class LineFeed {
  originalText = undefined;
  /**
   * @type {string[]}
   */
  feed = undefined;
  /**
   *
   * @param {string} markdown
   */
  constructor(markdown) {
    this.originalText = markdown;
    // TODO: Need to identify line endings
    this.feed = markdown.split("\n");
  }

  /**
   * @returns {string}
   */
  peek() {
    return this.feed[0] ?? undefined;
  }

  /**
   *
   * @returns {string}
   */
  claim() {
    const line = this.feed.shift();
    if (line === undefined) throw new Error("Feed is empty");
    return line;
  }

  /**
   *
   * @param {string} line
   */
  push(line) {
    if (line === undefined || line === null) return;
    this.feed = [line, ...this.feed];
  }

  /**
   *
   * @returns {boolean}
   */
  isEmpty() {
    return this.feed.length === 0;
  }
}

class Symbol {
  static canParse(line) {
    throw new Error("Not implemented");
  }
  static create(lineFeed, assetDirectory) {
    throw new Error("Not implemented");
  }
  /**
   *
   * @param {string} assetDirectory
   * @returns {void}
   */
  process(assetDirectory) {
    throw new Error("Not Implemented");
  }
  render() {
    throw new Error("Not implemented");
  }
}

class Heading extends Symbol {
  /**
   * @type {string}
   */
  text = "";
  /**
   * @type {number}
   */
  level = 1;
  /**
   *
   * @param {string} line
   * @returns {boolean}
   */
  static canParse(line) {
    return line.trim().startsWith("#");
  }

  /**
   *
   * @param {LineFeed} lineFeed
   * @returns {Symbol}
   */
  static create(lineFeed) {
    const instance = new Heading();
    const line = lineFeed.claim();
    instance.text = line.replaceAll("#", "").trim();
    instance.level = line.split("").reduce((aggregate, current) => {
      return current === "#" ? aggregate + 1 : aggregate;
    }, 0);
    return instance;
  }

  /**
   *
   * @param {string} assetDirectory
   * @returns {void}
   */
  process(assetDirectory) {
    return;
  }

  render() {
    return `<h${this.level}>${this.text}</h${this.level}>`;
  }
}

class JustALineBreak extends Symbol {
  /**
   *
   * @param {string} line
   * @returns {boolean}
   */
  static canParse(line) {
    return line === "";
  }

  /**
   *
   * @param {LineFeed} lineFeed
   * @returns {Symbol}
   */
  static create(lineFeed) {
    const instance = new JustALineBreak();
    lineFeed.claim();
    return instance;
  }

  /**
   *
   * @param {string} assetDirectory
   * @returns {void}
   */
  process(assetDirectory) {
    return;
  }

  render() {
    throw new Error("Symbol cannot be rendered directly");
  }
}

class Paragraph extends Symbol {
  /**
   * @type {string[]}
   */
  lines = [];
  /**
   * @type {Symbol[]}
   */
  children = [];
  /**
   *
   * @param {string} line
   * @returns {boolean}
   */
  static canParse(line) {
    return line === "";
  }

  /**
   *
   * @param {LineFeed} lineFeed
   * @returns {Symbol}
   */
  static create(lineFeed) {
    const instance = new Paragraph();
    lineFeed.claim();

    const lines = [];
    let endOfParagraph = false;
    while (!endOfParagraph && !lineFeed.isEmpty()) {
      const line = lineFeed.peek();
      if (line === "") {
        endOfParagraph = true;
        continue;
      }
      lines.push(lineFeed.claim());
    }

    instance.lines = lines;
    return instance;
  }

  /**
   *
   * @param {string} assetDirectory
   * @returns {void}
   */
  process(assetDirectory) {
    return;
  }

  render() {
    return `<p>${this.children.map((c) => c.render()).join("")}</p>`;
  }
}

class UnorderedListItem extends Symbol {
  /**
   * @type {string}
   */
  text = "";
  /**
   * @type {number}
   */
  level = 0;
  /**
   *
   * @param {string} line
   * @returns {boolean}
   */
  static canParse(line) {
    return line.trim().startsWith("- ");
  }

  /**
   *
   * @param {LineFeed} lineFeed
   * @returns {Symbol}
   */
  static create(lineFeed) {
    const instance = new UnorderedListItem();
    const line = lineFeed.claim();
    instance.text = line.replaceAll("-", "").trim();
    instance.level = getAmountOfTokenInBeginningOfFile("  ", line);
    return instance;
  }

