{ pkgs ? import <nixpkgs> {}, lib ? pkgs.lib, spec ? ./istio-schema.json }:

with lib;

let
  gen = rec {
    mkMerge = values: ''mkMerge [${concatMapStrings (value: "
      ${value}
    ") values}]'';

    toNixString = value: if isAttrs value || isList value
      then builtins.toJSON value
      else if isString value
      then ''"${value}"''
      else if value == null
      then "null"
      else builtins.toString value;

    removeEmptyLines = str: concatStringsSep "\n" (filter (l: (builtins.match "(  |)+" l) == null) (splitString "\n" str));

    mkOption = {
      description ? null,
      type ? null,
      default ? null,
      apply ? null
    }:  removeEmptyLines ''mkOption {
          ${optionalString (description != null) "description = ${builtins.toJSON description};"}
          ${optionalString (type != null) ''type = ${type};''}
          ${optionalString (default != null) ''default = ${toNixString default};''}
          ${optionalString (apply != null) ''apply = ${apply};''}
        }'';

    mkOverride = priority: value:  "mkOverride ${toString priority} ${toNixString value}";

    types = {
      unspecified = "types.unspecified";
      str = "types.str";
      int = "types.int";
      bool = "types.bool";
      attrs = "types.attrs";
      nullOr = val: "(types.nullOr ${val})";
      attrsOf = val: "(types.attrsOf ${val})";
      listOf = val: "(types.listOf ${val})";
      coercedTo = coercedType: coerceFunc: finalType:
        "(types.coercedTo ${coercedType} ${coerceFunc} ${finalType})";
      either = val1: val2: "(types.either ${val1} ${val2})";
      loaOf = type: "(types.loaOf ${type})";
    };

    hasTypeMapping = def:
      hasAttr "type" def &&
      elem def.type ["string" "integer" "boolean"];

    mergeValuesByKey = mergeKey: ''(mergeValuesByKey "${mergeKey}")'';

    mapType = def:
      if def.type == "string" then
        if hasAttr "format" def && def.format == "int-or-string"
        then types.either types.int types.str
        else types.str
      else if def.type == "integer" then types.int
      else if def.type == "number" then types.int
      else if def.type == "boolean" then types.bool
      else if def.type == "object" then types.attrs
      else throw "type ${def.type} not supported";

    submoduleOf = definitions: ref: ''(submoduleOf "${ref}")'';

    submoduleForDefinition = ref: name: kind: group: version:
      ''(submoduleForDefinition "${ref}" "${name}" "${kind}" "${group}" "${version}")'';

    coerceAttrsOfSubmodulesToListByKey = ref: mergeKey:
      ''(coerceAttrsOfSubmodulesToListByKey "${ref}" "${mergeKey}")'';

    attrsToList = "values: if values != null then mapAttrsToList (n: v: v) values else values";

    refDefinition = attr: head (tail (tail (splitString "/" attr."$ref")));
  };

  fixJSON = content: replaceStrings ["\\u"] ["u"] content;

  fetchSpecs = path: builtins.fromJSON (fixJSON (builtins.readFile path));

  genDefinitions = swagger: with gen; (mapAttrs (name: definition:
    # if $ref is in definition it means it's an alias of other definition
    if hasAttr "$ref" definition
    then definitions."${refDefinition definition}"

    else if !(hasAttr "properties" definition)
    then {
      type = mapType definition;
    }

    else {
      options = mapAttrs (propName: property:
        let
          isRequired = elem propName (definition.required or []);
          requiredOrNot = type: if isRequired then type else types.nullOr type;
          optionProperties =
            # if $ref is in property it references other definition,
            # but if other definition does not have properties, then just take it's type
            if hasAttr "$ref" property then
              if hasTypeMapping swagger.definitions.${refDefinition property} then {
                type = requiredOrNot (mapType swagger.definitions.${refDefinition property});
              }
              else {
                type = requiredOrNot (submoduleOf definitions (refDefinition property));
              }

            else if !(hasAttr "type" property) then {
              type = types.unspecified;
            }

            # if property has an array type
            else if property.type == "array" then

              # if reference is in items it can reference other type of another
              # definition
              if hasAttr "$ref" property.items then

                # if it is a reference to simple type
                if hasTypeMapping swagger.definitions.${refDefinition property.items}
                then {
                  type = requiredOrNot (types.listOf (mapType swagger.definitions.${refDefinition property.items}.type));
                }

                # if a reference is to complex type
                else
                  # if x-kubernetes-patch-merge-key is set then make it an
                  # attribute set of submodules
                  if hasAttr "x-kubernetes-patch-merge-key" property
                  then let
                    mergeKey = property."x-kubernetes-patch-merge-key";
                  in {
                    type = requiredOrNot (coerceAttrsOfSubmodulesToListByKey (refDefinition property.items) mergeKey);
                    apply = attrsToList;
                  }

                  # in other case it's a simple list
                  else {
                    type = requiredOrNot (types.listOf (submoduleOf definitions (refDefinition property.items)));
                  }

              # in other case it only references a simple type
              else {
                type = requiredOrNot (types.listOf (mapType property.items));
              }

            else if property.type == "object" && hasAttr "additionalProperties" property
            then
              # if it is a reference to simple type
              if (
                hasAttr "$ref" property.additionalProperties &&
                hasTypeMapping swagger.definitions.${refDefinition property.additionalProperties}
              ) then {
                type = requiredOrNot (types.attrsOf (mapType swagger.definitions.${refDefinition property.additionalProperties}));
              }

              else if hasAttr "$ref" property.additionalProperties
              then {
                type = requiredOrNot types.attrs;
              }

