package io.prometheus.metrics.model.snapshots;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.stream.Stream;

/** Immutable snapshot of a StateSet metric. */
public final class StateSetSnapshot extends MetricSnapshot {

  /**
   * To create a new {@link StateSetSnapshot}, you can either call the constructor directly or use
   * the builder with {@link StateSetSnapshot#builder()}.
   *
   * @param metadata See {@link MetricMetadata} for more naming conventions.
   * @param data the constructor will create a sorted copy of the collection.
   */
  public StateSetSnapshot(MetricMetadata metadata, Collection<StateSetDataPointSnapshot> data) {
    super(metadata, data);
    validate();
  }

  private void validate() {
    if (getMetadata().hasUnit()) {
      throw new IllegalArgumentException("An state set metric cannot have a unit.");
    }
    for (StateSetDataPointSnapshot entry : getDataPoints()) {
      if (entry.getLabels().contains(getMetadata().getPrometheusName())) {
        throw new IllegalArgumentException(
            "Label name " + getMetadata().getPrometheusName() + " is reserved.");
      }
    }
  }

  @SuppressWarnings("unchecked")
  @Override
  public List<StateSetDataPointSnapshot> getDataPoints() {
    return (List<StateSetDataPointSnapshot>) dataPoints;
  }

  public static class StateSetDataPointSnapshot extends DataPointSnapshot
      implements Iterable<State> {
    private final String[] names;
    private final boolean[] values;

    /**
     * To create a new {@link StateSetDataPointSnapshot}, you can either call the constructor
     * directly or use the Builder with {@link StateSetDataPointSnapshot#builder()}.
     *
     * @param names state names. Must have at least 1 entry. The constructor will create a copy of
     *     the array.
     * @param values state values. Must have the same length as {@code names}. The constructor will
     *     create a copy of the array.
     * @param labels must not be null. Use {@link Labels#EMPTY} if there are no labels.
     */
    public StateSetDataPointSnapshot(String[] names, boolean[] values, Labels labels) {
      this(names, values, labels, 0L);
    }

    /**
     * Constructor with an additional scrape timestamp. This is only useful in rare cases as the
     * scrape timestamp is usually set by the Prometheus server during scraping. Exceptions include
     * mirroring metrics with given timestamps from other metric sources.
     */
    public StateSetDataPointSnapshot(
        String[] names, boolean[] values, Labels labels, long scrapeTimestampMillis) {
      super(labels, 0L, scrapeTimestampMillis);
      if (names.length == 0) {
        throw new IllegalArgumentException("StateSet must have at least one state.");
      }
      if (names.length != values.length) {
        throw new IllegalArgumentException("names[] and values[] must have the same length");
      }
      String[] namesCopy = Arrays.copyOf(names, names.length);
      boolean[] valuesCopy = Arrays.copyOf(values, names.length);
      sort(namesCopy, valuesCopy);
      this.names = namesCopy;
      this.values = valuesCopy;
      validate();
    }

    public int size() {
      return names.length;
    }

    public String getName(int i) {
      return names[i];
    }

    public boolean isTrue(int i) {
      return values[i];
    }

    private void validate() {
      for (int i = 0; i < names.length; i++) {
        if (names[i].isEmpty()) {
          throw new IllegalArgumentException("Empty string as state name");
        }
        if (i > 0 && names[i - 1].equals(names[i])) {
          throw new IllegalArgumentException(names[i] + " duplicate state name");
        }
      }
    }

    private List<State> asList() {
      List<State> result = new ArrayList<>(size());
      for (int i = 0; i < names.length; i++) {
        result.add(new State(names[i], values[i]));
      }
      return Collections.unmodifiableList(result);
    }

    @Override
    public Iterator<State> iterator() {
      return asList().iterator();
    }

    public Stream<State> stream() {
      return asList().stream();
    }

    private static void sort(String[] names, boolean[] values) {
      // Bubblesort
      int n = names.length;
      for (int i = 0; i < n - 1; i++) {
        for (int j = 0; j < n - i - 1; j++) {
          if (names[j].compareTo(names[j + 1]) > 0) {
            swap(j, j + 1, names, values);
          }
        }
      }
    }

    private static void swap(int i, int j, String[] names, boolean[] values) {
      String tmpName = names[j];
      names[j] = names[i];
      names[i] = tmpName;
      boolean tmpValue = values[j];
      values[j] = values[i];
      values[i] = tmpValue;
    }

    public static Builder builder() {
      return new Builder();
    }

    public static class Builder extends DataPointSnapshot.Builder<Builder> {

      private final List<String> names = new ArrayList<>();
      private final List<Boolean> values = new ArrayList<>();

      private Builder() {}

      /** Add a state. Call multiple times to add multiple states. */
      public Builder state(String name, boolean value) {
        names.add(name);
        values.add(value);
        return this;
      }

      @Override
      protected Builder self() {
        return this;
      }

      public StateSetDataPointSnapshot build() {
        boolean[] valuesArray = new boolean[values.size()];
        for (int i = 0; i < values.size(); i++) {
          valuesArray[i] = values.get(i);
        }
        return new StateSetDataPointSnapshot(
            names.toArray(new String[] {}), valuesArray, labels, scrapeTimestampMillis);
      }
    }
  }

  public static class State {
    private final String name;
    private final boolean value;

    private State(String name, boolean value) {
      this.name = name;
      this.value = value;
    }

    public String getName() {
      return name;
    }

    public boolean isTrue() {
      return value;
    }
  }

  public static Builder builder() {
    return new Builder();
  }

  public static class Builder extends MetricSnapshot.Builder<Builder> {

    private final List<StateSetDataPointSnapshot> dataPoints = new ArrayList<>();

    private Builder() {}

    /** Add a data point. Call multiple times to add multiple data points. */
    public Builder dataPoint(StateSetDataPointSnapshot dataPoint) {
      dataPoints.add(dataPoint);
      return this;
    }

    @Override
    public Builder unit(Unit unit) {
      throw new IllegalArgumentException("StateSet metric cannot have a unit.");
    }

    @Override
    public StateSetSnapshot build() {
      return new StateSetSnapshot(buildMetadata(), dataPoints);
    }

    @Override
    protected Builder self() {
      return this;
    }
  }
}