local function coord_string(x, y)
    local str = tostring(x) .. '_'
    str = str .. tostring(y)
    return str
end

local function draw_cell(surface, cell, cell_size, wall_entity_name, force_name)
    local r = math.floor(cell_size * 0.5)
    local entities = {}
    if cell.north then
        for x = r * -1, r, 1 do
            entities[#entities + 1] = {position = {cell.position.x + x, cell.position.y - r}, name = wall_entity_name, force = force_name}
        end
    end
    if cell.south then
        for x = r * -1, r, 1 do
            entities[#entities + 1] = {position = {cell.position.x + x, cell.position.y + r}, name = wall_entity_name, force = force_name}
        end
    end
    if cell.east then
        for y = r * -1, r, 1 do
            entities[#entities + 1] = {position = {cell.position.x + r, cell.position.y + y}, name = wall_entity_name, force = force_name}
        end
    end
    if cell.west then
        for y = r * -1, r, 1 do
            entities[#entities + 1] = {position = {cell.position.x - r, cell.position.y - y}, name = wall_entity_name, force = force_name}
        end
    end
    for _, e in pairs(entities) do
        if surface.can_place_entity(e) then
            surface.create_entity(e)
        end
    end
end

local function draw_maze(maze_cells, surface, _, _, cell_size, wall_entity_name, force_name)
    for _, cell in pairs(maze_cells) do
        draw_cell(surface, cell, cell_size, wall_entity_name, force_name)
    end
end

local function get_random_occupied_cell(maze_cells)
    local occupied_cells = {}
    for c, cell in pairs(maze_cells) do
        if cell.occupied then
            if not cell.dead then
                occupied_cells[#occupied_cells + 1] = c
            end
        end
    end
    if not occupied_cells[1] then
        return
    end
    return occupied_cells[math.random(1, #occupied_cells)]
end

local function set_dead_cells(maze_cells)
    local directions = {
        {0, -1},
        {0, 1},
        {1, 0},
        {-1, 0}
    }

    for c, cell in pairs(maze_cells) do
        if not cell.dead then
            maze_cells[c].dead = true
            for i = 1, 4, 1 do
                local cell_string = coord_string(cell.cell_position.x + directions[i][1], cell.cell_position.y + directions[i][2])
                if maze_cells[cell_string] then
                    if not maze_cells[cell_string].occupied then
                        maze_cells[c].dead = false
                        break
                    end
                end
            end
        end
    end
end

local function expand_cell(maze_cells, current_cell)
    local expansion_raffle = {
        {0, -1, 'north', 'south'},
        {0, 1, 'south', 'north'},
        {1, 0, 'east', 'west'},
        {-1, 0, 'west', 'east'}
    }
    table.shuffle_table(expansion_raffle)
    for i = 1, 4, 1 do
        local direction = expansion_raffle[i]
        local cell_canditate = coord_string(current_cell.cell_position.x + direction[1], current_cell.cell_position.y + direction[2])
        if maze_cells[cell_canditate] then
            if not maze_cells[cell_canditate].occupied then
                maze_cells[cell_canditate].occupied = true
                current_cell[direction[3]] = false
                maze_cells[cell_canditate][direction[4]] = false
                return maze_cells[cell_canditate]
            end
        end
    end
    return false
end

local function expand(maze_cells)
    local current_cell = maze_cells[get_random_occupied_cell(maze_cells)]
    while true do
        current_cell = expand_cell(maze_cells, current_cell)
        if not current_cell then
            set_dead_cells(maze_cells)
            current_cell = maze_cells[get_random_occupied_cell()]
        end
        if not current_cell then
            break
        end
    end
end

local function disable_borders(maze_cells, size)
    for s = size * -1, size, 1 do
        maze_cells[coord_string(s, size * -1)].north = false
        maze_cells[coord_string(s, size)].south = false
        maze_cells[coord_string(size, s)].east = false
        maze_cells[coord_string(size * -1, s)].west = false
    end
end

local function create_maze(surface, position, size, cell_size, wall_entity_name, force_name, borderless)
    if not surface then
        game.print('No surface given.')
        return
    end
    if not position then
        game.print('No position given.')
        return
    end
    if not size then
        game.print('No size given.')
        return
    end
    if not cell_size then
        game.print('No cell_size given.')
        return
    end
    if not wall_entity_name then
        game.print('No wall_entity_name given.')
        return
    end

    local maze_cells = {}

    for x = size * -1, size, 1 do
        for y = size * -1, size, 1 do
            maze_cells[coord_string(x, y)] = {
                position = {x = position.x + x * (cell_size - 1), y = position.y + y * (cell_size - 1)},
                cell_position = {x = x, y = y},
                occupied = false,
                dead = false,
                north = true,
                south = true,
                east = true,
                west = true
            }
        end
    end

    maze_cells[coord_string(size * -1, 0)].occupied = true
    maze_cells[coord_string(size * -1, 0)].west = false
    maze_cells[coord_string(size, 0)].east = false

    if borderless then
        disable_borders(maze_cells, size)
    end

    expand(maze_cells)

    draw_maze(maze_cells, surface, position, size, cell_size, wall_entity_name, force_name)
end

return create_maze