local oklab = require "prismite.oklab"

local M = {}

function M.lerp(a, b, t)
    return a + t * (b - a)
end

function M.mix_oklch(a, b, t)
    if not (a.l and a.c and a.h) then
        error("`a` must be a valid OKLCH color", 2)
    end

    if not (b.l and b.c and b.h) then
        error("`b` must be a valid OKLCH color", 2)
    end

    if type(t) ~= "number" then
        error("'t' must be a number", 2)
    end

    local a_h = a.h
    local b_h = b.h

    -- https://drafts.csswg.org/css-color-4/#hue-shorter
    if b_h - a_h > 180 then
        print "adjusted +"
        a_h = a_h + 360
    end
    if b_h - a_h < -180 then
        print "adjusted -"
        b_h = b_h + 360
    end

    return { l = M.lerp(a.l, b.l, t), c = M.lerp(a.c, b.c, t), h = M.lerp(a_h, b_h, t) }
end

local function over(a, b, alpha)
    return a * alpha + b * (1 - alpha)
end

function M.overlay_oklch(a, b, alpha)
    if not (a.l and a.c and a.h) then
        error("`a` must be a valid OKLCH color", 2)
    end

    if not (b.l and b.c and b.h) then
        error("`b` must be a valid OKLCH color", 2)
    end

    if type(alpha) ~= "number" then
        error("'alpha' must be a number", 2)
    end

    local a_oklab = oklab.oklch2oklab(a)
    local b_oklab = oklab.oklch2oklab(b)

    local _l = over(a_oklab.l, b_oklab.l, alpha)
    local _a = over(a_oklab.a, b_oklab.a, alpha)
    local _b = over(a_oklab.b, b_oklab.b, alpha)

    return oklab.oklab2oklch { l = _l, a = _a, b = _b }
end

function M.is_oklch(oklch)
    return (oklch.l and oklch.c and oklch.h)
end

function M.oklch2hex(oklch)
    return oklab.rgb2hex(oklab.oklab2rgb(oklab.oklch2oklab(oklch)))
end

return M