feat: redesign the project structure

home/linux/common/ssh.nix

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+{
+  pkgs,
+  ...
+}: {
+  programs.ssh = {
+    enable = true;
+
+    # all my ssh private key are generated by `ssh-keygen -t ed25519 -C "ryan@nickname"`
+    # the config's format:
+    #   Host —  given the pattern used to match against the host name given on the command line.
+    #   HostName — specify nickname or abbreviation for host
+    #   IdentityFile — the location of your SSH key authentication file for the account.
+    # format in details:
+    #   https://www.ssh.com/academy/ssh/config
+    extraConfig = ''
+      Host 192.168.*
+        # allow to securely use local SSH agent to authenticate on the remote machine.
+        # It has the same effect as adding cli option `ssh -A user@host`
+        ForwardAgent yes
+        # romantic holds my homelab~
+        IdentityFile ~/.ssh/romantic
+        # Specifies that ssh should only use the identity file explicitly configured above
+        # required to prevent sending default identity files first.
+        IdentitiesOnly yes
+
+      Host github.com
+          # github is controlled by gluttony~
+          IdentityFile ~/.ssh/gluttony
+          # Specifies that ssh should only use the identity file explicitly configured above
+          # required to prevent sending default identity files first.
+          IdentitiesOnly yes
+    '';
+
+    # use ssh-agent so we only need to input passphrase once
+    # run `ssh-add /path/to/key` for every identity file
+    # check imported keys by `ssh-add -l`
+    # TODO `ssh-add` can only add keys temporary, use gnome-keyring to unlock all keys after login.
+  };
+}

home/linux/common/system-tools.nix

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+{pkgs, config, ...}: 
+
+
+{
+  # Linux Only Packages, not available on Darwin
+  home.packages = with pkgs; [
+    btop  # replacement of htop/nmon
+    htop
+    iotop
+    nmon
+
+    ## networking tools
+    wireguard-tools  # manage wireguard vpn manually, via wg-quick
+    iftop
+
+    # misc
+    libnotify
+
+    # system call monitoring
+    strace
+    ltrace  # library call monitoring
+    lsof
+
+    # system tools
+    ethtool
+    sysstat
+    lm_sensors  # for `sensors` command
+    cifs-utils  # for mounting windows shares
+  ];
+
+  # auto mount usb drives
+  services = {
+    udiskie.enable = true;
+  };
+
+  services = {
+    playerctld.enable = true;
+  };
+}

home/linux/common/xdg.nix

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+# XDG stands for "Cross-Desktop Group", with X used to mean "cross". 
+# It's a bunch of specifications from freedesktop.org intended to standardize desktops and 
+# other GUI applications on various systems (primarily Unix-like) to be interoperable: 
+#   https://www.freedesktop.org/wiki/Specifications/
+{config, pkgs, ...}: let
+  browser = ["firefox.desktop"];
+
+  # XDG MIME types
+  associations = {
+    "application/x-extension-htm" = browser;
+    "application/x-extension-html" = browser;
+    "application/x-extension-shtml" = browser;
+    "application/x-extension-xht" = browser;
+    "application/x-extension-xhtml" = browser;
+    "application/xhtml+xml" = browser;
+    "text/html" = browser;
+    "x-scheme-handler/about" = browser;
+    "x-scheme-handler/ftp" = browser;
+    "x-scheme-handler/http" = browser;
+    "x-scheme-handler/https" = browser;
+    "x-scheme-handler/unknown" = browser;
+
+    "audio/*" = ["mpv.desktop"];
+    "video/*" = ["mpv.dekstop"];
+    "image/*" = ["imv.desktop"];
+    "application/json" = browser;
+    "application/pdf" = browser;  # TODO: pdf viewer
+    "x-scheme-handler/discord" = ["discord.desktop"];
+    "x-scheme-handler/tg" = ["telegramdesktop.desktop"];
+  };
+in {
+  home.packages = with pkgs; [
+    xdg-utils
+    xdg-user-dirs
+  ];
+
+  xdg = {
+    enable = true;
+    cacheHome = config.home.homeDirectory + "/.local/cache";
+
+    mimeApps = {
+      enable = true;
+      defaultApplications = associations;
+    };
+
+    userDirs = {
+      enable = true;
+      createDirectories = true;
+      extraConfig = {
+        XDG_SCREENSHOTS_DIR = "${config.xdg.userDirs.pictures}/Screenshots";
+      };
+    };
+  };
+}