module NoUnusedExports exposing (rule)

{-| Forbid the use of modules that are never used in your project.


# Rule

@docs rule

-}

-- TODO Don't report type or type aliases (still `A(..)` though) if they are
-- used in exposed function arguments/return values.

import Dict exposing (Dict)
import Elm.Module
import Elm.Project
import Elm.Syntax.Declaration as Declaration exposing (Declaration)
import Elm.Syntax.Exposing as Exposing
import Elm.Syntax.Expression as Expression exposing (Expression)
import Elm.Syntax.Module as Module exposing (Module)
import Elm.Syntax.ModuleName exposing (ModuleName)
import Elm.Syntax.Node as Node exposing (Node(..))
import Elm.Syntax.Range exposing (Range)
import Elm.Syntax.TypeAnnotation as TypeAnnotation exposing (TypeAnnotation)
import Review.Rule as Rule exposing (Error, Rule)
import Scope2 as Scope
import Set exposing (Set)


{-| Forbid the use of modules that are never used in your project.

A module is considered unused if it does not contain a `main` function
(be it exposed or not), does not import `Test` module, and is never imported in
other modules. For packages, modules listed in the `elm.json`'s
`exposed-modules` are considered used. The `ReviewConfig` is also always
considered as used.

A module will be considered as used if it gets imported, even if none of its
functions or types are used. Other rules from this package will help detect and
remove code so that the import statement is removed.

    config =
        [ NoUnused.Modules.rule
        ]


# When (not) to use this rule

You may not want to enable this rule if you are not concerned about having
unused modules in your application or package.

-}
rule : Rule
rule =
    Rule.newProjectRuleSchema "NoUnused.Exports"
        { moduleVisitor = moduleVisitor
        , initProjectContext = initProjectContext
        , fromProjectToModule = fromProjectToModule
        , fromModuleToProject = fromModuleToProject
        , foldProjectContexts = foldProjectContexts
        }
        |> Scope.addProjectVisitors
        |> Rule.withContextFromImportedModules
        |> Rule.withProjectElmJsonVisitor elmJsonVisitor
        |> Rule.withFinalProjectEvaluation finalEvaluationForProject
        |> Rule.fromProjectRuleSchema


moduleVisitor : Rule.ModuleRuleSchema {} ModuleContext -> Rule.ModuleRuleSchema { hasAtLeastOneVisitor : () } ModuleContext
moduleVisitor schema =
    schema
        |> Scope.addModuleVisitors
        |> Rule.withModuleDefinitionVisitor moduleDefinitionVisitor
        |> Rule.withDeclarationListVisitor declarationListVisitor
        |> Rule.withExpressionVisitor expressionVisitor



-- CONTEXT


type alias ProjectContext =
    { scope : Scope.ProjectContext
    , projectType : ProjectType
    , modules :
        Dict ModuleName
            { moduleKey : Rule.ModuleKey
            , exposed : Dict String { range : Range, exposedElement : ExposedElement }
            }
    , used : Set ( ModuleName, String )
    }


type ProjectType
    = IsApplication
    | IsPackage (Set (List String))


type ExposedElement
    = Function
    | TypeOrTypeAlias
    | ExposedType


type alias ModuleContext =
    { scope : Scope.ModuleContext
    , exposesEverything : Bool
    , exposed : Dict String { range : Range, exposedElement : ExposedElement }
    , used : Set ( ModuleName, String )
    , elementsNotToReport : Set String
    }


initProjectContext : ProjectContext
initProjectContext =
    { scope = Scope.initProjectContext
    , projectType = IsApplication
    , modules = Dict.empty
    , used = Set.empty
    }


fromProjectToModule : Rule.ModuleKey -> Node ModuleName -> ProjectContext -> ModuleContext
fromProjectToModule moduleKey moduleName projectContext =
    { scope = Scope.fromProjectToModule projectContext.scope
    , exposesEverything = False
    , exposed = Dict.empty
    , used = Set.empty
    , elementsNotToReport = Set.empty
    }


