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* Represents a function that can be called to proceed to the next middleware in the chain.
* Should return a Promise that resolves when the next middleware has completed.
*
* @returns A Promise that resolves when the next middleware completes
*/
export type Next = () => Promise<void>;
/**
* A no-op implementation of the Next function that immediately resolves.
* Used as a default when no next function is provided.
*
* @returns A Promise that resolves immediately
*/
export function NextNoop() { return Promise.resolve(); }
/**
* Represents a handler function that processes a context and optionally calls next.
* Can be either a two-parameter function (context and next) or a one-parameter function (context only).
* One-parameter functions automatically call next after completion.
*
* @template Ctx - The type of the context object
* @param ctx - The context object to process
* @param next - Optional function to call the next middleware
* @returns A Promise that resolves when processing is complete
*/
export type Handler<Ctx> = (ctx: Ctx, next?:Next) => Promise<void>;
/**
* Represents metadata that can be attached to middleware for debugging, logging, or other purposes.
* Can contain any key-value pairs.
*/
export type Meta = Record<string, any>;
/**
* Represents a hierarchical structure of middleware metadata.
* Used for debugging and visualization of middleware chains.
*/
export type MetaHierarchy = { meta?: Meta, children?: MetaHierarchy[] }
/**
* Represents a middleware object that can process contexts and call the next middleware.
*
* @template Ctx - The type of the context object
*/
export type Middleware<Ctx> = {
/** Optional metadata associated with this middleware */
meta?: Meta;
/** Optional array of child middleware */
middleware?: Middleware<Ctx>[];
/**
* Processes the context and calls the next middleware
* @param ctx - The context to process
* @param next - Function to call the next middleware
* @returns A Promise that resolves when processing is complete
*/
process(ctx: Ctx, next: Next): Promise<void>;
}
/**
* Union type representing either a Handler function or a Middleware object.
*
* @template Ctx - The type of the context object
*/
export type Processor<Ctx> = Handler<Ctx> | Middleware<Ctx>
/**
* Interface defining the contract for Rowan middleware containers.
* Extends Middleware to provide additional functionality for managing middleware chains.
*
* @template Ctx - The type of the context object
*/
export interface IRowan<Ctx> extends Middleware<Ctx> {
/**
* Adds a processor to the middleware chain
* @param h - The processor to add
* @param meta - Optional metadata to associate with the processor
* @returns This instance for method chaining
*/
use(h: Processor<Ctx>, meta?: Meta): IRowan<Ctx>;
/** Read-only array of middleware in this container */
readonly middleware: Middleware<Ctx>[];
}
/**
* Main class for creating and managing middleware chains.
* Provides functionality to add middleware, process contexts, and manage metadata.
*
* @template Ctx - The type of the context object that will be processed
*
* @example
* ```typescript
* const app = new Rowan();
* app.use(async (ctx) => {
* console.log('Processing:', ctx);
* });
* await app.process({ data: 'example' });
* ```
*/
export class Rowan<Ctx = any> implements IRowan<Ctx>{
/** Array of middleware processors in this container */
middleware: Middleware<Ctx>[];
/**
* Creates a new Rowan middleware container.
*
* @param middleware - Initial array of processors to add to the container
* @param meta - Metadata to associate with this container
*
* @example
* ```typescript
* const rowan = new Rowan([
* async (ctx) => console.log('First'),
* async (ctx) => console.log('Second')
* ], { name: 'MyApp' });
* ```
*/
constructor(middleware: Processor<Ctx>[] = [], public meta: Meta = {}) {
this.middleware = middleware.map(function(x) { return Rowan.convertToMiddleware(x); });
}
/**
* Adds a processor to the middleware chain.
*
* @param input - The processor (handler function or middleware object) to add
* @param meta - Optional metadata to associate with the processor
* @returns This instance for method chaining
*
* @example
* ```typescript
* rowan
* .use(async (ctx) => console.log('First'))
* .use(async (ctx, next) => {
* console.log('Before');
* await next();
* console.log('After');
* });
* ```
*/
use(input: Processor<Ctx>, meta?: any): this {
this.middleware.push(Rowan.convertToMiddleware(input, meta));
return this;
}
/**
* Processes a context through the middleware chain.
