package org.checkerframework.checker.regex;

import com.sun.source.tree.ExpressionTree;
import com.sun.source.tree.LiteralTree;
import com.sun.source.tree.MemberSelectTree;
import com.sun.source.tree.MethodInvocationTree;
import com.sun.source.tree.Tree.Kind;
import javax.annotation.processing.ProcessingEnvironment;
import javax.lang.model.element.ExecutableElement;
import javax.lang.model.element.VariableElement;
import javax.lang.model.type.TypeMirror;
import org.checkerframework.checker.regex.qual.Regex;
import org.checkerframework.common.basetype.BaseTypeChecker;
import org.checkerframework.common.basetype.BaseTypeVisitor;
import org.checkerframework.framework.type.AnnotatedTypeMirror;
import org.checkerframework.javacutil.TreeUtils;

/**
 * A type-checking visitor for the Regex type system.
 *
 * <p>This visitor does the following:
 *
 * <ol>
 *   <li value="1">Allows any String to be passed to Pattern.compile if the Pattern.LITERAL flag is
 *       passed.
 *   <li value="2">Checks compound String concatenation to ensure correct usage of Regex Strings.
 *   <li value="3">Checks calls to {@code MatchResult.start}, {@code MatchResult.end} and {@code
 *       MatchResult.group} to ensure that a valid group number is passed.
 * </ol>
 *
 * @see RegexChecker
 */
public class RegexVisitor extends BaseTypeVisitor<RegexAnnotatedTypeFactory> {

  private final ExecutableElement matchResultEnd;
  private final ExecutableElement matchResultGroup;
  private final ExecutableElement matchResultStart;
  private final ExecutableElement patternCompile;
  private final VariableElement patternLiteral;

  /** Reference types that may be annotated with @Regex. */
  protected TypeMirror[] legalReferenceTypes;

  /**
   * Create a RegexVisitor.
   *
   * @param checker the associated RegexChecker
   */
  public RegexVisitor(BaseTypeChecker checker) {
    super(checker);
    ProcessingEnvironment env = checker.getProcessingEnvironment();
    this.matchResultEnd = TreeUtils.getMethod("java.util.regex.MatchResult", "end", 1, env);
    this.matchResultGroup = TreeUtils.getMethod("java.util.regex.MatchResult", "group", 1, env);
    this.matchResultStart = TreeUtils.getMethod("java.util.regex.MatchResult", "start", 1, env);
    this.patternCompile = TreeUtils.getMethod("java.util.regex.Pattern", "compile", 2, env);
    this.patternLiteral = TreeUtils.getField("java.util.regex.Pattern", "LITERAL", env);
  }

  /**
   * Case 1: Don't require a Regex annotation on the String argument to Pattern.compile if the
   * Pattern.LITERAL flag is passed.
   */
  @Override
  public Void visitMethodInvocation(MethodInvocationTree node, Void p) {
    ProcessingEnvironment env = checker.getProcessingEnvironment();
    if (TreeUtils.isMethodInvocation(node, patternCompile, env)) {
      ExpressionTree flagParam = node.getArguments().get(1);
      if (flagParam.getKind() == Kind.MEMBER_SELECT) {
        MemberSelectTree memSelect = (MemberSelectTree) flagParam;
        if (TreeUtils.isSpecificFieldAccess(memSelect, patternLiteral)) {
          // This is a call to Pattern.compile with the Pattern.LITERAL flag so the first parameter
          // doesn't need to be a @Regex String. Don't call the super method to skip checking if the
          // first parameter is a @Regex String, but make sure to still recurse on all of the
          // different parts of the method call.
          Void r = scan(node.getTypeArguments(), p);
          r = reduce(scan(node.getMethodSelect(), p), r);
          r = reduce(scan(node.getArguments(), p), r);
          return r;
        }
      }
    } else if (TreeUtils.isMethodInvocation(node, matchResultEnd, env)
        || TreeUtils.isMethodInvocation(node, matchResultGroup, env)
        || TreeUtils.isMethodInvocation(node, matchResultStart, env)) {
      /**
       * Case 3: Checks calls to {@code MatchResult.start}, {@code MatchResult.end} and {@code
       * MatchResult.group} to ensure that a valid group number is passed.
       */
      ExpressionTree group = node.getArguments().get(0);
      if (group.getKind() == Kind.INT_LITERAL) {
        LiteralTree literal = (LiteralTree) group;
        int paramGroups = (Integer) literal.getValue();
        ExpressionTree receiver = TreeUtils.getReceiverTree(node);
        if (receiver == null) {
          // When checking implementations of java.util.regex.MatcherResult, calls to group (and
          // other methods) don't have a receiver tree.  So, just do the regular checking. Verifying
          // an implemenation of a subclass of MatcherResult is out of the scope of this checker.
          return super.visitMethodInvocation(node, p);
        }
        int annoGroups = 0;
        AnnotatedTypeMirror receiverType = atypeFactory.getAnnotatedType(receiver);

        if (receiverType != null && receiverType.hasAnnotation(Regex.class)) {
          annoGroups = atypeFactory.getGroupCount(receiverType.getAnnotation(Regex.class));
        }
        if (paramGroups > annoGroups) {
          checker.reportError(group, "group.count", paramGroups, annoGroups, receiver);
        }
      } else {
        checker.reportWarning(group, "group.count.unknown");
      }
    }
    return super.visitMethodInvocation(node, p);
  }

  /** Case 2: Check String compound concatenation for valid Regex use. */
  // TODO: Remove this. This should be handled by flow.
  /*
  @Override
  public Void visitCompoundAssignment(CompoundAssignmentTree node, Void p) {
      // Default behavior from superclass
  }
  */

}