  /**
   *
   * @param {string} assetDirectory
   * @returns {void}
   */
  process(assetDirectory) {
    return;
  }

  render() {
    return `<li class="indent-${this.level}">${this.text} indentation level ${this.level}</li>`;
  }
}

class OrderedListItem extends Symbol {
  /**
   * @type {string}
   */
  text = "";
  /**
   * @type {number}
   */
  level = 0;
  /**
   *
   * @param {string} line
   * @returns {boolean}
   */
  static canParse(line) {
    return new RegExp(/^\d\. /).test(line.trim());
  }

  /**
   *
   * @param {LineFeed} lineFeed
   * @returns {Symbol}
   */
  static create(lineFeed) {
    const instance = new UnorderedListItem();
    const line = lineFeed.claim();
    instance.text = line.trim().replace(/^\d\. /, "");
    instance.level = getAmountOfTokenInBeginningOfFile("   ", line);
    return instance;
  }

  /**
   *
   * @param {string} assetDirectory
   * @returns {void}
   */
  process(assetDirectory) {
    return;
  }

  render() {
    return `<li class="indent-${this.level}">${this.text} indentation level ${this.level}</li>`;
  }
}
class Link extends Symbol {
  /**
   * @type {RegExp}
   */
  static canParseRegExp = new RegExp(/^\[.*\]\(.*\)/);
  /**
   * @type {RegExp}
   */
  static textAndLinkRegExp = new RegExp(/\[(?<text>.*)\]\((?<link>.*)\)/);
  /**
   * @type {string}
   */
  text = "";
  /**
   * @type {string}
   */
  link = "";
  /**
   *
   * @param {string} line
   * @returns {boolean}
   */
  static canParse(line) {
    return Link.canParseRegExp.test(line.trim());
  }

  /**
   *
   * @param {LineFeed} lineFeed
   * @returns {Symbol}
   */
  static create(lineFeed) {
    const instance = new Link();
    const line = lineFeed.claim().trim();
    const [linkLine, rest] = extractTokenAndRest(Link.textAndLinkRegExp, line);
    lineFeed.push(rest);
    const { text, link } = Link.textAndLinkRegExp.exec(linkLine)?.groups ?? {};
    instance.link = link ?? "";
    instance.text = text ?? "";
    return instance;
  }

  /**
   *
   * @param {string} assetDirectory
   * @returns {void}
   */
  process(assetDirectory) {
    return;
  }

  render() {
    return `<a href="${this.link}">${this.text}</a>`;
  }
}

class ImageLink extends Symbol {
  /**
   * @type {RegExp}
   */
  static canParseRegExp = new RegExp(/^!\[.*\]\(.*\)/);
  /**
   * @type {RegExp}
   */
  static textAndLinkRegExp = new RegExp(/!\[(?<text>.*)\]\((?<link>.*)\)/);
  /**
   * @type {string}
   */
  static assetDirectoryToken = "@asset/";
  /**
   * @type {string}
   */
  alt = "";
  /**
   * @type {string}
   */
  link = "";
  /**
   *
   * @param {string} line
   * @returns {boolean}
   */
  static canParse(line) {
    return ImageLink.canParseRegExp.test(line.trim());
  }

  /**
   *
   * @param {LineFeed} lineFeed
   * @returns {Symbol}
   */
  static create(lineFeed, assetDirectory) {
    const instance = new ImageLink();
    const line = lineFeed.claim().trim();
    const [linkLine, rest] = extractTokenAndRest(
      ImageLink.textAndLinkRegExp,
      line
    );
    lineFeed.push(rest);
    const { text, link } =
      ImageLink.textAndLinkRegExp.exec(linkLine)?.groups ?? {};
    instance.link =
      link.replace(ImageLink.assetDirectoryToken, assetDirectory) ?? "";
    instance.alt = text ?? "";
    return instance;
  }

  /**
   *
   * @param {string} assetDirectory
   * @returns {void}
   */
  process(assetDirectory) {
    return;
  }

  render() {
    return `<img src="${this.link}" alt="${this.alt}"/>`;
  }
}

class Italic extends Symbol {
  /**
   * @type {string}
   */
  text = "";
  /**
   *
   * @param {string} line
   * @returns {boolean}
   */
  static canParse(line) {
    return line.startsWith("_");
  }

