import RopeSequence from 'rope-sequence';
import { Mapping } from 'prosemirror-transform';
import { PluginKey, Plugin } from 'prosemirror-state';

// ProseMirror's history isn't simply a way to roll back to a previous
// state, because ProseMirror supports applying changes without adding
// them to the history (for example during collaboration).
//
// To this end, each 'Branch' (one for the undo history and one for
// the redo history) keeps an array of 'Items', which can optionally
// hold a step (an actual undoable change), and always hold a position
// map (which is needed to move changes below them to apply to the
// current document).
//
// An item that has both a step and a selection bookmark is the start
// of an 'event' — a group of changes that will be undone or redone at
// once. (It stores only the bookmark, since that way we don't have to
// provide a document until the selection is actually applied, which
// is useful when compressing.)

// Used to schedule history compression
var max_empty_items = 500;

var Branch = function Branch(items, eventCount) {
  this.items = items;
  this.eventCount = eventCount;
};

// : (EditorState, bool) → ?{transform: Transform, selection: ?SelectionBookmark, remaining: Branch}
// Pop the latest event off the branch's history and apply it
// to a document transform.
Branch.prototype.popEvent = function popEvent (state, preserveItems) {
    var this$1$1 = this;

  if (this.eventCount == 0) { return null }

  var end = this.items.length;
  for (;; end--) {
    var next = this.items.get(end - 1);
    if (next.selection) { --end; break }
  }

  var remap, mapFrom;
  if (preserveItems) {
    remap = this.remapping(end, this.items.length);
    mapFrom = remap.maps.length;
  }
  var transform = state.tr;
  var selection, remaining;
  var addAfter = [], addBefore = [];

  this.items.forEach(function (item, i) {
    if (!item.step) {
      if (!remap) {
        remap = this$1$1.remapping(end, i + 1);
        mapFrom = remap.maps.length;
      }
      mapFrom--;
      addBefore.push(item);
      return
    }

    if (remap) {
      addBefore.push(new Item(item.map));
      var step = item.step.map(remap.slice(mapFrom)), map;

      if (step && transform.maybeStep(step).doc) {
        map = transform.mapping.maps[transform.mapping.maps.length - 1];
        addAfter.push(new Item(map, null, null, addAfter.length + addBefore.length));
      }
      mapFrom--;
      if (map) { remap.appendMap(map, mapFrom); }
    } else {
      transform.maybeStep(item.step);
    }

    if (item.selection) {
      selection = remap ? item.selection.map(remap.slice(mapFrom)) : item.selection;
      remaining = new Branch(this$1$1.items.slice(0, end).append(addBefore.reverse().concat(addAfter)), this$1$1.eventCount - 1);
      return false
    }
  }, this.items.length, 0);

  return {remaining: remaining, transform: transform, selection: selection}
};

// : (Transform, ?SelectionBookmark, Object) → Branch
// Create a new branch with the given transform added.
Branch.prototype.addTransform = function addTransform (transform, selection, histOptions, preserveItems) {
  var newItems = [], eventCount = this.eventCount;
  var oldItems = this.items, lastItem = !preserveItems && oldItems.length ? oldItems.get(oldItems.length - 1) : null;

  for (var i = 0; i < transform.steps.length; i++) {
    var step = transform.steps[i].invert(transform.docs[i]);
    var item = new Item(transform.mapping.maps[i], step, selection), merged = (void 0);
    if (merged = lastItem && lastItem.merge(item)) {
      item = merged;
      if (i) { newItems.pop(); }
      else { oldItems = oldItems.slice(0, oldItems.length - 1); }
    }
    newItems.push(item);
    if (selection) {
      eventCount++;
      selection = null;
    }
    if (!preserveItems) { lastItem = item; }
  }
  var overflow = eventCount - histOptions.depth;
  if (overflow > DEPTH_OVERFLOW) {
    oldItems = cutOffEvents(oldItems, overflow);
    eventCount -= overflow;
  }
  return new Branch(oldItems.append(newItems), eventCount)
};

Branch.prototype.remapping = function remapping (from, to) {
  var maps = new Mapping;
  this.items.forEach(function (item, i) {
    var mirrorPos = item.mirrorOffset != null && i - item.mirrorOffset >= from
        ? maps.maps.length - item.mirrorOffset : null;
    maps.appendMap(item.map, mirrorPos);
  }, from, to);
  return maps
};

