/**
 * @fileoverview utilities to construct a static graph representation of the
 * import graph discovered in typescript inputs.
 */

import * as tsickle from 'tsickle';

/**
 * Recursively walk the import graph provided by tsickle, populating entries
 * in the result map such that if foo imports bar, foo will appear before bar
 * in the map.
 */
function topologicalSort(
    result: tsickle.FileMap<boolean>, current: string,
    modulesManifest: tsickle.ModulesManifest,
    visiting: tsickle.FileMap<boolean>) {
  const referencedModules = modulesManifest.getReferencedModules(current);
  if (!referencedModules) return;  // not in the local set of sources.
  for (const referencedModule of referencedModules) {
    const referencedFileName =
        modulesManifest.getFileNameFromModule(referencedModule);
    if (!referencedFileName) continue;  // Ambient modules.
    if (!result[referencedFileName]) {
      if (visiting[referencedFileName]) {
        const path = current + ' -> ' + Object.keys(visiting).join(' -> ');
        throw new Error('Cyclical dependency between files:\n' + path);
      }
      visiting[referencedFileName] = true;
      topologicalSort(result, referencedFileName, modulesManifest, visiting);
      delete visiting[referencedFileName];
    }
  }
  result[current] = true;
}

/**
 * Create the contents of the .es5.MF file which propagates partial ordering of
 * the import graph to later actions.
 * Each line in the resulting text corresponds with a workspace-relative file
 * path, and the lines are ordered to match the expected load order in a
 * browser.
 */
export function constructManifest(
    modulesManifest: tsickle.ModulesManifest,
    host: {flattenOutDir: (f: string) => string}): string {
  const result: tsickle.FileMap<boolean> = {};
  for (const file of modulesManifest.fileNames) {
    topologicalSort(result, file, modulesManifest, {});
  }

  // NB: The object literal maintains insertion order.
  return Object.keys(result).map(fn => host.flattenOutDir(fn)).join('\n') +
      '\n';
}