  /**
   *
   * @param {LineFeed} lineFeed
   * @returns {Symbol}
   */
  static create(lineFeed) {
    const instance = new Italic();
    const line = lineFeed.claim().trim();
    const lineWithoutStartingUnderscore = line.slice(1, line.length);
    const lineEndsWithUnderscore = lineWithoutStartingUnderscore.endsWith("_");
    if (lineEndsWithUnderscore) {
      const lineWithoutUnderscores = lineWithoutStartingUnderscore.slice(
        0,
        lineWithoutStartingUnderscore.length - 1
      );
      instance.text = lineWithoutUnderscores;
      return instance;
    }
    const endOfItalicString = lineWithoutStartingUnderscore.indexOf("_");
    const lineWithoutUnderscores = lineWithoutStartingUnderscore.slice(
      0,
      endOfItalicString
    );
    const rest = lineWithoutStartingUnderscore.slice(endOfItalicString + 1);
    lineFeed.push(rest);
    instance.text = lineWithoutUnderscores;
    return instance;
  }

  /**
   *
   * @param {string} assetDirectory
   * @returns {void}
   */
  process(assetDirectory) {
    return;
  }

  render() {
    return `<i>${this.text}</i>`;
  }
}

class Bold extends Symbol {
  /**
   * @type {string}
   */
  text = "";
  /**
   *
   * @param {string} line
   * @returns {boolean}
   */
  static canParse(line) {
    return line.startsWith("**");
  }

  /**
   *
   * @param {LineFeed} lineFeed
   * @returns {Symbol}
   */
  static create(lineFeed) {
    const instance = new Bold();
    const line = lineFeed.claim().trim();
    const lineWithoutStartingUnderscore = line.slice(2, line.length);
    const lineEndsWithStars = lineWithoutStartingUnderscore.endsWith("**");
    if (lineEndsWithStars) {
      const lineWithoutUnderscores = lineWithoutStartingUnderscore.slice(
        0,
        lineWithoutStartingUnderscore.length - 2
      );
      instance.text = lineWithoutUnderscores;
      return instance;
    }
    const endOfBoldString = lineWithoutStartingUnderscore.indexOf("**");
    const lineWithoutUnderscores = lineWithoutStartingUnderscore.slice(
      0,
      endOfBoldString
    );
    const rest = lineWithoutStartingUnderscore.slice(endOfBoldString + 2);
    lineFeed.push(rest);
    instance.text = lineWithoutUnderscores;
    return instance;
  }

  /**
   *
   * @param {string} assetDirectory
   * @returns {void}
   */
  process(assetDirectory) {
    return;
  }

  render() {
    return `<b>${this.text}</b>`;
  }
}

class SingleLineCode extends Symbol {
  /**
   * @type {string}
   */
  text = "";
  /**
   *
   * @param {string} line
   * @returns {boolean}
   */
  static canParse(line) {
    return line.startsWith("`");
  }

  /**
   *
   * @param {LineFeed} lineFeed
   * @returns {Symbol}
   */
  static create(lineFeed) {
    const instance = new SingleLineCode();
    const line = lineFeed.claim().trim();
    const lineWithoutStartingUnderscore = line.slice(1, line.length);
    const lineEndsWithUnderscore = lineWithoutStartingUnderscore.endsWith("`");
    if (lineEndsWithUnderscore) {
      const lineWithoutUnderscores = lineWithoutStartingUnderscore.slice(
        0,
        lineWithoutStartingUnderscore.length - 1
      );
      instance.text = lineWithoutUnderscores;
      return instance;
    }
    const endOfItalicString = lineWithoutStartingUnderscore.indexOf("`");
    const lineWithoutUnderscores = lineWithoutStartingUnderscore.slice(
      0,
      endOfItalicString
    );
    const rest = lineWithoutStartingUnderscore.slice(endOfItalicString + 1);
    lineFeed.push(rest);
    instance.text = lineWithoutUnderscores;
    return instance;
  }

