/**
 * DataModel document.
 *
 * @class
 * @extends {ve.Document}
 * @constructor
 * @param {Array} data Linear model data to start with
 * @param {ve.dm.Document} [parentDocument] Document to use as root for created nodes
 */
ve.dm.Document = function( data, parentDocument ) {
	// Inheritance
	ve.Document.call( this, new ve.dm.DocumentNode() );

	// Properties
	this.parentDocument = parentDocument;
	this.data = data || [];
	this.offsetMap = new Array( this.data.length );

	// Initialization
	var doc = parentDocument || this;
	this.documentNode.setDocument( doc );
	var root = doc.getDocumentNode();
	this.documentNode.setRoot( root );

	/*
	 * The offsetMap is always one element longer than data because it includes a reference to the
	 * root node at the offset just past the end. To make population work correctly, we have to
	 * start out with that one extra reference.
	 */
	this.offsetMap.push( this.documentNode );

	/*
	 * Build a tree of nodes and nodes that will be added to them after a full scan is complete,
	 * then from the bottom up add nodes to their potential parents. This avoids massive length
	 * updates being broadcast upstream constantly while building is underway. Also populate the
	 * offset map as we go.
	 */
	var node,
		textLength = 0,
		inTextNode = false,
		// Stack of stacks, each containing a
		stack = [[this.documentNode], []],
		children,
		openingIndex,
		currentStack = stack[1],
		parentStack = stack[0],
		currentNode = this.documentNode;
	for ( var i = 0, length = this.data.length; i < length; i++ ) {
		/*
		 * Set the node reference for this offset in the offset cache.
		 *
		 * This looks simple, but there are three cases that result in the same thing:
		 *
		 *   1. data[i] is an opening, so offset i is before the opening, so we need to point to the
		 *      parent of the opened element. currentNode will be set to the opened element later,
		 *      but right now its still set to the parent of the opened element.
		 *   2. data[i] is a closing, so offset i is before the closing, so we need to point to the
		 *      closed element. currentNode will be set to the parent of the closed element later,
		 *      but right now it's still set to the closed element.
		 *   3. data[i] is content, so offset i is in the middle of an element, so obviously we need
		 *      currentNode, which won't be changed by this iteration.
		 *
		 * We want to populate the offsetMap with branches only, but we've just written the actual
		 * node that lives at this offset. So if it's a leaf node, change it to its parent.
		 */
		this.offsetMap[i] = ve.dm.nodeFactory.canNodeHaveChildren( currentNode.getType() ) ?
			currentNode : parentStack[parentStack.length - 1];
		// Infer that if an item in the linear model has a type attribute than it must be an element
		if ( this.data[i].type === undefined ) {
			// Text node opening
			if ( !inTextNode ) {
				// Create a lengthless text node
				node = new ve.dm.TextNode();
				// Set the root pointer now, to prevent cascading updates
				node.setRoot( root );
				// Put the node on the current inner stack
				currentStack.push( node );
				currentNode = node;
				// Set a flag saying we're inside a text node
				inTextNode = true;
			}
			// Track the length
			textLength++;
		} else {
			// Text node closing
			if ( inTextNode ) {
				// Finish the text node by setting the length
				currentNode.setLength( textLength );
				// Put the state variables back as they were
				currentNode = parentStack[parentStack.length - 1];
				inTextNode = false;
				textLength = 0;
			}
			// Element open/close
			if ( this.data[i].type.charAt( 0 ) != '/' ) {
				// Branch or leaf node opening
				// Create a childless node
				node = ve.dm.nodeFactory.create( this.data[i].type, [], this.data[i].attributes );
				// Set the root pointer now, to prevent cascading updates
				node.setRoot( root );
				// Put the childless node on the current inner stack
				currentStack.push( node );
				if ( ve.dm.nodeFactory.canNodeHaveChildren( node.getType() ) ) {
					// Create a new inner stack for this node
					parentStack = currentStack;
					currentStack = [];
					stack.push( currentStack );
				}
				currentNode = node;
			} else {
				// Branch or leaf node closing
				if ( ve.dm.nodeFactory.canNodeHaveChildren( currentNode.getType() ) ) {
					// Pop this node's inner stack from the outer stack. It'll have all of the
					// node's child nodes fully constructed
					children = stack.pop();
					currentStack = parentStack;
					parentStack = stack[stack.length - 2];
					if ( !parentStack ) {
						// This can only happen if we got unbalanced data
						throw 'Unbalanced input passed to document';
					}

					if ( children.length === 0 &&
						ve.dm.nodeFactory.canNodeContainContent(
							currentNode.getType()
						)
					) {
						// Content nodes cannot be childless, add a zero-length text node
						children.push( new ve.dm.TextNode( 0 ) );
					}
					// Attach the children to the node
					ve.batchSplice( currentNode, 0, 0, children );
				}
				currentNode = parentStack[parentStack.length - 1];
			}
		}
	}

	if ( inTextNode ) {
		// Text node ended by end-of-input rather than by an element
		currentNode.setLength( textLength );
		// Don't bother updating currentNode et al, we don't use them below
	}
	// The end state is stack = [ [this.documentNode] [ array, of, its, children ] ]
	// so attach all nodes in stack[1] to the root node
	ve.batchSplice( this.documentNode, 0, 0, stack[1] );
};

