Move Lines Down

script

// Direction to move the lines.
var moveUp = false;

String.prototype.splitLines = function () {
	// Splits string into lines, each ending with a newline (\n).
	// Note: the last fragment might not end with a newline.
	return this.match(/[^\n]*\n/g);
};

function minRange(theRange) {
	// Returns index of start of theRange.
	return theRange[0];
}

function maxRange(theRange) {
	// Returns index immediately AFTER end of theRange.
	return theRange[0] + theRange[1];
}

String.prototype.lastChar = function () {
	return this.substring(this.length - 1, this.length);
};

String.prototype.inRange = function (theRange) {
	return this.substring(theRange[0], theRange[0] + theRange[1]);
}

function show(title, content) {
	alert(title + "\n#" + content + "#");
}

function showInRange(title, range, text) {
	show(title, text.substring(range[0], range[0] + range[1]));
}

/*
We need to distinguish between a user-selection which spans a newLine onto the following line, and a getSelectedLineRange() result which has automatically expanded to include a line's trailing newline.

This is for the case where getSelectedLineRange() is ambiguous:

- This occurs only when a user selection exists. If no selection exists, the insertion point is always on a single line.
- This occurs only when the user selection ends immediately after a newLine. Otherwise, there's no ambiguity in the range returned from getSelectedLineRange().
- It doesn't matter whether the following line is blank or not.
- This doesn't occur with a _preceding_ selected blank line, because getSelectedLineRange() will be different.

The ambiguity in getSelectedLineRange() arises because:

A. The getSelectedLineRange() might span the trailing linebreak because **the user selected past that point**.
B. The getSelectedLineRange() might span the trailing linebreak because **it auto-expands to include it**.

In situation A, the user wants to **also act on the following line**; they selected it explicitly.
In situation B, the user wants **not to act on the following line**; its preceding newline was just part of the line-range.

We can disambiguate by checking getSelectedLineRange() against getSelectedRange(). If both ranges end at the same maxRange, it's a user-selection, and we **should** include the following line (by expanding the candidate line-range up to and including the next newline). Otherwise, the range was auto-expanded to include the trailing newline, and we should **not** include the following line.
*/

// Do some sanity checking.
var newLine = "\n";
var lineRange = editor.getSelectedLineRange();
var selRange = editor.getSelectedRange();
var draftText = editor.getText();
var draftLength = draftText.length;
var proceed = true;
if (moveUp && minRange(lineRange) == 0) {
	// Can't move lines up.
	proceed = false;
	
} else if (!moveUp && maxRange(lineRange) >= draftLength) {
	// Can't move lines down.
	proceed = false;
}

if (proceed) {
	// Normalise, to ensure all lines end with a newLine.
	var addedNewLine = false;
	if (draftText.lastChar() != newLine) {
		draftText = draftText + newLine;
		addedNewLine = true;
		if (moveUp) {
			// Check to see if we need to adjust lineRange accordingly.
			// Doesn't apply when moving down, because we can't be on the last line.
			if (maxRange(lineRange) == draftLength) {
				// Last line of draft is selected. Expand length of range for added newLine.
				lineRange[1] = lineRange[1] + 1;
			}
		}
		draftLength = draftLength + 1;
	}

	// Handle ambiguous line-range case of user-selection spanning a trailing newLine.
	// (See full explanation above.)
	if (selRange[1] > 0) {
		// There's a selection.
		var selText = draftText.inRange(selRange);
		if (selText.lastChar() == newLine) {
			// Last char of user selection is a newline; expand lineRange to include next line.
			// (Because visually in terms of the iOS selection, that's the user's intention.)
			// Note: also include the newLine itself at the end of the next line.
			var nextNewLinePosn = draftText.indexOf(newLine, maxRange(selRange));
			lineRange[1] = lineRange[1] + (nextNewLinePosn - maxRange(lineRange)) + 1;
		}
	}
	
	// Expand lineRange to give us an extra line to move.
	if (moveUp) {
		// Moving up. Get extra line before the selected lines, to move down.
		// We offset by -2 to go back past the preceding lineBreak.
		var prevLineStart = draftText.lastIndexOf(newLine, minRange(lineRange) - 2);
		
		// Adjust prevLineStart so we don't capture the found newline itself.
		if (prevLineStart == -1) { // In case we hit start of draft.
			prevLineStart = 0;
		} else {
			// Exclude the newLine itself which preceeds the previous line.
			if ((minRange(lineRange) - prevLineStart) > 1) {
				prevLineStart = prevLineStart + 1;
			}
		}
		lineRange[1] = lineRange[1] + (lineRange[0] - prevLineStart);
		lineRange[0] = prevLineStart;
		
	} else {
		// Moving down. Get extra line after the selected lines, to move up.
		var nextLineEnd = draftText.indexOf(newLine, maxRange(lineRange));
		if (nextLineEnd == -1) { // We hit end of draft.
			nextLineEnd = draftLength;
		}
		lineRange[1] = (nextLineEnd + 1) - lineRange[0];
	}
	
	// Grab the relevant full lines of text.
	var selectedLines = draftText.substring(minRange(lineRange), maxRange(lineRange));
	
	// Rearrange lines.
	var lines = selectedLines.splitLines();
	var extraLineArray = [];
	if (moveUp) {
		// Shift first (extra) line to end, thus moving all others up.
		extraLineArray = lines.splice(0, 1);
		extraLineArray = lines.splice(lines.length, 0, extraLineArray[0]);
		
	} else {
		// Shift last (extra) line to start, thus moving all others down.
		extraLineArray = lines.splice(lines.length - 1, 1);
		extraLineArray = lines.splice(0, 0, extraLineArray[0]);
	}
	
	// Replace selected lines with reordered ones.
	var newLinesChunk = lines.join("");

	// If we added a newLine to the end of draftText originally,
	// and we're replacing in that portion, remove it again.
	if (addedNewLine && maxRange(lineRange) >= (draftLength - 1)) {
		newLinesChunk = newLinesChunk.substring(0, newLinesChunk.length - 1);
	}
	
	// Work out new selection range, to preserve selected lines.
	var newSelectionRange = [ lineRange[0], lineRange[1] ];
	newSelectionRange[1] = newLinesChunk.length;
	var delta = 0;
	if (moveUp) {
		// Should select all but the last (extra; moved down) line.
		delta = lines[lines.length - 1].length;
		newSelectionRange[1] = newSelectionRange[1] - delta;
		
	} else {
		// Should select all but the first (extra; moved up) line.
		delta = lines[0].length;
		newSelectionRange[0] = newSelectionRange[0] + delta;
		newSelectionRange[1] = newSelectionRange[1] - delta;
	}

	// Replace text in editor.
	editor.setTextInRange(lineRange[0], lineRange[1], newLinesChunk);
	
	// Maintain selection, ensuring it doesn't end in a spurious newLine.
	if (editor.getTextInRange(newSelectionRange[0], newSelectionRange[1]).lastChar() == newLine) {
		newSelectionRange[1] = newSelectionRange[1] - 1;
	}
	editor.setSelectedRange(newSelectionRange[0], newSelectionRange[1]);
}

/*

Test data below.

one
two
three
four

*/