// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

library js_backend.runtime_types_new;

import 'package:js_runtime/shared/recipe_syntax.dart';

import '../common_elements.dart' show JCommonElements, JElementEnvironment;
import '../elements/entities.dart';
import '../elements/types.dart';
import '../js/js.dart' as jsAst;
import '../js/js.dart' show js;
import '../js_model/type_recipe.dart';
import '../js_emitter/js_emitter.dart' show ModularEmitter;
import '../universe/class_hierarchy.dart';
import '../world.dart';
import 'namer.dart';
import 'native_data.dart';

import 'runtime_types.dart' show RuntimeTypesNeed, RuntimeTypesSubstitutions;

abstract class RecipeEncoder {
  /// Returns a [jsAst.Expression] representing the given [recipe] to be
  /// evaluated against a type environment with shape [structure].
  jsAst.Expression encodeRecipe(ModularEmitter emitter,
      TypeEnvironmentStructure environmentStructure, TypeRecipe recipe);

  jsAst.Expression encodeGroundRecipe(
      ModularEmitter emitter, TypeRecipe recipe);

  // TODO(sra): Still need a $signature function when the function type is a
  // function of closed type variables. See if the $signature method can always
  // be generated through SSA in those cases.
  jsAst.Expression encodeSignature(ModularNamer namer, ModularEmitter emitter,
      DartType type, jsAst.Expression this_);
}

class RecipeEncoderImpl implements RecipeEncoder {
  final JClosedWorld _closedWorld;
  final RuntimeTypesSubstitutions _rtiSubstitutions;
  final NativeBasicData _nativeData;
  final JElementEnvironment _elementEnvironment;
  final JCommonElements commonElements;
  final RuntimeTypesNeed _rtiNeed;

  RecipeEncoderImpl(this._closedWorld, this._rtiSubstitutions, this._nativeData,
      this._elementEnvironment, this.commonElements, this._rtiNeed);

  @override
  jsAst.Expression encodeRecipe(ModularEmitter emitter,
      TypeEnvironmentStructure environmentStructure, TypeRecipe recipe) {
    return _RecipeGenerator(this, emitter, environmentStructure, recipe).run();
  }

  @override
  jsAst.Expression encodeGroundRecipe(
      ModularEmitter emitter, TypeRecipe recipe) {
    return _RecipeGenerator(this, emitter, null, recipe).run();
  }

  @override
  jsAst.Expression encodeSignature(ModularNamer namer, ModularEmitter emitter,
      DartType type, jsAst.Expression this_) {
    // TODO(sra): These inputs (referenced to quell lints) are used by the old
    // rti signature generator. Do we need them?
    _rtiNeed;
    commonElements;
    _elementEnvironment;
    throw UnimplementedError('RecipeEncoderImpl.getSignatureEncoding');
  }
}

class _RecipeGenerator implements DartTypeVisitor<void, void> {
  final RecipeEncoderImpl _encoder;
  final ModularEmitter _emitter;
  final TypeEnvironmentStructure _environment;
  final TypeRecipe _recipe;

  final List<FunctionTypeVariable> functionTypeVariables = [];

  // Accumulated recipe.
  final List<jsAst.Literal> _fragments = [];
  final List<int> _codes = [];

  _RecipeGenerator(
      this._encoder, this._emitter, this._environment, this._recipe);

  JClosedWorld get _closedWorld => _encoder._closedWorld;
  NativeBasicData get _nativeData => _encoder._nativeData;
  RuntimeTypesSubstitutions get _rtiSubstitutions => _encoder._rtiSubstitutions;

  jsAst.Expression run() {
    _start(_recipe);
    assert(functionTypeVariables.isEmpty);
    if (_fragments.isEmpty) {
      return js.string(String.fromCharCodes(_codes));
    }
    _flushCodes();
    jsAst.LiteralString quote = jsAst.LiteralString('"');
    // TODO(37302): Use [quote, ..._fragments, quote].
    return jsAst.StringConcatenation(<jsAst.Literal>[quote]
      ..addAll(_fragments)
      ..add(quote));
  }

  void _start(TypeRecipe recipe) {
    if (recipe is TypeExpressionRecipe) {
      visit(recipe.type, null);
    } else if (recipe is SingletonTypeEnvironmentRecipe) {
      visit(recipe.type, null);
    } else if (recipe is FullTypeEnvironmentRecipe) {
      _startFullTypeEnvironmentRecipe(recipe, null);
    }
  }

