local p = {}
local getArgs = require('Module:Arguments').getArgs
local datePattern = "^(%d+)-(%d+)$"
local weatherTemplate = 'Template:Weather box'
local wrapsTemplate = 'User:Yurik/Weather box'

function p.weatherbox( frame )
    local args = getArgs(frame, { wrappers = wrapsTemplate })
    local dataPage = assert(args.data, 'Missing "data" parameter')
    args.data = nil

    local monthlyHigh, monthlyLow = {}, {}
    local highSum, highCount = {}, {}
    local lowSum, lowCount = {}, {}
    local avgHighSum, avgHighCount = {}, {}
    local avgLowSum, avgLowCount = {}, {}
    local precipSum, precipCount = {}, {}
    local snowfallSum, snowfallCount = {}, {}
    local precipDaysSum, precipDaysCount = {}, {}
    local snowfallDaysSum, snowfallDaysCount = {}, {}

	-- There is currently no established way to specify sources, suggestions needed
	-- For now, prepend the link to edit box to the first source
	local source = args['source'] or args['source 1']
	if source then source = '<br>' .. source end
	args['source'] = '[[commons:Data:'.. dataPage ..'|edit data]]' .. source
	args['source 1'] = nil

    for key, row in pairs(mw.ext.data.get(dataPage).data) do
        local date, highTemp, avgHighTemp, avgLowTemp, lowTemp, precip, snowfall, precipDays, snowfallDays = unpack(row)

        local year, month = date:match(datePattern)
        month = tonumber(month)

        if highTemp ~= nil and (monthlyHigh[month] == nil or monthlyHigh[month] < highTemp) then monthlyHigh[month] = highTemp end
        if lowTemp ~= nil and (monthlyLow[month] == nil or monthlyLow[month] > lowTemp) then monthlyLow[month] = lowTemp end
        recordAvg(highSum, highCount, month, highTemp)
        recordAvg(lowSum, lowCount, month, lowTemp)
        recordAvg(avgHighSum, avgHighCount, month, avgHighTemp)
        recordAvg(avgLowSum, avgLowCount, month, avgLowTemp)
        recordAvg(precipSum, precipCount, month, precip)
        recordAvg(snowfallSum, snowfallCount, month, snowfall)
        recordAvg(precipDaysSum, precipDaysCount, month, precipDays)
        recordAvg(snowfallDaysSum, snowfallDaysCount, month, snowfallDays)
    end

    local months = {'Jan','Feb','Mar','Apr','May','Jun','Jul','Aug','Sep','Oct','Nov','Dec'}
    for i=1, 12 do args[months[i] .. ' record high C'] = monthlyHigh[i] end
    for i=1, 12 do args[months[i] .. ' record low C'] = monthlyLow[i] end
    for i=1, 12 do args[months[i] .. ' avg record high C'] = string.format("%.1f", highSum[i] / highCount[i]) end
    for i=1, 12 do args[months[i] .. ' avg record low C'] = string.format("%.1f", lowSum[i] / lowCount[i]) end
    for i=1, 12 do args[months[i] .. ' high C'] = string.format("%.1f", avgHighSum[i] / avgHighCount[i]) end
    for i=1, 12 do args[months[i] .. ' low C'] = string.format("%.1f", avgLowSum[i] / avgLowCount[i]) end
    for i=1, 12 do args[months[i] .. ' precipitation mm'] = string.format("%.1f", precipSum[i] / precipCount[i]) end
    for i=1, 12 do args[months[i] .. ' snow mm'] = string.format("%.1f", snowfallSum[i] / snowfallCount[i]) end
    for i=1, 12 do args[months[i] .. ' precipitation days'] = string.format("%.1f", precipDaysSum[i] / precipDaysCount[i]) end
    for i=1, 12 do args[months[i] .. ' snow days'] = string.format("%.1f", snowfallDaysSum[i] / snowfallDaysCount[i]) end

    return frame:expandTemplate{ title = weatherTemplate, args = args }
end

function recordAvg(sumTbl, countTbl, month, value)
    if value ~= nil then
        sumTbl[month] = (sumTbl[month] or 0) + value
        countTbl[month] = (countTbl[month] or 0) + 1
    end
end

return p