feat: extract into remaining packages

There has been a cyclic dependency.
transaction
	-> treasure_chest
	-> transaction_recurring
	-> transaction

This has been temporarily solved by moving the GenerateTransactions
function into the transaction package. In the future, this function has
to be rewritten to use a proper Service insteas of direct DB access or
replaced with a different system entirely.

internal/core/settings.go

@@ -0,0 +1,109 @@
+package core
+
+import (
+	"context"
+	"errors"
+	"log/slog"
+)
+
+var (
+	ErrMissingConfig = errors.New("missing config")
+)
+
+type Settings struct {
+	Port string
+
+	BaseUrl     string
+	Environment string
+	Smtp        *SmtpSettings
+}
+
+type SmtpSettings struct {
+	Host     string
+	Port     string
+	User     string
+	Pass     string
+	FromMail string
+	FromName string
+}
+
+func NewSettingsFromEnv(ctx context.Context, env func(string) string) (*Settings, error) {
+	var (
+		smtp *SmtpSettings
+		err  error
+	)
+	if env("SMTP_ENABLED") == "true" {
+		smtp, err = getSmtpSettings(ctx, env)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	settings := &Settings{
+		Port:        env("PORT"),
+		BaseUrl:     env("BASE_URL"),
+		Environment: env("ENVIRONMENT"),
+		Smtp:        smtp,
+	}
+
+	if settings.BaseUrl == "" {
+		slog.ErrorContext(ctx, "BASE_URL must be set")
+		return nil, ErrMissingConfig
+	}
+	if settings.Port == "" {
+		slog.ErrorContext(ctx, "PORT must be set")
+		return nil, ErrMissingConfig
+	}
+	if settings.Environment == "" {
+		slog.ErrorContext(ctx, "ENVIRONMENT must be set")
+		return nil, ErrMissingConfig
+	}
+
+	slog.InfoContext(ctx, "settings read", "BASE_URL", settings.BaseUrl)
+	slog.InfoContext(ctx, "settings read", "ENVIRONMENT", settings.Environment)
+	slog.InfoContext(ctx, "settings read", "ENVIRONMENT", settings.Environment)
+
+	return settings, nil
+}
+
+func getSmtpSettings(ctx context.Context, env func(string) string) (*SmtpSettings, error) {
+	smtp := SmtpSettings{
+		Host:     env("SMTP_HOST"),
+		Port:     env("SMTP_PORT"),
+		User:     env("SMTP_USER"),
+		Pass:     env("SMTP_PASS"),
+		FromMail: env("SMTP_FROM_MAIL"),
+		FromName: env("SMTP_FROM_NAME"),
+	}
+
+	if smtp.Host == "" {
+		slog.ErrorContext(ctx, "SMTP_HOST must be set")
+		return nil, ErrMissingConfig
+	}
+	if smtp.Port == "" {
+		slog.ErrorContext(ctx, "SMTP_PORT must be set")
+		return nil, ErrMissingConfig
+	}
+	if smtp.User == "" {
+		slog.ErrorContext(ctx, "SMTP_USER must be set")
+		return nil, ErrMissingConfig
+	}
+	if smtp.Pass == "" {
+		slog.ErrorContext(ctx, "SMTP_PASS must be set")
+		return nil, ErrMissingConfig
+	}
+	if smtp.FromMail == "" {
+		slog.ErrorContext(ctx, "SMTP_FROM_MAIL must be set")
+		return nil, ErrMissingConfig
+	}
+	if smtp.FromName == "" {
+		slog.ErrorContext(ctx, "SMTP_FROM_NAME must be set")
+		return nil, ErrMissingConfig
+	}
+
+	return &smtp, nil
+}
+
+func IsOtelEnabled(env func(string) string) bool {
+	return env("OTEL_ENABLED") == "true"
+}