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package jdk.nashorn.internal.codegen;

import static jdk.nashorn.internal.runtime.linker.NashornCallSiteDescriptor.CALLSITE_OPTIMISTIC;

import java.util.Arrays;
import java.util.EnumSet;
import jdk.nashorn.internal.codegen.types.Type;
import jdk.nashorn.internal.ir.Symbol;
import jdk.nashorn.internal.runtime.ScriptObject;

A scope call or get operation that can be shared by several callsites. This generates a static
method that wraps the invokedynamic instructions to get or call scope variables.
The rationale for this is that initial linking of invokedynamic callsites is expensive,
so by sharing them we can reduce startup overhead and allow very large scripts to run that otherwise wouldn't.
Static methods generated by this class expect two parameters in addition to the parameters of the
function call: The current scope object and the depth of the target scope relative to the scope argument
for when this is known at compile-time (fast-scope access).
The second argument may be -1 for non-fast-scope symbols, in which case the scope chain is checked
for each call. This may cause callsite invalidation when the shared method is used from different
scopes, but such sharing of non-fast scope calls may still be necessary for very large scripts.
Scope calls must not be shared between normal callsites and callsites contained in a with
statement as this condition is not handled by current guards and will cause a runtime error.
/**
 * A scope call or get operation that can be shared by several callsites. This generates a static
 * method that wraps the invokedynamic instructions to get or call scope variables.
 * The rationale for this is that initial linking of invokedynamic callsites is expensive,
 * so by sharing them we can reduce startup overhead and allow very large scripts to run that otherwise wouldn't.
 *
 * <p>Static methods generated by this class expect two parameters in addition to the parameters of the
 * function call: The current scope object and the depth of the target scope relative to the scope argument
 * for when this is known at compile-time (fast-scope access).</p>
 *
 * <p>The second argument may be -1 for non-fast-scope symbols, in which case the scope chain is checked
 * for each call. This may cause callsite invalidation when the shared method is used from different
 * scopes, but such sharing of non-fast scope calls may still be necessary for very large scripts.</p>
 *
 * <p>Scope calls must not be shared between normal callsites and callsites contained in a <tt>with</tt>
 * statement as this condition is not handled by current guards and will cause a runtime error.</p>
 */
class SharedScopeCall {

    
Threshold for using shared scope calls with fast scope access. /** Threshold for using shared scope calls with fast scope access. */
    public static final int FAST_SCOPE_CALL_THRESHOLD = 4;
    
Threshold for using shared scope calls with slow scope access. /** Threshold for using shared scope calls with slow scope access. */
    public static final int SLOW_SCOPE_CALL_THRESHOLD = 500;
    
Threshold for using shared scope gets with fast scope access. /** Threshold for using shared scope gets with fast scope access. */
    public static final int FAST_SCOPE_GET_THRESHOLD  = 200;

    final Type valueType;
    final Symbol symbol;
    final Type returnType;
    final Type[] paramTypes;
    final int flags;
    final boolean isCall;
    private CompileUnit compileUnit;
    private String methodName;
    private String staticSignature;

    
Constructor.
Params:
symbol – the symbol
valueType – the type of the value
returnType – the return type
paramTypes – the function parameter types
flags – the callsite flags/**
     * Constructor.
     *
     * @param symbol the symbol
     * @param valueType the type of the value
     * @param returnType the return type
     * @param paramTypes the function parameter types
     * @param flags the callsite flags
     */
    SharedScopeCall(final Symbol symbol, final Type valueType, final Type returnType, final Type[] paramTypes, final int flags) {
        this.symbol = symbol;
        this.valueType = valueType;
        this.returnType = returnType;
        this.paramTypes = paramTypes;
        assert (flags & CALLSITE_OPTIMISTIC) == 0;
        this.flags = flags;
        // If paramTypes is not null this is a call, otherwise it's just a get.
        this.isCall = paramTypes != null;
    }

    @Override
    public int hashCode() {
        return symbol.hashCode() ^ returnType.hashCode() ^ Arrays.hashCode(paramTypes) ^ flags;
    }

