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 Function

  syntax keyword healthSuggestion SUGGESTION
  highlight link healthSuggestion String
endfunction

" Runs the specified healthchecks.
" Runs all discovered healthchecks if a:plugin_names is empty.
function! health#check(plugin_names) abort
  let report = ''

  let healthchecks = empty(a:plugin_names)
        \ ? s:discover_health_checks()
        \ : s:to_fn_names(a:plugin_names)

  if empty(healthchecks)
    let report = "ERROR: No healthchecks found."
  else
    for c in healthchecks
      let report .= printf("\n%s\n%s", c, repeat('=',80))
      try
        let report .= execute('call '.c.'()')
      catch /^Vim\%((\a\+)\)\=:E117/
        let report .= execute(
              \ 'call health#report_error(''No healthcheck found for "'
              \ .s:to_plugin_name(c)
              \ .'" plugin.'')')
      catch
        let report .= execute(
              \ 'call health#report_error(''Failed to run healthcheck for "'
              \ .s:to_plugin_name(c)
              \ .'" plugin. Exception:''."\n".v:exception)')
      endtry
      let report .= "\n"
    endfor
  endif

  tabnew
  setlocal bufhidden=wipe
  set filetype=markdown
  call s:enhance_syntax()
  call setline(1, split(report, "\n"))
  setlocal nomodified
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

" 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 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