src/extensions/context.ts

@@ -0,0 +1,288 @@
+import {
+  ExtensionContext,
+  ExtensionDatabase,
+  ExtensionInfo,
+  ApplicationInfo,
+  CreateInvoiceOptions,
+  CreatedInvoice,
+  PaymentReceivedData,
+  NostrEvent,
+  UnsignedNostrEvent,
+  RpcMethodHandler
+} from './types.js'
+
+/**
+ * Main Handler interface (from Lightning.Pub)
+ * This is a minimal interface - the actual MainHandler has more methods
+ */
+export interface MainHandlerInterface {
+  // Application management
+  applicationManager: {
+    getById(id: string): Promise<any>
+  }
+
+  // Payment operations
+  paymentManager: {
+    createInvoice(params: {
+      applicationId: string
+      amountSats: number
+      memo?: string
+      expiry?: number
+      metadata?: Record<string, any>
+    }): Promise<{
+      id: string
+      paymentRequest: string
+      paymentHash: string
+      expiry: number
+    }>
+
+    payInvoice(params: {
+      applicationId: string
+      paymentRequest: string
+      maxFeeSats?: number
+    }): Promise<{
+      paymentHash: string
+      feeSats: number
+    }>
+  }
+
+  // Nostr operations
+  sendNostrEvent(event: any): Promise<string | null>
+  sendEncryptedDM(applicationId: string, recipientPubkey: string, content: string): Promise<string>
+}
+
+/**
+ * Callback registries for extension events
+ */
+interface CallbackRegistries {
+  paymentReceived: Array<(payment: PaymentReceivedData) => Promise<void>>
+  nostrEvent: Array<(event: NostrEvent, applicationId: string) => Promise<void>>
+}
+
+/**
+ * Registered RPC method
+ */
+interface RegisteredMethod {
+  extensionId: string
+  handler: RpcMethodHandler
+}
+
+/**
+ * Extension Context Implementation
+ *
+ * Provides the interface for extensions to interact with Lightning.Pub.
+ * Each extension gets its own context instance.
+ */
+export class ExtensionContextImpl implements ExtensionContext {
+  private callbacks: CallbackRegistries = {
+    paymentReceived: [],
+    nostrEvent: []
+  }
+
+  constructor(
+    private extensionInfo: ExtensionInfo,
+    private database: ExtensionDatabase,
+    private mainHandler: MainHandlerInterface,
+    private methodRegistry: Map<string, RegisteredMethod>
+  ) {}
+
+  /**
+   * Get information about an application
+   */
+  async getApplication(applicationId: string): Promise<ApplicationInfo | null> {
+    try {
+      const app = await this.mainHandler.applicationManager.getById(applicationId)
+      if (!app) return null
+
+      return {
+        id: app.id,
+        name: app.name,
+        nostr_public: app.nostr_public,
+        balance_sats: app.balance || 0
+      }
+    } catch (e) {
+      this.log('error', `Failed to get application ${applicationId}:`, e)
+      return null
+    }
+  }
+
+  /**
+   * Create a Lightning invoice
+   */
+  async createInvoice(amountSats: number, options: CreateInvoiceOptions = {}): Promise<CreatedInvoice> {
+    // Note: In practice, this needs an applicationId. Extensions typically
+    // get this from the RPC request context. For now, we'll need to handle
+    // this in the actual implementation.
