" <https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html#variables>
let s:defaults = {
      \ 'XDG_CACHE_HOME': '~/.cache',
      \ 'XDG_CONFIG_HOME': '~/.config',
      \ 'XDG_CONFIG_DIRS': '/etc/xdg',
      \ 'XDG_DATA_HOME': '~/.local/share',
      \ 'XDG_DATA_DIRS': '/usr/local/share/:/usr/share/',
      \}

function! s:Get(name) abort
  let name = a:name
  let env = environ()
  if has_key(env, name) && strlen(env[name]) > 0
    return env[name]
  elseif has_key(s:defaults, name)
    return s:defaults[name]
  else
    return ''
  endif
endfunction

function! s:Absolute(path) abort
  return a:path !=# '^[/~]'
endfunction

function! xdg#CacheDir(name) abort
  let name = a:name
  let home = s:Get('XDG_CACHE_HOME')
  if !s:Absolute(home)
    return
  endif
  return join([home, name], '/')
endfunction

function! xdg#ConfigDirs(name) abort
  let name = a:name
  let home = s:Get('XDG_CONFIG_HOME')
  let dirs = split(s:Get('XDG_CONFIG_DIRS'), ':')
  return map(
        \ filter(insert(dirs, home), 's:Absolute(v:val)')
        \,'join([v:val, name], "/")'
        \)
endfunction

function! xdg#DataDirs(name) abort
  let name = a:name
  let home = s:Get('XDG_DATA_HOME')
  let dirs = split(s:Get('XDG_DATA_DIRS'), ':')
  return map(
        \ filter(insert(dirs, home), 's:Absolute(v:val)')
        \,'join([v:val, name], "/")'
        \)
endfunction