/**
 * The Cursor module contains functionality related to the cell with the cursor, i.e. a single
 * currently selected cell.
 */


import BaseView from 'app/client/components/BaseView';
import * as commands from 'app/client/components/commands';
import BaseRowModel from 'app/client/models/BaseRowModel';
import {LazyArrayModel} from 'app/client/models/DataTableModel';
import {CursorPos, UIRowId} from 'app/plugin/GristAPI';
import {Disposable} from 'grainjs';
import * as ko from 'knockout';

function nullAsUndefined<T>(value: T|null|undefined): T|undefined {
  return value == null ? undefined : value;
}

// ================ SequenceNum: used to keep track of cursor edits (lastEditedAt)
// basically just a global auto-incrementing counter, with some types to make intent a bit more clear
// Each cursor starts at SequenceNEVER (0), and after that all cursors using NextSequenceNum() will have
// a unique, monotonically increasing number for their lastEditedAt()
export type SequenceNum = number;
export const SequenceNEVER: SequenceNum = 0;
let latestGlobalSequenceNum = SequenceNEVER;
const nextSequenceNum = () => { return latestGlobalSequenceNum++; };

// Note: we don't make any provisions for handling overflow. It's fine because:
//   - Number.MAX_SAFE_INTEGER is 9,007,199,254,740,991 (9 * 10^15)
//   - even at 1000 cursor-edits per second, it would take ~300,000 yrs to overflow
//   - Plus it's client-side, so that's a single continuous 300-millenia-long session, which would be impressive uptime


/**
 * Cursor represents the location of the cursor in the viewsection. It is maintained by BaseView,
 * and implements the shared functionality related to the cursor cell.
 * @param {BaseView} baseView: The BaseView object to which this Cursor belongs.
 * @param {Object} optCursorPos: Optional object containing rowId and fieldIndex properties
 *  to which the cursor should be initialized.
 */
export class Cursor extends Disposable {
  /**
   * The commands closely tied to the cursor. They are active when the BaseView containing this
   * Cursor has focus. Some may need to be overridden by particular views.
   */
  public static editorCommands = {
    // The cursor up/down commands may need to be a bit different in non-grid views.
    cursorUp(this: Cursor) { this.rowIndex(this.rowIndex()! - 1); },
    cursorDown(this: Cursor) { this.rowIndex(this.rowIndex()! + 1); },
    cursorLeft(this: Cursor) { this.fieldIndex(this.fieldIndex() - 1); },
    cursorRight(this: Cursor) { this.fieldIndex(this.fieldIndex() + 1); },
    skipUp(this: Cursor) { this.rowIndex(this.rowIndex()! - 5); },
    skipDown(this: Cursor) { this.rowIndex(this.rowIndex()! + 5); },
    pageUp(this: Cursor) { this.rowIndex(this.rowIndex()! - 20); },    // TODO Not really pageUp
    pageDown(this: Cursor) { this.rowIndex(this.rowIndex()! + 20); },  // TODO Not really pageDown
    prevField(this: Cursor) { this.fieldIndex(this.fieldIndex() - 1); },
    nextField(this: Cursor) { this.fieldIndex(this.fieldIndex() + 1); },
    moveToFirstRecord(this: Cursor) { this.rowIndex(0); },
    moveToLastRecord(this: Cursor) { this.rowIndex(Infinity); },
    moveToFirstField(this: Cursor) { this.fieldIndex(0); },
    moveToLastField(this: Cursor) { this.fieldIndex(Infinity); },
  };

  public viewData: LazyArrayModel<BaseRowModel>;
  // observable with current cursor position
  public currentPosition: ko.Computed<CursorPos>;

  public rowIndex: ko.Computed<number|null>;     // May be null when there are no rows.
  public fieldIndex: ko.Observable<number>;

  private _rowId: ko.Observable<UIRowId|null>;     // May be null when there are no rows.

  // The cursor's _rowId property is always fixed across data changes. When isLive is true,
  // the rowIndex of the cursor is recalculated to match _rowId. When false, they will
  // be out of sync.
  private _isLive: ko.Observable<boolean> = ko.observable(true);
  private _sectionId: ko.Computed<number>;

  private _properRowId: ko.Computed<UIRowId|null>;
  private _lastEditedAt: ko.Observable<SequenceNum>;

  private _silentUpdatesFlag: boolean = false;
  // lastEditedAt is updated on rowIndex or fieldIndex update (including through setCursorPos)
  // _silentUpdatesFlag disables this, set when setCursorPos called from cursor link to prevent infinite loops
  // WARNING: the flag approach will only work if ko observables work synchronously, which they appear to do.

