function write_zip(wb/*:Workbook*/, opts/*:WriteOpts*/)/*:ZIP*/ {
	if(opts.bookType == "ods") return write_ods(wb, opts);
	if(opts.bookType == "xlsb") return write_zip_xlsxb(wb, opts);
	return write_zip_xlsx(wb, opts);
}

/* XLSX and XLSB writing are very similar.  Originally they were unified in one
   export function.  This is horrible for tree shaking in the common case (most
   applications need to export files in one format) so this function supports
   both formats while write_zip_xlsx only handles XLSX */
function write_zip_xlsxb(wb/*:Workbook*/, opts/*:WriteOpts*/)/*:ZIP*/ {
	_shapeid = 1024;
	if(wb && !wb.SSF) {
		wb.SSF = SSF.get_table();
	}
	if(wb && wb.SSF) {
		make_ssf(SSF); SSF.load_table(wb.SSF);
		// $FlowIgnore
		opts.revssf = evert_num(wb.SSF); opts.revssf[wb.SSF[65535]] = 0;
		opts.ssf = wb.SSF;
	}
	opts.rels = {}; opts.wbrels = {};
	opts.Strings = /*::((*/[]/*:: :any):SST)*/; opts.Strings.Count = 0; opts.Strings.Unique = 0;
	if(browser_has_Map) opts.revStrings = new Map();
	else { opts.revStrings = {}; opts.revStrings.foo = []; delete opts.revStrings.foo; }
	var wbext = opts.bookType == "xlsb" ? "bin" : "xml";
	var vbafmt = VBAFMTS.indexOf(opts.bookType) > -1;
	var ct = new_ct();
	fix_write_opts(opts = opts || {});
	var zip = zip_new();
	var f = "", rId = 0;

	opts.cellXfs = [];
	get_cell_style(opts.cellXfs, {}, {revssf:{"General":0}});

	if(!wb.Props) wb.Props = {};

	f = "docProps/core.xml";
	zip_add_file(zip, f, write_core_props(wb.Props, opts));
	ct.coreprops.push(f);
	add_rels(opts.rels, 2, f, RELS.CORE_PROPS);

	/*::if(!wb.Props) throw "unreachable"; */
	f = "docProps/app.xml";
	if(wb.Props && wb.Props.SheetNames){/* empty */}
	else if(!wb.Workbook || !wb.Workbook.Sheets) wb.Props.SheetNames = wb.SheetNames;
	else {
		var _sn = [];
		for(var _i = 0; _i < wb.SheetNames.length; ++_i)
			if((wb.Workbook.Sheets[_i]||{}).Hidden != 2) _sn.push(wb.SheetNames[_i]);
		wb.Props.SheetNames = _sn;
	}
	wb.Props.Worksheets = wb.Props.SheetNames.length;
	zip_add_file(zip, f, write_ext_props(wb.Props, opts));
	ct.extprops.push(f);
	add_rels(opts.rels, 3, f, RELS.EXT_PROPS);

	if(wb.Custprops !== wb.Props && keys(wb.Custprops||{}).length > 0) {
		f = "docProps/custom.xml";
		zip_add_file(zip, f, write_cust_props(wb.Custprops, opts));
		ct.custprops.push(f);
		add_rels(opts.rels, 4, f, RELS.CUST_PROPS);
	}

	for(rId=1;rId <= wb.SheetNames.length; ++rId) {
		var wsrels = {'!id':{}};
		var ws = wb.Sheets[wb.SheetNames[rId-1]];
		var _type = (ws || {})["!type"] || "sheet";
		switch(_type) {
		case "chart":
			/* falls through */
		default:
			f = "xl/worksheets/sheet" + rId + "." + wbext;
			zip_add_file(zip, f, write_ws(rId-1, f, opts, wb, wsrels));
			ct.sheets.push(f);
			add_rels(opts.wbrels, -1, "worksheets/sheet" + rId + "." + wbext, RELS.WS[0]);
		}

		if(ws) {
			var comments = ws['!comments'];
			var need_vml = false;
			if(comments && comments.length > 0) {
				var cf = "xl/comments" + rId + "." + wbext;
				zip_add_file(zip, cf, write_cmnt(comments, cf, opts));
				ct.comments.push(cf);
				add_rels(wsrels, -1, "../comments" + rId + "." + wbext, RELS.CMNT);
				need_vml = true;
			}
			if(ws['!legacy']) {
				if(need_vml) zip_add_file(zip, "xl/drawings/vmlDrawing" + (rId) + ".vml", write_comments_vml(rId, ws['!comments']));
			}
			delete ws['!comments'];
			delete ws['!legacy'];
		}