Branch.prototype.addMaps = function addMaps (array) {
  if (this.eventCount == 0) { return this }
  return new Branch(this.items.append(array.map(function (map) { return new Item(map); })), this.eventCount)
};

// : (Transform, number)
// When the collab module receives remote changes, the history has
// to know about those, so that it can adjust the steps that were
// rebased on top of the remote changes, and include the position
// maps for the remote changes in its array of items.
Branch.prototype.rebased = function rebased (rebasedTransform, rebasedCount) {
  if (!this.eventCount) { return this }

  var rebasedItems = [], start = Math.max(0, this.items.length - rebasedCount);

  var mapping = rebasedTransform.mapping;
  var newUntil = rebasedTransform.steps.length;
  var eventCount = this.eventCount;
  this.items.forEach(function (item) { if (item.selection) { eventCount--; } }, start);

  var iRebased = rebasedCount;
  this.items.forEach(function (item) {
    var pos = mapping.getMirror(--iRebased);
    if (pos == null) { return }
    newUntil = Math.min(newUntil, pos);
    var map = mapping.maps[pos];
    if (item.step) {
      var step = rebasedTransform.steps[pos].invert(rebasedTransform.docs[pos]);
      var selection = item.selection && item.selection.map(mapping.slice(iRebased + 1, pos));
      if (selection) { eventCount++; }
      rebasedItems.push(new Item(map, step, selection));
    } else {
      rebasedItems.push(new Item(map));
    }
  }, start);

  var newMaps = [];
  for (var i = rebasedCount; i < newUntil; i++)
    { newMaps.push(new Item(mapping.maps[i])); }
  var items = this.items.slice(0, start).append(newMaps).append(rebasedItems);
  var branch = new Branch(items, eventCount);

  if (branch.emptyItemCount() > max_empty_items)
    { branch = branch.compress(this.items.length - rebasedItems.length); }
  return branch
};

Branch.prototype.emptyItemCount = function emptyItemCount () {
  var count = 0;
  this.items.forEach(function (item) { if (!item.step) { count++; } });
  return count
};

// Compressing a branch means rewriting it to push the air (map-only
// items) out. During collaboration, these naturally accumulate
// because each remote change adds one. The `upto` argument is used
// to ensure that only the items below a given level are compressed,
// because `rebased` relies on a clean, untouched set of items in
// order to associate old items with rebased steps.
Branch.prototype.compress = function compress (upto) {
    if ( upto === void 0 ) upto = this.items.length;

  var remap = this.remapping(0, upto), mapFrom = remap.maps.length;
  var items = [], events = 0;
  this.items.forEach(function (item, i) {
    if (i >= upto) {
      items.push(item);
      if (item.selection) { events++; }
    } else if (item.step) {
      var step = item.step.map(remap.slice(mapFrom)), map = step && step.getMap();
      mapFrom--;
      if (map) { remap.appendMap(map, mapFrom); }
      if (step) {
        var selection = item.selection && item.selection.map(remap.slice(mapFrom));
        if (selection) { events++; }
        var newItem = new Item(map.invert(), step, selection), merged, last = items.length - 1;
        if (merged = items.length && items[last].merge(newItem))
          { items[last] = merged; }
        else
          { items.push(newItem); }
      }
    } else if (item.map) {
      mapFrom--;
    }
  }, this.items.length, 0);
  return new Branch(RopeSequence.from(items.reverse()), events)
};

Branch.empty = new Branch(RopeSequence.empty, 0);

function cutOffEvents(items, n) {
  var cutPoint;
  items.forEach(function (item, i) {
    if (item.selection && (n-- == 0)) {
      cutPoint = i;
      return false
    }
  });
  return items.slice(cutPoint)
}

var Item = function Item(map, step, selection, mirrorOffset) {
  // The (forward) step map for this item.
  this.map = map;
  // The inverted step
  this.step = step;
  // If this is non-null, this item is the start of a group, and
  // this selection is the starting selection for the group (the one
  // that was active before the first step was applied)
  this.selection = selection;
  // If this item is the inverse of a previous mapping on the stack,
  // this points at the inverse's offset
  this.mirrorOffset = mirrorOffset;
};

