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

local p = {}

-- Determine whether a query string matches a stored timespan string
-- Arguments:
--   s: query string
--   sub: standard name of timespan
-- Returns:
--   false if there is no match
--   prefix and suffix of match, otherwise
local function matches(s, sub)
	local sLen = mw.ustring.len(s)
	local subLen = mw.ustring.len(sub)
	if subLen > sLen then
		return false
	end
	local lowerS = mw.ustring.lower(s)
	local lowerSub = mw.ustring.lower(sub)
	local startOffset, endOffset = mw.ustring.find(lowerS,lowerSub,1,true)
	if not startOffset then
		return false
	end
	return (mw.ustring.sub(s,1,startOffset-1) or ""), (mw.ustring.sub(s,endOffset+1) or "")
end

-- Create list of strings to search corresponding to a standard timespan
-- Some timespans are disambiguated: first search for the dabbed title, then
-- the base title. Otherwise just search for the standard timespan string
-- Argument:
--   span = value in timespan lists (above)
-- Returns:
--   list of strings to search in query string
local function searchStringList(span)
	if type(span) == "table" then
		return {span.base.." "..span.dab, span.base}
	end
	return {span}
end

-- When an adjacent time span is found, this function returns the
-- corresponding basename for the page.
-- Arguments:
--   span: adjacent entry from table, above
--   prefix: prefix of query string before match
--   suffix: remainder of original query string beyond match
-- Returns:
--   page title
--
-- If the adjacent time span is dabbed, then return the dab if the suffix
-- is empty. If the suffix is non-empty (e.g., "life"), append it to the base
-- name of the span (e.g., "Oxfordian") --> "Oxfordian life"
local function matchedString(span, prefix, suffix)
	if type(span) == "table" then
		if prefix == "" and suffix == "" then
			return span.base.." "..span.dab
		end
		return prefix..span.base..suffix
	end
	return prefix..span..suffix
end

-- Function to find the page titles of time spans adjacent to a query string
-- Arguments:
--   s: query string to search for
local function find(s)
    -- lazy load list of geological timespans, 
    local data = mw.loadData('Module:Geological time/data')
	-- Search from most-specific to least, to catch "Cambrian Series 2" before "Cambrian"
	for _, level in ipairs({'age', 'epoch', 'series', 'period', 'era', 'eon'}) do
        local list = data[level]
		local listLen = data.listLen[level]
		for i, span in ipairs(list) do
			-- Each timespan might have more than one search string
			for _, searchString in ipairs(searchStringList(span)) do
				local prefix, suffix = matches(s, searchString)
				if suffix then
					local prevSpan = i > 1 and matchedString(list[i-1], prefix, suffix)
					local nextSpan = i < listLen and matchedString(list[i+1], prefix, suffix)
					-- return first match found
					return {prev=prevSpan, next=nextSpan}
				end
			end
		end
	end
	return nil		
end

-- Lua entry point to generate see also hatnote for geological time spans adjanct in time
-- Arguments:
--   args[1]: name of page to generate adjacency (current page if None)
-- Returns:
--   See also previous and next, formatted as a hatnote
function p._seeAlso(args)
	local title = args[1] and mw.title.new(args[1]) or mw.title.getCurrentTitle()
	local basetext = title.baseText
	local namespace = title.namespace
	local adjacent = find(basetext)
	if not adjacent then
		local warning = require('Module:If preview')._warning
		local warn = warning({"Cannot find geological time frame in "..basetext})
		if mw.title.getCurrentTitle().nsText ~= "Template" then
			warn = warn.."[[Category:Missing geological time frame]]"
		end
		return warn
	end
	local prevTitle = adjacent.prev and mw.title.new(adjacent.prev, namespace)
	local nextTitle = adjacent.next and mw.title.new(adjacent.next, namespace)
    local catPair = require('Module:Category pair')._pair
	return catPair(prevTitle, nextTitle)
end

-- Function to find timespan before argument
function p._before(s)
	local findOut = s and find(tostring(s))
	return findOut and findOut.prev
end

-- Function to find timespan after argument
function p._after(s)
	local findOut = s and find(tostring(s))
	return findOut and findOut.next
end

-- Template entry points
function p.seeAlso(frame)
	local args = getArgs(frame)
	return p._seeAlso(args)
end

function p.before(frame)
	local args = getArgs(frame)
	return p._before(args[1]) or ""
end

function p.after(frame)
	local args = getArgs(frame)
	return p._after(args[1]) or ""
end

return p