/* Static methods */

/**
 * Checks if content can be inserted at an offset in document data.
 *
 * This method assumes that any value that has a type property that's a string is an element object.
 *
 * @example Content offsets:
 *      <heading> a </heading> <paragraph> b c <img> </img> </paragraph>
 *     .         ^ ^          .           ^ ^ ^     .      ^            .
 *
 * @example Content offsets:
 *      <list> <listItem> </listItem> <list>
 *     .      .          .           .      .
 *
 * @static
 * @method
 * @param {Array} data Document data
 * @param {Integer} offset Document offset
 * @returns {Boolean} Content can be inserted at offset
 */
ve.dm.Document.isContentOffset = function( data, offset ) {
	// Edges are never content
	if ( offset === 0 || offset === data.length ) {
		return false;
	}
	var left = data[offset - 1],
		right = data[offset],
		factory = ve.dm.nodeFactory;
	return (
		// Data exists at offsets
		( left !== undefined && right !== undefined ) &&
		(
			// If there's content on the left or the right of the offset than we are good
			// <paragraph>|a|</paragraph>
			( typeof left === 'string' || typeof right === 'string' ) ||
			// Same checks but for annotated characters - isArray is slower, try it next
			( ve.isArray( left ) || ve.isArray( right ) ) ||
			// The most expensive test are last, these deal with elements
			(
				// Right of a leaf
				// <paragraph><image></image>|</paragraph>
				(
					// Is an element
					typeof left.type === 'string' &&
					// Is a closing
					left.type.charAt( 0 ) === '/' &&
					// Is a leaf
					factory.isNodeContent( left.type.substr( 1 ) )
				) ||
				// Left of a leaf
				// <paragraph>|<image></image></paragraph>
				(
					// Is an element
					typeof right.type === 'string' &&
					// Is not a closing
					right.type.charAt( 0 ) !== '/' &&
					// Is a leaf
					factory.isNodeContent( right.type )
				) ||
				// Inside empty content branch
				// <paragraph>|</paragraph>
				(
					// Inside empty element
					'/' + left.type === right.type &&
					// Both are content branches (right is the same type)
					factory.canNodeContainContent( left.type )
				)
			)
		)
	);
};

/**
 * Checks if structure can be inserted at an offset in document data.
 *
 * If the {unrestricted} param is true than only offsets where any kind of element can be inserted
 * will return true. This can be used to detect the difference between a location that a paragraph
 * can be inserted, such as between two tables but not direclty inside a table.
 *
 * This method assumes that any value that has a type property that's a string is an element object.
 *
 * @example Structural offsets (unrestricted = false):
 *      <heading> a </heading> <paragraph> b c <img> </img> </paragraph>
 *     ^         . .          ^           . . .     .      .            ^
 *
 * @example Structural offsets (unrestricted = true):
 *      <heading> a </heading> <paragraph> b c <img> </img> </paragraph>
 *     ^         . .          ^           . . .     .      .            ^
 *
 * @example Structural offsets (unrestricted = false):
 *      <list> <listItem> </listItem> <list>
 *     ^      ^          ^           ^      ^
 *
 * @example Content branch offsets (unrestricted = true):
 *      <list> <listItem> </listItem> <list>
 *     ^      .          ^           .      ^
 *
 * @static
 * @method
 * @param {Array} data Document data
 * @param {Integer} offset Document offset
 * @param {Boolean} [unrestricted] Only return true if any kind of element can be inserted at offset
 * @returns {Boolean} Structure can be inserted at offset
 */
ve.dm.Document.isStructuralOffset = function( data, offset, unrestricted ) {
	// Edges are always structural
	if ( offset === 0 || offset === data.length ) {
		return true;
	}
	// Offsets must be within range and both sides must be elements
	var left = data[offset - 1],
		right = data[offset],
		factory = ve.dm.nodeFactory;
	return (
		(
			left !== undefined &&
			right !== undefined &&
			typeof left.type === 'string' &&
			typeof right.type === 'string'
		) &&
		(
			// Right of a branch
			// <list><listItem><paragraph>a</paragraph>|</listItem>|</list>|
			(
				// Is a closing
				left.type.charAt( 0 ) === '/' &&
				// Is a branch or non-content leaf
				(
					factory.canNodeHaveChildren( left.type.substr( 1 ) ) ||
					!factory.isNodeContent( left.type.substr( 1 ) )
				) &&
				(
					// Only apply this rule in unrestricted mode
					!unrestricted ||
					// Right of an unrestricted branch
					// <list><listItem><paragraph>a</paragraph>|</listItem></list>|
					// Both are non-content branches that can have any kind of child
					factory.getParentNodeTypes( left.type.substr( 1 ) ) === null
				)
			) ||
			// Left of a branch
			// |<list>|<listItem>|<paragraph>a</paragraph></listItem></list>
			(
				// Is not a closing
				right.type.charAt( 0 ) !== '/' &&
				// Is a branch or non-content leaf
				(
					factory.canNodeHaveChildren( right.type ) ||
					!factory.isNodeContent( right.type )
				) &&
				(
					// Only apply this rule in unrestricted mode
					!unrestricted ||
					// Left of an unrestricted branch
					// |<list><listItem>|<paragraph>a</paragraph></listItem></list>
					// Both are non-content branches that can have any kind of child
					factory.getParentNodeTypes( right.type ) === null
				)
			) ||
			// Inside empty non-content branch
			// <list>|</list> or <list><listItem>|</listItem></list>
			(
				// Inside empty element
				'/' + left.type === right.type &&
				// Both are non-content branches (right is the same type)
				factory.canNodeHaveGrandchildren( left.type ) &&
				(
					// Only apply this rule in unrestricted mode
					!unrestricted ||
					// Both are non-content branches that can have any kind of child
					factory.getChildNodeTypes( left.type ) === null
				)
			)
		)
	);
};

