{ config, pkgs, lib, ... }:
with builtins // lib;
let
  cfg = config.build;

  copyFileFunc = ''
    function copyFile() {
      local SOURCE="$1"
      local RELTARGET="$2"
      local EXECUTABLE="3"

      local TARGET
      TARGET="$(realpath -m "$REALOUT/$RELTARGET")"
      if [[ ! $TARGET == $REALOUT* ]]; then
        echo "Error installing file $RELTARGET outside of kobo src" >&2
        exit 1
      fi

      mkdir -pv "$(dirname "$TARGET")"
      if [[ -d "$SOURCE" ]]; then
        if [[ -d "$TARGET" ]]; then
          cp -rfv "$SOURCE/." "$TARGET/"
        else
          cp -rfv "$SOURCE" "$TARGET"
        fi
      else
        cp -fv "$SOURCE" "$TARGET"
      fi

      if [[ "$EXECUTABLE" == "inherit" ]]; then
        :
      elif [[ "$EXECUTABLE" ]]; then
        chmod +x "$TARGET"
      else
        chmod -x "$TARGET"
      fi
    }
  '';

  copyFile = { source, executable, target, ... }: ''
    copyFile ${escapeShellArgs [
      source
      (if executable == null then "inherit" else toString executable)
    ]}
  '';

  installFile = writeShellApplication {
    name = "kobo-install-file";
    runtimeInputs = [ pkgs.coreutils ];
    text = ''
      DRY_RUN_ARG="''${1-}"
      LOCAL_DIR="''${2-}"
      KOBO_DIR="''${3-}"
      LOCAL_FILE="''${4-}"

      FILENAME="''${LOCAL_FILE/#$LOCAL_DIR}"
      KOBO_FILE="$KOBO_DIR/$FILENAME"

      ${toShellVar "MANIFEST" (cfg.manifestLookupFor "$LOCAL_FILE" "$KOBO_FILE")}

      ACTION="''${MANIFEST["$FILENAME"]}"

      if [[ -n "$ACTION" ]]; then
        $DRY_RUN_ARG eval "$ACTION"
      elif [[ -d "$LOCAL_FILE" ]]; then
        $DRY_RUN_ARG mkdir -p "$KOBO_FILE"
      else
        $DRY_RUN_ARG mkdir -p "$(dirname "$KOBO_FILE")"
        $DRY_RUN_ARG cp -f "$LOCAL_FILE" "$KOBO_FILE"
      fi
    '';
  };
in {
  options.build = {
    allFiles = mkOption {
      readOnly = true;
      internal = true;
      default = with config; concatMap (_: attrValues) [
        file
        kfmon.file
        kobo.file
        koreader.file
        nickel.file
        plato.file
      ];
      apply = filter (v: v.enable);
    };

    allManifests = mkOption {
      readOnly = true;
      internal = true;
      default = with config; concatMap (_: attrValues) [
        manifest
        kfmon.manifest
        kobo.manifest
        koreader.manifest
        nickel.manifest
        plato.manifest
      ];
      apply = filter (v: v.enable);
    };

    manifestLookup = mkOption {
      readOnly = true;
      internal = true;
      type = with types; attrsOf (functionTo (functionTo str));
      default =
      let
        split = concatMap ({ targets, mergeTool, ... }: map (name: { inherit name; value = mergeTool; }) targets);
      in listToAttrs split;
    };

    manifestLookupFor = mkOption {
      readOnly = true;
      internal = true;
      type = with types; functionTo (functionTo (attrsOf str));
      default = x: y: mapAttrs (_: f: f x y) cfg.manifestLookup;
    };

    src = mkOption {
      type = types.package;
      readOnly = true;
      internal = true;
      default = pkgs.stdenv.mkDerivation {
        inherit (config) src;
        name = "kobo_src";
        phases = [ "installPhase" ];
        installPhase = ''
          mkdir -pv $out
          cp -rv $src/. $out/
          chmod -R +w $out

          REALOUT="$(realpath -m "$out")"

          ${copyFileFunc}

          ${concatStringsSep "\n" (
            mapAttrsToList (_: copyFile) cfg.allFiles
          )}
        '';
      };
    };

    installer = mkOption {
      type = types.package;
      readOnly = true;
      internal = true;
      default = pkgs.writeShellApplication {
        name = "kobo-installer";
        runtimeInputs = [
          pkgs.coreutils
          pkgs.util-linux
        ];
        text = '' #TODO DRY_RUN_ARG
          KOBO_LABEL="''${1:-KOBOeReader}"

          KOBO_MOUNTPOINT="$(findmnt -nlo TARGET LABEL="$KOBO_LABEL")"
          if [[ -z "$KOBO_MOUNTPOINT" ]]; then
            echo "Couldn't find a Kobo eReader volume with label $KOBO_LABEL. Are you sure one is actually mounted?"
            exit 255
          fi

          KOBO_DIR="$KOBO_MOUNTPOINT/.kobo"
          if [[ ! -d "$KOBO_DIR" ]]; then
            echo "It doesn't seem like $KOBO_MOUNTPOINT actually points to a Kobo eReader since it doesn't contain a .kobo directory . . . "
            exit 255
          fi

          find "${cfg.src}/" -not -path "${cfg.src}/" -exec ${installFile}/bin/kobo-install-file "" "${cfg.src}" "$KOBO_DIR" {} \;
        '';
      };
    };
  };
}