import { Plugin } from 'prosemirror-state';
import { Slice, Fragment, Node as PMNode } from 'prosemirror-model';

/** Flattens a multi-block document into a single paragraph, keeping marks. */
export function flattenToSingleParagraph(doc: PMNode): PMNode {
  if (doc.childCount <= 1) return doc;
  const schema = doc.type.schema;
  const inline: PMNode[] = [];
  doc.descendants(node => {
    if (node.isInline) {
      if (node.type === schema.nodes.hard_break) return false;
      inline.push(node);
      return false;
    }
    return true;
  });
  return schema.nodes.doc.create(null, schema.nodes.paragraph.create(null, inline));
}

/**
 * Constrains the document to a single paragraph: Enter is inert, pasted
 * multi-block content is flattened to one line, and any transaction that
 * would still produce extra blocks is rejected.
 */
export function singleLinePlugin(): Plugin {
  return new Plugin({
    filterTransaction(tr) {
      return !tr.docChanged || tr.doc.childCount <= 1;
    },
    props: {
      handleKeyDown(_view, event) {
        return event.key === 'Enter';
      },
      transformPasted(slice) {
        const inline: PMNode[] = [];
        slice.content.descendants(node => {
          if (node.isInline) {
            inline.push(node);
            return false;
          }
          return true;
        });
        return new Slice(Fragment.from(inline), 0, 0);
      },
    },
  });
}