ns_cavegen/init.lua

-- DEVELOPMENT ONLY: Timer module for debugging performance
local modpath = minetest.get_modpath(minetest.get_current_modname())

dofile(modpath.."/lua/timer.lua")

-- DEVELOPMENT ONLY: End of timer module

-- Local variables used for programming
local internal =
    { a = nil

    -- Average size of a cave biome
    , biome_size  = { x =   50, y =   50, z =   50 }

    -- Average blob size of connectivity noise params
    , cnct_blob   = { x =  250, y =  100, z =  250 }

    -- The margin that a voxelmanip gives around the chunk being generated
    , mapgen_buffer = 16

    -- Enum type used during cave generation for classifying different types
    -- of cave nodes. Do not touch unless you're changing the code
    , node_types =
        { stick_edge = 0
        , air = 1
        , stone = 2
        , floor = 3
        , wall = 4
        , ceiling = 5
        , floor_deco = 6
        }

    -- Point that can be used for generating Voronoi graphs
    -- The number can be anything, as long as it reasonably far away from
    -- the range 0 - 100
    , outlandish_point = -1e3

    -- Random seeds used to influence noise
    , seeds =
        { connectivity =  297948
        , heat         =  320523
        , humidity     = 9923473
        , verticality  =   35644
        }

    -- Size of blocks being combined to simplify cave shape generation
    -- Higher values means better performance, but lower detail and variations
    , shape_cluster = { x =   32, y =   32, z =   32 }

    -- Average size of a shape biome
    , shape_size    = { x =   50, y =   50, z =   50 }

    -- Average blob size of verticality noise params
    , vrtcl_blob    = { x =  100, y =  250, z =  100 }

    -- If another mod doesn't override this value, we will assume that this is
    -- the world's depth.
    , world_depth   = -60

    -- Lower bound for the entire world
    , world_minp    = { x = -1e6, y = -1e6, z = -1e6 }

    -- Upper bound for cave generation
    , world_maxp    = { x =  1e6, y =  1e6, z =  1e6 }
    }

-------------------------------------------------------------------------------
-- Flat3dArray
-------------------------------------------------------------------------------
-- The Flat3dArray helps translate, transform and read data from different
-- 1-dimensional flat tables that all represent some 3-dimensional set.
local Flat3dArray = {}
Flat3dArray.__index = Flat3dArray

-- Global variable that can be used by other mods
-- Please see API.md for reference
noordstar_caves =
    { a = nil

    -- The `cave_vastness` is a variable that determines the size of caves.
    -- The function takes in an x, y and z variable, and returns a number
    -- between 0 and 1.
    -- Low numbers mean very rare and tiny caves, while high numbers mean
    -- massive caves, with massive open spaces.
    -- If you wish to overwrite this function, it is good to keep in mind to:
    --  - Make sure that the output changes VERY SLOWLY over time
    --  - Keep the function performant as it will be executed many, many times
    , cave_vastness = function(pos)
        return pos.y / internal.world_depth
    end

    -- A public list of all registered biomes
    , registered_biomes = {}

    -- A public list of all registered decorations
    , registered_decorations = {}

    -- A public list of all registered shapes
    , registered_shapes = {}

    }

-- Remove all registered biomes and start with a clean slate
function noordstar_caves.clear_registered_biomes()
    noordstar_caves.registered_biomes = {}
end

-- Remove all registered decorations and start with a clean slate
function noordstar_caves.clear_registered_decoration()
    noordstar_caves.registered_decorations = {}
end

-- Remove all registered shapes and start with a clean slate
function noordstar_caves.clear_registered_shapes()
    noordstar_caves.registered_shapes = {}
end

-- Register a new cave biome
function noordstar_caves.register_biome(def)
    local d = internal.clean_biome_def(def)

    if d then
        noordstar_caves.registered_biomes[d.name] = d
    end
end

-- Register a new cave decoration
function noordstar_caves.register_decoration(def)
    local d = internal.clean_deco_def(def)

    if d then
        table.insert(noordstar_caves.registered_decorations, d)
    end
end

-- Register a new cave shape
function noordstar_caves.register_shape(def)
    local d = internal.clean_shape_def(def)

    if d then
        noordstar_caves.registered_shapes[d.name] = d
    end
end

-- Override the world's depth
function noordstar_caves.set_world_depth(h)
    internal.world_depth = h
end
noordstar_caves.set_world_depth(internal.world_depth)

-- Remove a specific registered cave biome
function noordstar_caves.unregister_biome(name)
    noordstar_caves.registered_biomes[name] = nil
end

