local M = {}

---@class CmdWithSubcommand
---@field impl fun(args:string[], opts: table) The command implementation
---@field complete? fun(subcmd_arg_lead: string): string[] Command completions callback

---@param name string The command name
---@param desc string The command description
---@param subcommand_tbl table<string, CmdWithSubcommand> Table of sub commands
M.register = function(name, desc, subcommand_tbl)
  ---@param opts table :h lua-guide-commands-create
  local function cmd(opts)
    local fargs = opts.fargs
    local subcommand_key = fargs[1]
    -- Get the subcommand's arguments, if any
    local args = #fargs > 1 and vim.list_slice(fargs, 2, #fargs) or {}
    local subcommand = subcommand_tbl[subcommand_key]
    if not subcommand then
      vim.notify(
        name .. ": Unknown command: " .. subcommand_key,
        vim.log.levels.ERROR
      )
      return
    end
    -- Invoke the subcommand
    subcommand.impl(args, opts)
  end

  vim.api.nvim_create_user_command(name, cmd, {
    nargs = "+",
    desc = desc,
    complete = function(arg_lead, cmdline, _)
      -- Get the subcommand.
      local subcmd_key, subcmd_arg_lead =
        cmdline:match("^['<,'>]*" .. name .. "[!]*%s(%S+)%s(.*)$")
      if
        subcmd_key
        and subcmd_arg_lead
        and subcommand_tbl[subcmd_key]
        and subcommand_tbl[subcmd_key].complete
      then
        -- The subcommand has completions. Return them.
        return subcommand_tbl[subcmd_key].complete(subcmd_arg_lead)
      end

      -- Check if cmdline is a subcommand
      if cmdline:match("^['<,'>]*" .. name .. "[!]*%s+%w*$") then
        -- Filter subcommands that match
        local subcommand_keys = vim.tbl_keys(subcommand_tbl)
        return vim
          .iter(subcommand_keys)
          :filter(function(key)
            return key:find(arg_lead) ~= nil
          end)
          :totable()
      end
    end,
    -- bang = true, -- If you want to support ! modifiers
  })
end

return M