feat(backend): Databank initialiseren

Verbinding met databank aangemaakt, eerste entities toegevoegd, centrale API aangemaakt om omgevingsvariabelen voor onze app op te vragen.

backend/src/util/envvars.ts

@@ -0,0 +1,42 @@
+const PREFIX = "DWENGO_";
+const DB_PREFIX = PREFIX + "DB_";
+
+type EnvVar = {[key: string]: {name: string, required?: boolean, defaultValue?: boolean}};
+
+export const EnvVars: EnvVar = {
+    DbHost: {key: DB_PREFIX + "HOST", required: true},
+    DbPort: {key: DB_PREFIX + "PORT", defaultValue: 5432},
+    DbName: {key: DB_PREFIX + "NAME", defaultValue: "dwengo"},
+    DbUsername: {key: DB_PREFIX + "USERNAME", required: true},
+    DbPassword: {key: DB_PREFIX + "PASSWORD", required: true},
+    DbUpdate: {key: DB_PREFIX + "UPDATE", defaultValue: false},
+} as const;
+
+/**
+ * Returns the value of the given environment variable if it is set.
+ * Otherwise,
+ * - throw an error if the environment variable was required,
+ * - return the default value if there is one and it was not required,
+ * - return an empty string if the environment variable is not required and there is also no default.
+ * @param envVar The properties of the environment variable (from the EnvVar object).
+ */
+export function getEnvVar(envVar: EnvVar): string {
+    const value: string | undefined = process.env[envVar.key];
+    if (value) {
+        return value;
+    } else if (envVar.required) {
+        throw new Error(`Missing environment variable: ${envVar.key}`);
+    } else {
+        return envVar.defaultValue || "";
+    }
+}
+
+export function getNumericEnvVar(envVar: EnvVar): number {
+    const valueString = getEnvVar(envVar);
+    const value = parseInt(valueString);
+    if (isNaN(value)) {
+        throw new Error(`Invalid value for environment variable ${envVar.key}: ${valueString}. Expected a number.`)
+    } else {
+        return value;
+    }
+}