define([
	"underscore",
	"crel",
	"extensions/markdownExtra",
	"classes/Extension",
	"text!html/partialRenderingSettingsBlock.html",
], function(_, crel, markdownExtra, Extension, partialRenderingSettingsBlockHTML) {

	var partialRendering = new Extension("partialRendering", "Partial Rendering", true);
	partialRendering.settingsBlock = partialRenderingSettingsBlockHTML;

	var converter;
	var doFootnotes = false;
	var hasFootnotes = false;
	var currentSectionList = [];

	var sectionList = [];
	var linkDefinition;
	var sectionsToRemove = [];
	var modifiedSections = [];
	var insertBeforeSection;
	var fileChanged = false;

	function updateSectionList() {
		var newSectionList = [];
		var newLinkDefinition = '\n';
		hasFootnotes = false;
		_.each(currentSectionList, function(section) {
			var text = '\n<div class="se-preview-section-delimiter"></div>\n\n' + section.text + '\n\n';

			// Strip footnotes
			if(doFootnotes) {
				text = text.replace(/^```.*\n[\s\S]*?\n```|\n[ ]{0,3}\[\^(.+?)\]\:[ \t]*\n?([\s\S]*?)\n{1,2}((?=\n[ ]{0,3}\S)|$)/gm, function(wholeMatch, footnote) {
					if(footnote) {
						hasFootnotes = true;
						newLinkDefinition += wholeMatch.replace(/^\s*\n/gm, '') + '\n';
						return "";
					}
					return wholeMatch;
				});
			}

			// Strip link definitions
			text = text.replace(/^```.*\n[\s\S]*?\n```|^[ ]{0,3}\[(.+)\]:[ \t]*\n?[ \t]*<?(\S+?)>?(?=\s|$)[ \t]*\n?[ \t]*((\n*)["(](.+?)[")][ \t]*)?(?:\n+)/gm, function(wholeMatch, link) {
				if(link) {
					newLinkDefinition += wholeMatch.replace(/^\s*\n/gm, '') + '\n';
					return "";
				}
				return wholeMatch;
			});

			// Add section to the newSectionList
			newSectionList.push({
				id: section.id,
				text: text + '\n'
			});
		});

		modifiedSections = [];
		sectionsToRemove = [];
		insertBeforeSection = undefined;

		// Render everything if file or linkDefinition changed
		if(fileChanged === true || linkDefinition != newLinkDefinition) {
			fileChanged = false;
			linkDefinition = newLinkDefinition;
			sectionsToRemove = sectionList;
			sectionList = newSectionList;
			modifiedSections = newSectionList;
			return;
		}

		// Find modified section starting from top
		var leftIndex = sectionList.length;
		_.some(sectionList, function(section, index) {
			if(index >= newSectionList.length || section.text != newSectionList[index].text) {
				leftIndex = index;
				return true;
			}
		});

		// Find modified section starting from bottom
		var rightIndex = -sectionList.length;
		_.some(sectionList.slice().reverse(), function(section, index) {
			if(index >= newSectionList.length || section.text != newSectionList[newSectionList.length - index - 1].text) {
				rightIndex = -index;
				return true;
			}
		});

		if(leftIndex - rightIndex > sectionList.length) {
			// Prevent overlap
			rightIndex = leftIndex - sectionList.length;
		}

		// Create an array composed of left unmodified, modified, right
		// unmodified sections
		var leftSections = sectionList.slice(0, leftIndex);
		modifiedSections = newSectionList.slice(leftIndex, newSectionList.length + rightIndex);
		var rightSections = sectionList.slice(sectionList.length + rightIndex, sectionList.length);
		insertBeforeSection = _.first(rightSections);
		sectionsToRemove = sectionList.slice(leftIndex, sectionList.length + rightIndex);
		sectionList = leftSections.concat(modifiedSections).concat(rightSections);
	}

	var footnoteMap = {};
	var footnoteFragment = document.createDocumentFragment();
	// Store one footnote elt in the footnote map
	function storeFootnote(footnoteElt) {
		var id = footnoteElt.id.substring(3);
		var oldFootnote = footnoteMap[id];
		oldFootnote && footnoteFragment.removeChild(oldFootnote);
		footnoteMap[id] = footnoteElt;
		footnoteFragment.appendChild(footnoteElt);
	}