fromModuleToProject : Rule.ModuleKey -> Node ModuleName -> ModuleContext -> ProjectContext
fromModuleToProject moduleKey moduleName moduleContext =
    { scope = Scope.fromModuleToProject moduleName moduleContext.scope
    , projectType = IsApplication
    , modules =
        Dict.singleton
            (Node.value moduleName)
            { moduleKey = moduleKey
            , exposed = moduleContext.exposed
            }
    , used =
        moduleContext.elementsNotToReport
            |> Set.map (Tuple.pair <| Node.value moduleName)
            |> Set.union moduleContext.used
    }


foldProjectContexts : ProjectContext -> ProjectContext -> ProjectContext
foldProjectContexts newContext previousContext =
    { scope = Scope.foldProjectContexts previousContext.scope newContext.scope
    , projectType = previousContext.projectType
    , modules = Dict.union previousContext.modules newContext.modules
    , used = Set.union newContext.used previousContext.used
    }


registerAsUsed : ( ModuleName, String ) -> ModuleContext -> ModuleContext
registerAsUsed ( moduleName, name ) moduleContext =
    { moduleContext | used = Set.insert ( moduleName, name ) moduleContext.used }


registerMultipleAsUsed : List ( ModuleName, String ) -> ModuleContext -> ModuleContext
registerMultipleAsUsed usedElements moduleContext =
    { moduleContext | used = Set.union (Set.fromList usedElements) moduleContext.used }



-- ELM JSON VISITOR


elmJsonVisitor : Maybe { a | project : Elm.Project.Project } -> ProjectContext -> ProjectContext
elmJsonVisitor maybeProject projectContext =
    case maybeProject |> Maybe.map .project of
        Just (Elm.Project.Package { exposed }) ->
            let
                exposedModuleNames : List Elm.Module.Name
                exposedModuleNames =
                    case exposed of
                        Elm.Project.ExposedList names ->
                            names

                        Elm.Project.ExposedDict fakeDict ->
                            List.concatMap Tuple.second fakeDict
            in
            { projectContext
                | projectType =
                    exposedModuleNames
                        |> List.map (Elm.Module.toString >> String.split ".")
                        |> Set.fromList
                        |> IsPackage
            }

        _ ->
            { projectContext | projectType = IsApplication }



-- PROJECT EVALUATION


finalEvaluationForProject : ProjectContext -> List Error
finalEvaluationForProject projectContext =
    projectContext.modules
        |> removeExposedPackages projectContext
        |> Dict.toList
        |> List.concatMap
            (\( moduleName, { moduleKey, exposed } ) ->
                exposed
                    |> removeApplicationExceptions projectContext moduleName
                    |> removeReviewConfig moduleName
                    |> Dict.filter (\name _ -> not <| Set.member ( moduleName, name ) projectContext.used)
                    |> Dict.toList
                    |> List.map
                        (\( name, { range, exposedElement } ) ->
                            let
                                what : String
                                what =
                                    case exposedElement of
                                        Function ->
                                            "Exposed function or value"

                                        TypeOrTypeAlias ->
                                            "Exposed type or type alias"

                                        ExposedType ->
                                            "Exposed type"
                            in
                            Rule.errorForFile moduleKey
                                { message = what ++ " `" ++ name ++ "` is never used outside this module."
                                , details = [ "This exposed element is never used. You may want to remove it to keep your project clean, and maybe detect some unused code in your project." ]
                                }
                                range
                        )
            )


removeExposedPackages : ProjectContext -> Dict ModuleName a -> Dict ModuleName a
removeExposedPackages projectContext dict =
    case projectContext.projectType of
        IsApplication ->
            dict