-- Remove a specific registered cave shape
function noordstar_caves.unregister_shape(name)
    noordstar_caves.registered_shapes[name] = nil
end


-- Calculate the distance of a given biome to a given point
function internal.biome_def_distance(def, heat, humidity)
    local dx = math.abs(humidity - def.humidity_point)
    local dy = math.abs(heat - def.heat_point)

    return dx^2 + dy^2
end

-- While a public `noordstar_caves.cave_vastness` function is exposed,
-- this mod uses an improved internal function to keep the edges pleasant
-- and to avoid potential errors.
function internal.cave_vastness(pos)
    -- Calculate value and put it in bounds
    local v = noordstar_caves.cave_vastness(pos)
    v = math.min(v, 1)
    v = math.max(v, 0)

    local d = internal.world_depth

    if pos.y > d + 20 then
        return v
    elseif pos.y > d + 5 then
        return v * (pos.y - (d + 5)) / 15
    else
        return 0
    end
end

-- Clean the user input on a biome definition before inserting it.
function internal.clean_biome_def(def)
    if type(def.name) ~= "string" then
        return nil
    end
    if type(def.heat_point) ~= "number" then
        return nil
    end
    if type(def.humidity_point) ~= "number" then
        return nil
    end

    local d = {
        name = def.name,
        heat_point = def.heat_point,
        humidity_point = def.humidity_point,
    }

    -- Position
    if type(def.min_pos) == "table" then
        d.minp = {
            x = def.min_pos.x or internal.world_minp.x,
            y = def.min_pos.y or internal.world_minp.y,
            z = def.min_pos.z or internal.world_minp.z,
        }
    elseif type(def.y_min) == "number" then
        d.minp = { 
            x = internal.world_minp.x,
            y = def.y_min,
            z = internal.world_minp.z,
        }
    else
        d.minp = {
            x = internal.world_minp.x,
            y = internal.world_minp.y,
            z = internal.world_minp.z,
        }
    end

    if type(def.max_pos) == "table" then
        d.maxp = {
            x = def.max_pos.x or internal.world_maxp.x,
            y = def.max_pos.y or internal.world_maxp.y,
            z = def.max_pos.z or internal.world_maxp.z,
        }
    elseif type(def.y_max) == "number" then
        d.maxp = {
            x = internal.world_maxp.x,
            y = def.y_max,
            z = internal.world_maxp.z,
        }
    else
        d.maxp = {
            x = internal.world_maxp.x,
            y = internal.world_maxp.y,
            z = internal.world_maxp.z,
        }
    end

    -- Optional nodes
    if type(def.node_dust) == "string" then
        d.node_dust = def.node_dust
    end
    if type(def.node_floor) == "string" then
        d.node_floor = def.node_floor
    end
    if type(def.node_wall) == "string" then
        d.node_wall = def.node_wall
    end
    if type(def.node_roof) == "string" then
        d.node_roof = def.node_roof
    end
    if type(def.node_air) == "string" then
        d.node_air = def.node_air
    end
    if type(def.node_shell) == "string" then
        d.node_shell = def.node_shell
    end
    if type(def.depth_shell) == "number" then
        d.depth_shell = def.depth_shell
    else
        d.depth_shell = 0
    end

    return d
end

-- Clean the user input on a decoration definition before inserting it.
function internal.clean_deco_def(def)
    if def.deco_type ~= "simple" and def.deco_type ~= "schematic" then
        return nil
    end
    if def.deco_type == "simple" and type(def.decoration) ~= "string" then
        return nil
    end
    if def.deco_type == "schematic" then
        if type(def.schematic) == "string" then
        elseif type(def.schematic) == "table" then
        else
            return nil
        end
    end
    if type(def.fill_ratio) ~= "number" then
        return nil
    end

    local d = {
        deco_type = def.deco_type,
        decoration = def.decoration,
        schematic = def.schematic,
        fill_ratio = def.fill_ratio,
        biomes = def.biomes,
    }

    if def.place_on == "floor" or def.place_on == "ceiling" then
        d.place_on = def.place_on
    else
        d.place_on = "floor"
    end

    local function place(key, t, default)
        if type(def[key]) == t then
            d[key] = def[key]
        else
            d[key] = default
        end
    end

    place("y_min", "number", internal.world_minp.y)
    place("y_max", "number", internal.world_maxp.y)
    place("height_max", "number", 0)
    place("height", "number", 1)
    place("place_offset_y", "number", 0)
    place("replacements", "table", {})
    place("flags", "string", "")
    place("rotation", "string", "0")

