{ config, pkgs, lib, ... }:
let
  c = config.lib.stylix.colors;
  # One dot per base16 slot. The literal \u001b in the format string stays a
  # JSON escape here — fastfetch's JSONC parser turns it into a real ESC byte.
  # Foreground glyph, not a background-coloured space: a coloured space is
  # invisible anywhere the colour is stripped (copy/paste, piped output).
  swatch = n: "\\u001b[38;2;${c."${n}-rgb-r"};${c."${n}-rgb-g"};${c."${n}-rgb-b"}m● ";
  paletteRow = names: lib.concatMapStrings swatch names + "\\u001b[0m";
  isDesktop = lib.elem config.networking.hostName [ "FredOS-Gaming" "FredOS-Macbook" ];
in
{
  # Install fastfetch
  environment.systemPackages = with pkgs; [
    fastfetch
  ];

  # Install Nerd Fonts for icon support
  fonts.packages = with pkgs; [
    nerd-fonts.fira-code
    nerd-fonts.fira-mono
    nerd-fonts.jetbrains-mono
    nerd-fonts.meslo-lg
  ];

  # Simple fastfetch config — run `fastfetch` manually for system info
  environment.etc."fastfetch/config.jsonc".text = ''
    {
      "$schema": "https://github.com/fastfetch-cli/fastfetch/raw/dev/doc/json_schema.json",
      "logo": {
        "source": "none"
      },
      "display": {
        "separator": " ",
        "color": {
          "keys": "blue",
          "title": "cyan"
        },
        "key": {
          "type": "icon"
        }
      },
      "modules": [
        {
          "type": "title",
          "format": "{user-name}@{host-name}"
        },
        "separator",
        "os",
        "kernel",
        "uptime",
        "memory",
        "break",
        "wm",${lib.optionalString isDesktop ''

        {
          "type": "custom",
          "key": "Shell",
          "keyIcon": "󰕮",
          "format": "Quickshell ${pkgs.quickshell.version} (bar, launcher, lock)"
        },''}
        "shell",
        "terminal",
        "break",
        {
          "type": "custom",
          "key": "Palette",
          "keyIcon": "󰸌",
          "format": "${paletteRow [ "base00" "base01" "base02" "base03" "base04" "base05" "base06" "base07" "base08" "base09" "base0A" "base0B" "base0C" "base0D" "base0E" "base0F" ]}"
        }
      ]
    }
  '';

  # Fish shell settings and custom powerline prompt
  programs.fish.interactiveShellInit = ''
    # Disable default greeting
    set -g fish_greeting

    # Custom powerline prompt
    function fish_prompt
      set -l last_status $status

      # Nix-shell indicator
      if set -q IN_NIX_SHELL
        set_color -o yellow
        printf "[nix-shell] "
        set_color normal
      end

      # --- Line 1: powerline segments ---
      # Left round cap + NixOS icon
      set_color 394b70
      printf ""
      set_color 7dcfff -b 394b70
      printf " "

      # Arrow transition: nix -> hostname
      set_color 394b70 -b e0af68
      printf ""
      set_color 000000 -b e0af68
      printf " %s " (hostname)

      # Path segments - each folder gets its own color
      set -l realhome (string escape --style=regex -- $HOME)
      set -l rawpath (string replace -r "^$realhome" "~" $PWD)
      set -l parts (string split "/" $rawpath)
      set -l path_colors 41a6b5 9ece6a 7aa2f7

      set -l prev_bg e0af68
      set -l seg_count 0

      for part in $parts
        if test -n "$part"
          set seg_count (math $seg_count + 1)
          set -l cidx (math "(" $seg_count - 1 ")" "%" 3 + 1)
          set -l seg_bg $path_colors[$cidx]

          # Arrow from previous segment
          set_color $prev_bg -b $seg_bg
          printf ""
          set_color 1a1b26 -b $seg_bg
          printf " %s " $part

          set prev_bg $seg_bg
        end
      end

      # Git branch (if in a repo)
      set -l branch (command git branch --show-current 2>/dev/null)
      if test -n "$branch"
        set_color $prev_bg -b bb9af7
        printf ""
        set_color 1a1b26 -b bb9af7
        printf "  %s " $branch
        set prev_bg bb9af7
      end

      # Final arrow to terminal bg
      set_color $prev_bg -b normal
      printf ""
      set_color normal
      printf "\n"

      # --- Line 2: prompt character ---
      if test $last_status -ne 0
        set_color red
      else
        set_color magenta
      end
      printf "❯ "
      set_color normal
    end

    function fish_right_prompt; end

    # GPU load, averaged. A single read of gpu_busy_percent is worthless —
    # it catches whatever transient the card was in at that instant. Settle
    # first, then sample, and report the spread as well as the mean: a
    # steady 30% and a 0-to-70% sawtooth are different problems.
    function gpumean --description "Mean GPU busy % — 5s settle, then N seconds at 5Hz (default 10)"
      set -l secs 10
      test (count $argv) -gt 0; and set secs $argv[1]
      # find, not a glob: an unmatched wildcard is an error in fish and would
      # abort the function before the emptiness check below. -L is required —
      # /sys/class/drm/cardN is a symlink, so a plain find never descends into
      # it and silently reports no GPUs at all.
      set -l cards (find -L /sys/class/drm -maxdepth 3 -name gpu_busy_percent 2>/dev/null | sort)
      if test (count $cards) -eq 0
        echo "no gpu_busy_percent found (amdgpu/i915 only — nvidia doesn't expose it)"
        return 1
      end
      sleep 5
      set -l sum; set -l lo; set -l hi
      for c in $cards
        set -a sum 0; set -a lo 100; set -a hi 0
      end
      set -l n (math "$secs * 5")
      for i in (seq $n)
        for j in (seq (count $cards))
          set -l v (cat $cards[$j])
          set sum[$j] (math "$sum[$j] + $v")
          test $v -lt $lo[$j]; and set lo[$j] $v
          test $v -gt $hi[$j]; and set hi[$j] $v
        end
        sleep 0.2
      end
      for j in (seq (count $cards))
        set -l name (string replace -r '.*/(card[0-9]+)/.*' '$1' $cards[$j])
        echo "$name mean="(math -s0 "$sum[$j] / $n")"% min=$lo[$j]% max=$hi[$j]% ($secs""s)"
      end
    end
  '';
}