vim.o.foldcolumn = "1" -- '0' is not bad
vim.o.foldlevel = 99 -- Using ufo provider need a large value, feel free to decrease the value
vim.o.foldlevelstart = 99
vim.o.foldenable = true
vim.o.fillchars = [[eob: ,fold: ,foldopen:,foldsep: ,foldclose:]]
vim.o.statuscolumn = "%s" -- sign column
  .. "%="
  .. "%{%" -- evaluate this, and then evaluate what it returns
  .. "&number ?"
  .. "(v:relnum ?"
  -- when showing relative numbers, make sure to pad so things don't shift as you move the cursor
  .. 'printf("%"..len(line("$")).."s", v:relnum)'
  .. ":"
  .. "v:lnum"
  .. ")"
  .. ":"
  .. '""'
  .. "%}"
  .. "%#FoldColumn#" -- highlight group for fold
  .. "%{" -- expression for showing fold expand/colapse
  .. "foldlevel(v:lnum) > foldlevel(v:lnum - 1)" -- any folds?
  .. "? (foldclosed(v:lnum) == -1" -- currently open?
  .. '? ""' -- point down
  .. ': ""' -- point to right
  .. ")"
  .. ': " "' -- blank for no fold, or inside fold
  .. "}"
  .. " "

local ftMap = {
  vim = "indent",
  python = { "indent" },
  git = "",
}

---@param bufnr number
---@return Promise
local function customizeSelector(bufnr)
  local function handleFallbackException(err, providerName)
    if type(err) == "string" and err:match("UfoFallbackException") then
      return require("ufo").getFolds(bufnr, providerName)
    else
      return require("promise").reject(err)
    end
  end

  return require("ufo")
    .getFolds(bufnr, "lsp")
    :catch(function(err)
      return handleFallbackException(err, "treesitter")
    end)
    :catch(function(err)
      return handleFallbackException(err, "indent")
    end)
end

local handler = function(virtText, lnum, endLnum, width, truncate)
  local newVirtText = {}
  local suffix = ("  %d "):format(endLnum - lnum)
  local sufWidth = vim.fn.strdisplaywidth(suffix)
  local targetWidth = width - sufWidth
  local curWidth = 0
  for _, chunk in ipairs(virtText) do
    local chunkText = chunk[1]
    local chunkWidth = vim.fn.strdisplaywidth(chunkText)
    if targetWidth > curWidth + chunkWidth then
      table.insert(newVirtText, chunk)
    else
      chunkText = truncate(chunkText, targetWidth - curWidth)
      local hlGroup = chunk[2]
      table.insert(newVirtText, { chunkText, hlGroup })
      chunkWidth = vim.fn.strdisplaywidth(chunkText)
      -- str width returned from truncate() may less than 2nd argument, need padding
      if curWidth + chunkWidth < targetWidth then
        suffix = suffix .. (" "):rep(targetWidth - curWidth - chunkWidth)
      end
      break
    end
    curWidth = curWidth + chunkWidth
  end
  table.insert(newVirtText, { suffix, "MoreMsg" })
  return newVirtText
end

require("ufo").setup({
  provider_selector = function(_, filetype, _)
    return ftMap[filetype] or customizeSelector
  end,
  fold_virt_text_handler = handler,
})

-- Using ufo provider need remap `zR` and `zM`. If Neovim is 0.6.1, remap yourself
require("which-key").register({
  z = {
    R = { require("ufo").openAllFolds, "Open all folds" },
    M = { require("ufo").closeAllFolds, "Close all folds" },
  },
})