/**
 * A placed container's content is resolved from its template on every read. Per-instance changes live
 * in sparse `instanceEdits` keyed by template-id path; derived ids `<instance>~<path>` are never stored.
 */
import type { ContainerAsset } from './Asset';
import { groupedOrder, type ObjectTree } from './hierarchy';
import {
  type Axis,
  type Position,
  type PropertyBag,
  type PropertyValue,
  sameValue,
  setBagValue,
  type Vec2,
} from './Properties';
import { findAssetOf, type ObjectHolder, objectHolders, type Project } from './Project';
import type { SceneObject } from './SceneObject';

/** Neither character can occur inside an id (see `newId`), so a derived id parses back uniquely. */
const ID_SEP = '~';
const PATH_SEP = '/';

/** A container inside a container inside … – the same guard `instantiate` needs against cycles. */
const MAX_NESTING = 8;

const AXES: readonly Axis[] = ['x', 'y', 'z'];

/** Sparse deviations of one resolved object; everything absent follows the template. */
export interface InstanceEdit {
  name?: string;
  position: Partial<Record<Axis, number>>;
  editorOffset?: Vec2;
  overrides: PropertyBag;
}

export function emptyEdit(): InstanceEdit {
  return { position: {}, overrides: {} };
}

export function isEmptyEdit(edit: InstanceEdit): boolean {
  return (
    edit.name === undefined &&
    edit.editorOffset === undefined &&
    Object.keys(edit.position).length === 0 &&
    Object.keys(edit.overrides).length === 0
  );
}

function copyEdit(edit: InstanceEdit): InstanceEdit {
  return {
    ...(edit.name === undefined ? {} : { name: edit.name }),
    ...(edit.editorOffset === undefined ? {} : { editorOffset: { ...edit.editorOffset } }),
    position: { ...edit.position },
    overrides: { ...edit.overrides },
  };
}

/** The outer edit wins per field and per key; anything it leaves out keeps the inner value. */
function mergeEdits(
  inner: InstanceEdit | undefined,
  outer: InstanceEdit | undefined,
): InstanceEdit | undefined {
  if (!inner) return outer;
  if (!outer) return inner;
  return {
    name: outer.name ?? inner.name,
    editorOffset: outer.editorOffset ?? inner.editorOffset,
    position: { ...inner.position, ...outer.position },
    overrides: { ...inner.overrides, ...outer.overrides },
  };
}

function containerAssetOf(project: Project, object: SceneObject): ContainerAsset | undefined {
  return findAssetOf(project, object.assetId, 'container');
}

/**
 * The placed containers still showing their template, with the asset behind each. Content spelled
 * out in the holder means the instance was unpacked (or baked for a play run) and is an ordinary
 * parent from then on.
 */
function liveInstances(project: Project, holder: ObjectTree): Map<SceneObject, ContainerAsset> {
  const parents = new Set(holder.objects.map((o) => o.parentId));
  const live = new Map<SceneObject, ContainerAsset>();
  for (const object of holder.objects) {
    if (parents.has(object.id)) continue;
    const asset = containerAssetOf(project, object);
    if (asset) live.set(object, asset);
  }
  return live;
}

export function isLiveInstance(project: Project, holder: ObjectTree, object: SceneObject): boolean {
  return liveInstances(project, holder).has(object);
}

export function instanceChildId(instanceId: string, path: string): string {
  return `${instanceId}${ID_SEP}${path}`;
}

/** Splits a derived id back into the instance it belongs to and the template path below it. */
export function splitInstanceId(id: string): { instanceId: string; path: string } | undefined {
  const at = id.indexOf(ID_SEP);
  if (at < 0) return undefined;
  return { instanceId: id.slice(0, at), path: id.slice(at + 1) };
}

/** The template path an id of a holder's own view stands for once the holder is placed: `q~x` → `q/x`. */
export function pathOfId(id: string): string {
  return id.replace(ID_SEP, PATH_SEP);
}

/** The id a holder's own view gives the object at a template path: `q/x` → `q~x`. */
export function idOfPath(path: string): string {
  return path.replace(PATH_SEP, ID_SEP);
}

