Part the source into adf/ and markdown/ ahead of the parser

src/markdown/emit/image.ts

@@ -0,0 +1,27 @@
+import type { AdfNode } from '../../adf/document.ts'
+import { carriesOnly } from '../../adf/document.ts'
+import type { ConvertErrorPath } from '../../result.ts'
+import { serializeCanonicalJson } from '../../canonical-json.ts'
+import { tryImageLine } from './inline-line.ts'
+
+const centeredMediaSingle = '{"layout":"center"}'
+const imageAttributes = ['alt', 'type', 'url']
+
+export function tryImage(node: AdfNode, path: ConvertErrorPath): string | undefined {
+  const image = imageShape(node)
+  if (image === undefined) return undefined
+  return tryImageLine(image.alt, image.url, [...path, 'content', 0])
+}
+
+function imageShape(node: AdfNode): { alt: string | undefined; url: string } | undefined {
+  const content = node.content ?? []
+  const media = content[0]
+  if (!carriesOnly(node, ['layout']) || serializeCanonicalJson(node.attrs ?? {}, 'compact') !== centeredMediaSingle) return undefined
+  if (media === undefined || content.length !== 1 || media.type !== 'media' || !carriesOnly(media, imageAttributes) || (media.content ?? []).length > 0) return undefined
+  const attrs = media.attrs ?? {}
+  const alt = attrs['alt']
+  const url = attrs['url']
+  if (attrs['type'] !== 'external' || typeof url !== 'string') return undefined
+  if (alt !== undefined && (typeof alt !== 'string' || alt === '')) return undefined
+  return { alt, url }
+}