local function load(path)
    local image = { w = 0, h = 0, scale = 1.0, palette = {}, lines = {} }

    local fp, err = io.open(path, "rb")
    if not fp then return nil, err end

    local magic = fp:read(4)
    if magic ~= "CCPI" then
        return nil, "Invalid header: expected CCPI got " .. magic
    end

    image.w, image.h = string.byte(fp:read(1)), string.byte(fp:read(1))
    image.scale = 0.5 + string.byte(fp:read(1)) * 5 / 255
    for i = 1, 16 do
        image.palette[i] = bit.blshift(string.byte(fp:read(1)), 16)
        image.palette[i] = bit.bor(image.palette[i], bit.blshift(string.byte(fp:read(1)), 8))
        image.palette[i] = bit.bor(image.palette[i], string.byte(fp:read(1)))
    end

    for y = 1, image.h do
        local line = { s = "", bg = "", fg = "" }
        for x = 1, image.w do
            line.s = line.s .. fp:read(1)
            local char = fp:read(1)
            if char == nil then
                return nil, string.format("Failed to read color data for x=%d y=%d", x, y)
            end
            local color = string.byte(char)
            line.bg = line.bg .. string.format("%x", bit.band(0xF, color))
            line.fg = line.fg .. string.format("%x", bit.band(0xF, bit.brshift(color, 4)))
        end
        table.insert(image.lines, line)
    end

    fp:close()

    return image
end

local function draw(img, ox, oy, monitor)
    -- todo: add expect()
    local t = monitor or term.current()
    ox = ox or 1
    oy = oy or 1

    for i = 1, 16 do
        t.setPaletteColor(bit.blshift(1, i - 1), img.palette[i])
    end

    t.setTextScale(img.scale)

    for y = 1, img.h do
        t.setCursorPos(ox, oy + y - 1)
        t.blit(img.lines[y].s, img.lines[y].fg, img.lines[y].bg)
    end
end

return {
    load = load,
    draw = draw
}