/**
 * Checks if a data at a given offset is an element.
 *
 * This method assumes that any value that has a type property that's a string is an element object.
 *
 * @example Element data:
 *      <heading> a </heading> <paragraph> b c <img></img> </paragraph>
 *     ^         . ^          ^           . . ^     ^     ^            .
 *
 * @static
 * @method
 * @param {Array} data Document data
 * @param {Integer} offset Document offset
 * @returns {Boolean} Data at offset is an element
 */
ve.dm.Document.isElementData = function( data, offset ) {
	// Data exists at offset and appears to be an element
	return data[offset] !== undefined && typeof data[offset].type === 'string';
};

/**
 * Checks for elements in document data.
 *
 * This method assumes that any value that has a type property that's a string is an element object.
 * Elements are discovered by iterating through the entire data array (backwards).
 *
 * @static
 * @method
 * @param {Array} data Document data
 * @returns {Boolean} At least one elements exists in data
 */
ve.dm.Document.containsElementData = function( data ) {
	var i = data.length;
	while ( i-- ) {
		if ( data[i].type !== undefined ) {
			return true;
		}
	}
	return false;
};

/**
 * Checks for non-content elements in document data.
 *
 * This method assumes that any value that has a type property that's a string is an element object.
 * Elements are discovered by iterating through the entire data array.
 *
 * @static
 * @method
 * @param {Array} data Document data
 * @returns {Boolean} True if all elements in data are content elements
 */
ve.dm.Document.isContentData = function( data ) {
	for ( var i = 0, len = data.length; i < len; i++ ) {
		if ( data[i].type !== undefined &&
			data[i].type.charAt( 0 ) !== '/' &&
			!ve.dm.nodeFactory.isNodeContent( data[i].type )
		) {
			return false;
		}
	}
	return true;
};

/* Methods */

/**
 * Gets slice or copy of the document data.
 *
 * @method
 * @param {ve.Range} [range] Range of data to get, all data will be given by default
 * @param {Boolean} [deep=false] Whether to return a deep copy (WARNING! This may be very slow)
 * @returns {Array} Slice or copy of document data
 */
ve.dm.Document.prototype.getData = function( range, deep ) {
	var start = 0,
		end;
	if ( range !== undefined ) {
		range.normalize();
		start = Math.max( 0, Math.min( this.data.length, range.start ) );
		end = Math.max( 0, Math.min( this.data.length, range.end ) );
	}
	// IE work-around: arr.slice( 0, undefined ) returns [] while arr.slice( 0 ) behaves correctly
	var data = end === undefined ? this.data.slice( start ) : this.data.slice( start, end );
	// Return either the slice or a deep copy of the slice
	return deep ? ve.copyArray( data ) : data;
};

ve.dm.Document.prototype.getOffsetMap = function() {
	return this.offsetMap;
};

ve.dm.Document.prototype.getNodeFromOffset = function( offset ) {
	return this.offsetMap[offset];
};

/**
 * Gets the content data of a node.
 *
 * @method
 * @param {ve.dm.Node} node Node to get content data for
 * @returns {Array|null} List of content and elements inside node or null if node is not found
 */
ve.dm.Document.prototype.getDataFromNode = function( node ) {
	var length = node.getLength(),
		offset = this.documentNode.getOffsetFromNode( node );
	if ( offset >= 0 ) {
		// XXX: If the node is wrapped in an element than we should increment the offset by one so
		// we only return the content inside the element.
		if ( node.isWrapped() ) {
			offset++;
		}
		return this.data.slice( offset, offset + length );
	}
	return null;
};

