'use strict';

const { access, mkdir, readdir, readFile, rmdir, writeFile } = require('fs/promises');
const { ncp } = require('ncp');
const { join } = require('path');
const Marked = require('marked');
const { debuglog, promisify } = require('util');

const StaticGenerator = require('./generators/static');
const HTMLGenerator = require('./generators/html');
const RSSGenerator = require('./generators/rss');

const internals = {

  // Promisified functions
  ncp: promisify(ncp),

  debuglog: debuglog('blog'),

  // constants

  kFileNotFoundError: 'ENOENT',
  kMarkdownRe: /\.md$/i,
  kMetadataFilename: 'metadata.json',

  // Strings

  strings: {
    markdownNotFound: 'Markdown file was not found in blog directory. Please update.'
  }
};

/**
 * The Blog class is the blog generator, it's in charge of adding and
 * updating posts, and handling the publishing.
 *
 * @class Blog
 * @param {Blog.tConfiguration} config the initialization options to
 * extend the instance
 */
module.exports = class Blog {

  constructor(config) {

    Object.assign(this, config);
  }

  /**
   * Shifts the blog posts, adds the passed path to slot 0, and
   * generates files.
   *
   * @function add
   * @memberof Blog
   * @param {string} postLocation the path to the directory containing
   * the post structure
   * @return {Promise<undefined>} empty promise, returns no value
   * @instance
   */
  async add(postLocation) {

    await this._ensurePostsDirectoryExists();
    await this._shift();
    await this.update(postLocation);
  }

  /**
   * Adds the passed path to slot 0, and generates files.
   *
   * @function update
   * @memberof Blog
   * @param {string} postLocation the path to the directory containing
   * the post structure
   * @return {Promise<undefined>} empty promise, returns no value
   * @instance
   */
  async update(postLocation) {

    const metadata = await this._getMetadata();
    await this._ensurePostsDirectoryExists();
    await this._copyPost(postLocation);
    await this._writeMetadata(metadata);

    await this._generate();
  }

  /**
   * Publishes the files to a static host.
   *
   * @function publish
   * @memberof Blog
   * @return {Promise<undefined>} empty promise, returns no value
   * @instance
   */
  publish() {

    console.error('Publishing not yet implemented');
    return Promise.resolve();
  }

  // Parses markdown for each page, copies assets and generates index.

  async _generate() {

    internals.debuglog('Generating output');

    const posts = await this._readPosts(this.postsDirectory);

    await StaticGenerator(this.postsDirectory, this.staticDirectory, posts);
    await HTMLGenerator(this.templatesDirectory, this.staticDirectory, posts);
    await RSSGenerator(this.templatesDirectory, this.staticDirectory, posts);
  }

  // Reads the posts into an array

  async _readPosts(source) {

    internals.debuglog('Reading posts');
    const posts = [];

    for (let i = 0; i < this.maxPosts; ++i) {
      const postSourcePath = join(source, `${i}`);

      internals.debuglog(`Reading ${postSourcePath} into posts array`);

      try {
        await access(postSourcePath);

        const metadata = await this._getMetadata(i);

        const postContentPath = await this._findBlogContent(postSourcePath);
        internals.debuglog(`Reading ${postContentPath}`);
        const postContent = await readFile(postContentPath, { encoding: 'utf8' });

        internals.debuglog('Parsing markdown');
        posts.push({
          ...metadata,
          html: Marked(postContent)
        });
      }
      catch (error) {
        if (error.code === internals.kFileNotFoundError) {
          internals.debuglog(`Skipping ${i}`);
          continue;
        }

        throw error;
      }
    }

    return posts;
  }

  // Shift the posts, delete any remainder.

  async _shift() {


    for (let i = this.maxPosts - 1; i >= 0; --i) {
      const targetPath = join(this.postsDirectory, `${i}`);
      const sourcePath = join(this.postsDirectory, `${i - 1}`);

      try {
        internals.debuglog(`Removing ${targetPath}`);
        await rmdir(targetPath, { recursive: true });

        await access(sourcePath); // check the source path

        internals.debuglog(`Shifting blog post ${sourcePath} to ${targetPath}`);
        await internals.ncp(sourcePath, targetPath);
      }
      catch (error) {
        if (error.code === internals.kFileNotFoundError) {
          internals.debuglog(`Skipping ${sourcePath}: Does not exist.`);
          continue;
        }

        throw error;
      }
    }
  }

  // Attempts to read existing metadata. Otherwise generates new set.

  async _getMetadata(index = 0) {

    const metadataTarget = join(this.postsDirectory, String(index), internals.kMetadataFilename);

    try {
      internals.debuglog(`Looking for metadata at ${metadataTarget}`);
      return JSON.parse(await readFile(metadataTarget, { encoding: 'utf8' }));
    }
    catch (e) {
      internals.debuglog(`Metadata not found or unreadable. Generating new set.`);
      const createdOn = Date.now();
      const metadata = {
        id: String(createdOn),
        createdOn
      };

      return metadata;
    }
  }

  // Writes metadata. Assumes post 0 since it only gets written
  // on create

  async _writeMetadata(metadata) {

    const metadataTarget = join(this.postsDirectory, '0', internals.kMetadataFilename);
    internals.debuglog(`Writing ${metadataTarget}`);
    await writeFile(metadataTarget, JSON.stringify(metadata, null, 2));
  }

  // Copies a post directory to the latest slot.

  async _copyPost(postLocation) {

    const targetPath = join(this.postsDirectory, '0');

    internals.debuglog(`Removing ${targetPath}`);
    await rmdir(targetPath, { recursive: true });

    internals.debuglog(`Adding ${postLocation} to ${targetPath}`);
    await internals.ncp(postLocation, targetPath);
  }

  // Ensures the posts directory exists.

  async _ensurePostsDirectoryExists() {

    internals.debuglog(`Checking if ${this.postsDirectory} exists.`);
    try {
      await access(this.postsDirectory);
    }
    catch (error) {
      if (error.code === internals.kFileNotFoundError) {
        internals.debuglog('Creating posts directory');
        await mkdir(this.postsDirectory);
        return;
      }

      throw error;
    }
  }

  // Looks for a `.md` file in the blog directory, and returns the path

  async _findBlogContent(directory) {

    const entries = await readdir(directory);

    const markdownEntries = entries
      .filter((entry) => internals.kMarkdownRe.test(entry))
      .map((entry) => join(directory, entry));

    if (markdownEntries.length > 0) {
      internals.debuglog(`Found markdown file: ${markdownEntries[0]}`);
      return markdownEntries[0];
    }

    throw new Error(internals.strings.markdownNotFound);
  }
};