// Copyright (c) 2013, 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 dart2js.ir_builder;

import 'ir_nodes.dart';
import '../elements/elements.dart';
import '../dart2jslib.dart';
import '../source_file.dart';
import '../tree/tree.dart';
import '../scanner/scannerlib.dart' show Token;
import '../js_backend/js_backend.dart' show JavaScriptBackend;
import 'ir_pickler.dart' show Unpickler;

/**
 * This task iterates through all resolved elements and builds [IrNode]s. The
 * nodes are stored in the [nodes] map and accessible through [hasIr] and
 * [getIr].
 *
 * The functionality of the IrNodes is added gradually, therefore elements might
 * have an IR or not, depending on the language features that are used. For
 * elements that do have an IR, the tree [Node]s and the [Token]s are not used
 * in the rest of the compilation. This is ensured by setting the element's
 * cached tree to [:null:] and also breaking the token stream to crash future
 * attempts to parse.
 *
 * The type inferrer works on either IR nodes or tree nodes. The IR nodes are
 * then translated into the SSA form for optimizations and code generation.
 * Long-term, once the IR supports the full language, the backend can be
 * re-implemented to work directly on the IR.
 */
class IrBuilderTask extends CompilerTask {
  final Map<Element, IrNode> nodes = new Map<Element, IrNode>();

  IrBuilderTask(Compiler compiler) : super(compiler);

  String get name => 'IR builder';

  bool hasIr(Element element) => nodes.containsKey(element.implementation);

  IrNode getIr(Element element) => nodes[element.implementation];

  void buildNodes() {
    if (!irEnabled()) return;
    measure(() {
      Map<Element, TreeElements> resolved =
          compiler.enqueuer.resolution.resolvedElements;
      resolved.forEach((Element element, TreeElements elementsMapping) {
        if (canBuild(element)) {
          element = element.implementation;

          SourceFile sourceFile = elementSourceFile(element);
          IrNodeBuilderVisitor visitor =
              new IrNodeBuilderVisitor(elementsMapping, compiler, sourceFile);
          IrNode irNode;
          ElementKind kind = element.kind;
          if (kind == ElementKind.GENERATIVE_CONSTRUCTOR) {
            // TODO(lry): build ir for constructors.
          } else if (kind == ElementKind.GENERATIVE_CONSTRUCTOR_BODY ||
              kind == ElementKind.FUNCTION ||
              kind == ElementKind.GETTER ||
              kind == ElementKind.SETTER) {
            irNode = visitor.buildMethod(element);
          } else if (kind == ElementKind.FIELD) {
            // TODO(lry): build ir for lazy initializers of static fields.
          } else {
            compiler.internalErrorOnElement(element,
                'unexpected element kind $kind');
          }

          if (irNode != null) {
            assert(() {
              // In host-checked mode, serialize and de-serialize the IrNode.
              List<int> data = irNode.pickle();
              irNode = new Unpickler(compiler).unpickle(data);
              return true;
            });
            nodes[element] = irNode;
            unlinkTreeAndToken(element);
          }
        }
      });
    });
  }

  bool irEnabled() {
    // TODO(lry): support checked-mode checks.
    if (compiler.enableTypeAssertions ||
        compiler.backend is !JavaScriptBackend ||
        compiler.enableConcreteTypeInference) {
      return false;
    }
    return true;
  }

  bool canBuild(Element element) {
    // TODO(lry): support lazy initializers.
    FunctionElement function = element.asFunctionElement();
    if (function == null) return false;

    // TODO(lry): support functions with parameters.
    FunctionSignature signature = function.computeSignature(compiler);
    if (signature.parameterCount > 0) return false;

    // TODO(lry): support intercepted methods. Then the dependency on
    // JavaScriptBackend will go away.
    JavaScriptBackend backend = compiler.backend;
    if (backend.isInterceptedMethod(element)) return false;

    // TODO(lry): support native functions (also in [visitReturn]).
    if (function.isNative()) return false;

    return true;
  }

  void unlinkTreeAndToken(element) {
    element.beginToken.next = null;
    element.cachedNode = null;
  }

  SourceFile elementSourceFile(Element element) {
    if (element is FunctionElement) {
      FunctionElement functionElement = element;
      if (functionElement.patch != null) element = functionElement.patch;
    }
    return element.getCompilationUnit().script.file;
  }
}

/**
 * A tree visitor that builds [IrNodes]. The visit methods add statements using
 * to the [builder] and return the last added statement for trees that represent
 * an expression.
 */
class IrNodeBuilderVisitor extends ResolvedVisitor<IrNode> {
  final SourceFile sourceFile;

  IrNodeBuilderVisitor(
      TreeElements elements,
      Compiler compiler,
      this.sourceFile)
    : super(elements, compiler);

  IrBuilder builder;

  /**
   * Builds the [IrFunction] for a function element. In case the function
   * uses features that cannot be expressed in the IR, this function returns
   * [:null:].
   */
  IrFunction buildMethod(FunctionElement functionElement) {
    return nullIfGiveup(() => buildMethodInternal(functionElement));
  }

