local p = {}

-- Conversion matrices (YCbCr to RGB)
local matrices = {

    ["BT.601"] = {
        kr = 0.299,
        kb = 0.114
    },

    ["BT.709"] = {
        kr = 0.2126,
        kb = 0.0722
    },

    ["BT.2020"] = {
        kr = 0.2627,
        kb = 0.0593
    }
}

local function clamp(x, min, max)
    if x < min then return min end
    if x > max then return max end
    return x
end

-- sRGB gamma encoding
local function linearToSRGB(c)
    if c <= 0 then return 0 end
    if c <= 0.0031308 then
        return 12.92 * c
    else
        return 1.055 * (c ^ (1/2.4)) - 0.055
    end
end

function p.convert(frame)

local args = frame:getParent().args

    local Y  = tonumber(args.Y)  or 0
    local Cb = tonumber(args.Cb) or 0
    local Cr = tonumber(args.Cr) or 0

    local standard = args.standard or "BT.601"
    local bitdepth = tonumber(args.bitdepth) or 8
    local range    = args.range or "limited"
    local format   = args.format or "hex"

    local m = matrices[standard] or matrices["BT.601"]

    local maxValue = (2 ^ bitdepth) - 1

    local Yf, Cbf, Crf

    if range == "full" then
        Yf  = Y  / maxValue
        Cbf = (Cb / maxValue) - 0.5
        Crf = (Cr / maxValue) - 0.5
    else
        -- Limited (TV range)
        local offsetY  = 16  * (2 ^ (bitdepth - 8))
        local offsetC  = 128 * (2 ^ (bitdepth - 8))
        local scaleY   = 219 * (2 ^ (bitdepth - 8))
        local scaleC   = 224 * (2 ^ (bitdepth - 8))

        Yf  = (Y  - offsetY) / scaleY
        Cbf = (Cb - offsetC) / scaleC
        Crf = (Cr - offsetC) / scaleC
    end

    local kr = m.kr
    local kb = m.kb
    local kg = 1 - kr - kb

    -- Linear RGB
    local R_lin = Yf + (2 - 2 * kr) * Crf
    local B_lin = Yf + (2 - 2 * kb) * Cbf
    local G_lin = Yf - ( (2 * kb * (1 - kb) / kg) * Cbf )
                    - ( (2 * kr * (1 - kr) / kg) * Crf )

    -- Gamma encode
    local R = clamp(linearToSRGB(R_lin), 0, 1)
    local G = clamp(linearToSRGB(G_lin), 0, 1)
    local B = clamp(linearToSRGB(B_lin), 0, 1)

    local r8 = math.floor(R * 255 + 0.5)
    local g8 = math.floor(G * 255 + 0.5)
    local b8 = math.floor(B * 255 + 0.5)

    local hex = string.format("#%02X%02X%02X", r8, g8, b8)

    if format == "swatch" then
        return string.format(
            '<span style="display:inline-block;width:1.5em;height:1.5em;border:1px solid #000;background-color:%s;"></span> %s',
            hex, hex
        )
    else
        return "&#35;" .. string.sub(hex:gsub("\n",""):gsub("%s+",""), 2)
    end
end

return p