-- Average size of each cave biome
local BIOME_SIZE = { x = 250, y = 250, z = 250 }

-- Average step size of connectivity params
-- Given that connectivity is mostly a horizontal feature, it mostly changes
-- on a vertical scale, and barely on a horizontal scale.
local CONNECTIVITY_BLOB = { x =  250, y =  100, z =  250 }

local ENUM_AIR = 1
local ENUM_CEILING = 2
local ENUM_CEILING_DECORATION = 3
local ENUM_FLOOR = 4
local ENUM_FLOOR_DECORATION = 5
local ENUM_STONE = 6
local ENUM_WALL = 7

-- Point that is so out of the normal connectivity/verticality scope (0 - 100)
-- that it is only selected when no other items are registered.
local OUTLANDISH_POINT = -1e3

-- Average size of each cave shape
local SHAPE_SIZE = { x = 128, y = 128, z = 128 }

-- Several seeds for mapgen
local SEED_CONNECTIVITY   =  297948
local SEED_HEAT           =  320523
local SEED_HUMIDITY       = 9923473
local SEED_VERTICALITY    =   35644

-- Average step size of verticality params
-- Given that verticality is mostly a vertical feature, it mostly changes on a
-- horizontal scale, and barely on a vertical scale.
local VERTICALITY_BLOB = { x =  100, y =  250, z =  100 }

-- Lower bound for cave generation
local WORLD_MINP = { x = -1e6, y = -1e6, z = -1e6 }

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

local WORLD_DEPTH = -60

local internal = {}

-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
-------------------------------- INTERNAL API ---------------------------------
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------

function internal.cave_vastness(pos)
    local v = ns_caves.cave_vastness(pos)

    if not v then
        return 0
    elseif v < 0 then
        return 0
    elseif v > 1 then
        return 1
    else
        return v
    end
end

-- Classify all nodes in the chunk into what they are
-- TODO: Perhaps instead of iterating over ALL nodes, we can sort all node types
-- TODO: into separate tables, effectively allowing us to process the nodes
-- TODO: independently, saving computation time.
function internal.classify_nodes(used_shapes, minp, maxp)
    local sminp = vector.offset(minp,  1,  1,  1)
    local smaxp = vector.offset(maxp, -1, -1, -1)
    local sva = VoxelArea(sminp, smaxp)
    local va = VoxelArea(minp, maxp)

    local items = {}
    
    for i in sva:iterp(sminp, smaxp) do
        
        local pos = sva:position(i)
        local bi = va:index(pos.x, pos.y, pos.z)
        
        local function is_part_of_cave(v)
            return used_shapes[va:index(v.x, v.y, v.z)]
        end

        if used_shapes[bi] == true then
            -- Part of cave
            if not used_shapes[va:index(pos.x, pos.y + 1, pos.z)] then
                items[i] = ENUM_CEILING_DECORATION
            elseif not used_shapes[va:index(pos.x, pos.y - 1, pos.z)] then
                items[i] = ENUM_FLOOR_DECORATION
            else
                items[i] = ENUM_AIR
            end
        else
            -- Not part of cave
            if used_shapes[va:index(pos.x, pos.y + 1, pos.z)] then
                items[i] = ENUM_FLOOR
            elseif used_shapes[va:index(pos.x, pos.y - 1, pos.z)] then
                items[i] = ENUM_CEILING
            elseif used_shapes[va:index(pos.x - 1, pos.y, pos.z)] then
                items[i] = ENUM_WALL
            elseif used_shapes[va:index(pos.x + 1, pos.y, pos.z)] then
                items[i] = ENUM_WALL
            elseif used_shapes[va:index(pos.x, pos.y, pos.z - 1)] then
                items[i] = ENUM_WALL
            elseif used_shapes[va:index(pos.x, pos.y, pos.z + 1)] then
                items[i] = ENUM_WALL
            else
                items[i] = ENUM_STONE
            end
        end
    end
    
    local custom_y = -13
    if sminp.y < custom_y and custom_y < smaxp.y then
        for i in sva:iterp({ x = sminp.x, y = custom_y, z = sminp.z }, { x = smaxp.x, y = custom_y, z = smaxp.z }) do
            items[i] = ENUM_CEILING
        end
    end

    return items
end

function internal.clean_biome_def(def)
    assert(type(def) == "table")
    assert(type(def.name) == "string")
    assert(type(def.heat_point) == "number")
    assert(type(def.humidity_point) == "number")

