" :h pattern-delimiter
let s:delimiter_pattern = "[!@$%^&*()=+~`',.;:<>/?_-]"

function! s:echoerr(msg) abort
  echohl ErrorMsg
  echomsg a:msg
  echohl NONE
endfunction

function! s:make_cases(str) abort
  const words = split(a:str, '[^[:alnum:]]\|\ze\u\l')
  const snake = tolower(join(words, '_'))
  const scream = toupper(snake)
  const kebab = substitute(snake, '_', '-', 'g')
  const dots = substitute(snake, '_', '.', 'g')
  const camel = substitute(snake, '_\(.\)', '\u\1', 'g')
  const pascal = substitute(camel, '.', '\u\0', '')
  return [snake, scream, kebab, dots, camel, pascal]
endfunction

const s:s_flags_pattern = '[#&cegiIlnpr]'
function! mi#subs#parse_flags(flags) abort
  return [
        \ substitute(a:flags, '[^#&cegiIlnpr]', '', 'g'),
        \ substitute(a:flags, s:s_flags_pattern, '', 'g'),
        \ ]
endfunction

function! mi#subs#titute(line1, line2, args) abort
  const delimiter = a:args[0]
  if delimiter !~# s:delimiter_pattern
    return s:echoerr(printf('[mi#subs] invalid delimiter: %s. see :h E146', delimiter))
  endif

  const args = split(a:args, delimiter)
  if a:args[1] ==# delimiter
    " use last search pattern
    call insert(args, getreg('/'))
  endif
  const from = get(args, 0, '')
  const to = get(args, 1, '')
  const flags = get(args, 2, '')

  if empty(from) || empty(to)
    return s:echoerr('[mi#subs] arguments required. see :h E471')
  elseif !empty(get(args, 3, ''))
    return s:echoerr('[mi#subs] trailling characters. see :h E488')
  endif

  for i in range(a:line1, a:line2)
    call setline(i, mi#subs#line(getline(i), from, to, flags))
  endfor
endfunction

function! mi#subs#line(line, from, to, flags) abort
  " ensure 'e' flag to avoid to display unmatch error
  const [builtin_flags, user_flags] = mi#subs#parse_flags(a:flags .. 'e')


  let line = a:line
  for user_flag in split(user_flags, '\zs')
    if has_key(s:subs_user_flags, user_flag)
      " let line = s:subs_user_flags[user_flag](line, a:from, a:to, builtin_flags)
      let [from, to] = mi#subs#flags_list(user_flag)(line, a:from, a:to, builtin_flags)
      let line = substitute(line, from, to, builtin_flags)
    else
      " just skip undefined flags
      " call s:echoerr(printf('[mi#subs] undefined flag: %s. see :h s_flag', user_flag))
    endif
  endfor

  return substitute(line, a:from, a:to, builtin_flags)
endfunction

augroup subs#augroup#cased
  autocmd!
augroup END
function! mi#subs#cased(_line, from, to, _flags) abort
  const from = substitute(a:from, '\\<\|\\>', '', 'g')
  const from_cases = s:make_cases(from)
  const to_cases = s:make_cases(a:to)
  if get(g:, '_subs_last_from', '') !=# from || get(g:, '_subs_last_to', '') !=# a:to
    let g:_subs_last_from = from
    let g:_subs_last_to = a:to
    let g:_subs_case_dict = {}
    for i in range(len(from_cases))
      let g:_subs_case_dict[from_cases[i]] = to_cases[i]
    endfor
    autocmd! subs#augroup#cased
    autocmd subs#augroup#cased CmdlineLeave : ++once
          \ unlet! g:_subs_case_dict g:_subs_last_from g:_subs_last_to
  endif

  return [
        \ printf('\C%s', join(from_cases, '\|')),
        \ printf('\=get(g:_subs_case_dict, submatch(0), submatch(0))'),
        \ ]
  " return substitute(
  "       \ a:line,
  "       \ printf('\C%s', join(from_cases, '\|')),
  "       \ printf('\=get(g:_subs_case_dict, submatch(0), submatch(0))'),
  "       \ a:flags)
endfunction

let s:subs_user_flags = {}
function! mi#subs#flags_list() abort
  return s:subs_user_flags
endfunction
function! mi#subs#flags_let(key, fn) abort
  if a:key =~# s:s_flags_pattern
    return s:echoerr(printf('[mi#subs] do not let builtin flag: %s. see :h :s_flags', a:key))
  endif
  let s:subs_user_flags[a:key] = a:fn
  return s:subs_user_flags
endfunction
function! mi#subs#flags_unlet(key) abort
  unlet! s:subs_user_flags[a:key]
  return s:subs_user_flags
endfunction
function! mi#subs#flags_clear() abort
  unlet! s:subs_user_flags
  let s:subs_user_flags = {}
  return mi#subs#flags_list()
endfunction

call mi#subs#flags_let('j', funcref('mi#subs#cased'))

command! -range -nargs=+ Substitute call mi#subs#titute(<line1>, <line2>, <q-args>)

" one_hart ONE_HART OneHart oneHart one-hart one.hart
" TWO_TIME TwoTime twoTime two-time two_time
" two_time TWO_TIME twoTime two-time TwoTime
" two_time TwoTime twoTime two-time TWO_TIME