  /**
   *
   * @param {string} assetDirectory
   * @returns {void}
   */
  process(assetDirectory) {
    return;
  }

  render() {
    return `<code>${this.text}</code>`;
  }
}

class MultiLineCode extends Symbol {
  /**
   * @type {string}
   */
  text = "";
  /**
   *
   * @param {string} line
   * @returns {boolean}
   */
  static canParse(line) {
    const trimmedLine = line.trim();
    return trimmedLine.startsWith("```");
  }

  /**
   *
   * @param {LineFeed} lineFeed
   * @returns {Symbol}
   */
  static create(lineFeed) {
    const instance = new MultiLineCode();
    const line = lineFeed.claim().trim();
    const lineWithoutStartTag = line.slice(3, line.length);

    const sameLineContainsEnding = lineWithoutStartTag.includes("```");
    if (sameLineContainsEnding) {
      const endsWithTag = lineWithoutStartTag.endsWith("```");
      if (endsWithTag) {
        instance.text = lineWithoutStartTag.slice(
          0,
          lineWithoutStartTag.length - 3
        );
        return instance;
      }
      const [text, rest] = splitStringAtToken("```", lineWithoutStartTag);
      lineFeed.push(rest);
      instance.text = text;
      return instance;
    }
    const lines = [lineWithoutStartTag];

    let endTokenFound = false;
    while (!endTokenFound && !lineFeed.isEmpty()) {
      const nextLine = lineFeed.claim();
      if (!nextLine.includes("```")) {
        lines.push(nextLine);
        continue;
      }
      if (nextLine.endsWith("```")) {
        lines.push(nextLine.slice(0, nextLine.length - 3));
        break;
      }
      const [lastLine, rest] = splitStringAtToken("```", nextLine);
      lineFeed.push(rest);
      lines.push(lastLine);
      break;
    }

    instance.text = lines.join("\n");
    return instance;
  }

  /**
   *
   * @param {string} assetDirectory
   * @returns {void}
   */
  process(assetDirectory) {
    return;
  }

  render() {
    return `<pre><code>${this.text}</code></pre>`;
  }
}

class TextRow extends Symbol {
  /**
   * @type {string}
   */
  text = "";
  /**
   * @type {Symbol[]}
   */
  children = [];
  /**
   * @type {Symbol[]}
   */
  allowedChildren = [
    Bold,
    Italic,
    ImageLink,
    Link,
    MultiLineCode,
    SingleLineCode,
    TextRow,
  ];
  /**
   *
   * @param {string} line
   * @returns {boolean}
   */
  static canParse(line) {
    return true;
  }

  /**
   *
   * @param {LineFeed} lineFeed
   * @returns {Symbol}
   */
  static create(lineFeed) {
    const instance = new TextRow();
    instance.text = lineFeed.claim();
    return instance;
  }

  /**
   *
   * @param {string} assetDirectory
   * @returns {void}
   */
  process(assetDirectory) {
    for (let i = 0; i < this.text.length; i++) {
      if (i === this.text.length - 1) {
        const plainText = new PlainText();
        plainText.text = this.text;
        this.children = [plainText];
        break;
      }
      const line = this.text.slice(i);
      const symbols = toSymbols(line, assetDirectory, this.allowedChildren);
      const symbolsIsOnlyOneTextRow =
        symbols.length === 1 && symbols[0] instanceof TextRow;
      if (!symbols.length || symbolsIsOnlyOneTextRow) {
        continue;
      }
      const plainText = new PlainText();
      plainText.text = this.text.slice(0, i);
      this.children = [plainText, ...symbols];
      break;
    }
    this.children.forEach((c) => c.process(assetDirectory));
  }

  render() {
    return this.children.map((c) => c.render()).join("");
  }
}

class PlainText extends Symbol {
  /**
   * @type {string}
   */
  text = "";
  /**
   * @type {Symbol[]}
   */
  children = [];
  /**
   *
   * @param {string} line
   * @returns {boolean}
   */
  static canParse(line) {
    return true;
  }

  /**
   *
   * @param {LineFeed} lineFeed
   * @returns {Symbol}
   */
  static create(lineFeed) {
    const instance = new PlainText();
    instance.text = lineFeed.claim();
    return instance;
  }

