rgb2xterm256.jl

# Ported from https://gist.github.com/MicahElliott/719710
# Credit goes to Micah Elliott

using Colors
using OrderedCollections

CLUT = Tuple{String, String}[  # color look-up table
#    8-bit, RGB hex

    # Primary 3-bit (8 colors). Unique representation!
    ("00",  "000000"), ("01",  "800000"), ("02",  "008000"), ("03",  "808000"), ("04",  "000080"), ("05",  "800080"), ("06",  "008080"), ("07",  "c0c0c0"),

    # Equivalent "bright" versions of original 8 colors.
    ("08",  "808080"), ("09",  "ff0000"), ("10",  "00ff00"), ("11",  "ffff00"), ("12",  "0000ff"), ("13",  "ff00ff"), ("14",  "00ffff"), ("15",  "ffffff"),

    # Strictly ascending.
    ("16",  "000000"), ("17",  "00005f"), ("18",  "000087"), ("19",  "0000af"), ("20",  "0000d7"), ("21",  "0000ff"), ("22",  "005f00"), ("23",  "005f5f"), ("24",  "005f87"), ("25",  "005faf"), ("26",  "005fd7"), ("27",  "005fff"), ("28",  "008700"), ("29",  "00875f"), ("30",  "008787"), ("31",  "0087af"), ("32",  "0087d7"),("33",  "0087ff"), ("34",  "00af00"), ("35",  "00af5f"), ("36",  "00af87"), ("37",  "00afaf"), ("38",  "00afd7"), ("39",  "00afff"), ("40",  "00d700"), ("41",  "00d75f"), ("42",  "00d787"), ("43",  "00d7af"), ("44",  "00d7d7"), ("45",  "00d7ff"), ("46",  "00ff00"), ("47",  "00ff5f"), ("48",  "00ff87"), ("49",  "00ffaf"), ("50",  "00ffd7"), ("51",  "00ffff"), ("52",  "5f0000"), ("53",  "5f005f"), ("54",  "5f0087"), ("55",  "5f00af"), ("56",  "5f00d7"), ("57",  "5f00ff"), ("58",  "5f5f00"), ("59",  "5f5f5f"),("60",  "5f5f87"), ("61",  "5f5faf"), ("62",  "5f5fd7"), ("63",  "5f5fff"), ("64",  "5f8700"), ("65",  "5f875f"), ("66",  "5f8787"), ("67",  "5f87af"), ("68",  "5f87d7"), ("69",  "5f87ff"), ("70",  "5faf00"), ("71",  "5faf5f"), ("72",  "5faf87"), ("73",  "5fafaf"), ("74",  "5fafd7"), ("75",  "5fafff"), ("76",  "5fd700"), ("77",  "5fd75f"), ("78",  "5fd787"), ("79",  "5fd7af"), ("80",  "5fd7d7"), ("81",  "5fd7ff"), ("82",  "5fff00"), ("83",  "5fff5f"), ("84",  "5fff87"), ("85",  "5fffaf"), ("86",  "5fffd7"), ("87",  "5fffff"), ("88",  "870000"), ("89",  "87005f"), ("90",  "870087"), ("91",  "8700af"), ("92",  "8700d7"), ("93",  "8700ff"), ("94",  "875f00"), ("95",  "875f5f"), ("96",  "875f87"), ("97",  "875faf"), ("98",  "875fd7"), ("99",  "875fff"), ("100", "878700"), ("101", "87875f"), ("102", "878787"), ("103", "8787af"), ("104", "8787d7"), ("105", "8787ff"), ("106", "87af00"), ("107", "87af5f"), ("108", "87af87"), ("109", "87afaf"), ("110", "87afd7"), ("111", "87afff"), ("112", "87d700"), ("113", "87d75f"), ("114", "87d787"), ("115", "87d7af"), ("116", "87d7d7"), ("117", "87d7ff"), ("118", "87ff00"), ("119", "87ff5f"), ("120", "87ff87"), ("121", "87ffaf"), ("122", "87ffd7"), ("123", "87ffff"), ("124", "af0000"), ("125", "af005f"), ("126", "af0087"), ("127", "af00af"), ("128", "af00d7"), ("129", "af00ff"), ("130", "af5f00"), ("131", "af5f5f"), ("132", "af5f87"), ("133", "af5faf"), ("134", "af5fd7"), ("135", "af5fff"), ("136", "af8700"), ("137", "af875f"), ("138", "af8787"), ("139", "af87af"), ("140", "af87d7"), ("141", "af87ff"), ("142", "afaf00"), ("143", "afaf5f"), ("144", "afaf87"), ("145", "afafaf"), ("146", "afafd7"), ("147", "afafff"), ("148", "afd700"), ("149", "afd75f"), ("150", "afd787"), ("151", "afd7af"), ("152", "afd7d7"), ("153", "afd7ff"), ("154", "afff00"), ("155", "afff5f"), ("156", "afff87"), ("157", "afffaf"), ("158", "afffd7"), ("159", "afffff"), ("160", "d70000"), ("161", "d7005f"), ("162", "d70087"), ("163", "d700af"), ("164", "d700d7"), ("165", "d700ff"), ("166", "d75f00"), ("167", "d75f5f"), ("168", "d75f87"), ("169", "d75faf"), ("170", "d75fd7"), ("171", "d75fff"), ("172", "d78700"), ("173", "d7875f"), ("174", "d78787"), ("175", "d787af"), ("176", "d787d7"), ("177", "d787ff"), ("178", "d7af00"), ("179", "d7af5f"), ("180", "d7af87"), ("181", "d7afaf"), ("182", "d7afd7"), ("183", "d7afff"), ("184", "d7d700"), ("185", "d7d75f"), ("186", "d7d787"), ("187", "d7d7af"), ("188", "d7d7d7"), ("189", "d7d7ff"), ("190", "d7ff00"), ("191", "d7ff5f"), ("192", "d7ff87"), ("193", "d7ffaf"), ("194", "d7ffd7"), ("195", "d7ffff"), ("196", "ff0000"), ("197", "ff005f"), ("198", "ff0087"), ("199", "ff00af"), ("200", "ff00d7"), ("201", "ff00ff"), ("202", "ff5f00"), ("203", "ff5f5f"), ("204", "ff5f87"), ("205", "ff5faf"), ("206", "ff5fd7"), ("207", "ff5fff"), ("208", "ff8700"), ("209", "ff875f"), ("210", "ff8787"), ("211", "ff87af"), ("212", "ff87d7"), ("213", "ff87ff"), ("214", "ffaf00"), ("215", "ffaf5f"), ("216", "ffaf87"), ("217", "ffafaf"), ("218", "ffafd7"), ("219", "ffafff"), ("220", "ffd700"), ("221", "ffd75f"), ("222", "ffd787"), ("223", "ffd7af"), ("224", "ffd7d7"), ("225", "ffd7ff"), ("226", "ffff00"), ("227", "ffff5f"), ("228", "ffff87"), ("229", "ffffaf"), ("230", "ffffd7"), ("231", "ffffff"),

