local statusline = {}

local theme = {
  light_green  = { fg = '#262626', bg = '#59946f' },
  light_blue   = { fg = '#262626', bg = '#5c91bf' },
  light_orange = { fg = '#262626', bg = '#b6927b' },
  light_red    = { fg = '#262626', bg = '#e46876' },
  light_grey   = { fg = '#262626', bg = '#808080' },
  light_violet = { fg = '#262626', bg = '#957fb8' },
  dark_white   = { fg = '#ffffff', bg = '#121212' },
  dark_yellow  = { fg = '#c4b28a', bg = '#121212' },
  dark_grey    = { fg = '#808080', bg = '#121212' },
}

local modes = {}
modes[110]  = { name = 'Normal', color = 'light_green' }
modes[105]  = { name = 'Insert', color = 'light_blue' }
modes[99]   = { name = 'Command', color = 'light_green' }
modes[118]  = { name = 'Visual', color = 'light_violet' }
modes[86]   = { name = 'V-Line', color = 'light_violet' }
modes[22]   = { name = 'V-Block', color = 'light_violet' }
modes[82]   = { name = 'Replace', color = 'light_red' }
modes[115]  = { name = 'Select', color = 'light_orange' }
modes[83]   = { name = 'S-Line', color = 'light_orange' }
modes[19]   = { name = 'S-Block', color = 'light_orange' }
modes[116]  = { name = 'Terminal', color = 'light_blue' }
modes[33]   = { name = 'Shell', color = 'light_grey' }

local function highlight(group, color, attrs)
  local args = { group, 'guifg=' .. color.fg, 'guibg=' .. color.bg }
  if attrs then
    table.insert(args, 'gui=' .. attrs)
  end
  vim.cmd.highlight(args)
end

-- StatusLineLight is shows the mode and cursor information, it is dynamically
-- changed by statusline#mode(), give it a default.
highlight('StatusLineLight', theme.light_grey)
-- StatusLineDusk is shows additional information which is not always present,
-- give it a muted color.
highlight('StatusLineDusk', theme.light_grey, 'bold')
-- StatusLineDark shows the filename and filetype and takes up most of the
-- statusline, give it a dark background.
highlight('StatusLineDark', theme.dark_white)
-- StatusLineChange shows changes in the file by changing the colour of the
-- filename, give if a dark background.
highlight('StatusLineChange', theme.dark_yellow)
-- StatusLineFade shows the status of completion engines but using colors which
-- fade into the background to avoid grabbing attention.
highlight('StatusLineDuskFade', theme.dark_grey)

-- Get statusline mode and update StatusLineLight.
local function get_mode()
  -- Map modes to a human readable name and a color.
  local current_mode = modes[vim.fn.char2nr(vim.fn.mode())]
  -- Update the StatusLineLight color.
  highlight('StatusLineLight', theme[current_mode.color], 'bold')
  return current_mode.name
end

-- Display cusor line/total and column
local position = '# %l/%L:%2c '

-- Construct a statusline for special buffer types.
local function special(group, name, title)
  -- Display current mode with dynamic highlights.
  local line = '%#' .. group .. '# ' .. name .. ' '
  -- Display filename with dark highlights.
  line = line .. '%#StatusLineDark# ' .. title
  -- Display current/total lines and column with dynamic highlights.
  line = line .. '%=' .. '%#' .. group .. position
  -- Combine the elements into a single string to be evaluated.
  return line
end