+    throw new Error('createInvoice requires applicationId from request context')
+  }
+
+  /**
+   * Create invoice with explicit application ID
+   * This is the internal method used by extensions
+   */
+  async createInvoiceForApp(
+    applicationId: string,
+    amountSats: number,
+    options: CreateInvoiceOptions = {}
+  ): Promise<CreatedInvoice> {
+    const result = await this.mainHandler.paymentManager.createInvoice({
+      applicationId,
+      amountSats,
+      memo: options.memo,
+      expiry: options.expiry,
+      metadata: {
+        ...options.metadata,
+        extension: this.extensionInfo.id
+      }
+    })
+
+    return {
+      id: result.id,
+      paymentRequest: result.paymentRequest,
+      paymentHash: result.paymentHash,
+      expiry: result.expiry
+    }
+  }
+
+  /**
+   * Pay a Lightning invoice
+   */
+  async payInvoice(
+    applicationId: string,
+    paymentRequest: string,
+    maxFeeSats?: number
+  ): Promise<{ paymentHash: string; feeSats: number }> {
+    return this.mainHandler.paymentManager.payInvoice({
+      applicationId,
+      paymentRequest,
+      maxFeeSats
+    })
+  }
+
+  /**
+   * Send an encrypted DM via Nostr
+   */
+  async sendEncryptedDM(
+    applicationId: string,
+    recipientPubkey: string,
+    content: string
+  ): Promise<string> {
+    return this.mainHandler.sendEncryptedDM(applicationId, recipientPubkey, content)
+  }
+
+  /**
+   * Publish a Nostr event
+   */
+  async publishNostrEvent(event: UnsignedNostrEvent): Promise<string | null> {
+    return this.mainHandler.sendNostrEvent(event)
+  }
+
+  /**
+   * Subscribe to payment received callbacks
+   */
+  onPaymentReceived(callback: (payment: PaymentReceivedData) => Promise<void>): void {
+    this.callbacks.paymentReceived.push(callback)
+  }
+
+  /**
+   * Subscribe to incoming Nostr events
+   */
+  onNostrEvent(callback: (event: NostrEvent, applicationId: string) => Promise<void>): void {
+    this.callbacks.nostrEvent.push(callback)
+  }
+
+  /**
+   * Register an RPC method
+   */
+  registerMethod(name: string, handler: RpcMethodHandler): void {
+    const fullName = name.startsWith(`${this.extensionInfo.id}.`)
+      ? name
+      : `${this.extensionInfo.id}.${name}`
+
+    if (this.methodRegistry.has(fullName)) {
+      throw new Error(`RPC method ${fullName} already registered`)
+    }
+
+    this.methodRegistry.set(fullName, {
+      extensionId: this.extensionInfo.id,
+      handler
+    })
+
+    this.log('debug', `Registered RPC method: ${fullName}`)
+  }
+
+  /**
+   * Get the extension's database
+   */
+  getDatabase(): ExtensionDatabase {
+    return this.database
+  }
+
+  /**
+   * Log a message
+   */
+  log(level: 'debug' | 'info' | 'warn' | 'error', message: string, ...args: any[]): void {
+    const prefix = `[Extension:${this.extensionInfo.id}]`
+    switch (level) {
+      case 'debug':
+        console.debug(prefix, message, ...args)
+        break
+      case 'info':
+        console.info(prefix, message, ...args)
+        break
+      case 'warn':
+        console.warn(prefix, message, ...args)
+        break
+      case 'error':
+        console.error(prefix, message, ...args)
+        break
+    }
+  }
+
+  // ===== Internal Methods (called by ExtensionLoader) =====
+
+  /**
+   * Dispatch payment received event to extension callbacks
+   */
+  async dispatchPaymentReceived(payment: PaymentReceivedData): Promise<void> {
+    for (const callback of this.callbacks.paymentReceived) {
+      try {
+        await callback(payment)
+      } catch (e) {
+        this.log('error', 'Error in payment callback:', e)
+      }
+    }
+  }
+
+  /**
+   * Dispatch Nostr event to extension callbacks
+   */
+  async dispatchNostrEvent(event: NostrEvent, applicationId: string): Promise<void> {
+    for (const callback of this.callbacks.nostrEvent) {
+      try {
+        await callback(event, applicationId)
+      } catch (e) {
+        this.log('error', 'Error in Nostr event callback:', e)
+      }
+    }
+  }
+
+  /**
+   * Get registered callbacks for external access
+   */
+  getCallbacks(): CallbackRegistries {
+    return this.callbacks
+  }
+}
+
+/**
+ * Create an extension context
+ */
+export function createExtensionContext(
+  extensionInfo: ExtensionInfo,
+  database: ExtensionDatabase,
+  mainHandler: MainHandlerInterface,
+  methodRegistry: Map<string, RegisteredMethod>
+): ExtensionContextImpl {
+  return new ExtensionContextImpl(extensionInfo, database, mainHandler, methodRegistry)
+}

src/extensions/database.ts

@@ -0,0 +1,148 @@
+import Database from 'better-sqlite3'
+import path from 'path'
+import fs from 'fs'
+import { ExtensionDatabase } from './types.js'
+
+/**
+ * Extension Database Implementation
+ *
+ * Provides isolated SQLite database access for each extension.