		if(wsrels['!id'].rId1) zip_add_file(zip, get_rels_path(f), write_rels(wsrels));
	}

	if(opts.Strings != null && opts.Strings.length > 0) {
		f = "xl/sharedStrings." + wbext;
		zip_add_file(zip, f, write_sst(opts.Strings, f, opts));
		ct.strs.push(f);
		add_rels(opts.wbrels, -1, "sharedStrings." + wbext, RELS.SST);
	}

	f = "xl/workbook." + wbext;
	zip_add_file(zip, f, write_wb(wb, f, opts));
	ct.workbooks.push(f);
	add_rels(opts.rels, 1, f, RELS.WB);

	/* TODO: something more intelligent with themes */

	f = "xl/theme/theme1.xml";
	zip_add_file(zip, f, write_theme(wb.Themes, opts));
	ct.themes.push(f);
	add_rels(opts.wbrels, -1, "theme/theme1.xml", RELS.THEME);

	/* TODO: something more intelligent with styles */

	f = "xl/styles." + wbext;
	zip_add_file(zip, f, write_sty(wb, f, opts));
	ct.styles.push(f);
	add_rels(opts.wbrels, -1, "styles." + wbext, RELS.STY);

	if(wb.vbaraw && vbafmt) {
		f = "xl/vbaProject.bin";
		zip_add_file(zip, f, wb.vbaraw);
		ct.vba.push(f);
		add_rels(opts.wbrels, -1, "vbaProject.bin", RELS.VBA);
	}

	f = "xl/metadata." + wbext;
	zip_add_file(zip, f, write_xlmeta(f));
	ct.metadata.push(f);
	add_rels(opts.wbrels, -1, "metadata." + wbext, RELS.XLMETA);

	zip_add_file(zip, "[Content_Types].xml", write_ct(ct, opts));
	zip_add_file(zip, '_rels/.rels', write_rels(opts.rels));
	zip_add_file(zip, 'xl/_rels/workbook.' + wbext + '.rels', write_rels(opts.wbrels));

	delete opts.revssf; delete opts.ssf;
	return zip;
}

function write_zip_xlsx(wb/*:Workbook*/, opts/*:WriteOpts*/)/*:ZIP*/ {
	_shapeid = 1024;
	if(wb && !wb.SSF) {
		wb.SSF = SSF.get_table();
	}
	if(wb && wb.SSF) {
		make_ssf(SSF); SSF.load_table(wb.SSF);
		// $FlowIgnore
		opts.revssf = evert_num(wb.SSF); opts.revssf[wb.SSF[65535]] = 0;
		opts.ssf = wb.SSF;
	}
	opts.rels = {}; opts.wbrels = {};
	opts.Strings = /*::((*/[]/*:: :any):SST)*/; opts.Strings.Count = 0; opts.Strings.Unique = 0;
	if(browser_has_Map) opts.revStrings = new Map();
	else { opts.revStrings = {}; opts.revStrings.foo = []; delete opts.revStrings.foo; }
	var wbext = "xml";
	var vbafmt = VBAFMTS.indexOf(opts.bookType) > -1;
	var ct = new_ct();
	fix_write_opts(opts = opts || {});
	var zip = zip_new();
	var f = "", rId = 0;

	opts.cellXfs = [];
	get_cell_style(opts.cellXfs, {}, {revssf:{"General":0}});

	if(!wb.Props) wb.Props = {};

	f = "docProps/core.xml";
	zip_add_file(zip, f, write_core_props(wb.Props, opts));
	ct.coreprops.push(f);
	add_rels(opts.rels, 2, f, RELS.CORE_PROPS);

	/*::if(!wb.Props) throw "unreachable"; */
	f = "docProps/app.xml";
	if(wb.Props && wb.Props.SheetNames){/* empty */}
	else if(!wb.Workbook || !wb.Workbook.Sheets) wb.Props.SheetNames = wb.SheetNames;
	else {
		var _sn = [];
		for(var _i = 0; _i < wb.SheetNames.length; ++_i)
			if((wb.Workbook.Sheets[_i]||{}).Hidden != 2) _sn.push(wb.SheetNames[_i]);
		wb.Props.SheetNames = _sn;
	}
	wb.Props.Worksheets = wb.Props.SheetNames.length;
	zip_add_file(zip, f, write_ext_props(wb.Props, opts));
	ct.extprops.push(f);
	add_rels(opts.rels, 3, f, RELS.EXT_PROPS);

