add core lib

dotenv/dotenv.go

@@ -0,0 +1,52 @@
+package config
+
+import (
+	"bufio"
+	"os"
+	"strings"
+)
+
+// LoadDotEnvCandidates loads KEY=VALUE pairs from the first existing file in paths.
+// Existing process env vars are preserved (file values only fill missing keys).
+func LoadDotEnvCandidates(paths []string) {
+	for _, path := range paths {
+		if loadDotEnvFile(path) {
+			return
+		}
+	}
+}
+
+func loadDotEnvFile(path string) bool {
+	file, err := os.Open(path)
+	if err != nil {
+		return false
+	}
+	defer file.Close()
+
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		line := strings.TrimSpace(scanner.Text())
+		if line == "" || strings.HasPrefix(line, "#") {
+			continue
+		}
+
+		key, value, ok := strings.Cut(line, "=")
+		if !ok {
+			continue
+		}
+
+		key = strings.TrimSpace(key)
+		value = strings.TrimSpace(value)
+		value = strings.Trim(value, `"'`)
+		if key == "" {
+			continue
+		}
+
+		if _, exists := os.LookupEnv(key); exists {
+			continue
+		}
+		_ = os.Setenv(key, value)
+	}
+
+	return true
+}

dotenv/dotenv_test.go

@@ -0,0 +1,76 @@
+package config
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestLoadDotEnvFileParsesAndPreservesExistingValues(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, ".env")
+	content := "" +
+		"# comment\n" +
+		"KEY1 = value1\n" +
+		"KEY2='quoted value'\n" +
+		"KEY3=\"double quoted\"\n" +
+		"INVALID_LINE\n" +
+		"=missing_key\n"
+
+	if err := os.WriteFile(path, []byte(content), 0o600); err != nil {
+		t.Fatalf("write env file: %v", err)
+	}
+
+	t.Setenv("KEY1", "existing")
+	_ = os.Unsetenv("KEY2")
+	_ = os.Unsetenv("KEY3")
+
+	if ok := loadDotEnvFile(path); !ok {
+		t.Fatal("expected loadDotEnvFile to return true")
+	}
+
+	if got := os.Getenv("KEY1"); got != "existing" {
+		t.Fatalf("expected KEY1 to preserve existing value, got %q", got)
+	}
+	if got := os.Getenv("KEY2"); got != "quoted value" {
+		t.Fatalf("expected KEY2 parsed value, got %q", got)
+	}
+	if got := os.Getenv("KEY3"); got != "double quoted" {
+		t.Fatalf("expected KEY3 parsed value, got %q", got)
+	}
+}
+
+func TestLoadDotEnvCandidatesStopsAtFirstExistingFile(t *testing.T) {
+	dir := t.TempDir()
+	first := filepath.Join(dir, "first.env")
+	second := filepath.Join(dir, "second.env")
+
+	if err := os.WriteFile(first, []byte("KEY_A=first\nKEY_B=from_first\n"), 0o600); err != nil {
+		t.Fatalf("write first env file: %v", err)
+	}
+	if err := os.WriteFile(second, []byte("KEY_A=second\nKEY_C=from_second\n"), 0o600); err != nil {
+		t.Fatalf("write second env file: %v", err)
+	}
+
+	_ = os.Unsetenv("KEY_A")
+	_ = os.Unsetenv("KEY_B")
+	_ = os.Unsetenv("KEY_C")
+
+	LoadDotEnvCandidates([]string{filepath.Join(dir, "missing.env"), first, second})
+
+	if got := os.Getenv("KEY_A"); got != "first" {
+		t.Fatalf("expected KEY_A from first file, got %q", got)
+	}
+	if got := os.Getenv("KEY_B"); got != "from_first" {
+		t.Fatalf("expected KEY_B from first file, got %q", got)
+	}
+	if got := os.Getenv("KEY_C"); got != "" {
+		t.Fatalf("expected KEY_C to remain unset, got %q", got)
+	}
+}
+
+func TestLoadDotEnvFileReturnsFalseWhenMissing(t *testing.T) {
+	if ok := loadDotEnvFile(filepath.Join(t.TempDir(), "does-not-exist.env")); ok {
+		t.Fatal("expected loadDotEnvFile to return false for missing file")
+	}
+}