/**
 * Gets a list of annotations that a given offset is covered by.
 *
 * @method
 * @param {Integer} offset Offset to get annotations for
 * @returns {Object[]} A copy of all annotation objects offset is covered by
 */
ve.dm.Document.prototype.getAnnotationsFromOffset = function( offset ) {
	var annotations;
	// Since annotations are not stored on a closing leaf node,
	// rewind offset by 1 to return annotations for that structure
	if (
		ve.isPlainObject( this.data[offset] ) && // structural offset
		this.data[offset].hasOwnProperty('type') && // just in case
		this.data[offset].type.charAt( 0 ) === '/' && // closing offset
		ve.dm.nodeFactory.canNodeHaveChildren(
			this.data[offset].type.substr( 1 )
		) === false // leaf node
	){
		offset = this.getRelativeContentOffset( offset, -1 );
	}

	annotations = ve.isArray( this.data[offset] ) ?
		this.data[offset][1] : this.data[offset].annotations;

	if ( ve.isPlainObject( annotations ) ) {
		return ve.getObjectValues( annotations );
	}
	return [];
};

/**
 * Does this offset contain the specified annotation
 *
 * @method
 * @param {Integer} offset Offset to look at
 * @param {Object} annotation Object to look for
 * @returns {Boolean} Whether an offset contains the specified annotation
 */
ve.dm.Document.prototype.offsetContainsAnnotation = function ( offset, annotation ) {
	var annotations = this.getAnnotationsFromOffset( offset );
	for ( var a=0; a<annotations.length; a++ ) {
		if ( ve.compareObjects( annotations[a], annotation ) ){
			return true;
		}
	}
	return false;
};

/**
 * Gets the range of content surrounding a given offset that's covered by a given annotation.
 *
 * @param {Integer} offset Offset to begin looking forward and backward from
 * @param {Object} annotation Annotation to test for coverage with
 * @returns {ve.Range|null} Range of content covered by annotation, or null if offset is not covered
 */
ve.dm.Document.prototype.getAnnotatedRangeFromOffset = function ( offset, annotation ) {
	var start = offset,
		end = offset;
	if ( this.offsetContainsAnnotation( offset, annotation ) === false ) {
		return null;
	}
	while ( start > 0 ) {
		start--;
		if ( this.offsetContainsAnnotation( start, annotation ) === false ) {
			start++;
			break;
		}
	}
	while ( end < this.data.length ) {
		if ( this.offsetContainsAnnotation(end, annotation ) === false ) {
			break;
		}
		end++;
	}
	return new ve.Range( start, end );
};

/**
 * Checks if a character has matching annotations.
 *
 * @static
 * @method
 * @param {Integer} offset Offset of annotated character
 * @param {RegExp} pattern Regular expression pattern to match with
 * @returns {Boolean} Character has matching annotations
 */
ve.dm.Document.prototype.offsetContainsMatchingAnnotations = function( offset, pattern ) {
	if ( !( pattern instanceof RegExp ) ) {
		throw 'Invalid Pattern. Pattern not instance of RegExp';
	}
	var annotations = ve.isArray( this.data[offset] ) ?
		this.data[offset][1] : this.data[offset].annotations;
	if ( ve.isPlainObject( annotations ) ) {
		for ( var hash in annotations ) {
			if ( pattern.test( annotations[hash].type ) ) {
				return true;
			}
		}
	}
	return false;
};

/**
 * Gets a list of annotations that match a regular expression at an offset
 *
 * @method
 * @param {Integer} offset Offset of annotated character
 * @param {RegExp} pattern Regular expression pattern to match with
 * @returns {Object} Annotations that match the pattern
 */
ve.dm.Document.prototype.getMatchingAnnotationsFromOffset = function( offset, pattern ) {
	if ( !( pattern instanceof RegExp ) ) {
		throw 'Invalid Pattern. Pattern not instance of RegExp';
	}
	var matches = {},
		annotations = ve.isArray( this.data[offset] ) ?
			this.data[offset][1] : this.data[offset].annotations;
	if ( ve.isPlainObject( annotations ) ) {
		for ( var hash in annotations ) {
			if ( pattern.test( annotations[hash].type ) ){
				matches[hash] = annotations[hash];
			}
		}
	}
	return matches;
};

/**
 * Gets a list of annotations annotations that match a regular expression.
 *
 * @static
 * @method
 * @param {Array} annotations Annotations to search through
 * @param {RegExp} pattern Regular expression pattern to match with
 * @returns {Object} Annotations that match the pattern
 */
ve.dm.Document.getMatchingAnnotations = function( annotations, pattern ) {
	if ( !( pattern instanceof RegExp ) ) {
		throw 'Invalid Pattern. Pattern not instance of RegExp';
	}
	var matches = null;
	if ( ve.isPlainObject( annotations ) ) {
		for ( var hash in annotations ) {
			if ( pattern.test( annotations[hash].type ) ){
				matches[hash] = annotations[hash];
			}
		}
	}
	return matches;
};