    d.height     = math.max(d.height    ,  0)
    d.height     = math.min(d.height    , 16)
    d.height_max = math.max(d.height_max,  0)
    d.height_max = math.min(d.height_max, 16)

    return d
end

-- Clean the user input on a shape definition before inserting it.
function internal.clean_shape_def(def)
    if type(def.name) ~= "string" then
        return nil
    end
    if type(def.connectivity_point) ~= "number" then
        return nil
    end
    if type(def.verticality_point) ~= "number" then
        return nil
    end

    local d = {
        name = def.name,
        connectivity_point = def.connectivity_point,
        verticality_point = def.verticality_point,

        y_min = def.y_min or internal.world_minp.y,
        y_max = def.y_max or internal.world_maxp.y,
    }

    if type(def.noise_params) == "table" then
        d.noise_params = def.noise_params
    end

    local func = function(pos, v) return v end
    if type(def.func) == "function" then
        func = def.func
    end
    d.func = internal.enhanced_shape_func(def.name, func)

    return d
end

-- Get the most nearby cave biome
function internal.closest_cave_biome(heat, humidity, pos)
    local biome = internal.default_biome()
    local d = internal.biome_def_distance(biome, heat, humidity)

    for _, def in pairs(noordstar_caves.registered_biomes) do
        if internal.is_valid_pos(pos, def.minp, def.maxp) then
            local new_d = internal.biome_def_distance(def, heat, humidity)
    
            if new_d <= d then
                biome = def
                d = new_d
            end
        end
    end

    return biome
end

-- Get the most nearby cave shape
function internal.closest_cave_shape(cnct, vrtcl, y)
    local shape = internal.default_shape()
    local d = internal.shape_def_distance(shape, cnct, vrtcl)

    for key, def in pairs(noordstar_caves.registered_shapes) do
        if def.y_min <= y and y <= def.y_max then
            local new_d = internal.shape_def_distance(def, cnct, vrtcl)
    
            if new_d <= d then
                shape = def
                d = new_d
            end
        end
    end

    return shape
end

-- Get connectivity noise params
function internal.connectivity_noise_params()
    local factor = math.max(
        math.abs(#noordstar_caves.registered_shapes) ^ 0.5
        , 1
    )

    return {
        offset = 50,
        scale = 50,
        spread =
            internal.reduced_shape_pos(
                { x = factor * internal.cnct_blob.x
                , y = factor * internal.cnct_blob.y
                , z = factor * internal.cnct_blob.z
                }
            ),
        seed = internal.seeds.connectivity,
        octaves = 2,
        persistence = 0.2,
        lacunarity = 2.0,
        flags = "eased"
    }
end

-- Get a default cave biome in case no biomes are registered
function internal.default_biome()
    return internal.clean_biome_def(
        { name = "noordstar_caves:default_biome"
        , heat_point = internal.outlandish_point
        , humidity_point = internal.outlandish_point
        }
    )
end

-- Get a default cave shape in case no shapes are registered
function internal.default_shape()
    return internal.clean_shape_def(
        { name = "noordstar_caves:none"
        , connectivity_point = internal.outlandish_point
        , verticality_point = internal.outlandish_point
        , func = function (pos, v) return 0 end
        }
    )
end

-- This library decides not to trust that the user is giving a proper input
-- on its function field. To help the developer insert a proper function, a few
-- error messages are inserted to give the developer more insight in how their
-- function behaves.
function internal.enhanced_shape_func(name, func)
    if type(func) ~= "function" then
        error("Expected function, found type `" .. type(func) .. "`")
    end

    return function (pos, n)
        local out = func(pos, n)

        if type(out) == "number" then
            return out
        elseif n == nil then
            error(
                table.concat(
                    { "Shape"
                    , name
                    , "function must return a number."
                    , "Your function's input `n` was nil."
                    , "Perhaps your `noise_params` field is invalid?"
                    }
                    , " "
                )
            )
        else
            error(
                table.concat(
                    { "Shape"
                    , name
                    , "function must return a number."
                    }
                    , " "
                )
            )
        end
    end
end

-- Get a Flat3dArray showing whether nodes are cave bools
function internal.flat_from_cave_bools(minp, maxp)
    -- Calculate connectivity and verticality for each point
    local connectivity = internal.flat_from_noise_params(
        internal.connectivity_noise_params(),
        internal.reduced_shape_pos(minp),
        internal.reduced_shape_pos(maxp)
    )
    local verticality = internal.flat_from_noise_params(
        internal.verticality_noise_params(),
        internal.reduced_shape_pos(minp),
        internal.reduced_shape_pos(maxp)
    )
    