        IsPackage exposedModuleNames ->
            Dict.filter (\name _ -> not <| Set.member name exposedModuleNames) dict


removeApplicationExceptions : ProjectContext -> ModuleName -> Dict String a -> Dict String a
removeApplicationExceptions projectContext moduleName dict =
    case projectContext.projectType of
        IsApplication ->
            Dict.remove "main" dict

        IsPackage _ ->
            dict


removeReviewConfig : ModuleName -> Dict String a -> Dict String a
removeReviewConfig moduleName dict =
    if moduleName == [ "ReviewConfig" ] then
        Dict.remove "config" dict

    else
        dict



-- MODULE DEFINITION VISITOR


moduleDefinitionVisitor : Node Module -> ModuleContext -> ( List Error, ModuleContext )
moduleDefinitionVisitor moduleNode moduleContext =
    case Module.exposingList (Node.value moduleNode) of
        Exposing.All _ ->
            ( [], { moduleContext | exposesEverything = True } )

        Exposing.Explicit list ->
            ( [], { moduleContext | exposed = exposedElements list } )


exposedElements : List (Node Exposing.TopLevelExpose) -> Dict String { range : Range, exposedElement : ExposedElement }
exposedElements nodes =
    nodes
        |> List.filterMap
            (\node ->
                case Node.value node of
                    Exposing.FunctionExpose name ->
                        Just <| ( name, { range = Node.range node, exposedElement = Function } )

                    Exposing.TypeOrAliasExpose name ->
                        Just <| ( name, { range = Node.range node, exposedElement = TypeOrTypeAlias } )

                    Exposing.TypeExpose { name } ->
                        Just <| ( name, { range = Node.range node, exposedElement = ExposedType } )

                    Exposing.InfixExpose name ->
                        Nothing
            )
        |> Dict.fromList



-- DECLARATION LIST VISITOR


declarationListVisitor : List (Node Declaration) -> ModuleContext -> ( List Error, ModuleContext )
declarationListVisitor declarations moduleContext =
    let
        declaredNames : Set String
        declaredNames =
            declarations
                |> List.filterMap (Node.value >> declarationName)
                |> Set.fromList

        typesUsedInDeclaration_ : List ( List ( ModuleName, String ), Bool )
        typesUsedInDeclaration_ =
            declarations
                |> List.map (typesUsedInDeclaration moduleContext)

        testFunctions : List String
        testFunctions =
            declarations
                |> List.filterMap (testFunctionName moduleContext.scope)

        allUsedTypes : List ( ModuleName, String )
        allUsedTypes =
            typesUsedInDeclaration_
                |> List.concatMap Tuple.first

        contextWithUsedElements : ModuleContext
        contextWithUsedElements =
            registerMultipleAsUsed allUsedTypes moduleContext
    in
    ( []
    , { contextWithUsedElements
        | exposed =
            contextWithUsedElements.exposed
                |> (if moduleContext.exposesEverything then
                        identity

                    else
                        Dict.filter (\name _ -> Set.member name declaredNames)
                   )
        , elementsNotToReport =
            typesUsedInDeclaration_
                |> List.concatMap
                    (\( list, comesFromCustomTypeWithHiddenConstructors ) ->
                        if comesFromCustomTypeWithHiddenConstructors then
                            []

                        else
                            List.filter (\( moduleName, name ) -> isType name && moduleName == []) list
                    )
                |> List.map Tuple.second
                |> List.append testFunctions
                |> Set.fromList
      }
    )


isType : String -> Bool
isType string =
    case String.uncons string of
        Nothing ->
            False

        Just ( char, _ ) ->
            Char.isUpper char


declarationName : Declaration -> Maybe String
declarationName declaration =
    case declaration of
        Declaration.FunctionDeclaration function ->
            function.declaration
                |> Node.value
                |> .name
                |> Node.value
                |> Just

        Declaration.CustomTypeDeclaration type_ ->
            Just <| Node.value type_.name

        Declaration.AliasDeclaration alias_ ->
            Just <| Node.value alias_.name

