VIM: Bind F11 and F12 to increase/decrease font size

function! AdjustFontSize(amount)
    if !has("gui_running")
        return
    endif

    let l:min_font_size = 5
    let l:max_font_size = 64

    let l:font_info = GetFontInfo()
    if l:font_info.name == '' || l:font_info.size == ''
        return
    endif

    let l:font_name = l:font_info.name
    let l:font_size = l:font_info.size

    " Decrease font size.
    if a:amount == '-'
        let l:font_size = l:font_size - 1

    " Increase font size.
    elseif a:amount == '+'
        let l:font_size = l:font_size + 1

    " Use a specific font size.
    elseif str2nr(a:amount)
        let l:font_size = str2nr(a:amount)
    endif

    " Clamp font size.
    let l:font_size = max([l:min_font_size, min([l:max_font_size, l:font_size])])

    if matchstr(&guifont, ':') == '' " Linux guifont style.
        " \v           Very magical.
        " (\d+$)       Capture group:       Match [0-9] one-or-more times, at the end of the string.
        let l:font_size_pattern = '\v(\d+$)'
    else " Windows and macOS guifont style.
        " \v           Very magical.
        " (:h)@<=      Positive lookbehind: Match ':h'.
        " (\d+)        Capture group:       Match [0-9] one-or-more times.
        let l:font_size_pattern = '\v(:h)@<=(\d+)'
    endif

    " Update vim font size.
    let &guifont = substitute(&guifont, l:font_size_pattern, l:font_size, '')

    call DisplayFontInfo()
endfunction

function! DisplayFontSelector()
    if !has("gui_running")
        return
    endif

    " Display font selector.
    " NOTE: This only changes &guifont to '*' in terminal vim.
    set guifont=*

    " Display font info after font selector closes.
    call DisplayFontInfo()
endfunction

function! DisplayFontInfo()
    let l:font_info = GetFontInfo()
    if l:font_info.name == '' || l:font_info.size == ''
        return
    endif

    " Display font name and size.
    redraw | echomsg l:font_info.name . ' ' . l:font_info.size . '%'
endfunction

function! GetFontInfo()
    " Windows and macOS &guifont: Hack NF:h11:cANSI
    "                             3270Medium_NF:h10:W500:cANSI:qDRAFT
    " Linux &guifont: Hack Nerd Font Mono Regular 10

    if matchstr(&guifont, ':') == '' " Linux guifont style.
        " \v           Very magical.
        " (^.{-1,})    Capture group:       Anchored at the start of the string, match any character one-or-more times non-greedy.
        " ( \d+$)@=    Positive lookahead:  Match ' ' followed by [0-9] one-or-more times, at the end of the string.
        let l:font_name_pattern = '\v(^.{-1,})( \d+$)@='

        " \v           Very magical.
        " (\d+$)       Capture group:       Match [0-9] one-or-more times, at the end of the string.
        let l:font_size_pattern = '\v(\d+$)'
    else " Windows and macOS guifont style.
        " \v           Very magical.
        " (^.{-1,})    Capture group:       Anchored at the start of the string, match any character one-or-more times non-greedy.
        " (:)@=        Positive lookahead:  Match ':'.
        let l:font_name_pattern = '\v(^.{-1,})(:)@='

        " \v           Very magical.
        " (:h)@<=      Positive lookbehind: Match ':h'.
        " (\d+)        Capture group:       Match [0-9] one-or-more times.
        let l:font_size_pattern = '\v(:h)@<=(\d+)'
    endif

    let l:font_name = matchstr(&guifont, l:font_name_pattern)
    let l:font_size = matchstr(&guifont, l:font_size_pattern)

    return { 'name' : l:font_name, 'size' : l:font_size }
endfunction

" Bind Control + Mouse-wheel to zoom text.
" NOTE: Starting in version 9.0 this works in Windows. Previously it only worked in Linux and macOS. SEE: :h scroll-mouse-wheel
map <silent> <C-ScrollWheelDown> :call AdjustFontSize('-')<CR>
map <silent> <C-ScrollWheelUp> :call AdjustFontSize('+')<CR>

" Decrease font size.
nnoremap <silent> <F11> :call AdjustFontSize('-')<CR>
inoremap <silent> <F11> <Esc>:call AdjustFontSize('-')<CR>
vnoremap <silent> <F11> <Esc>:call AdjustFontSize('-')<CR>
cnoremap <silent> <F11> <Esc>:call AdjustFontSize('-')<CR>
onoremap <silent> <F11> <Esc>:call AdjustFontSize('-')<CR>

" Increase font size.
nnoremap <silent> <F12> :call AdjustFontSize('+')<CR>
inoremap <silent> <F12> <Esc>:call AdjustFontSize('+')<CR>
vnoremap <silent> <F12> <Esc>:call AdjustFontSize('+')<CR>
cnoremap <silent> <F12> <Esc>:call AdjustFontSize('+')<CR>
onoremap <silent> <F12> <Esc>:call AdjustFontSize('+')<CR>

" Set font size to my preferred size (10).
nnoremap <silent> <S-F11> :call AdjustFontSize(10)<CR>
inoremap <silent> <S-F11> <Esc>:call AdjustFontSize(10)<CR>
vnoremap <silent> <S-F11> <Esc>:call AdjustFontSize(10)<CR>
cnoremap <silent> <S-F11> <Esc>:call AdjustFontSize(10)<CR>
onoremap <silent> <S-F11> <Esc>:call AdjustFontSize(10)<CR>

" TODO: Sadly cannot bind Ctrl + 0 yet:
" It would allow me to get rid of F11 F12 binding completely,
" so just C-ScrollWheel and C-0 would be needed, and maybe Shift-0 to open font selector.
" https://vi.stackexchange.com/questions/19358/cannot-map-ctrl-number-except-6-or
" https://vimhelp.org/vim_faq.txt.html#faq-20.5
"
" Set font size to my preferred size (10).
" nnoremap <silent> <C-0> :call AdjustFontSize(10)<CR>
" inoremap <silent> <C-0> <Esc>:call AdjustFontSize(10)<CR>
" vnoremap <silent> <C-0> <Esc>:call AdjustFontSize(10)<CR>
" cnoremap <silent> <C-0> <Esc>:call AdjustFontSize(10)<CR>
" onoremap <silent> <C-0> <Esc>:call AdjustFontSize(10)<CR>

" Display font selector.
nnoremap <silent> <S-F12> :call DisplayFontSelector()<CR>
inoremap <silent> <S-F12> <Esc>:call DisplayFontSelector()<CR>
vnoremap <silent> <S-F12> <Esc>:call DisplayFontSelector()<CR>
cnoremap <silent> <S-F12> <Esc>:call DisplayFontSelector()<CR>
onoremap <silent> <S-F12> <Esc>:call DisplayFontSelector()<CR>