    def.y_min = def.y_min or (def.min_pos and def.min_pos.y) or WORLD_MINP.y
    def.y_max = def.y_max or (def.max_pos and def.max_pos.y) or WORLD_MAXP.y

    def.min_pos = def.min_pos or { x = WORLD_MINP.x, y = def.y_min, z = WORLD_MINP.z }
    def.max_pos = def.max_pos or { x = WORLD_MAXP.x, y = def.y_max, z = WORLD_MAXP.z }

    assert(type(def.y_min) == "number")
    assert(type(def.y_max) == "number")
    assert(type(def.min_pos) == "table")
    assert(type(def.max_pos) == "table")
    assert(type(def.min_pos.x) == "number")
    assert(type(def.max_pos.x) == "number")
    assert(type(def.min_pos.y) == "number")
    assert(type(def.max_pos.y) == "number")
    assert(type(def.min_pos.z) == "number")
    assert(type(def.max_pos.z) == "number")

    def.node_air = def.node_air or "air"

    assert(def.node_dust == nil or type(def.node_dust) == "string")
    assert(def.node_floor == nil or type(def.node_floor) == "string")
    assert(def.node_wall == nil or type(def.node_wall) == "string")
    assert(def.node_roof == nil or type(def.node_roof) == "string")
    assert(type(def.node_air) == "string")

    return def
end

function internal.clean_shape_def(def)
    assert(
        type(def) == "table",
        "Shape def is meant to be a table type"
    )
    assert(type(def.name) == "string", "Shape name is meant to be a string")
    assert(type(def.connectivity_point) == "number")
    assert(type(def.verticality_point) == "number")

    def.y_min = def.y_min or WORLD_MINP.y
    def.y_max = def.y_max or WORLD_MAXP.y
    def.func = def.func or function(_, n) return n end

    assert(type(def.y_min) == "number")
    assert(type(def.y_max) == "number")
    assert(type(def.func) == "function")
    assert(def.noise_params == nil or type(def.noise_params) == "table")

    return def
end

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

    return {
        offset = 50,
        scale = 50,
        spread = {
            x = factor * CONNECTIVITY_BLOB.x,
            y = factor * CONNECTIVITY_BLOB.y,
            z = factor * CONNECTIVITY_BLOB.z,
        },
        seed = SEED_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 = OUTLANDISH_POINT
        , humidity_point = 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 = OUTLANDISH_POINT
        , verticality_point = OUTLANDISH_POINT
        , func = function (pos, v) return 0 end
        }
    )
end

-- Get a (sorta) Euclidian distance. The exact distance doesn't matter,
-- it just needs to correctly determine whichever value is closer in a
-- Euclidian space. Consequently, the square root is ignored as optimization.
function internal.euclidian(x1, x2, y1, y2)
    return (x1 - x2) ^ 2 + (y1 - y2) ^ 2
end

-- For each node, determine which cave biome they're in.
function internal.find_biome_allocations(heat, humidity)
    assert(#heat == #humidity)

    local allocs = {}
    local default_biome = internal.default_biome()

    for i = 1, #heat, 1 do
        local e, u = heat[i], humidity[i]
        local d = internal.euclidian(
            e, default_biome.heat_point,
            u, default_biome.humidity_point
        )
        local biome_name

        -- Find the appropriate biome
        for name, def in pairs(ns_caves.registered_biomes) do
            local def_d = internal.euclidian(
                e, def.heat_point, u, def.humidity_point
            )

            if def_d < d then
                d = def_d
                biome_name = name
            end
        end

        allocs[i] = biome_name
    end

    return allocs
end

-- For each node, determine which cave shape they follow.
function internal.find_shape_allocations(connectivity, verticality)
    assert(#connectivity == #verticality)

    local allocs = {}
    local default_shape = internal.default_shape()

    for i = 1, #connectivity, 1 do
        local c, v = connectivity[i], verticality[i]
        local d = internal.euclidian(
            c, default_shape.connectivity_point,
            v, default_shape.verticality_point
        )
        local shape_name

        -- Find the appropriate shape
        for name, def in pairs(ns_caves.registered_shapes) do
            local def_d = internal.euclidian(
                c, def.connectivity_point, v, def.verticality_point
            )

            if def_d < d then
                d = def_d
                shape_name = name
            end
        end

