package org.simantics.db.layer0.scl;

import java.util.ArrayList;
import java.util.List;

import org.simantics.databoard.Bindings;
import org.simantics.db.ReadGraph;
import org.simantics.db.Resource;
import org.simantics.db.exception.DatabaseException;
import org.simantics.db.exception.RuntimeDatabaseException;
import org.simantics.db.request.Read;
import org.simantics.layer0.Layer0;
import org.simantics.scl.compiler.common.names.Name;
import org.simantics.scl.compiler.constants.StringConstant;
import org.simantics.scl.compiler.elaboration.expressions.EApply;
import org.simantics.scl.compiler.elaboration.expressions.EConstant;
import org.simantics.scl.compiler.elaboration.expressions.ELiteral;
import org.simantics.scl.compiler.elaboration.expressions.ESimpleLet;
import org.simantics.scl.compiler.elaboration.expressions.EVariable;
import org.simantics.scl.compiler.elaboration.expressions.Expression;
import org.simantics.scl.compiler.elaboration.expressions.Variable;
import org.simantics.scl.compiler.environment.AbstractLocalEnvironment;
import org.simantics.scl.compiler.environment.Environment;
import org.simantics.scl.compiler.environment.LocalEnvironment;
import org.simantics.scl.compiler.errors.CompilationError;
import org.simantics.scl.compiler.runtime.RuntimeEnvironment;
import org.simantics.scl.compiler.top.ExpressionEvaluator;
import org.simantics.scl.compiler.top.SCLExpressionCompilationException;
import org.simantics.scl.compiler.types.TCon;
import org.simantics.scl.compiler.types.Type;
import org.simantics.scl.compiler.types.Types;
import org.simantics.scl.compiler.types.exceptions.MatchException;
import org.simantics.scl.compiler.types.kinds.Kinds;
import org.simantics.scl.compiler.types.util.MultiFunction;
import org.simantics.scl.runtime.SCLContext;
import org.simantics.scl.runtime.function.Function1;
import org.simantics.utils.datastructures.Pair;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import gnu.trove.map.hash.THashMap;

/**
 * <p>This is a base implementation for compiling expressions stored into 
 * graph. It provides a skeleton and a set of methods that must be
 * implemented to get a concrete compilation request.
 * 
 * <p>The request returns an SCL function with type {@code EvaluationContext -> Result}
 * where {@code EvaluationContext} is the type given by {@link #getContextVariableType()}
 * and {@code Result} is the type of the expression that can be optionally restricted
 * by {@link #getExpectedType(ReadGraph, AbstractExpressionCompilationContext)}.
 * 
 * <p>Compilation calls {@link #getCompilationContext(ReadGraph)} to read all information
 * that is needed about the context of the resource during compilation. The result must
 * extend the type {@link AbstractExpressionCompilationContext} including at least information about 
 * {@link RuntimeEnvironment}.
 * 
 * <p>Compilation calls {@link #getVariableAccessExpression(ReadGraph, AbstractExpressionCompilationContext, Variable, String)}
 * to get access to local environment. The method may return null if the variable is not defined.
 * 
 * @author Hannu Niemist&ouml;
 *
 * @param <Context>
 */
public abstract class AbstractExpressionCompilationRequest<CompilationContext extends AbstractExpressionCompilationContext,EvaluationContext>
implements Read<Function1<EvaluationContext,Object>> {

    private static final Logger LOGGER = LoggerFactory.getLogger(AbstractExpressionCompilationRequest.class);

    protected static final Type RESOURCE = Types.con("Simantics/DB", "Resource");
    protected static final Type VARIABLE = Types.con("Simantics/Variables", "Variable");
    protected static Name PROPERTY_VALUE = Name.create("Simantics/Variables", "propertyValue");
    protected static Name VARIABLE_PARENT = Name.create("Simantics/Variables", "variableParent");
    protected static Name FROM_DOUBLE = Name.create("Prelude", "fromDouble");
    protected static Name TO_DOUBLE = Name.create("Prelude", "toDouble");
    protected static Name FROM_DYNAMIC = Name.create("Prelude", "fromDynamic");

    private static final Type DEFAULT_EXPECTED_EFFECT = Types.union(new Type[] {Types.PROC, Types.READ_GRAPH});

    /**
     * Returns the expression that will be compiled in textual form.
     */
    protected abstract String getExpressionText(ReadGraph graph) throws DatabaseException;
    /**
     * Returns the context that is used for the compilation of the expression. The context
     * contains information about available constants and variables.
     */
    protected abstract CompilationContext getCompilationContext(ReadGraph graph) throws DatabaseException;
    /**
     * This should return the SCL type corresponding to generic type parameter {@code EvaluationContext}.
     */
    protected abstract Type getContextVariableType();
    /**
     * Returns <code>null</code>, if variable {@code name} is not defined.
     */
    protected abstract Expression getVariableAccessExpression(ReadGraph graph,
            CompilationContext context, Variable contextVariable, String name) throws DatabaseException;

    protected Type getExpectedType(ReadGraph graph, CompilationContext context) throws DatabaseException {
        return Types.metaVar(Kinds.STAR);
    }

    protected Type getExpectedEffect(ReadGraph graph, CompilationContext context) throws DatabaseException {
        return DEFAULT_EXPECTED_EFFECT;
    }
    
