lambda-middlewares/dist/compose_middlewares.js

Middlewares framework for AWS Lambda.

"use strict";
var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, generator) {
    return new (P || (P = Promise))(function (resolve, reject) {
        function fulfilled(value) { try { step(generator.next(value)); } catch (e) { reject(e); } }
        function rejected(value) { try { step(generator["throw"](value)); } catch (e) { reject(e); } }
        function step(result) { result.done ? resolve(result.value) : new P(function (resolve) { resolve(result.value); }).then(fulfilled, rejected); }
        step((generator = generator.apply(thisArg, _arguments || [])).next());
    });
};
Object.defineProperty(exports, "__esModule", { value: true });
const middleware_1 = require("./middleware");
function buildDependencyGraph(entrypoints) {
    const dependencies = new Map();
    const dependents = new Map();
    const initialize = (middleware) => {
        if (!dependencies.has(middleware)) {
            dependencies.set(middleware, new Set());
        }
        if (!dependents.has(middleware)) {
            dependents.set(middleware, new Set());
        }
    };
    const stack = [...entrypoints];
    const visited = new Set(entrypoints);
    while (stack.length > 0) {
        const current = stack.pop();
        initialize(current);
        current.dependencies.forEach((dependency) => {
            initialize(dependency);
            dependencies.get(current).add(dependency);
            dependents.get(dependency).add(current);
            if (!visited.has(dependency)) {
                stack.push(dependency);
                visited.add(dependency);
            }
        });
    }
    return { dependencies, dependents };
}
function topologicalSort(graph) {
    const { dependencies, dependents } = graph;
    const queue = [];
    for (let [key, value] of dependencies.entries()) {
        if (value.size === 0) {
            queue.push(key);
        }
    }
    const output = [];
    while (queue.length > 0) {
        const current = queue.shift();
        output.push(current);
        dependents.get(current).forEach((dependent) => {
            dependencies.get(dependent).delete(current);
            if (dependencies.get(dependent).size === 0) {
                queue.push(dependent);
            }
        });
    }
    if (output.length !== dependencies.size) {
        return null;
    }
    return output;
}
function composeMiddlewares(...entrypoints) {
    const dependencyGraph = buildDependencyGraph(entrypoints);
    const middlewares = topologicalSort(dependencyGraph);
    if (middlewares === null) {
        throw new Error('Cyclic dependency detected.');
    }
    ;
    return new middleware_1.default((handler) => {
        return (event) => __awaiter(this, void 0, void 0, function* () {
            const makeHandler = (i) => {
                if (i >= middlewares.length) {
                    return handler;
                }
                return middlewares[i].toHandler((event) => __awaiter(this, void 0, void 0, function* () {
                    return yield makeHandler(i + 1)(event);
                }));
            };
            return yield makeHandler(0)(event);
        });
    });
}
exports.default = composeMiddlewares;