/**
 * Gets an array of common annnotations across a range.
 *
 * @method
 * @param {Integer} offset Offset to get annotations for
 * @returns {Object[]} A copy of all annotation objects offset is covered by
 */
ve.dm.Document.prototype.getAnnotationsFromRange = function( range ) {
	var	currentChar = {},
		annotations = [],
		charCount = 0,
		map = {};
		
	range.normalize();
	for ( var i = range.start; i < range.end; i++ ) {
		// skip non characters
		if ( ve.dm.Document.isElementData( this.data, i ) ) {
			continue;
		}
		//current character annotations
		currentChar = this.data[i][1];
		// if a non annotated character, no commonality.
		if ( currentChar === undefined ) {
			return [];
		}
		charCount++;
		// if current char annotations are not the same as previous char.
		if ( ve.compareObjects( map, currentChar ) === false) {
			//retain common annotations
			if ( charCount > 1 ) {
				// look for annotation in map
				for ( var a in currentChar ) {
					if( map[a] === undefined ) {
						delete currentChar[a];
					}
				}
			}
		}
		//save map
		map = currentChar;
	}
	// build array of annotations
	for ( var key in map ) {
		annotations.push( map[key] );
	}
	return annotations;
};

/**
 * Rebuild one or more nodes following a change in linear model data.
 *
 * The data provided to this method may contain either one node or multiple sibling nodes, but it
 * must be balanced and valid. Data provided to this method also may not contain any content at the
 * top level. The tree and offset map are updated during this operation.
 *
 * Process:
 *  1. Nodes between {index} and {index} + {numNodes} in {parent} will be removed
 *  2. Data will be retrieved from this.data using {offset} and {newLength}
 *  3. A document fragment will be generated from the retrieved data
 *  4. The document fragment's offset map will be inserted into this document at {offset}
 *  5. The document fragment's nodes will be inserted into {parent} at {index}
 *
 * Use cases:
 *  1. Rebuild old nodes and offset data after a change to the linear model.
 *  2. Insert new nodes and offset data after a insertion in the linear model.
 *
 * @param {ve.dm.Node} parent Parent of the node(s) being rebuilt
 * @param {Integer} index Index within parent to rebuild or insert nodes
 *   - If {numNodes} == 0: Index to insert nodes at
 *   - If {numNodes} >= 1: Index of first node to rebuild
 * @param {Integer} numNodes Total number of nodes to rebuild
 *   - If {numNodes} == 0: Nothing  will be rebuilt, but the node(s) built from data will be
 *     inserted before {index}. To insert nodes at the end, use number of children in {parent}
 *   - If {numNodes} == 1: Only the node at {index} will be rebuilt
 *   - If {numNodes} > 1: The node at {index} and the next {numNodes-1} nodes will be rebuilt
 * @param {Integer} offset Linear model offset to rebuild or insert offset map data
 *   - If {numNodes} == 0: Offset to insert offset map data at
 *   - If {numNodes} >= 1: Offset to remove old and insert new offset map data at
 * @param {Integer} newLength Length of data in linear model to rebuild or insert nodes for
 * @returns {ve.dm.Node[]} Array containing the rebuilt/inserted nodes
 */
ve.dm.Document.prototype.rebuildNodes = function( parent, index, numNodes, offset, newLength ) {
	// Compute the length of the old nodes (so we can splice their offsets out of the offset map)
	var oldLength = 0;
	for ( var i = index; i < index + numNodes; i++ ) {
		oldLength += parent.children[i].getOuterLength();
	}
	// Get a slice of the document where it's been changed
	var data = this.data.slice( offset, offset + newLength );
	// Build document fragment from data
	var fragment = new ve.dm.Document( data, this );
	// Get generated child nodes from the document fragment
	var nodes = fragment.getDocumentNode().getChildren();
	// Replace nodes in the model tree
	ve.batchSplice( parent, index, numNodes, nodes );
	// Update offset map
	ve.batchSplice( this.offsetMap, offset, oldLength, fragment.getOffsetMap() );
	// Return inserted nodes
	return nodes;
};

/**
 * Gets an offset a given distance from another using a callback to check if offsets are valid.
 *
 * - If {offset} is not already valid, one step will be used to move it to an valid one.
 * - If {distance} is zero the result will either be {offset} if it's already valid or the
 *   nearest valid offset to the right if possible and to the left otherwise.
 * - If {offset} is after the last valid offset and {distance} is >= 1, or if {offset} if
 *   before the first valid offset and {distance} <= 1 than the result will be the nearest
 *   valid offset in the opposite direction.
 * - If the document does not contain a single valid offset the result will be -1
 *
 * @method
 * @param {Integer} offset Offset to start from
 * @param {Integer} distance Number of valid offsets to move
 * @param {Function} callback Function to call to check if an offset is valid which will be
 * given two intital arguments of data and offset
 * @param {Mixed} [...] Additional arguments to pass to the callback
 * @returns {Integer} Relative valid offset or -1 if there are no valid offsets in document
 */
ve.dm.Document.prototype.getRelativeOffset = function( offset, distance, callback ) {
	var args = Array.prototype.slice.call( arguments, 3 );
	// If offset is already a structural offset and distance is zero than no further work is needed,
	// otherwise distance should be 1 so that we can get out of the invalid starting offset
	if ( distance === 0 ) {
		if ( callback.apply( window, [this.data, offset].concat( args ) ) ) {
			return offset;
		} else {
			distance = 1;
		}
	}
	var direction = (
			offset <= 0 ? 1 : (
				offset >= this.data.length ? -1 : (
					distance > 0 ? 1 : -1
				)
			)
		),
		start = offset,
		i = start + direction,
		steps = 0,
		turnedAround = false;
	distance = Math.abs( distance );
	offset = -1;
	while ( i >= 0 && i <= this.data.length ) {
		if ( callback.apply( window, [this.data, i].concat( args ) ) ) {
			steps++;
			offset = i;
			if ( distance === steps ) {
				return offset;
			}
		} else if (
			// Don't keep turning around over and over
			!turnedAround &&
			// Only turn around if not a single step could be taken
			steps === 0 &&
			// Only turn around if we're about to reach the edge
			( ( direction < 0 && i === 0 ) || ( direction > 0 && i === this.data.length ) )
		) {
			// Start over going in the opposite direction
			direction *= -1;
			i = start;
			distance = 1;
			turnedAround = true;
		}
		i += direction;
	}
	return offset;
};