        -- Assign the chosen name
        allocs[i] = shape_name
    end

    return allocs
end

-- Once it has been figured out which node belongs to which shape,
-- get noise values from the respective shapes.
-- This function does its operations in-place.
function internal.find_shape_values(used_shapes, minp, maxp, va)
    -- Cache shapes so they don't need to be recalculated.
    local captured_shapes = {}
    local default_shape = internal.default_shape()

    for i in va:iterp(minp, maxp) do
        -- Get shape values per item
        local name = used_shapes[i]
        local shape

        if name == nil then
            shape = default_shape
        else
            shape = ns_caves.registered_shapes[name]
        end

        if captured_shapes[shape] == nil then
            -- minetest.debug("Generating new shape! " .. shape.name)
            captured_shapes[shape] = internal.generate_shape(shape, minp, maxp, va)
        end

        used_shapes[i] = captured_shapes[shape][i]
        if used_shapes[i] == nil then
            error(
                "Noise value ended up nil unexpectedly: i = " .. i .. ", shape = " .. shape.name
            )
        end
    end

    -- minetest.debug("Finished generating shapes.")
end

function internal.generate_connectivity_noise(minp, maxp)
    return internal.generate_perlin_noise(
        internal.connectivity_noise_params(), minp, maxp
    )
end

function internal.generate_heat_noise(minp, maxp)
    return internal.generate_perlin_noise(
        internal.heat_noise_params(), minp, maxp
    )
end

function internal.generate_humidity_noise(minp, maxp)
    return internal.generate_perlin_noise(
        internal.humidity_noise_params(), minp, maxp
    )
end

-- Generate Perlin noise within given boundaries
function internal.generate_perlin_noise(noiseparams, minp, maxp)
    local size = {
        x = 1 + maxp.x - minp.x,
        y = 1 + maxp.y - minp.y,
        z = 1 + maxp.z - minp.z,
    }

    return PerlinNoiseMap(noiseparams, size):get_3d_map_flat(minp)
end

function internal.generate_shape(def, minp, maxp, va)
    -- local noise_flat = {}

    -- Get random noise if noise_params are given
    if def.noise_params then
        return internal.generate_perlin_noise(def.noise_params, minp, maxp)
    else
        return {}
        -- for i in va:iterp(minp, maxp) do
        --     noise_flat[i] = 0
        -- end
    end

    -- -- Update noise with custom defined function
    -- for i in va:iterp(minp, maxp) do
    --     noise_flat[i] = def.func(va:position(i), noise_flat[i])
    -- end

    -- return noise_flat
end

-- Generate verticality noise within given boundaries
function internal.generate_verticality_noise(minp, maxp)
    return internal.generate_perlin_noise(
        internal.verticality_noise_params(), minp, maxp
    )
end

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

-- Take all necessary steps to execute the mapgen
function internal.mapgen(minp, maxp, blockseed, vm, va)
    -- Create bordered VoxelArea.
    -- The point of this is so walls and ceilings can be determined using
    -- bordering nodes in different chunks.
    local bminp = vector.offset(minp, -1, -1, -1)
    local bmaxp = vector.offset(maxp,  1,  1,  1)
    local bva = VoxelArea(bminp, bmaxp)

    -- Find cave shape params
    local connectivity = internal.generate_connectivity_noise(bminp, bmaxp)
    local verticality = internal.generate_verticality_noise(bminp, bmaxp)

    -- Draw cave shapes
    local used_shapes = internal.find_shape_allocations(connectivity, verticality)
    internal.find_shape_values(used_shapes, bminp, bmaxp, bva)
    internal.shape_to_air(used_shapes, bminp, bmaxp, bva)

    -- Find cave biome params
    local heat = internal.generate_heat_noise(minp, maxp)
    local humidity = internal.generate_humidity_noise(minp, maxp)

    -- -- DEBUG: Write to air (or not)
    -- local air = 0

    -- for i in small_va:iterp(minp, maxp) do
    --     if used_shapes[i] == true then
    --         local pos = small_va:position(i)
    --         local vmi = va:index(pos.x, pos.y, pos.z)
    --         data[vmi] = minetest.CONTENT_AIR

    --         air = air + 1
    --     end
    -- end

    -- Classify various nodes as walls, floors, ceilings
    local classified_nodes = internal.classify_nodes(used_shapes, bminp, bmaxp)

    -- Draw cave biomes
    local used_biomes = internal.find_biome_allocations(heat, humidity)