    -- Using the calculated noise, determine the cave shape per shape chunk
    local reduced = Flat3dArray:from_func(
        internal.reduced_shape_pos(minp),
        internal.reduced_shape_pos(maxp),
        function (i, pos)
            -- DEVELOPMENT ONLY: Unittest
            if connectivity:pos_to_index(pos) ~= i then
                error("Connectivity index doesn't match local index")
            end
            if verticality:pos_to_index(pos) ~= i then
                error("Verticality index doesn't match local index")
            end
            -- DEVELOPMENT ONLY: End unittest

            local cnct = connectivity:get_index(i)
            local vrtcl = verticality:get_index(i)

            local def = internal.closest_cave_shape(cnct, vrtcl, pos.y)
            
            return def.name
    end)

    -- Calculate noise for each shape
    local noise = {}
    for key, shape in pairs(noordstar_caves.registered_shapes) do
        noise[key] = internal.flat_from_shape_def(shape, minp, maxp)
    end

    local default = internal.default_shape()
    noise[default.name] = internal.flat_from_shape_def(default, minp, maxp)

    -- Create a flat array of bools
    local bools = Flat3dArray:from_func(minp, maxp, function (i, pos)
        local key = reduced:get_pos(internal.reduced_shape_pos(pos))

        if noise[key] == nil then
            error("Key " .. key .. " gave no value on noise")
        end

        local n = noise[key]:get_index(i)
        local v = internal.cave_vastness(pos)

        return internal.is_cave_node(n, v)
    end)

    return bools
end

function internal.flat_from_node_types(bools, minp, maxp)
    local nt = internal.node_types

    -- local bools = internal.flat_from_cave_bools(minp, maxp)

    local node_types = Flat3dArray:from_func(minp, maxp, function (i, pos)
        -- Simplify calculation by ignoring edges
        if pos.x == minp.x or pos.x == maxp.x then
            return nt.stick_edge
        elseif pos.y == minp.y or pos.y == maxp.y then
            return nt.stick_edge
        elseif pos.z == maxp.z or pos.z == minp.z then
            return nt.stick_edge
        end
        
        if bools:get_index(i) then
            -- PART OF CAVE

            if bools:get_index(i + bools.down) == false then
                -- Block is right on the floor
                return nt.floor_deco
            end

            return nt.air
        else
            -- NOT PART OF CAVE

            -- Floor
            if bools:get_index(i + bools.up) then
                return nt.floor
            end

            -- Ceiling
            if bools:get_index(i + bools.down) then
                return nt.ceiling
            end

            -- Walls
            if bools:get_index(i + bools.north) then
                return nt.wall
            end
            if bools:get_index(i + bools.east) then
                return nt.wall
            end
            if bools:get_index(i + bools.south) then
                return nt.wall
            end
            if bools:get_index(i + bools.west) then
                return nt.wall
            end

            return nt.stone
        end
    end)

    return node_types
end

-- Get a Flat3dArray using noise_params
function internal.flat_from_noise_params(noise_params, minp, maxp)
    local nx = maxp.x - minp.x + 1
    local ny = maxp.y - minp.y + 1
    local nz = maxp.z - minp.z + 1

    local buffer = {}

    local p = PerlinNoiseMap(noise_params, { x = nx, y = ny, z = nz })

    if nz == 1 then
        p:get_2d_map_flat(minp, buffer)
    else
        p:get_3d_map_flat(minp, buffer)
    end

    return Flat3dArray:new(minp, maxp, buffer)
end

-- Get a Flat3dArray about shape noise
-- This function is defined differently from other definitions because the
-- noise_params are optional in the shape definition
function internal.flat_from_shape_def(def, minp, maxp)
    local noise_flat_map = {}

    local nx = maxp.x - minp.x + 1
    local ny = maxp.y - minp.y + 1
    local nz = maxp.z - minp.z + 1

    if def.noise_params then
        local p = PerlinNoiseMap(def.noise_params, { x = nx, y = ny, z = nz })
        
        if nz == 1 then
            p:get_2d_map_flat(minp, noise_flat_map)
        else
            p:get_3d_map_flat(minp, noise_flat_map)
        end
    end

    internal.iter_3d_area(minp, maxp, function (i, pos)
        noise_flat_map[i] = def.func(pos, noise_flat_map[i])
    end)

    return Flat3dArray:new(minp, maxp, noise_flat_map)
end

-- Convert 3d relative coordinates to an index on a flat array
function internal.from_3d_to_flat(dx, dy, dz, nx, ny)
    return (nx * ny * dz) + (nx * dy) + dx + 1
end

