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✏️ Editing: mark-selection.js

// CodeMirror, copyright (c) by Marijn Haverbeke and others
// Distributed under an MIT license: https://codemirror.net/LICENSE

// Because sometimes you need to mark the selected *text*.
//
// Adds an option 'styleSelectedText' which, when enabled, gives
// selected text the CSS class given as option value, or
// "CodeMirror-selectedtext" when the value is not a string.

(function(mod) {
  if (typeof exports == "object" && typeof module == "object") // CommonJS
    mod(require("../../lib/codemirror"));
  else if (typeof define == "function" && define.amd) // AMD
    define(["../../lib/codemirror"], mod);
  else // Plain browser env
    mod(CodeMirror);
})(function(CodeMirror) {
  "use strict";

CodeMirror.defineOption("styleSelectedText", false, function(cm, val, old) {
    var prev = old && old != CodeMirror.Init;
    if (val && !prev) {
      cm.state.markedSelection = [];
      cm.state.markedSelectionStyle = typeof val == "string" ? val : "CodeMirror-selectedtext";
      reset(cm);
      cm.on("cursorActivity", onCursorActivity);
      cm.on("change", onChange);
    } else if (!val && prev) {
      cm.off("cursorActivity", onCursorActivity);
      cm.off("change", onChange);
      clear(cm);
      cm.state.markedSelection = cm.state.markedSelectionStyle = null;
    }
  });

function onCursorActivity(cm) {
    if (cm.state.markedSelection)
      cm.operation(function() { update(cm); });
  }

function onChange(cm) {
    if (cm.state.markedSelection && cm.state.markedSelection.length)
      cm.operation(function() { clear(cm); });
  }

var CHUNK_SIZE = 8;
  var Pos = CodeMirror.Pos;
  var cmp = CodeMirror.cmpPos;

function clear(cm) {
    var array = cm.state.markedSelection;
    for (var i = 0; i < array.length; ++i) array[i].clear();
    array.length = 0;
  }

function reset(cm) {
    clear(cm);
    var ranges = cm.listSelections();
    for (var i = 0; i < ranges.length; i++)
      coverRange(cm, ranges[i].from(), ranges[i].to());
  }

function update(cm) {
    if (!cm.somethingSelected()) return clear(cm);
    if (cm.listSelections().length > 1) return reset(cm);

var from = cm.getCursor("start"), to = cm.getCursor("end");

var array = cm.state.markedSelection;
    if (!array.length) return coverRange(cm, from, to);

var coverStart = array[0].find(), coverEnd = array[array.length - 1].find();
    if (!coverStart || !coverEnd || to.line - from.line <= CHUNK_SIZE ||
        cmp(from, coverEnd.to) >= 0 || cmp(to, coverStart.from) <= 0)
      return reset(cm);

while (cmp(from, coverStart.from) > 0) {
      array.shift().clear();
      coverStart = array[0].find();
    }
    if (cmp(from, coverStart.from) < 0) {
      if (coverStart.to.line - from.line < CHUNK_SIZE) {
        array.shift().clear();
        coverRange(cm, from, coverStart.to, 0);
      } else {
        coverRange(cm, from, coverStart.from, 0);
      }
    }

while (cmp(to, coverEnd.to) < 0) {
      array.pop().clear();
      coverEnd = array[array.length - 1].find();
    }
    if (cmp(to, coverEnd.to) > 0) {
      if (to.line - coverEnd.from.line < CHUNK_SIZE) {
        array.pop().clear();
        coverRange(cm, coverEnd.from, to);
      } else {
        coverRange(cm, coverEnd.to, to);
      }
    }
  }
});

MR SKB