function! s:enhance_syntax() abort
  syntax keyword healthError ERROR
  highlight link healthError Error

  syntax keyword healthWarning WARNING
  highlight link healthWarning WarningMsg

  syntax keyword healthInfo INFO
  highlight link healthInfo ModeMsg

  syntax keyword healthSuccess SUCCESS
  highlight link healthSuccess ModeMsg

  syntax keyword healthSuggestion SUGGESTIONS
  highlight link healthSuggestion String

  syntax match healthHelp "|.\{-}|" contains=healthBar
  syntax match healthBar  "|" contained conceal
  highlight link healthHelp Identifier

  " We do not care about markdown syntax errors in :CheckHealth output.
  highlight! link markdownError Normal

  " We don't need code blocks.
  silent! syntax clear markdownCodeBlock
endfunction

" Runs the specified healthchecks.
" Runs all discovered healthchecks if a:plugin_names is empty.
function! health#check(plugin_names) abort
  let healthchecks = empty(a:plugin_names)
        \ ? s:discover_health_checks()
        \ : s:to_fn_names(a:plugin_names)

  tabnew
  setlocal wrap breakindent
  setlocal filetype=markdown bufhidden=wipe
  setlocal conceallevel=2 concealcursor=nc
  setlocal keywordprg=:help
  call s:enhance_syntax()

  if empty(healthchecks)
    call setline(1, 'ERROR: No healthchecks found.')
  else
    redraw|echo 'Running healthchecks...'
    for c in healthchecks
      let output = ''
      call append('$', split(printf("\n%s\n%s", c, repeat('=',72)), "\n"))
      try
        let output = "\n\n".execute('call '.c.'()')
      catch
        if v:exception =~# '^Vim\%((\a\+)\)\=:E117.*\V'.c
          let output = execute(
                \ 'call health#report_error(''No healthcheck found for "'
                \ .s:to_plugin_name(c)
                \ .'" plugin.'')')
        else
          let output = execute(
                \ 'call health#report_error(''Failed to run healthcheck for "'
                \ .s:to_plugin_name(c)
                \ .'" plugin. Exception:''."\n".v:throwpoint."\n".v:exception)')
        endif
      endtry
      call append('$', split(output, "\n") + [''])
      redraw
    endfor
  endif

  setlocal nomodified
  redraw|echo ''
endfunction

" Starts a new report.
function! health#report_start(name) abort
  echo "\n## " . a:name
endfunction

" Indents lines *except* line 1 of a string if it contains newlines.
function! s:indent_after_line1(s, columns) abort
  let lines = split(a:s, "\n", 0)
  if len(lines) < 2  " We do not indent line 1, so nothing to do.
    return a:s
  endif
  for i in range(1, len(lines)-1)  " Indent lines after the first.
    let lines[i] = substitute(lines[i], '^\s*', repeat(' ', a:columns), 'g')
  endfor
  return join(lines, "\n")
endfunction

" Changes ':help clipboard' to '|clipoard|'. Also removes surrounding quotes.
function! s:help_to_link(s) abort
  return substitute(a:s, '\v[''"]?:h%[elp] ([^''"]+)[''"]?', '|\1|', 'g')
endfunction

" Format a message for a specific report item
function! s:format_report_message(status, msg, ...) abort " {{{
  let output = '  - ' . a:status . ': ' . s:indent_after_line1(a:msg, 4)
  let suggestions = []

  " Optional parameters
  if a:0 > 0
    let suggestions = type(a:1) == type("") ? [a:1] : a:1
    if type(suggestions) != type([])
      echoerr "Expected String or List"
    endif
  endif

  " Report each suggestion
  if len(suggestions) > 0
    let output .= "\n    - SUGGESTIONS:"
  endif
  for suggestion in suggestions
    let output .= "\n      - " . s:indent_after_line1(suggestion, 10)
  endfor

  return s:help_to_link(output)
endfunction " }}}

" Use {msg} to report information in the current section
function! health#report_info(msg) abort " {{{
  echo s:format_report_message('INFO', a:msg)
endfunction " }}}

" Reports a successful healthcheck.
function! health#report_ok(msg) abort " {{{
  echo s:format_report_message('SUCCESS', a:msg)
endfunction " }}}

" Reports a health warning.
function! health#report_warn(msg, ...) abort " {{{
  if a:0 > 0
    echo s:format_report_message('WARNING', a:msg, a:1)
  else
    echo s:format_report_message('WARNING', a:msg)
  endif
endfunction " }}}

" Reports a failed healthcheck.
function! health#report_error(msg, ...) abort " {{{
  if a:0 > 0
    echo s:format_report_message('ERROR', a:msg, a:1)
  else
    echo s:format_report_message('ERROR', a:msg)
  endif
endfunction " }}}

function! s:filepath_to_function(name) abort
  return substitute(substitute(substitute(a:name, ".*autoload/", "", ""),
        \ "\\.vim", "#check", ""), "/", "#", "g")
endfunction

function! s:discover_health_checks() abort
  let healthchecks = globpath(&runtimepath, 'autoload/health/*.vim', 1, 1)
  let healthchecks = map(healthchecks, '<SID>filepath_to_function(v:val)')
  return healthchecks
endfunction

" Translates a list of plugin names to healthcheck function names.
function! s:to_fn_names(plugin_names) abort
  let healthchecks = []
  for p in a:plugin_names
    call add(healthchecks, 'health#'.p.'#check')
  endfor
  return healthchecks
endfunction

" Extracts 'foo' from 'health#foo#check'.
function! s:to_plugin_name(fn_name) abort
  return substitute(a:fn_name,
        \ '\v.*health\#(.+)\#check.*', '\1', '')
endfunction