/*
 * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 */

package jdk.nashorn.internal.codegen;

import static jdk.nashorn.internal.ir.Node.NO_FINISH;
import static jdk.nashorn.internal.ir.Node.NO_LINE_NUMBER;
import static jdk.nashorn.internal.ir.Node.NO_TOKEN;

import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Deque;
import java.util.List;
import java.util.Objects;
import jdk.nashorn.internal.ir.AccessNode;
import jdk.nashorn.internal.ir.BinaryNode;
import jdk.nashorn.internal.ir.Block;
import jdk.nashorn.internal.ir.BlockLexicalContext;
import jdk.nashorn.internal.ir.BreakNode;
import jdk.nashorn.internal.ir.CallNode;
import jdk.nashorn.internal.ir.CaseNode;
import jdk.nashorn.internal.ir.ContinueNode;
import jdk.nashorn.internal.ir.Expression;
import jdk.nashorn.internal.ir.ExpressionStatement;
import jdk.nashorn.internal.ir.FunctionNode;
import jdk.nashorn.internal.ir.GetSplitState;
import jdk.nashorn.internal.ir.IdentNode;
import jdk.nashorn.internal.ir.IfNode;
import jdk.nashorn.internal.ir.JumpStatement;
import jdk.nashorn.internal.ir.JumpToInlinedFinally;
import jdk.nashorn.internal.ir.LiteralNode;
import jdk.nashorn.internal.ir.Node;
import jdk.nashorn.internal.ir.ReturnNode;
import jdk.nashorn.internal.ir.SetSplitState;
import jdk.nashorn.internal.ir.SplitNode;
import jdk.nashorn.internal.ir.SplitReturn;
import jdk.nashorn.internal.ir.Statement;
import jdk.nashorn.internal.ir.SwitchNode;
import jdk.nashorn.internal.ir.VarNode;
import jdk.nashorn.internal.ir.visitor.NodeVisitor;
import jdk.nashorn.internal.parser.Token;
import jdk.nashorn.internal.parser.TokenType;

A node visitor that replaces SplitNodes with anonymous function invocations and some additional constructs to support control flow across splits. By using this transformation, split functions are translated into ordinary JavaScript functions with nested anonymous functions. The transformations however introduce several AST nodes that have no JavaScript source representations (GetSplitState, SetSplitState, and SplitReturn), and therefore such function is no longer reparseable from its source. For that reason, split functions and their fragments are serialized in-memory and deserialized when they need to be recompiled either for deoptimization or for type specialization. NOTE: all leave*() methods for statements are returning their input nodes. That way, they will not mutate the original statement list in the block containing the statement, which is fine, as it'll be replaced by the lexical context when the block is left. If we returned something else (e.g. null), we'd cause a mutation in the enclosing block's statement list that is otherwise overwritten later anyway. /**
 * A node visitor that replaces {@link SplitNode}s with anonymous function invocations and some additional constructs
 * to support control flow across splits. By using this transformation, split functions are translated into ordinary
 * JavaScript functions with nested anonymous functions. The transformations however introduce several AST nodes that
 * have no JavaScript source representations ({@link GetSplitState}, {@link SetSplitState}, and {@link SplitReturn}),
 * and therefore such function is no longer reparseable from its source. For that reason, split functions and their
 * fragments are serialized in-memory and deserialized when they need to be recompiled either for deoptimization or
 * for type specialization.
 * NOTE: all {@code leave*()} methods for statements are returning their input nodes. That way, they will not mutate
 * the original statement list in the block containing the statement, which is fine, as it'll be replaced by the
 * lexical context when the block is left. If we returned something else (e.g. null), we'd cause a mutation in the
 * enclosing block's statement list that is otherwise overwritten later anyway.
 */
final class SplitIntoFunctions extends NodeVisitor<BlockLexicalContext> {
    private static final int FALLTHROUGH_STATE = -1;
    private static final int RETURN_STATE = 0;
    private static final int BREAK_STATE = 1;
    private static final int FIRST_JUMP_STATE = 2;

    private static final String THIS_NAME = CompilerConstants.THIS.symbolName();
    private static final String RETURN_NAME = CompilerConstants.RETURN.symbolName();
    // Used as the name of the formal parameter for passing the current value of :return symbol into a split fragment.
    private static final String RETURN_PARAM_NAME = RETURN_NAME + "-in";

    private final Deque<FunctionState> functionStates = new ArrayDeque<>();
    private final Deque<SplitState> splitStates = new ArrayDeque<>();
    private final Namespace namespace;

    private boolean artificialBlock = false;