  constructor(baseView: BaseView, optCursorPos?: CursorPos) {
    super();
    optCursorPos = optCursorPos || {};
    this.viewData = baseView.viewData;

    this._sectionId = this.autoDispose(ko.computed(() => baseView.viewSection.id()));
    this._rowId = ko.observable<UIRowId|null>(optCursorPos.rowId || 0);
    this.rowIndex = this.autoDispose(ko.computed({
      read: () => {
        if (!this._isLive()) { return this.rowIndex.peek(); }
        const rowId = this._rowId();
        return rowId == null ? null : this.viewData.clampIndex(this.viewData.getRowIndexWithSub(rowId));
      },
      write: (index) => {
        const rowIndex = index === null ? null : this.viewData.clampIndex(index);
        this._rowId(rowIndex == null ? null : this.viewData.getRowId(rowIndex));
      },
    }));

    this.fieldIndex = baseView.viewSection.viewFields().makeLiveIndex(optCursorPos.fieldIndex || 0);

    this.autoDispose(commands.createGroup(Cursor.editorCommands, this, baseView.viewSection.hasFocus));

    // RowId might diverge from the one stored in _rowId when the data changes (it is filtered out). So here
    // we will calculate rowId based on rowIndex (so in reverse order), to have a proper value.
    this._properRowId = this.autoDispose(ko.computed(() => {
      const rowIndex = this.rowIndex();
      const rowId = rowIndex === null ? null : this.viewData.getRowId(rowIndex);
      return rowId;
    }));

    this._lastEditedAt = ko.observable(SequenceNEVER);

    // update the section's activeRowId and lastCursorEdit when needed
    this.autoDispose(this._properRowId.subscribe((rowId) => baseView.viewSection.activeRowId(rowId)));
    this.autoDispose(this._lastEditedAt.subscribe((seqNum) => baseView.viewSection.lastCursorEdit(seqNum)));

    // Update the cursor edit time if either the row or column change
    // IMPORTANT: need to subscribe AFTER the properRowId->activeRowId subscription.
    //  (Cursor-linking observables depend on edit-version, and only peek at activeRowId. Therefore, make sure
    //   we set all values correctly, and only update version after that's been done)
    this.autoDispose(this._properRowId.subscribe(() => { this.cursorEdited(); }));
    this.autoDispose(this.fieldIndex.subscribe(() => { this.cursorEdited(); }));

    // On dispose, save the current cursor position to the section model.
    this.onDispose(() => { baseView.viewSection.lastCursorPos = this.getCursorPos(); });

    // calculate current position
    this.currentPosition = this.autoDispose(ko.computed(() => this._isLive() ? this.getCursorPos() : {}));
  }

  // Returns the cursor position with rowId, rowIndex, and fieldIndex.
  public getCursorPos(): CursorPos {
    return {
      rowId: nullAsUndefined(this._properRowId()),
      rowIndex: nullAsUndefined(this.rowIndex()),
      fieldIndex: this.fieldIndex(),
      sectionId: this._sectionId()
    };
  }

  /**
   * Moves the cursor to the given position. Only moves the row if rowId or rowIndex is valid,
   * preferring rowId.
   *
   * silentUpdate prevents lastEditedAt from being updated, so linking doesn't cause an infinite loop of updates
   * @param cursorPos: Position as { rowId?, rowIndex?, fieldIndex? }, as from getCursorPos().
   * @param silentUpdate: should only be set if this is a cascading update from cursor-linking
   */
  public setCursorPos(cursorPos: CursorPos, silentUpdate: boolean = false): void {
    //If updating as a result of links, we want to NOT update lastEditedAt
    if(silentUpdate) { this._silentUpdatesFlag = true; }
    //console.log(`CURSOR: ${silentUpdate}, silentUpdate=${this._silentUpdatesFlag},
    //            lastUpdated = ${this.lastUpdated.peek()}`) //TODO JV DEBUG TEMP

    if (cursorPos.rowId !== undefined && this.viewData.getRowIndex(cursorPos.rowId) >= 0) {
      this.rowIndex(this.viewData.getRowIndex(cursorPos.rowId) );
    } else if (cursorPos.rowIndex !== undefined && cursorPos.rowIndex >= 0) {
      this.rowIndex(cursorPos.rowIndex);
    } else {
      // Write rowIndex to itself to force an update of rowId if needed.
      this.rowIndex(this.rowIndex.peek());
    }
    if (cursorPos.fieldIndex !== undefined) {
      this.fieldIndex(cursorPos.fieldIndex);
    }

    //console.log(`CURSOR-END: silentUpdate=${this._silentUpdatesFlag},
    //            lastEditedAt = ${this._lastEditedAt.peek()}  `); //TODO JV DEBUG TEMP
    this._silentUpdatesFlag = false;
  }




  public setLive(isLive: boolean): void {
    this._isLive(isLive);
  }

  //Should be called whenever the cursor is updated
  //EXCEPT FOR: when cursor is set by linking
  //this is used to determine which widget/cursor has most recently been touched,
  //and therefore which one should be used to drive linking if there's a conflict
  public cursorEdited(): void {
    //If updating as a result of links, we want to NOT update lastEdited
    if(!this._silentUpdatesFlag)
      { this._lastEditedAt(nextSequenceNum()); }
  }
}