-- Generate caves given a voxelmanip array
function internal.generate_caves(data, minp, maxp)
    -- Increased voxelmanip size
    local vminp =
        { x = minp.x - internal.mapgen_buffer
        , y = minp.y - internal.mapgen_buffer
        , z = minp.z - internal.mapgen_buffer
        }
    local vmaxp =
        { x = maxp.x + internal.mapgen_buffer
        , y = maxp.y + internal.mapgen_buffer
        , z = maxp.z + internal.mapgen_buffer
        }

    -- Increased node type size to account for unknown edges
    local bminp =
        { x = minp.x - 1
        , y = minp.y - 1
        , z = minp.z - 1
        }
    local bmaxp =
        { x = maxp.x + 1
        , y = maxp.y + 1
        , z = maxp.z + 1
        }

    -- Load data
    local vmanip = Flat3dArray:new(vminp, vmaxp, data)
    
    -- Get cave bools
    local bools = internal.flat_from_cave_bools(bminp, bmaxp)

    -- Get node types
    local nts = internal.flat_from_node_types(bools, bminp, bmaxp)

    -- Calculate biome heat & humidity
    local heat_points = internal.flat_from_noise_params(
        internal.heat_noise_params(), bminp, bmaxp
    )
    local humidity_points = internal.flat_from_noise_params(
        internal.humidity_noise_params(), bminp, bmaxp
    )

    local air = minetest.get_content_id("air")
    local schems = {}

    -- Place blocks where necessary
    internal.iter_3d_area(bminp, bmaxp, function (i, pos)
        
        local vi = vmanip:pos_to_index(pos)
        local function place(name)

            if vmanip:get_index(vi) == air then
            elseif type(name) == "string" then
                vmanip:set_index(vi, minetest.get_content_id(name))
            elseif type(name) == "nil" then
            else
                error("Inserted invalid type " .. type(name) .. " into voxelmanip array")
            end
        end

        local nt = nts:get_index(i)

        if nt == internal.node_types.stone then
        elseif nt == internal.node_types.stick_edge then
        elseif nt == internal.node_types.air then
            place("air")
        else
            -- Find appropriate biome
            local heat = heat_points:get_index(i)
            local humidity = humidity_points:get_index(i)

            local def = internal.closest_cave_biome(heat, humidity, pos)

            if nt == internal.node_types.floor then
                place(def.node_floor)
            elseif nt == internal.node_types.wall then
                place(def.node_wall)
            elseif nt == internal.node_types.ceiling then
                place(def.node_roof)
            elseif nt == internal.node_types.floor_deco then
                local schem_placed = false

                if not schem_placed then
                    -- Prevent decorations from spawning in the air
                    if vmanip:get_index(vi) == air then
                        schem_placed = true
                    end
                end

                if not schem_placed then
                    for _, deco in ipairs(noordstar_caves.registered_decorations) do
                        if deco.place_on ~= "floor" then
                        elseif math.random() > deco.fill_ratio then
                        elseif not internal.is_deco_biome(deco, def.name) then
                        else
                            table.insert(schems, { pos = pos, deco = deco })
                            schem_placed = true
                            break
                        end
                    end
                end

                if not schem_placed then
                    place(def.node_dust or "air")
                end
            else
                error(
                    table.concat(
                        { "Found unknown node type "
                        , nt
                        , " (type "
                        , type(nt)
                        , ")"
                        }
                        , ""
                    )
                )
            end
        end
    end)

    return vmanip, schems
end

-- Get the noise params for the cave biome temperature.
function internal.heat_noise_params()
    return {
        offset = 50,
        scale = 50,
        spread = internal.biome_size,
        seed = internal.seeds.heat,
        octaves = 2,
        persistence = 0.1,
        lacunarity = 2.0,
        flags = ""
    }
end

-- Get the noise params for the cave biome humidity.
function internal.humidity_noise_params()
    return { 
        offset = 50,
        scale = 50,
        spread = internal.biome_size,
        seed = internal.seeds.humidity,
        octaves = 2,
        persistence = 0.1,
        lacunarity = 2.0,
        flags = ""
    }
end

-- Return whether a node is part of a cave
function internal.is_cave_node(noise, vastness)
    return noise > 1 - vastness
end

