import type { BlockView } from './types'

/**
 * 同一时刻能编辑的几段源码不重叠，同一行不会同时在两处能改：
 * ① 块编辑时，编辑范围和它重叠的子孙块不画（库规则的卡片编辑整个类，留下的方法也在这段里；
 *    一行写完的 `if x: return 1`，子块和头部在同一行），它们下面的子孙也跟着不画；
 * ② 点「编辑」时，编辑范围和这块重叠的别的块退出编辑。
 */

type Lines = Pick<BlockView, 'startLine' | 'endLine'>

function overlaps(a: Lines, b: Lines): boolean {
  return a.startLine <= b.endLine && b.startLine <= a.endLine
}

/** 正在编辑的块盖住、不画的块 → 盖住它的那块（页面上画着的、正在编辑的祖先）：跳到定义落在被盖住的块上时改闪它。 */
export function coveredByEditing(blocks: readonly BlockView[], editing: ReadonlySet<string>): Map<string, string> {
  const covered = new Map<string, string>()
  const visit = (list: readonly BlockView[], editors: readonly BlockView[], owner: string | undefined): void => {
    for (const block of list) {
      const by = owner ?? editors.find(editor => overlaps(editor, block))?.id
      if (by !== undefined) {
        covered.set(block.id, by)
        visit(block.children, editors, by)
      }
      else {
        visit(block.children, editing.has(block.id) ? [...editors, block] : editors, undefined)
      }
    }
  }
  visit(blocks, [], undefined)
  return covered
}

function* allBlocks(blocks: readonly BlockView[]): Generator<BlockView> {
  for (const block of blocks) {
    yield block
    yield* allBlocks(block.children)
  }
}

/** 点了 id 这块的「编辑」之后正在编辑的块：加上它，编辑范围和它重叠的别的块退出编辑。 */
export function startEditing(blocks: readonly BlockView[], editing: readonly string[], id: string): string[] {
  const byId = new Map([...allBlocks(blocks)].map(block => [block.id, block]))
  const target = byId.get(id)
  const others = editing.filter((other) => {
    const block = byId.get(other)
    return other !== id && !(target && block && overlaps(target, block))
  })
  return [...others, id]
}