import { type Command, CommandError } from '../core/commands/Command';
import { CommandStack } from '../core/commands/CommandStack';
import type { Asset, SceneAsset } from '../core/model/Asset';
import { findObject } from '../core/model/hierarchy';
import { resolvedHolder } from '../core/model/instance';
import {
  createEmptyProject,
  findAsset,
  findAssetOf,
  findGraphAsset,
  findObjectHolder,
  findScene,
  type Project,
  startScene,
} from '../core/model/Project';
import { deserializeProject, serializeProject } from '../core/store/serialize';
import { requestRender } from '../ui';
import { consoleLog } from './console/log';
import { type PlayFrom, settings, updateSettings } from './settings';

export type Selection =
  | { kind: 'asset'; assetId: string }
  /**
   * One or more objects of a scene or of a container's template (`holderId` names which).
   * `objectId` is the primary one (the last picked – the inspector shows it); `objectIds`
   * holds the whole selection, primary included.
   */
  | { kind: 'object'; holderId: string; objectId: string; objectIds: string[] }
  /** One or more nodes of a behavior's graph, `nodeId` being the primary one (as with objects). */
  | { kind: 'node'; assetId: string; nodeId: string; nodeIds: string[] }
  /** A frame rectangle inside a texture asset (the Texture tab). */
  | { kind: 'frame'; assetId: string; frameId: string }
  | null;

/**
 * Which list the List tab edits. Deliberately not a `Selection`: a list is not something one
 * selects, it is a value inside something already selected, and exactly three places hold one.
 * `field` names a list held by a struct field one level down; a struct item of a list needs no
 * such step, because the List tab renders it inline.
 */
export type ListSlot = { field?: string } & (
  | { kind: 'asset'; assetId: string; key: string }
  | { kind: 'object'; holderId: string; objectId: string; key: string }
  | { kind: 'node'; assetId: string; nodeId: string; key: string }
);

export function sameSlot(a: ListSlot | null, b: ListSlot | null): boolean {
  if (!a || !b) return a === b;
  if (a.field !== b.field) return false;
  switch (a.kind) {
    case 'asset':
      return b.kind === 'asset' && b.assetId === a.assetId && b.key === a.key;
    case 'object':
      return b.kind === 'object' && b.holderId === a.holderId && b.objectId === a.objectId && b.key === a.key;
    case 'node':
      return b.kind === 'node' && b.assetId === a.assetId && b.nodeId === a.nodeId && b.key === a.key;
  }
}

/** Builds an object selection; the last id is the primary one unless given explicitly. */
export function objectSelection(holderId: string, objectIds: readonly string[], primary?: string): Selection {
  const picked = pickIds(objectIds, primary);
  return picked && { kind: 'object', holderId, objectId: picked.primary, objectIds: picked.ids };
}

/** Builds a node selection; the last id is the primary one unless given explicitly. */
export function nodeSelection(assetId: string, nodeIds: readonly string[], primary?: string): Selection {
  const picked = pickIds(nodeIds, primary);
  return picked && { kind: 'node', assetId, nodeId: picked.primary, nodeIds: picked.ids };
}

function pickIds(input: readonly string[], primary?: string): { ids: string[]; primary: string } | null {
  const ids = [...new Set(input)];
  if (ids.length === 0) return null;
  return { ids, primary: primary && ids.includes(primary) ? primary : ids[ids.length - 1]! };
}

export type EditorMode = 'edit' | 'play';
export type SaveStatus = 'saved' | 'dirty' | 'saving' | 'error' | 'conflict';

export type EditorEvent =
  /** The model changed (command, undo, preview, load). */
  | 'project'
  /** A different project was loaded. */
  | 'load'
  | 'selection'
  /** The List tab was pointed at another list (or at none). */
  | 'list'
  /** An asset was opened (double-click, Enter, or just created): its tab should show. */
  | 'open'
  | 'mode'
  | 'save'
  | 'notice'
  /** The running world advanced a frame (play mode): values may have changed without a command. */
  | 'runtime';

type Listener = () => void;

/** How a notice reaches the console panel: as a line, as a red line, or not at all. */
export type NoticeLevel = 'info' | 'error' | 'quiet';

