/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this file,
 * You can obtain one at http://mozilla.org/MPL/2.0/. */
"use strict";

const { assert, reportException } = require("devtools/shared/DevToolsUtils");
const { getSnapshot, breakdownEquals, createSnapshot } = require("../utils");
const { actions, snapshotState: states } = require("../constants");

/**
 * A series of actions are fired from this task to save, read and generate the initial
 * census from a snapshot.
 *
 * @param {MemoryFront}
 * @param {HeapAnalysesClient}
 * @param {Object}
 */
const takeSnapshotAndCensus = exports.takeSnapshotAndCensus = function (front, heapWorker) {
  return function *(dispatch, getState) {
    let snapshot = yield dispatch(takeSnapshot(front));

    yield dispatch(readSnapshot(heapWorker, snapshot));
    if (snapshot.state === states.READ) {
      yield dispatch(takeCensus(heapWorker, snapshot));
    }
  };
};

/**
 * Selects a snapshot and if the snapshot's census is using a different
 * breakdown, take a new census.
 *
 * @param {HeapAnalysesClient}
 * @param {Snapshot}
 */
const selectSnapshotAndRefresh = exports.selectSnapshotAndRefresh = function (heapWorker, snapshot) {
  return function *(dispatch, getState) {
    dispatch(selectSnapshot(snapshot));
    yield dispatch(refreshSelectedCensus(heapWorker));
  };
};

/**
 * @param {MemoryFront}
 */
const takeSnapshot = exports.takeSnapshot = function (front) {
  return function *(dispatch, getState) {
    let snapshot = createSnapshot();
    dispatch({ type: actions.TAKE_SNAPSHOT_START, snapshot });
    dispatch(selectSnapshot(snapshot));

    let path;
    try {
      path = yield front.saveHeapSnapshot();
    } catch (error) {
      reportException("takeSnapshot", error);
      dispatch({ type: actions.SNAPSHOT_ERROR, snapshot, error });
      return;
    }

    dispatch({ type: actions.TAKE_SNAPSHOT_END, snapshot, path });
    return snapshot;
  };
};

/**
 * Reads a snapshot into memory; necessary to do before taking
 * a census on the snapshot. May only be called once per snapshot.
 *
 * @param {HeapAnalysesClient}
 * @param {Snapshot} snapshot,
 */
const readSnapshot = exports.readSnapshot = function readSnapshot (heapWorker, snapshot) {
  return function *(dispatch, getState) {
    assert(snapshot.state === states.SAVED,
      `Should only read a snapshot once. Found snapshot in state ${snapshot.state}`);

    let creationTime;

    dispatch({ type: actions.READ_SNAPSHOT_START, snapshot });
    try {
      yield heapWorker.readHeapSnapshot(snapshot.path);
      creationTime = yield heapWorker.getCreationTime(snapshot.path);
    } catch (error) {
      reportException("readSnapshot", error);
      dispatch({ type: actions.SNAPSHOT_ERROR, snapshot, error });
      return;
    }

    dispatch({ type: actions.READ_SNAPSHOT_END, snapshot, creationTime });
  };
};

/**
 * @param {HeapAnalysesClient} heapWorker
 * @param {Snapshot} snapshot,
 *
 * @see {Snapshot} model defined in devtools/client/memory/models.js
 * @see `devtools/shared/heapsnapshot/HeapAnalysesClient.js`
 * @see `js/src/doc/Debugger/Debugger.Memory.md` for breakdown details
 */
const takeCensus = exports.takeCensus = function (heapWorker, snapshot) {
  return function *(dispatch, getState) {
    assert([states.READ, states.SAVED_CENSUS].includes(snapshot.state),
      `Can only take census of snapshots in READ or SAVED_CENSUS state, found ${snapshot.state}`);

    let census;
    let inverted = getState().inverted;
    let breakdown = getState().breakdown;

    // If breakdown and inversion haven't changed, don't do anything.
    if (inverted === snapshot.inverted && breakdownEquals(breakdown, snapshot.breakdown)) {
      return;
    }

    // Keep taking a census if the breakdown changes during. Recheck
    // that the breakdown used for the census is the same as
    // the state's breakdown.
    do {
      inverted = getState().inverted;
      breakdown = getState().breakdown;
      dispatch({ type: actions.TAKE_CENSUS_START, snapshot, inverted, breakdown });
      let opts = inverted ? { asInvertedTreeNode: true } : { asTreeNode: true };

      try {
        census = yield heapWorker.takeCensus(snapshot.path, { breakdown }, opts);
      } catch(error) {
        reportException("takeCensus", error);
        dispatch({ type: actions.SNAPSHOT_ERROR, snapshot, error });
        return;
      }
    }
    while (inverted !== getState().inverted ||
           !breakdownEquals(breakdown, getState().breakdown));

    dispatch({ type: actions.TAKE_CENSUS_END, snapshot, breakdown, inverted, census });
  };
};

/**
 * Refresh the selected snapshot's census data, if need be (for example,
 * breakdown configuration changed).
 *
 * @param {HeapAnalysesClient} heapWorker
 */
const refreshSelectedCensus = exports.refreshSelectedCensus = function (heapWorker) {
  return function*(dispatch, getState) {
    let snapshot = getState().snapshots.find(s => s.selected);

    // Intermediate snapshot states will get handled by the task action that is
    // orchestrating them. For example, if the snapshot's state is
    // SAVING_CENSUS, then the takeCensus action will keep taking a census until
    // the inverted property matches the inverted state. If the snapshot is
    // still in the process of being saved or read, the takeSnapshotAndCensus
    // task action will follow through and ensure that a census is taken.
    if (snapshot && snapshot.state === states.SAVED_CENSUS) {
      yield dispatch(takeCensus(heapWorker, snapshot));
    }
  };
};

/**
 * @param {Snapshot}
 * @see {Snapshot} model defined in devtools/client/memory/models.js
 */
const selectSnapshot = exports.selectSnapshot = function (snapshot) {
  return {
    type: actions.SELECT_SNAPSHOT,
    snapshot
  };
};