-- Return whether a given decoration definition can spawn in a given biome name
function internal.is_deco_biome(def, biome_name)
    if type(def.biomes) == "nil" then
        return true
    elseif type(def.biomes) == "string" then
        return def.biomes == biome_name
    elseif type(def.biomes) == "table" then
        for _, name in pairs(def.biomes) do
            if name == biome_name then
                return true
            end
        end
    end

    return false
end

-- Return a bool whether a position is within a given volume
function internal.is_valid_pos(pos, minp, maxp)
    if minp.x <= pos.x and pos.x <= maxp.x then
        if minp.y <= pos.y and pos.y <= maxp.y then
            if minp.z <= pos.z and pos.z <= maxp.z then
                return true
            end
        end
    end

    return false
end

-- Iterate over a 3d area, both indexing by the index and the ansolute position
function internal.iter_3d_area(minp, maxp, callback)
    local nx = maxp.x - minp.x + 1
    local ny = maxp.y - minp.y + 1
    -- local nz = maxp.z - minp.z + 1

    local i = 0

    for z = minp.z, maxp.z, 1 do
        for y = minp.y, maxp.y, 1 do
            for x = minp.x, maxp.x, 1 do
                local pos = { x = x, y = y, z = z }
                i = i + 1

                -- DEVELOPMENT ONLY: This function only serves as a unittest
                -- DEVELOPMENT ONLY: to verify that the iteration across a 3D
                -- DEVELOPMENT ONLY: table works appropriately.
                -- DEVELOPMENT ONLY: This calculation is highly inefficient and
                -- DEVELOPMENT ONLY: unnecessary so it is highly recommended
                -- DEVELOPMENT ONLY: to remove this code in production.
                local dx = x - minp.x
                local dy = y - minp.y
                local dz = z - minp.z
                local si = internal.from_3d_to_flat(dx, dy, dz, nx, ny)

                if i ~= si then
                    error(
                        table.concat(
                            { "Expected position"
                            , internal.pos_to_str(pos)
                            , "to correspond to index"
                            , si
                            , "but our iteration arrived at index"
                            , i
                            }
                            , " "
                        )
                    )
                end
                -- DEVELOPMENT ONLY:
                -- DEVELOPMENT ONLY: This is the bottom of the unittest.
                -- DEVELOPMENT ONLY: Please remove this code in a future commit
                -- DEVELOPMENT ONLY: before the mod is assumed to be
                -- DEVELOPMENT ONLY: production-ready.
                -- DEVELOPMENT ONLY:

                callback(i, pos)
            end
        end
    end
end

-- -- Log text to the Minetest chat
-- function internal.log(text)
--     minetest.chat_send_all(os.time() .. " - " .. text)
-- end

-- Place all schematic decorations into the world
function internal.place_schematic_decorations(vmanip, schems)
    for _, schem in ipairs(schems) do
        local pos  = schem.pos
        local deco = schem.deco

        if deco.deco_type ~= "schematic" then
        else
            minetest.place_schematic_on_vmanip(
                vmanip, pos,
                deco.schematic, deco.rotation, deco.replacement,
                true, deco.flags
            )
        end
    end
end

-- Place all simple decorations into the world
function internal.place_simple_decorations(flat, schems)
    for _, schem in ipairs(schems) do
        if schem.deco.deco_type == "simple" then
            local pos  = schem.pos
            local deco = schem.deco
            
            local i = flat:pos_to_index(pos)
            
            local dir = nil
            
            if deco.place_on == "floor" then
                dir = flat.up
            elseif deco.place_on == "ceiling" then
                dir = flat.down
            else
                error("Invalid place_on value `" .. deco.place_on .. "`")
            end
            
            local h_min = deco.height
            local h_max = math.max(deco.height, deco.height_max)
            
            for dy = 0, math.random(h_min, h_max) - 1, 1 do
                local li = i + dir * dy
                
                flat:set_index(li, minetest.get_content_id(deco.decoration))
            end
        
        end
    end
end

-- Helper function to convert a set of coordinates to a readable string
function internal.pos_to_str(pos)
    return "(" .. pos.x .. ", " .. pos.y .. ", " .. pos.z .. " )"
end

-- Get a reduced position based on the chunks
function internal.reduced_shape_pos(pos)
    return
        { x = math.floor(pos.x / internal.shape_cluster.x)
        , y = math.floor(pos.y / internal.shape_cluster.y)
        , z = math.floor(pos.z / internal.shape_cluster.z)
        }
end

-- Calculate the relative index change to move downwards one position
function internal.relative_get_down(nx, ny)
    return internal.relative_index_diff(0, -1, 0, nx, ny)
end

-- Calculate the relative index change to move eastwards one position
function internal.relative_get_east(nx, ny)
    return internal.relative_index_diff(1, 0, 0, nx, ny)
end

-- Calculate the relative index change to move northwards one position
function internal.relative_get_north(nx, ny)
    return internal.relative_index_diff(0, 0, 1, nx, ny)
end