/**
 * Single source of truth for the editor. Play mode swaps `project` for a deep clone (same ids)
 * with its own undo stack; panels and commands keep working on it, and `exitPlay()` discards it.
 */
export class EditorState {
  project: Project = createEmptyProject('', 'Untitled');
  revision = 0;
  commands = new CommandStack(this.project);
  selection: Selection = null;
  listSlot: ListSlot | null = null;
  mode: EditorMode = 'edit';
  /**
   * A sub-state of play rather than a third mode: the runtime copy, the keyboard and unsaved edits all
   * still apply.
   */
  paused = false;
  saveStatus: SaveStatus = 'saved';
  /** Last user-facing message (errors, hints). */
  notice = '';
  /** The real (saved) model and its undo stack while `project` is the play-mode copy. */
  private edit: { project: Project; commands: CommandStack } | null = null;

  private readonly listeners = new Map<EditorEvent, Set<Listener>>();

  on(event: EditorEvent, listener: Listener): () => void {
    let set = this.listeners.get(event);
    if (!set) this.listeners.set(event, (set = new Set()));
    set.add(listener);
    return () => set.delete(listener);
  }

  emit(event: EditorEvent): void {
    // The one choke point every model change passes: what a listener repaints is drawn even when
    // it repaints without going through `invalidate()`.
    requestRender();
    for (const listener of this.listeners.get(event) ?? []) listener();
  }

  loadProject(project: Project, revision: number): void {
    this.edit = null;
    this.mode = 'edit';
    this.paused = false;
    this.project = project;
    this.revision = revision;
    this.commands = new CommandStack(project);
    this.selection = null;
    this.listSlot = null;
    this.saveStatus = 'saved';
    this.emit('load');
    this.emit('project');
    this.emit('selection');
    this.emit('save');
    this.emit('mode');
  }

  /** Returns the runtime copy; the selection survives because ids are identical. */
  enterPlay(): Project {
    if (this.mode === 'play') return this.project;
    const copy = deserializeProject(serializeProject(this.project), this.project.id);
    this.edit = { project: this.project, commands: this.commands };
    this.project = copy;
    this.commands = new CommandStack(copy);
    this.mode = 'play';
    this.paused = false;
    this.emit('mode');
    this.emit('project');
    return copy;
  }

  /** Ignored outside play mode. */
  setPaused(paused: boolean): void {
    if (this.mode !== 'play' || this.paused === paused) return;
    this.paused = paused;
    this.emit('mode');
  }

  exitPlay(): void {
    if (this.mode !== 'play') return;
    if (this.edit) {
      this.project = this.edit.project;
      this.commands = this.edit.commands;
      this.edit = null;
    }
    this.mode = 'edit';
    this.paused = false;
    this.emit('mode');
    this.emit('project');
    this.validateSelection();
    // A save postponed while playing runs now.
    this.emit('save');
  }

  get activeScene(): SceneAsset | undefined {
    return findScene(this.project, this.project.activeSceneId);
  }

  /** The play-mode copy while a run is on, else null – what a scene swap rebuilds its world from. */
  get runtimeProject(): Project | null {
    return this.mode === 'play' ? this.project : null;
  }

  /**
   * Which scene Play builds its world from. Two answers rather than one, because the project has
   * two: where the game begins, and what you are working on this minute. The switch says which
   * question Play is asking; without a start scene the two are the same thing anyway.
   */
  sceneToPlay(): SceneAsset | undefined {
    return this.playFrom === 'active' ? this.activeScene : startScene(this.project);
  }

  get playFrom(): PlayFrom {
    return settings().playFrom;
  }

  setPlayFrom(playFrom: PlayFrom): void {
    if (playFrom === this.playFrom) return;
    updateSettings({ playFrom });
    this.emit('mode');
  }

  /**
   * Runs a command through the undo stack. Returns false (and sets a notice) when invalid.
   * In play mode the command changes the runtime copy only (see `enterPlay`).
   */
  execute(command: Command): boolean {
    return this.runEdit(() => {
      this.commands.execute(command);
      return true;
    });
  }

  undo(): void {
    this.runEdit(() => this.commands.undo());
  }

  redo(): void {
    this.runEdit(() => this.commands.redo());
  }

  /**
   * Runs one history operation. A `CommandError` is a command rejecting the edit, so it becomes
   * a notice; anything else is a real defect and keeps travelling.
   */
  private runEdit(operation: () => boolean): boolean {
    try {
      if (!operation()) return false;
    } catch (error) {
      if (error instanceof CommandError) {
        this.setNotice(error.message);
        return false;
      }
      throw error;
    }
    this.markDirty();
    return true;
  }