        Declaration.PortDeclaration port_ ->
            Just <| Node.value port_.name

        Declaration.InfixDeclaration { operator } ->
            Just <| Node.value operator

        Declaration.Destructuring _ _ ->
            Nothing


testFunctionName : Scope.ModuleContext -> Node Declaration -> Maybe String
testFunctionName scope declaration =
    case Node.value declaration of
        Declaration.FunctionDeclaration function ->
            case
                function.signature
                    |> Maybe.map (Node.value >> .typeAnnotation >> Node.value)
            of
                Just (TypeAnnotation.Typed (Node _ ( moduleName, name )) _) ->
                    case Scope.realFunctionOrType moduleName name scope of
                        ( [ "Test" ], "Test" ) ->
                            function.declaration
                                |> Node.value
                                |> .name
                                |> Node.value
                                |> Just

                        _ ->
                            Nothing

                _ ->
                    Nothing

        _ ->
            Nothing


typesUsedInDeclaration : ModuleContext -> Node Declaration -> ( List ( ModuleName, String ), Bool )
typesUsedInDeclaration moduleContext declaration =
    case Node.value declaration of
        Declaration.FunctionDeclaration function ->
            ( function.signature
                |> Maybe.map (Node.value >> .typeAnnotation >> collectTypesFromTypeAnnotation moduleContext.scope)
                |> Maybe.withDefault []
            , False
            )

        Declaration.CustomTypeDeclaration type_ ->
            ( type_.constructors
                |> List.concatMap (Node.value >> .arguments)
                |> List.concatMap (collectTypesFromTypeAnnotation moduleContext.scope)
            , not <|
                case Dict.get (Node.value type_.name) moduleContext.exposed |> Maybe.map .exposedElement of
                    Just ExposedType ->
                        True

                    _ ->
                        False
            )

        Declaration.AliasDeclaration alias_ ->
            ( collectTypesFromTypeAnnotation moduleContext.scope alias_.typeAnnotation, False )

        Declaration.PortDeclaration _ ->
            ( [], False )

        Declaration.InfixDeclaration _ ->
            ( [], False )

        Declaration.Destructuring _ _ ->
            ( [], False )


collectTypesFromTypeAnnotation : Scope.ModuleContext -> Node TypeAnnotation -> List ( ModuleName, String )
collectTypesFromTypeAnnotation scope node =
    case Node.value node of
        TypeAnnotation.FunctionTypeAnnotation a b ->
            collectTypesFromTypeAnnotation scope a ++ collectTypesFromTypeAnnotation scope b

        TypeAnnotation.Typed (Node _ ( moduleName, name )) params ->
            Scope.realFunctionOrType moduleName name scope
                :: List.concatMap (collectTypesFromTypeAnnotation scope) params

        TypeAnnotation.Record list ->
            list
                |> List.map (Node.value >> Tuple.second)
                |> List.concatMap (collectTypesFromTypeAnnotation scope)

        TypeAnnotation.GenericRecord name list ->
            list
                |> Node.value
                |> List.map (Node.value >> Tuple.second)
                |> List.concatMap (collectTypesFromTypeAnnotation scope)

        TypeAnnotation.Tupled list ->
            List.concatMap (collectTypesFromTypeAnnotation scope) list

        TypeAnnotation.GenericType _ ->
            []

        TypeAnnotation.Unit ->
            []



-- EXPRESSION VISITOR


expressionVisitor : Node Expression -> Rule.Direction -> ModuleContext -> ( List Error, ModuleContext )
expressionVisitor node direction moduleContext =
    case ( direction, Node.value node ) of
        ( Rule.OnEnter, Expression.FunctionOrValue moduleName name ) ->
            ( []
            , registerAsUsed
                (Scope.realFunctionOrType moduleName name moduleContext.scope)
                moduleContext
            )

        _ ->
            ( [], moduleContext )