{ config, lib, pkgs, ... }:
with lib;
let
  inherit (pkgs) ipfs runCommand makeWrapper;

  cfg = config.services.ipfs;

  ipfsFlags = toString ([
    (optionalString  cfg.autoMount                   "--mount")
    #(optionalString  cfg.autoMigrate                 "--migrate")
    (optionalString  cfg.enableGC                    "--enable-gc")
    (optionalString (cfg.serviceFdlimit != null)     "--manage-fdlimit=false")
    (optionalString (cfg.defaultMode == "offline")   "--offline")
    (optionalString (cfg.defaultMode == "norouting") "--routing=none")
  ] ++ cfg.extraFlags);

  defaultDataDir = if versionAtLeast config.system.stateVersion "17.09" then
    "/var/lib/ipfs" else
    "/var/lib/ipfs/.ipfs";

  # Wrapping the ipfs binary with the environment variable IPFS_PATH set to dataDir because we can't set it in the user environment
  wrapped = runCommand "ipfs" { buildInputs = [ makeWrapper ]; } ''
    mkdir -p "$out/bin"
    makeWrapper "${ipfs}/bin/ipfs" "$out/bin/ipfs" \
      --set IPFS_PATH ${cfg.dataDir} \
      --prefix PATH : /run/wrappers/bin
  '';


  commonEnv = {
    environment.IPFS_PATH = cfg.dataDir;
    path = [ wrapped ];
    serviceConfig.User = cfg.user;
    serviceConfig.Group = cfg.group;
  };

  baseService = recursiveUpdate commonEnv {
    wants = [ "ipfs-init.service" ];
    # NB: migration must be performed prior to pre-start, else we get the failure message!
    preStart = ''
      ipfs repo fsck # workaround for BUG #4212 (https://github.com/ipfs/go-ipfs/issues/4214)
      ipfs --local config Addresses.API ${cfg.apiAddress}
      ipfs --local config Addresses.Gateway ${cfg.gatewayAddress}
    '' + optionalString cfg.autoMount ''
      ipfs --local config Mounts.FuseAllowOther --json true
      ipfs --local config Mounts.IPFS ${cfg.ipfsMountDir}
      ipfs --local config Mounts.IPNS ${cfg.ipnsMountDir}
    '' + concatStringsSep "\n" (collect
          isString
          (mapAttrsRecursive
            (path: value:
            # Using heredoc below so that the value is never improperly quoted
            ''
              read value <<EOF
              ${builtins.toJSON value}
              EOF
              ipfs --local config --json "${concatStringsSep "." path}" "$value"
            '')
            cfg.extraConfig)
        );
    serviceConfig = {
      ExecStart = "${wrapped}/bin/ipfs daemon ${ipfsFlags}";
      Restart = "on-failure";
      RestartSec = 1;
    } // optionalAttrs (cfg.serviceFdlimit != null) { LimitNOFILE = cfg.serviceFdlimit; };
  };
in {

  ###### interface

  options = {

    services.ipfs = {

      enable = mkEnableOption "Interplanetary File System";

      user = mkOption {
        type = types.str;
        default = "ipfs";
        description = "User under which the IPFS daemon runs";
      };

      group = mkOption {
        type = types.str;
        default = "ipfs";
        description = "Group under which the IPFS daemon runs";
      };

      dataDir = mkOption {
        type = types.str;
        default = defaultDataDir;
        description = "The data dir for IPFS";
      };

      defaultMode = mkOption {
        type = types.enum [ "online" "offline" "norouting" ];
        default = "online";
        description = "systemd service that is enabled by default";
      };

      /*
      autoMigrate = mkOption {
        type = types.bool;
        default = false;
        description = ''
          Whether IPFS should try to migrate the file system automatically.

          The daemon will need to be able to download a binary from https://ipfs.io to perform the migration.
        '';
      };
      */

      autoMount = mkOption {
        type = types.bool;
        default = false;
        description = "Whether IPFS should try to mount /ipfs and /ipns at startup.";
      };

      ipfsMountDir = mkOption {
        type = types.str;
        default = "/ipfs";
        description = "Where to mount the IPFS namespace to";
      };

      ipnsMountDir = mkOption {
        type = types.str;
        default = "/ipns";
        description = "Where to mount the IPNS namespace to";
      };

      gatewayAddress = mkOption {
        type = types.str;
        default = "/ip4/127.0.0.1/tcp/8080";
        description = "Where the IPFS Gateway can be reached";
      };