    // -1 is program; we need to use negative ones
    private int nextFunctionId = -2;

    public SplitIntoFunctions(final Compiler compiler) {
        super(new BlockLexicalContext() {
            @Override
            protected Block afterSetStatements(final Block block) {
                for(final Statement stmt: block.getStatements()) {
                    assert !(stmt instanceof SplitNode);
                }
                return block;
            }
        });
        namespace = new Namespace(compiler.getScriptEnvironment().getNamespace());
    }

    @Override
    public boolean enterFunctionNode(final FunctionNode functionNode) {
        functionStates.push(new FunctionState(functionNode));
        return true;
    }

    @Override
    public Node leaveFunctionNode(final FunctionNode functionNode) {
        functionStates.pop();
        return functionNode;
    }

    @Override
    protected Node leaveDefault(final Node node) {
        if (node instanceof Statement) {
            appendStatement((Statement)node);
        }
        return node;
    }

    @Override
    public boolean enterSplitNode(final SplitNode splitNode) {
        getCurrentFunctionState().splitDepth++;
        splitStates.push(new SplitState(splitNode));
        return true;
    }

    @Override
    public Node leaveSplitNode(final SplitNode splitNode) {
        // Replace the split node with an anonymous function expression call.

        final FunctionState fnState = getCurrentFunctionState();

        final String name = splitNode.getName();
        final Block body = splitNode.getBody();
        final int firstLineNumber = body.getFirstStatementLineNumber();
        final long token = body.getToken();
        final int finish = body.getFinish();

        final FunctionNode originalFn = fnState.fn;
        assert originalFn == lc.getCurrentFunction();
        final boolean isProgram = originalFn.isProgram();

        // Change SplitNode({...}) into "function () { ... }", or "function (:return-in) () { ... }" (for program)
        final long newFnToken = Token.toDesc(TokenType.FUNCTION, nextFunctionId--, 0);
        final FunctionNode fn = new FunctionNode(
                originalFn.getSource(),
                body.getFirstStatementLineNumber(),
                newFnToken,
                finish,
                newFnToken,
                NO_TOKEN,
                namespace,
                createIdent(name),
                originalFn.getName() + "$" + name,
                isProgram ? Collections.singletonList(createReturnParamIdent()) : Collections.<IdentNode>emptyList(),
                null,
                FunctionNode.Kind.NORMAL,
                // We only need IS_SPLIT conservatively, in case it contains any array units so that we force
                // the :callee's existence, to force :scope to never be in a slot lower than 2. This is actually
                // quite a horrible hack to do with CodeGenerator.fixScopeSlot not trampling other parameters
                // and should go away once we no longer have array unit handling in codegen. Note however that
                // we still use IS_SPLIT as the criteria in CompilationPhase.SERIALIZE_SPLIT_PHASE.
                FunctionNode.IS_ANONYMOUS | FunctionNode.USES_ANCESTOR_SCOPE | FunctionNode.IS_SPLIT,
                body,
                null,
                originalFn.getModule(),
                originalFn.getDebugFlags()
        )
        .setCompileUnit(lc, splitNode.getCompileUnit());

        // Call the function:
        //     either "(function () { ... }).call(this)"
        //     or     "(function (:return-in) { ... }).call(this, :return)"
        // NOTE: Function.call() has optimized linking that basically does a pass-through to the function being invoked.
        // NOTE: CompilationPhase.PROGRAM_POINT_PHASE happens after this, so these calls are subject to optimistic
        // assumptions on their return value (when they return a value), as they should be.
        final IdentNode thisIdent = createIdent(THIS_NAME);
        final CallNode callNode = new CallNode(firstLineNumber, token, finish, new AccessNode(NO_TOKEN, NO_FINISH, fn, "call"),
                isProgram ? Arrays.<Expression>asList(thisIdent, createReturnIdent())
                          : Collections.<Expression>singletonList(thisIdent),
                false);

        final SplitState splitState = splitStates.pop();
        fnState.splitDepth--;

        final Expression callWithReturn;
        final boolean hasReturn = splitState.hasReturn;
        if (hasReturn && fnState.splitDepth > 0) {
            final SplitState parentSplit = splitStates.peek();
            if (parentSplit != null) {
                // Propagate hasReturn to parent split
                parentSplit.hasReturn = true;
            }
        }
        if (hasReturn || isProgram) {
            // capture return value: ":return = (function () { ... })();"
            callWithReturn = new BinaryNode(Token.recast(token, TokenType.ASSIGN), createReturnIdent(), callNode);
        } else {
            // no return value, just call : "(function () { ... })();"
            callWithReturn = callNode;
        }
        appendStatement(new ExpressionStatement(firstLineNumber, token, finish, callWithReturn));

