// Copyright 2014 Google Inc. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//    http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package com.google.devtools.build.lib.syntax;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableSet;
import com.google.common.hash.HashCode;
import com.google.devtools.build.lib.events.Event;
import com.google.devtools.build.lib.events.EventHandler;
import com.google.devtools.build.lib.events.Location;
import com.google.devtools.build.lib.packages.CachingPackageLocator;
import com.google.devtools.build.lib.vfs.Path;
import com.google.devtools.build.lib.vfs.PathFragment;

import java.io.IOException;
import java.util.List;

import javax.annotation.Nullable;

/**
 * Abstract syntax node for an entire BUILD file.
 */
public class BuildFileAST extends ASTNode {

  private final ImmutableList<Statement> stmts;

  private final ImmutableList<Comment> comments;

  private ImmutableSet<PathFragment> loads;

  private ImmutableSet<Label> includes;

  /**
   * Whether any errors were encountered during scanning or parsing.
   */
  private final boolean containsErrors;

  private final String contentHashCode;

  private BuildFileAST(Lexer lexer, List<Statement> preludeStatements, Parser.ParseResult result) {
    this(lexer, preludeStatements, result, null);
  }

  private BuildFileAST(Lexer lexer, List<Statement> preludeStatements,
      Parser.ParseResult result, String contentHashCode) {
    this.stmts = ImmutableList.<Statement>builder()
        .addAll(preludeStatements)
        .addAll(result.statements)
        .build();
    this.comments = ImmutableList.copyOf(result.comments);
    this.containsErrors = result.containsErrors;
    this.contentHashCode = contentHashCode;
    if (!result.statements.isEmpty()) {
      setLocation(lexer.createLocation(
          result.statements.get(0).getLocation().getStartOffset(),
          result.statements.get(result.statements.size() - 1).getLocation().getEndOffset()));
    } else {
      setLocation(Location.fromPathFragment(lexer.getFilename()));
    }
  }

  private ImmutableSet<Label> fetchIncludes(List<Statement> stmts) {
    ImmutableSet.Builder<Label> result = new ImmutableSet.Builder<>();
    for (Statement stmt : stmts) {
      if (!(stmt instanceof ExpressionStatement)) {
        continue;
      }

      ExpressionStatement expr = (ExpressionStatement) stmt;
      if (!(expr.getExpression() instanceof FuncallExpression)) {
        continue;
      }

      FuncallExpression funcall = (FuncallExpression) expr.getExpression();
      if (!funcall.getFunction().getName().equals("include")
          || funcall.getArguments().size() != 1) {
        continue;
      }

      Expression arg = funcall.getArguments().get(0).value;
      if (!(arg instanceof StringLiteral)) {
        continue;
      }

      try {
        Label label = Label.parseAbsolute(((StringLiteral) arg).getValue());
        result.add(label);
      } catch (Label.SyntaxException e) {
        // Ignore. This will be reported when the BUILD file is actually evaluated.
      }
    }

    return result.build();
  }

  /** Collects paths from all load statements */
  private ImmutableSet<PathFragment> fetchLoads(List<Statement> stmts) {
    ImmutableSet.Builder<PathFragment> loads = new ImmutableSet.Builder<>();
    for (Statement stmt : stmts) {
      if (stmt instanceof LoadStatement) {
        LoadStatement imp = (LoadStatement) stmt;
        loads.add(imp.getImportPath());
      }
    }
    return loads.build();
  }

  /**
   * Returns true if any errors were encountered during scanning or parsing. If
   * set, clients should not rely on the correctness of the AST for builds or
   * BUILD-file editing.
   */
  public boolean containsErrors() {
    return containsErrors;
  }

  /**
   * Returns an (immutable, ordered) list of statements in this BUILD file.
   */
  public ImmutableList<Statement> getStatements() {
    return stmts;
  }

  /**
   * Returns an (immutable, ordered) list of comments in this BUILD file.
   */
  public ImmutableList<Comment> getComments() {
    return comments;
  }

  /**
   * Returns a set of loads in this BUILD file.
   */
  public synchronized ImmutableSet<PathFragment> getImports() {
    if (loads == null) {
      loads = fetchLoads(stmts);
    }
    return loads;
  }

  public synchronized ImmutableSet<Label> getIncludes() {
    if (includes == null) {
      includes = fetchIncludes(stmts);
    }

