import fs from "fs/promises";
import path from "path";

import { parse } from "date-fns";
import matter from "gray-matter";
import truncateMarkdown from "markdown-truncate";
import { MDXRemoteSerializeResult } from "next-mdx-remote";
import { serialize } from "next-mdx-remote/serialize";

import {
  isTerm,
  Term,
  TERMS,
  DATE_FORMAT,
  getLocalDateFromEST,
  TermYear,
  getTermYear,
  getCurrentTermYear,
} from "@/utils";

export const NEWS_PATH = path.join("content", "news");

export interface Metadata {
  author: string;
  date: string;
  permalink: string;
}

export interface News {
  content: MDXRemoteSerializeResult;
  metadata: Metadata;
}

export async function getNewsYears(): Promise<string[]> {
  return (await fs.readdir(NEWS_PATH, { withFileTypes: true }))
    .filter((dirent) => dirent.isDirectory())
    .map((dirent) => dirent.name)
    .sort();
}

export async function getNewsTermsByYear(year: string): Promise<Term[]> {
  return (
    await fs.readdir(path.join(NEWS_PATH, year), {
      withFileTypes: true,
    })
  )
    .filter((dirent) => dirent.isDirectory() && isTerm(dirent.name))
    .map((dirent) => dirent.name as Term)
    .sort((a, b) => TERMS.indexOf(a) - TERMS.indexOf(b));
}

export async function getNewsDateByTerm(
  year: string,
  term: Term
): Promise<string[]> {
  return (await getNewsByTerm(year, term)).map(
    (news) => news.split("-").slice(0, 3).join("-") // retrieves date from filename
  );
}

export async function getNewsByTerm(
  year: string,
  term: Term
): Promise<string[]> {
  return (
    await fs.readdir(path.join(NEWS_PATH, year, term), {
      withFileTypes: true,
    })
  )
    .filter((dirent) => dirent.isFile() && dirent.name.endsWith(".md"))
    .map((dirent) => dirent.name.slice(0, -".md".length));
}

export async function getNewsBySlug(
  year: string,
  term: Term,
  slug: string,
  shortened = false
): Promise<News> {
  const raw = await fs.readFile(
    path.join(NEWS_PATH, year, term, `${slug}.md`),
    "utf-8"
  );
  const { content: rawContent, data: metadata } = matter(raw);
  const slugDate = slug.split("-").slice(0, 3).join("-");
  const content: string = shortened
    ? truncateMarkdown(rawContent, {
        limit: 150,
        ellipsis: true,
      })
    : rawContent;

  return {
    content: await serialize(content),
    metadata: {
      ...metadata,
      date: getLocalDateFromEST(
        parse(metadata.date as string, DATE_FORMAT, new Date())
      ).toString(),
      permalink: `/news/${year}/${term}/${slugDate}`,
    } as Metadata,
  };
}

export async function getRecentNews(): Promise<News[]> {
  const terms: TermYear[] = [];

  // Get news for the last two terms
  for (const termYear of getTermYear(getCurrentTermYear(), {
    goBackwards: true,
  })) {
    if (terms.length >= 2) {
      break;
    }

    terms.push(termYear);
  }

  const news: News[] = (
    await Promise.all(
      terms.map(async ({ year, term }) => {
        try {
          const newsInTerm = await getNewsByTerm(year.toString(), term);
          return await Promise.all(
            newsInTerm.map((slug) => {
              return getNewsBySlug(year.toString(), term, slug, true);
            })
          );
        } catch (error) {
          return [];
        }
      })
    )
  ).flat();

  return news.sort((a, b) => {
    return (
      new Date(b.metadata.date).getTime() - new Date(a.metadata.date).getTime()
    );
  });
}