    # Gray-scale range.
    ("232", "080808"), ("233", "121212"), ("234", "1c1c1c"), ("235", "262626"), ("236", "303030"), ("237", "3a3a3a"), ("238", "444444"), ("239", "4e4e4e"), ("240", "585858"), ("241", "626262"), ("242", "6c6c6c"), ("243", "767676"), ("244", "808080"), ("245", "8a8a8a"), ("246", "949494"), ("247", "9e9e9e"), ("248", "a8a8a8"), ("249", "b2b2b2"), ("250", "bcbcbc"), ("251", "c6c6c6"), ("252", "d0d0d0"), ("253", "dadada"), ("254", "e4e4e4"), ("255", "eeeeee"),
]

_str2hex(hexstr::String) = parse(Int, hexstr, base = 16)
_strip_hash(rgb::String) = startswith(rgb, '#') ? rgb[2:end] : rgb
SHORT2RGB_DICT = OrderedDict{String, String}(CLUT)
RGB2SHORT_DICT = OrderedDict{String, String}(reverse(p) for p in SHORT2RGB_DICT)

short2rgb(short::String) = SHORT2RGB_DICT[short]
function print_all()
    for (short, rgb) in CLUT
        println("\033[48;5;$(short)m$(short):$(rgb)\033[0m  \033[38;5;$(short)m$(short):$(rgb)\033[0m")
    end
    println("Printed all codes.")
    println("You can translate a hex or 0-255 code by providing an argument.")
    return nothing
end

"Find the closest xterm-256 approximation to the given RGB value."
function rgb2short(rgb::String)
    rgb = _strip_hash(rgb)
    incs = (0x00, 0x5f, 0x87, 0xaf, 0xd7, 0xff)
    # Break 6-char RGB code into 3 integer vals.
    parts = Int[parse(Int, h, base = 16) for h in match(r"(..)(..)(..)", rgb).captures]
    res = Int[]
    for part in parts
        i = 1
        while i < length(incs)
            s, b = incs[i], incs[i + 1]  # smaller, bigger
            # println("$s $b")
            if s <= part <= b
                s1 = abs(s - part)
                b1 = abs(b - part)
                s1 < b1 ? push!(res, s) : push!(res, b)
                break
            end
            i += 1
        end
    end
    res = join(String[string(i, base = 16, pad = 2) for i in res])
    equiv = RGB2SHORT_DICT[res]
    return equiv, res
end

function main_exact(i::String)
    rgb = short2rgb(i)
    println("xterm color \033[38;5;$(i)m$(i)\033[0m -> RGB exact \033[38;5;$(i)m$(rgb)\033[0m\033[0m")
    return nothing
end
function main_approx(i::String)
    short, rgb = rgb2short(i)
    println("RGB $(i) -> xterm color approx \033[38;5;$(short)m$(short) ($(rgb))\033[0m\033[0m")
    return nothing
end

main() = print_all()
main(i::String) = length(i) < 4 && parse(Int, i) < 256 ? main_exact(i) : main_approx(i)
main(i1::Float64, i2::Float64, i3::Float64) = main(hex(RGB(i1, i2, i3)))
main(i1::Int, i2::Int, i3::Int) = all(i -> 0 .≤ i .< 256, (i1, i2, i3)) ? main(i1 / 255, i2 / 255, i3 / 255) : error("RGB values out of bounds")
main(i1::String, i2::String, i3::String) = main(parse.(Real, (i1, i2, i3))...)
main(i...) = length(i) < 4 ? main(i...) : error("It's \"RGB\", not \"$("RGB" * join(map(_ -> rand("ABCDEFGHIJKLMNOPQRSTUVWXYZ"), 1:(length(i) - 3))))\"")