        Statement splitStateHandler;

        final List<JumpStatement> jumpStatements = splitState.jumpStatements;
        final int jumpCount = jumpStatements.size();
        // There are jumps (breaks or continues) that need to be propagated outside the split node. We need to
        // set up a switch statement for them:
        // switch(:scope.getScopeState()) { ... }
        if (jumpCount > 0) {
            final List<CaseNode> cases = new ArrayList<>(jumpCount + (hasReturn ? 1 : 0));
            if (hasReturn) {
                // If the split node also contained a return, we'll slip it as a case in the switch statement
                addCase(cases, RETURN_STATE, createReturnFromSplit());
            }
            int i = FIRST_JUMP_STATE;
            for (final JumpStatement jump: jumpStatements) {
                addCase(cases, i++, enblockAndVisit(jump));
            }
            splitStateHandler = new SwitchNode(NO_LINE_NUMBER, token, finish, GetSplitState.INSTANCE, cases, null);
        } else {
            splitStateHandler = null;
        }

        // As the switch statement itself is breakable, an unlabelled break can't be in the switch statement,
        // so we need to test for it separately.
        if (splitState.hasBreak) {
            // if(:scope.getScopeState() == Scope.BREAK) { break; }
            splitStateHandler = makeIfStateEquals(firstLineNumber, token, finish, BREAK_STATE,
                    enblockAndVisit(new BreakNode(NO_LINE_NUMBER, token, finish, null)), splitStateHandler);
        }

        // Finally, if the split node had a return statement, but there were no external jumps, we didn't have
        // the switch statement to handle the return, so we need a separate if for it.
        if (hasReturn && jumpCount == 0) {
            // if (:scope.getScopeState() == Scope.RETURN) { return :return; }
            splitStateHandler = makeIfStateEquals(NO_LINE_NUMBER, token, finish, RETURN_STATE,
                    createReturnFromSplit(), splitStateHandler);
        }

        if (splitStateHandler != null) {
            appendStatement(splitStateHandler);
        }

        return splitNode;
    }

    private static void addCase(final List<CaseNode> cases, final int i, final Block body) {
        cases.add(new CaseNode(NO_TOKEN, NO_FINISH, intLiteral(i), body));
    }

    private static LiteralNode<Number> intLiteral(final int i) {
        return LiteralNode.newInstance(NO_TOKEN, NO_FINISH, i);
    }

    private static Block createReturnFromSplit() {
        return new Block(NO_TOKEN, NO_FINISH, createReturnReturn());
    }

    private static ReturnNode createReturnReturn() {
        return new ReturnNode(NO_LINE_NUMBER, NO_TOKEN, NO_FINISH, createReturnIdent());
    }

    private static IdentNode createReturnIdent() {
        return createIdent(RETURN_NAME);
    }

    private static IdentNode createReturnParamIdent() {
        return createIdent(RETURN_PARAM_NAME);
    }

    private static IdentNode createIdent(final String name) {
        return new IdentNode(NO_TOKEN, NO_FINISH, name);
    }

    private Block enblockAndVisit(final JumpStatement jump) {
        artificialBlock = true;
        final Block block = (Block)new Block(NO_TOKEN, NO_FINISH, jump).accept(this);
        artificialBlock = false;
        return block;
    }

    private static IfNode makeIfStateEquals(final int lineNumber, final long token, final int finish,
            final int value, final Block pass, final Statement fail) {
        return new IfNode(lineNumber, token, finish,
                new BinaryNode(Token.recast(token, TokenType.EQ_STRICT),
                        GetSplitState.INSTANCE, intLiteral(value)),
                pass,
                fail == null ? null : new Block(NO_TOKEN, NO_FINISH, fail));
    }

    @Override
    public boolean enterVarNode(final VarNode varNode) {
        // ES6 block scoped declarations are already placed at their proper position by splitter
        if (!inSplitNode() || varNode.isBlockScoped()) {
            return super.enterVarNode(varNode);
        }

        final Expression init = varNode.getInit();