/**
 * Gets a content offset a given distance forwards or backwards from another.
 *
 * This method is a wrapper around {getRelativeOffset}, using {ve.dm.Document.isContentOffset} as
 * the offset validation callback.
 *
 * @method
 * @param {Integer} offset Offset to start from
 * @param {Integer} distance Number of content offsets to move
 * @returns {Integer} Relative content offset or -1 if there are no valid offsets in document
 */
ve.dm.Document.prototype.getRelativeContentOffset = function( offset, distance ) {
	return this.getRelativeOffset( offset, distance, ve.dm.Document.isContentOffset );
};

/**
 * Gets the nearest content offset to a given offset.
 *
 * If the offset is already a valid offset, it will be returned unchanged. This method differs from
 * calling {getRelativeContentOffset} with a zero length differece because the direction can be
 * controlled without nessecarily moving the offset if it's already valid. Also, if the direction
 * is 0 or undefined than nearest offsets will be found to the left and right and the one with the
 * shortest distance will be used.
 *
 * This method is a wrapper around {getRelativeOffset}, using {ve.dm.Document.isContentOffset} as
 * the offset validation callback.
 *
 * @method
 * @param {Integer} offset Offset to start from
 * @param {Integer} [direction] Direction to prefer matching offset in, -1 for left and 1 for right
 * @returns {Integer} Nearest content offset or -1 if there are no valid offsets in document
 */
ve.dm.Document.prototype.getNearestContentOffset = function( offset, direction ) {
	if ( ve.dm.Document.isContentOffset( this.data, offset ) ) {
		return offset;
	}
	if ( direction === undefined ) {
		var left = this.getRelativeOffset( offset, -1, ve.dm.Document.isContentOffset ),
			right = this.getRelativeOffset( offset, 1, ve.dm.Document.isContentOffset );
		return offset - left < right - offset ? left : right;
	} else {
		return this.getRelativeOffset(
			offset, direction > 0 ? 1 : -1, ve.dm.Document.isContentOffset
		);
	}
};

/**
 * Gets a structural offset a given distance forwards or backwards from another.
 *
 * This method is a wrapper around {getRelativeOffset}, using {ve.dm.Document.isStructuralOffset} as
 * the offset validation callback.
 *
 * @method
 * @param {Integer} offset Offset to start from
 * @param {Integer} distance Number of structural offsets to move
 * @param {Boolean} [unrestricted] Only return true if any kind of element can be inserted at offset
 * @returns {Integer} Relative structural offset
 */
ve.dm.Document.prototype.getRelativeStructuralOffset = function( offset, distance, unrestricted ) {
	// Optimization: start and end are always unrestricted structural offsets
	if ( distance === 0 && ( offset === 0 || offset === this.data.length ) ) {
		return offset;
	}
	return this.getRelativeOffset(
		offset, distance, ve.dm.Document.isStructuralOffset, unrestricted
	);
};

/**
 * Gets the nearest structural offset to a given offset.
 *
 * If the offset is already a valid offset, it will be returned unchanged. This method differs from
 * calling {getRelativeStructuralOffset} with a zero length differece because the direction can be
 * controlled without nessecarily moving the offset if it's already valid. Also, if the direction
 * is 0 or undefined than nearest offsets will be found to the left and right and the one with the
 * shortest distance will be used.
 *
 * This method is a wrapper around {getRelativeOffset}, using {ve.dm.Document.isStructuralOffset} as
 * the offset validation callback.
 *
 * @method
 * @param {Integer} offset Offset to start from
 * @param {Integer} [direction] Direction to prefer matching offset in, -1 for left and 1 for right
 * @param {Boolean} [unrestricted] Only return true if any kind of element can be inserted at offset
 * @returns {Integer} Nearest structural offset
 */
ve.dm.Document.prototype.getNearestStructuralOffset = function( offset, direction, unrestricted ) {
	if ( ve.dm.Document.isStructuralOffset( this.data, offset, unrestricted ) ) {
		return offset;
	}
	if ( !direction ) {
		var left = this.getRelativeOffset(
				offset, -1, ve.dm.Document.isStructuralOffset, unrestricted
			),
			right = this.getRelativeOffset(
				offset, 1, ve.dm.Document.isStructuralOffset, unrestricted
			);
		return offset - left < right - offset ? left : right;
	} else {
		return this.getRelativeOffset(
			offset, direction > 0 ? 1 : -1, ve.dm.Document.isStructuralOffset, unrestricted
		);
	}
};