+ * Uses better-sqlite3 for synchronous, high-performance access.
+ */
+export class ExtensionDatabaseImpl implements ExtensionDatabase {
+  private db: Database.Database
+  private extensionId: string
+
+  constructor(extensionId: string, databaseDir: string) {
+    this.extensionId = extensionId
+
+    // Ensure database directory exists
+    if (!fs.existsSync(databaseDir)) {
+      fs.mkdirSync(databaseDir, { recursive: true })
+    }
+
+    // Create database file for this extension
+    const dbPath = path.join(databaseDir, `${extensionId}.db`)
+    this.db = new Database(dbPath)
+
+    // Enable WAL mode for better concurrency
+    this.db.pragma('journal_mode = WAL')
+
+    // Enable foreign keys
+    this.db.pragma('foreign_keys = ON')
+
+    // Create metadata table for tracking migrations
+    this.db.exec(`
+      CREATE TABLE IF NOT EXISTS _extension_meta (
+        key TEXT PRIMARY KEY,
+        value TEXT NOT NULL
+      )
+    `)
+  }
+
+  /**
+   * Execute a write query (INSERT, UPDATE, DELETE, CREATE, etc.)
+   */
+  async execute(sql: string, params: any[] = []): Promise<{ changes?: number; lastId?: number }> {
+    try {
+      const stmt = this.db.prepare(sql)
+      const result = stmt.run(...params)
+
+      return {
+        changes: result.changes,
+        lastId: result.lastInsertRowid as number
+      }
+    } catch (e) {
+      console.error(`[Extension:${this.extensionId}] Database execute error:`, e)
+      throw e
+    }
+  }
+
+  /**
+   * Execute a read query (SELECT)
+   */
+  async query<T = any>(sql: string, params: any[] = []): Promise<T[]> {
+    try {
+      const stmt = this.db.prepare(sql)
+      return stmt.all(...params) as T[]
+    } catch (e) {
+      console.error(`[Extension:${this.extensionId}] Database query error:`, e)
+      throw e
+    }
+  }
+
+  /**
+   * Execute multiple statements in a transaction
+   */
+  async transaction<T>(fn: () => Promise<T>): Promise<T> {
+    const runTransaction = this.db.transaction(() => {
+      // Note: better-sqlite3 transactions are synchronous
+      // We wrap the async function but it executes synchronously
+      return fn()
+    })
+
+    return runTransaction() as T
+  }
+
+  /**
+   * Get a metadata value
+   */
+  async getMeta(key: string): Promise<string | null> {
+    const rows = await this.query<{ value: string }>(
+      'SELECT value FROM _extension_meta WHERE key = ?',
+      [key]
+    )
+    return rows.length > 0 ? rows[0].value : null
+  }
+
+  /**
+   * Set a metadata value
+   */
+  async setMeta(key: string, value: string): Promise<void> {
+    await this.execute(
+      `INSERT INTO _extension_meta (key, value) VALUES (?, ?)
+       ON CONFLICT(key) DO UPDATE SET value = excluded.value`,
+      [key, value]
+    )
+  }
+
+  /**
+   * Get current migration version
+   */
+  async getMigrationVersion(): Promise<number> {
+    const version = await this.getMeta('migration_version')
+    return version ? parseInt(version, 10) : 0
+  }
+
+  /**
+   * Set migration version
+   */
+  async setMigrationVersion(version: number): Promise<void> {
+    await this.setMeta('migration_version', String(version))
+  }
+
+  /**
+   * Close the database connection
+   */
+  close(): void {
+    this.db.close()
+  }
+
+  /**
+   * Get the underlying database for advanced operations
+   * (Use with caution - bypasses isolation)
+   */
+  getUnderlyingDb(): Database.Database {
+    return this.db
+  }
+}
+
+/**
+ * Create an extension database instance
+ */
+export function createExtensionDatabase(
+  extensionId: string,
+  databaseDir: string
+): ExtensionDatabaseImpl {
+  return new ExtensionDatabaseImpl(extensionId, databaseDir)
+}

src/extensions/index.ts

@@ -0,0 +1,56 @@
+/**
+ * Lightning.Pub Extension System
+ *
+ * This module provides the extension infrastructure for Lightning.Pub.
