import {Action} from '@ngrx/store';

import {difference, liftAction} from './utils';
import {ActionTypes, StoreDevtoolActions} from './actions';


export const INIT_ACTION = { type: '@@ngrx/INIT' };

/**
* Computes the next entry in the log by applying an action.
*/
function computeNextEntry(reducer, action, state, error) {
  if (error) {
    return {
      state,
      error: 'Interrupted by an error up the chain'
    };
  }

  let nextState = state;
  let nextError;
  try {
    nextState = reducer(state, action);
  } catch (err) {
    nextError = err.toString();
    if (typeof window === 'object' && typeof (<any>window).chrome !== 'undefined') {
      // In Chrome, rethrowing provides better source map support
      setTimeout(() => { throw err; });
    } else {
      console.error(err.stack || err);
    }
  }

  return {
    state: nextState,
    error: nextError
  };
}

/**
* Runs the reducer on invalidated actions to get a fresh computation log.
*/
function recomputeStates(
  computedStates,
  minInvalidatedStateIndex,
  reducer,
  committedState,
  actionsById,
  stagedActionIds,
  skippedActionIds
) {
  // Optimization: exit early and return the same reference
  // if we know nothing could have changed.
  if (
    minInvalidatedStateIndex >= computedStates.length &&
    computedStates.length === stagedActionIds.length
  ) {
    return computedStates;
  }

  const nextComputedStates = computedStates.slice(0, minInvalidatedStateIndex);
  for (let i = minInvalidatedStateIndex; i < stagedActionIds.length; i++) {
    const actionId = stagedActionIds[i];
    const action = actionsById[actionId].action;

    const previousEntry = nextComputedStates[i - 1];
    const previousState = previousEntry ? previousEntry.state : committedState;
    const previousError = previousEntry ? previousEntry.error : undefined;

    const shouldSkip = skippedActionIds.indexOf(actionId) > -1;
    const entry = shouldSkip ?
    previousEntry :
    computeNextEntry(reducer, action, previousState, previousError);

    nextComputedStates.push(entry);
  }

  return nextComputedStates;
}

export interface LiftedState {
  monitorState: any;
  nextActionId: number;
  actionsById: { [id: number]: { action: Action } };
  stagedActionIds: number[];
  skippedActionIds: number[];
  committedState: any;
  currentStateIndex: number;
  computedStates: { state: any, error: any }[];
}

/**
* Creates a history state reducer from an app's reducer.
*/
export function liftReducerWith(reducer, initialCommittedState?: any, monitorReducer?: any) {
  const initialLiftedState: LiftedState = {
    monitorState: monitorReducer(undefined, {}),
    nextActionId: 1,
    actionsById: { 0: liftAction(INIT_ACTION) },
    stagedActionIds: [0],
    skippedActionIds: [],
    committedState: initialCommittedState,
    currentStateIndex: 0,
    computedStates: []
  };

  /**
  * Manages how the history actions modify the history state.
  */
  return (liftedState = initialLiftedState, liftedAction): LiftedState => {
    let {
      monitorState,
      actionsById,
      nextActionId,
      stagedActionIds,
      skippedActionIds,
      committedState,
      currentStateIndex,
      computedStates
    } = liftedState;

    // By default, agressively recompute every state whatever happens.
    // This has O(n) performance, so we'll override this to a sensible
    // value whenever we feel like we don't have to recompute the states.
    let minInvalidatedStateIndex = 0;

    switch (liftedAction.type) {
      case ActionTypes.RESET: {
        // Get back to the state the store was created with.
        actionsById = { 0: liftAction(INIT_ACTION) };
        nextActionId = 1;
        stagedActionIds = [0];
        skippedActionIds = [];
        committedState = initialCommittedState;
        currentStateIndex = 0;
        computedStates = [];
        break;
      }
      case ActionTypes.COMMIT: {
        // Consider the last committed state the new starting point.
        // Squash any staged actions into a single committed state.
        actionsById = { 0: liftAction(INIT_ACTION) };
        nextActionId = 1;
        stagedActionIds = [0];
        skippedActionIds = [];
        committedState = computedStates[currentStateIndex].state;
        currentStateIndex = 0;
        computedStates = [];
        break;
      }
      case ActionTypes.ROLLBACK: {
        // Forget about any staged actions.
        // Start again from the last committed state.
        actionsById = { 0: liftAction(INIT_ACTION) };
        nextActionId = 1;
        stagedActionIds = [0];
        skippedActionIds = [];
        currentStateIndex = 0;
        computedStates = [];
        break;
      }
      case ActionTypes.TOGGLE_ACTION: {
        // Toggle whether an action with given ID is skipped.
        // Being skipped means it is a no-op during the computation.
        const { id: actionId } = liftedAction;
        const index = skippedActionIds.indexOf(actionId);
        if (index === -1) {
          skippedActionIds = [actionId, ...skippedActionIds];
        } else {
          skippedActionIds = skippedActionIds.filter(id => id !== actionId);
        }
        // Optimization: we know history before this action hasn't changed
        minInvalidatedStateIndex = stagedActionIds.indexOf(actionId);
        break;
      }
      case ActionTypes.JUMP_TO_STATE: {
        // Without recomputing anything, move the pointer that tell us
        // which state is considered the current one. Useful for sliders.
        currentStateIndex = liftedAction.index;
        // Optimization: we know the history has not changed.
        minInvalidatedStateIndex = Infinity;
        break;
      }
      case ActionTypes.SWEEP: {
        // Forget any actions that are currently being skipped.
        stagedActionIds = difference(stagedActionIds, skippedActionIds);
        skippedActionIds = [];
        currentStateIndex = Math.min(currentStateIndex, stagedActionIds.length - 1);
        break;
      }
      case ActionTypes.PERFORM_ACTION: {
        if (currentStateIndex === stagedActionIds.length - 1) {
          currentStateIndex++;
        }
        const actionId = nextActionId++;
        // Mutation! This is the hottest path, and we optimize on purpose.
        // It is safe because we set a new key in a cache dictionary.
        actionsById[actionId] = liftedAction;
        stagedActionIds = [...stagedActionIds, actionId];
        // Optimization: we know that only the new action needs computing.
        minInvalidatedStateIndex = stagedActionIds.length - 1;
        break;
      }
      case ActionTypes.IMPORT_STATE: {
        // Completely replace everything.
        ({
          monitorState,
          actionsById,
          nextActionId,
          stagedActionIds,
          skippedActionIds,
          committedState,
          currentStateIndex,
          computedStates
        } = liftedAction.nextLiftedState);
        break;
      }
      case '@@ngrx/INIT': {
        // Always recompute states on hot reload and init.
        minInvalidatedStateIndex = 0;
        break;
      }
      default: {
        // If the action is not recognized, it's a monitor action.
        // Optimization: a monitor action can't change history.
        minInvalidatedStateIndex = Infinity;
        break;
      }
    }

    computedStates = recomputeStates(
      computedStates,
      minInvalidatedStateIndex,
      reducer,
      committedState,
      actionsById,
      stagedActionIds,
      skippedActionIds
    );
    monitorState = monitorReducer(monitorState, liftedAction);
    return {
      monitorState,
      actionsById,
      nextActionId,
      stagedActionIds,
      skippedActionIds,
      committedState,
      currentStateIndex,
      computedStates
    };
  };
}