import type { Definition, Root, RootContent } from 'mdast'
import { fromMarkdown } from 'mdast-util-from-markdown'
import { gfmFromMarkdown } from 'mdast-util-gfm'
import { gfm } from 'micromark-extension-gfm'

// An answer's Markdown read into a tree, which the chat draws as React elements, never as HTML, the
// way the markdown plugin draws a document: GitHub-flavored, links https only, HTML as its text
// except <br>. Pure, so the reading can be checked in a test.

/** A <br> models put in a table cell, or anywhere, for a line break. */
const LINE_BREAK = /^<br\s*\/?>$/i

export function parseMarkdown(source: string): Root {
  return fromMarkdown(source, { extensions: [gfm()], mdastExtensions: [gfmFromMarkdown()] })
}

/** The address a link opens, or null: main opens https links only, so nothing else is a link here. */
export function linkHref(url: string): string | null {
  try {
    return new URL(url).protocol === 'https:' ? url : null
  } catch {
    return null
  }
}

export function isLineBreak(html: string): boolean {
  return LINE_BREAK.test(html)
}

/** The definitions reference links point at, by the label mdast gives both, wherever they sit. */
export function definitionsOf(tree: Root): Map<string, Definition> {
  const found = new Map<string, Definition>()
  const visit = (nodes: RootContent[]): void => {
    for (const node of nodes) {
      if (node.type === 'definition') {
        if (!found.has(node.identifier)) found.set(node.identifier, node)
      } else if ('children' in node) visit(node.children)
    }
  }
  visit(tree.children)
  return found
}