              # if is an array
              else if property.additionalProperties.type == "array"
              then {
                type = requiredOrNot (types.loaOf (mapType property.additionalProperties.items));
              }

              else {
                type = requiredOrNot (types.attrsOf (mapType property.additionalProperties));
              }

            # just a simple property
            else {
              type = requiredOrNot (mapType property);
            };
        in mkOption ({
          description = property.description or "";
        } // optionProperties)
      ) definition.properties;
      config =
      let
        optionalProps = filterAttrs (propName: property:
          !(elem propName (definition.required or []))
        ) definition.properties;
      in mapAttrs (name: property: mkOverride 1002 null) optionalProps;
    }
  ) swagger.definitions);

  genResources = swagger: (mapAttrsToList (name: property: rec {
    splittedType = splitString "." (removePrefix "me.snowdrop.istio.api." property.javaType);
    group = (concatStringsSep "." (take ((length splittedType) - 2) splittedType)) + ".istio.io";
    kind = removeSuffix "Spec" (last splittedType);
    version = last (take ((length splittedType) - 1) splittedType);
    ref = removePrefix "#/definitions/" property."$ref";
  })
  (filterAttrs (name: property:
    (hasPrefix "me.snowdrop.istio.api" property.javaType) &&
    hasSuffix "Spec" property.javaType
  ) swagger.properties)) ++ (mapAttrsToList (name: property: rec {
    splittedType = splitString "." (removePrefix "me.snowdrop.istio.mixer." property.javaType);
    group = "config.istio.io";
    version = "v1alpha2";
    kind = head (tail splittedType);
    ref = removePrefix "#/definitions/" property."$ref";
  }) (filterAttrs (name: property:
    (hasPrefix "me.snowdrop.istio.mixer" property.javaType) &&
    hasSuffix "Spec" property.javaType
  ) swagger.properties));

  swagger = fetchSpecs spec;

  definitions = genDefinitions swagger;
in pkgs.writeText "gen.nix"
"# This file was generated with kubenix k8s generator, do not edit
{lib, config, ... }:

with lib;

let
  types = lib.types // rec {
    str = mkOptionType {
      name = \"str\";
      description = \"string\";
      check = isString;
      merge = mergeEqualOption;
    };

    # Either value of type `finalType` or `coercedType`, the latter is
    # converted to `finalType` using `coerceFunc`.
    coercedTo = coercedType: coerceFunc: finalType:
    mkOptionType rec {
      name = \"coercedTo\";
      description = \"\${finalType.description} or \${coercedType.description}\";
      check = x: finalType.check x || coercedType.check x;
      merge = loc: defs:
        let
          coerceVal = val:
            if finalType.check val then val
            else let
              coerced = coerceFunc val;
            in assert finalType.check coerced; coerced;

        in finalType.merge loc (map (def: def // { value = coerceVal def.value; }) defs);
      getSubOptions = finalType.getSubOptions;
      getSubModules = finalType.getSubModules;
      substSubModules = m: coercedTo coercedType coerceFunc (finalType.substSubModules m);
      typeMerge = t1: t2: null;
      functor = (defaultFunctor name) // { wrapped = finalType; };
    };
  };

  mkOptionDefault = mkOverride 1001;

  extraOptions = {
    kubenix = {};
  };

  mergeValuesByKey = mergeKey: values:
    listToAttrs (map
      (value: nameValuePair (
        if isAttrs value.\${mergeKey}
        then toString value.\${mergeKey}.content
        else (toString value.\${mergeKey})
      ) value)
    values);

  submoduleOf = ref: types.submodule ({name, ...}: {
    options = definitions.\"\${ref}\".options;
    config = definitions.\"\${ref}\".config;
  });

  submoduleWithMergeOf = ref: mergeKey: types.submodule ({name, ...}: let
    convertName = name:
      if definitions.\"\${ref}\".options.\${mergeKey}.type == types.int
      then toInt name
      else name;
  in {
    options = definitions.\"\${ref}\".options;
    config = definitions.\"\${ref}\".config // {
      \${mergeKey} = mkOverride 1002 (convertName name);
    };
  });

  submoduleForDefinition = ref: resource: kind: group: version:
    types.submodule ({name, ...}: {
      options = definitions.\"\${ref}\".options // extraOptions;
      config = mkMerge ([
        definitions.\"\${ref}\".config
        {
          kind = mkOptionDefault kind;
          apiVersion = mkOptionDefault version;

          # metdata.name cannot use option default, due deep config
          metadata.name = mkOptionDefault name;
        }
      ] ++ (config.defaults.\${resource} or [])
        ++ (config.defaults.all or []));
    });

  coerceAttrsOfSubmodulesToListByKey = ref: mergeKey: (types.coercedTo
    (types.listOf (submoduleOf ref))
    (mergeValuesByKey mergeKey)
    (types.attrsOf (submoduleWithMergeOf ref mergeKey))
  );

  definitions = {
    ${concatStrings (mapAttrsToList (name: value: "
    \"${name}\" = {${optionalString (hasAttr "options" value) "
      options = {${concatStrings (mapAttrsToList (name: value: "
        \"${name}\" = ${value};
      ") value.options)}};
    "}${optionalString (hasAttr "config" value) "
      config = {${concatStrings (mapAttrsToList (name: value: "
        \"${name}\" = ${value};
      ") value.config)}};
    "}};
    ") definitions)}
  };
in {
  kubernetes.customResources = [
  ${concatMapStrings (resource: ''{
    group = "${resource.group}";
    version = "${resource.version}";
    kind = "${resource.kind}";
    description = "";
    module = definitions."${resource.ref}";
  }'') (genResources swagger)}
  ];
}
"