-- load image from custom resources
-- read pixels and write them to a buffer
local function create_buffer_from_image(filename)
    local png = assert(sys.load_resource(filename))
    local loaded_image = image.load(png)
    local width = loaded_image.width
    local height = loaded_image.height
    local pixels = loaded_image.buffer

    local buffer_declaration = {
        {
            name = hash("rgba"),
            type = buffer.VALUE_TYPE_UINT8,
            count = 4
        }
    }
    local pixel_buffer = buffer.create(width * height, buffer_declaration)
    local pixel_stream = buffer.get_stream(pixel_buffer, hash("rgba"))
    for y = 1, height do
        for x = 1, width do
            -- flip image
            local pixels_index = ((height - y) * width * 4) + ((x - 1) * 4) + 1
            local r = pixels:byte(pixels_index + 0)
            local g = pixels:byte(pixels_index + 1)
            local b = pixels:byte(pixels_index + 2)
            local a = pixels:byte(pixels_index + 3)

            -- write to buffer stream
            local stream_index = ((y - 1) * width * 4) + ((x - 1) * 4) + 1
            pixel_stream[stream_index + 0] = r
            pixel_stream[stream_index + 1] = g
            pixel_stream[stream_index + 2] = b
            pixel_stream[stream_index + 3] = a
        end
    end

    return pixel_buffer, width, height
end

local function replace_atlas_image()
    -- get table with information about an atlas
    local atlas = resource.get_atlas("/example/modify_atlas.a.texturesetc")
    -- get table with information about the textured used by the atlas
    local texture = resource.get_texture_info(atlas.texture)
    pprint(atlas)
    pprint(texture)

    -- load an image as a Defold buffer
    local pixel_buffer, width, height = create_buffer_from_image("/example/resources/shipYellow_manned.png")

    -- get the UV coordinates of the first image in the atlas
    local first_uvs = atlas.geometries[1].uvs

    -- this offset should not be necessary but it seems like there is an issue with the
    -- UVs in Defold 1.5.0
    local x = first_uvs[1] - 0
    local y = first_uvs[2] - 6
    print(x, y)
    print(width, height)

    -- create a table with texture update information
    -- we want to update only a sub region of the atlas starting at a
    -- certain position and with a certain size
    local texture_info = {
        type = resource.TEXTURE_TYPE_2D,
        width = width,
        height = height,
        format = resource.TEXTURE_FORMAT_RGBA,
        x = x,
        y = y,
        compression_type = resource.COMPRESSION_TYPE_DEFAULT,
        num_mip_maps = texture.mipmaps,
    }
    -- update the atlas texture with the pixels from the provided buffer
    resource.set_texture(atlas.texture, texture_info, pixel_buffer)
end


function init(self)
    msg.post(".", "acquire_input_focus")
end

function on_input(self, action_id, action)
    if action.pressed then
        replace_atlas_image()
    end
end