Item.prototype.merge = function merge (other) {
  if (this.step && other.step && !other.selection) {
    var step = other.step.merge(this.step);
    if (step) { return new Item(step.getMap().invert(), step, this.selection) }
  }
};

// The value of the state field that tracks undo/redo history for that
// state. Will be stored in the plugin state when the history plugin
// is active.
var HistoryState = function HistoryState(done, undone, prevRanges, prevTime) {
  this.done = done;
  this.undone = undone;
  this.prevRanges = prevRanges;
  this.prevTime = prevTime;
};

var DEPTH_OVERFLOW = 20;

// : (HistoryState, EditorState, Transaction, Object)
// Record a transformation in undo history.
function applyTransaction(history, state, tr, options) {
  var historyTr = tr.getMeta(historyKey), rebased;
  if (historyTr) { return historyTr.historyState }

  if (tr.getMeta(closeHistoryKey)) { history = new HistoryState(history.done, history.undone, null, 0); }

  var appended = tr.getMeta("appendedTransaction");

  if (tr.steps.length == 0) {
    return history
  } else if (appended && appended.getMeta(historyKey)) {
    if (appended.getMeta(historyKey).redo)
      { return new HistoryState(history.done.addTransform(tr, null, options, mustPreserveItems(state)),
                              history.undone, rangesFor(tr.mapping.maps[tr.steps.length - 1]), history.prevTime) }
    else
      { return new HistoryState(history.done, history.undone.addTransform(tr, null, options, mustPreserveItems(state)),
                              null, history.prevTime) }
  } else if (tr.getMeta("addToHistory") !== false && !(appended && appended.getMeta("addToHistory") === false)) {
    // Group transforms that occur in quick succession into one event.
    var newGroup = history.prevTime == 0 || !appended && (history.prevTime < (tr.time || 0) - options.newGroupDelay ||
                                                          !isAdjacentTo(tr, history.prevRanges));
    var prevRanges = appended ? mapRanges(history.prevRanges, tr.mapping) : rangesFor(tr.mapping.maps[tr.steps.length - 1]);
    return new HistoryState(history.done.addTransform(tr, newGroup ? state.selection.getBookmark() : null,
                                                      options, mustPreserveItems(state)),
                            Branch.empty, prevRanges, tr.time)
  } else if (rebased = tr.getMeta("rebased")) {
    // Used by the collab module to tell the history that some of its
    // content has been rebased.
    return new HistoryState(history.done.rebased(tr, rebased),
                            history.undone.rebased(tr, rebased),
                            mapRanges(history.prevRanges, tr.mapping), history.prevTime)
  } else {
    return new HistoryState(history.done.addMaps(tr.mapping.maps),
                            history.undone.addMaps(tr.mapping.maps),
                            mapRanges(history.prevRanges, tr.mapping), history.prevTime)
  }
}

function isAdjacentTo(transform, prevRanges) {
  if (!prevRanges) { return false }
  if (!transform.docChanged) { return true }
  var adjacent = false;
  transform.mapping.maps[0].forEach(function (start, end) {
    for (var i = 0; i < prevRanges.length; i += 2)
      { if (start <= prevRanges[i + 1] && end >= prevRanges[i])
        { adjacent = true; } }
  });
  return adjacent
}

function rangesFor(map) {
  var result = [];
  map.forEach(function (_from, _to, from, to) { return result.push(from, to); });
  return result
}

function mapRanges(ranges, mapping) {
  if (!ranges) { return null }
  var result = [];
  for (var i = 0; i < ranges.length; i += 2) {
    var from = mapping.map(ranges[i], 1), to = mapping.map(ranges[i + 1], -1);
    if (from <= to) { result.push(from, to); }
  }
  return result
}