+ * Extensions can add functionality like marketplaces, subscriptions,
+ * tipping, and more.
+ *
+ * Usage:
+ *
+ * ```typescript
+ * import { createExtensionLoader, ExtensionLoaderConfig } from './extensions'
+ *
+ * const config: ExtensionLoaderConfig = {
+ *   extensionsDir: './extensions',
+ *   databaseDir: './data/extensions'
+ * }
+ *
+ * const loader = createExtensionLoader(config, mainHandler)
+ * await loader.loadAll()
+ *
+ * // Call extension methods
+ * const result = await loader.callMethod(
+ *   'marketplace.createStall',
+ *   { name: 'My Shop', currency: 'sat', shipping_zones: [...] },
+ *   applicationId
+ * )
+ * ```
+ */
+
+// Export types
+export {
+  Extension,
+  ExtensionInfo,
+  ExtensionContext,
+  ExtensionDatabase,
+  ExtensionModule,
+  ExtensionConstructor,
+  LoadedExtension,
+  ExtensionLoaderConfig,
+  ApplicationInfo,
+  CreateInvoiceOptions,
+  CreatedInvoice,
+  PaymentReceivedData,
+  NostrEvent,
+  UnsignedNostrEvent,
+  RpcMethodHandler
+} from './types.js'
+
+// Export loader
+export { ExtensionLoader, createExtensionLoader } from './loader.js'
+
+// Export database utilities
+export { ExtensionDatabaseImpl, createExtensionDatabase } from './database.js'
+
+// Export context utilities
+export { ExtensionContextImpl, createExtensionContext, MainHandlerInterface } from './context.js'

src/extensions/loader.ts

@@ -0,0 +1,406 @@
+import path from 'path'
+import fs from 'fs'
+import {
+  Extension,
+  ExtensionInfo,
+  ExtensionModule,
+  LoadedExtension,
+  ExtensionLoaderConfig,
+  RpcMethodHandler,
+  PaymentReceivedData,
+  NostrEvent
+} from './types.js'
+import { ExtensionDatabaseImpl, createExtensionDatabase } from './database.js'
+import { ExtensionContextImpl, createExtensionContext, MainHandlerInterface } from './context.js'
+
+/**
+ * Registered RPC method entry
+ */
+interface RegisteredMethod {
+  extensionId: string
+  handler: RpcMethodHandler
+}
+
+/**
+ * Extension Loader
+ *
+ * Discovers, loads, and manages Lightning.Pub extensions.
+ * Provides lifecycle management and event dispatching.
+ */
+export class ExtensionLoader {
+  private config: ExtensionLoaderConfig
+  private mainHandler: MainHandlerInterface
+  private extensions: Map<string, LoadedExtension> = new Map()
+  private contexts: Map<string, ExtensionContextImpl> = new Map()
+  private methodRegistry: Map<string, RegisteredMethod> = new Map()
+  private initialized = false
+
+  constructor(config: ExtensionLoaderConfig, mainHandler: MainHandlerInterface) {
+    this.config = config
+    this.mainHandler = mainHandler
+  }
+
+  /**
+   * Discover and load all extensions
+   */
+  async loadAll(): Promise<void> {
+    if (this.initialized) {
+      throw new Error('Extension loader already initialized')
+    }
+
+    console.log('[Extensions] Loading extensions from:', this.config.extensionsDir)
+
+    // Ensure directories exist
+    if (!fs.existsSync(this.config.extensionsDir)) {
+      console.log('[Extensions] Extensions directory does not exist, creating...')
