local M = {}

-- Helper to get label for each tab page
local function tab_label(n)
  local buflist = vim.fn.tabpagebuflist(n)
  local winnr = vim.fn.tabpagewinnr(n)
  local bufname = vim.fn.bufname(buflist[winnr])

  if bufname == '' then
    bufname = '[No Name]'
  else
    bufname = vim.fn.fnamemodify(bufname, ':t') -- tail only
  end

  -- Determine window count reliably
  local win_count = vim.fn.tabpagewinnr(n, '$')

  -- Check if any buffer in the tab is modified
  local modified = false
  for _, buf in ipairs(buflist) do
    if vim.fn.getbufvar(buf, '&modified') == 1 then
      modified = true
      break
    end
  end

  -- Construct label according to rules:
  --  single clean: File
  --  single edited: +:File
  --  multi clean: 2:File
  --  multi edited: 2+:File
  if win_count == 1 then
    if modified then
      bufname = '+:' .. bufname
    end
  else
    local prefix = tostring(win_count)
    if modified then
      prefix = prefix .. '+'
    end
    bufname = prefix .. ':' .. bufname
  end

  -- Truncate overly long names
  if #bufname > 20 then
    bufname = bufname:sub(1, 17) .. '…'
  end

  return bufname
end

-- Main tabline builder
function M.tabline()
  local s = ''
  local num_tabs = vim.fn.tabpagenr('$')

  for i = 1, num_tabs do
    -- Highlight current tab
    if i == vim.fn.tabpagenr() then
      s = s .. '%#TabLineSel#'
    else
      s = s .. '%#TabLine#'
    end

    -- Mouse click target
    s = s .. '%' .. i .. 'T'

    -- Label
    s = s .. ' ' .. tab_label(i) .. ' '
  end

  -- Fill empty space
  s = s .. '%#TabLineFill#%T'

  return s
end

function M.setup()
  vim.o.showtabline = 1
  vim.o.tabline = "%!v:lua.require'plugins.tabline'.tabline()"
end

return M