this.$onChange = function()

in lib/ace/range_list.js [184:293]
102 lines of code
42 McCabe index (conditional complexity)

    this.$onChange = function(delta) {
        var start = delta.start;
        var end = delta.end;
        var startRow = start.row;
        var endRow = end.row;
        var ranges = this.ranges;
        for (var i = 0, n = ranges.length; i < n; i++) {
            var r = ranges[i];
            if (r.end.row >= startRow)
                break;
        }
        
        if (delta.action == "insert") {
            var lineDif = endRow - startRow;
            var colDiff = -start.column + end.column;
            for (; i < n; i++) {
                var r = ranges[i];
                if (r.start.row > startRow)
                    break;
    
                if (r.start.row == startRow && r.start.column >= start.column) {
                    if (r.start.column == start.column && this.$bias <= 0) {
                        // do nothing
                    } else {
                        r.start.column += colDiff;
                        r.start.row += lineDif;
                    }
                }
                if (r.end.row == startRow && r.end.column >= start.column) {
                    if (r.end.column == start.column && this.$bias < 0) {
                        continue;
                    }
                    // special handling for the case when two ranges share an edge
                    if (r.end.column == start.column && colDiff > 0 && i < n - 1) {
                        if (r.end.column > r.start.column && r.end.column == ranges[i+1].start.column)
                            r.end.column -= colDiff;
                    }
                    r.end.column += colDiff;
                    r.end.row += lineDif;
                }
            }
        } else {
            var lineDif = startRow - endRow;
            var colDiff = start.column - end.column;
            for (; i < n; i++) {
                var r = ranges[i];
                
                if (r.start.row > endRow)
                    break;
                    
                if (r.end.row < endRow
                    && (
                        startRow < r.end.row 
                        || startRow == r.end.row && start.column < r.end.column
                    )
                ) {
                    r.end.row = startRow;
                    r.end.column = start.column;
                }
                else if (r.end.row == endRow) {
                    if (r.end.column <= end.column) {
                        if (lineDif || r.end.column > start.column) {
                            r.end.column = start.column;
                            r.end.row = start.row;
                        }
                    }
                    else {
                        r.end.column += colDiff;
                        r.end.row += lineDif;
                    }
                }
                else if (r.end.row > endRow) {
                    r.end.row += lineDif;
                }
                
                if (r.start.row < endRow
                    && (
                        startRow < r.start.row 
                        || startRow == r.start.row && start.column < r.start.column
                    )
                ) {
                    r.start.row = startRow;
                    r.start.column = start.column;
                }
                else if (r.start.row == endRow) {
                    if (r.start.column <= end.column) {
                        if (lineDif || r.start.column > start.column) {
                            r.start.column = start.column;
                            r.start.row = start.row;
                        }
                    }
                    else {
                        r.start.column += colDiff;
                        r.start.row += lineDif;
                    }
                }
                else if (r.start.row > endRow) {
                    r.start.row += lineDif;
                }
            }
        }

        if (lineDif != 0 && i < n) {
            for (; i < n; i++) {
                var r = ranges[i];
                r.start.row += lineDif;
                r.end.row += lineDif;
            }
        }
    };