local userregs = require("vim.userregs")

-- ASCII-safe register name
local regname = "\22"

-- Return the contents of the last visual selection
local function read_last_visual()
  local bufnr = vim.api.nvim_get_current_buf()

  local start_pos = vim.fn.getpos("'<")
  local end_pos = vim.fn.getpos("'>")

  if not start_pos or not end_pos then
    vim.notify("[userregs] No visual selection", vim.log.levels.WARN)
    return { lines = {}, type = "V" }
  end

  local start_lnum = start_pos[2] - 1  -- 0-indexed
  local end_lnum = end_pos[2]         -- end line is exclusive

  local lines = vim.api.nvim_buf_get_lines(bufnr, start_lnum, end_lnum, false)
  return {
    lines = lines,
    type = "V",  -- Assume linewise for now
    additional_data = {},
  }
end

-- Replace the last visual selection with new content
local function write_last_visual(_, content)
  local bufnr = vim.api.nvim_get_current_buf()

  local start_pos = vim.fn.getpos("'<")
  local end_pos = vim.fn.getpos("'>")

  if not start_pos or not end_pos then
    vim.notify("[userregs] No visual selection to write into", vim.log.levels.ERROR)
    return
  end

  local start_lnum = start_pos[2] - 1
  local end_lnum = end_pos[2]

  -- Replace the range with the new content
  vim.api.nvim_buf_set_lines(bufnr, start_lnum, end_lnum, false, content.lines or {})
end

userregs.register_handler(regname, {
  put = function() return read_last_visual() end,
  yank = write_last_visual,
})