if not modules then modules = { } end modules ['grph-downsample'] = {
  version   = 1.104,
  comment   = "companion to grph-inc.mkiv",
  author    = "Peter Münster and Henning Hraban Ramm",
  copyright = "PRAGMA ADE / ConTeXt Development Team",
  license   = "see context related readme files"
}

-- todo:
-- figures.cachepaths.path = "cache" -- should be a setup-option
-- threshold should be a setup-option

local function round(x)
    return math.floor(x + 0.5)
end

local format = string.format
local report = logs.reporter("DOWNSAMPLE")

local function sample_down(oldname, newname, resolution)
    report("sample_down %s to %s (%s)", oldname, newname, resolution)
    local request = figures.current().request
    local width   = request.width
    local height  = request.height
    if resolution == "" or (not width and not height) then
        report("Nothing to do: %s, %s, %s", oldname, newname, resolution)
        return
    else
        report("Requested: %s, %s, %s dpi, %s sp x %s sp", oldname, newname,
               resolution, width or "???", height or "???")
    end
    -- requested size must be smaller than original size
    -- multiplied by this threshold:
    local threshold = 0.8
    local inch      = 72.27 * 65536   -- an inch in scaled points
    local image     = figures.getinfo(oldname, 1)
    image = image.status.private

    local xy = image.xsize / image.ysize
    if not width then
        width = height * xy
    end
    if not height then
        height = width / xy
    end
    local xsize = round(resolution * width  / inch)
    local ysize = round(resolution * height / inch)
    report("resize %d x %d to %d x %d:", image.xsize, image.ysize,
           xsize, ysize)
    if xsize < image.xsize * threshold or ysize < image.ysize * threshold then
        local s = format("gm convert -resize %dx%d %s %s",
                         xsize, ysize, oldname, newname)
        report("calling: %s", s)
        os.execute(s)
    else
        report("Nothing to do: %s, %s, %s", oldname, newname, resolution)
        report("xsize = %d, ysize = %d", xsize, ysize)
    end
end

local formats = {"png", "jpg", "gif"}

for _, s in ipairs(formats) do
    figures.converters[s] = figures.converters[s] or {}
    figures.converters[s]["lowres." .. s] = sample_down
end