#let cnfont = ("Noto Sans CJK SC", "Noto Sans SC", "Source Han Sans CN")
#let cnmainfont = ("Noto Serif CJK SC", "Source Han Serif CN")
#let labelfont = ("Atkinson Hyperlegible")

#let tab = h(2em)
#let halftab = h(1em)

#let footer_title = state("footer_title", "")
#let skip_footer = state("skip_footer", false)

#let thispage_number(loc) = {
	counter(page).at(loc).first()
}

#let problem_id = counter("pid")
#let identp = h(2em)

#let project(title: "", logo: none, body) = {
	set document(title: title)
	set text(font: cnmainfont, lang: "zh")
	set page(
		// width: 195mm,
		// height: 270mm,
		// margin: (top: 20mm)
		paper: "iso-b5"
	)

	show par: set block(above: 1.2em, below: 1.2em)
	show heading: set text(font: cnfont, weight: "semibold")
	set list(marker: (sym.square.filled.small, [--]), indent: .5em)
	set ref(supplement: it => {
		if it.func() == math.equation {
			"式"
		} else {
			auto
		}
	})
	// show math.equation: set ref(supplement: "式")
	// show ref: it => {
	// 	let eq = math.equation
	// 	let el = it.element
	// 	if el != none and el.func() == eq {
	// 		// Override equation references.
	// 		"式 "
	// 		str(counter(eq).at(el.location()).at(0))
	// 	} else {
	// 		// Other references as usual.
	// 		it
	// 	}
	// }

	set par(leading: 0.75em)

	v(0.6fr)
	if logo != none {
		align(right, image(logo, width: 26%))
	}
	v(9.6fr)

	text(4em, weight: "light", font: cnfont, title)
	v(2.4fr)

	pagebreak()
	pagebreak()

	outline(depth: 1)
[
	#set page(footer: locate(loc => {
		if skip_footer.at(loc) {
			return
		}

		let thispage = thispage_number(loc)
		let is_mainpart = query(selector(<MainStarted>).before(loc), loc) != ()
		let footer_content = if is_mainpart {
			[\##problem_id.at(loc).first() #footer_title.at(loc)]
		} else {
			none
		}

		let isleft = calc.even(thispage)
		set align(left)  if isleft
		set align(right) if not isleft
		set text(font: cnmainfont)
		stack(dir: if isleft { ltr } else { rtl },
			spacing: 1em,
			str(thispage),
			[#underline(offset: 2pt, footer_content)]
		)
	}))

	// Main body.
	#set par(justify: true)
	#set text(13pt)

	#counter(page).update(1)
	#body
]
}