/**
 * Whether the object is only resolved from a template rather than stored in the holder. The
 * question is where it lives, not what its id looks like: unpacking keeps the derived id – so the
 * selection and the running game survive it – and the object is an ordinary one from then on.
 */
export function isTemplateContent(holder: ObjectTree, objectId: string): boolean {
  return !holder.objects.some((o) => o.id === objectId);
}

function resolveChild(
  template: SceneObject,
  edit: InstanceEdit | undefined,
  id: string,
  parentId: string,
): SceneObject {
  const position = { ...template.position };
  for (const axis of AXES) {
    const own = edit?.position[axis];
    if (own !== undefined) position[axis] = own;
  }
  return {
    id,
    assetId: template.assetId,
    name: edit?.name ?? template.name,
    position,
    editorOffset: edit?.editorOffset ? { ...edit.editorOffset } : { x: 0, y: 0 },
    overrides: { ...template.overrides, ...edit?.overrides },
    parentId,
    instanceEdits: {},
  };
}

function expand(
  project: Project,
  asset: ContainerAsset,
  instanceId: string,
  prefix: string,
  editAt: (path: string) => InstanceEdit | undefined,
  rootParentId: string,
  depth: number,
  out: SceneObject[],
): void {
  // In the order the template lists its top level, groups together, so equal `z` ties the same way.
  for (const template of groupedOrder(asset.objects)) {
    const path = prefix ? `${prefix}${PATH_SEP}${template.id}` : template.id;
    const id = instanceChildId(instanceId, path);
    const parentId = template.parentId
      ? instanceChildId(instanceId, prefix ? `${prefix}${PATH_SEP}${template.parentId}` : template.parentId)
      : rootParentId;
    out.push(resolveChild(template, editAt(path), id, parentId));
    const nested = containerAssetOf(project, template);
    const spelledOut = asset.objects.some((o) => o.parentId === template.id);
    if (!nested || spelledOut || depth >= MAX_NESTING) continue;
    // The template object's own edits are the base, the outer instance's edits sit on top of them.
    // `editAt` always takes the full path; the base is keyed relative to the nested container.
    const own = template.instanceEdits;
    const below = (full: string) => mergeEdits(own[full.slice(path.length + 1)], editAt(full));
    expand(project, nested, instanceId, path, below, id, depth + 1, out);
  }
}

/**
 * The holder's objects with the content of every live container instance woven in. Stored objects
 * are passed through by reference – only instance content is freshly built and must not be written
 * to (see `objectRef`). Without a live instance the stored list is returned unchanged.
 */
export function resolveObjects(project: Project, holder: ObjectTree): SceneObject[] {
  const live = liveInstances(project, holder);
  if (live.size === 0) return holder.objects;
  const out: SceneObject[] = [];
  for (const object of holder.objects) {
    out.push(object);
    const asset = live.get(object);
    if (asset) expand(project, asset, object.id, '', (p) => object.instanceEdits[p], object.id, 0, out);
  }
  return out;
}

/** The holder with its resolved objects – a read-only view for anything that walks the tree. */
export function resolvedHolder(project: Project, holder: ObjectHolder): ObjectHolder {
  const objects = resolveObjects(project, holder);
  return objects === holder.objects ? holder : { ...holder, objects };
}

export interface InstanceTarget {
  /** The stored container object the edits live on. */
  instance: SceneObject;
  path: string;
  /** The container asset that declares `template` – the one to open to change it for good. */
  asset: ContainerAsset;
  template: SceneObject;
  /**
   * The template with the edits of every container in between woven in – this, not `template`, decides
   * whether an edit deviates. Built fresh on every read, since "apply" writes into `template` first.
   */
  readonly base: SceneObject;
}

/** Where a derived id points: the instance holding the edits, and the template object behind it. */
export function instanceTargetOf(
  project: Project,
  holder: ObjectTree,
  objectId: string,
): InstanceTarget | undefined {
  if (!isTemplateContent(holder, objectId)) return undefined;
  const split = splitInstanceId(objectId);
  const instance = split && holder.objects.find((o) => o.id === split.instanceId);
  if (!split || !instance) return undefined;
  const segments = split.path.split(PATH_SEP);
  let asset = containerAssetOf(project, instance);
  let template: SceneObject | undefined;
  // Each container on the way holds edits for what lies below it, keyed relative to itself.
  const between: { holder: SceneObject; key: string }[] = [];
  for (const [index, segment] of segments.entries()) {
    const next = template ? containerAssetOf(project, template) : asset;
    if (!next) return undefined;
    asset = next;
    template = next.objects.find((t) => t.id === segment);
    if (!template) return undefined;
    if (index < segments.length - 1)
      between.push({ holder: template, key: segments.slice(index + 1).join(PATH_SEP) });
  }
  if (!asset || !template) return undefined;
  const leaf = template;
  return {
    instance,
    path: split.path,
    asset,
    template: leaf,
    get base() {
      let edit: InstanceEdit | undefined;
      // Outermost wins, as in `expand`: it sits closest to the instance being edited.
      for (let i = between.length - 1; i >= 0; i--)
        edit = mergeEdits(edit, between[i]!.holder.instanceEdits[between[i]!.key]);
      return resolveChild(leaf, edit, leaf.id, leaf.parentId);
    },
  };
}

