{ config, lib, pkgs, ... }:

with lib;

let
  cfg = config.programs.neovim.extras;
  nvr = "${pkgs.neovim-remote}/bin/nvr";

  shellConfig = with cfg.nvrAliases; ''
    # START programs.neovim.extras config ----------------------------------------------------------
  '' + optionalString cfg.termBufferAutoChangeDir ''
    # If shell is running in a Neovim terminal buffer, set the PWD of the buffer to `$PWD`.
    if test -n "$NVIM_LISTEN_ADDRESS"; nvim-sync-term-buffer-pwd; end
  '' + optionalString cfg.nvrAliases.enable ''
    # Neovim Remote aliases
    if test -n "$NVIM_LISTEN_ADDRESS"
      alias ${edit} "${nvr}"
      alias ${split} "${nvr} -o"
      alias ${vsplit} "${nvr} -O"
      alias ${tabedit} "${nvr} --remote-tab"
      alias ${nvim} "command nvim"
      alias nvim "echo 'This shell is running in a Neovim termainal buffer. Use \'${nvim}\' to a nested instance of Neovim, otherwise use ${edit}, ${split}, ${vsplit}, or ${tabedit} to open files in the this Neovim instance.'"
    else
      alias ${edit} "nvim"
    end
  '' + ''
    # END programs.neovim.extras config ------------------------------------------------------------
  '';
in
{
  options.programs.neovim.extras = {
    termBufferAutoChangeDir = mkOption {
      type = types.bool;
      default = false;
      description = ''
        When enabled, the <literal>pwd</literal> of terminal buffers in Neovim are automatically
        updated to match <literal>$PWD</literal> of the shell running inside them.
        Note that you cannot use this option if you are using
        <option>programs.neovim.configure</option>, use <option>programs.neovim.extraConfig</option>
        and <option>programs.neovim.plugins</option> instead.
        (Currently only works with Fish shell.)
      '';
    };

    nvrAliases = {
      enable = mkOption {
        type = types.bool;
        default = false;
        description = ''
          When enabled, shell aliases for helpful Neovim Remote commands are created if the shell is
          running inside a Neovim terminal buffer. Additionally, running <command>nvim</command>
          won't open a nested Neovim instance but instead print a message listing the available
          <command>nvr</command> aliases, as well as the command to run if you actually want to open
          a nested Neovim instance.
          Note that you cannot use this option if you are using
          <option>programs.neovim.configure</option>, use
          <option>programs.neovim.extraConfig</option> and <option>programs.neovim.plugins</option>
          instead.
          (Currently only works with Fish shell.)
        '';
      };

      edit = mkOption {
        type = types.str;
        default = "n";
        description = ''
          Equivalent to Neovim's <command>:edit</command> command, i.e., running
          <command>n [file]</command> will open the file in the current window.
          When not in Neovim this also acts as an alias for <command>nvim</command>.
          (Alias for <command>nvr</command>.)
        '';
      };

      split = mkOption {
        type = types.str;
        default = "ns";
        description = ''
          Equivalent to Neovim's <command>:split/command> command.
          (Alias for <command>nvr -o</command>.)
        '';
      };

      vsplit = mkOption {
        type = types.str;
        default = "nv";
        description = ''
          Equivalent to Neovim's <command>:vsplit/command> command.
          (Alias for <command>nvr -O</command>.)
        '';
      };

      tabedit = mkOption {
        type = types.str;
        default = "nt";
        description = ''
          Equivalent to Neovim's <command>:tabedit</command> command.
          (Alias for <command>nvr --remote-tab</command>.)
        '';
      };

      nvim = mkOption {
        type = types.str;
        default = "neovim";
        description = ''
          Opens a nested Neovim instance.
        '';
      };
    };

    luaPackages = mkOption {
      type = with types; listOf package;
      default = [ ];
      example = [ pkgs.luajitPackages.busted pkgs.luajitPackages.luafilesystem ];
      description = ''
        Lua packages to make available in Neovim Lua environment.
        Note that you cannot use this option if you are using
        <option>programs.neovim.configure</option>, use <option>programs.neovim.extraConfig</option>
        and <option>programs.neovim.plugins</option> instead.
      '';
    };
  };

  config = mkIf config.programs.neovim.enable {
    programs.fish.functions.nvim-sync-term-buffer-pwd = mkIf cfg.termBufferAutoChangeDir {
      body = ''
        if test -n "$NVIM_LISTEN_ADDRESS"
          ${nvr} -c "let g:term_buffer_pwds.$fish_pid = '$PWD' | call Set_term_buffer_pwd() "
        end
      '';
      onVariable = "PWD";
    };

    programs.neovim.extraConfig = mkIf cfg.termBufferAutoChangeDir ''
      " START programs.neovim.extras.termBufferAutoChangeDir config --------------------------------
      " Dictionary used to track the PWD of terminal buffers. Keys should be PIDs and values are is
      " PWD of the shell with that PID. These values are updated from the shell using `nvr`.
      let g:term_buffer_pwds = {}
      " Function to call to update the PWD of the current terminal buffer.
      function Set_term_buffer_pwd() abort
        if &buftype == 'terminal' && exists('g:term_buffer_pwds[b:terminal_job_pid]')
          execute 'lchd ' . g:term_buffer_pwds[b:terminal_job_pid]
        endif
      endfunction
      " Sometimes the PWD the shell in a terminal buffer will change when in another buffer, so
      " when entering a terminal buffer we update try to update it's PWD.
      augroup NvimTermPwd
      au!
      au BufEnter * if &buftype == 'terminal' | call Set_term_buffer_pwd() | endif
      augroup END
      " END programs.neovim.extras.termBufferAutoChangeDir config ----------------------------------
    '';

    programs.fish.interactiveShellInit = mkIf
      (cfg.termBufferAutoChangeDir || cfg.nvrAliases.enable)
      shellConfig;

    programs.neovim.plugins = lib.singleton (
      pkgs.vimUtils.buildVimPluginFrom2Nix {
        name = "lua-env";
        src = pkgs.linkFarm "neovim-lua-env" (
          lib.forEach cfg.luaPackages (
            p: { name = "lua"; path = "${p}/lib/lua/${p.lua.luaversion}"; }
          )
        );
      }
    );
  };
}