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

let
  cfg = config.dataPro.wallpaper; # custom namespace

  # Where we keep a runtime-editable config for the user.
  runtimeConfDir = "${config.xdg.configHome}/wallpaper";
  runtimeConfPath = "${runtimeConfDir}/wallpaper.conf";

  rotateScript = pkgs.writeShellScript "wallpaper-rotate" ''
    set -euo pipefail

    export PATH=${lib.makeBinPath [
      pkgs.coreutils
      pkgs.findutils
      pkgs.gnugrep
      pkgs.gawk
      pkgs.util-linux
      pkgs.swww
    ]}

    # Defaults (can be overridden by wallpaper.conf)
    SOURCE_DIR="${cfg.sourceDir}"
    TARGET_DIR="${cfg.targetDir}"
    ROTATION_DIR="${cfg.rotationDir}"
    TRANSITION_TYPE="fade"
    TRANSITION_DURATION="2.5"
    TRANSITION_FPS="60"
    PICK_MODE="random"   # random | sequential
    LAST_FILE="${config.xdg.stateHome}/wallpaper/last.txt"

    # Load user config if present (KEY=VALUE lines; '#' comments allowed)
    if [ -f "${runtimeConfPath}" ]; then
      # shellcheck disable=SC1090
      . "${runtimeConfPath}"
    fi

    mkdir -p "$TARGET_DIR" "${config.xdg.stateHome}/wallpaper"

    # Ensure swww-daemon is running
    if ! pgrep -x swww-daemon >/dev/null 2>&1; then
      swww-daemon >/dev/null 2>&1 &
      sleep 0.3
    fi

    # Pick image
    if [ ! -d "$ROTATION_DIR" ]; then
      echo "Rotation directory does not exist: $ROTATION_DIR" >&2
      exit 0
    fi

    # Build list once per run
    mapfile -d '' -t imgs < <(
      find "$ROTATION_DIR" -type f \
        \( -iname '*.jpg' -o -iname '*.jpeg' -o -iname '*.png' -o -iname '*.webp' \) \
        -print0
    )

    if [ "${#imgs[@]}" -eq 0 ]; then
      echo "No images found in: $ROTATION_DIR" >&2
      exit 0
    fi

    img=""
    if [ "$PICK_MODE" = "sequential" ]; then
      last=""
      if [ -f "$LAST_FILE" ]; then
        last="$(cat "$LAST_FILE" || true)"
      fi

      # Sort for stable order
      IFS=$'\n' sorted=($(printf '%s\n' "${imgs[@]}" | sort))
      unset IFS

      # Find next after last
      next=""
      found_last=0
      for f in "${sorted[@]}"; do
        if [ "$found_last" -eq 1 ]; then
          next="$f"
          break
        fi
        if [ "$f" = "$last" ]; then
          found_last=1
        fi
      done
      if [ -z "$next" ]; then
        next="${sorted[0]}"
      fi
      img="$next"
      printf '%s' "$img" > "$LAST_FILE"
    else
      # random
      img="$(printf '%s\0' "${imgs[@]}" | shuf -z -n 1 | tr -d '\0')"
    fi

    # Smooth transition wallpaper set
    swww img "$img" \
      --transition-type "$TRANSITION_TYPE" \
      --transition-duration "$TRANSITION_DURATION" \
      --transition-fps "$TRANSITION_FPS"
  '';
in
{
  options.dataPro.wallpaper = {
    enable = lib.mkEnableOption "Hourly wallpaper rotation with swww (Hyprland/Wayland)";

    # You asked to make this easy to change:
    sourceDir = lib.mkOption {
      type = lib.types.str;
      default = "${config.home.homeDirectory}/nixos/files/wallpaper/picture";
      description = "Folder containing wallpapers to rotate (source of truth).";
    };

    targetDir = lib.mkOption {
      type = lib.types.str;
      default = "${config.home.homeDirectory}/wallpaper";
      description = "Folder in the user's home where wallpapers are copied to.";
    };

    rotationDir = lib.mkOption {
      type = lib.types.str;
      default = "${config.home.homeDirectory}/wallpaper/picture";
      description = "Folder used by the rotator to pick wallpapers from (usually inside targetDir).";
    };
  };

  config = lib.mkIf cfg.enable {
    home.packages = [
      pkgs.swww
      pkgs.coreutils
      pkgs.findutils
      pkgs.gnugrep
      pkgs.gawk
      pkgs.util-linux
    ];

    # Copy wallpapers from sourceDir into rotationDir (real copy) at activation.
    home.activation.wallpaperCopy = lib.hm.dag.entryAfter [ "writeBoundary" ] ''
      set -euo pipefail
      mkdir -p "${cfg.targetDir}" "${cfg.rotationDir}"

      if [ -d "${cfg.sourceDir}" ]; then
        # Copy source into rotationDir (contents only).
        cp -a "${cfg.sourceDir}/." "${cfg.rotationDir}/"
      fi
    '';

    # Install a runtime-editable config into ~/.config/wallpaper/wallpaper.conf
    # First-time copy from repo if present; then never overwrite if user edited it.
    home.activation.wallpaperConf = lib.hm.dag.entryAfter [ "writeBoundary" ] ''
      set -euo pipefail
      mkdir -p "${runtimeConfDir}"

      if [ ! -f "${runtimeConfPath}" ]; then
        if [ -f "${config.home.homeDirectory}/nixos/files/conf/wallpaper/wallpaper.conf" ]; then
          cp -a "${config.home.homeDirectory}/nixos/files/conf/wallpaper/wallpaper.conf" "${runtimeConfPath}"
        else
          cat > "${runtimeConfPath}" <<'EOF'
# wallpaper.conf — runtime settings for the wallpaper rotator (swww)
# Lines are KEY=VALUE. '#' starts a comment.

# Folder to copy wallpapers from (source of truth)
#SOURCE_DIR="$HOME/nixos/files/wallpaper/picture"

# Where wallpapers are copied to (a folder in your home)
#TARGET_DIR="$HOME/wallpaper"

# Folder used for rotation (where images are selected from)
#ROTATION_DIR="$HOME/wallpaper/picture"

# random | sequential
#PICK_MODE="random"

# swww transition settings
#TRANSITION_TYPE="fade"
#TRANSITION_DURATION="2.5"
#TRANSITION_FPS="60"
EOF
        fi
      fi
    '';

    # Start swww daemon on graphical session start
    systemd.user.services.swww-daemon = {
      Unit = {
        Description = "swww wallpaper daemon";
        After = [ "graphical-session.target" ];
        PartOf = [ "graphical-session.target" ];
      };
      Service = {
        ExecStart = "${pkgs.swww}/bin/swww-daemon";
        Restart = "on-failure";
      };
      Install = {
        WantedBy = [ "graphical-session.target" ];
      };
    };

    # Rotate wallpaper hourly
    systemd.user.services.wallpaper-rotate = {
      Unit = {
        Description = "Rotate wallpaper (hourly)";
        After = [ "swww-daemon.service" ];
      };
      Service = {
        Type = "oneshot";
        ExecStart = "${rotateScript}";
      };
    };

    systemd.user.timers.wallpaper-rotate = {
      Unit = {
        Description = "Hourly wallpaper rotation timer";
      };
      Timer = {
        OnBootSec = "2m";
        OnUnitActiveSec = "1h";
        Unit = "wallpaper-rotate.service";
      };
      Install = {
        WantedBy = [ "timers.target" ];
      };
    };
  };
}