Module:Infobox/dates/sandbox

 -- This module provides functions to format date ranges according to [[MOS:DATERANGE]].
 local p = {}

 local getArgs = require('Module:Arguments').getArgs

 -- Define constants for reuse throughout the module
 local DASH = '–' -- en dash
 local DASH_BREAK = '&nbsp;–<br />' -- en dash with line break
 local DEFAULT_ERROR_CATEGORY = 'Pages with incorrectly formatted date ranges'
 local MONTHS = {
	January = 1, February = 2, March = 3, April = 4, 
	May = 5, June = 6, July = 7, August = 8, 
	September = 9, October = 10, November = 11, December = 12
 }

 -- =============================================
 -- Template validation
 -- =============================================
 -- Template should be moved eventually to the infobox television season module.

 --- Validates date formats in infobox templates.
 -- @param frame Frame object from Wikipedia
 -- @return Error category string if validation fails, nil otherwise
 function p.start_end_date_template_validation(frame)
	local args = getArgs(frame)
	local error_category = args.error_category or DEFAULT_ERROR_CATEGORY

	local start_date = args.first_aired or args.released or args.airdate or args.release_date or args.airdate_overall
	if start_date then
		if not start_date:find("dtstart") then
			return error_category
		end
	end

	local end_date = args.last_aired
	if end_date then
		if not end_date:find("dtend") and end_date ~= "present" then
			return error_category
		end
	end
	
	return nil -- Return nil if validation passes
 end

 -- =============================================
 -- Helper functions
 -- =============================================

 --- Replace non-breaking spaces with regular spaces.
 -- @param value String to process
 -- @return Processed string with regular spaces
 local function replace_space(value)
	if value then
		return value:gsub("&nbsp;", " ")
	end
	return value
 end

 --- Extract the hidden span portion from text if it exists.
 -- @param text Input text that may contain a span element
 -- @return The span portion or empty string
 local function extract_span(text)
	if not text then
		return ""
	end
	
	local span_start = string.find(text, "<span")
	if span_start then
		return string.sub(text, span_start)
	end
	return ""
 end

 --- Extract visible part (before any span).
 -- @param text Input text
 -- @return Visible portion of the text
 local function extract_visible(text)
	if not text then
		return ""
	end
	return text:match("^(.-)<span") or text
 end

 --- Parse date components from visible text.
 -- @param visible_text The visible portion of a date string
 -- @return Table with date components and format
 local function parse_date(visible_text)
	if not visible_text then
		return {
			prefix = "",
			month = nil,
			day = nil,
			year = nil,
			suffix = "",
			format = nil
		}
	end
	
	local date_format = "mdy" -- Default format
	local prefix, month, day, year, suffix
	
	-- Try MDY format first (e.g., "January 15, 2020")
	prefix, month, day, year, suffix = string.match(visible_text, '(.-)(%u%a+)%s(%d+),%s(%d+)(.*)')
	
	-- If MDY failed, try DMY format (e.g., "15 January 2020")
	if year == nil then
		date_format = "dmy"
		prefix, day, month, year, suffix = string.match(visible_text, '(.-)(%d%d?)%s(%u%a+)%s(%d+)(.*)')
	end
	
	-- If month and year only (e.g., "April 2015")
	if year == nil then
		month, year = visible_text:match('(%u%a+)%s(%d%d%d%d)')
		prefix, suffix, day = "", "", nil
	end
	
	-- If year only (e.g., "2015")
	if year == nil then
		year = visible_text:match('(%d%d%d%d)')
		prefix, suffix, month, day = "", "", nil, nil
	end
	
	-- Handle "present" case
	if visible_text:find("present") then
		year = "present"
		prefix, suffix, month, day = "", "", nil, nil
	end
	
	-- Set default empty strings for optional components
	suffix = suffix or ''
	prefix = prefix or ''
	
	return {
		prefix = prefix,
		month = month,
		day = day,
		year = year,
		suffix = suffix,
		format = date_format
	}
 end

 --- Get month number from name.
 -- @param month_name Name of the month
 -- @return Number corresponding to the month or nil if invalid
 local function get_month_number(month_name)
	return month_name and MONTHS[month_name]
 end

 --- Format date range for same year according to Wikipedia style.
 -- @param date1 First date components
 -- @param date2 Second date components
 -- @param span1 First date span HTML
 -- @param span2 Second date span HTML
 -- @return Formatted date range string
 local function format_same_year(date1, date2, span1, span2)
	-- Both dates have just year, no month or day
	if date1.month == nil and date2.month == nil then
		return date1.prefix .. date1.year .. span1 .. DASH .. date2.year .. span2
	end
	
	-- Both dates have month and year, but no day
	if date1.day == nil and date2.day == nil then
		return date1.prefix .. date1.month .. span1 .. DASH .. date2.month .. ' ' .. date1.year .. span2
	end
	
