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/*
 * Copyright (C) 2017 - present by OpenGamma Inc. and the OpenGamma group of companies
 *
 * Please see distribution for license.
 */
package com.opengamma.strata.market.curve;

import java.time.LocalDate;
import java.time.Period;

import com.google.common.collect.ImmutableList;
import com.opengamma.strata.basics.ReferenceData;
import com.opengamma.strata.collect.array.DoubleArray;
import com.opengamma.strata.data.MarketData;
import com.opengamma.strata.market.ValueType;

/**
 * Provides the definition of how to calibrate a curve.
 * 
 * A curve is built from a number of parameters and described by metadata.
 * Calibration is based on a list of {@link CurveNode} instances that specify the underlying instruments.
 */
public interface CurveDefinition {

  /**
   * Gets the curve name.
   *
   * @return the curve name
   */
  public abstract CurveName getName();

  /**
   * Gets the number of parameters in the curve.
   * 

   * This returns the number of parameters in the curve, which is not necessarily equal the size of {@code getNodes()}.
   * 
   * @return the number of parameters
   */
  public abstract int getParameterCount();

  /**
   * Gets the y-value type, providing meaning to the y-values of the curve.
   * 

   * This type provides meaning to the y-values. For example, the y-value might
   * represent a zero rate, as represented using {@link ValueType#ZERO_RATE}.
   * 
   * @return the y-value type
   */
  public abstract ValueType getYValueType();

  /**
   * Gets the nodes that define the curve.
   * 

   * The nodes are used to calibrate the curve.
   * If the objective curve is a nodal curve, each node is used to produce a parameter in the final curve.
   * 
   * @return the nodes
   */
  public abstract ImmutableList getNodes();

  /**
   * Returns a filtered version of this definition with no invalid nodes.
   * 

   * A curve is formed of a number of nodes, each of which has an associated date.
   * To be valid, the curve node dates must be in order from earliest to latest.
   * Each node has certain rules, {@link CurveNodeDateOrder}, that are used to determine
   * what happens if the date of one curve node is equal or earlier than the date of the previous node.
   * 

   * Filtering occurs in two stages. The first stage looks at each node in turn. The previous and next
   * nodes are checked for clash. If clash occurs, then one of the two nodes is dropped according to
   * the {@linkplain CurveNodeClashAction clash action} "drop" values. The second stage then looks
   * again at the nodes, and if there are still any invalid nodes, an exception is thrown.
   * 

   * This approach means that in most cases, only those nodes that have fixed dates,
   * such as futures, need to be annotated with {@code CurveNodeDateOrder}.
   * 
   * @param valuationDate  the valuation date
   * @param refData  the reference data
   * @return the resolved definition, that should be used in preference to this one
   * @throws IllegalArgumentException if the curve nodes are invalid
   */
  public abstract CurveDefinition filtered(LocalDate valuationDate, ReferenceData refData);

  /**
   * Creates the curve metadata.
   * 

   * This method returns metadata about the curve and the curve parameters.
   * 

   * For example, a curve may be defined based on financial instruments.
   * The parameters might represent 1 day, 1 week, 1 month, 3 months, 6 months and 12 months.
   * The metadata could be used to describe each parameter in terms of a {@link Period}.
   * 

   * The optional parameter-level metadata will be populated on the resulting metadata.
   * The size of the parameter-level metadata will match the number of parameters of this curve.
   *
   * @param valuationDate  the valuation date
   * @param refData  the reference data
   * @return the metadata
   */
  public abstract CurveMetadata metadata(LocalDate valuationDate, ReferenceData refData);

  /**
   * Creates the curve from an array of parameter values.
   * 

   * The meaning of the parameters is determined by the implementation.
   * The size of the array must match the {@linkplain #getParameterCount() count of parameters}.
   * 
   * @param valuationDate  the valuation date
   * @param metadata  the curve metadata
   * @param parameters  the array of parameters
   * @return the curve
   */
  public abstract Curve curve(LocalDate valuationDate, CurveMetadata metadata, DoubleArray parameters);

  /**
   * Converts this definition to the summary form.
   * 

   * The {@link CurveParameterSize} class provides a summary of this definition
   * consisting of the name and parameter size.
   * 
   * @return the summary form
   */
  public default CurveParameterSize toCurveParameterSize() {
    return CurveParameterSize.of(getName(), getParameterCount());
  }

  /**
   * Gets the list of all initial guesses.
   * 
   * This returns initial guess for the curve parameters.
   * The valuation date is defined by the market data.
   * 
   * @param marketData  the market data required to build a trade for the instrument, including the valuation date
   * @return the initial guess
   */
  public abstract ImmutableList initialGuess(MarketData marketData);

}