    -- Manipulate `data` table by adding classified nodes based on which biome
    -- they're in.
    local data = vm:get_data()

    internal.write_classified_biome_nodes(
        data, va, classified_nodes, used_biomes, minp, maxp
    )

    vm:set_data(data)
    vm:write_to_map()
end

-- Place items
function internal.place_node_on_data(data, i, name)
    if name == nil then
        return
    end

    local node_id = minetest.get_content_id(name)

    if node_id == nil then
        return
    end

    data[i] = node_id
end

-- Register a new biome
function internal.register_biome(biome)
    biome = internal.clean_biome_def(biome)
    ns_caves.registered_biomes[biome.name] = biome
end

-- Register a new shape
function internal.register_shape(shape)
    shape = internal.clean_shape_def(shape)
    ns_caves.registered_shapes[shape.name] = shape
end

-- Convert all shape noise into clarifications whether a node is wall or air.
-- This function does its operations in-place.
function internal.shape_to_air(noise_values, minp, maxp, va)
    for i in va:iterp(minp, maxp) do
        local vastness = internal.cave_vastness(va:position(i))

        if noise_values[i] == nil then
            error(
                "Noise value ended up nil unexpectedly"
            )
        elseif noise_values[i] >= 1 - vastness then
            noise_values[i] = true
        else
            noise_values[i] = false
        end
    end
end

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

    return {
        offset = 50,
        scale = 50,
        spread = {
            x = factor * VERTICALITY_BLOB.x,
            y = factor * VERTICALITY_BLOB.y,
            z = factor * VERTICALITY_BLOB.z,
        },
        seed = SEED_VERTICALITY,
        octaves = 2,
        persistence = 0.2,
        lacunarity = 2.0,
        flags = "eased"
    }
end

function internal.write_classified_biome_nodes(vm_data, va, classified_nodes, used_biomes, minp, maxp)
    local small_va = VoxelArea(minp, maxp)

    -- assert(#classified_nodes == #used_biomes)
    -- assert(#classified_nodes == small_va:getVolume())

    local default_biome = internal.default_biome()
    local schems = {}

    for i in va:iterp(minp, maxp) do
        local pos = va:position(i)
        local si = small_va:index(pos.x, pos.y, pos.z)

        local node_type = classified_nodes[si]
        local biome = used_biomes[si]

        if biome == nil then
            biome = default_biome
        else
            biome = ns_caves.registered_biomes[biome] or default_biome
        end

        if node_type == ENUM_AIR then
            internal.place_node_on_data(vm_data, i, biome.node_air)
        elseif node_type == ENUM_CEILING then
            internal.place_node_on_data(vm_data, i, biome.node_roof)
        elseif node_type == ENUM_CEILING_DECORATION then
            -- TODO: Return schematics to be placed
            internal.place_node_on_data(vm_data, i, biome.node_air)
        elseif node_type == ENUM_FLOOR then
            internal.place_node_on_data(vm_data, i, biome.node_floor)
        elseif node_type == ENUM_FLOOR_DECORATION then
            -- TODO: Return schematics to be placed
            internal.place_node_on_data(vm_data, i, biome.node_air)
        elseif node_type == ENUM_STONE then
            -- Nothing needs to be placed
        elseif node_type == ENUM_WALL then
            internal.place_node_on_data(vm_data, i, biome.node_wall)
        else
            if node_type == nil then
                error(
                    "Expected enum value, encountered nil at index " .. si .. " (originally " .. i .. ")"
                )
            end
            error(
                "Encountered unknown node type enum value " .. node_type
            )
        end
    end

    return schems
end

-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
--------------------------------- PUBLIC API ----------------------------------
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------

minetest.register_on_generated(function(minp, maxp, blockseed)
    if maxp.y < WORLD_DEPTH then
        return
    end

    local vm = minetest.get_mapgen_object("voxelmanip")
    local va = VoxelArea(vm:get_emerged_area())

    internal.mapgen(minp, maxp, blockseed, vm, va)
end)

ns_caves = {
    cave_vastness = function(pos)
        if pos.y > 0 or pos.y < WORLD_DEPTH then
            return 0
        end

        local y = math.abs(pos.y)
        local d = math.abs(WORLD_DEPTH / 2)
        return 1 - (math.abs(y - d) / d)
    end,

    register_biome = internal.register_biome,

    register_shape = internal.register_shape,

    registered_biomes = {},

    registered_shapes = {},
}

dofile(minetest.get_modpath(minetest.get_current_modname()) .. "/lua/register.lua")