-- Module:LuminanceChroma to sRGB
-- Converts:
--   Luminance (%) 
--   Chroma angle (degrees)
--   Chroma (% or signed custom range)
-- to sRGB hex
--
-- Features:
--   • Preserves luminance (HSL model)
--   • Hue offset support
--   • Signed chroma scaling via Cmax
--   • format = hex (default)
--   • format = swatch

local p = {}

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

------------------------------------------------
-- Convert sRGB (0–1) to hex
------------------------------------------------
local function rgbToHex(r, g, b)
    r = clamp(math.floor(r * 255 + 0.5), 0, 255)
    g = clamp(math.floor(g * 255 + 0.5), 0, 255)
    b = clamp(math.floor(b * 255 + 0.5), 0, 255)
    return string.format("#%02X%02X%02X", r, g, b)
end

------------------------------------------------
-- HSL-style cylindrical model
------------------------------------------------
local function hslToRgb(L, C, H)

    H = H % 360
    local Hp = H / 60
    local X = C * (1 - math.abs((Hp % 2) - 1))

    local r1, g1, b1 = 0, 0, 0

    if Hp >= 0 and Hp < 1 then
        r1, g1, b1 = C, X, 0
    elseif Hp < 2 then
        r1, g1, b1 = X, C, 0
    elseif Hp < 3 then
        r1, g1, b1 = 0, C, X
    elseif Hp < 4 then
        r1, g1, b1 = 0, X, C
    elseif Hp < 5 then
        r1, g1, b1 = X, 0, C
    else
        r1, g1, b1 = C, 0, X
    end

    local m = L - C / 2

    return r1 + m, g1 + m, b1 + m
end

------------------------------------------------
-- Main conversion
------------------------------------------------
function p.convert(frame)

    local args = frame.args

    local L = tonumber(args.L)
    local H = tonumber(args.H)
    local C = tonumber(args.C)

    local offset = tonumber(args.offset) or 0
    local Cmax = tonumber(args.Cmax)

    local format = args.format or "hex"

    if not L or not H or not C then
        return "Error: L, H, and C must be numeric."
    end

    ------------------------------------------------
    -- Normalize luminance
    ------------------------------------------------
    L = clamp(L, 0, 100) / 100

    ------------------------------------------------
    -- Handle chroma
    ------------------------------------------------
    if Cmax then
        -- Signed chroma range [-Cmax, Cmax]
        C = clamp(C, -Cmax, Cmax)
        C = math.abs(C) / Cmax * 100
    end

    C = clamp(C, 0, 100) / 100

    ------------------------------------------------
    -- Apply hue offset
    ------------------------------------------------
    H = (H + offset) % 360

    ------------------------------------------------
    -- Convert
    ------------------------------------------------
    local R, G, B = hslToRgb(L, C, H)

    R = clamp(R, 0, 1)
    G = clamp(G, 0, 1)
    B = clamp(B, 0, 1)

    local hex = rgbToHex(R, G, B)

    ------------------------------------------------
    -- Output
    ------------------------------------------------
    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;vertical-align:middle;margin-right:0.4em;"></span><code>%s</code>',
            hex,
            hex
        )
    end

    return "&#35;" .. string.sub(hex, 2)
end

return p