-- Construct a statusline for generic buffer types.
local function generic(group, name)
  -- Display current mode with dynamic highlights.
  local line = '%#' .. group .. '# ' .. name .. ' '
  -- Display spell or paste if set with dusk highlights in a group to swallow
  -- the spaces when empty.
  line = line .. '%#StatusLineDusk#%( ' .. '%{&spell ? "Spell " : ""}' ..
      '%{&paste ? "Paste " : ""}' .. '%)'
  -- Display filename with dark or changed highlights.
  if vim.o.modified then
    line = line .. '%#StatusLineChange#'
  else
    line = line .. '%#StatusLineDark#'
  end
  line = line .. ' %<%f'
  -- Display readonly and nomodifiable if set.
  line = line
      .. '%#StatusLineDark#'
      .. '%{&readonly ? " 🔒" : ""}'
      .. '%{&modifiable ? "" : " ⛔"}'
  -- Display filetype if set.
  line = line .. '%=' .. '%#StatusLineDark# %{&filetype} '
  -- Display fileencoding if not utf-8 and fileformat if not unix with dusk
  -- highlights in a group to swallow spaces when empty.
  line = line .. '%#StatusLineDusk#%( ' ..
      '%{&fileencoding ==# "utf-8" ? "" : &fileencoding}' ..
      '%{&fileformat ==# "unix" ? "" : "[".&fileformat."]"}' .. ' %)'
  -- Display current/total lines and column with dynamic highlights.
  line = line .. '%#' .. group .. position
  -- Combine the elements into a single string to be evaluated.
  return line
end

-- Define active statusline, this statusline is dynamic with StatusLineLight
-- being updated based on the current mode and only used for current buffer.
function _G.statusline_active()
  local mode = get_mode()
  if vim.o.buftype == 'help' then
    if mode == 'Normal' then mode = 'Help' end
    return special('StatusLineDusk', 'Help', '%F')
  elseif vim.o.buftype == 'quickfix' then
    -- Quickfix list and location list have the same buftype, the window has a
    -- loclist flag, query the window info.
    local info = vim.fn.getwininfo(vim.fn.win_getid())[1]
    if mode == 'Normal' then
      if info.loclist == 1 then
        mode = 'Location'
      else
        mode = 'Quickfix'
      end
    end
    local title = info.variables.quickfix_title
    return special('StatusLineLight', mode, title)
  elseif vim.o.buftype == 'terminal' then
    return special('StatusLineLight', 'Terminal', '%f')
  elseif vim.o.previewwindow then
    if mode == 'Normal' then mode = 'Preview' end
    return generic('StatusLineLight', mode)
  elseif vim.o.filetype == 'man' then
    return special('StatusLineDusk', 'Manual', '%f')
  end
  return generic('StatusLineLight', mode)
end

function _G.statusline_inactive()
  local mode = modes[vim.fn.char2nr(vim.fn.mode())].name
  local line = ''
  if vim.o.buftype == 'help' then
    line = special('StatusLineDusk', 'Help', '%F')
  elseif vim.o.buftype == 'quickfix' then
    -- Quickfix list and location list have the same buftype, the window has a
    -- loclist flag, query the window info.
    local info = vim.fn.getwininfo(vim.fn.win_getid())[1]
    if info['loclist'] then mode = 'Location' else mode = 'Quickfix' end
    line = special('StatusLineDusk', mode, info.variables.quickfix_title)
  elseif vim.o.buftype == 'terminal' then
    line = special('StatusLineDusk', 'Terminal', '%f')
  elseif vim.o.previewwindow then
    line = generic('StatusLineDusk', 'Preview')
  elseif vim.o.filetype == 'man' then
    line = special('StatusLineDusk', 'Manual', '%f')
  else
    line = generic('StatusLineDusk', 'Idle')
  end
  return line
end

-- Setup autocmds to set the statusline per buffer.
local group = vim.api.nvim_create_augroup('statusline', { clear = true })
-- Dynamically update the current buffer mode and color changes using %! to
-- call a function which is always evaluated on statusline update.
vim.api.nvim_create_autocmd({ 'BufEnter', 'WinEnter', 'BufWinEnter' }, {
  pattern = '*',
  group = group,
  callback = function()
    vim.cmd.setlocal("statusline=%{%v:lua.statusline_active()%}")
  end
})

-- Statically set the statusline when leaving the buffer.
vim.api.nvim_create_autocmd({ 'BufLeave', 'WinLeave' }, {
  pattern = '*',
  group = group,
  callback = function()
    vim.cmd.setlocal("statusline=%{%v:lua.statusline_inactive()%}")
  end
})

return statusline