export type SessionRunQueuedPrompt = {
  id: string;
  text: string;
};

export type SessionRunPhase = 'idle' | 'posting' | 'running' | 'aborting';

export type SessionRunTerminalReason = 'completed' | 'aborted' | 'failed';

export type SessionRunState<TPrompt extends SessionRunQueuedPrompt = SessionRunQueuedPrompt> = {
  phase: SessionRunPhase;
  runId: number | null;
  promptId: string | null;
  queue: TPrompt[];
  terminalReason: SessionRunTerminalReason | null;
  error: string | null;
  suppressNextAbortError: boolean;
};

export type SessionRunEvent<TPrompt extends SessionRunQueuedPrompt = SessionRunQueuedPrompt> =
  | { type: 'send_started'; runId: number; promptId: string }
  | { type: 'post_accepted'; runId: number }
  | { type: 'remote_busy'; runId: number }
  | { type: 'remote_idle'; runId: number }
  | { type: 'remote_aborted'; runId: number }
  | { type: 'remote_failed'; runId: number; error: string }
  | { type: 'abort_requested'; runId: number }
  | { type: 'abort_confirmed'; runId: number }
  | { type: 'abort_failed'; runId: number; error: string }
  | { type: 'queue_prompt'; prompt: TPrompt }
  | { type: 'cancel_queued_prompt'; promptId: string };

export function createIdleSessionRunState<TPrompt extends SessionRunQueuedPrompt>(
  queue: TPrompt[] = [],
): SessionRunState<TPrompt> {
  return {
    phase: 'idle',
    runId: null,
    promptId: null,
    queue,
    terminalReason: null,
    error: null,
    suppressNextAbortError: false,
  };
}

export function isCurrentRunEvent<TPrompt extends SessionRunQueuedPrompt>(
  state: SessionRunState<TPrompt>,
  runId: number,
): boolean {
  return state.runId === runId;
}

export function isSessionRunActive<TPrompt extends SessionRunQueuedPrompt>(
  state: SessionRunState<TPrompt>,
): boolean {
  return state.phase === 'posting' || state.phase === 'running';
}

export function canStartQueuedPrompt<TPrompt extends SessionRunQueuedPrompt>(
  state: SessionRunState<TPrompt>,
): boolean {
  return state.phase === 'idle'
    && state.terminalReason !== 'failed'
    && state.queue.length > 0;
}

export function takeNextQueuedPrompt<TPrompt extends SessionRunQueuedPrompt>(
  state: SessionRunState<TPrompt>,
): {
  prompt: TPrompt | null;
  state: SessionRunState<TPrompt>;
} {
  const [prompt, ...queue] = state.queue;
  return {
    prompt: prompt ?? null,
    state: {
      ...state,
      queue,
    },
  };
}

export function didSuppressAbortError<TPrompt extends SessionRunQueuedPrompt>(
  previousState: SessionRunState<TPrompt>,
  nextState: SessionRunState<TPrompt>,
): boolean {
  return previousState.suppressNextAbortError
    && !nextState.suppressNextAbortError
    && previousState.phase === nextState.phase
    && previousState.runId === nextState.runId
    && previousState.promptId === nextState.promptId
    && nextState.terminalReason === previousState.terminalReason
    && nextState.error === null;
}

export function transitionSessionRunState<TPrompt extends SessionRunQueuedPrompt>(
  state: SessionRunState<TPrompt>,
  event: SessionRunEvent<TPrompt>,
): SessionRunState<TPrompt> {
  if (event.type === 'send_started') {
    return {
      phase: 'posting',
      runId: event.runId,
      promptId: event.promptId,
      queue: state.queue,
      terminalReason: null,
      error: null,
      suppressNextAbortError: state.suppressNextAbortError,
    };
  }

  if (event.type === 'queue_prompt') {
    return {
      ...state,
      queue: [...state.queue, event.prompt],
      error: null,
    };
  }

  if (event.type === 'cancel_queued_prompt') {
    return {
      ...state,
      queue: state.queue.filter((prompt) => prompt.id !== event.promptId),
    };
  }

  if (!isCurrentRunEvent(state, event.runId)) {
    return state;
  }

  if (
    state.phase === 'idle'
    && state.terminalReason !== null
    && (
      event.type === 'post_accepted'
      || event.type === 'remote_busy'
      || event.type === 'remote_idle'
    )
  ) {
    return state;
  }

  switch (event.type) {
    case 'post_accepted':
      return state;
    case 'remote_busy':
      return {
        ...state,
        phase: 'running',
        terminalReason: null,
        error: null,
      };
    case 'remote_idle':
      if (state.phase === 'posting') return state;
      return {
        ...state,
        phase: 'idle',
        terminalReason: 'completed',
        error: null,
        suppressNextAbortError: false,
      };
    case 'remote_aborted':
      if (state.suppressNextAbortError) {
        return {
          ...state,
          error: null,
          suppressNextAbortError: false,
        };
      }
      return {
        ...state,
        phase: 'idle',
        queue: [],
        terminalReason: 'aborted',
        error: null,
        suppressNextAbortError: false,
      };
    case 'remote_failed':
      return {
        ...state,
        phase: 'idle',
        queue: [],
        terminalReason: 'failed',
        error: event.error,
        suppressNextAbortError: false,
      };
    case 'abort_requested':
      return {
        ...state,
        phase: 'aborting',
        queue: [],
        terminalReason: 'aborted',
        error: null,
        suppressNextAbortError: true,
      };
    case 'abort_confirmed':
      return {
        ...state,
        phase: 'idle',
        queue: [],
        terminalReason: 'aborted',
        error: null,
        suppressNextAbortError: false,
      };
    case 'abort_failed':
      return {
        ...state,
        phase: 'idle',
        queue: [],
        terminalReason: 'failed',
        error: event.error,
        suppressNextAbortError: false,
      };
    default:
      return state;
  }
}