local export = {}
local pos_functions = {}

local lang = require("Module:languages").getByCode("gmh")

local legal_verb_classes = {
	["1"] = true,
	["2"] = true,
	["3"] = true,
	["4"] = true,
	["5"] = true,
	["6"] = true,
	["7"] = true,
}

local function ine(val)
	if val == "" then return nil else return val end
end


local function glossary_link(entry, text)
	text = text or entry
	return "[[Appendix:Glossary#" .. entry .. "|" .. text .. "]]"
end


local function track(page)
	require("Module:debug").track("gmh-headword/" .. page)
	return true
end


-- The main entry point.
-- This is the only function that can be invoked from a template.
function export.show(frame)
	local args = frame:getParent().args
	PAGENAME = mw.title.getCurrentTitle().text

	local poscat = frame.args[1] or error("Part of speech has not been specified. Please pass parameter 1 to the module invocation.")
	local class = frame.args[2]; if class == "" then class = nil end

	local data = {lang = lang, pos_category = poscat, categories = {}, heads = {}, genders = {}, inflections = {}}

	if pos_functions[poscat] then
		pos_functions[poscat](class, args, data)
	end

	return
		require("Module:headword").full_headword(data)
end

pos_functions.verbs = function(class, args, data)
	if args[2] then -- old-style
		local params = {
			[1] = {list = "pres", required = true},
			["pres_qual"] = {list = "pres\1_qual", allow_holes = true},
			[2] = {list = "past", required = true},
			["past_qual"] = {list = "past\1_qual", allow_holes = true},
			[3] = {list = "pp", required = true},
			["pp_qual"] = {list = "pp\1_qual", allow_holes = true},
			[4] = {list = "pastsubj"},
			["pastsubj_qual"] = {list = "pastsubj\1_qual", allow_holes = true},
			["aux"] = {list = true},
			["aux_qual"] = {list = "aux\1_qual", allow_holes = true},
			["head"] = {list = true},
			["class"] = {list = true},
		}

		local args = require("Module:parameters").process(args, params)
		data.heads = args["head"]

		local function collect_forms(label, accel_form, forms, qualifiers)
			if forms[1] == "-" then
				return {label = "no " .. label}
			else
				local into_table = accel_form and {label = label, accel = {form = accel_form}} or {label = label}
				for i, form in ipairs(forms) do
					table.insert(into_table, {term = form, q = qualifiers[i] and {qualifiers[i]} or nil})
				end
				return into_table
			end
		end

		if #args.class > 0 then
			local class_descs, cats = require("Module:de-verb").process_verb_classes(args.class)
			for _, cats in ipairs(cats) do
				table.insert(data.categories, cats)
			end
			table.insert(data.inflections, {label = require("Module:table").serialCommaJoin(class_descs, {conj = "or"})})
		end
		table.insert(data.inflections, collect_forms("third-person singular present", "3|s|pres", args[1], args.pres_qual))
		table.insert(data.inflections, collect_forms("past tense", "1//3|s|pret", args[2], args.past_qual))
		table.insert(data.inflections, collect_forms("past participle", "perf|part", args[3], args.pp_qual))
		if #args[4] > 0 then
			table.insert(data.inflections, collect_forms("past subjunctive", "1//3|s|sub|II", args[4], args.pastsubj_qual))
		end
		if #args.aux > 0 then
			table.insert(data.inflections, collect_forms("auxiliary", nil, args.aux, args.aux_qual))
		end
		return
	end

	local function get_headword_inflection(forms, label, accel_form)
		if forms then
			local inflection = accel_form and {label = label, accel = {form = accel_form}} or {label = label}
			for _, form in ipairs(forms) do
				local qualifiers
				if form.footnotes then
					qualifiers = {}
					for _, footnote in ipairs(form.footnotes) do
						footnote = footnote:gsub("^%[(.*)%]$", "%1")
						table.insert(qualifiers, footnote)
					end
				end
				table.insert(inflection, {term = form.form, q = qualifiers})
			end
			return inflection
		elseif label then
			return {label = "no " .. label}
		else
			return {}
		end
	end

	local alternant_multiword_spec = require("Module:gmh-verb").do_generate_forms(args, "from headword")
	for _, cat in ipairs(alternant_multiword_spec.categories) do
		table.insert(data.categories, cat)
	end
	table.insert(data.inflections, {label = table.concat(alternant_multiword_spec.verb_types, " or ")})

	if #data.heads == 0 then
		data.no_redundant_head_cat = true
		for _, head in ipairs(alternant_multiword_spec.forms.infinitive_linked) do
			table.insert(data.heads, head.form)
		end
	end
	table.insert(data.inflections, get_headword_inflection(alternant_multiword_spec.forms.pres_3s,
		"third-person singular present", "3|s|pres"))
	local pret_3s = alternant_multiword_spec.forms.pret_3s
	table.insert(data.inflections, get_headword_inflection(pret_3s, "past tense", "1//3|s|pret"))
	table.insert(data.inflections, get_headword_inflection(alternant_multiword_spec.forms.perf_part,
		"past participle", "perf|part"))
	-- See if we need the past subjunctive, i.e. there exist past subjunctive forms whose stem is not the
	-- same as some past tense form. To facilitate comparison, we truncate final -e in both preterite 3s
	-- and past subjunctive 3s, to handle cases like subjunctive 'ginge aus' vs. preterite 'ging aus'.
	-- We need to compare 3s forms (and not e.g. 3p forms, where the issue with truncating -e doesn't
	-- occur) so we work correctly with impersonal verbs.
	local need_past_subj
	local truncated_pret_3s_forms = {}
	if pret_3s then
		for _, form in ipairs(pret_3s) do
			local truncated_form = form.form:gsub("e$", ""):gsub("e ", " ") -- discard 2nd retval
			table.insert(truncated_pret_3s_forms, truncated_form)
		end
	end
	local subii_3s = alternant_multiword_spec.forms.subii_3s
	local truncated_subii_3s_forms = {}
	if subii_3s then
		for _, form in ipairs(subii_3s) do
			local truncated_form = form.form:gsub("e$", ""):gsub("e ", " ") -- discard 2nd retval
			table.insert(truncated_subii_3s_forms, truncated_form)
		end
	end
	for _, past_subj_form in ipairs(truncated_subii_3s_forms) do
		local saw_same = false
		for _, pret_3s_form in ipairs(truncated_pret_3s_forms) do
			if past_subj_form == pret_3s_form then
				saw_same = true
				break
			end
		end
		if not saw_same then
			need_past_subj = true
			break
		end
	end
	if need_past_subj then
		table.insert(data.inflections, get_headword_inflection(subii_3s, "past subjunctive", "1//3|s|sub|II"))
	end

	local auxes = alternant_multiword_spec.forms.aux
	table.insert(data.inflections, get_headword_inflection(auxes, "auxiliary"))
end

return export