    return includes;
  }

  /**
   * Executes this build file in a given Environment.
   *
   * <p>If, for any reason, execution of a statement cannot be completed, an
   * {@link EvalException} is thrown by {@link Statement#exec(Environment)}.
   * This exception is caught here and reported through reporter and execution
   * continues on the next statement.  In effect, there is a "try/except" block
   * around every top level statement.  Such exceptions are not ignored, though:
   * they are visible via the return value.  Rules declared in a package
   * containing any error (including loading-phase semantical errors that
   * cannot be checked here) must also be considered "in error".
   *
   * <p>Note that this method will not affect the value of {@link
   * #containsErrors()}; that refers only to lexer/parser errors.
   *
   * @return true if no error occurred during execution.
   */
  public boolean exec(Environment env, EventHandler eventHandler) throws InterruptedException {
    boolean ok = true;
    for (Statement stmt : stmts) {
      try {
        stmt.exec(env);
      } catch (EvalException e) {
        ok = false;
        // Do not report errors caused by a previous parsing error, as it has already been
        // reported.
        if (e.isDueToIncompleteAST()) {
          continue;
        }
        // When the exception is raised from another file, report first the location in the
        // BUILD file (as it is the most probable cause for the error).
        Location exnLoc = e.getLocation();
        Location nodeLoc = stmt.getLocation();
        if (exnLoc == null || !nodeLoc.getPath().equals(exnLoc.getPath())) {
          eventHandler.handle(Event.error(nodeLoc,
                  e.getMessage() + " (raised from " + exnLoc + ")"));
        } else {
          eventHandler.handle(Event.error(exnLoc, e.getMessage()));
        }
      }
    }
    return ok;
  }

  @Override
  public String toString() {
    return "BuildFileAST" + getStatements();
  }

  @Override
  public void accept(SyntaxTreeVisitor visitor) {
    visitor.visit(this);
  }

  /**
   * Parse the specified build file, returning its AST. All errors during
   * scanning or parsing will be reported to the reporter.
   *
   * @throws IOException if the file cannot not be read.
   */
  public static BuildFileAST parseBuildFile(Path buildFile, EventHandler eventHandler,
                                            CachingPackageLocator locator, boolean parsePython)
      throws IOException {
    ParserInputSource inputSource = ParserInputSource.create(buildFile);
    return parseBuildFile(inputSource, eventHandler, locator, parsePython);
  }

  /**
   * Parse the specified build file, returning its AST. All errors during
   * scanning or parsing will be reported to the reporter.
   */
  public static BuildFileAST parseBuildFile(ParserInputSource input,
                                            List<Statement> preludeStatements,
                                            EventHandler eventHandler,
                                            CachingPackageLocator locator,
                                            boolean parsePython) {
    Lexer lexer = new Lexer(input, eventHandler, parsePython);
    Parser.ParseResult result = Parser.parseFile(lexer, eventHandler, locator, parsePython);
    return new BuildFileAST(lexer, preludeStatements, result);
  }

  public static BuildFileAST parseBuildFile(ParserInputSource input, EventHandler eventHandler,
      CachingPackageLocator locator, boolean parsePython) {
    Lexer lexer = new Lexer(input, eventHandler, parsePython);
    Parser.ParseResult result = Parser.parseFile(lexer, eventHandler, locator, parsePython);
    return new BuildFileAST(lexer, ImmutableList.<Statement>of(), result);
  }

  /**
   * Parse the specified build file, returning its AST. All errors during
   * scanning or parsing will be reported to the reporter.
   */
  public static BuildFileAST parseBuildFile(Lexer lexer, EventHandler eventHandler) {
    Parser.ParseResult result = Parser.parseFile(lexer, eventHandler, null, false);
    return new BuildFileAST(lexer, ImmutableList.<Statement>of(), result);
  }

  /**
   * Parse the specified Skylark file, returning its AST. All errors during
   * scanning or parsing will be reported to the reporter.
   *
   * @throws IOException if the file cannot not be read.
   */
  public static BuildFileAST parseSkylarkFile(Path file, EventHandler eventHandler,
      CachingPackageLocator locator, ValidationEnvironment validationEnvironment)
          throws IOException {
    ParserInputSource input = ParserInputSource.create(file);
    Lexer lexer = new Lexer(input, eventHandler, false);
    Parser.ParseResult result =
        Parser.parseFileForSkylark(lexer, eventHandler, locator, validationEnvironment);
    return new BuildFileAST(lexer, ImmutableList.<Statement>of(), result,
        HashCode.fromBytes(file.getMD5Digest()).toString());
  }

  /**
   * Parse the specified build file, without building the AST.
   *
   * @return true if the input file is syntactically valid
   */
  public static boolean checkSyntax(ParserInputSource input,
                                    EventHandler eventHandler, boolean parsePython) {
    return !parseBuildFile(input, eventHandler, null, parsePython).containsErrors();
  }

  /**
   * Returns a hash code calculated from the string content of the source file of this AST.
   */
  @Nullable public String getContentHashCode() {
    return contentHashCode;
  }
}