// Copyright 2018 The Bazel Authors. 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.analysis.config;

import static com.google.devtools.build.lib.analysis.config.transitions.ConfigurationTransition.PATCH_TRANSITION_KEY;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.devtools.build.lib.events.Event;
import com.google.devtools.build.lib.events.EventHandler;
import com.google.devtools.build.lib.packages.BazelStarlarkContext;
import com.google.devtools.build.lib.packages.StructImpl;
import com.google.devtools.build.lib.skylarkbuildapi.config.ConfigurationTransitionApi;
import com.google.devtools.build.lib.syntax.Dict;
import com.google.devtools.build.lib.syntax.EvalException;
import com.google.devtools.build.lib.syntax.Location;
import com.google.devtools.build.lib.syntax.Mutability;
import com.google.devtools.build.lib.syntax.Printer;
import com.google.devtools.build.lib.syntax.Sequence;
import com.google.devtools.build.lib.syntax.Starlark;
import com.google.devtools.build.lib.syntax.StarlarkCallable;
import com.google.devtools.build.lib.syntax.StarlarkSemantics;
import com.google.devtools.build.lib.syntax.StarlarkThread;
import java.util.List;
import java.util.Map;
import java.util.Objects;

/**
 * Implementation of {@link ConfigurationTransitionApi}.
 *
 * <p>Represents a configuration transition across a dependency edge defined in Starlark.
 */
public abstract class StarlarkDefinedConfigTransition implements ConfigurationTransitionApi {

  private final List<String> inputs;
  private final List<String> outputs;
  private final Location location;

  private StarlarkDefinedConfigTransition(
      List<String> inputs, List<String> outputs, Location location) {
    this.inputs = inputs;
    this.outputs = outputs;
    this.location = location;
  }

  /**
   * Returns true if this transition is for analysis testing. If true, then only attributes of rules
   * with {@code analysis_test=true} may use this transition object.
   */
  public abstract Boolean isForAnalysisTesting();

  /**
   * Returns the input option keys for this transition. Only option keys contained in this list will
   * be provided in the 'settings' argument given to the transition implementation function.
   */
  public List<String> getInputs() {
    return inputs;
  }

  /**
   * Returns the output option keys for this transition. The transition implementation function must
   * return a dictionary where the option keys exactly match the elements of this list.
   */
  public List<String> getOutputs() {
    return outputs;
  }

  /**
   * Returns the location of the Starlark code responsible for determining the transition's changed
   * settings for purposes of error reporting.
   */
  public Location getLocationForErrorReporting() {
    return location;
  }

  /**
   * Given a map of a subset of the "previous" build settings, returns the changed build settings as
   * a result of applying this transition.
   *
   * @param previousSettings a map representing the previous build settings
   * @return a map of changed build setting maps; each element of the map represents a different
   *     child configuration (split transitions will have multiple elements in this map with keys
   *     provided by the transition impl, patch transitions should have a single element keyed by
   *     {@code PATCH_TRANSITION_KEY}). Each build setting map is a map from build setting to target
   *     setting value; all other build settings will remain unchanged
   * @throws EvalException if there is an error evaluating the transition
   * @throws InterruptedException if evaluating the transition is interrupted
   */
  public abstract ImmutableMap<String, Map<String, Object>> evaluate(
      Map<String, Object> previousSettings, StructImpl attributeMap, EventHandler eventHandler)
      throws EvalException, InterruptedException;

  public static StarlarkDefinedConfigTransition newRegularTransition(
      StarlarkCallable impl,
      List<String> inputs,
      List<String> outputs,
      StarlarkSemantics semantics,
      StarlarkThread thread) {
    return new RegularTransition(
        impl, inputs, outputs, semantics, BazelStarlarkContext.from(thread));
  }

  public static StarlarkDefinedConfigTransition newAnalysisTestTransition(
      Map<String, Object> changedSettings, Location location) {
    return new AnalysisTestTransition(changedSettings, location);
  }

  private static class AnalysisTestTransition extends StarlarkDefinedConfigTransition {
    private final Map<String, Object> changedSettings;

    public AnalysisTestTransition(Map<String, Object> changedSettings, Location location) {
      super(ImmutableList.of(), ImmutableList.copyOf(changedSettings.keySet()), location);
      this.changedSettings = changedSettings;
    }

    @Override
    public Boolean isForAnalysisTesting() {
      return true;
    }

    @Override
    public ImmutableMap<String, Map<String, Object>> evaluate(
        Map<String, Object> previousSettings,
        StructImpl attributeMapper,
        EventHandler eventHandler) {
      return ImmutableMap.of(PATCH_TRANSITION_KEY, changedSettings);
    }

    @Override
    public void repr(Printer printer) {
      printer.append("<analysis_test_transition object>");
    }

    @Override
    public boolean equals(Object object) {
      if (object == this) {
        return true;
      }
      if (object instanceof AnalysisTestTransition) {
        AnalysisTestTransition otherTransition = (AnalysisTestTransition) object;
        return Objects.equals(otherTransition.getInputs(), this.getInputs())
            && Objects.equals(otherTransition.getOutputs(), this.getOutputs())
            && Objects.equals(otherTransition.changedSettings, this.changedSettings);
      }
      return false;
    }

    @Override
    public int hashCode() {
      return Objects.hash(this.getInputs(), this.getOutputs(), this.changedSettings);
    }
  }

