//
// Copyright 2023 DXOS.org
//

import { completionKeymap } from '@codemirror/autocomplete';
import { defaultKeymap, indentWithTab } from '@codemirror/commands';
import { jsonLanguage } from '@codemirror/lang-json';
import { insertNewlineContinueMarkupCommand, markdown, markdownLanguage } from '@codemirror/lang-markdown';
import { type LanguageDescription, foldNodeProp, syntaxHighlighting } from '@codemirror/language';
import { languages } from '@codemirror/language-data';
import { type Extension, Prec } from '@codemirror/state';
import { keymap } from '@codemirror/view';
import { type MarkdownConfig } from '@lezer/markdown';

import { isTruthy } from '@dxos/util';

import { mermaidHighlighting, mermaidLanguageDescription } from '../mermaid/index.ts';
import { markdownHighlightStyle, markdownTagsExtensions } from './highlight.ts';

export type MarkdownBundleOptions = {
  /** Additional fenced-code languages prepended to the standard language-data list. */
  codeLanguages?: LanguageDescription[];
  extensions?: MarkdownConfig[];
  indentWithTab?: boolean;
  setextHeading?: boolean;
};

/**
 * Creates markdown extensions.
 * To be used in conjunction with createBasicExtensions.
 *
 * Refs:
 * https://codemirror.net/docs/community
 * https://codemirror.net/docs/ref/#codemirror.basicSetup
 */
export const createMarkdownExtensions = (options: MarkdownBundleOptions = {}): Extension[] => {
  return [
    Prec.high(keymap.of([{ key: 'Enter', run: insertNewlineContinueMarkupCommand({ nonTightLists: false }) }])),

    // Main extension.
    // https://github.com/codemirror/lang-markdown
    // https://codemirror.net/5/mode/markdown/index.html (demo).
    markdown({
      // GRM by default (vs strict CommonMark):
      // Table, TaskList, Strikethrough, and Autolink.
      // NOTE: This extends the parser; it doesn't affect rendering.
      // https://github.github.com/gfm
      // https://github.com/lezer-parser/markdown?tab=readme-ov-file#github-flavored-markdown
      base: markdownLanguage,

      // Languages for syntax highlighting fenced code blocks.
      // Caller-supplied languages are checked first so they can override defaults.
      // Mermaid is registered here rather than by plugin-mermaid: `codeLanguages` is read once when
      // the parser is built, so an extension contributed later cannot add a fenced-code language.
      defaultCodeLanguage: jsonLanguage,
      codeLanguages: [...(options.codeLanguages ?? []), mermaidLanguageDescription, ...languages],

      // Don't complete HTML tags.
      completeHTMLTags: false,

      // Parser extensions.
      extensions: [
        // GFM provided by default.
        markdownTagsExtensions,
        ...(options.extensions ?? defaultExtensions()),
        // Disable folding for fenced code blocks by overriding foldNodeProp.
        // Note: returning null from foldService does not prevent syntaxFolding fallback,
        // so we must override the node prop directly on the FencedCode node type.
        noFencedCodeFolding,
      ],
    }),

    // Custom styles.
    // Fenced mermaid uses custom tags, so it needs its own style alongside markdown's.
    mermaidHighlighting(),
    syntaxHighlighting(markdownHighlightStyle()),

    keymap.of(
      [
        // https://codemirror.net/docs/ref/#commands.indentWithTab
        options.indentWithTab !== false && indentWithTab,

        // https://codemirror.net/docs/ref/#commands.defaultKeymap
        ...defaultKeymap,

        // TODO(burdon): Remove?
        ...completionKeymap,
      ].filter(isTruthy),
    ),
  ];
};

/**
 * Disables folding for fenced code blocks.
 *
 * foldService cannot block folding because returning null just defers to the next service,
 * and CodeMirror always falls back to syntaxFolding (which reads foldNodeProp).
 * The only reliable fix is to override foldNodeProp on FencedCode to return null.
 */
const noFencedCodeFolding: MarkdownConfig = {
  props: [
    foldNodeProp.add({
      FencedCode: () => null,
    }),
  ],
};

/**
 * Default customizations.
 * https://github.com/lezer-parser/markdown/blob/main/src/markdown.ts
 */
export const defaultExtensions = (): MarkdownConfig[] => [noSetExtHeading, noHtml];

/**
 * Remove SetextHeading (e.g., headings created from "---").
 */
const noSetExtHeading: MarkdownConfig = {
  remove: ['SetextHeading'],
};

/**
 * Remove HTML and XML parsing.
 */
const noHtml: MarkdownConfig = {
  // remove: ['HTMLBlock', 'HTMLTag'],
};