+      fs.mkdirSync(this.config.extensionsDir, { recursive: true })
+      this.initialized = true
+      return
+    }
+
+    if (!fs.existsSync(this.config.databaseDir)) {
+      fs.mkdirSync(this.config.databaseDir, { recursive: true })
+    }
+
+    // Discover extensions
+    const extensionDirs = await this.discoverExtensions()
+    console.log(`[Extensions] Found ${extensionDirs.length} extension(s)`)
+
+    // Load extensions in dependency order
+    const loadOrder = await this.resolveDependencies(extensionDirs)
+
+    for (const extDir of loadOrder) {
+      try {
+        await this.loadExtension(extDir)
+      } catch (e) {
+        console.error(`[Extensions] Failed to load extension from ${extDir}:`, e)
+      }
+    }
+
+    this.initialized = true
+    console.log(`[Extensions] Loaded ${this.extensions.size} extension(s)`)
+  }
+
+  /**
+   * Discover extension directories
+   */
+  private async discoverExtensions(): Promise<string[]> {
+    const entries = fs.readdirSync(this.config.extensionsDir, { withFileTypes: true })
+    const extensionDirs: string[] = []
+
+    for (const entry of entries) {
+      if (!entry.isDirectory()) continue
+
+      const extDir = path.join(this.config.extensionsDir, entry.name)
+      const indexPath = path.join(extDir, 'index.ts')
+      const indexJsPath = path.join(extDir, 'index.js')
+
+      // Check for index file
+      if (fs.existsSync(indexPath) || fs.existsSync(indexJsPath)) {
+        // Check enabled/disabled lists
+        if (this.config.disabledExtensions?.includes(entry.name)) {
+          console.log(`[Extensions] Skipping disabled extension: ${entry.name}`)
+          continue
+        }
+
+        if (this.config.enabledExtensions &&
+            !this.config.enabledExtensions.includes(entry.name)) {
+          console.log(`[Extensions] Skipping non-enabled extension: ${entry.name}`)
+          continue
+        }
+
+        extensionDirs.push(extDir)
+      }
+    }
+
+    return extensionDirs
+  }
+
+  /**
+   * Resolve extension dependencies and return load order
+   */
+  private async resolveDependencies(extensionDirs: string[]): Promise<string[]> {
+    // For now, simple alphabetical order
+    // TODO: Implement proper dependency resolution with topological sort
+    return extensionDirs.sort()
+  }
+
+  /**
+   * Load a single extension
+   */
+  private async loadExtension(extensionDir: string): Promise<void> {
+    const dirName = path.basename(extensionDir)
+    console.log(`[Extensions] Loading extension: ${dirName}`)
+
+    // Determine index file path
+    let indexPath = path.join(extensionDir, 'index.js')
+    if (!fs.existsSync(indexPath)) {
+      indexPath = path.join(extensionDir, 'index.ts')
+    }
+
+    // Dynamic import
+    const moduleUrl = `file://${indexPath}`
+    const module = await import(moduleUrl) as ExtensionModule
+
+    if (!module.default) {
+      throw new Error(`Extension ${dirName} has no default export`)
+    }
+
+    // Instantiate extension
+    const ExtensionClass = module.default
+    const instance = new ExtensionClass() as Extension
+
+    if (!instance.info) {
+      throw new Error(`Extension ${dirName} has no info property`)
+    }
+
+    const info = instance.info
+
+    // Validate extension ID matches directory name
+    if (info.id !== dirName) {
+      console.warn(
+        `[Extensions] Extension ID '${info.id}' doesn't match directory '${dirName}'`
+      )
+    }
+
+    // Check for duplicate
+    if (this.extensions.has(info.id)) {
+      throw new Error(`Extension ${info.id} already loaded`)
+    }
+
+    // Create isolated database
+    const database = createExtensionDatabase(info.id, this.config.databaseDir)
+
+    // Create context
+    const context = createExtensionContext(
+      info,
+      database,
+      this.mainHandler,