    protected ExpressionEvaluator prepareEvaluator(final ReadGraph graph, final CompilationContext context, Type expectedType) throws DatabaseException {
        final Variable contextVariable = new Variable("context", getContextVariableType());
        LocalEnvironment localEnvironment = new AbstractLocalEnvironment() {
            THashMap<String,Pair<Variable,Expression>> precalculatedVariables = new THashMap<String,Pair<Variable,Expression>>(); 
            @Override
            public Expression resolve(Environment environment, String localName) {
                Pair<Variable,Expression> precalculatedVariable = precalculatedVariables.get(localName);
                if(precalculatedVariable == null) {
                    try {
                        Expression value = getVariableAccessExpression(graph, context, contextVariable, localName);
                        if(value == null)
                            return null;
                        Variable variable = new Variable(localName);
                        precalculatedVariable = Pair.make(variable, value);
                        precalculatedVariables.put(localName, precalculatedVariable);
                    } catch (DatabaseException e) {
                        throw new RuntimeDatabaseException(e);
                    }
                }
                return new EVariable(precalculatedVariable.first);
            }
            @Override
            public Expression preDecorateExpression(Expression expression) {
                for(Pair<Variable,Expression> precalculatedVariable : precalculatedVariables.values())
                    expression = new ESimpleLet(precalculatedVariable.first, precalculatedVariable.second, expression);
                return expression;
            }
            @Override
            protected Variable[] getContextVariables() {
                return new Variable[] { contextVariable };
            }
        };

        String expressionText = getExpressionText(graph);
        return new ExpressionEvaluator(context.runtimeEnvironment, expressionText)
            .localEnvironment(localEnvironment)
            .expectedType(expectedType)
            .parseAsBlock(parseAsBlock());
    }
    
    protected boolean parseAsBlock() {
        return false;
    }

    /*
     * Override this to provide location information in compilation error situations. 
     */
    protected String getContextDescription(ReadGraph graph) throws DatabaseException {
        return toString();
    }
    
    @SuppressWarnings("unchecked")
    protected Function1<EvaluationContext, Object> eval(ExpressionEvaluator evaluator, ReadGraph graph) throws DatabaseException {
        Object oldGraph = SCLContext.getCurrent().put("graph", graph);
        try {
            return (Function1<EvaluationContext,Object>)evaluator.eval();
        } catch(RuntimeDatabaseException e) {
            LOGGER.error("Failed to evaluate SCL expression", e);
            if(e.getCause() instanceof DatabaseException)
                throw (DatabaseException)e.getCause();
            else
                throw e;
        } catch (SCLExpressionCompilationException e) {
            StringBuilder b = new StringBuilder();
            b.append("Couldn't compile '");
            b.append(evaluator.getExpressionText());
            b.append("' in ");
            b.append(getContextDescription(graph));
            b.append("':\n");
            StringBuilder b2 = new StringBuilder();
            for(CompilationError error : e.getErrors()) {
                b2.append(error.description);
                b2.append('\n');
            }
            SCLDatabaseException exception = new SCLDatabaseException(b.toString()+b2.toString(), b2.toString(), e.getErrors()); 
            throw exception; 
        } catch(Throwable e) {
            // Should not happen!
            LOGGER.error("This error should never happen", e);
            throw new RuntimeException(e);
        } finally {
            SCLContext.getCurrent().put("graph", oldGraph);
        }
    }

    public List<TCon> getExpressionEffects(final ReadGraph graph) throws DatabaseException {
        CompilationContext context = getCompilationContext(graph);
        Type type = Types.metaVar(Kinds.STAR);
        eval(prepareEvaluator(graph, context, type), graph);

        try {
            MultiFunction mfun = Types.matchFunction(type, 1);
            ArrayList<TCon> concreteEffects = new ArrayList<TCon>();
            mfun.effect.collectConcreteEffects(concreteEffects);
            return concreteEffects;
        } catch(MatchException e) {
            // Should not happen!
            LOGGER.error("Failed to get expression effects", e);
            throw new RuntimeException(e);
        }
    }

    @Override
    public Function1<EvaluationContext,Object> perform(final ReadGraph graph) throws DatabaseException {
        CompilationContext context = getCompilationContext(graph);
        return eval(prepareEvaluator(graph, context, getExpectedType(graph, context)), graph);
    }

    protected static Expression getProperty(Environment environment, Expression variable, String propertyName, Type type) {
        return new EApply(
                new EConstant(environment.getValue(FROM_DYNAMIC), type),
                new EApply(
                        new EConstant(environment.getValue(PROPERTY_VALUE), Types.DYNAMIC),
                        variable,
                        new ELiteral(new StringConstant(propertyName))));
    }

    protected static Expression getPropertyFlexible(Environment environment, Expression variable, String propertyName, Type type) {
        return makeTypeFlexible(environment, getProperty(environment, variable, propertyName, type), type);
    }

    protected static Expression makeTypeFlexible(Environment environment, Expression base, Type originalType) {
        if(originalType.equals(Types.DOUBLE))
            return new EApply(
                    new EConstant(environment.getValue(FROM_DOUBLE)),
                    base);
        else if(originalType.equals(Types.FLOAT))
            return new EApply(
                    new EConstant(environment.getValue(FROM_DOUBLE)),
                    new EApply(
                            new EConstant(environment.getValue(TO_DOUBLE), Types.FLOAT),
                            base));
        else
            return base;
    }

    protected static String resolveExpectedValueType(ReadGraph graph, Resource predicate) throws DatabaseException {
        Layer0 L0 = Layer0.getInstance(graph);
        return graph.getPossibleRelatedValue(predicate, L0.RequiresValueType, Bindings.STRING);
    }

    @Override
    public abstract int hashCode();

    @Override
    public abstract boolean equals(Object obj);
}