// : (HistoryState, EditorState, (tr: Transaction), bool)
// Apply the latest event from one branch to the document and shift the event
// onto the other branch.
function histTransaction(history, state, dispatch, redo) {
  var preserveItems = mustPreserveItems(state), histOptions = historyKey.get(state).spec.config;
  var pop = (redo ? history.undone : history.done).popEvent(state, preserveItems);
  if (!pop) { return }

  var selection = pop.selection.resolve(pop.transform.doc);
  var added = (redo ? history.done : history.undone).addTransform(pop.transform, state.selection.getBookmark(),
                                                                  histOptions, preserveItems);

  var newHist = new HistoryState(redo ? added : pop.remaining, redo ? pop.remaining : added, null, 0);
  dispatch(pop.transform.setSelection(selection).setMeta(historyKey, {redo: redo, historyState: newHist}).scrollIntoView());
}

var cachedPreserveItems = false, cachedPreserveItemsPlugins = null;
// Check whether any plugin in the given state has a
// `historyPreserveItems` property in its spec, in which case we must
// preserve steps exactly as they came in, so that they can be
// rebased.
function mustPreserveItems(state) {
  var plugins = state.plugins;
  if (cachedPreserveItemsPlugins != plugins) {
    cachedPreserveItems = false;
    cachedPreserveItemsPlugins = plugins;
    for (var i = 0; i < plugins.length; i++) { if (plugins[i].spec.historyPreserveItems) {
      cachedPreserveItems = true;
      break
    } }
  }
  return cachedPreserveItems
}

// :: (Transaction) → Transaction
// Set a flag on the given transaction that will prevent further steps
// from being appended to an existing history event (so that they
// require a separate undo command to undo).
function closeHistory(tr) {
  return tr.setMeta(closeHistoryKey, true)
}

var historyKey = new PluginKey("history");
var closeHistoryKey = new PluginKey("closeHistory");

// :: (?Object) → Plugin
// Returns a plugin that enables the undo history for an editor. The
// plugin will track undo and redo stacks, which can be used with the
// [`undo`](#history.undo) and [`redo`](#history.redo) commands.
//
// You can set an `"addToHistory"` [metadata
// property](#state.Transaction.setMeta) of `false` on a transaction
// to prevent it from being rolled back by undo.
//
//   config::-
//   Supports the following configuration options:
//
//     depth:: ?number
//     The amount of history events that are collected before the
//     oldest events are discarded. Defaults to 100.
//
//     newGroupDelay:: ?number
//     The delay between changes after which a new group should be
//     started. Defaults to 500 (milliseconds). Note that when changes
//     aren't adjacent, a new group is always started.
function history(config) {
  config = {depth: config && config.depth || 100,
            newGroupDelay: config && config.newGroupDelay || 500};
  return new Plugin({
    key: historyKey,

    state: {
      init: function init() {
        return new HistoryState(Branch.empty, Branch.empty, null, 0)
      },
      apply: function apply(tr, hist, state) {
        return applyTransaction(hist, state, tr, config)
      }
    },

    config: config,

    props: {
      handleDOMEvents: {
        beforeinput: function beforeinput(view, e) {
          var command = e.inputType == "historyUndo" ? undo : e.inputType == "historyRedo" ? redo : null;
          if (!command) { return false }
          e.preventDefault();
          return command(view.state, view.dispatch)
        }
      }
    }
  })
}

// :: (EditorState, ?(tr: Transaction)) → bool
// A command function that undoes the last change, if any.
function undo(state, dispatch) {
  var hist = historyKey.getState(state);
  if (!hist || hist.done.eventCount == 0) { return false }
  if (dispatch) { histTransaction(hist, state, dispatch, false); }
  return true
}

// :: (EditorState, ?(tr: Transaction)) → bool
// A command function that redoes the last undone change, if any.
function redo(state, dispatch) {
  var hist = historyKey.getState(state);
  if (!hist || hist.undone.eventCount == 0) { return false }
  if (dispatch) { histTransaction(hist, state, dispatch, true); }
  return true
}

// :: (EditorState) → number
// The amount of undoable events available in a given state.
function undoDepth(state) {
  var hist = historyKey.getState(state);
  return hist ? hist.done.eventCount : 0
}

// :: (EditorState) → number
// The amount of redoable events available in a given editor state.
function redoDepth(state) {
  var hist = historyKey.getState(state);
  return hist ? hist.undone.eventCount : 0
}

export { HistoryState, closeHistory, history, redo, redoDepth, undo, undoDepth };
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