  /**
   * The model was mutated directly (live preview while scrubbing). Notifies listeners
   * but does not touch the undo stack or the save status – the committing command does.
   */
  preview(): void {
    this.emit('project');
  }

  /** The world ticked: panels showing live values refresh (no model event, nothing to save). */
  runtimeTick(): void {
    this.emit('runtime');
  }

  /**
   * A behavior running outside play mode (see `EditorRun`) wrote into the saved model. The change
   * is saved like any other, but nothing was pushed onto the undo stack – it cannot be undone.
   */
  runtimeEdit(): void {
    this.setSaveStatus('dirty');
    this.emit('runtime');
  }

  private markDirty(): void {
    this.validateSelection();
    // Play-mode edits live in the runtime copy and are never saved.
    if (this.mode === 'edit') this.saveStatus = 'dirty';
    this.emit('project');
    this.emit('save');
  }

  /**
   * Points the List tab at a list. No tab knows the `Editor`, so this is how the button on a
   * list row gets there: the state changes, the editor switches.
   */
  openList(slot: ListSlot | null): void {
    if (sameSlot(this.listSlot, slot)) {
      if (slot) this.emit('list');
      return;
    }
    this.listSlot = slot;
    this.emit('list');
  }

  /**
   * Selects the asset and asks for its tab. Selecting alone never switches tabs (a click in the
   * Assets panel is a look at the inspector); this is the way a double-click or a fresh asset gets
   * there, and like `openList` it works without knowing the `Editor`.
   */
  openAsset(assetId: string): void {
    this.select({ kind: 'asset', assetId });
    this.emit('open');
  }

  select(selection: Selection): void {
    // Test hooks pass the short form `{ kind: 'object', holderId, objectId }` without `objectIds`.
    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
    if (selection?.kind === 'object' && !selection.objectIds)
      selection = objectSelection(selection.holderId, [selection.objectId]);
    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
    if (selection?.kind === 'node' && !selection.nodeIds)
      selection = nodeSelection(selection.assetId, [selection.nodeId]);
    if (sameSelection(this.selection, selection)) return;
    this.selection = selection;
    this.emit('selection');
  }

  toggleObject(holderId: string, objectId: string): void {
    const s = this.selection;
    const current = s?.kind === 'object' && s.holderId === holderId ? s.objectIds : [];
    const next = current.includes(objectId)
      ? current.filter((id) => id !== objectId)
      : [...current, objectId];
    this.select(objectSelection(holderId, next, current.includes(objectId) ? undefined : objectId));
  }

  toggleNode(assetId: string, nodeId: string): void {
    const s = this.selection;
    const current = s?.kind === 'node' && s.assetId === assetId ? s.nodeIds : [];
    const held = current.includes(nodeId);
    const next = held ? current.filter((id) => id !== nodeId) : [...current, nodeId];
    // Emptied by the toggle, the behavior itself stays selected – the graph must not close.
    this.select(nodeSelection(assetId, next, held ? undefined : nodeId) ?? { kind: 'asset', assetId });
  }

  get selectedObjectIds(): string[] {
    return this.selection?.kind === 'object' ? this.selection.objectIds : [];
  }

  get selectedNodeIds(): string[] {
    return this.selection?.kind === 'node' ? this.selection.nodeIds : [];
  }

  /** Drops selected targets that no longer exist (after delete/undo). */
  private validateSelection(): void {
    const s = this.selection;
    if (!s) return;
    if (s.kind === 'asset' && !findAsset(this.project, s.assetId)) this.select(null);
    if (s.kind === 'object') {
      const holder = findObjectHolder(this.project, s.holderId);
      const view = holder && resolvedHolder(this.project, holder);
      const alive = view ? s.objectIds.filter((id) => findObject(view, id)) : [];
      if (alive.length !== s.objectIds.length) this.select(objectSelection(s.holderId, alive, s.objectId));
    }
    if (s.kind === 'node') {
      const asset = findGraphAsset(this.project, s.assetId);
      // Fall back to the asset so the graph stays open when its node vanished (undo).
      if (!asset) this.select(null);
      else {
        const alive = s.nodeIds.filter((id) => asset.graph.nodes.some((n) => n.id === id));
        if (alive.length !== s.nodeIds.length)
          this.select(nodeSelection(s.assetId, alive, s.nodeId) ?? { kind: 'asset', assetId: s.assetId });
      }
    }
    if (s.kind === 'frame') {
      const asset = findAssetOf(this.project, s.assetId, 'texture');
      // Same fallback as a graph node: the texture stays open when its frame vanished.
      if (!asset) this.select(null);
      else if (!asset.frames.some((f) => f.id === s.frameId))
        this.select({ kind: 'asset', assetId: s.assetId });
    }
  }

