_Kerman
125 lines
3.5 KiB
TypeScript
125 lines
3.5 KiB
TypeScript
/**
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* Markdown-to-plain-text projection for compact summaries and labels.
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* Parsing shares the renderer's GFM grammar; raw HTML stays literal, links
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* keep their labels, images keep alt text, and code keeps its source text.
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*/
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import { fromMarkdown } from 'mdast-util-from-markdown'
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import { gfmFromMarkdown } from 'mdast-util-gfm'
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import { gfm } from 'micromark-extension-gfm'
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/** Amount of parsed Markdown content returned by the extractor. */
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export type MarkdownPlainTextMode = 'all' | 'first-line' | 'first-paragraph'
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/** Options for {@link extractMarkdownPlainText}. */
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export interface MarkdownPlainTextOptions {
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/** Projection boundary; defaults to the complete document. */
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mode?: MarkdownPlainTextMode
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}
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interface MarkdownNode {
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type: string
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value?: string
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alt?: string
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children?: MarkdownNode[]
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}
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function inlineText(node: MarkdownNode): string {
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switch (node.type) {
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case 'text':
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case 'inlineCode':
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case 'code':
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return node.value ?? ''
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case 'image':
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case 'imageReference':
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return node.alt ?? ''
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case 'break':
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return '\n'
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case 'html':
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return node.value ?? ''
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default:
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return node.children?.map(inlineText).join('') ?? ''
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}
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}
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function compactInline(text: string): string {
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return text.replace(/\s+/g, ' ').trim()
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}
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function blockText(node: MarkdownNode): string {
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switch (node.type) {
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case 'root':
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case 'blockquote':
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return node.children?.map(blockText).filter(Boolean).join('\n\n') ?? ''
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case 'paragraph':
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case 'heading':
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return compactInline(inlineText(node))
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case 'code':
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return node.value?.trim() ?? ''
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case 'list':
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return node.children?.map(blockText).filter(Boolean).join('\n') ?? ''
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case 'listItem':
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return node.children?.map(blockText).filter(Boolean).join(' ') ?? ''
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case 'table':
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return node.children?.map(blockText).filter(Boolean).join('\n') ?? ''
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case 'tableRow':
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return node.children?.map(blockText).join('\t') ?? ''
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case 'tableCell':
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return compactInline(inlineText(node))
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case 'html':
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return node.value ?? ''
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case 'thematicBreak':
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case 'definition':
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return ''
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default:
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return compactInline(inlineText(node))
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}
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}
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function findFirstParagraph(node: MarkdownNode): string | undefined {
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if (node.type === 'paragraph') {
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const text = compactInline(inlineText(node))
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if (text !== '') return text
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}
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for (const child of node.children ?? []) {
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const text = findFirstParagraph(child)
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if (text !== undefined) return text
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}
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return undefined
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}
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function fullText(root: MarkdownNode): string {
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return blockText(root)
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.split('\n')
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.map(line => line.trim())
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.join('\n')
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.replace(/\n{3,}/g, '\n\n')
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.trim()
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}
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/**
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* Parse GFM Markdown, remove its presentation markup, and preserve raw HTML literally.
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* @param markdown - Markdown source.
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* @param options - Optional extraction boundary.
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* @returns Plain text for the whole document, first visible line, or first semantic paragraph.
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*/
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export function extractMarkdownPlainText(
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markdown: string,
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options: MarkdownPlainTextOptions = {},
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): string {
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const { mode = 'all' } = options
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const root = fromMarkdown(markdown, {
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extensions: [gfm()],
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mdastExtensions: [gfmFromMarkdown()],
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}) as MarkdownNode
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const all = fullText(root)
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switch (mode) {
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case 'all':
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return all
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case 'first-line':
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return all.split('\n').find(line => line !== '') ?? ''
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case 'first-paragraph':
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return findFirstParagraph(root) ?? all.split('\n').find(line => line !== '') ?? ''
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}
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}
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