-- frontier.lua — "where haven't I been yet?"
--
-- The level view IS the map. level.rememberedFoV (modules/level.lua:576) keeps
-- every tile the player has ever seen drawn on screen, and a sighted player pans
-- over it with Ctrl+arrows and reads the shape of the fog edge at a glance: that
-- corridor dead-ends, that one carries on, I never went back for the door in the
-- north wall.
--
-- Nothing in the mod answered that. The surroundings scan is local, the examine
-- cursor is one tile at a time, and the tracker only finds things it already
-- knows about -- none of them say where there is still to GO. This does, in one
-- keypress and with no mode to enter.
--
--------------------------------------------------------------------------------
-- What counts as a frontier
--------------------------------------------------------------------------------
--
-- A frontier tile is one that is seen (FoV or rememberedFoV), NOT blocking
-- movement, and has at least one neighbour that is in bounds and not seen.
--
-- Both restrictions are load-bearing:
--
--   * in bounds -- otherwise every walkable tile along the grid boundary is a
--     frontier, and the report is nothing but map edge.
--   * CARDINAL neighbours only, not all eight -- the diagonal test fires on the
--     unseen tile tucked behind a wall corner, which is not anywhere you can
--     walk. Standing in a lit corridor would otherwise report an "unexplored
--     way" for every corner you can see. Cardinal removes almost all of those.
--
-- Clustering is 8-connected, so a wide doorway is one way rather than three, but
-- two separate openings that both happen to lie north stay two ways.
--
--------------------------------------------------------------------------------
-- Not a cheat
--------------------------------------------------------------------------------
--
-- This reads only FoV and rememberedFoV, and reports only THAT an opening exists
-- -- never what lies beyond it. That is exactly the information the fog edge
-- gives a sighted player. Nothing about an unseen tile is ever spoken.

local speech = require("accessibility.speech")
local describe = require("accessibility.describe")

local frontier = {}

frontier.config = {
	-- How many ways to name before falling back to "and N more". Four is about
	-- as much as fits in one utterance and still be held in the head.
	maxSpoken = 4,
}

--------------------------------------------------------------------------------
-- Level access
--------------------------------------------------------------------------------

local function getLevel()
	local ok, world = pcall(require, "models.world")
	if not ok or not world.currentLevel then
		return nil
	end
	return world.currentLevel
end

local function seenAt(level, x, y)
	if level.FoV and level.FoV[x] and level.FoV[x][y] then
		return true
	end
	if level.rememberedFoV and level.rememberedFoV[x] and level.rememberedFoV[x][y] then
		return true
	end
	return false
end

local function inBounds(level, x, y)
	return x >= 1 and y >= 1
		and x <= (level.xMax or 0) and y <= (level.yMax or 0)
		and level.grid[x] and level.grid[x][y] and true or false
end

local function blocksMovement(level, x, y)
	local stack = level.grid[x][y]
	if type(stack) ~= "table" then
		return true
	end

	for i = #stack, 1, -1 do
		local tile = stack[i]
		if tile and not tile.isHidden and tile.blocksMovement then
			return true
		end
	end

	return false
end

--------------------------------------------------------------------------------
-- Scanning
--------------------------------------------------------------------------------

local CARDINALS = {{0, -1}, {1, 0}, {0, 1}, {-1, 0}}

local function isFrontier(level, x, y)
	if not seenAt(level, x, y) or blocksMovement(level, x, y) then
		return false
	end

	for _, dir in ipairs(CARDINALS) do
		local nx, ny = x + dir[1], y + dir[2]
		if inBounds(level, nx, ny) and not seenAt(level, nx, ny) then
			return true
		end
	end

	return false
end

-- Every frontier tile on the level, as a set keyed "x,y" plus a flat list.
local function collect(level)
	local set, list = {}, {}

	for x = 1, level.xMax or 0 do
		if level.grid[x] then
			for y = 1, level.yMax or 0 do
				if level.grid[x][y] and isFrontier(level, x, y) then
					set[x .. "," .. y] = true
					list[#list + 1] = {x = x, y = y}
				end
			end
		end
	end

	return set, list
end

--------------------------------------------------------------------------------
-- Clustering
--------------------------------------------------------------------------------

-- 8-connected components, flood filled with an explicit stack rather than
-- recursion: a long wall of frontier tiles would otherwise be deep enough to
-- matter, and LuaJIT's C stack is not worth betting on here.
--
-- Each cluster is reduced to its member nearest the player, which is the one the
-- player would actually walk to.
local function cluster(set, list, px, py)
	local clusters = {}

	for _, seed in ipairs(list) do
		local seedKey = seed.x .. "," .. seed.y

		if set[seedKey] then
			set[seedKey] = nil

			local best = seed
			local bestDistance = describe.distance(seed.x - px, seed.y - py)
			local size = 0
			local stack = {seed}

			while #stack > 0 do
				local tile = table.remove(stack)
				size = size + 1

				local distance = describe.distance(tile.x - px, tile.y - py)
				if distance < bestDistance then
					best, bestDistance = tile, distance
				end

				for dx = -1, 1 do
					for dy = -1, 1 do
						local key = (tile.x + dx) .. "," .. (tile.y + dy)
						if set[key] then
							set[key] = nil
							stack[#stack + 1] = {x = tile.x + dx, y = tile.y + dy}
						end
					end
				end
			end

			clusters[#clusters + 1] = {
				x = best.x,
				y = best.y,
				distance = bestDistance,
				size = size,
			}
		end
	end

	table.sort(clusters, function(a, b)
		if a.distance ~= b.distance then
			return a.distance < b.distance
		end
		-- Stable tie-break, so repeating the key repeats the sentence.
		if a.x ~= b.x then
			return a.x < b.x
		end
		return a.y < b.y
	end)

	return clusters
end

--------------------------------------------------------------------------------
-- Public
--------------------------------------------------------------------------------

-- Returns the cluster list, nearest first, or nil if there is no level.
function frontier.scan()
	local level = getLevel()
	local actor = level and level.playerActor

	if not level or not level.grid or not actor then
		return nil
	end

	local set, list = collect(level)
	return cluster(set, list, actor.x, actor.y)
end

-- The spoken sentence, or nil if there is no level to report on.
function frontier.report()
	local clusters = frontier.scan()

	if not clusters then
		return nil
	end

	if #clusters == 0 then
		return "No unexplored ways from here"
	end

	local spoken = math.min(#clusters, frontier.config.maxSpoken)
	local actor = getLevel().playerActor

	local parts = {}
	for i = 1, spoken do
		local entry = clusters[i]
		parts[#parts + 1] = describe.offset(entry.x - actor.x, entry.y - actor.y)
	end

	local sentence = string.format("%d unexplored %s: %s",
		#clusters, #clusters == 1 and "way" or "ways", table.concat(parts, ", "))

	if #clusters > spoken then
		sentence = sentence .. ", and " .. (#clusters - spoken) .. " more"
	end

	return sentence
end

-- End: say it.
function frontier.announce()
	local sentence = frontier.report()

	if not sentence then
		speech.say("Not on a map", true)
		return
	end

	speech.say(sentence, true)
end

function frontier.registerKeys(hotkeys)
	hotkeys.bind("end", nil, frontier.announce)
end

return frontier