile(p)
+	_ = EnsureBlock(p, "a", "x")
+	after, _ := os.ReadFile(p)
+	if string(before) != string(after) {
+		t.Fatalf("not idempotent: %q vs %q", before, after)
+	}
+}
+
+func TestHasBlockTrueFalse(t *testing.T) {
+	dir := t.TempDir()
+	p := filepath.Join(dir, "rc")
+	has, err := HasBlock(p, "a")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if has {
+		t.Fatal("missing file should report has=false")
+	}
+	_ = os.WriteFile(p, []byte("no blocks here\n"), 0o644)
+	has, _ = HasBlock(p, "a")
+	if has {
+		t.Fatal("unblocked file should report has=false")
+	}
+	_ = EnsureBlock(p, "a", "x")
+	has, _ = HasBlock(p, "a")
+	if !has {
+		t.Fatal("blocked file should report has=true")
+	}
+}
+
+func TestRemoveBlock(t *testing.T) {
+	dir := t.TempDir()
+	p := filepath.Join(dir, "rc")
+	_ = os.WriteFile(p, []byte("head\n# >>> a >>>\nmid\n# <<< a <<<\ntail\n"), 0o644)
+	if err := RemoveBlock(p, "a"); err != nil {
+		t.Fatal(err)
+	}
+	got, _ := os.ReadFile(p)
+	if strings.Contains(string(got), ">>> a >>>") {
+		t.Fatalf("block not removed: %q", got)
+	}
+	if !strings.Contains(string(got), "head") || !strings.Contains(string(got), "tail") {
+		t.Fatalf("surrounding content lost: %q", got)
+	}
+}