local p = {}

function rgb2hsv(r, g, b)
    local max = math.max(r, g, b)
    local min = math.min(r, g, b)
    local c = max - min
    
    -- calculate hue
    local h
    if c == 0 then
        h = 0
    elseif max == r then
        h = 60 * (0 + ((g - b)/c))
    elseif max == g then
        h = 60 * (2 + ((b - r)/c))
    elseif max == b then
        h = 60 * (4 + ((r - g)/c))
    end
    if h < 0 then h = h + 360 end
    
    -- calculate value
    local v = max
    
    -- calculate luminance
    -- local l = (max + min) / 2
    
    -- calculate saturation
    local s
    if c == 0 then
        s = 0
    else
        s = c/v
    end
    
    return h, s, v
end

function hsv2rgb(h, s, v)
    local hi = math.floor(h / 60)
    local f = ((h / 60) - hi)
    
    local p = v * (1 - s)
    local q = v * (1 - s * f)
    local t = v * (1 - s * (1 - f))
    
    if hi == 1 then
        return q, v, p
    elseif hi == 2 then
        return p, v, t
    elseif hi == 3 then
        return p, q, v
    elseif hi == 4 then
        return t, p, v
    elseif hi == 5 then
        return v, p, q
    else
        return v, t, p
    end
end

function decodeRGBHex(rgb)
    local r = string.sub(rgb, 1, 2)
    local g = string.sub(rgb, 3, 4)
    local b = string.sub(rgb, 5, 6)
    return tonumber(r, 16), tonumber(g, 16), tonumber(b, 16)
end

function getRGB(args)
    local r, g, b, i
    if string.len(args[1]) == 6 then
        r, g, b = decodeRGBHex(args[1])
        i = 2
    else
        r = args[1]
        g = args[2]
        b = args[3]
        i = 4
    end
    return r / 255, g / 255, b / 255, i
end

--[[toHSV
Description: Converts a RGB color to a HSV color.

Usage: {{#invoke:HSV|toHSV|R|G|B}} or {{#invoke:HSV|toHSV|RGBhex}}

Output: hue [0°..360°]/saturation [0..1]/value [0..1]
]]
function p.toHSV(frame)
    local r, g, b = getRGB(frame.args)
    local h, s, v = rgb2hsv(r, g, b)
    return h .. "/" .. s .. "/" .. v
end

--[[hue
Description: Returns the hue of a RGB color.

Usage: {{#invoke:HSV|hue|R|G|B}} or {{#invoke:HSV|hue|RGBhex}}

Output: hue [0°..360°]
]]
function p.hue(frame)
    local r, g, b = getRGB(frame.args)
    local h, s, v = rgb2hsv(r, g, b)
    return h
end

--[[saturation
Description: Returns the saturation of a RGB color.

Usage: {{#invoke:HSV|saturation|R|G|B}} or {{#invoke:HSV|saturation|RGBhex}}

Output: saturation [0..1]
]]
function p.saturation(frame)
    local r, g, b = getRGB(frame.args)
    local h, s, v = rgb2hsv(r, g, b)
    return s
end

--[[value
Description: Returns the hue of a RGB color.

Usage: {{#invoke:HSV|value|R|G|B}} or {{#invoke:HSV|value|RGBhex}}

Output: value [0..1]
]]
function p.value(frame)
    local r, g, b = getRGB(frame.args)
    local h, s, v = rgb2hsv(r, g, b)
    return v
end

--[[saturate
Description: Saturates a RGB color by a given factor.

Usage: {{#invoke:HSV|saturate|R|G|B|factor}} or {{#invoke:HSV|saturate|RGBhex|factor}}
Optionally "factor" can be followed by another parameter with the value "hex" can be given to return the RGB color in a hexadecimal representation.

Output: saturated RGB
]]
function p.saturate(frame)
    local r, g, b, i = getRGB(frame.args)
    -- convert to HSV
    local h, s, v = rgb2hsv(r, g, b)
    -- saturate
    s = s * frame.args[i]
    if s < 0 then
        s = 0
    elseif s > 1 then
        s = 1
    end
    -- convert back to RGB
    local r, g, b = hsv2rgb(h, s, v)
    r = math.floor(r * 255 + 0.5)
    g = math.floor(g * 255 + 0.5)
    b = math.floor(b * 255 + 0.5)
    -- return values
    if frame.args[i + 1] == "hex" then
        return string.format("%.2X%.2X%.2X", r, g, b)
    else
        return r .. "/" .. g .. "/" .. b
    end
end

--[[toRGB
Description: Converts a HSV color to a RGB color.

Usage: {{#invoke:HSV|toRGB|H|S|V}} with H in [0°..360°], S in [0..1] and V in [0..1].
Optionally a 4th parameter with the value "hex" can be given to return the RGB color in a hexadecimal representation.

Output: R/G/B
]]
function p.toRGB(frame)
    local r, g, b = hsv2rgb(frame.args[1], frame.args[2], frame.args[3])
    -- transform from real [0..1] to integer [0..255]
    r = math.floor(r * 255 + 0.5)
    g = math.floor(g * 255 + 0.5)
    b = math.floor(b * 255 + 0.5)
    -- return values
    if frame.args[4] == "hex" then
        return string.format("%.2X%.2X%.2X", r, g, b)
    else
        return r .. "/" .. g .. "/" .. b
    end
end

return p