Module:Highest archive number

-- 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