  void _startFullTypeEnvironmentRecipe(FullTypeEnvironmentRecipe recipe, _) {
    if (recipe.classType == null) {
      _emitCode(Recipe.pushDynamic);
      assert(recipe.types.isNotEmpty);
    } else {
      visit(recipe.classType, null);
      // TODO(sra): The separator can be omitted when the parser will have
      // reduced to the top of stack to an Rti value.
      _emitCode(Recipe.toType);
    }

    if (recipe.types.isNotEmpty) {
      _emitCode(Recipe.startTypeArguments);
      bool first = true;
      for (DartType type in recipe.types) {
        if (!first) {
          _emitCode(Recipe.separator);
        }
        visit(type, _);
        first = false;
      }
      _emitCode(Recipe.endTypeArguments);
    }
  }

  void _emitCode(int code) {
    // TODO(sra): We should permit codes with short escapes (like '\n') for
    // infrequent operators.
    assert(code >= 0x20 && code <= 0x7E && code != 0x22);
    _codes.add(code);
  }

  void _flushCodes() {
    if (_codes.isEmpty) return;
    // TODO(sra): codes need some escaping.
    _fragments.add(StringBackedName(String.fromCharCodes(_codes)));
    _codes.clear();
  }

  void _emitInteger(int value) {
    if (_codes.isEmpty ? _fragments.isNotEmpty : Recipe.isDigit(_codes.last)) {
      _emitCode(Recipe.separator);
    }
    _emitStringUnescaped('$value');
  }

  void _emitStringUnescaped(String string) {
    for (int code in string.codeUnits) {
      _emitCode(code);
    }
  }

  void _emitName(jsAst.Name name) {
    if (_fragments.isNotEmpty && _codes.isEmpty) {
      _emitCode(Recipe.separator);
    }
    _flushCodes();
    _fragments.add(name);
  }

  void _emitExtensionOp(int value) {
    _emitInteger(value);
    _emitCode(Recipe.extensionOp);
  }

  @override
  void visit(DartType type, _) => type.accept(this, _);

  @override
  void visitTypeVariableType(TypeVariableType type, _) {
    TypeEnvironmentStructure environment = _environment;
    if (environment is SingletonTypeEnvironmentStructure) {
      if (type == environment.variable) {
        _emitInteger(0);
        return;
      }
    }
    if (environment is FullTypeEnvironmentStructure) {
      int i = environment.bindings.indexOf(type);
      if (i >= 0) {
        // Indexes are 1-based since '0' encodes using the entire type for the
        // singleton structure.
        _emitInteger(i + 1);
        return;
      }

      int index = _indexIntoClassTypeVariables(type);
      if (index != null) {
        // Indexed class type variables come after the bound function type
        // variables.
        _emitInteger(1 + environment.bindings.length + index);
        return;
      }
      // TODO(sra): Encode type variables names via namer.
    }
    // TODO(sra): Handle missing cases. This just emits some readable junk. The
    // backticks ensure it won't parse at runtime.
    '`$type`'.codeUnits.forEach(_emitCode);
  }

  int /*?*/ _indexIntoClassTypeVariables(TypeVariableType variable) {
    TypeVariableEntity element = variable.element;
    ClassEntity cls = element.typeDeclaration;

    // TODO(sra): We might be in a context where the class type variable has an
    // index, even though in the general case it is not at a specific index.

    if (_closedWorld.isUsedAsMixin(cls)) return null;

    ClassHierarchy classHierarchy = _closedWorld.classHierarchy;
    if (classHierarchy.anyStrictSubclassOf(cls, (ClassEntity subclass) {
      return !_rtiSubstitutions.isTrivialSubstitution(subclass, cls);
    })) {
      return null;
    }
    return element.index;
  }

  @override
  void visitFunctionTypeVariable(FunctionTypeVariable type, _) {
    int position = functionTypeVariables.indexOf(type);
    assert(position >= 0);
    // See [visitFunctionType] for explanation.
    _emitInteger(functionTypeVariables.length - position - 1);
    _emitCode(Recipe.genericFunctionTypeParameterIndex);
  }

