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

with lib;
let
  cfg = config.submodules;
  parentConfig = config;

  matchesVersion = requiredVersion: version:
    if requiredVersion != null then
      if hasPrefix "~" requiredVersion
      then (builtins.match (removePrefix "~" requiredVersion) version) != null
      else requiredVersion == version
    else true;

  getDefaults = { name, version, tags, features }:
    catAttrs "default" (filter
      (submoduleDefault:
        (submoduleDefault.name == null || submoduleDefault.name == name) &&
        (matchesVersion submoduleDefault.version version) &&
        (
          (length submoduleDefault.tags == 0) ||
          (length (intersectLists submoduleDefault.tags tags)) > 0
        ) &&
        (
          (length submoduleDefault.features == 0) ||
          (length (intersectLists submoduleDefault.features features)) > 0
        )
      )
      config.submodules.defaults);

  specialArgs = cfg.specialArgs // {
    parentConfig = config;
  };

  findSubmodule = { name, version ? null, latest ? true }:
    let
      matchingSubmodules = filter
        (el:
          el.definition.name == name &&
          (matchesVersion version el.definition.version)
        )
        cfg.imports;

      versionSortedSubmodules = sort
        (s1: s2:
          if builtins.compareVersions s1.definition.version s2.definition.version > 0
          then true else false
        )
        matchingSubmodules;

      matchingModule =
        if length versionSortedSubmodules == 0
        then throw "No module found ${name}/${if version == null then "latest" else version}"
        else head versionSortedSubmodules;
    in
    matchingModule;

  passthruConfig = mapAttrsToList
    (name: opt: {
      ${name} = mkMerge (mapAttrsToList
        (_: inst:
          if inst.passthru.enable
          then inst.config.submodule.passthru.${name} or { }
          else { }
        )
        config.submodules.instances);

      _module.args = mkMerge (mapAttrsToList
        (_: inst:
          if inst.passthru.enable
          then inst.config.submodule.passthru._module.args or { }
          else { }
        )
        config.submodules.instances);
    })
    (removeAttrs options [ "_definedNames" "_module" "_m" "submodules" ]);

  submoduleWithSpecialArgs = opts: specialArgs:
    let
      opts' = toList opts;
      inherit (lib.modules) evalModules;
    in
    mkOptionType rec {
      name = "submodule";
      check = x: isAttrs x || isFunction x;
      merge = loc: defs:
        let
          coerce = def: if isFunction def then def else { config = def; };
          modules = opts' ++ map (def: { _file = def.file; imports = [ (coerce def.value) ]; }) defs;
        in
        (evalModules {
          inherit modules specialArgs;
          prefix = loc;
        }).config;
      getSubOptions = prefix: (evalModules
        {
          modules = opts'; inherit prefix specialArgs;
          # This is a work-around due to the fact that some sub-modules,
          # such as the one included in an attribute set, expects a "args"
          # attribute to be given to the sub-module. As the option
          # evaluation does not have any specific attribute name, we
          # provide a default one for the documentation.
          #
          # This is mandatory as some option declaration might use the
          # "name" attribute given as argument of the submodule and use it
          # as the default of option declarations.
          #
          # Using lookalike unicode single angle quotation marks because
          # of the docbook transformation the options receive. In all uses
          # > and < wouldn't be encoded correctly so the encoded values
          # would be used, and use of `<` and `>` would break the XML document.
          # It shouldn't cause an issue since this is cosmetic for the manual.
          args.name = "‹name›";
        }).options;
      getSubModules = opts';
      substSubModules = m: submoduleWithSpecialArgs m specialArgs;
      functor = (defaultFunctor name) // {
        # Merging of submodules is done as part of mergeOptionDecls, as we have to annotate
        # each submodule with its location.
        payload = [ ];
        binOp = lhs: rhs: [ ];
      };
    };
in
{
  imports = [ ./base.nix ];

  options = {
    submodules.specialArgs = mkOption {
      description = "Special args to pass to submodules. These arguments can be used for imports";
      type = types.attrs;
      default = { };
    };

    submodules.defaults = mkOption {
      description = "List of defaults to apply to submodule instances";
      type = types.listOf (types.submodule ({ config, ... }: {
        options = {
          name = mkOption {
            description = "Name of the submodule to apply defaults for";
            type = types.nullOr types.str;
            default = null;
          };

          version = mkOption {
            description = ''
              Version of submodule to apply defaults for. If version starts with
              "~" it is threated as regex pattern for example "~1.0.*
            '';
            type = types.nullOr types.str;
            default = null;
          };

          tags = mkOption {
            description = "List of tags to apply defaults for";
            type = types.listOf types.str;
            default = [ ];
          };