    @Override
    public boolean equals(final Object obj) {
        if (obj instanceof SharedScopeCall) {
            final SharedScopeCall c = (SharedScopeCall) obj;
            return symbol.equals(c.symbol)
                    && flags == c.flags
                    && returnType.equals(c.returnType)
                    && Arrays.equals(paramTypes, c.paramTypes);
        }
        return false;
    }

    
Set the compile unit and method name.
Params:
compileUnit – the compile unit
methodName – the method name/**
     * Set the compile unit and method name.
     * @param compileUnit the compile unit
     * @param methodName the method name
     */
    protected void setClassAndName(final CompileUnit compileUnit, final String methodName) {
        this.compileUnit = compileUnit;
        this.methodName  = methodName;
    }

    
Generate the invoke instruction for this shared scope call.
Params:
method – the method emitter
Returns:
the method emitter/**
     * Generate the invoke instruction for this shared scope call.
     * @param method the method emitter
     * @return the method emitter
     */
    public MethodEmitter generateInvoke(final MethodEmitter method) {
        return method.invokestatic(compileUnit.getUnitClassName(), methodName, getStaticSignature());
    }

    
Generate the method that implements the scope get or call.
/**
     * Generate the method that implements the scope get or call.
     */
    protected void generateScopeCall() {
        final ClassEmitter classEmitter = compileUnit.getClassEmitter();
        final EnumSet<ClassEmitter.Flag> methodFlags = EnumSet.of(ClassEmitter.Flag.STATIC);

        // This method expects two fixed parameters in addition to any parameters that may be
        // passed on to the function: A ScriptObject representing the caller's current scope object,
        // and an int specifying the distance to the target scope containing the symbol we want to
        // access, or -1 if this is not known at compile time (e.g. because of a "with" or "eval").

        final MethodEmitter method = classEmitter.method(methodFlags, methodName, getStaticSignature());
        method.begin();

        // Load correct scope by calling getProto() on the scope argument as often as specified
        // by the second argument.
        final Label parentLoopStart = new Label("parent_loop_start");
        final Label parentLoopDone  = new Label("parent_loop_done");
        method.load(Type.OBJECT, 0);
        method.label(parentLoopStart);
        method.load(Type.INT, 1);
        method.iinc(1, -1);
        method.ifle(parentLoopDone);
        method.invoke(ScriptObject.GET_PROTO);
        method._goto(parentLoopStart);
        method.label(parentLoopDone);

        assert !isCall || valueType.isObject(); // Callables are always objects
        // If flags are optimistic, but we're doing a call, remove optimistic flags from the getter, as they obviously
        // only apply to the call.
        method.dynamicGet(valueType, symbol.getName(), isCall ? CodeGenerator.nonOptimisticFlags(flags) : flags, isCall, false);

        // If this is a get we're done, otherwise call the value as function.
        if (isCall) {
            method.convert(Type.OBJECT);
            // ScriptFunction will see CALLSITE_SCOPE and will bind scope accordingly.
            method.loadUndefined(Type.OBJECT);
            int slot = 2;
            for (final Type type : paramTypes) {
                method.load(type, slot);
                slot += type.getSlots();
            }
            // Shared scope calls disabled in optimistic world. TODO is this right?
            method.dynamicCall(returnType, 2 + paramTypes.length, flags, symbol.getName());
        }

        method._return(returnType);
        method.end();
    }

    private String getStaticSignature() {
        if (staticSignature == null) {
            if (paramTypes == null) {
                staticSignature = Type.getMethodDescriptor(returnType, Type.typeFor(ScriptObject.class), Type.INT);
            } else {
                final Type[] params = new Type[paramTypes.length + 2];
                params[0] = Type.typeFor(ScriptObject.class);
                params[1] = Type.INT;
                System.arraycopy(paramTypes, 0, params, 2, paramTypes.length);
                staticSignature = Type.getMethodDescriptor(returnType, params);
            }
        }
        return staticSignature;
    }

    @Override
    public String toString() {
        return methodName + " " + staticSignature;
    }

}