  @override
  void visitDynamicType(DynamicType type, _) {
    _emitCode(Recipe.pushDynamic);
  }

  @override
  void visitInterfaceType(InterfaceType type, _) {
    jsAst.Name name = _emitter.typeAccessNewRti(type.element);
    if (type.typeArguments.isEmpty) {
      // Push the name, which is later converted by an implicit toType
      // operation.
      _emitName(name);
    } else {
      _emitName(name);
      _emitCode(Recipe.startTypeArguments);
      bool first = true;
      for (DartType argumentType in type.typeArguments) {
        if (!first) {
          _emitCode(Recipe.separator);
        }
        if (_nativeData.isJsInteropClass(type.element)) {
          // Emit 'any' type.
          _emitExtensionOp(Recipe.pushAnyExtension);
        } else {
          visit(argumentType, _);
        }
        first = false;
      }
      _emitCode(Recipe.endTypeArguments);
    }
  }

  @override
  void visitFunctionType(FunctionType type, _) {
    if (type.typeVariables.isNotEmpty) {
      // Enter generic function scope.
      //
      // Function type variables are encoded as a modified de Bruin index. We
      // count variables from the current scope outwards, counting the variables
      // in the same scope left-to-right.
      //
      // If we push the current scope's variables in reverse, then the index is
      // the position measured from the end.
      //
      //    foo<AA,BB>() => ...
      //      //^0 ^1
      //    functionTypeVariables: [BB,AA]
      //
      //    foo<AA,BB>() => <UU,VV,WW>() => ...
      //        ^3 ^4        ^0 ^1 ^2
      //    functionTypeVariables: [BB,AA,WW,VV,UU]
      //
      for (FunctionTypeVariable variable in type.typeVariables.reversed) {
        functionTypeVariables.add(variable);
      }
    }

    visit(type.returnType, _);
    _emitCode(Recipe.startFunctionArguments);

    bool first = true;
    for (DartType parameterType in type.parameterTypes) {
      if (!first) {
        _emitCode(Recipe.separator);
      }
      visit(parameterType, _);
      first = false;
    }

    if (type.optionalParameterTypes.isNotEmpty) {
      first = true;
      _emitCode(Recipe.startOptionalGroup);
      for (DartType parameterType in type.optionalParameterTypes) {
        if (!first) {
          _emitCode(Recipe.separator);
        }
        visit(parameterType, _);
        first = false;
      }
      _emitCode(Recipe.endOptionalGroup);
    }

    void emitNamedGroup(List<String> names, List<DartType> types) {
      assert(names.length == types.length);
      first = true;
      _emitCode(Recipe.startNamedGroup);
      for (int i = 0; i < names.length; i++) {
        if (!first) {
          _emitCode(Recipe.separator);
        }
        _emitStringUnescaped(names[i]);
        _emitCode(Recipe.nameSeparator);
        visit(types[i], _);
        first = false;
      }
      _emitCode(Recipe.endNamedGroup);
    }

    // TODO(sra): These are optional named parameters. Handle required named
    // parameters the same way when they are implemented.
    if (type.namedParameterTypes.isNotEmpty) {
      emitNamedGroup(type.namedParameters, type.namedParameterTypes);
    }

    _emitCode(Recipe.endFunctionArguments);

    // Emit generic type bounds.
    if (type.typeVariables.isNotEmpty) {
      bool first = true;
      _emitCode(Recipe.startTypeArguments);
      for (FunctionTypeVariable typeVariable in type.typeVariables) {
        if (!first) {
          _emitCode(Recipe.separator);
        }
        visit(typeVariable.bound, _);
      }
      _emitCode(Recipe.endTypeArguments);
    }

    if (type.typeVariables.isNotEmpty) {
      // Exit generic function scope. Remove the type variables pushed at entry.
      functionTypeVariables.length -= type.typeVariables.length;
    }
  }

  @override
  void visitVoidType(VoidType type, _) {
    _emitCode(Recipe.pushVoid);
  }

  @override
  void visitTypedefType(TypedefType type, _) {
    visit(type.unaliased, _);
  }

  @override
  void visitFutureOrType(FutureOrType type, _) {
    visit(type.typeArgument, _);
    _emitCode(Recipe.wrapFutureOr);
  }
}