        // Move a declaration-only var statement to the top of the outermost function.
        getCurrentFunctionState().varStatements.add(varNode.setInit(null));
        // If it had an initializer, replace it with an assignment expression statement. Note that "var" is a
        // statement, so it doesn't contribute to :return of the programs, therefore we are _not_ adding a
        // ":return = ..." assignment around the original assignment.
        if (init != null) {
            final long token = Token.recast(varNode.getToken(), TokenType.ASSIGN);
            new ExpressionStatement(varNode.getLineNumber(), token, varNode.getFinish(),
                    new BinaryNode(token, varNode.getName(), varNode.getInit())).accept(this);
        }

        return false;
    }

    @Override
    public Node leaveBlock(final Block block) {
        if (!artificialBlock) {
            if (lc.isFunctionBody()) {
                // Prepend declaration-only var statements to the top of the statement list.
                lc.prependStatements(getCurrentFunctionState().varStatements);
            } else if (lc.isSplitBody()) {
                appendSplitReturn(FALLTHROUGH_STATE, NO_LINE_NUMBER);
                if (getCurrentFunctionState().fn.isProgram()) {
                    // If we're splitting the program, make sure every shard ends with "return :return" and
                    // begins with ":return = :return-in;".
                    lc.prependStatement(new ExpressionStatement(NO_LINE_NUMBER, NO_TOKEN, NO_FINISH,
                            new BinaryNode(Token.toDesc(TokenType.ASSIGN, 0, 0), createReturnIdent(), createReturnParamIdent())));
                }
            }
        }
        return block;
    }

    @Override
    public Node leaveBreakNode(final BreakNode breakNode) {
        return leaveJumpNode(breakNode);
    }

    @Override
    public Node leaveContinueNode(final ContinueNode continueNode) {
        return leaveJumpNode(continueNode);
    }

    @Override
    public Node leaveJumpToInlinedFinally(final JumpToInlinedFinally jumpToInlinedFinally) {
        return leaveJumpNode(jumpToInlinedFinally);
    }

    private JumpStatement leaveJumpNode(final JumpStatement jump) {
        if (inSplitNode()) {
            final SplitState splitState = getCurrentSplitState();
            final SplitNode splitNode = splitState.splitNode;
            if (lc.isExternalTarget(splitNode, jump.getTarget(lc))) {
                appendSplitReturn(splitState.getSplitStateIndex(jump), jump.getLineNumber());
                return jump;
            }
        }
        appendStatement(jump);
        return jump;
    }

    private void appendSplitReturn(final int splitState, final int lineNumber) {
        appendStatement(new SetSplitState(splitState, lineNumber));
        if (getCurrentFunctionState().fn.isProgram()) {
            // If we're splitting the program, make sure every fragment passes back :return
            appendStatement(createReturnReturn());
        } else {
            appendStatement(SplitReturn.INSTANCE);
        }
    }

    @Override
    public Node leaveReturnNode(final ReturnNode returnNode) {
        if(inSplitNode()) {
            appendStatement(new SetSplitState(RETURN_STATE, returnNode.getLineNumber()));
            getCurrentSplitState().hasReturn = true;
        }
        appendStatement(returnNode);
        return returnNode;
    }

    private void appendStatement(final Statement statement) {
        lc.appendStatement(statement);
    }

    private boolean inSplitNode() {
        return getCurrentFunctionState().splitDepth > 0;
    }

    private FunctionState getCurrentFunctionState() {
        return functionStates.peek();
    }

    private SplitState getCurrentSplitState() {
        return splitStates.peek();
    }

    private static class FunctionState {
        final FunctionNode fn;
        final List<Statement> varStatements = new ArrayList<>();
        int splitDepth;

        FunctionState(final FunctionNode fn) {
            this.fn = fn;
        }
    }

    private static class SplitState {
        final SplitNode splitNode;
        boolean hasReturn;
        boolean hasBreak;

        final List<JumpStatement> jumpStatements = new ArrayList<>();

        int getSplitStateIndex(final JumpStatement jump) {
            if (jump instanceof BreakNode && jump.getLabelName() == null) {
                // Unlabelled break is a special case
                hasBreak = true;
                return BREAK_STATE;
            }

            int i = 0;
            for(final JumpStatement exJump: jumpStatements) {
                if (jump.getClass() == exJump.getClass() && Objects.equals(jump.getLabelName(), exJump.getLabelName())) {
                    return i + FIRST_JUMP_STATE;
                }
                ++i;
            }
            jumpStatements.add(jump);
            return i + FIRST_JUMP_STATE;
        }

        SplitState(final SplitNode splitNode) {
            this.splitNode = splitNode;
        }
    }
}