	var footnoteContainerElt;
	var previewContentsElt;

	function refreshSections() {

		// Remove outdated sections
		_.each(sectionsToRemove, function(section) {
			var sectionElt = document.getElementById("wmd-preview-section-" + section.id);
			previewContentsElt.removeChild(sectionElt);
		});

		var wmdPreviewElt = document.getElementById("wmd-preview");
		var childNode = wmdPreviewElt.firstChild;

		function createSectionElt(section) {
			var sectionElt = crel('div', {
				id: 'wmd-preview-section-' + section.id,
				class: 'wmd-preview-section preview-content'
			});
			var isNextDelimiter = false;
			while(childNode) {
				var nextNode = childNode.nextSibling;
				var isDelimiter = childNode.className == 'se-preview-section-delimiter';
				if(isNextDelimiter === true && childNode.tagName == 'DIV' && isDelimiter) {
					// Stop when encountered the next delimiter
					break;
				}
				isNextDelimiter = true;
				if(childNode.tagName == 'DIV' && childNode.className == 'footnotes') {
					_.each(childNode.querySelectorAll("ol > li"), storeFootnote);
				}
				else {
					isDelimiter || sectionElt.appendChild(childNode);
				}
				childNode = nextNode;
			}
			return sectionElt;
		}

		var newSectionEltList = document.createDocumentFragment();
		_.each(modifiedSections, function(section) {
			newSectionEltList.appendChild(createSectionElt(section));
		});
		wmdPreviewElt.innerHTML = '';
		var insertBeforeElt = footnoteContainerElt;
		if(insertBeforeSection !== undefined) {
			insertBeforeElt = document.getElementById("wmd-preview-section-" + insertBeforeSection.id);
		}
		previewContentsElt.insertBefore(newSectionEltList, insertBeforeElt);

		// Rewrite footnotes in the footer and update footnote numbers
		footnoteContainerElt.innerHTML = '';
		var usedFootnoteIds = [];
		if(hasFootnotes === true) {
			var footnoteElts = crel('ol');
			_.each(previewContentsElt.querySelectorAll('a.footnote'), function(elt, index) {
				elt.textContent = index + 1;
				var id = elt.id.substring(6);
				usedFootnoteIds.push(id);
				var footnoteElt = footnoteMap[id];
				footnoteElt && footnoteElts.appendChild(footnoteElt.cloneNode(true));
			});
			if(usedFootnoteIds.length > 0) {
				// Append the whole footnotes at the end of the document
				footnoteContainerElt.appendChild(crel('div', {
					class: 'footnotes'
				}, crel('hr'), footnoteElts));
			}
			// Keep used footnotes only in our map
			Object.keys(footnoteMap).forEach(function(key) {
				if(usedFootnoteIds.indexOf(key) === -1) {
					footnoteFragment.removeChild(footnoteMap[key]);
					delete footnoteMap[key];
				}
			});
		}
	}

	partialRendering.onSectionsCreated = function(sectionListParam) {
		currentSectionList = sectionListParam;
	};

	partialRendering.onPagedownConfigure = function(editor) {
		converter = editor.getConverter();
		converter.hooks.chain("preConversion", function() {
			updateSectionList();
			var result = _.map(modifiedSections, function(section) {
				return section.text;
			});
			result.push(linkDefinition + "\n\n");
			return result.join("");
		});
		editor.hooks.chain("onPreviewRefresh", function() {
			refreshSections();
		});
	};

	partialRendering.onInit = function() {
		if(markdownExtra.enabled) {
			if(_.some(markdownExtra.config.extensions, function(extension) {
				return extension == "footnotes";
			})) {
				doFootnotes = true;
			}
		}
	};

	partialRendering.onReady = function() {
		footnoteContainerElt = crel('div', {
			id: 'wmd-preview-section-footnotes',
			class: 'preview-content'
		});
		previewContentsElt = document.getElementById("preview-contents");
		previewContentsElt.appendChild(footnoteContainerElt);
	};

	partialRendering.onFileSelected = function() {
		fileChanged = true;
	};

	return partialRendering;
});