+      this.methodRegistry
+    )
+
+    // Track as loading
+    const loaded: LoadedExtension = {
+      info,
+      instance,
+      database,
+      status: 'loading',
+      loadedAt: Date.now()
+    }
+    this.extensions.set(info.id, loaded)
+    this.contexts.set(info.id, context)
+
+    try {
+      // Initialize extension
+      await instance.initialize(context, database)
+
+      loaded.status = 'ready'
+      console.log(`[Extensions] Extension ${info.id} v${info.version} loaded successfully`)
+    } catch (e) {
+      loaded.status = 'error'
+      loaded.error = e as Error
+      console.error(`[Extensions] Extension ${info.id} initialization failed:`, e)
+      throw e
+    }
+  }
+
+  /**
+   * Unload a specific extension
+   */
+  async unloadExtension(extensionId: string): Promise<void> {
+    const loaded = this.extensions.get(extensionId)
+    if (!loaded) {
+      throw new Error(`Extension ${extensionId} not found`)
+    }
+
+    console.log(`[Extensions] Unloading extension: ${extensionId}`)
+
+    try {
+      // Call shutdown if available
+      if (loaded.instance.shutdown) {
+        await loaded.instance.shutdown()
+      }
+
+      loaded.status = 'stopped'
+    } catch (e) {
+      console.error(`[Extensions] Error during ${extensionId} shutdown:`, e)
+    }
+
+    // Close database
+    if (loaded.database instanceof ExtensionDatabaseImpl) {
+      loaded.database.close()
+    }
+
+    // Remove registered methods
+    for (const [name, method] of this.methodRegistry.entries()) {
+      if (method.extensionId === extensionId) {
+        this.methodRegistry.delete(name)
+      }
+    }
+
+    // Remove from maps
+    this.extensions.delete(extensionId)
+    this.contexts.delete(extensionId)
+  }
+
+  /**
+   * Shutdown all extensions
+   */
+  async shutdown(): Promise<void> {
+    console.log('[Extensions] Shutting down all extensions...')
+
+    for (const extensionId of this.extensions.keys()) {
+      try {
+        await this.unloadExtension(extensionId)
+      } catch (e) {
+        console.error(`[Extensions] Error unloading ${extensionId}:`, e)
+      }
+    }
+
+    console.log('[Extensions] All extensions shut down')
+  }
+
+  /**
+   * Get a loaded extension
+   */
+  getExtension(extensionId: string): LoadedExtension | undefined {
+    return this.extensions.get(extensionId)
+  }
+
+  /**
+   * Get all loaded extensions
+   */
+  getAllExtensions(): LoadedExtension[] {
+    return Array.from(this.extensions.values())
+  }
+
+  /**
+   * Check if an extension is loaded and ready
+   */
+  isReady(extensionId: string): boolean {
+    const ext = this.extensions.get(extensionId)
+    return ext?.status === 'ready'
+  }
+
+  /**
+   * Get all registered RPC methods
+   */
+  getRegisteredMethods(): Map<string, RegisteredMethod> {
+    return this.methodRegistry
+  }
+
+  /**
+   * Call an extension RPC method
+   */
+  async callMethod(
+    methodName: string,
+    request: any,
+    applicationId: string,
+    userPubkey?: string
+  ): Promise<any> {
+    const method = this.methodRegistry.get(methodName)
+    if (!method) {
+      throw new Error(`Unknown method: ${methodName}`)
+    }
+
+    const ext = this.extensions.get(method.extensionId)
+    if (!ext || ext.status !== 'ready') {
+      throw new Error(`Extension ${method.extensionId} not ready`)
+    }
+
+    return method.handler(request, applicationId, userPubkey)
+  }
+
+  /**
+   * Check if a method exists
+   */
+  hasMethod(methodName: string): boolean {
+    return this.methodRegistry.has(methodName)
+  }
+
+  /**
+   * Dispatch payment received event to all extensions
+   */
+  async dispatchPaymentReceived(payment: PaymentReceivedData): Promise<void> {
+    for (const context of this.contexts.values()) {
+      try {
+        await context.dispatchPaymentReceived(payment)
