Organise files more consistently

Signed-off-by: Rūdolfs Ošiņš <rudolfs@osins.org>

src/lib/error.ts

@@ -0,0 +1,69 @@
+export interface Err {
+  type: Failure;
+  txHash?: string;
+  message?: string;
+}
+
+export enum Failure {
+  TransactionFailed = 1,
+  NotAuthenticated = 2,
+  InsufficientBalance = 3,
+}
+
+export class Unreachable extends Error {
+  constructor(value?: never) {
+    if (value) {
+      super("unreachable value reached: " + value);
+    } else {
+      super("unreachable code reached");
+    }
+  }
+}
+
+export class NotFoundError extends Error {
+  constructor(message?: string) {
+    if (message) {
+      super(`not found: ${message}`);
+    } else {
+      super(`not found`);
+    }
+  }
+}
+
+export class MissingReverseRecord extends Error {
+  constructor(message?: string) {
+    if (message) {
+      super(`missing reverse record: ${message}`);
+    } else {
+      super(`missing reverse record`);
+    }
+  }
+}
+
+class AssertionError extends Error {
+  constructor(message?: string) {
+    if (message) {
+      super(`assertion failed: ${message}`);
+    } else {
+      super(`assertion failed`);
+    }
+  }
+}
+
+export function assert(value: unknown, message?: string): asserts value {
+  if (!value) {
+    throw new AssertionError(message);
+  }
+}
+
+export function assertEq(
+  actual: unknown,
+  expected: unknown,
+  message?: string,
+): void {
+  if (actual !== expected) {
+    throw new AssertionError(
+      `assertion failed: expected '${expected}', got '${actual}': ${message}`,
+    );
+  }
+}