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

let
  inherit (pkgs.stdenv.hostPlatform) isDarwin;
  inherit (lib.generators) toPlist;

  cfg = config.launchd;
  labelPrefix = "org.nix-community.home.";
  dstDir = "${config.home.homeDirectory}/Library/LaunchAgents";

  launchdConfig =
    { config, name, ... }:
    {
      options = {
        enable = lib.mkEnableOption name;
        config = lib.mkOption {
          type = lib.types.submodule (import ./launchd.nix);
          default = { };
          example = lib.literalExpression ''
            {
              ProgramArguments = [ "/usr/bin/say" "Good afternoon" ];
              StartCalendarInterval = [
                {
                  Hour = 12;
                  Minute = 0;
                }
              ];
            }
          '';
          description = ''
            Define a launchd job. See {manpage}`launchd.plist(5)` for details.
          '';
        };
      };

      config = {
        config.Label = lib.mkDefault "${labelPrefix}${name}";
      };
    };

  toAgent = config: pkgs.writeText "${config.Label}.plist" (toPlist { escape = true; } config);

  agentPlists = lib.mapAttrs' (n: v: lib.nameValuePair "${v.config.Label}.plist" (toAgent v.config)) (
    lib.filterAttrs (n: v: v.enable) cfg.agents
  );

  agentsDrv = pkgs.runCommand "home-manager-agents" { } ''
    mkdir -p "$out"

    declare -A plists
    plists=(${
      lib.concatStringsSep " " (lib.mapAttrsToList (name: value: "['${name}']='${value}'") agentPlists)
    })

    for dest in "''${!plists[@]}"; do
      src="''${plists[$dest]}"
      ln -s "$src" "$out/$dest"
    done
  '';
in
{
  meta.maintainers = with lib.maintainers; [
    khaneliman
    midchildan
  ];

  options.launchd = {
    enable = lib.mkOption {
      type = lib.types.bool;
      default = isDarwin;
      defaultText = lib.literalExpression "pkgs.stdenv.hostPlatform.isDarwin";
      description = ''
        Whether to enable Home Manager to define per-user daemons by making use
        of launchd's LaunchAgents.
      '';
    };

    agents = lib.mkOption {
      type = with lib.types; attrsOf (submodule launchdConfig);
      default = { };
      description = "Define LaunchAgents.";
    };
  };

  config = lib.mkMerge [
    {
      assertions = [
        {
          assertion = (cfg.enable && agentPlists != { }) -> isDarwin;
          message =
            let
              names = lib.concatStringsSep ", " (lib.attrNames agentPlists);
            in
            "Must use Darwin for modules that require Launchd: " + names;
        }
      ];
    }

    (lib.mkIf isDarwin {
      home.extraBuilderCommands = ''
        ln -s "${agentsDrv}" $out/LaunchAgents
      '';

      # NOTE: Launch Agent configurations can't be symlinked from the Nix store
      # because it needs to be owned by the user running it.
      home.activation.setupLaunchAgents =
        lib.hm.dag.entryAfter [ "writeBoundary" ] # Bash
          ''
            # Disable errexit to ensure we process all agents even if some fail
            set +e

            # Stop an agent if it's running
            bootoutAgent() {
              local domain="$1"
              local agentName="$2"

              verboseEcho "Stopping agent '$domain/$agentName'..."
              local bootout_output
              bootout_output=$(run /bin/launchctl bootout "$domain/$agentName" 2>&1) || {
                # Only show warning if it's not the common "No such process" error
                if [[ "$bootout_output" != *"No such process"* ]]; then
                  warnEcho "Failed to stop agent '$domain/$agentName': $bootout_output"
                else
                  verboseEcho "Agent '$domain/$agentName' was not running"
                fi
              }

              # Give the system a moment to fully unload the agent
              sleep 1
            }

            installAndBootstrapAgent() {
              local srcPath="$1"
              local dstPath="$2"
              local domain="$3"
              local agentName="$4"

              verboseEcho "Installing agent file to $dstPath"
              if ! run install -Dm444 -T "$srcPath" "$dstPath"; then
                errorEcho "Failed to install agent file for '$agentName'"
                return 1
              fi

              verboseEcho "Starting agent '$domain/$agentName'"
              local bootstrap_output
              bootstrap_output=$(run /bin/launchctl bootstrap "$domain" "$dstPath" 2>&1) || {
                local error_code=$?