+      } catch (e) {
+        console.error('[Extensions] Error dispatching payment:', e)
+      }
+    }
+  }
+
+  /**
+   * Dispatch Nostr event to all extensions
+   */
+  async dispatchNostrEvent(event: NostrEvent, applicationId: string): Promise<void> {
+    for (const context of this.contexts.values()) {
+      try {
+        await context.dispatchNostrEvent(event, applicationId)
+      } catch (e) {
+        console.error('[Extensions] Error dispatching Nostr event:', e)
+      }
+    }
+  }
+
+  /**
+   * Run health checks on all extensions
+   */
+  async healthCheck(): Promise<Map<string, boolean>> {
+    const results = new Map<string, boolean>()
+
+    for (const [id, ext] of this.extensions.entries()) {
+      if (ext.status !== 'ready') {
+        results.set(id, false)
+        continue
+      }
+
+      try {
+        if (ext.instance.healthCheck) {
+          results.set(id, await ext.instance.healthCheck())
+        } else {
+          results.set(id, true)
+        }
+      } catch (e) {
+        results.set(id, false)
+      }
+    }
+
+    return results
+  }
+
+  /**
+   * Get extension status summary
+   */
+  getStatus(): {
+    total: number
+    ready: number
+    error: number
+    extensions: Array<{ id: string; name: string; version: string; status: string }>
+  } {
+    const extensions = this.getAllExtensions().map(ext => ({
+      id: ext.info.id,
+      name: ext.info.name,
+      version: ext.info.version,
+      status: ext.status
+    }))
+
+    return {
+      total: extensions.length,
+      ready: extensions.filter(e => e.status === 'ready').length,
+      error: extensions.filter(e => e.status === 'error').length,
+      extensions
+    }
+  }
+}
+
+/**
+ * Create an extension loader instance
+ */
+export function createExtensionLoader(
+  config: ExtensionLoaderConfig,
+  mainHandler: MainHandlerInterface
+): ExtensionLoader {
+  return new ExtensionLoader(config, mainHandler)
+}

src/extensions/types.ts

@@ -0,0 +1,231 @@
+/**
+ * Extension System Core Types
+ *
+ * These types define the contract between Lightning.Pub and extensions.
+ */
+
+/**
+ * Extension metadata
+ */
+export interface ExtensionInfo {
+  id: string                    // Unique identifier (lowercase, no spaces)
+  name: string                  // Display name
+  version: string               // Semver version
+  description: string           // Short description
+  author: string                // Author name or organization
+  minPubVersion?: string        // Minimum Lightning.Pub version required
+  dependencies?: string[]       // Other extension IDs this depends on
+}
+
+/**
+ * Extension database interface
+ * Provides isolated database access for each extension
+ */
+export interface ExtensionDatabase {
+  /**
+   * Execute a write query (INSERT, UPDATE, DELETE, CREATE, etc.)
+   */
+  execute(sql: string, params?: any[]): Promise<{ changes?: number; lastId?: number }>
+
+  /**
+   * Execute a read query (SELECT)
+   */
+  query<T = any>(sql: string, params?: any[]): Promise<T[]>
+
+  /**
+   * Execute multiple statements in a transaction
+   */
+  transaction<T>(fn: () => Promise<T>): Promise<T>
+}
+
+/**
+ * Application info provided to extensions
+ */
+export interface ApplicationInfo {
+  id: string
+  name: string
+  nostr_public: string          // Application's Nostr pubkey (hex)
+  balance_sats: number
+}
+
+/**
+ * Invoice creation options
+ */
+export interface CreateInvoiceOptions {
+  memo?: string
+  expiry?: number               // Seconds until expiry
+  metadata?: Record<string, any>  // Custom metadata for callbacks
+}
+
+/**
+ * Created invoice result
+ */
+export interface CreatedInvoice {
+  id: string                    // Internal invoice ID
+  paymentRequest: string        // BOLT11 invoice string
+  paymentHash: string           // Payment hash (hex)
