Implement SimpleNote Web API - full REST API with Express

- Express server with CORS, JSON middleware
- Auth middleware (Bearer token)
- Document CRUD with markdown storage
- Library CRUD with nested support
- Tag indexing and search
- Error handler middleware
- Config from env vars
- Init script for data structure

src/utils/errors.js

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+/**
+ * SimpleNote Web - Custom Errors
+ */
+
+export class AppError extends Error {
+  constructor(message, statusCode = 500, code = 'INTERNAL_ERROR') {
+    super(message);
+    this.statusCode = statusCode;
+    this.code = code;
+    this.name = 'AppError';
+  }
+}
+
+export class NotFoundError extends AppError {
+  constructor(resource = 'Resource') {
+    super(`${resource} not found`, 404, 'NOT_FOUND');
+    this.name = 'NotFoundError';
+  }
+}
+
+export class UnauthorizedError extends AppError {
+  constructor(message = 'Unauthorized') {
+    super(message, 401, 'UNAUTHORIZED');
+    this.name = 'UnauthorizedError';
+  }
+}
+
+export class ValidationError extends AppError {
+  constructor(message) {
+    super(message, 400, 'VALIDATION_ERROR');
+    this.name = 'ValidationError';
+  }
+}
+
+export default { AppError, NotFoundError, UnauthorizedError, ValidationError };

src/utils/fsHelper.js

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+/**
+ * SimpleNote Web - Filesystem Helper
+ */
+
+import { existsSync, mkdirSync, readFileSync, writeFileSync, rmSync, readdirSync, statSync } from 'fs';
+import { join, resolve, relative, sep } from 'path';
+import { fileURLToPath } from 'url';
+import { dirname } from 'path';
+
+export function ensureDir(dirPath) {
+  if (!existsSync(dirPath)) {
+    mkdirSync(dirPath, { recursive: true });
+  }
+}
+
+export function readJSON(filePath) {
+  if (!existsSync(filePath)) return null;
+  const content = readFileSync(filePath, 'utf-8');
+  return JSON.parse(content);
+}
+
+export function writeJSON(filePath, data) {
+  ensureDir(dirname(filePath));
+  writeFileSync(filePath, JSON.stringify(data, null, 2), 'utf-8');
+}
+
+export function deletePath(path) {
+  if (existsSync(path)) {
+    rmSync(path, { recursive: true, force: true });
+  }
+}
+
+export function pathExists(path) {
+  return existsSync(path);
+}
+
+export function listDir(dirPath) {
+  if (!existsSync(dirPath)) return [];
+  return readdirSync(dirPath, 'utf-8');
+}
+
+export function isDirectory(path) {
+  try {
+    return statSync(path).isDirectory();
+  } catch {
+    return false;
+  }
+}
+
+export function resolveSafe(base, target) {
+  const resolved = resolve(base, target);
+  if (!resolved.startsWith(resolve(base))) {
+    throw new Error('Path traversal detected');
+  }
+  return resolved;
+}
+
+export default { ensureDir, readJSON, writeJSON, deletePath, pathExists, listDir, isDirectory, resolveSafe };

src/utils/markdown.js

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+/**
+ * SimpleNote Web - Markdown Utilities
+ * Helpers for parsing frontmatter and serializing markdown documents
+ */
+
+import matter from 'gray-matter';
+import { generateId } from './uuid.js';
+
+const VALID_TYPES = ['requirement', 'note', 'spec', 'general'];
+const VALID_STATUSES = ['draft', 'approved', 'implemented'];
+const VALID_PRIORITIES = ['high', 'medium', 'low'];
+
+export function parseMarkdown(content) {
+  try {
+    const { data, content: body } = matter(content);
+    return {
+      metadata: {
+        id: data.id || null,
+        title: data.title || 'Untitled',
+        type: VALID_TYPES.includes(data.type) ? data.type : 'general',
+        status: VALID_STATUSES.includes(data.status) ? data.status : 'draft',
+        priority: VALID_PRIORITIES.includes(data.priority) ? data.priority : 'medium',
+        tags: Array.isArray(data.tags) ? data.tags : [],
+        createdBy: data.createdBy || null,
+        createdAt: data.createdAt || new Date().toISOString(),
+      },
+      body: body.trim(),
+    };
+  } catch (err) {
+    return {
+      metadata: {
+        id: null,
+        title: 'Untitled',
+        type: 'general',
+        status: 'draft',
+        priority: 'medium',
+        tags: [],
+        createdBy: null,
+        createdAt: new Date().toISOString(),
+      },
+      body: content,
+    };
+  }
+}
+
+export function serializeMarkdown(metadata, body = '') {
+  const frontmatter = [
+    '---',
+    `id: ${metadata.id || generateId()}`,
+    `title: ${metadata.title || 'Untitled'}`,
+    `type: ${metadata.type || 'general'}`,
+    `priority: ${metadata.priority || 'medium'}`,
+    `status: ${metadata.status || 'draft'}`,
+    `tags: [${(metadata.tags || []).join(', ')}]`,
+    metadata.createdBy ? `createdBy: ${metadata.createdBy}` : null,
+    `createdAt: ${metadata.createdAt || new Date().toISOString().split('T')[0]}`,
+    '---',
+  ].filter(Boolean).join('\n');
+
+  return `${frontmatter}\n\n${body}`;
+}
+
+export function buildDefaultContent(title, type = 'general') {
+  const typeLabel = type.charAt(0).toUpperCase() + type.slice(1);
+  return `# ${title}\n\n## Descripción\nDescripción del ${typeLabel}.\n\n## Criterios de Aceptación\n- [ ] Criterio 1\n- [ ] Criterio 2\n`;
+}
+
+export default { parseMarkdown, serializeMarkdown, buildDefaultContent };

src/utils/uuid.js

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+/**
+ * SimpleNote Web - UUID Helper
+ */
+
+import { v4 as uuidv4 } from 'uuid';
+
+export function generateId() {
+  return uuidv4();
+}
+
+export default { generateId };