package org.basex.query.expr.gflwor;

import static org.basex.query.QueryText.*;

import java.util.*;

import org.basex.query.*;
import org.basex.query.expr.*;
import org.basex.query.func.*;
import org.basex.query.iter.*;
import org.basex.query.util.*;
import org.basex.query.value.*;
import org.basex.query.value.item.*;
import org.basex.query.value.node.*;
import org.basex.query.value.type.*;
import org.basex.query.var.*;
import org.basex.util.ft.*;
import org.basex.util.hash.*;

/**
 * FLWOR {@code let} clause, binding an expression to a variable.
 *
 * @author BaseX Team 2005-23, BSD License
 * @author Leo Woerteler
 */
public final class Let extends ForLet {
  /**
   * Constructor.
   * @param var variable
   * @param expr expression
   */
  public Let(final Var var, final Expr expr) {
    this(var, expr, false);
  }

  /**
   * Constructor.
   * @param var variable
   * @param expr expression
   * @param scoring scoring flag
   */
  public Let(final Var var, final Expr expr, final boolean scoring) {
    super(var.info, scoring ? SeqType.DOUBLE_O : SeqType.ITEM_ZM, var, expr, scoring, var);
  }

  @Override
  LetEval eval(final Eval sub) {
    if(!(sub instanceof LetEval)) return new LetEval(this, sub);
    final LetEval eval = (LetEval) sub;
    eval.lets.add(this);
    return eval;
  }

  /**
   * Converts the let binding to a for loop.
   * @param cc compilation context
   * @return for expression
   * @throws QueryException query exception
   */
  For toFor(final CompileContext cc) throws QueryException {
    return new For(var, scoring ? cc.function(Function._FT_SCORE, info(), expr) : expr);
  }

  @Override
  public Let optimize(final CompileContext cc) throws QueryException {
    // skip redundant type check
    if(!scoring && expr instanceof TypeCheck) {
      final TypeCheck tc = (TypeCheck) expr;
      if(tc.isRedundant(var) || var.adoptCheck(tc.seqType(), tc.promote)) {
        cc.info(OPTTYPE_X, this);
        expr = tc.expr;
      }
    }
    // promote at compile time
    if(expr instanceof Value) {
      expr = var.checkType((Value) expr, cc.qc, true);
    }

    // assign type to clause and variable
    if(scoring) {
      var.expr(Dbl.ZERO);
    } else {
      adoptType(expr);
      var.expr(expr);
    }
    var.refineType(seqType(), size(), cc);
    return this;
  }

  @Override
  public Let copy(final CompileContext cc, final IntObjMap<Var> vm) {
    return copyType(new Let(cc.copy(var, vm), expr.copy(cc, vm), scoring));
  }

  @Override
  public boolean accept(final ASTVisitor visitor) {
    return expr.accept(visitor) && visitor.declared(var);
  }

  @Override
  Expr inlineExpr(final CompileContext cc) throws QueryException {
    return scoring ? null : var.checked(expr, cc);
  }

  @Override
  public boolean equals(final Object obj) {
    return this == obj || obj instanceof Let && super.equals(obj);
  }

  @Override
  public void toXml(final QueryPlan plan) {
    final FElem elem = plan.attachVariable(plan.create(this), var, false);
    if(scoring) plan.addAttribute(elem, SCORE, true);
    plan.add(elem, expr);
  }

  @Override
  public void toString(final QueryString qs) {
    qs.token(LET);
    if(scoring) qs.token(SCORE);
    qs.token(var).token(":=").token(expr);
  }

  /** Evaluator for a block of {@code let} expressions. */
  private static class LetEval extends Eval {
    /** Let expressions of the current block, in declaration order. */
    private final ArrayList<Let> lets;
    /** Sub-evaluator. */
    private final Eval sub;

    /**
     * Constructor for the first let binding in the block.
     * @param let first let binding
     * @param sub sub-evaluator
     */
    LetEval(final Let let, final Eval sub) {
      lets = new ArrayList<>();
      lets.add(let);
      this.sub = sub;
    }

    @Override
    boolean next(final QueryContext qc) throws QueryException {
      if(!sub.next(qc)) return false;
      for(final Let let : lets) {
        qc.set(let.var, let.scoring ? score(let.expr, qc) : let.expr.value(qc));
      }
      return true;
    }

    /**
     * Calculates the score for the given expression.
     * @param expr expression
     * @param qc query context
     * @return score
     * @throws QueryException evaluation exception
     */
    private static Value score(final Expr expr, final QueryContext qc) throws QueryException {
      final boolean scoring = qc.scoring;
      try {
        qc.scoring = true;
        double s = 0;
        int c = 0;
        final Iter iter = expr.iter(qc);
        for(Item item; (item = qc.next(iter)) != null; c++) {
          s += item.score();
        }
        return Dbl.get(Scoring.avg(s, c));
      } finally {
        qc.scoring = scoring;
      }
    }
  }
}