+  expiry: number                // Expiry timestamp
+}
+
+/**
+ * Payment received callback data
+ */
+export interface PaymentReceivedData {
+  invoiceId: string
+  paymentHash: string
+  amountSats: number
+  metadata?: Record<string, any>
+}
+
+/**
+ * Nostr event structure (minimal)
+ */
+export interface NostrEvent {
+  id: string
+  pubkey: string
+  created_at: number
+  kind: number
+  tags: string[][]
+  content: string
+  sig?: string
+}
+
+/**
+ * Unsigned Nostr event for publishing
+ */
+export interface UnsignedNostrEvent {
+  kind: number
+  pubkey: string
+  created_at: number
+  tags: string[][]
+  content: string
+}
+
+/**
+ * RPC method handler function
+ */
+export type RpcMethodHandler = (
+  request: any,
+  applicationId: string,
+  userPubkey?: string
+) => Promise<any>
+
+/**
+ * Extension context - interface provided to extensions for interacting with Lightning.Pub
+ */
+export interface ExtensionContext {
+  /**
+   * Get information about an application
+   */
+  getApplication(applicationId: string): Promise<ApplicationInfo | null>
+
+  /**
+   * Create a Lightning invoice
+   */
+  createInvoice(amountSats: number, options?: CreateInvoiceOptions): Promise<CreatedInvoice>
+
+  /**
+   * Pay a Lightning invoice (requires sufficient balance)
+   */
+  payInvoice(applicationId: string, paymentRequest: string, maxFeeSats?: number): Promise<{
+    paymentHash: string
+    feeSats: number
+  }>
+
+  /**
+   * Send an encrypted DM via Nostr (NIP-44)
+   */
+  sendEncryptedDM(applicationId: string, recipientPubkey: string, content: string): Promise<string>
+
+  /**
+   * Publish a Nostr event (signed by application's key)
+   */
+  publishNostrEvent(event: UnsignedNostrEvent): Promise<string | null>
+
+  /**
+   * Subscribe to payment received callbacks
+   */
+  onPaymentReceived(callback: (payment: PaymentReceivedData) => Promise<void>): void
+
+  /**
+   * Subscribe to incoming Nostr events for the application
+   */
+  onNostrEvent(callback: (event: NostrEvent, applicationId: string) => Promise<void>): void
+
+  /**
+   * Register an RPC method
+   */
+  registerMethod(name: string, handler: RpcMethodHandler): void
+
+  /**
+   * Get the extension's isolated database
+   */
+  getDatabase(): ExtensionDatabase
+
+  /**
+   * Log a message (prefixed with extension ID)
+   */
+  log(level: 'debug' | 'info' | 'warn' | 'error', message: string, ...args: any[]): void
+}
+
+/**
+ * Extension interface - what extensions must implement
+ */
+export interface Extension {
+  /**
+   * Extension metadata
+   */
+  readonly info: ExtensionInfo
+
+  /**
+   * Initialize the extension
+   * Called once when the extension is loaded
+   */
+  initialize(ctx: ExtensionContext, db: ExtensionDatabase): Promise<void>
+
+  /**
+   * Shutdown the extension
+   * Called when Lightning.Pub is shutting down
+   */
+  shutdown?(): Promise<void>
+
+  /**
+   * Health check
+   * Return true if extension is healthy
+   */
+  healthCheck?(): Promise<boolean>
+}
+
+/**
+ * Extension constructor type
+ */
+export type ExtensionConstructor = new () => Extension
+
+/**
+ * Extension module default export
+ */
+export interface ExtensionModule {
+  default: ExtensionConstructor
+}
+
+/**
+ * Loaded extension state
+ */
+export interface LoadedExtension {
+  info: ExtensionInfo
+  instance: Extension
+  database: ExtensionDatabase
+  status: 'loading' | 'ready' | 'error' | 'stopped'
+  error?: Error
+  loadedAt: number
+}
+
+/**
+ * Extension loader configuration
+ */
+export interface ExtensionLoaderConfig {
+  extensionsDir: string         // Directory containing extensions
+  databaseDir: string           // Directory for extension databases
+  enabledExtensions?: string[]  // If set, only load these extensions
+  disabledExtensions?: string[] // Extensions to skip
+}