export const IME_COMPOSITION_SCHEMA_VERSION = 1 as const;

export interface IMECompositionState {
  schemaVersion: typeof IME_COMPOSITION_SCHEMA_VERSION;
  composing: boolean;
  revision: number;
  pendingText: string;
  lastEvent: "IDLE" | "START" | "UPDATE" | "END";
}

export type IMECompositionEvent =
  | { type: "compositionstart"; data?: string }
  | { type: "compositionupdate"; data?: string }
  | { type: "compositionend"; data?: string };

export function createIMECompositionState(): IMECompositionState {
  return { schemaVersion: IME_COMPOSITION_SCHEMA_VERSION, composing: false, revision: 0, pendingText: "", lastEvent: "IDLE" };
}

export function reduceIMEComposition(state: IMECompositionState, event: IMECompositionEvent): IMECompositionState {
  if (!state || state.schemaVersion !== IME_COMPOSITION_SCHEMA_VERSION) throw new Error("IME_STATE_INVALID");
  const text = typeof event.data === "string" ? event.data : "";
  if (event.type === "compositionstart") return { schemaVersion: 1, composing: true, revision: state.revision + 1, pendingText: text, lastEvent: "START" };
  if (event.type === "compositionupdate") {
    if (!state.composing) return state;
    return { schemaVersion: 1, composing: true, revision: state.revision + 1, pendingText: text, lastEvent: "UPDATE" };
  }
  return { schemaVersion: 1, composing: false, revision: state.revision + 1, pendingText: text, lastEvent: "END" };
}

export function shouldBlockOperatorShortcuts(state: IMECompositionState, eventIsComposing = false): boolean {
  if (!state || state.schemaVersion !== IME_COMPOSITION_SCHEMA_VERSION) throw new Error("IME_STATE_INVALID");
  return state.composing || eventIsComposing;
}