-- Arguments
-- map_data: The cartographer map data table
local map_data = ...;

-- Constants
local CHUNK_SIZE = _cartographer.CHUNK_SIZE;

-- Register a new tile in map data
-- x: The x position in map coordinates
-- y: The y position in map coordinates
-- biome: The tile's biome id
-- height: The tile's height
-- (Optional): manual_scan: Indicates if this was a 'manual' (non-generated)
--                          scan. Manual scans are overridden by generated
--                          scans under normal circumstances.
local function register_tile(x, y, biome, height, manual_scan)
    if not map_data.generated[x] then
        map_data.generated[x] = {
            [y] = {
                biome = biome,
                height = height,
            }
        };
        if manual_scan ~= nil then
            map_data.generated[x][y].manual_scan = manual_scan;
        end
    elseif not map_data.generated[x][y] or map_data.generated[x][y].height < height then
        map_data.generated[x][y] = {
                biome = biome,
                height = height,
            };
        if manual_scan ~= nil or map_data.generated[x][y].manual_scan then
            map_data.generated[x][y].manual_scan = manual_scan;
        end
    end
end

local function get_mapgen_biome(min, max, mmin, mmax)
    local UNDERGROUND = minetest.get_biome_id("underground");
    local DEFAULT = minetest.get_biome_id("default");

    local biomes = minetest.get_mapgen_object("biomemap");
    local heights = minetest.get_mapgen_object("heightmap");

    local xx = max.x - min.x;
    local yy = max.y - min.y;
    local zz = max.z - min.z;

    local xxx = mmax.x - mmin.x;
    local yyy = mmax.y - mmin.y;
    local zzz = mmax.z - mmin.z;

    local startx = min.x - mmin.x;
    local starty = min.y - mmin.y;
    local startz = min.z - mmin.z;
    
    local scan_biomes = {};
    local scan_heights = {};

    for i = startx,startx + xx,1 do
        for k = startz,startz + zz,1 do
            local b = biomes[i + (k * (xxx + 1))];
            if b ~= nil and b ~= UNDERGROUND and b ~= DEFAULT then
                scan_biomes[b] = (scan_biomes[b] or 0) + 1;
                scan_heights[b] = (scan_heights[b] or 0) + heights[i + (k * (xxx + 1))];
            end
        end
    end

    local biome = nil;
    local high = 0;
    for k,v in pairs(scan_biomes) do
        if v > high then
            biome = k;
            high = v;
        end
    end

    local avg_height = 0;
    if high > 0 then
        avg_height = scan_heights[biome] / high;
    end

    return biome, avg_height;
end

local function get_biome(min, max)
    local UNDERGROUND = minetest.get_biome_id("underground");
    local DEFAULT = minetest.get_biome_id("default");
    local WATER_SOURCE = minetest.registered_aliases["mapgen_water_source"];

    local xx = max.x - min.x;
    local yy = max.y - min.y;
    local zz = max.z - min.z;

    local scan_biomes = {};
    local scan_heights = {};

    for i = min.x,max.x,1 do
        for j = min.y,max.y,1 do
            for k = min.z,max.z,1 do
                local pos = { x=i, y=j, z=k };
                local b = minetest.get_biome_data(pos).biome;
                local node = minetest.get_node(pos).name;
                if b ~= nil and b ~= UNDERGROUND and b ~= DEFAULT and node ~= "air" and node ~= WATER_SOURCE then
                    pos.y = pos.y + 1;
                    node = minetest.get_node(pos).name;
                    if node == "air" or node == WATER_SOURCE then
                        scan_biomes[b] = (scan_biomes[b] or 0) + 1;
                        scan_heights[b] = (scan_heights[b] or 0) + j;
                    end
                end
            end
        end
    end

    local biome = nil;
    local high = 0;
    for k,v in pairs(scan_biomes) do
        if v > high then
            biome = k;
            high = v;
        end
    end

    local avg_height = 0;
    if high > 0 then
        avg_height = scan_heights[biome] / high;
    end

    return biome, avg_height;
end

local function on_generated(min, max, blockseed)
    local chunk = {
        x = tochunk(min.x),
        y = tochunk(min.z),
    };

    for i = tochunk(min.x),tochunk(max.x),1 do
        for j = tochunk(min.z),tochunk(max.z),1 do

            local sub_min = {
                x = i * CHUNK_SIZE,
                y = min.y,
                z = j * CHUNK_SIZE,
            };
            local sub_max = {
                x = i * CHUNK_SIZE + CHUNK_SIZE,
                y = max.y,
                z = j * CHUNK_SIZE + CHUNK_SIZE,
            };
            local biome, height = get_mapgen_biome(sub_min, sub_max, min, max);
            if  biome ~= nil then
                register_tile(i, j, biome, height)
            end

        end
    end
end

-- Is the scan of this position already handled?
-- x: The x position, in map coordinates
-- y: The y position, in world coordinates
-- x: The z position, in map coordinates
--
-- Returns true if the position is handled by the current map data
local function is_scan_handled(x, y, z)
    if not map_data.generated[x] then
        return false;
    end

    local tile = map_data.generated[x][z];

    return tile and ((not tile.manual_scan and tile.height > 0) or tile.height >= y);
end

-- Queue a tile for manual scanning
-- pos: The position as a table, in world coordinates
function cartographer.queue_region(pos)
    local converted = {
        x = fromchunk(tochunk(pos.x)),
        y = fromchunk(tochunk(pos.y)),
        z = fromchunk(tochunk(pos.z)),
    };

    if is_scan_handled(tochunk(pos.x), pos.y, tochunk(pos.z)) then
        return;
    end

    for _,queued_pos in ipairs(cartographer.scan_queue) do
        if vector.equals(converted, queued_pos) then
            return;
        end
    end

    cartographer.scan_queue[#cartographer.scan_queue + 1] = converted;
end

-- Scan the next tile on the queue, and remove it
function cartographer.scan_regions()
    local len = #cartographer.scan_queue;

    if len == 0 then
        return;
    end

    local startpos = cartographer.scan_queue[1];
    local endpos = {
        x = startpos.x + CHUNK_SIZE,
        y = startpos.y + CHUNK_SIZE,
        z = startpos.z + CHUNK_SIZE,
    };

    if is_scan_handled(tochunk(startpos.x), startpos.y, tochunk(startpos.z)) then
        table.remove(cartographer.scan_queue, 1);
        return;
    end

    local biome,height = get_biome(startpos, endpos);
    if  biome ~= nil then
        register_tile(tochunk(startpos.x), tochunk(startpos.z), biome, height, true)
    end

    table.remove(cartographer.scan_queue, 1);
end

minetest.register_on_generated(on_generated);