" Hex color conversion functions are from https://github.com/vim-scripts/desert256.vim/blob/master/colors/desert256.vim

" Returns an approximate grey index for the given grey level
function! GreyNumber(x)
    if &t_Co == 88
        if a:x < 23
            return 0
        elseif a:x < 69
            return 1
        elseif a:x < 103
            return 2
        elseif a:x < 127
            return 3
        elseif a:x < 150
            return 4
        elseif a:x < 173
            return 5
        elseif a:x < 196
            return 6
        elseif a:x < 219
            return 7
        elseif a:x < 243
            return 8
        else
            return 9
        endif
    else
        if a:x < 14
            return 0
        else
            let l:n = (a:x - 8) / 10
            let l:m = (a:x - 8) % 10
            if l:m < 5
                return l:n
            else
                return l:n + 1
            endif
        endif
    endif
endfun

" Returns the actual grey level represented by the grey index
function! GreyLevel(n)
    if &t_Co == 88
        if a:n == 0
            return 0
        elseif a:n == 1
            return 46
        elseif a:n == 2
            return 92
        elseif a:n == 3
            return 115
        elseif a:n == 4
            return 139
        elseif a:n == 5
            return 162
        elseif a:n == 6
            return 185
        elseif a:n == 7
            return 208
        elseif a:n == 8
            return 231
        else
            return 255
        endif
    else
        if a:n == 0
            return 0
        else
            return 8 + (a:n * 10)
        endif
    endif
endfun

" Returns the palette index for the given grey index
function! GreyColor(n)
    if &t_Co == 88
        if a:n == 0
            return 16
        elseif a:n == 9
            return 79
        else
            return 79 + a:n
        endif
    else
        if a:n == 0
            return 16
        elseif a:n == 25
            return 231
        else
            return 231 + a:n
        endif
    endif
endfun

" Returns an approximate colour index for the given colour level
function! RGBNumber(x)
    if &t_Co == 88
        if a:x < 69
            return 0
        elseif a:x < 172
            return 1
        elseif a:x < 230
            return 2
        else
            return 3
        endif
    else
        if a:x < 75
            return 0
        else
            let l:n = (a:x - 55) / 40
            let l:m = (a:x - 55) % 40
            if l:m < 20
                return l:n
            else
                return l:n + 1
            endif
        endif
    endif
endfun

" Returns the actual colour level for the given colour index
function! RGBLevel(n)
    if &t_Co == 88
        if a:n == 0
            return 0
        elseif a:n == 1
            return 139
        elseif a:n == 2
            return 205
        else
            return 255
        endif
    else
        if a:n == 0
            return 0
        else
            return 55 + (a:n * 40)
        endif
    endif
endfun

" Returns the palette index for the given R/G/B colour indices
function! RGBColor(x, y, z)
    if &t_Co == 88
        return 16 + (a:x * 16) + (a:y * 4) + a:z
    else
        return 16 + (a:x * 36) + (a:y * 6) + a:z
    endif
endfun

" Returns the palette index to approximate the given R/G/B colour levels
function! Color(r, g, b)
    " Get the closest grey
    let l:gx = GreyNumber(a:r)
    let l:gy = GreyNumber(a:g)
    let l:gz = GreyNumber(a:b)

    " Get the closest colour
    let l:x = RGBNumber(a:r)
    let l:y = RGBNumber(a:g)
    let l:z = RGBNumber(a:b)

    if l:gx == l:gy && l:gy == l:gz
        " There are two possibilities
        let l:dgr = GreyLevel(l:gx) - a:r
        let l:dgg = GreyLevel(l:gy) - a:g
        let l:dgb = GreyLevel(l:gz) - a:b
        let l:dgrey = (l:dgr * l:dgr) + (l:dgg * l:dgg) + (l:dgb * l:dgb)
        let l:dr = RGBLevel(l:gx) - a:r
        let l:dg = RGBLevel(l:gy) - a:g
        let l:db = RGBLevel(l:gz) - a:b
        let l:drgb = (l:dr * l:dr) + (l:dg * l:dg) + (l:db * l:db)
        if l:dgrey < l:drgb
            " Use the grey
            return GreyColor(l:gx)
        else
            " Use the colour
            return RGBColor(l:x, l:y, l:z)
        endif
    else
        " Only one possibility
        return RGBColor(l:x, l:y, l:z)
    endif
endfun

" Returns the palette index to approximate the 'rrggbb' hex string
function! RGB(rgb)
    let l:r = ("0x" . strpart(a:rgb, 0, 2)) + 0
    let l:g = ("0x" . strpart(a:rgb, 2, 2)) + 0
    let l:b = ("0x" . strpart(a:rgb, 4, 2)) + 0

    return Color(l:r, l:g, l:b)
endfun

" Sets the highlighting for the given group
function! X(group, fg, bg, attr)
    if a:fg != ""
        exec "hi " . a:group . " guifg=#" . a:fg . " ctermfg=" . RGB(a:fg)
    endif
    if a:bg != ""
        exec "hi " . a:group . " guibg=#" . a:bg . " ctermbg=" . RGB(a:bg)
    endif
    if a:attr != ""
        exec "hi " . a:group . " gui=" . a:attr . " cterm=" . a:attr
    endif
endfun