" Falling motions for Vim. "Falling" means moving the cursor down until it hits
" text that doesn't match a pattern.

" Returns an expression to be used in normal mode that results in the falling
" motion. The semantics are as follows:
"
" The motion moves in the direction given by a:dir (which must be 'j' or 'k').
" The motion moves while the character under the cursor does not match the
" pattern, then it moves while the character under the cursor matches the
" pattern stopping when the character under the cursor does not match the
" pattern once again.
"
" ex.
"
" fall#fall('j', '^\s*$')
"
" for
"
" | t⌷is is some text
" | this is some other text
" |
" |
" | this is some bottom text
" | this is some other bottom text
"
" will return an expression to update the cursor position to:
"
" | this is some text
" | this is some other text
" |
" |
" | t⌷is is some bottom text
" | this is some other bottom text
"
" This works pretty well for navigating around languages that use indentation
" and lack braces for bodies, i.e. vimscript, ruby. Less well for python, but
" still okay.
function! fall#fall(dir, pattern) abort
  let i = 0
  let n = 0

  if a:dir == 'j'
    let delta = 1
  else
    let delta = -1
  endif

  let line = line('.')
  let column = col('.')
  let c = v:count
  if c == 0
    let c = 1
  endif

  while i < c
    let match = matchstr(getline(line), '\%' . column . 'c.')

    while ! (match =~ a:pattern)
      let n += 1
      let line += delta
      if line <= 0 || line >= line('$')
        return "m'" . n . a:dir
      endif
      let match = matchstr(getline(line), '\%' . column . 'c.')
    endwhile

    while (match =~ a:pattern)
      let n += 1
      let line += delta
      if line <= 0 || line >= line('$')
        return "m'" . n . a:dir
      endif
      let match = matchstr(getline(line), '\%' . column . 'c.')
    endwhile

    let i += 1
  endwhile

  return "m'" . n . a:dir
endfunction

function! fall#visual_same_character(dir)
  let start_line = line(".")
  let line = start_line
  let column = col(".")
  let char_to_match = matchstr(getline(line), '\%' . column . 'c.')

  let expr = ""

  if a:dir =~ 'k'
    while line > 1
      let line -= 1
      if matchstr(getline(line), '\%' . column . 'c.') != char_to_match
        break
      endif
      let expr .= 'k'
    endwhile
  endif

  if a:dir == 'jk'
    let expr .= 'o'
    let line = start_line
  endif

  if a:dir =~ 'j'
    while line <= line("$")
      let line += 1
      if matchstr(getline(line), '\%' . column . 'c.') != char_to_match
        break
      endif
      let expr .= 'j'
    endwhile
  endif

  return expr
endfunction

function! fall#visual_vertical_word(dir, def_class)
  let start_line = line(".")
  let line = start_line
  let column = col(".")

  let start_char = matchstr(getline(line), '\%' . column . 'c.')
  if (start_char =~# '\s')
    let class = '\s'
  elseif (start_char =~# a:def_class)
    let class = a:def_class
  else
    return ""
  endif

  let expr = ""

  if a:dir =~ 'k'
    while line > 1
      let line -= 1
      if ! (matchstr(getline(line), '\%' . column . 'c.') =~# class)
        break
      endif
      let expr .= 'k'
    endwhile
  endif

  if a:dir == 'jk'
    let expr .= 'o'
    let line = start_line
  endif

  if a:dir =~ 'j'
    while line <= line("$")
      let line += 1
      if ! (matchstr(getline(line), '\%' . column . 'c.') =~# class)
        break
      endif
      let expr .= 'j'
    endwhile
  endif

  return expr
endfunction