/**
 * Read/write access to a placed object, whether it is stored in the holder or resolved from a
 * container template. `object` is the current state either way; the setters keep an instance edit
 * to exactly what deviates from the template, so a value put back to the template's follows again.
 */
export interface ObjectRef {
  readonly object: SceneObject;
  /** The instance edits belong to, undefined for a stored object. */
  readonly target: InstanceTarget | undefined;
  setName(name: string): void;
  setPosition(position: Position): void;
  setEditorOffset(offset: Vec2): void;
  setOverride(key: string, value: PropertyValue | undefined): void;
}

function editOf(target: InstanceTarget): InstanceEdit {
  const existing = target.instance.instanceEdits[target.path];
  if (existing) return existing;
  const edit = emptyEdit();
  target.instance.instanceEdits[target.path] = edit;
  return edit;
}

function prune(target: InstanceTarget): void {
  const edit = target.instance.instanceEdits[target.path];
  if (edit && isEmptyEdit(edit)) delete target.instance.instanceEdits[target.path];
}

function instanceRef(target: InstanceTarget, object: SceneObject): ObjectRef {
  const write = (mutate: (edit: InstanceEdit) => void): void => {
    mutate(editOf(target));
    prune(target);
  };
  return {
    object,
    target,
    setName: (name) =>
      write((edit) => {
        if (name === target.base.name) delete edit.name;
        else edit.name = name;
      }),
    setPosition: (position) =>
      write((edit) => {
        for (const axis of AXES) {
          if (position[axis] === target.base.position[axis]) delete edit.position[axis];
          else edit.position[axis] = position[axis];
        }
      }),
    setEditorOffset: (offset) =>
      write((edit) => {
        if (offset.x === 0 && offset.y === 0) delete edit.editorOffset;
        else edit.editorOffset = { x: offset.x, y: offset.y };
      }),
    setOverride: (key, value) =>
      write((edit) => {
        if (sameValue(value, target.base.overrides[key])) delete edit.overrides[key];
        else setBagValue(edit.overrides, key, value);
      }),
  };
}

function storedRef(object: SceneObject): ObjectRef {
  return {
    object,
    target: undefined,
    setName: (name) => {
      object.name = name;
    },
    setPosition: (position) => {
      object.position = { ...position };
    },
    setEditorOffset: (offset) => {
      object.editorOffset = { x: offset.x, y: offset.y };
    },
    setOverride: (key, value) => setBagValue(object.overrides, key, value),
  };
}

export function objectRef(project: Project, holder: ObjectTree, objectId: string): ObjectRef | undefined {
  const stored = holder.objects.find((o) => o.id === objectId);
  if (stored) return storedRef(stored);
  const target = instanceTargetOf(project, holder, objectId);
  const object = resolveObjects(project, holder).find((o) => o.id === objectId);
  return target && object ? instanceRef(target, object) : undefined;
}

/** Everything a value edit can change, snapshotted so a command can put it back exactly. */
export type ObjectMemo =
  | {
      kind: 'stored';
      object: SceneObject;
      name: string;
      position: Position;
      editorOffset: Vec2;
      overrides: PropertyBag;
    }
  | { kind: 'edit'; instance: SceneObject; path: string; edit: InstanceEdit | undefined };

export function captureObject(ref: ObjectRef): ObjectMemo {
  if (ref.target) {
    const edit = ref.target.instance.instanceEdits[ref.target.path];
    return {
      kind: 'edit',
      instance: ref.target.instance,
      path: ref.target.path,
      edit: edit && copyEdit(edit),
    };
  }
  const { object } = ref;
  return {
    kind: 'stored',
    object,
    name: object.name,
    position: { ...object.position },
    editorOffset: { ...object.editorOffset },
    overrides: { ...object.overrides },
  };
}

export function restoreObject(memo: ObjectMemo): void {
  if (memo.kind === 'edit') {
    if (memo.edit) memo.instance.instanceEdits[memo.path] = copyEdit(memo.edit);
    else delete memo.instance.instanceEdits[memo.path];
    return;
  }
  memo.object.name = memo.name;
  memo.object.position = { ...memo.position };
  memo.object.editorOffset = { ...memo.editorOffset };
  memo.object.overrides = { ...memo.overrides };
}