  IrFunction buildMethodInternal(FunctionElement functionElement) {
    assert(invariant(functionElement, functionElement.isImplementation));
    FunctionExpression function = functionElement.parseNode(compiler);
    assert(function != null);
    assert(!function.modifiers.isExternal());
    assert(elements[function] != null);

    int endPosition = function.getEndToken().charOffset;
    int namePosition = elements[function].position().charOffset;
    IrFunction result = new IrFunction(
        nodePosition(function), endPosition, namePosition, <IrNode>[]);
    builder = new IrBuilder(this);
    builder.enterBlock();
    if (function.hasBody()) {
      function.body.accept(this);
      ensureReturn(function);
      result.statements
        ..addAll(builder.constants.values)
        ..addAll(builder.block.statements);
    }
    builder.exitBlock();
    return result;
  }

  ConstantSystem get constantSystem => compiler.backend.constantSystem;

  /* int | PositionWithIdentifierName */ nodePosition(Node node) {
    Token token = node.getBeginToken();
    if (token.isIdentifier()) {
      return new PositionWithIdentifierName(token.charOffset, token.value);
    } else {
      return token.charOffset;
    }
  }

  bool get blockReturns => builder.block.hasReturn;

  /**
   * Add an explicit [:return null:] for functions that don't have a return
   * statement on each branch. This includes functions with an empty body,
   * such as [:foo(){ }:].
   */
  void ensureReturn(FunctionExpression node) {
    if (blockReturns) return;
    IrConstant nullValue =
        builder.addConstant(constantSystem.createNull(), node);
    builder.addStatement(new IrReturn(nodePosition(node), nullValue));
  }

  IrNode visitBlock(Block node) {
    for (Node n in node.statements.nodes) {
      n.accept(this);
      if (blockReturns) return null;
    }
  }

  IrNode visitReturn(Return node) {
    assert(!blockReturns);
    IrNode value;
    // TODO(lry): support native returns.
    if (node.beginToken.value == 'native') return giveup();
    if (node.expression == null) {
      value = builder.addConstant(constantSystem.createNull(), node);
    } else {
      value = node.expression.accept(this);
    }
    builder.addStatement(new IrReturn(nodePosition(node), value));
    builder.block.hasReturn = true;
  }

  IrConstant visitLiteralBool(LiteralBool node) {
    return builder.addConstant(constantSystem.createBool(node.value), node);
  }

  IrConstant visitLiteralDouble(LiteralDouble node) {
    return builder.addConstant(constantSystem.createDouble(node.value), node);
  }

  IrConstant visitLiteralInt(LiteralInt node) {
    return builder.addConstant(constantSystem.createInt(node.value), node);
  }

  IrConstant visitLiteralString(LiteralString node) {
    Constant value = constantSystem.createString(node.dartString);
    return builder.addConstant(value, node);
  }

  IrConstant visitLiteralNull(LiteralNull node) {
    return builder.addConstant(constantSystem.createNull(), node);
  }

//  TODO(lry): other literals.
//  IrNode visitLiteralList(LiteralList node) => visitExpression(node);
//  IrNode visitLiteralMap(LiteralMap node) => visitExpression(node);
//  IrNode visitLiteralMapEntry(LiteralMapEntry node) => visitNode(node);
//  IrNode visitLiteralSymbol(LiteralSymbol node) => visitExpression(node);

  IrNode visitAssert(Send node) {
    return giveup();
  }

  IrNode visitClosureSend(Send node) {
    return giveup();
  }

  IrNode visitDynamicSend(Send node) {
    return giveup();
  }

  IrNode visitGetterSend(Send node) {
    return giveup();
  }

  IrNode visitOperatorSend(Send node) {
    return giveup();
  }

  IrNode visitStaticSend(Send node) {
    return giveup();
  }

  IrNode visitSuperSend(Send node) {
    return giveup();
  }

  IrNode visitTypeReferenceSend(Send node) {
    return giveup();
  }

  static final String ABORT_IRNODE_BUILDER = "IrNode builder aborted";

  IrNode giveup() => throw ABORT_IRNODE_BUILDER;

  IrNode nullIfGiveup(IrNode action()) {
    try {
      return action();
    } catch(e) {
      if (e == ABORT_IRNODE_BUILDER) return null;
      rethrow;
    }
  }

  void internalError(String reason, {Node node}) {
    giveup();
  }
}

class IrBuilder {
  final IrNodeBuilderVisitor visitor;
  IrBuilder(this.visitor);

  List<BlockBuilder> blockBuilders = <BlockBuilder>[];

  BlockBuilder get block => blockBuilders.last;

  Map<Constant, IrConstant> constants = <Constant, IrConstant>{};

  IrConstant addConstant(Constant value, Node node) {
    return constants.putIfAbsent(
      value, () => new IrConstant(visitor.nodePosition(node), value));
  }

  IrNode addStatement(IrNode statement) {
    block.statements.add(statement);
    return statement;
  }

  void enterBlock() {
    blockBuilders.add(new BlockBuilder());
  }

  void exitBlock() {
    blockBuilders.removeLast();
  }
}

class BlockBuilder {
  List<IrNode> statements = <IrNode>[];
  bool hasReturn = false;
}