feat(errors): add error class and functions

packages/error-handling/.mocharc.json

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+{
+  "extension": [
+    "ts"
+  ],
+  "spec": "**/*.test.ts",
+  "require": [
+    "ts-node/register"
+  ],
+  "recursive": true
+}

packages/error-handling/README.md

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+# HTTP Error Handling Module
+
+This module provides a comprehensive system for managing errors within the indexer package. It is meant to be a centralized constants repository for Indexer related errors

packages/error-handling/eslint.config.js

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+ // .eslintrc.js in the new package
+module.exports = {
+  root:true,
+  extends: ['@repo/eslint-config/library.js'],
+};
+

packages/error-handling/package.json

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+{
+  "name": "@repo/error-handling",
+  "version": "0.0.1",
+  "description": "",
+  "main": "index.js",
+  "scripts": {
+    "build": "tsc -b",
+    "build:check": "tsc --noEmit",
+    "watch": "tsc -b --watch",
+    "fix": "pnpm format && pnpm lint",
+    "format": "prettier --write src",
+    "format:check": "prettier src --check",
+    "lint": "eslint --fix",
+    "lint:check": "eslint",
+    "check": "pnpm format:check && pnpm lint:check && pnpm build:check",
+    "test": "mocha",
+    "coverage": "nyc mocha",
+    "test:watch": "mocha --watch"
+  },
+  "keywords": [],
+  "author": "",
+  "license": "ISC",
+  "dependencies": {
+    "http-status-codes": "^2.3.0"
+  },
+  "exports": {
+    ".": "./dist/index.js"
+  },
+  "devDependencies": {
+    "@istanbuljs/nyc-config-typescript": "^1.0.2",
+    "@repo/eslint-config": "workspace:*",
+    "@repo/typescript-config": "workspace:*",
+    "@types/chai": "^4.3.17",
+    "@types/mocha": "^10.0.7",
+    "@types/node": "^16.11.10",
+    "chai": "^4.5.0",
+    "eslint": "^8.57.0",
+    "mocha": "^10.7.0",
+    "nyc": "^17.0.0",
+    "prettier": "^3.3.3",
+    "source-map-support": "^0.5.21",
+    "ts-node": "^10.9.2",
+    "typescript": "^5.5.4",
+    "winston": "^3.13.1"
+  }
+}

packages/error-handling/src/errors/AssertError.ts

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+import { IndexerError } from "./IndexerError";
+
+export class AssertError extends IndexerError {
+  constructor(message: string) {
+    super(AssertError.name, message);
+  }
+}

packages/error-handling/src/errors/IndexerError.ts

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+/**
+ * Generic Error class that should be used in the Indexer to
+ * provide common error patterns to log
+ */
+export abstract class IndexerError extends Error {
+  constructor(
+    private readonly errorName: string,
+    private readonly errorMessage: string,
+    private readonly errorData?: Record<string, string>,
+  ) {
+    super(errorMessage);
+  }
+
+  /**
+   * A function used by `JSON.stringify` to specify which data will be serialized
+   * @returns A formatted JSON
+   */
+  public toJSON(): Record<string, unknown> {
+    return {
+      error: this.errorName,
+      message: this.errorMessage,
+      data: this.errorData,
+    };
+  }
+}

packages/error-handling/src/errors/IndexerHTTPError.ts

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+import { StatusCodes } from "http-status-codes";
+import { IndexerError } from "./IndexerError";
+
+/**
+ * Used to distinguish a similar design pattern as {@link IndexerError} but with
+ * additional HTTP context
+ * @see {@link IndexerError}
+ */
+export abstract class IndexerHTTPError extends IndexerError {
+  constructor(
+    private readonly httpStatusCode: StatusCodes,
+    errorName: string,
+    errorMessage: string,
+    errorData?: Record<string, string>,
+  ) {
+    super(errorName, errorMessage, errorData);
+  }
+
+  /**
+   * A function used by `JSON.stringify` to specify which data will be serialized
+   * @returns A formatted JSON
+   */
+  public toJSON(): Record<string, unknown> {
+    return {
+      statusCode: this.httpStatusCode,
+      ...super.toJSON(),
+    };
+  }
+}

packages/error-handling/src/errors/index.ts

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+export * from "./IndexerError";
+export * from "./IndexerHTTPError";
+export * from "./AssertError";

packages/error-handling/src/index.ts

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+export * from "./errors";
+export * from "./utils";

packages/error-handling/src/main.test.ts

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+import { describe, it } from "mocha";
+import { expect } from "chai";
+import assert from "assert";
+import { AssertError } from "./errors";
+import { isIndexerError, assert as customAssert } from "./utils";
+
+describe("Error handling Tests", function () {
+  it("should run the toJSON in Stringify", () => {
+    const e = new AssertError("test");
+    const jsonStringifyDirectly = JSON.stringify(e.toJSON());
+    const jsonIndirectly = JSON.stringify(e);
+    expect(jsonIndirectly).to.eq(jsonStringifyDirectly);
+  });
+
+  describe("typeguards", function () {
+    it("should validate IndexerError", () => {
+      const e = new AssertError("test");
+      expect(isIndexerError(e)).to.be.true;
+    });
+  });
+
+  describe("utils", () => {
+    it("should run assert as expected", () => {
+      expect(() => assert(false, "")).to.throw;
+      expect(() => customAssert(false, "")).to.throw;
+
+      expect(() => assert(true, "")).to.not.throw;
+      expect(() => customAssert(true, "")).to.not.throw;
+    });
+  });
+});

packages/error-handling/src/utils/assert.ts

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+import * as assertModule from "assert";
+import { AssertError } from "../errors/AssertError";
+
+/**
+ * A stand-in assert function that returns a formatted error payload
+ * @param value An arbitrary predicate that will be asserted for truthiness
+ * @param message An error message that will be passed if the assert fails
+ * @returns An assertion of `value`.
+ * @throws {@link AssertError} if assert's validity fails
+ */
+export function assert(value: unknown, message: string): asserts value {
+  try {
+    return assertModule.ok(value, message);
+  } catch (e: unknown) {
+    throw new AssertError(message);
+  }
+}

packages/error-handling/src/utils/index.ts

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+export * from "./assert";
+export * from "./typeguards";

packages/error-handling/src/utils/typeguards.ts

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+import { IndexerError, IndexerHTTPError } from "../errors";
+
+/**
+ * Typeguard to confirm that an object is an IndexerError
+ * @param error The error object to validate
+ * @returns Whether this object is an instance of `IndexerError` (or a descendent)
+ */
+export function isIndexerError(error: unknown): error is IndexerError {
+  return error instanceof IndexerError;
+}
+
+/**
+ * Typeguard to confirm that an object is an IndexerHTTPError
+ * @param error The error object to validate
+ * @returns Whether this object is an instance of `IndexerHTTPError` (or a descendent)
+ */
+export function isIndexerHTTPError(error: unknown): error is IndexerHTTPError {
+  return error instanceof IndexerHTTPError;
+}

packages/error-handling/tsconfig.json

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+{
+  "extends":"@repo/typescript-config/base.json",
+  "compilerOptions": {
+    "outDir": "./dist"                                   /* Specify an output folder for all emitted files. */
+  }
+}