feat: overhaul config loading

app/server/config/error.ts

@@ -0,0 +1,74 @@
+interface ErrorCodes {
+	CONFLICTING_SECRET_PATH_FIELD: {
+		fieldName: string;
+	};
+
+	INVALID_REQUIRED_FIELDS: {
+		messages: string[];
+	};
+
+	MISSING_INTERPOLATION_VARIABLE: {
+		pathKey: string;
+		variableName: string;
+	};
+
+	MISSING_SECRET_FILE: {
+		pathKey: string;
+		filePath: string;
+	};
+}
+
+const translationsWithVars: {
+	[K in keyof ErrorCodes]: (vars: ErrorCodes[K]) => string;
+} = {
+	CONFLICTING_SECRET_PATH_FIELD: ({ fieldName }) =>
+		`Both "${fieldName}" and "${fieldName}_path" are set; please provide only one of these fields.`,
+	INVALID_REQUIRED_FIELDS: ({ messages }) =>
+		`The configuration is missing required fields or has invalid values:\n- ${messages.join('\n- ')}`,
+	MISSING_INTERPOLATION_VARIABLE: ({ pathKey, variableName }) =>
+		`Could not resolve environment variable "${variableName}" for configuration key "${pathKey}".`,
+
+	MISSING_SECRET_FILE: ({ pathKey, filePath }) =>
+		`The secret file specified in "${pathKey}" could not be accessed at path "${filePath}". Please ensure the file exists and is readable.`,
+} as const;
+
+/**
+ * Custom error class for configuration-related errors.
+ */
+export class ConfigError extends Error {
+	/**
+	 * The error code representing the type of configuration error.
+	 */
+	code: keyof ErrorCodes;
+
+	/**
+	 * Creates a new ConfigError instance.
+	 *
+	 * @param code The error code
+	 * @param vars The variables to interpolate into the error message
+	 */
+	constructor(code: keyof ErrorCodes, vars: unknown) {
+		super(
+			translationsWithVars[code](
+				vars as (typeof translationsWithVars)[typeof code] extends (
+					vars: infer U,
+				) => string
+					? U
+					: never,
+			),
+		);
+		this.code = code;
+		this.name = 'ConfigError';
+	}
+
+	/**
+	 * Factory method to create a ConfigError instance.
+	 *
+	 * @param code The error code
+	 * @param vars The variables to interpolate into the error message
+	 * @returns A new ConfigError instance
+	 */
+	static from<K extends keyof ErrorCodes>(code: K, vars: ErrorCodes[K]) {
+		return new ConfigError(code, vars);
+	}
+}