"use strict";

const h = require("highland");
const fs = require("fs");
const path = require("path");
const toml = require("toml");
const { promisify } = require("util");
const matter = require("gray-matter");
const markdown = require("../modules/markdown.js");
const predentation = require("predentation");
const { indentForTemplate, postIndentLevel } = require("../responders.js");

const grayMatterOptions = {
  lang: "toml",
  delims: "+++",
  engines: {
    toml: toml.parse.bind(toml)
  }
};

function* lowercaseKeys(iterator) {
  for (let [k, v] of iterator) {
    yield [String(k).toLowerCase(), v];
  }
}

function canonicaliseMetadata(meta) {
  if (meta.data) {
    meta.data = new Map(lowercaseKeys(Object.entries(meta.data)));
  } else {
    meta.data = new Map();
  }
  return meta;
}

function getTitle(file) {
  return path.basename(file.path, path.extname(file.path));
}

async function indentBody(content) {
  return await h(
    h
      .of(content)
      .map(markdown)
      .map(html => indentForTemplate(html, postIndentLevel))
      .pipe(predentation())
  )
    .invoke("toString", ["utf-8"])
    .toPromise(Promise);
}

async function get(getURL, filename) {
  const fileMatter = matter.read(filename, grayMatterOptions);
  fileMatter.basename = getTitle(fileMatter);
  delete fileMatter.orig;
  fileMatter.body = await indentBody(fileMatter.content);
  fileMatter.url = getURL(fileMatter.basename);
  return Promise.resolve(canonicaliseMetadata(fileMatter));
}

async function getFolder(folder, getURL) {
  const files = (await promisify(fs.readdir)(folder)).map(f =>
    path.resolve(folder, f)
  );

  const posts = await Promise.all(files.map(get.bind(this, getURL)));

  return new Map(posts.map(f => [getTitle(f), f]));
}

function tag(posts) {
  const tags = new Map();

  for (let [, post] of posts) {
    if (post.data.has("tags")) {
      for (let term of post.data.get("tags")) {
        const current = tags.get(term);
        tags.set(term, current ? current.concat(post) : [post]);
      }
    }
  }

  return tags;
}

module.exports = async function(config, getURL) {
  const posts = await getFolder(config.folder, getURL);
  const tags = tag(posts);
  const lastPostDate = Math.max(Array.from(posts.values(), p => p.date));
  return {
    lastPostDate,
    posts,
    tags,
    get
  };
};