fix: MacOS MDM based Deployment (#277)

* fix: MacOS MDM deployment script

* fix: Handle shell alias for bash on macos

* fix: Code review fixes

* fix: Code review fixes

* feat: Add support for global config file

* feat: Add support for global config file

* fix: Code review fixes

* fix: Avoid blocking CLI for analytics flush

internal/alias/shells.go

@@ -3,6 +3,8 @@ package alias
 import (
 	"fmt"
 	"os"
+	"path/filepath"
+	"runtime"
 	"strings"
 )
 
@@ -10,7 +12,16 @@ type Shell interface {
 	Source(rcPath string) string
 	PathExport(binDir string) string
 	Name() string
-	Path() string
+
+	// InstallRcFiles returns the rc files PMG should write its source/PATH lines
+	// into. Existing files are always included. When create is true (the user's
+	// primary shell) and no rc file exists, it creates the canonical one so the
+	// lines have somewhere to live.
+	InstallRcFiles(homeDir string, create bool) ([]string, error)
+
+	// CandidateRcFiles returns every rc file this shell might use, for removal
+	// and install detection. The files need not exist.
+	CandidateRcFiles(homeDir string) []string
 }
 
 var commentForRemovingShellSource = "# remove aliases by running `pmg setup remove` or deleting the line"
@@ -36,3 +47,146 @@ func DetectShell() (string, error) {
 
 	return shellName, nil
 }
+
+// PrimaryShellName returns the user's main shell. It reads $SHELL and falls back
+// to the OS default (zsh on macOS, bash elsewhere) when $SHELL is unset. The
+// result decides which shell gets its rc file created when none exists yet.
+func PrimaryShellName() string {
+	if name, err := DetectShell(); err == nil && name != "" {
+		return name
+	}
+
+	if runtime.GOOS == "darwin" {
+		return "zsh"
+	}
+
+	return "bash"
+}
+
+func fileExists(path string) bool {
+	info, err := os.Stat(path)
+	return err == nil && !info.IsDir()
+}
+
+// ensureFile creates an empty file, and any missing parent directories, when it
+// does not already exist.
+func ensureFile(path string) error {
+	if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
+		return fmt.Errorf("failed to create directory for %s: %w", path, err)
+	}
+
+	f, err := os.OpenFile(path, os.O_CREATE|os.O_WRONLY, 0o644)
+	if err != nil {
+		return fmt.Errorf("failed to create %s: %w", path, err)
+	}
+
+	return f.Close()
+}
+
+// firstExistingFile returns the first of names (joined with homeDir) that exists,
+// or "" when none do.
+func firstExistingFile(homeDir string, names []string) string {
+	for _, name := range names {
+		path := filepath.Join(homeDir, name)
+		if fileExists(path) {
+			return path
+		}
+	}
+
+	return ""
+}
+
+// singleRcFile resolves shells that use one rc file (zsh, fish): return it when
+// present, create it when create is set, otherwise skip.
+func singleRcFile(path string, create bool) ([]string, error) {
+	if fileExists(path) {
+		return []string{path}, nil
+	}
+
+	if !create {
+		return nil, nil
+	}
+
+	if err := ensureFile(path); err != nil {
+		return nil, err
+	}
+
+	return []string{path}, nil
+}
+
+// RewriteFileDroppingLines rewrites path, removing every line for which drop
+// returns true (the line is passed without its trailing newline). It preserves
+// the rest of the file byte for byte and its permissions, replaces the file
+// atomically via a temp file, and skips the write when no line is dropped. A
+// missing file is a no-op. It reads the file in one shot rather than scanning,
+// so it has no per-line length limit.
+func RewriteFileDroppingLines(path string, drop func(line string) bool) error {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil
+		}
+		return err
+	}
+
+	var b strings.Builder
+	b.Grow(len(data))
+
+	dropped := false
+	for _, line := range strings.SplitAfter(string(data), "\n") {
+		// SplitAfter keeps the newline on each line; the final element is the
+		// empty remainder after the last newline.
+		if line == "" {
+			continue
+		}
+		if drop(strings.TrimRight(line, "\r\n")) {
+			dropped = true
+			continue
+		}
+		b.WriteString(line)
+	}
+
+	if !dropped {
+		return nil
+	}
+
+	info, err := os.Stat(path)
+	if err != nil {
+		return err
+	}
+
+	return writeFileAtomic(path, []byte(b.String()), info.Mode())
+}
+
+// writeFileAtomic writes data to a temp file in the target directory, then
+// renames it over path so a crash never leaves a half-written file.
+func writeFileAtomic(path string, data []byte, perm os.FileMode) error {
+	tempFile, err := os.CreateTemp(filepath.Dir(path), ".tmp-"+filepath.Base(path))
+	if err != nil {
+		return err
+	}
+	tempPath := tempFile.Name()
+
+	if _, err := tempFile.Write(data); err != nil {
+		_ = tempFile.Close()
+		_ = os.Remove(tempPath)
+		return err
+	}
+
+	if err := tempFile.Close(); err != nil {
+		_ = os.Remove(tempPath)
+		return err
+	}
+
+	if err := os.Chmod(tempPath, perm); err != nil {
+		_ = os.Remove(tempPath)
+		return err
+	}
+
+	if err := os.Rename(tempPath, path); err != nil {
+		_ = os.Remove(tempPath)
+		return err
+	}
+
+	return nil
+}