import type { Department } from '@/api/types'

/**
 * Tree node consumed by `<el-tree :data>`. Element Plus looks at `label` for
 * the text and `children` for sub-nodes (both configurable via props).
 */
export interface DeptTreeNode {
  dept_id: string
  label: string
  raw: Department
  children: DeptTreeNode[]
}

/**
 * Build a department forest from the backend's flat `parent_id` list.
 *
 * - Roots = departments with no `parent_id` (or whose parent is missing).
 * - Children are sorted by `path` then `dept_id` to mirror the backend ordering
 *   (the API already returns ordered by path, but orphans re-ordering is cheap
 *   insurance).
 * - Falls back gracefully on cycles / dangling parent_ids (orphans become roots
 *   rather than disappearing).
 */
export function buildDeptTree(departments: Department[]): DeptTreeNode[] {
  const nodes = new Map<string, DeptTreeNode>()
  for (const d of departments) {
    nodes.set(d.dept_id, {
      dept_id: d.dept_id,
      label: d.name?.trim() || d.dept_id,
      raw: d,
      children: [],
    })
  }

  const roots: DeptTreeNode[] = []
  for (const d of departments) {
    const node = nodes.get(d.dept_id)!
    const parent = d.parent_id ? nodes.get(d.parent_id) : undefined
    if (parent) {
      parent.children.push(node)
    } else {
      roots.push(node)
    }
  }

  const sortRec = (list: DeptTreeNode[]) => {
    list.sort((a, b) =>
      (a.raw.path ?? a.dept_id).localeCompare(b.raw.path ?? b.dept_id),
    )
    for (const n of list) sortRec(n.children)
  }
  sortRec(roots)
  return roots
}