  /** The texture asset the current selection refers to (the asset itself or one of its frames). */
  get selectedTextureId(): string | null {
    const s = this.selection;
    if (!s) return null;
    if (s.kind !== 'asset' && s.kind !== 'frame') return null;
    return findAssetOf(this.project, s.assetId, 'texture')?.id ?? null;
  }

  get selectedAnimationId(): string | null {
    const s = this.selection;
    return s?.kind === 'asset' ? (findAssetOf(this.project, s.assetId, 'animation')?.id ?? null) : null;
  }

  /** The behavior asset the current selection refers to (asset, placed object or node), if any. */
  get selectedBehaviorId(): string | null {
    return this.selectedGraphId('behavior');
  }

  /** The state machine the current selection refers to: the asset, or one of its states. */
  get selectedStateMachineId(): string | null {
    return this.selectedGraphId('statemachine');
  }

  /** The shader the current selection refers to: the asset, or one of its nodes. */
  get selectedShaderId(): string | null {
    return this.selectedGraphId('shader');
  }

  /** The particle asset the selection refers to: the asset, a placed source, or one of its nodes. */
  get selectedParticlesId(): string | null {
    return this.selectedGraphId('particles');
  }

  private selectedGraphId(type: 'behavior' | 'statemachine' | 'shader' | 'particles'): string | null {
    const s = this.selection;
    if (!s) return null;
    if (s.kind === 'frame') return null;
    // A node names its asset; which tab that is depends on what the asset is.
    const asset = s.kind === 'node' ? findAsset(this.project, s.assetId) : this.assetBehind(s);
    return asset && asset.type === type ? asset.id : null;
  }

  /**
   * The container the current selection refers to: the asset itself, a placed container, or the
   * template being edited – selecting one of its objects keeps the Container tab on it.
   */
  get selectedContainerId(): string | null {
    const s = this.selection;
    if (!s) return null;
    if (s.kind === 'object' && findAsset(this.project, s.holderId)?.type === 'container') return s.holderId;
    const asset = this.assetBehind(s);
    return asset && asset.type === 'container' ? asset.id : null;
  }

  /** The asset a selection stands for: itself, or the one a selected object was placed from. */
  private assetBehind(s: NonNullable<Selection>): Asset | undefined {
    if (s.kind === 'asset') return findAsset(this.project, s.assetId);
    if (s.kind !== 'object') return undefined;
    const holder = findObjectHolder(this.project, s.holderId);
    const view = holder && resolvedHolder(this.project, holder);
    const assetId = view && findObject(view, s.objectId)?.assetId;
    return assetId ? findAsset(this.project, assetId) : undefined;
  }

  setSaveStatus(status: SaveStatus): void {
    if (this.saveStatus === status) return;
    this.saveStatus = status;
    this.emit('save');
  }

  /**
   * Shows `message` in the toolbar and, unless `quiet`, keeps it in the console panel. Quiet is
   * for the play status lines, which state a mode rather than report an event.
   */
  setNotice(message: string, level: NoticeLevel = 'info'): void {
    this.notice = message;
    if (message !== '' && level !== 'quiet') consoleLog.push(level, message);
    this.emit('notice');
  }
}

/** Whether two selections mean the same thing (same kind, same ids, same order). */
export function sameSelection(a: Selection, b: Selection): boolean {
  if (a === b) return true;
  if (!a || !b || a.kind !== b.kind) return false;
  if (a.kind === 'asset' && b.kind === 'asset') return a.assetId === b.assetId;
  if (a.kind === 'object' && b.kind === 'object') {
    return (
      a.holderId === b.holderId &&
      a.objectId === b.objectId &&
      a.objectIds.length === b.objectIds.length &&
      a.objectIds.every((id, i) => id === b.objectIds[i])
    );
  }
  if (a.kind === 'node' && b.kind === 'node') {
    return (
      a.assetId === b.assetId &&
      a.nodeId === b.nodeId &&
      a.nodeIds.length === b.nodeIds.length &&
      a.nodeIds.every((id, i) => id === b.nodeIds[i])
    );
  }
  if (a.kind === 'frame' && b.kind === 'frame') return a.assetId === b.assetId && a.frameId === b.frameId;
  return false;
}