1 files changed, 81 insertions, 20 deletions
diff --git a/internal/config/config.go b/internal/config/config.go
index b9ae6c2..b8d0532 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -13,8 +13,12 @@ import (
 	"strings"
 )
 
-// configPath is the location of the optional user config file.
-const configPath = "~/.config/foostore.json"
+const (
+	// configPath is the location of the optional user config file.
+	configPath = "~/.config/foostore.json"
+	// fallbackHomeDirName is used when we cannot resolve a valid home directory.
+	fallbackHomeDirName = "foostore-home"
+)
 
 // Config holds all application-wide configuration values.
 // JSON field names use snake_case to match the original geheim.rb Config::DEFAULTS keys.
@@ -31,14 +35,53 @@ type Config struct {
 	SyncRepos         []string `json:"sync_repos"`
 }
 
-// defaultConfig returns a Config populated with built-in defaults.
-// EditCmd honours the $EDITOR environment variable and falls back to "vi"
-// when the variable is unset or empty, so users get their preferred editor
-// automatically without touching the config file.
-// It calls os.UserHomeDir() so that path fields expand correctly at runtime.
-func defaultConfig() Config {
-	home, _ := os.UserHomeDir()
+// resolveHomeDir resolves the current user's home directory from OS state.
+// If resolution succeeds with os.UserHomeDir, error is nil.
+// If resolution falls back to HOME or a temp-based directory, an explanatory
+// non-nil error is returned so callers can warn without failing hard.
+func resolveHomeDir() (string, error) {
+	return resolveHomeDirFrom(os.UserHomeDir, os.Getenv("HOME"), os.TempDir())
+}
+
+// resolveHomeDirFrom is a test seam for home directory resolution.
+func resolveHomeDirFrom(userHomeDir func() (string, error), envHome, tempDir string) (string, error) {
+	home, err := userHomeDir()
+	if err == nil && home != "" {
+		return home, nil
+	}
+
+	if envHome != "" && filepath.IsAbs(envHome) {
+		if err != nil {
+			return envHome, fmt.Errorf("os.UserHomeDir failed; using HOME=%q: %w", envHome, err)
+		}
+		return envHome, fmt.Errorf("os.UserHomeDir returned empty home; using HOME=%q", envHome)
+	}
+
+	fallbackHome := filepath.Join(tempDir, fallbackHomeDirName)
+	if envHome != "" && !filepath.IsAbs(envHome) {
+		if err != nil {
+			return fallbackHome, fmt.Errorf("os.UserHomeDir failed; HOME is not absolute (%q), using %q: %w", envHome, fallbackHome, err)
+		}
+		return fallbackHome, fmt.Errorf("os.UserHomeDir returned empty home; HOME is not absolute (%q), using %q", envHome, fallbackHome)
+	}
+
+	if err != nil {
+		return fallbackHome, fmt.Errorf("os.UserHomeDir failed and HOME is unavailable; using %q: %w", fallbackHome, err)
+	}
+	return fallbackHome, fmt.Errorf("os.UserHomeDir returned empty home and HOME is unavailable; using %q", fallbackHome)
+}
+
+// homeDirOrFallback resolves a usable home path and logs fallback reasons.
+func homeDirOrFallback() string {
+	home, err := resolveHomeDir()
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Warning: %v\n", err)
+	}
+	return home
+}
 
+// defaultConfigWithHome returns built-in defaults using the supplied home path.
+func defaultConfigWithHome(home string) Config {
 	// Prefer $EDITOR; fall back to vi if not set.
 	editCmd := os.Getenv("EDITOR")
 	if editCmd == "" {
@@ -59,22 +102,39 @@ func defaultConfig() Config {
 	}
 }
 
-// expandTilde replaces a leading "~" in path with the user's home directory.
-// Non-tilde paths and empty strings are returned unchanged.
-func expandTilde(path string) string {
+// defaultConfig returns a Config populated with built-in defaults.
+// EditCmd honours the $EDITOR environment variable and falls back to "vi"
+// when the variable is unset or empty, so users get their preferred editor
+// automatically without touching the config file.
+func defaultConfig() Config {
+	return defaultConfigWithHome(homeDirOrFallback())
+}
+
+// expandTildeWithHome replaces a leading "~" in path with the supplied home.
+func expandTildeWithHome(path, home string) string {
 	if path == "" || !strings.HasPrefix(path, "~") {
 		return path
 	}
-	home, _ := os.UserHomeDir()
 	// Replace only the leading "~"; preserve any subdirectory suffix.
 	return home + path[1:]
 }
 
+// expandTilde replaces a leading "~" in path with the user's home directory.
+// Non-tilde paths and empty strings are returned unchanged.
+func expandTilde(path string) string {
+	return expandTildeWithHome(path, homeDirOrFallback())
+}
+
+// expandPathFieldsWithHome tilde-expands every path-typed field in cfg in place.
+func expandPathFieldsWithHome(cfg *Config, home string) {
+	cfg.DataDir = expandTildeWithHome(cfg.DataDir, home)
+	cfg.ExportDir = expandTildeWithHome(cfg.ExportDir, home)
+	cfg.KeyFile = expandTildeWithHome(cfg.KeyFile, home)
+}
+
 // expandPathFields tilde-expands every path-typed field in cfg in place.
 func expandPathFields(cfg *Config) {
-	cfg.DataDir = expandTilde(cfg.DataDir)
-	cfg.ExportDir = expandTilde(cfg.ExportDir)
-	cfg.KeyFile = expandTilde(cfg.KeyFile)
+	expandPathFieldsWithHome(cfg, homeDirOrFallback())
 }
 
 // Load reads ~/.config/foostore.json and merges it over the built-in defaults.
@@ -86,8 +146,9 @@ func expandPathFields(cfg *Config) {
 // Note: the Ruby reference uses puts (stdout) for this warning; we use stderr
 // intentionally because warnings belong on the error stream.
 func Load() Config {
-	cfg := defaultConfig()
-	path := expandTilde(configPath)
+	home := homeDirOrFallback()
+	cfg := defaultConfigWithHome(home)
+	path := expandTildeWithHome(configPath, home)
 
 	data, err := os.ReadFile(path)
 	if err != nil {
@@ -103,12 +164,12 @@ func Load() Config {
 	// JSON document are overwritten; all others retain their default values.
 	if err := json.Unmarshal(data, &cfg); err != nil {
 		fmt.Fprintf(os.Stderr, "Unable to read %s, using defaults! %v\n", path, err)
-		return defaultConfig()
+		return defaultConfigWithHome(home)
 	}
 
 	// Tilde-expand path fields that may have been supplied as "~/…" strings
 	// in the JSON file (defaultConfig() already returns absolute paths, but
 	// user-supplied values might use "~").
-	expandPathFields(&cfg)
+	expandPathFieldsWithHome(&cfg, home)
 	return cfg
 }