      apiAddress = mkOption {
        type = types.str;
        default = "/ip4/127.0.0.1/tcp/5001";
        description = "Where IPFS exposes its API to";
      };

      enableGC = mkOption {
        type = types.bool;
        default = false;
        description = "Whether to enable automatic garbage collection";
      };

      emptyRepo = mkOption {
        type = types.bool;
        default = false;
        description = "If set to true, the repo won't be initialized with help files";
      };

      extraConfig = mkOption {
        type = types.attrs;
        description = ''
          Attrset of daemon configuration to set using <command>ipfs config</command>, every time the daemon starts.
          These are applied last, so may override configuration set by other options in this module.
          Keep in mind that this configuration is stateful; i.e., unsetting anything in here does not reset the value to the default!
        '';
        default = {};
        example = {
          Datastore.StorageMax = "100GB";
          Discovery.MDNS.Enabled = false;
          Bootstrap = [
            "/ip4/128.199.219.111/tcp/4001/ipfs/QmSoLSafTMBsPKadTEgaXctDQVcqN88CNLHXMkTNwMKPnu"
            "/ip4/162.243.248.213/tcp/4001/ipfs/QmSoLueR4xBeUbY9WZ9xGUUxunbKWcrNFTDAadQJmocnWm"
          ];
          Swarm.AddrFilters = null;
        };

      };

      extraFlags = mkOption {
        type = types.listOf types.str;
        description = "Extra flags passed to the IPFS daemon";
        default = [];
      };

      serviceFdlimit = mkOption {
        type = types.nullOr types.int;
        default = null;
        description = "The fdlimit for the IPFS systemd unit or <literal>null</literal> to have the daemon attempt to manage it";
        example = 64*1024;
      };

    };
  };

  ###### implementation

  config = mkIf cfg.enable {
    environment.systemPackages = [ wrapped ];
    environment.etc."fuse.conf" = mkIf cfg.autoMount { text = ''
      user_allow_other
    ''; };

    users.extraUsers = mkIf (cfg.user == "ipfs") {
      ipfs = {
        group = cfg.group;
        home = cfg.dataDir;
        createHome = false;
        uid = config.ids.uids.ipfs;
        description = "IPFS daemon user";
      };
    };

    users.extraGroups = mkIf (cfg.group == "ipfs") {
      ipfs.gid = config.ids.gids.ipfs;
    };

    systemd.services.ipfs-init = recursiveUpdate commonEnv {
      description = "IPFS Initializer";

      after = [ "local-fs.target" ];
      before = [ "ipfs.service" "ipfs-offline.service" "ipfs-norouting.service" ];

      preStart = ''
        install -m 0755 -o ${cfg.user} -g ${cfg.group} -d ${cfg.dataDir}
      '' + optionalString cfg.autoMount ''
        install -m 0755 -o ${cfg.user} -g ${cfg.group} -d ${cfg.ipfsMountDir}
        install -m 0755 -o ${cfg.user} -g ${cfg.group} -d ${cfg.ipnsMountDir}
      '';
      script = ''
        if [[ ! -f ${cfg.dataDir}/config ]]; then
          ipfs init ${optionalString cfg.emptyRepo "-e"}
        fi
      '';

      serviceConfig = {
        Type = "oneshot";
        RemainAfterExit = true;
        PermissionsStartOnly = true;
      };
    };

    # TODO These 3 definitions possibly be further abstracted through use of a function
    # like: mutexServices "ipfs" [ "", "offline", "norouting" ] { ... shared conf here ... }

    systemd.services.ipfs = recursiveUpdate baseService {
      description = "IPFS Daemon";
      wantedBy = mkIf (cfg.defaultMode == "online") [ "multi-user.target" ];
      after = [ "network.target" "local-fs.target" "ipfs-init.service" ];
      conflicts = [ "ipfs-offline.service" "ipfs-norouting.service"];
    };

    systemd.services.ipfs-offline = recursiveUpdate baseService {
      description = "IPFS Daemon (offline mode)";
      wantedBy = mkIf (cfg.defaultMode == "offline") [ "multi-user.target" ];
      after = [ "local-fs.target" "ipfs-init.service" ];
      conflicts = [ "ipfs.service" "ipfs-norouting.service"];
    };

    systemd.services.ipfs-norouting = recursiveUpdate baseService {
      description = "IPFS Daemon (no routing mode)";
      wantedBy = mkIf (cfg.defaultMode == "norouting") [ "multi-user.target" ];
      after = [ "local-fs.target" "ipfs-init.service" ];
      conflicts = [ "ipfs.service" "ipfs-offline.service"];
    };

  };
}