local p = {}

-- Make a calculator widget using {{calculator}}

local function getDisplay()
	-- Normal calculators don't display "Infinity" when dividing by 0.
	return 'iffinite(ifzero(displayY,x,y),ifzero(displayY,x,y),nan)'
end

local function pressDecimal()
	return {
		{'decimal', 'ifequal(decimal,0,1,decimal)'},
		{ 'y', 'ifzero(equalFlag,y,0)' },
		{ 'x', 'ifzero(displayY,x,0)' },
		{ 'equalFlag', 0 },
		{ 'displayY', '0' }
	}
end

-- This is sketch because x should happen before decimal.
function pressNumber(n)
	return { {'x', 'ifequal(decimal,0,not(displayY)*x*10+(ifpositive(not(displayY)*x,1,-1))*' .. n .. ','
		.. 'x+(ifpositive(x,1,-1))*(' .. n .. '/pow(10,decimal)))'},
		{'decimal','ifzero(decimal,0,decimal+1)'},
		{ 'y', 'ifzero(equalFlag,y,0)' },
		{ 'op', 'ifzero(equalFlag,op,0)' },
		{ 'equalFlag', 0 },
		{ 'displayY', '0' },
	}
end

function getClear()
	return {
		{ 'x', '0' },
		{ 'y', '0' },
		{ 'op', '0' },
		{ 'decimal', '0' },
		{ 'percentFlag', '0' },
		{ 'equalFlag', '0' },
		{ 'displayY', '0' },
	}
end

-- Compute a function
-- 0: add 1: subtract 2: multiply 4: divide 5: square root.
function compute(op)
	local res = {
		{ 'x', 'ifzero(equalFlag,ifequal(percentFlag, 1, x*y/100, x),ifgreater(op,1,1,0))' },
		{ 'y', 'switch(op,0,x+y,1,y-x,2,x*y,3,y/x,4,y)' },
		--{ 'x', '0' },
		{ 'decimal', '0' },
		{ 'displayY', '1' },
		{ 'percentFlag', 0 },
		{ 'op', tostring(op) },
		{ 'equalFlag', 0 }
	}
	return res
end

-- Equal key is a bit weird
-- If you press equal a second time, it should repeat operation "10 + 5 = = = =" gives 30
-- If you press equal and then a number, we start a new calc "10 + 5 = 2 + 1" gives 3
-- If you press an operation, you use the current result as the first number in operation "10 + 5 = + 2" gives 17
function computeEqual()
	local res = {
		{ 'x', 'ifequal(percentFlag, 1, x*y/100, x)' },
		{ 'y', 'switch(op,0,x+y,1,y-x,2,x*y,3,y/x,4,sqrt(y))' },
		--{ 'x', '0' },
		{ 'decimal', '0' },
		{ 'displayY', '1' },
		{ 'percentFlag', 0 },
		{ 'equalFlag', 1 }
	}
	return res
end

-- only arg is "fallback". Set to "all" (Default) to show everything when no-js
--   set to "keypad" to show only keypad to non-js users. set to "none" to show nothing.
function p.getWidget( frame )
	local buttons = {
		{ "MC", {{"mem", "0"}}, "Memory clear" },
		{ "MR", {{"x", "mem"},{"displayY", 0}}, "Memory recall" },
		{ "M−", {{"mem", "ifzero(displayY,mem-x,mem-y)"}}, "Subtract from memory" },
		{ "M+", {{"mem", "ifzero(displayY,mem+x,mem+y)"}}, "Add to memory" },
		{ "C", getClear(), "Clear" },
		-- Its a bit unclear what the expected behaviour of pressing ± immediately after equal.
		{ "±", {{'x', '0-x'}}, "Change sign" },
		{ "%", {{'percentFlag', '1'}} },
		-- A bit hacky, sqrt is the only unary operator. We want to make
		-- sure it does it again if you press 25 √ = =
		{ "√", {{'x','sqrt(ifzero(equalFlag,x,y))'},{'op','4'},{'equalFlag','1'},{'y','x'}} },
		{ "7", pressNumber(7) },
		{ "8", pressNumber(8) },
		{ "9", pressNumber(9) },
		{ "÷", compute(3) },
		{ "4", pressNumber(4) },
		{ "5", pressNumber(5) },
		{ "6", pressNumber(6) },
		{ "×", compute(2), "Multiply" },
		{ "1", pressNumber(1) },
		{ "2", pressNumber(2) },
		{ "3", pressNumber(3) },
		{ "−", compute(1), "Subtract" },
		{ "0", pressNumber(0) },
		{ ".", pressDecimal(), "Decimal point" },
		{ "=", computeEqual() },
		{ "+", compute(0), "Add" },
	}

	local calc = '<div class="calculatorwidget calculator-container" style="display:grid;grid-template-columns:repeat(4, 1fr);grid-gap:5px;min-width:256px;width:20ch;border:thin solid gray;padding: 5px;">'
	if frame.args['fallback'] == 'none' then
		-- if no js, hide.
		calc = '<div style="display:none;" class="calculatorgadget-enabled">' .. calc
	end
	-- On Calculator page, we want to show the layout of buttons on print, but
	-- not the answer field.
	calc = calc .. '<div style="grid-column:1/5;'
	if frame.args['fallback'] == 'keypad' then
		-- for non-js users only show keypad but not answer widget.
		calc = calc .. 'display:none" class="calculatorgadget-enabled'
	end
	calc = calc .. '">{{Calculator codex text|default=0|id=ans|formula=' .. getDisplay() .. '|style=text-align:right;font-weight:bold;|readonly=1|NaN-text=Error|aria-label=Result}}</div>'
	for i, v in ipairs(buttons) do
		local calcType, calcWeight
		if v[1] == 'C' then
			calcType = 'destructive'
			calcWeight = 'normal'
		elseif v[1] == '=' then
			calcType = 'progressive'
			calcWeight = 'primary'
		else
			calcType = 'default'
			calcWeight = 'normal'
		end
		-- maybe make "=" be progressive instead of default. Perhaps weight = primary?
		local forVar = ''
		local formula = ''
		for i2, v2 in ipairs( v[2] ) do
			forVar = forVar .. ';' .. v2[1]
			formula = formula .. ';' .. v2[2]
		end
		-- Should the alt text also be a title attribute to make a tooltip?
		local alt = v[3] ~= nil and '|alt=' .. v[3] or ''
		calc = calc .. '{{calculator button|type='.. calcType ..'|weight='.. calcWeight .. alt .. '|for=' .. string.sub(forVar,2) .. '|formula=' .. string.sub(formula,2) .. '|contents='.. v[1] .. '}}'
	end
	calc = calc .. '{{calculator|type=hidden|id=x|default=0}}'
	calc = calc .. '{{calculator|type=hidden|id=y|default=0}}'
	calc = calc .. '{{calculator|type=hidden|id=mem|default=0}}'
	calc = calc .. '{{calculator|type=hidden|id=op|default=0}}'
	calc = calc .. '{{calculator|type=hidden|id=decimal|default=0}}'
	calc = calc .. '{{calculator|type=hidden|id=displayY|default=0}}'
	calc = calc .. '{{calculator|type=hidden|id=percentFlag|default=0}}'
	calc = calc .. '{{calculator|type=hidden|id=equalFlag|default=0}}'
	calc = calc .. '<templatestyles src="Module:Calculator widget/style.css"/>'
	calc = calc .. '</div>'
	if frame.args['fallback'] == 'none' then
		-- if no js, hide.
		calc = calc .. '</div>'
	end
	return frame:preprocess(calc)
end

return p