	if(wb.Custprops !== wb.Props && keys(wb.Custprops||{}).length > 0) {
		f = "docProps/custom.xml";
		zip_add_file(zip, f, write_cust_props(wb.Custprops, opts));
		ct.custprops.push(f);
		add_rels(opts.rels, 4, f, RELS.CUST_PROPS);
	}

	var people = ["SheetJ5"];
	opts.tcid = 0;

	for(rId=1;rId <= wb.SheetNames.length; ++rId) {
		var wsrels = {'!id':{}};
		var ws = wb.Sheets[wb.SheetNames[rId-1]];
		var _type = (ws || {})["!type"] || "sheet";
		switch(_type) {
		case "chart":
			/* falls through */
		default:
			f = "xl/worksheets/sheet" + rId + "." + wbext;
			zip_add_file(zip, f, write_ws_xml(rId-1, opts, wb, wsrels));
			ct.sheets.push(f);
			add_rels(opts.wbrels, -1, "worksheets/sheet" + rId + "." + wbext, RELS.WS[0]);
		}

		if(ws) {
			var comments = ws['!comments'];
			var need_vml = false;
			if(comments && comments.length > 0) {
				var needtc = false;
				comments.forEach(function(carr) {
					carr[1].forEach(function(c) { if(c.T == true) needtc = true; });
				});
				if(needtc) {
					cf = "xl/threadedComments/threadedComment" + rId + "." + wbext;
					zip_add_file(zip, cf, write_tcmnt_xml(comments, people, opts));
					ct.threadedcomments.push(cf);
					add_rels(wsrels, -1, "../threadedComments/threadedComment" + rId + "." + wbext, RELS.TCMNT);
				}

				var cf = "xl/comments" + rId + "." + wbext;
				zip_add_file(zip, cf, write_comments_xml(comments, opts));
				ct.comments.push(cf);
				add_rels(wsrels, -1, "../comments" + rId + "." + wbext, RELS.CMNT);
				need_vml = true;
			}
			if(ws['!legacy']) {
				if(need_vml) zip_add_file(zip, "xl/drawings/vmlDrawing" + (rId) + ".vml", write_comments_vml(rId, ws['!comments']));
			}
			delete ws['!comments'];
			delete ws['!legacy'];
		}

		if(wsrels['!id'].rId1) zip_add_file(zip, get_rels_path(f), write_rels(wsrels));
	}

	if(opts.Strings != null && opts.Strings.length > 0) {
		f = "xl/sharedStrings." + wbext;
		zip_add_file(zip, f, write_sst_xml(opts.Strings, opts));
		ct.strs.push(f);
		add_rels(opts.wbrels, -1, "sharedStrings." + wbext, RELS.SST);
	}

	f = "xl/workbook." + wbext;
	zip_add_file(zip, f, write_wb_xml(wb, opts));
	ct.workbooks.push(f);
	add_rels(opts.rels, 1, f, RELS.WB);

	/* TODO: something more intelligent with themes */

	f = "xl/theme/theme1.xml";
	zip_add_file(zip, f, write_theme(wb.Themes, opts));
	ct.themes.push(f);
	add_rels(opts.wbrels, -1, "theme/theme1.xml", RELS.THEME);

	/* TODO: something more intelligent with styles */

	f = "xl/styles." + wbext;
	zip_add_file(zip, f, write_sty_xml(wb, opts));
	ct.styles.push(f);
	add_rels(opts.wbrels, -1, "styles." + wbext, RELS.STY);

	if(wb.vbaraw && vbafmt) {
		f = "xl/vbaProject.bin";
		zip_add_file(zip, f, wb.vbaraw);
		ct.vba.push(f);
		add_rels(opts.wbrels, -1, "vbaProject.bin", RELS.VBA);
	}

	f = "xl/metadata." + wbext;
	zip_add_file(zip, f, write_xlmeta_xml());
	ct.metadata.push(f);
	add_rels(opts.wbrels, -1, "metadata." + wbext, RELS.XLMETA);

	if(people.length > 1) {
		f = "xl/persons/person.xml";
		zip_add_file(zip, f, write_people_xml(people, opts));
		ct.people.push(f);
		add_rels(opts.wbrels, -1, "persons/person.xml", RELS.PEOPLE);
	}

	zip_add_file(zip, "[Content_Types].xml", write_ct(ct, opts));
	zip_add_file(zip, '_rels/.rels', write_rels(opts.rels));
	zip_add_file(zip, 'xl/_rels/workbook.' + wbext + '.rels', write_rels(opts.wbrels));

	delete opts.revssf; delete opts.ssf;
	return zip;
}