/**
 * An object's place names another object of the same scene by its id (#258): `{"$object": "<id>"}`,
 * empty for none. Inside a container the id is the one the template gives it, so every placement of
 * the container points at its own copy – which is why a reference is looked up from where it sits.
 */
import { findAsset, type Project } from './Project';
import { treeOrder, type ObjectTree } from './hierarchy';
import { resolveObjects } from './instance';
import { isList, isStruct, type PropertyBag, type PropertyValue, tagged, tagOf, untag } from './Properties';
import type { SceneObject } from './SceneObject';
import { Recorder } from '../util/recorder';

/** The id an object's place names; '' for none and for anything that is no object's place. */
export function referencedId(value: PropertyValue | undefined): string {
  if (tagOf(value) !== 'object') return '';
  const id = untag(value);
  return typeof id === 'string' ? id : '';
}

export function objectReference(id: string): PropertyValue {
  return tagged('object', id);
}

/**
 * What a derived id (`<instance>~<path>`) has in front of the template id of its own container:
 * `inst~a/b` → `inst~a/`. A stored object has none.
 */
function scopeOf(objectId: string): string {
  const at = Math.max(objectId.lastIndexOf('/'), objectId.lastIndexOf('~'));
  return at < 0 ? '' : objectId.slice(0, at + 1);
}

/**
 * The ids `ref`, written on the object `fromId`, may stand for, nearest first: the copy in the same
 * container placement, then the id as written (a reference out of unpacked content keeps its id).
 */
export function referenceCandidates(fromId: string, ref: string): string[] {
  if (!ref) return [];
  const scope = scopeOf(fromId);
  return scope ? [scope + ref, ref] : [ref];
}

export interface ObjectChoice {
  /** What the reference stores. */
  ref: string;
  label: string;
  depth: number;
}

/**
 * What an object's place on `objectId` may name, in hierarchy order: every object of the holder,
 * or – for content of a placed container – the objects of that container, named as its template
 * names them. The object itself is one of them.
 */
export function objectChoices(project: Project, holder: ObjectTree, objectId: string): ObjectChoice[] {
  const objects = resolveObjects(project, holder);
  const stored = holder.objects.some((o) => o.id === objectId);
  const scope = stored ? '' : scopeOf(objectId);
  const choices: ObjectChoice[] = [];
  for (const { object, depth } of treeOrder({ ...holder, objects })) {
    if (!object.id.startsWith(scope)) continue;
    const label = object.name || findAsset(project, object.assetId)?.name || object.id;
    choices.push({ ref: object.id.slice(scope.length), label, depth });
  }
  if (!scope) return choices;
  // The container's own content sits one level below it in the tree.
  const top = Math.min(...choices.map((c) => c.depth));
  return choices.map((c) => ({ ...c, depth: c.depth - top }));
}

/**
 * Renames the references the objects' own values and their container edits hold, as `swap` says,
 * through `recorder` so an undo takes it back.
 */
export function swapReferences(
  objects: readonly SceneObject[],
  swap: (ref: string) => string | undefined,
  recorder: Recorder,
): void {
  const inBag = (bag: PropertyBag) => {
    for (const [key, value] of Object.entries(bag)) {
      const next = withReferences(value, swap);
      if (next !== value) recorder.set(bag, key, next);
    }
  };
  for (const object of objects) {
    inBag(object.overrides);
    for (const edit of Object.values(object.instanceEdits)) inBag(edit.overrides);
  }
}

/**
 * Spells out the references of content just written into its holder (unpacked): a template id
 * becomes the id of the copy among `objects`, so the inspector finds it among the holder's own.
 */
export function anchorReferences(objects: readonly SceneObject[]): void {
  const ids = new Set(objects.map((o) => o.id));
  for (const object of objects)
    swapReferences(
      [object],
      (ref) => referenceCandidates(object.id, ref).find((id) => ids.has(id)),
      new Recorder(),
    );
}

/**
 * `value` with every reference `swap` has an answer for renamed – '' empties it. Untouched parts
 * keep their identity, so a caller can tell whether anything changed.
 */
function withReferences(value: PropertyValue, swap: (ref: string) => string | undefined): PropertyValue {
  if (tagOf(value) === 'object') {
    const ref = referencedId(value);
    const next = ref ? swap(ref) : undefined;
    return next === undefined || next === ref ? value : objectReference(next);
  }
  if (isList(value)) {
    const items = value.map((item) => withReferences(item, swap));
    return items.some((item, i) => item !== value[i]) ? items : value;
  }
  if (isStruct(value) && tagOf(value) === undefined) {
    const entries = Object.entries(value);
    const mapped = entries.map(([key, field]) => [key, withReferences(field, swap)] as const);
    return mapped.some(([, field], i) => field !== entries[i]![1]) ? Object.fromEntries(mapped) : value;
  }
  return value;
}