	-- Same month and year
	if date1.month == date2.month then
		if date1.format == "dmy" then
			-- Format: d1–d2 m1 y1 (5–7 January 1979)
			return date1.prefix .. date1.day .. span1 .. DASH .. date2.day .. ' ' .. date1.month .. ' ' .. date1.year .. span2
		else
			-- Format: m1 d1–d2, y1 (January 5–7, 1979)
			return date1.prefix .. date1.month .. ' ' .. date1.day .. span1 .. DASH .. date2.day .. ', ' .. date1.year .. span2
		end
	else
		-- Different months, same year
		if date1.format == "dmy" then
			-- Format: d1 m1 – d2 m2 y1 (3 June –<br/> 18 August 1952)
			return date1.prefix .. date1.day .. ' ' .. date1.month .. span1 .. DASH_BREAK .. date2.day .. ' ' .. date2.month .. ' ' .. date1.year .. span2
		else
			-- Format: m1 d1 – m2 d2, y1 (June 3 –<br/> August 18, 1952)
			return date1.prefix .. date1.month .. ' ' .. date1.day .. span1 .. DASH_BREAK .. date2.month .. ' ' .. date2.day .. ', ' .. date1.year .. span2
		end
	end
 end

 --- Format date range with "present" as the end date
 -- @param date1 Start date components
 -- @param span1 Start date span HTML
 -- @return Formatted date range string with "present" as end date
 local function format_present_range(date1, span1)
	-- Year only
	if date1.month == nil then
		return date1.prefix .. date1.year .. span1 .. DASH .. "present"
	end
	
	-- Month and year, no day
	if date1.day == nil then
		return date1.prefix .. date1.month .. ' ' .. date1.year .. span1 .. " " .. DASH .. " present"
	end
	
	-- Full date (with line break)
	if date1.format == "dmy" then
		return date1.prefix .. date1.day .. ' ' .. date1.month .. ' ' .. date1.year .. span1 .. DASH_BREAK .. "present"
	else
		return date1.prefix .. date1.month .. ' ' .. date1.day .. ', ' .. date1.year .. span1 .. DASH_BREAK .. "present"
	end
 end

 --- Format date range for different years.
 -- @param date1 First date components
 -- @param date2 Second date components
 -- @param visible_text1 Visible text of first date
 -- @param visible_text2 Visible text of second date
 -- @param span1 First date span HTML
 -- @param span2 Second date span HTML
 -- @return Formatted date range string for different years
 local function format_different_years(date1, date2, visible_text1, visible_text2, span1, span2)
	-- If both entries are just years, use simple dash without line break
	if date1.month == nil and date2.month == nil then
		return visible_text1 .. span1 .. DASH .. visible_text2 .. span2
	end
	
	-- If one of them has a month or day, use dash with line break
	return visible_text1 .. span1 .. DASH_BREAK .. visible_text2 .. span2
 end

 --- Validate that date2 is after date1
 -- @param date1 First date components
 -- @param date2 Second date components
 -- @return Boolean indicating if date range is valid
 local function validate_date_range(date1, date2)
	-- Skip validation if one date is just a year or if second date is "present"
	if not date1.month or not date2.month or date2.year == "present" then
		return true
	end
	
	local month1_number = get_month_number(date1.month)
	local month2_number = get_month_number(date2.month)
	
	-- If invalid month names, consider validation failed
	if not month1_number or not month2_number then
		return false
	end
	
	-- Convert year strings to numbers
	local year1 = tonumber(date1.year)
	local year2 = tonumber(date2.year)
	
	if not year1 or not year2 then
		return false
	end
	
	-- If years are different, comparison is simple
	if year1 < year2 then
		return true
	elseif year1 > year2 then
		return false
	end
	
	-- Same year, compare months
	if month1_number < month2_number then
		return true
	elseif month1_number > month2_number then
		return false
	end
	
	-- Same year and month, compare days if available
	if date1.day and date2.day then
		local day1 = tonumber(date1.day)
		local day2 = tonumber(date2.day)
		
		if not day1 or not day2 then
			return false
		end
		
		return day1 <= day2
	end
	
	-- Same year and month, no days to compare
	return true
 end

 -- =============================================
 -- Main function
 -- =============================================

 --- Format date ranges according to Wikipedia style.
 -- @param frame Frame object from Wikipedia
 -- @return Formatted date range string
 function p.dates(frame)
	local args = getArgs(frame)

	-- Handle missing or empty arguments cases
	if not args[1] and not args[2] then
		return ''
	elseif not args[1] then
		return args[2] or ''
	elseif not args[2] then
		return args[1] or ''
	end

	-- Get spans from original inputs
	local span1 = extract_span(args[1])
	local span2 = extract_span(args[2])

	-- Get visible parts only
	local visible_text1 = extract_visible(args[1])
	local visible_text2 = extract_visible(args[2])

	-- Clean up spaces
	visible_text1 = replace_space(visible_text1)
	visible_text2 = replace_space(visible_text2)

	-- Parse dates
	local date1 = parse_date(visible_text1)
	local date2 = parse_date(visible_text2)

	-- Handle unparsable dates (fallback to original format)
	if date1.year == nil or (date2.year == nil and not string.find(visible_text2 or "", "present")) then
		return (args[1] or '') .. DASH .. (args[2] or '')
	end

	-- Handle "present" as end date
	if (visible_text2 and visible_text2:find("present")) or date2.year == "present" then
		return format_present_range(date1, span1)
	end
	
	-- Validate date range
	if not validate_date_range(date1, date2) then
		return 'Invalid date range'
	end
	
	-- Format based on whether years are the same
	if date1.year == date2.year then
		return format_same_year(date1, date2, span1, span2)
	else
		-- Different years
		return format_different_years(date1, date2, visible_text1, visible_text2, span1, span2)
	end
 end

 return p