/**
 * One sparse override bag with the asset whose schema governs it: a placed object's own, or a container
 * instance's edits for its content. Project-wide rewrites must cover both or they miss container content.
 */
export interface OverrideSite {
  holder: ObjectHolder;
  /** The stored object the bag lives on – the placed object itself, or the container instance. */
  object: SceneObject;
  /** Template path inside `object`; empty when the bag is the object's own overrides. */
  path: string;
  assetId: string;
  bag: PropertyBag;
}

export function overrideSites(project: Project, wanted: (assetId: string) => boolean): OverrideSite[] {
  const sites: OverrideSite[] = [];
  for (const holder of objectHolders(project)) {
    for (const object of holder.objects) {
      if (wanted(object.assetId))
        sites.push({ holder, object, path: '', assetId: object.assetId, bag: object.overrides });
      for (const [path, edit] of Object.entries(object.instanceEdits)) {
        const target = instanceTargetOf(project, holder, instanceChildId(object.id, path));
        if (target && wanted(target.template.assetId))
          sites.push({ holder, object, path, assetId: target.template.assetId, bag: edit.overrides });
      }
    }
  }
  return sites;
}

/**
 * The resolved content of an instance as objects that can be stored. The derived ids are kept:
 * they are unique already, and anything pointing at one – the selection, a running game, a check
 * script – keeps working across the unpack.
 */
export function materializeInstance(
  project: Project,
  holder: ObjectTree,
  instance: SceneObject,
): SceneObject[] {
  return resolveObjects(project, holder)
    .filter((o) => splitInstanceId(o.id)?.instanceId === instance.id)
    .map((o) => ({
      ...o,
      position: { ...o.position },
      editorOffset: { ...o.editorOffset },
      overrides: { ...o.overrides },
      instanceEdits: {},
    }));
}

/**
 * The id the object at `path` below `ownerId` has – one level deeper when the owner is content
 * itself, so the content of `q~a` is `q~a/b`, the id a template path through nested containers gives.
 */
export function contentId(ownerId: string, path: string): string {
  const split = splitInstanceId(ownerId);
  return split
    ? instanceChildId(split.instanceId, `${split.path}${PATH_SEP}${path}`)
    : instanceChildId(ownerId, path);
}

/**
 * `object` as `id` below `parentId`, followed by its container content with the ids below that one –
 * how a composition puts its objects into a scene (#417). Copies, free to be stored and written to.
 */
export function placedWithContent(
  project: Project,
  object: SceneObject,
  id: string,
  parentId: string,
): SceneObject[] {
  const rename = (at: string) => (at === object.id ? id : contentId(id, at.slice(object.id.length + 1)));
  const { groupId: _, ...top } = object;
  return resolveObjects(project, { objects: [{ ...top, parentId: '' }] }).map((o) => ({
    ...o,
    id: rename(o.id),
    parentId: o.id === object.id ? parentId : rename(o.parentId),
    position: { ...o.position },
    editorOffset: { ...o.editorOffset },
    overrides: { ...o.overrides },
    instanceEdits: {},
  }));
}

/**
 * Spells out every live instance of the holder. The runtime needs it: entities are built from
 * stored objects, and a behavior may destroy or move one of them – which a resolved copy could
 * not remember. Returns true when something was written.
 */
export function bakeInstances(project: Project, holder: ObjectTree): boolean {
  const parents = new Set(holder.objects.map((o) => o.parentId));
  const live = holder.objects.filter((o) => !parents.has(o.id) && containerAssetOf(project, o) !== undefined);
  if (live.length === 0) return false;
  for (const instance of live) {
    holder.objects.push(...materializeInstance(project, holder, instance));
    instance.instanceEdits = {};
  }
  return true;
}