// TODO this function needs more work but it seems to work, mostly
/**
 * Fix up data so it can safely be inserted into the linear model at offset.
 * @param data {Array} Snippet of linear model data to insert
 * @param offset {Integer} Offset in the linear model where the caller wants to insert data
 * @returns {Array} A (possibly modified) copy of data
 */
ve.dm.Document.prototype.fixupInsertion = function( data, offset ) {
	var
		// Array where we build the return value
		newData = [],

		// *** Stacks ***
		// Array of element openings (object). Openings in data are pushed onto this stack
		// when they are encountered and popped off when they are closed
		openingStack = [],
		// Array of element types (strings). Closings in data that close nodes that were
		// not opened in data (i.e. were already in the document) are pushed onto this stack
		// and popped off when balanced out by an opening in data
		closingStack = [],
		// Array of objects describing wrappers that need to be fixed up when a given
		// element is closed.
		//     'expectedType': closing type that triggers this fixup. Includes initial '/'
		//     'openings': array of opening elements that should be closed (in reverse order)
		//     'reopenElements': array of opening elements to insert (in reverse order)
		fixupStack = [],

		// *** State persisting across iterations of the outer loop ***
		// The node (from the document) we're currently in. When in a node that was opened
		// in data, this is set to its first ancestor that is already in the document
		parentNode,
		// The type of the node we're currently in, even if that node was opened within data
		parentType,

		// *** Temporary variables that do not persist across iterations ***
		// The type of the node we're currently inserting. When the to-be-inserted node
		// is wrapped, this is set to the type of the outer wrapper.
		childType,
		// Stores the return value of getParentNodeTypes( childType )
		allowedParents,
		// Stores the return value of getChildNodeTypes( parentType )
		allowedChildren,
		// Whether parentType matches allowedParents
		parentsOK,
		// Whether childType matches allowedChildren
		childrenOK,
		// Array of opening elements to insert (for wrapping the to-be-inserted element)
		openings,
		// Array of closing elements to insert (for splitting nodes)
		closings,
		// Array of opening elements matching the elements in closings (in the same order)
		reopenElements,
		// Temporary variable for building a clone of the current element
		clonedElement,

		// *** Other variables ***
		// Used to store values popped from various stacks
		popped,
		// Loop variables
		i, j;

	/**
	 * Append a linear model element to newData and update the state.
	 *
	 * This function updates parentNode, parentType, openingStack and closingStack.
	 *
	 * @param {Object|Array|String} element Linear model element
	 * @param {Number} index Index in data that this element came from. Used for error reporting only
	 */
	function writeElement( element, index ) {
		var expectedType;
		if ( element.type === undefined ) {
			// Content, do nothing
		} else if ( element.type.charAt( 0 ) !== '/' ) {
			// Opening
			// Check if this opening balances an earlier closing of a node
			// that was already in the document. This is only the case if
			// openingStack is empty (otherwise we still have unclosed nodes from
			// within data) and if this opening matches the top of closingStack
			if ( openingStack.length === 0 && closingStack.length > 0 &&
				closingStack[closingStack.length - 1] === element.type
			) {
				// The top of closingStack is now balanced out, so remove it
				closingStack.pop();
			} else {
				// This opens something new, put it on openingStack
				openingStack.push( element );
			}
			parentType = element.type;
		} else {
			// Closing
			// Make sure that this closing matches the currently opened node
			if ( openingStack.length > 0 ) {
				// The opening was on openingStack, so we're closing
				// a node that was opened within data. Don't track
				// that on closingStack
				expectedType = openingStack.pop().type;
			} else {
				// openingStack is empty, so we're closing a node that
				// was already in the document. This means we have to
				// reopen it later, so track this on closingStack
				expectedType = parentNode.getType();
				closingStack.push( expectedType );
				parentNode = parentNode.getParent();
				if ( !parentNode ) {
					throw 'Inserted data is trying to close the root node ' +
						'(at index ' + index + ')';
				}
			}
			parentType = expectedType;

			// Validate
			// FIXME this breaks certain input, should fix it up, not scream and die
			if ( element.type !== '/' + expectedType ) {
				throw 'Type mismatch, expected /' + expectedType +
					' but got ' + element.type + ' (at index ' + index + ')';
			}
		}
		newData.push( element );
	}

	parentNode = this.getNodeFromOffset( offset );
	parentType = parentNode.getType();
	for ( i = 0; i < data.length; i++ ) {
		if ( data[i].type === undefined ||  data[i].type.charAt( 0 ) !== '/' ) {
			childType = data[i].type || 'text';
			openings = [];
			closings = [];
			reopenElements = [];
			// Opening or content
			// Make sure that opening this element here does not violate the
			// parent/children/content rules. If it does, insert stuff to fix it

