Module:Highest archive number

This module finds the highest archive number for a given set of numbered archive pages. The only input required is the prefix of the archive set. For example, for Talk:France/Archive 1, Talk:France/Archive 2, etc., the prefix would be "Talk:France/Archive ".

The module uses an exponential search algorithm, so it will make relatively few expensive function calls even for large numbers of archives. (The expensive function call is necessary to determine whether an individual archive exists.) For 1-10 archive pages, the module typically uses 4-6 expensive function calls; for 20-100 archives, it uses 6-12 calls; and for hundreds of archives, it uses 12-20 calls.

Because the module uses an exponential search, no gaps are allowed in the archive numbers; if there are any gaps, then the module may return the number of any archive page that exists where the following archive page does not exist. However, archive numbers do not have to start at 1; if they start at a higher number, you can specify this number in the start parameter.

Usage

From wikitext

From wikitext this module is usually used via the {{highest archive number}} template. However, it is also possible to use it directly from invoke with the syntax {{#invoke:highest archive number|main|prefix|start=start}}.

From Lua

Load the module with the following code:

local mHAN = require('Module:Highest archive number')

You can then use it like this:

mHAN._main(prefix, start)

The prefix variable is the prefix of the archive set.

Examples

#invoke code	Lua code	Result
{{#invoke:highest archive number|main|Wikipedia:Administrators' noticeboard/IncidentArchive}}	mHAN._main("Wikipedia:Administrators' noticeboard/IncidentArchive")
{{#invoke:highest archive number|main|Talk:Byzantine Empire/Archive }}	mHAN._main("Talk:Byzantine Empire/Archive ")
{{#invoke:highest archive number|main|Wikipedia talk:WikiProject Chemicals/Archive |start=2005}}	mHAN._main("Wikipedia talk:WikiProject Chemicals/Archive ", 2005)

---

-- This module finds the highest existing archive number for a set of talk
-- archive pages.

local expSearch = require('Module:Exponential search')
local p = {}

local function raiseStartNumberError(start)
	error(string.format(
		'Invalid start number "%s" supplied to [[Module:Highest archive number]] (must be an integer)',
		tostring(start)
	), 3)
end

local function pageExists(page)
	local success, exists = pcall(function()
		return mw.title.new(page).exists
	end)
	return success and exists
end

function p._main(prefix, start)
	-- Check our inputs
	if type(prefix) ~= 'string' or not prefix:find('%S') then
		error('No prefix supplied to [[Module:Highest archive number]]', 2)
	end
	if start ~= nil and (type(start) ~= "number" or math.floor(start) ~= start) then
		raiseStartNumberError(start)
	end
	start = start or 1
	
	-- Do an exponential search for the highest archive number
	local result = expSearch(function (i)
		local archiveNumber = i + start - 1
		local page = prefix .. tostring(archiveNumber)
		return pageExists(page)
	end, 10)
	
	if result == nil then
		-- We didn't find any archives for our prefix + start number
		return nil
	else
		-- We found the highest archive, but the number is always 1-based, so
		-- adjust it for our start number
		return result + start - 1
	end
end

function p.main(frame)
	local args = require('Module:Arguments').getArgs(frame, {
		trim = false,
		removeBlanks = false,
		wrappers = 'Template:Highest archive number'
	})
	local prefix = args[1]
	
	-- Get the start archive number, if specified.
	local start = args.start
	if start == "" then
		start = nil
	elseif start then
		start = tonumber(start)
		if not start then
			raiseStartNumberError(args.start)
		end
	end

	return p._main(prefix, start)
end

return p