*
* @param ctx - The context object to process
* @param next - Optional function to call after all middleware has been processed
* @returns A Promise that resolves when all middleware has completed
*
* @example
* ```typescript
* await rowan.process({ userId: 123, data: 'example' });
* ```
*/
process(ctx: Ctx, next: Next = NextNoop): Promise<void> {
return Rowan.process(this.middleware, ctx, next);
}
/**
* Static method to process a middleware array with a context.
* Sets up the middleware chain and executes it in reverse order.
*
* @param middleware - Array of middleware to process
* @param ctx - The context object to process
* @param next - Optional function to call after all middleware has been processed
* @returns A Promise that resolves when all middleware has completed
*
* @example
* ```typescript
* const middleware = [
* { process: async (ctx, next) => { console.log('1'); await next(); } },
* { process: async (ctx, next) => { console.log('2'); await next(); } }
* ];
* await Rowan.process(middleware, { data: 'test' });
* ```
*/
static process<Ctx>(middleware: Middleware<Ctx>[], ctx: Ctx, next: Next = NextNoop): Promise<void> {
for (let index = middleware.length - 1; index >= 0; index -= 1) {
const item = middleware[index];
next = item.process.bind(item, ctx, next);
}
return next();
}
/**
* Converts a processor (handler function or middleware object) into a standardized middleware object.
* Handles different types of input and normalizes them to the Middleware interface.
*
* @param input - The processor to convert
* @param meta - Optional metadata to associate with the middleware
* @returns A standardized middleware object
*
* @example
* ```typescript
* // Convert a handler function
* const middleware = Rowan.convertToMiddleware(async (ctx) => console.log(ctx));
*
* // Convert with metadata
* const middleware2 = Rowan.convertToMiddleware(
* async (ctx, next) => { await next(); },
* { name: 'Logger' }
* );
* ```
*/
static convertToMiddleware<Ctx>(input: Processor<Ctx>, meta?: Meta) {
if (isMiddleware(input)) {
input.meta = input.meta || meta;
return input;
} else {
return {
meta: (input as any)["meta"] || meta,
process: isAutoHandler(input) ? function (ctx, next) { return input(ctx, undefined).then(function(_) { return next(); }); } : input
} as Middleware<Ctx>;
}
}
/**
* Returns the metadata hierarchy of middleware for debugging and visualization.
* Recursively traverses the middleware tree to build a hierarchical structure.
*
* @param input - The middleware to analyze
* @returns A hierarchical representation of the middleware metadata
*
* @example
* ```typescript
* const hierarchy = Rowan.hierarchy(rowan);
* console.log(JSON.stringify(hierarchy, null, 2));
* // {
* // "meta": { "name": "MyApp" },
* // "children": [
* // { "meta": { "name": "Logger" } },
* // { "meta": { "name": "Auth" } }
* // ]
* // }
* ```
*/
static hierarchy<Ctx>(input: Middleware<Ctx>): MetaHierarchy {
return {
meta: input.meta,
children: input.middleware ? input.middleware.map(function(item) { return Rowan.hierarchy(item); }) : undefined
}
}
}
/**
* Type guard to determine if an object is a middleware object.
* Checks if the object has a 'process' method and is not null.
*
* @param obj - The object to check
* @returns True if the object is a middleware, false otherwise
*
* @example
* ```typescript
* const middleware = { process: async (ctx, next) => next() };
* const handler = async (ctx) => {};
*
* console.log(isMiddleware(middleware)); // true
* console.log(isMiddleware(handler)); // false
* ```
*/
export function isMiddleware(obj: any): obj is Middleware<any> {
return typeof (obj) === "object" && obj !== null && typeof (obj["process"]) === "function";
}
/**
* Type guard to determine if a function is an auto-handler.
* Auto-handlers are functions with 0 or 1 parameters that automatically call next() after completion.
* Functions with 2 or more parameters are considered manual handlers that must call next() explicitly.
*
* @param obj - The object to check
* @returns True if the object is an auto-handler function, false otherwise
*
* @example
* ```typescript
* const autoHandler = async (ctx) => console.log(ctx);
* const manualHandler = async (ctx, next) => { await next(); };
*
* console.log(isAutoHandler(autoHandler)); // true
* console.log(isAutoHandler(manualHandler)); // false
* ```
*/
export function isAutoHandler(obj: any): boolean {
return typeof (obj) === "function" && obj.length <= 1;
}
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