Module:Month

local p = {}

local months = { "January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December", }

local month_numbers = {}

for number, name in pairs(months) do	month_numbers[name] = number end

function valid_month(month) month_number = tonumber(month)

if (month_number == nil) then month_number = month_numbers[month] end

if (month_number == nil or month_number < 1 or month_number > 12) then return nil end

return month_number end

function invalid_month_message(month) return string.format("%s is not a valid month", month) end

function valid_year(year) year_number = tonumber(year)

if (year_number == nil) then return nil end

return year_number end

function invalid_year_message(year) return string.format("%s is not a valid year", year) end

function next_month(this_month, this_year) month = {}

this_month_number = valid_month(this_month)

if (not this_month_number) then month["month"] = invalid_month_message(this_month) month["month_number"] = invalid_month_message(this_month) end

this_year_number = valid_year(this_year)

if (not this_year_number) then month["year"] = invalid_year_message(this_year) end

if (this_month_number == 12) then month["month"] = months[1] month["month_number"] = 1 if (this_year_number) then month["year"] = this_year_number + 1 end else if (this_month_number) then next_month_number = this_month_number + 1 month["month"] = months[next_month_number] month["month_number"] = next_month_number end if (this_year_number) then month["year"] = this_year_number end end

return month end

function p.next_month_name(frame) this_month = frame.args[1] this_year = frame.args[2] return next_month(this_month, this_year).month end

function p.next_month_number(frame) this_month = frame.args[1] this_year = frame.args[2] return next_month(this_month, this_year).month_number end

function p.next_month_year(frame) this_month = frame.args[1] this_year = frame.args[2] return next_month(this_month, this_year).year end

function previous_month(this_month, this_year) month = {}

this_month_number = valid_month(this_month)

if (not this_month_number) then month["month"] = invalid_month_message(this_month) end

this_year_number = valid_year(this_year)

if (not this_year_number) then month["year"] = invalid_year_message(this_year) end

if (this_month_number == 1) then month["month"] = months[12] if (this_year_number) then month["year"] = this_year_number - 1 end else previous_month_number = this_month_number - 1 if (this_month_number) then month["month"] = months[previous_month_number] month["month_number"] = previous_month_number end if (this_year_number) then month["year"] = this_year_number end end

return month end

function p.previous_month_name(frame) this_month = frame.args[1] this_year = frame.args[2] return previous_month(this_month, this_year).month end

function p.previous_month_number(frame) this_month = frame.args[1] this_year = frame.args[2] return previous_month(this_month, this_year).month_number end

function p.previous_month_year(frame) this_month = frame.args[1] this_year = frame.args[2] return previous_month(this_month, this_year).year end

return p