  /** A transition with a user-defined implementation function. */
  public static class RegularTransition extends StarlarkDefinedConfigTransition {
    private final StarlarkCallable impl;
    private final StarlarkSemantics semantics;
    private final BazelStarlarkContext starlarkContext;

    RegularTransition(
        StarlarkCallable impl,
        List<String> inputs,
        List<String> outputs,
        StarlarkSemantics semantics,
        BazelStarlarkContext context) {
      super(inputs, outputs, impl.getLocation());
      this.impl = impl;
      this.semantics = semantics;
      this.starlarkContext = context;
    }

    @Override
    public Boolean isForAnalysisTesting() {
      return false;
    }

    /**
     * This method evaluates the implementation function of the transition.
     *
     * <p>In the case of a {@link
     * com.google.devtools.build.lib.analysis.config.transitions.PatchTransition}, the impl fxn
     * returns a {@link Dict} of option name strings to option value object.
     *
     * <p>In the case of {@link
     * com.google.devtools.build.lib.analysis.config.transitions.SplitTransition}, the impl fxn can
     * return either a {@link Dict} of String keys to {@link Dict} values. Or it can return a list
     * of {@link Dict}s in cases where the consumer doesn't care about differentiating between the
     * splits (i.e. accessing later via {@code ctx.split_attrs}).
     *
     * @param previousSettings a map representing the previous build settings
     * @param attributeMapper a map of attributes
     */
    // TODO(bazel-team): integrate dict-of-dicts return type with ctx.split_attr
    @Override
    public ImmutableMap<String, Map<String, Object>> evaluate(
        Map<String, Object> previousSettings, StructImpl attributeMapper, EventHandler eventHandler)
        throws EvalException, InterruptedException {
      Object result;
      try {
        result =
            evalFunction(impl, ImmutableList.of(previousSettings, attributeMapper), eventHandler);
      } catch (EvalException e) {
        throw new EvalException(impl.getLocation(), e.getMessage());
      }

      if (result instanceof Dict) {
        // If we're receiving an empty dictionary, it's an error. Even if a
        // transition function sometimes evaluates to a no-op, it needs to return the passed in
        // settings. Return early for now since better error reporting will happen in
        // {@link FunctionTransitionUtil#validateFunctionOutputsMatchesDeclaredOutputs}
        if (((Dict) result).isEmpty()) {
          return ImmutableMap.of("error", ImmutableMap.of());
        }
        // TODO(bazel-team): integrate keys with ctx.split_attr. Currently ctx.split_attr always
        // keys on cpu value - we should be able to key on the keys returned here.
        try {
          Map<String, ?> dictOfDict =
              Dict.cast(result, String.class, Dict.class, "dictionary of options dictionaries");
          ImmutableMap.Builder<String, Map<String, Object>> builder = ImmutableMap.builder();
          for (Map.Entry<String, ?> entry : dictOfDict.entrySet()) {
            builder.put(
                entry.getKey(),
                Dict.cast(entry.getValue(), String.class, Object.class, "an option dictionary"));
          }
          return builder.build();
        } catch (EvalException e) {
          // fall through
        }
        try {
          // Try if this is a patch transition.
          return ImmutableMap.of(
              PATCH_TRANSITION_KEY,
              Dict.cast(result, String.class, Object.class, "dictionary of options"));
        } catch (EvalException e) {
          throw new EvalException(impl.getLocation(), e.getMessage());
        }
      } else if (result instanceof Sequence) {
        ImmutableMap.Builder<String, Map<String, Object>> builder = ImmutableMap.builder();
        try {
          int i = 0;
          for (Dict<?, ?> toOptions :
              Sequence.cast(result, Dict.class, "dictionary of options dictionaries")) {
            // TODO(b/146347033): Document this behavior.
            builder.put(
                Integer.toString(i++),
                Dict.cast(toOptions, String.class, Object.class, "dictionary of options"));
          }
        } catch (EvalException e) {
          throw new EvalException(impl.getLocation(), e.getMessage());
        }
        return builder.build();
      } else {
        throw new EvalException(
            impl.getLocation(),
            "Transition function must return a dictionary or list of dictionaries.");
      }
    }

    @Override
    public void repr(Printer printer) {
      printer.append("<transition object>");
    }

    /** Evaluate the input function with the given argument, and return the return value. */
    private Object evalFunction(
        StarlarkCallable function, ImmutableList<Object> args, EventHandler eventHandler)
        throws InterruptedException, EvalException {
      try (Mutability mu = Mutability.create("eval_transition_function")) {
        StarlarkThread thread = new StarlarkThread(mu, semantics);
        thread.setPrintHandler(Event.makeDebugPrintHandler(eventHandler));
        starlarkContext.storeInThread(thread);
        return Starlark.call(thread, function, args, /*kwargs=*/ ImmutableMap.of());
      }
    }

    @Override
    public boolean equals(Object object) {
      if (object == this) {
        return true;
      }
      if (object instanceof RegularTransition) {
        RegularTransition otherTransition = (RegularTransition) object;
        return Objects.equals(otherTransition.getInputs(), this.getInputs())
            && Objects.equals(otherTransition.getOutputs(), this.getOutputs())
            && Objects.equals(otherTransition.impl, this.impl);
      }
      return false;
    }

    @Override
    public int hashCode() {
      return Objects.hash(this.getInputs(), this.getOutputs(), this.impl);
    }
  }
}