                if [[ "$bootstrap_output" == *"Bootstrap failed: 5: Input/output error"* ]]; then
                  errorEcho "Failed to start agent '$domain/$agentName' with I/O error (code 5)"
                  errorEcho "This typically happens when the agent wasn't unloaded before attempting to bootstrap the new agent."
                else
                  errorEcho "Failed to start agent '$domain/$agentName' with error: $bootstrap_output"
                fi

                return 1
              }

              verboseEcho "Successfully started agent '$domain/$agentName'"
              return 0
            }

            processAgent() {
              local srcPath="$1"
              local dstDir="$2"
              local domain="$3"

              local agentFile="''${srcPath##*/}"
              local agentName="''${agentFile%.plist}"
              local dstPath="$dstDir/$agentFile"

              # Skip if unchanged
              if cmp -s "$srcPath" "$dstPath"; then
                verboseEcho "Agent '$agentName' is already up-to-date"
                return 0
              fi

              verboseEcho "Processing agent '$agentName'"

              # Stop/Unload agent if it's already running
              if [[ -f "$dstPath" ]]; then
                bootoutAgent "$domain" "$agentName"
              fi

              installAndBootstrapAgent "$srcPath" "$dstPath" "$domain" "$agentName"
              # Note: We continue processing even if this agent fails
              return 0
            }

            removeAgent() {
              local srcPath="$1"
              local dstDir="$2"
              local newDir="$3"
              local domain="$4"

              local agentFile="''${srcPath##*/}"
              local agentName="''${agentFile%.plist}"
              local dstPath="$dstDir/$agentFile"

              if [[ -e "$newDir/$agentFile" ]]; then
                verboseEcho "Agent '$agentName' still exists in new generation, skipping cleanup"
                return 0
              fi

              if [[ ! -e "$dstPath" ]]; then
                verboseEcho "Agent file '$dstPath' already removed"
                return 0
              fi

              if ! cmp -s "$srcPath" "$dstPath"; then
                warnEcho "Skipping deletion of '$dstPath', since its contents have diverged"
                return 0
              fi

              # Stop and remove the agent
              bootoutAgent "$domain" "$agentName"

              verboseEcho "Removing agent file '$dstPath'"
              if run rm -f $VERBOSE_ARG "$dstPath"; then
                verboseEcho "Successfully removed agent file for '$agentName'"
              else
                warnEcho "Failed to remove agent file '$dstPath'"
              fi

              return 0
            }

            setupLaunchAgents() {
              local oldDir newDir dstDir domain

              newDir="$(readlink -m "$newGenPath/LaunchAgents")"
              dstDir=${lib.escapeShellArg dstDir}
              domain="gui/$UID"

              if [[ -n "''${oldGenPath:-}" ]]; then
                oldDir="$(readlink -m "$oldGenPath/LaunchAgents")"
                if [[ ! -d "$oldDir" ]]; then
                  verboseEcho "No previous LaunchAgents directory found"
                  oldDir=""
                fi
              else
                oldDir=""
              fi

              verboseEcho "Setting up LaunchAgents in $dstDir"
              [[ -d "$dstDir" ]] || run mkdir -p "$dstDir"

              verboseEcho "Processing new/updated LaunchAgents..."
              find -L "$newDir" -maxdepth 1 -name '*.plist' -type f | while read -r srcPath; do
                processAgent "$srcPath" "$dstDir" "$domain"
              done

              # Skip cleanup if there's no previous generation
              if [[ -z "$oldDir" || ! -d "$oldDir" ]]; then
                verboseEcho "LaunchAgents setup complete"
                return
              fi

              verboseEcho "Cleaning up removed LaunchAgents..."
              find -L "$oldDir" -maxdepth 1 -name '*.plist' -type f | while read -r srcPath; do
                removeAgent "$srcPath" "$dstDir" "$newDir" "$domain"
              done
            }

            setupLaunchAgents

            # Restore errexit
            if [[ -o errexit ]]; then
              set -e
            fi
          '';
    })
  ];
}