  /**
   *
   * @param {string} assetDirectory
   * @returns {void}
   */
  process(assetDirectory) {
    return;
  }

  render() {
    return `<span>${this.text}</span>`;
  }
}

/**
 *
 * @param {string|RexExp} token
 * @param {string} string
 * @returns {string[]}
 */
const splitStringAtToken = (token, string) => {
  let index = 0;
  let length = 0;
  if (typeof token?.exec === "function") {
    const exp = new RegExp(token);
    const match = exp.exec(string);
    index = match?.index ?? -1;
    length = match?.[0].length ?? 0;
  } else {
    index = string.indexOf(token);
    length = token.length;
  }

  const splitTokenNotFound = index === -1;
  if (splitTokenNotFound) return [string, ""];
  return [string.slice(0, index), string.slice(index + length)];
};

/**
 *
 * @param {string|RexExp} token
 * @param {string} string
 * @returns {string[]}
 */
const extractTokenAndRest = (token, string) => {
  let index = 0;
  let length = 0;
  if (typeof token?.exec === "function") {
    const exp = new RegExp(token);
    const match = exp.exec(string);
    index = match?.index ?? -1;
    length = match?.[0].length ?? 0;
  } else {
    index = string.indexOf(token);
    length = token.length;
  }

  const splitTokenNotFound = index === -1;
  if (splitTokenNotFound) return [string, ""];
  return [string.slice(0, index + length), string.slice(index + length)];
};

/**
 *
 * @param {string} token
 * @param {string} string
 */
const getAmountOfTokenInBeginningOfFile = (token, string) => {
  let count = 0;
  let searchIndex = 0;
  while (true) {
    if (searchIndex + (token.length - 1) > string.length) return count;

    const index = string.slice(searchIndex).indexOf(token);
    const indexNotAtStartOfString = index !== 0;
    if (indexNotAtStartOfString) return count;

    count++;
    searchIndex += token.length;
  }
};

/**
 * @type {Symbol[]}
 */
const AllSymbols = [
  JustALineBreak,
  Heading,
  UnorderedListItem,
  OrderedListItem,
  Bold,
  Italic,
  ImageLink,
  Link,
  MultiLineCode,
  SingleLineCode,
  TextRow,
];

/**
 *
 * @param {string} markdown
 * @param {string} assetDirectory
 * @returns {string}
 */
export const toHtml = (markdown, assetDirectory) => {
  // Stage one, markdown to symbols
  const symbols = toSymbols(markdown, assetDirectory);

  // Stage two, expanding symbols
  symbols.forEach((s) => s.process(assetDirectory));

  // Stage three, operations based on symbol relationship
  const stageThree = stageThreeProcessing(symbols);
  // Stage four, rendering
  const html = stageThree
    // .filter((s) => !(s instanceof JustALineBreak))
    .map((s) => s.render())
    .join("");
  return `<div>${html}</div>`;
};

/**
 *
 * @param {Symbol[]} symbols
 * @returns {Symbol[]}
 */
const stageThreeProcessing = (symbols) => {
  const localSymbols = [...symbols];
  // Turn line break pairs into paragraphs
  while (localSymbols.filter((s) => s instanceof JustALineBreak).length !== 0) {
    const startIndex = localSymbols.findIndex(
      (s) => s instanceof JustALineBreak
    );
    const subEndIndex = localSymbols
      .slice(startIndex + 1)
      .findIndex((s) => s instanceof JustALineBreak);
    const endIndex =
      subEndIndex === -1
        ? localSymbols.length - 1
        : startIndex + 1 + subEndIndex;
    const lastItemIsNotLineBreak = subEndIndex === -1;
    const children = localSymbols.slice(
      startIndex + 1,
      lastItemIsNotLineBreak ? localSymbols.length : endIndex
    );
    const paragraph = new Paragraph();
    paragraph.children = children;
    localSymbols.splice(startIndex, children.length + 1, paragraph);
  }
  // Fix indentation of bullet elements
  return localSymbols;
};

/**
 *
 * @param {string} markdown
 * @param {string} assetDirectory
 * @param {Symbol[]} allowedSymbols
 * @returns {Symbol[]}
 */
const toSymbols = (markdown, assetDirectory, allowedSymbols = AllSymbols) => {
  const lineFeed = new LineFeed(markdown);
  const symbols = [];

  while (!lineFeed.isEmpty()) {
    const line = lineFeed.peek();
    const factory = allowedSymbols.find((factory) => factory.canParse(line));
    const symbol = factory.create(lineFeed, assetDirectory);
    symbols.push(symbol);
  }

  return symbols;
};