feat(config): env-based configuration with validation

go.mod

@@ -0,0 +1,3 @@
+module github.com/vasyansk/imap-copier
+
+go 1.26.4

internal/config/config.go

@@ -0,0 +1,60 @@
+package config
+
+import (
+	"encoding/base64"
+	"fmt"
+	"os"
+	"strconv"
+)
+
+type Config struct {
+	HTTPAddr          string
+	DatabaseURL       string
+	AuthUser          string
+	AuthPass          string
+	EncKey            []byte
+	SessionSecret     []byte
+	WorkerConcurrency int
+}
+
+func Load() (Config, error) {
+	c := Config{
+		HTTPAddr:          getenv("HTTP_ADDR", ":8080"),
+		DatabaseURL:       os.Getenv("DATABASE_URL"),
+		AuthUser:          os.Getenv("AUTH_USER"),
+		AuthPass:          os.Getenv("AUTH_PASS"),
+		SessionSecret:     []byte(os.Getenv("SESSION_SECRET")),
+		WorkerConcurrency: 4,
+	}
+	if v := os.Getenv("WORKER_CONCURRENCY"); v != "" {
+		n, err := strconv.Atoi(v)
+		if err != nil || n < 1 {
+			return Config{}, fmt.Errorf("WORKER_CONCURRENCY invalid: %q", v)
+		}
+		c.WorkerConcurrency = n
+	}
+	for k, v := range map[string]string{
+		"DATABASE_URL": c.DatabaseURL, "AUTH_USER": c.AuthUser,
+		"AUTH_PASS": c.AuthPass, "SESSION_SECRET": string(c.SessionSecret),
+	} {
+		if v == "" {
+			return Config{}, fmt.Errorf("%s is required", k)
+		}
+	}
+	key, err := base64.StdEncoding.DecodeString(os.Getenv("ENC_KEY"))
+	if err != nil {
+		return Config{}, fmt.Errorf("ENC_KEY must be base64: %w", err)
+	}
+	if len(key) != 32 {
+		return Config{}, fmt.Errorf("ENC_KEY must decode to 32 bytes, got %d", len(key))
+	}
+	c.EncKey = key
+	return c, nil
+}
+
+func getenv(k, def string) string {
+	if v := os.Getenv(k); v != "" {
+		return v
+	}
+	return def
+}

internal/config/config_test.go

@@ -0,0 +1,37 @@
+package config
+
+import (
+	"encoding/base64"
+	"testing"
+)
+
+func TestLoadRequiresEncKey32Bytes(t *testing.T) {
+	t.Setenv("DATABASE_URL", "postgres://x")
+	t.Setenv("AUTH_USER", "admin")
+	t.Setenv("AUTH_PASS", "pass")
+	t.Setenv("SESSION_SECRET", "secret")
+	t.Setenv("ENC_KEY", base64.StdEncoding.EncodeToString(make([]byte, 16))) // wrong size
+
+	if _, err := Load(); err == nil {
+		t.Fatal("expected error for 16-byte ENC_KEY, got nil")
+	}
+}
+
+func TestLoadDefaults(t *testing.T) {
+	t.Setenv("DATABASE_URL", "postgres://x")
+	t.Setenv("AUTH_USER", "admin")
+	t.Setenv("AUTH_PASS", "pass")
+	t.Setenv("SESSION_SECRET", "secret")
+	t.Setenv("ENC_KEY", base64.StdEncoding.EncodeToString(make([]byte, 32)))
+
+	cfg, err := Load()
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if cfg.HTTPAddr != ":8080" {
+		t.Errorf("HTTPAddr = %q, want :8080", cfg.HTTPAddr)
+	}
+	if cfg.WorkerConcurrency != 4 {
+		t.Errorf("WorkerConcurrency = %d, want 4", cfg.WorkerConcurrency)
+	}
+}