-- Calculate the relative index change to move southwards one position
function internal.relative_get_south(nx, ny)
    return internal.relative_index_diff(0, 0, -1, nx, ny)
end

-- Calculate the relative index change to move upwards one position
function internal.relative_get_up(nx, ny)
    return internal.relative_index_diff(0, 1, 0, nx, ny)
end

-- Calculate the relative index change to move westwards one position
function internal.relative_get_west(nx, ny)
    return internal.relative_index_diff(-1, 0, 0, nx, ny)
end

-- Calculate the difference in index to relative coordinates.
-- Used to speed up index lookup on flat 3d arrays.
function internal.relative_index_diff(dx, dy, dz, nx, ny)
    return
        ( internal.from_3d_to_flat(dx, dy, dz, nx, ny)
        - internal.from_3d_to_flat( 0,  0,  0, nx, ny)
        )
end

-- Calculate the distance of a given shape to a given point
function internal.shape_def_distance(def, cnct, vrtcl)
    local dx = math.abs(cnct - def.connectivity_point)
    local dy = math.abs(vrtcl - def.verticality_point)

    return dx^2 + dy^2
end

-- Get verticality noise params
function internal.verticality_noise_params()
    local factor = math.max(
        math.abs(#noordstar_caves.registered_shapes) ^ 0.5
        , 1
    )

    return {
        offset = 50,
        scale = 50,
        spread =
            internal.reduced_shape_pos(
                { x = factor * internal.vrtcl_blob.x
                , y = factor * internal.vrtcl_blob.y
                , z = factor * internal.vrtcl_blob.z
                }
            ),
        seed = internal.seeds.verticality,
        octaves = 2,
        persistence = 0.2,
        lacunarity = 2.0,
        flags = "eased"
    }
end

-- Determine whether a position is within given bounds
function internal.within_bounds(pos, minp, maxp)
    if minp.x <= pos.x and pos.x <= maxp.x then
        if minp.y <= pos.y and pos.y <= maxp.y then
            if minp.z <= pos.z and pos.z <= maxp.z then
                return true
            end
        end
    end

    return false
end


-- Create a new flat 3d array based on a function callback that gets the index
-- and position as inputs
function Flat3dArray:from_func(minp, maxp, callback)
    local arr = {}

    internal.iter_3d_area(minp, maxp, function (i, pos)
        arr[i] = callback(i, pos)
    end)

    return self:new(minp, maxp, arr)
end

-- Get the Flat3dArray's value on the i'th index
function Flat3dArray:get_index(i)
    local out = self.arr[i]
    if out == nil then
        error(
            "Index " .. i .. " not found in array of length " .. #self.arr
        )
    end
    return out
end

-- Get a value at a given position
function Flat3dArray:get_pos(pos)
    -- pos_to_index already validates so there's no need to validate here
    return self:get_index(self:pos_to_index(pos))
end

-- Create a new Flat3dArray instance
function Flat3dArray:new(minp, maxp, arr)
    local instance = {}
    setmetatable(instance, Flat3dArray)

    local nx = maxp.x - minp.x + 1
    local ny = maxp.y - minp.y + 1
    local nz = maxp.z - minp.z + 1

    if #arr ~= nx * ny * nz then
        error(
            "Input array doesn't match dimension lengths: " .. nx .. " x " ..
            ny .. " x " .. nz .. " = " .. (nx*ny*nz) .. ", but found " .. #arr
        )
    end

    -- Variables
    instance.nx    = nx
    instance.ny    = ny
    instance.nz    = nz
    instance.minp  = minp
    instance.maxp  = maxp
    instance.arr   = arr

    -- Constants
    instance.up    = internal.relative_get_up(nx, ny)
    instance.down  = internal.relative_get_down(nx, ny)
    instance.north = internal.relative_get_north(nx, ny)
    instance.east  = internal.relative_get_east(nx, ny)
    instance.south = internal.relative_get_south(nx, ny)
    instance.west  = internal.relative_get_west(nx, ny)

    return instance
end

-- Convert a position to an index
function Flat3dArray:pos_to_index(pos)
    self:validate_pos(pos)

    local dx = pos.x - self.minp.x
    local dy = pos.y - self.minp.y
    local dz = pos.z - self.minp.z

    return internal.from_3d_to_flat(dx, dy, dz, self.nx, self.ny)
end

-- Override a value at a given index
function Flat3dArray:set_index(i, val)
    self:validate_index(i)
    self.arr[i] = val
end