			// If this node is content, check that the containing node can contain
			// content. If not, wrap in a paragraph
			if ( ve.dm.nodeFactory.isNodeContent( childType ) &&
				!ve.dm.nodeFactory.canNodeContainContent( parentType )
			) {
				childType = 'paragraph';
				openings.unshift ( { 'type': 'paragraph' } );                            
			}

			// Check that this node is allowed to have the containing node as its
			// parent. If not, wrap it until it's fixed
			do {
				allowedParents = ve.dm.nodeFactory.getParentNodeTypes( childType );
				parentsOK = allowedParents === null ||
					$.inArray( parentType, allowedParents ) !== -1;
				if ( !parentsOK ) {
					// We can't have this as the parent
					if ( allowedParents.length === 0 ) {
						throw 'Cannot insert ' + childType + ' because it ' +
							' cannot have a parent (at index ' + i + ')';
					}
					// Open an allowed node around this node
					childType = allowedParents[0];
					openings.unshift( { 'type': childType } );
				}
			} while ( !parentsOK );

			// Check that the containing node can have this node as its child. If not,
			// close nodes until it's fixed
			do {
				allowedChildren = ve.dm.nodeFactory.getChildNodeTypes( parentType );
				childrenOK = allowedChildren === null ||
					$.inArray( childType, allowedChildren ) !== -1;
				// Also check if we're trying to insert structure into a node that
				// has to contain content
				childrenOK = childrenOK && !(
					!ve.dm.nodeFactory.isNodeContent( childType ) &&
					ve.dm.nodeFactory.canNodeContainContent( parentType )
				);
				if ( !childrenOK ) {
					// We can't insert this into this parent
					// Close the parent and try one level up
					closings.push( { 'type': '/' + parentType } );
					if ( openingStack.length > 0 ) {
						popped = openingStack.pop();
						parentType = popped.type;
						reopenElements.push( ve.copyObject( popped ) );
						// The opening was on openingStack, so we're closing
						// a node that was opened within data. Don't track
						// that on closingStack
					} else {
						// openingStack is empty, so we're closing a node that
						// was already in the document. This means we have to
						// reopen it later, so track this on closingStack
						closingStack.push( parentType );
						clonedElement = { 'type': parentType };
						if ( !$.isEmptyObject( parentNode.getAttributes() ) ) {
							clonedElement.attributes = ve.copyObject( parentNode.getAttributes() );
						}
						reopenElements.push( clonedElement );
						parentNode = parentNode.getParent();
						if ( !parentNode ) {
							throw 'Cannot insert ' + childType + ' even ' +
								' after closing all containing nodes ' +
								'(at index ' + i + ')';
						}
						parentType = parentNode.getType();
					}
				}
			} while( !childrenOK );

			for ( j = 0; j < closings.length; j++ ) {
				// writeElement() would update openingStack/closingStack, but
				// we've already done that for closings
				//writeElement( closings[j], i );
				newData.push( closings[j] );
			}
			for ( j = 0; j < openings.length; j++ ) {
				writeElement( openings[j], i );
			}
			writeElement( data[i], i );
			if ( data[i].type === undefined ) {
				// Special treatment for text nodes
				if ( openings.length > 0 ) {
					// We wrapped the text node, update parentType
					parentType = childType;
					fixupStack.push( { 'expectedType': '/' + childType, 'openings': openings, 'reopenElements': reopenElements } );
				}
				// If we didn't wrap the text node, then the node we're inserting
				// into can have content, so we couldn't have closed anything
			} else {
				fixupStack.push( { 'expectedType': '/' + data[i].type, 'openings': openings, 'reopenElements': reopenElements } );
				parentType = data[i].type;
			}
		} else {
			// Closing
			writeElement( data[i], i );
			// TODO don't close fixup stuff if the next thing immediately needs to be fixed up as well;
			// instead, merge the two wrappers
			if ( fixupStack.length > 0 && fixupStack[fixupStack.length - 1].expectedType == data[i].type ) {
				popped = fixupStack.pop();
				// Go through these in reverse!
				for ( j = popped.openings.length - 1; j >= 0; j-- ) {
					writeElement( { 'type': '/' + popped.openings[j].type }, i );
				}
				for ( j = popped.reopenElements.length - 1; j >= 0; j-- ) {
					writeElement( popped.reopenElements[j], i );
				}
			}
			parentType = openingStack.length > 0 ? openingStack[openingStack.length - 1] : parentNode.getType();
		}
	}

	// Close unclosed openings
	while ( openingStack.length > 0 ) {
		popped = openingStack[openingStack.length - 1];
		// writeElement() will perform the actual pop() that removes
		// popped from openingStack
		writeElement( { 'type': '/' + popped.type }, i );
	}
	// Re-open closed nodes
	while ( closingStack.length > 0 ) {
		popped = closingStack[closingStack.length - 1];
		// writeElement() will perform the actual pop() that removes
		// popped from closingStack
		writeElement( { 'type': popped }, i );
	}

	return newData;
};

/* Inheritance */

ve.extendClass( ve.dm.Document, ve.Document );