local export = {}

-- A helper function to escape magic characters in a string
-- Magic characters: ^$()%.[]*+-?
local plain = require("Module:string").pattern_escape

-- A helper function that removes empty numeric indexes in a table,
-- so that the values are tightly packed like in a normal Lua table.
local remove_holes = require("Module:table").compressSparseArray

function export.process(args, params, return_unknown)
	local args_new = {}
	
	-- Process parameters for specific properties
	local required = {}
	local patterns = {}
	local names_with_equal_sign = {}
	local list_from_index = nil
	
	for name, param in pairs(params) do
		if param.required then
			if param.alias_of then
				require("Module:debug").track("parameters/required alias")
			end
			required[name] = true
		end
		
		if param.list then
			local key = name
			if type(name) == "string" then
				key = string.gsub(name, "=", "")
			end
			if param.default ~= nil then
				args_new[key] = {param.default, maxindex = 1}
			else
				args_new[key] = {maxindex = 0}
			end
			
			if type(param.list) == "string" then
				-- If the list property is a string, then it represents the name
				-- to be used as the prefix for list items. This is for use with lists
				-- where the first item is a numbered parameter and the
				-- subsequent ones are named, such as 1, pl2, pl3.
				if string.find(param.list, "=") then
					patterns["^" .. string.gsub(plain(param.list), "=", "(%%d+)") .. "$"] = name
				else
					patterns["^" .. plain(param.list) .. "(%d+)$"] = name
				end
			elseif type(name) == "number" then
				-- If the name is a number, then all indexed parameters from
				-- this number onwards go in the list.
				list_from_index = name
			else
				if string.find(name, "=") then
					patterns["^" .. string.gsub(plain(name), "=", "(%%d+)") .. "$"] = string.gsub(name, "=", "")
				else
					patterns["^" .. plain(name) .. "(%d+)$"] = name
				end
			end
			
			if string.find(name, "=") then
				-- DO NOT SIDE-EFFECT A TABLE WHILE ITERATING OVER IT.
				-- Some elements may be skipped or processed twice if you do.
				-- Instead, track the changes we want to make to `params`, and
				-- do them after the iteration over `params` is done.
				table.insert(names_with_equal_sign, name)
			end
		elseif param.default ~= nil then
			args_new[name] = param.default
		end
	end

	--Process required changes to `params`
	for _, name in ipairs(names_with_equal_sign) do
		require("Module:debug").track("parameters/name with equals")
		params[string.gsub(name, "=", "")] = params[name]
		params[name] = nil
	end

	-- Process the arguments
	local args_unknown = {}
	
	for name, val in pairs(args) do
		local index = nil
		
		if type(name) == "number" then
			if list_from_index ~= nil and name >= list_from_index then
				index = name - list_from_index + 1
				name = list_from_index
			end
		else
			-- Does this argument name match a pattern?
			for pattern, pname in pairs(patterns) do
				index = mw.ustring.match(name, pattern)
				
				-- It matches, so store the parameter name and the
				-- numeric index extracted from the argument name.
				if index then
					index = tonumber(index)
					name = pname
					break
				end
			end
		end
		
		local param = params[name]
		
		-- If a parameter without the trailing index was found, and
		-- require_index is set on the param, set the param to nil to treat it
		-- as if it isn't recognized.
		if not index and param and param.require_index then
			param = nil
		end
		
		-- If no index was found, use 1 as the default index.
		-- This makes list parameters like g, g2, g3 put g at index 1.
		index = index or 1
		
		-- If the argument is not in the list of parameters, trigger an error.
		-- return_unknown suppresses the error, and stores it in a separate list instead.
		if not param then
			if return_unknown then
				args_unknown[name] = val
			else
				error("The parameter \"" .. name .. "\" is not used by this template.", 2)
			end
		else
			-- Remove leading and trailing whitespace unless allow_whitespace is true.
			if not param.allow_whitespace then
				val = mw.text.trim(val)
			end
			
			-- Empty string is equivalent to nil unless allow_empty is true.
			if val == "" and not param.allow_empty then
				val = nil
			end
			
			-- Convert to proper type if necessary.
			if param.type == "boolean" then
				val = not (not val or val == "" or val == "0" or val == "no" or val == "n" or val == "false")
			elseif param.type == "number" then
				val = tonumber(val)
			elseif param.type then
				require("Module:debug").track {
					"parameters/unrecognized type",
					"parameters/unrecognized type/" .. tostring(param.type)
				}
			end
			
			-- Can't use "if val" alone, because val may be a boolean false.
			if val ~= nil then
				-- Mark it as no longer required, as it is present.
				required[param.alias_of or name] = nil
				
				-- Store the argument value.
				if param.list then
					-- If the parameter is an alias of another, store it as the original,
					-- but avoid overwriting it; the original takes precedence.
					if not param.alias_of then
						args_new[name][index] = val
						
						-- Store the highest index we find.
						args_new[name].maxindex = math.max(index, args_new[name].maxindex)
					elseif args[param.alias_of] == nil then
						if params[param.alias_of] and params[param.alias_of].list then
							args_new[param.alias_of][index] = val
							
							-- Store the highest index we find.
							args_new[param.alias_of].maxindex = math.max(1, args_new[param.alias_of].maxindex)
						else
							args_new[param.alias_of] = val
						end
					end
				else
					-- If the parameter is an alias of another, store it as the original,
					-- but avoid overwriting it; the original takes precedence.
					if not param.alias_of then
						args_new[name] = val
					elseif args[param.alias_of] == nil then
						if params[param.alias_of] and params[param.alias_of].list then
							args_new[param.alias_of][1] = val
							
							-- Store the highest index we find.
							args_new[param.alias_of].maxindex = math.max(1, args_new[param.alias_of].maxindex)
						else
							args_new[param.alias_of] = val
						end
					end
				end
			end
		end
	end
	
	-- The required table should now be empty.
	-- If any entry remains, trigger an error, unless we're in the template namespace.
	if mw.title.getCurrentTitle().nsText ~= "Template" then
		local list = {}
		for name, param in pairs(required) do
			table.insert(list, name)
		end
		
		local count = #list
		if count == 1 then
			error('The parameter "' .. list[1] .. '" is required.', 2)
		elseif count == 2 then
			error('The parameters "' .. table.concat(list, '" and "') .. '" are required.', 2)
		elseif count > 2 then
			error('The parameters "' .. mw.text.listToText(list, '", "', '", and "') .. '" are required.', 2)
		end
	end
	
	-- Remove holes in any list parameters if needed.
	for name, val in pairs(args_new) do
		if type(val) == "table" and not params[name].allow_holes then
			args_new[name] = remove_holes(val)
		end
	end
	
	if return_unknown then
		return args_new, args_unknown
	else
		return args_new
	end
end

return export