-- Validate an index to be in the Flat3dArray
function Flat3dArray:validate_index(i)
    if i < 1 or i > #self.arr then
        error(
            table.concat(
                { "Index"
                , i
                , "is not in range 1 -"
                , #self.arr
                }
                , " "
            )
        )
    end
end

-- Validate a position to be in the Flat3dArray
function Flat3dArray:validate_pos(pos)
    if not internal.is_valid_pos(pos, self.minp, self.maxp) then
        error(
            table.concat(
                { "Position"
                , internal.pos_to_str(pos)
                , "is not within minp ="
                , internal.pos_to_str(self.minp)
                , "and maxp ="
                , internal.pos_to_str(self.maxp)
                }
                , " "
            )
        )
    end
end

-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
minetest.register_on_generated(function(minp, maxp, blockseed)
    math.randomseed(blockseed)

    local vm = minetest.get_mapgen_object("voxelmanip")
    local flat, schems = internal.generate_caves(vm:get_data(), minp, maxp)

    internal.place_simple_decorations(flat, schems)

    vm:set_data(flat.arr)
    vm:write_to_map()

    internal.place_schematic_decorations(vm, schems)
end)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------

-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
-- For show, the following code COULD in theory be run elsewhere
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------

noordstar_caves.register_shape({
    name = "noordstar_caves:bubbles",
    
    noise_params = {
        offset = 0.5,
        scale = 0.5,
        spread = { x = 20, y = 20, z = 20 },
        seed = 248039,
        octaves = 2,
        persistence = 0.6,
        lacunarity = 2.0,
        flags = "eased"
    },

    func = function(pos, n)
        return n
    end,

    -- TODO: Implement y limits
    -- y_min = -31000,
    -- y_max = 31000,

    connectivity_point = 10,
    verticality_point = 40,
})
-- noordstar_caves.register_shape({
--     name = "noordstar_caves:cliffs",
    
--     noise_params = {
--         offset = 0.4,
--         scale = 0.5,
--         spread = { x = 20, y = 100, z = 20 },
--         seed = 97354,
--         octaves = 4,
--         persistence = 0.6,
--         lacunarity = 2.0,
--         flags = ""
--     },

--     func = function(pos, n)
--         return n
--     end,

--     connectivity_point = 30,
--     verticality_point = 80,
-- })
-- noordstar_caves.register_shape({
--     name = "noordstar_caves:donuts",
    
--     noise_params = {
--         offset = 0.0,
--         scale = 1.0,
--         spread = { x = 30, y = 30, z = 30 },
--         seed = 3934,
--         octaves = 1,
--         persistence = 0.6,
--         lacunarity = 2.0,
--         flags = "eased"
--     },

--     func = function(pos, n)
--         return 1 - 2 * math.abs(n)^0.5
--     end,

--     connectivity_point = 50,
--     verticality_point = 40,
-- })
-- noordstar_caves.register_shape({
--     name = "noordstar_caves:wall",

--     func = function(pos, n)
--         return -0.5
--     end,

--     connectivity_point = 0,
--     verticality_point = 0,
-- })

-- noordstar_caves.set_world_depth(-60)
-- noordstar_caves.cave_vastness = function(pos) return math.abs(pos.y - 60) / 120 end

noordstar_caves.register_biome({
    name = "test",
    node_floor = "mcl_core:crying_obsidian",
    node_wall = "mcl_core:sand",
    node_roof = "mcl_ocean:sea_lantern",
    node_dust = "mcl_core:snow",
    heat_point = 80,
    humidity_point = 80,
})
noordstar_caves.register_biome({
    name = "test2",
    node_floor = "mcl_amethyst:amethyst_block",
    node_wall = "mcl_crimson:shroomlight",
    node_roof = "mcl_colorblocks:glazed_terracotta_silver",
    heat_point = 100,
    humidity_point = 100,
})
-- noordstar_caves.register_biome({
--     name = "test3",
--     heat_point = 50,
--     humidity_point = 50,
-- })

noordstar_caves.register_decoration({
    deco_type = "simple",
    place_on = "floor",
    fill_ratio = 0.01,
    decoration = "mcl_core:cactus",
    height = 3,
    height_max = 8,
    biomes = { "test" },
})
noordstar_caves.register_decoration({
    deco_type = "simple",
    place_on = "floor",
    fill_ratio = 0.1,
    decoration = "mcl_ocean:sea_lantern",
    height = 1,
    height_max = 4,
    biomes = { "test2" },
})
noordstar_caves.register_decoration({
    deco_type = "schematic",
    place_on = "floor",
    fill_ratio = 0.005,
    schematic = squeak,
    rotation = "random",
    -- place_offset_y = 5,
})