import { promises as fs } from 'fs';
import path from 'path';
import { createRequire } from 'module';
import pkgUp from 'pkg-up';
import findUp from 'find-up';
import crypto from 'crypto';
import util from 'util';

// Type definitions for a subset of what package.json generally contains.
// (See also https://docs.npmjs.com/cli/v7/configuring-npm/package-json)
interface PackageJSON {
  name: string;
  version: string;
  description?: string;
  license?: string | { type: string };
  licenses?: { type: string }[];
  dependencies?: { [key: string]: string };
  optionalDependencies?: { [key: string]: string };
  author?: string | { name: string; email?: string; url?: string; };
  contributors?: (string | { name: string; email?: string; url?: string; })[];
  private?: boolean;
}

interface Package extends PackageJSON {
  path: string;
  licenseFiles: {filename: string, content: string}[];
}

const relevantPackageKeys: (keyof Package)[] = [
  'name', 'version', 'license', 'licenses', 'dependencies',
  'optionalDependencies', 'private', 'licenseFiles'
];
const licenseRegexp = /^(license|copyright|copying)/i;

// Return the package.json file and license files for a given package.
async function getPackageInfo(packagePath: string): Promise<Package> {
  const packageJSONPath = path.join(packagePath, 'package.json');
  let packageJSON: PackageJSON;
  try {
    packageJSON = JSON.parse(await fs.readFile(packageJSONPath, 'utf8'));
  } catch (e) {
    throw new Error(`Could not read ${packageJSONPath}: ${e.message}`);
  }
  // Normalize the 'contributors' list.
  packageJSON.contributors =
    [...new Set([packageJSON.author, packageJSON.contributors].flat())].filter(Boolean) as any;

  const licenseFiles = await Promise.all(
    (await fs.readdir(packagePath))
      .filter(filename => filename.match(licenseRegexp))
      .sort()
      .map(async filename => ({
        filename,
        content: await fs.readFile(path.join(packagePath, filename), 'utf8')
      })));

  return {
    ...packageJSON,
    path: packagePath,
    licenseFiles
  };
}

// Recursively look up dependencies of a package at `startPath`, and return
// the package information for all of these packages.
// Each package name + version combination is only reported once.
export async function gatherLicenses(startPath: string): Promise<Package[]> {
  const packages = new Map<string, Package>();

  packages.set(startPath, await getPackageInfo(startPath));
  for (const pkg of packages.values()) {
    const require = createRequire(path.resolve(pkg.path, 'index.js'));
    for (const depsKey of ['dependencies', 'optionalDependencies'] as const) {
      for (const dep of Object.keys(pkg[depsKey] ?? {})) {
        let resolved;
        try {
          resolved = require.resolve(dep);
          if (!path.isAbsolute(resolved)) {
            continue; // Node.js builtin
          }
        } catch (err) {
          resolved = await findUp(async directory => {
            const candidate = path.join(directory, 'node_modules', dep, 'package.json');
            return await findUp.exists(candidate) ? candidate : undefined;
          }, { cwd: path.resolve(pkg.path) });
        }
        if (!resolved) {
          if (depsKey === 'optionalDependencies') {
            continue;
          }
          throw new Error(`Could not resolve ${dep} require from ${pkg.path}`);
        }
        const pkgJson = await pkgUp({ cwd: path.dirname(resolved) });
        if (!pkgJson) {
          throw new Error(`Could not find package.json for ${dep} required from ${pkg.path}`);
        }
        const pkgBase = path.relative(process.cwd(), await fs.realpath(path.dirname(pkgJson)));
        if (!packages.has(pkgBase)) {
          packages.set(pkgBase, await getPackageInfo(pkgBase));
        }
      }
    }
  }

  // Deduplicate by package name and version.
  const packageByNameAndVersion = new Map<string, Package>();
  for (const pkg of packages.values()) {
    const nameAndVersion = id(pkg);
    const existing = packageByNameAndVersion.get(nameAndVersion);
    if (existing) {
      if (!pkgEqual(pkg, existing)) {
        throw new Error(`Two entries for the same package name and version differ! (${JSON.stringify([pkg, existing])})`);
      }
    } else {
      packageByNameAndVersion.set(nameAndVersion, pkg);
    }
  }
  return [...packageByNameAndVersion.values()].sort((a, b) => a.name.localeCompare(b.name));
}

// Helper function for making sure that if we do encounter a package twice,
// the package information roughly match.
function pkgEqual(a: Package, b: Package): boolean {
  for (const key of relevantPackageKeys) {
    if (!util.isDeepStrictEqual(a[key], b[key])) {
      return false;
    }
  }
  return true;
}

// Generatex a hex id for any package name + version combination.
function id(pkg: Package): string {
  return crypto
    .createHash('sha256')
    .update(`${pkg.name}@${pkg.version}`)
    .digest('hex');
}

// Return a short summary of a package's licensing information.
function shortlicense(pkg: Package): string {
  if (typeof pkg.license === 'string') {
    return pkg.license;
  }
  if (typeof pkg.license?.type === 'string') {
    return pkg.license.type;
  }
  if (Array.isArray(pkg.licenses)) {
    return pkg.licenses.map(({ type }) => type).filter(Boolean).join(', ');
  }
  return `See [details](#${id(pkg)})`;
}

function indent(input: string, depth: number): string {
  return input.replace(/^/mg, ' '.repeat(depth));
}

// Generate a markdown file containing information about all the packages'
// licensing data.
export function generateLicenseInformation(productName: string, packages: Package[]): string {
  let output = `\
The following third-party software is used by and included in **${productName}**.
This document was automatically generated on ${new Date().toDateString()}.

## List of dependencies

Package|Version|License
-------|-------|-------
${packages.map(pkg => (
  `**[${pkg.name}](#${id(pkg)})**|${pkg.version}|${shortlicense(pkg)}`
)).join('\n')}

## Package details
`;

  for (const pkg of packages) {
    const linkedPackageName =
      pkg.private ? pkg.name : `[${pkg.name}](https://www.npmjs.com/package/${pkg.name})`;
    output += `
<a id="${id(pkg)}"></a>
### ${linkedPackageName} (version ${pkg.version})
<!-- initially found at ${pkg.path} -->
`;
    if (pkg.description) {
      output += `> ${pkg.description}\n\n`;
    }

    output += `License tags: ${shortlicense(pkg)}\n\n`;

    if (pkg.licenseFiles?.length) {
      output += 'License files:\n';
      for (const file of pkg.licenseFiles) {
        output += `* ${file.filename}:\n\n${indent(file.content, 6)}\n\n`;
      }
    }

    if (pkg.contributors?.length) {
      output += 'Authors:\n';
      for (const person of pkg.contributors) {
        const name = typeof person !== 'object' ? person :
          person.name
            + (person.email ? ` <[${person.email}](nomail)>` : '')
            + (person.url ? ` (${person.url})` : '');
        output += `* ${name}\n`;
      }
      output += '\n';
    }
  }
  return output;
}

// Usage: ts-node gather-licenses.ts <path/to/initial/package>
(async () => {
  const packageTree = await gatherLicenses(process.argv[2]);
  const output = generateLicenseInformation('mongosh', packageTree);
  process.stdout.write(output);
})().catch(err => process.nextTick(() => { throw err; }));