import { AnyNode, Elem, Fragment, TextNode } from "../core/node.ts";
import { isNil } from "../core/utils.ts";
import { Parser } from "./types.ts";

const RE_NEW_LINE = /^\r?\n/;

const RE_OPEN_ATX_HEADING = /^\s{0,3}(#{1,6})(\s|$)/;
const RE_CLOSE_ATX_HEADING = /(^|\s+)#*\s*$/;

export class MarkdownParser implements Parser {
  parse(input: string): AnyNode {
    const ast: AstDocument = { kind: AstKind.Document, content: [] };

    let readStr = input;

    while (readStr.trim().length) {
      {
        // 1. clear new line character
        const match = RE_NEW_LINE.exec(readStr);
        if (!isNil(match)) {
          readStr = readStr.slice(match[0].length);
        }
      }

      // 2. try to find atx heading sequence
      const match = RE_OPEN_ATX_HEADING.exec(readStr);
      if (!isNil(match)) {
        readStr = readStr.slice(match[0].length);

        const atxHeading: AstAtxHeading = {
          kind: AstKind.AtxHeading,
          level: match[1].length as HeadingLevel,
          content: [],
        };
        ast.content.push(atxHeading);

        if (match[2].length > 0) {
          const endMatch = RE_CLOSE_ATX_HEADING.exec(readStr);

          const headingContent = !isNil(endMatch)
            ? readStr.slice(0, endMatch.index)
            : readStr.includes("\n")
            ? readStr.slice(0, readStr.indexOf("\n") + 1)
            : readStr;
          readStr = readStr.slice(
            headingContent.length + (endMatch?.[0].length ?? 0),
          );

          if (headingContent.length) {
            const text: AstText = {
              kind: AstKind.Text,
              content: headingContent.trim(),
            };
            atxHeading.content.push(text);
          }
        }
      } else {
        break;
      }
    }

    return new Fragment(ast.content.map(Heading));
  }
}

function Heading(ast: AstAtxHeading): Elem {
  return new Elem(`h${ast.level}`, {}, ast.content.map(Text));
}

function Text(ast: AstText): TextNode {
  return new TextNode(ast.content);
}

// AST

type AstDocument = BaseAstItem<AstKind.Document, AstDocumentChild[]>;
type AstDocumentChild = AstAtxHeading;

interface AstAtxHeading extends BaseAstItem<AstKind.AtxHeading, AstText[]> {
  level: HeadingLevel;
}

type AstText = BaseAstItem<AstKind.Text, string>;

type HeadingLevel = 1 | 2 | 3 | 4 | 5 | 6;

interface BaseAstItem<K extends AstKind, Cont> {
  kind: K;
  content: Cont;
}

enum AstKind {
  Document,
  AtxHeading,
  Text,
}