local mlvec = modlib.vector

local media_paths = epidermis.media_paths

local bad_character_b3d_path = modlib.mod.get_resource"character_without_normals.b3d"
local bad_character_b3d_hash = minetest.sha1(modlib.file.read(bad_character_b3d_path))
local fixed_character_b3d_path = modlib.mod.get_resource"character_with_normals.b3d"

return setmetatable({}, {__index = function(self, filename)
	local _, ext = modlib.file.get_extension(filename)
	if not ext or  ext:lower() ~= "b3d" then
		-- Only B3D support currently
		return
	end
	local path = assert(media_paths[filename], filename)
	-- HACK replace a "bad" character.b3d with a fixed version that includes normals
	-- Susceptible to SHA1 collisions, but so is MT's media loading process
	-- See https://github.com/minetest/minetest_game/pull/2902
	if filename == "character.b3d" and minetest.sha1(modlib.file.read(path)) == bad_character_b3d_hash then
		path = fixed_character_b3d_path
	end
	local model = io.open(path, "rb")
	local character = assert(modlib.b3d.read(model))
	assert(not model:read(1))
	model:close()
	local mesh = assert(character.node.mesh)
	local vertices = assert(mesh.vertices)
	for _, vertex in ipairs(vertices) do
		-- Minetest hardcodes a blocksize of 10 model units
		vertex.pos = mlvec.divide_scalar(vertex.pos, 10)
	end
	-- Triangle sets by texture index
	local tris_by_tex = {}
	local func = modlib.func
	for _, set in pairs(assert(mesh.triangle_sets)) do
		local tris = set.vertex_ids
		for _, tri in pairs(tris) do
			modlib.table.map(tri, func.curry(func.index, vertices))
			tri.poses = {tri[1].pos, tri[2].pos, tri[3].pos}
		end
		local brush_id = tris.brush_id or mesh.brush_id
		local tex_id
		if brush_id then
			tex_id = assert(character.brushes[brush_id].texture_id[1])
		else
			-- No brush, default to first texture
			tex_id = 1
		end
		tris_by_tex[tex_id] = tris_by_tex[tex_id] and modlib.table.append(tris_by_tex[tex_id], tris) or tris
	end
	self[filename] = {
		vertices = vertices,
		triangle_sets = tris_by_tex,
		frames = (character.node.animation or {}).frames or 1
	}
	return self[filename]
end})