/**
 * How long a shared value lives. `local` is one per behavior instance, `global` one for the whole
 * run, `scene` one per scene: rebuilt from the declarations whenever a scene is loaded, so what a
 * level counts is gone with the level while a score is not (#164).
 *
 * Everything was `local` before scopes existed, so a missing field means `local` and old projects
 * load unchanged. Variables are shared by living on a Variables asset instead (#91) – that asset is
 * shared by its nature, so a missing field means `global` there (see `sharedScopeOf`).
 */
export type Scope = 'local' | 'global' | 'scene';

/** The scopes of something that is shared either way: a Variables asset has no `local`. */
export type SharedScope = 'global' | 'scene';

export interface Scoped {
  scope?: Scope;
}

export function scopeOf(owner: Scoped): Scope {
  if (owner.scope === 'global') return 'global';
  return owner.scope === 'scene' ? 'scene' : 'local';
}

/** Whether the value is shared at all: both `global` and `scene` are one value for many instances. */
export function isShared(owner: Scoped): boolean {
  return owner.scope === 'global' || owner.scope === 'scene';
}

/** Whether a scene swap rebuilds the value instead of handing it over. */
export function isPerScene(owner: Scoped): boolean {
  return owner.scope === 'scene';
}

/** Reads a scope out of loaded data, where anything but the two known words means `local`. */
export function readScope(raw: unknown): Scope {
  if (raw === 'global') return 'global';
  return raw === 'scene' ? 'scene' : 'local';
}

/** Keeps `local` out of the document: the field is present only when it says more than that. */
export function setScope(owner: Scoped, scope: Scope): void {
  if (scope === 'local') delete owner.scope;
  else owner.scope = scope;
}

/** The scope of something shared by nature, where a missing field is `global` rather than `local`. */
export function sharedScopeOf(owner: Scoped): SharedScope {
  return owner.scope === 'scene' ? 'scene' : 'global';
}

/** Reads the scope of something shared by nature out of loaded data. */
export function readSharedScope(raw: unknown): SharedScope {
  return raw === 'scene' ? 'scene' : 'global';
}

/** Keeps the default out of the document the other way round: only `scene` is written. */
export function setSharedScope(owner: Scoped, scope: SharedScope): void {
  if (scope === 'scene') owner.scope = 'scene';
  else delete owner.scope;
}