          features = mkOption {
            description = "List of features that submodule has to have to apply defaults";
            type = types.listOf types.str;
            default = [ ];
          };

          default = mkOption {
            description = "Default to apply to submodule instance";
            type = types.unspecified;
            default = { };
          };
        };
      }));
      default = [ ];
    };

    submodules.propagate.enable = mkOption {
      description = "Whether to propagate defaults and imports from parent to child";
      type = types.bool;
      default = true;
    };

    submodules.imports = mkOption {
      description = "List of submodule imports";
      type = types.listOf (
        types.coercedTo
          types.path
          (module: { inherit module; })
          (types.submodule ({ name, config, ... }:
            let
              evaledSubmodule' = evalModules {
                inherit specialArgs;
                modules = config.modules ++ [ ./base.nix ];
                check = false;
              };

              evaledSubmodule =
                if (!(elem "submodule" evaledSubmodule'.config._m.features))
                then throw "no submodule defined"
                else evaledSubmodule';
            in
            {
              options = {
                module = mkOption {
                  description = "Module defining submodule";
                  type = types.unspecified;
                };

                modules = mkOption {
                  description = "List of modules defining submodule";
                  type = types.listOf types.unspecified;
                  default = [ config.module ];
                };

                features = mkOption {
                  description = "List of features exposed by submodule";
                  type = types.listOf types.str;
                };

                definition = mkOption {
                  description = "Submodule definition";
                  type = types.attrs;
                };

                exportAs = mkOption {
                  description = "Name under which to register exports";
                  type = types.nullOr types.str;
                  default = null;
                };
              };

              config = {
                definition = {
                  inherit (evaledSubmodule.config.submodule) name description version tags exports;
                };

                features = evaledSubmodule.config._m.features;
              };
            })
          )
      );
      default = [ ];
    };

    submodules.instances = mkOption {
      description = "Attribute set of submodule instances";
      default = { };
      type = types.attrsOf (types.submodule ({ name, config, options, ... }:
        let
          # submodule associated with
          submodule = findSubmodule {
            name = config.submodule;
            version = config.version;
          };

          # definition of a submodule
          submoduleDefinition = submodule.definition;

          # submodule defaults
          defaults = getDefaults {
            name = submoduleDefinition.name;
            version = submoduleDefinition.version;
            tags = submoduleDefinition.tags;
            features = submodule.features;
          };
        in
        {
          options = {
            name = mkOption {
              description = "Submodule instance name";
              type = types.str;
              default = name;
            };

            submodule = mkOption {
              description = "Name of the submodule to use";
              type = types.str;
              default = name;
            };

            version = mkOption {
              description = ''
                Version of submodule to use, if version starts with "~" it is
                threated as regex pattern for example "~1.0.*"
              '';
              type = types.nullOr types.str;
              default = null;
            };

            passthru.enable = mkOption {
              description = "Whether to passthru submodule resources";
              type = types.bool;
              default = true;
            };

            config = mkOption {
              description = "Submodule instance ${config.name} for ${submoduleDefinition.name}:${submoduleDefinition.version} config";
              type = submoduleWithSpecialArgs
                ({ ... }: {
                  imports = submodule.modules ++ defaults ++ [ ./base.nix ];
                  _module.args.pkgs = pkgs;
                  _module.args.name = config.name;
                  _module.args.submodule = config;
                  submodule.args = mkAliasDefinitions options.args;
                })
                specialArgs;
              default = { };
            };

            args = mkOption {
              description = "Submodule arguments (alias of config.submodule.args)";
            };
          };
        }));
    };
    default = { };
  };

  config = mkMerge ([
    {
      # register exported functions as args
      _module.args = mkMerge (map
        (submodule: {
          ${submodule.exportAs} = submodule.definition.exports;
        })
        (filter (submodule: submodule.exportAs != null) cfg.imports));

      _m.features = [ "submodules" ];

      submodules.specialArgs.kubenix = kubenix;

      # passthru kubenix.project to submodules
      submodules.defaults = mkMerge [
        [{
          default = {
            kubenix.project = parentConfig.kubenix.project;
          };
        }]

        (map
          (propagate: {
            features = propagate.features;
            default = propagate.module;
          })
          config._m.propagate)
      ];
    }

    (mkIf cfg.propagate.enable {
      # if propagate is enabled and submodule has submodules included propagage defaults and imports
      submodules.defaults = [{
        features = [ "submodules" ];
        default = {
          submodules = {
            defaults = cfg.defaults;
            imports = cfg.imports;
          };
        };
      }];
    })
  ] ++ passthruConfig);
}