# Mapping.java

    package org.codefilarete.stalactite.mapping;

    import java.util.HashMap;
    import java.util.HashSet;
    import java.util.Map;
    import java.util.Map.Entry;
    import java.util.Set;

    import org.codefilarete.reflection.ReversibleAccessor;
    import org.codefilarete.reflection.ValueAccessPoint;
    import org.codefilarete.reflection.ValueAccessPointMap;
    import org.codefilarete.stalactite.mapping.RowTransformer.TransformerListener;
    import org.codefilarete.stalactite.sql.ddl.structure.Column;
    import org.codefilarete.stalactite.sql.ddl.structure.Table;
    import org.codefilarete.stalactite.sql.result.ColumnedRow;
    import org.codefilarete.tool.collection.KeepOrderSet;
    import org.codefilarete.tool.function.Converter;

    /**
     * A very general contract for mapping a type to a database table. Not expected to be used as this (for instance it lacks deletion contract)
     *
     * @author Guillaume Mary
     */
    public interface Mapping<C, T extends Table<T>> {

    	/**
    	 * Returns columns that must be inserted
    	 *
    	 * @param c the instance to be inserted,
    	 * 					may be null when this method is called to manage relation
    	 * @return a mapping between columns that must be put in the SQL insert order and there values
    	 */
    	Map<Column<T, ?>, ?> getInsertValues(C c);

    	/**
    	 * Returns columns that must be updated because of change between 2 instances.
    	 *
    	 * @param modified the modified instance,
    	 * 					may be null when this method is called to manage relation
    	 * @param unmodified the non modified instance or "previous state" (coming from database for instance),
    	 * 					may be null to generate a rough update statement (allColumn doesn't matter in this case)
    	 * @param allColumns indicates if allColumns must be returned, even if they are not all modified (necessary for JDBC batch optimization)
    	 * @return a mapping between columns that must be put in the SQL update order and there values,
    	 * 			thus a distinction between columns to be updated and columns necessary to the where clause must be done, this is done through {@link UpwhereColumn},
    	 * 			so returned value may contain duplicates regarding {@link Column} (they can be in update & where part, especially for optimist lock columns)
    	 */
    	Map<UpwhereColumn<T>, ?> getUpdateValues(C modified, C unmodified, boolean allColumns);

    	/**
    	 * Transforms the given row into a new bean. It is not "alias proof" so it is not expected to be used in a select which columns haven't their
    	 * name in the select clause, over all with alias.
    	 *
    	 * @param row a row coming from a select clause of this entity
    	 * @return a new bean which properties have been filled by row values
    	 */
    	C transform(ColumnedRow row);

    	RowTransformer<C> getRowTransformer();

    	/**
    	 * Adds a column for insert. This column is not expected to be already mapped to a bean property of the &lt;T&gt; class
    	 * Here are some use case examples :
    	 * - getting the creation timestamp of a bean without the need to map it to a bean property,
    	 * - completing a table with a value that is not expected by the bean but by the table
    	 *
    	 * It is not expected to use it to tamper with the value of a mapped property, even this is not forbidden and may work, it is not guaranteed to
    	 * be a feature.
    	 *
    	 * This method might have no purpose for many classes implementing {@link Mapping}.
    	 *
    	 * @param valueProvider the column value provider
    	 */
    	default void addShadowColumnInsert(ShadowColumnValueProvider<C, T> valueProvider) {
    		// does nothing by default
    	}

    	/**
    	 * Adds a column for update. This column is not expected to be already mapped to a bean property of the &lt;T&gt; class
    	 * Here are some use case examples :
    	 * - timestamping a bean without the need to map the timestamp to a bean property,
    	 * - completing a table with a value that is not expected by the bean but by the table
    	 *
    	 * It is not expected to use it to tamper with the value of a mapped property, even this is not forbidden and may work, it is not guaranteed to
    	 * be a feature.
    	 *
    	 * This method might have no purpose for many classes implementing {@link Mapping}.
    	 *
    	 * @param valueProvider the column value provider
    	 */
    	default void addShadowColumnUpdate(ShadowColumnValueProvider<C, T> valueProvider) {
    		// does nothing by default
    	}

    	/**
    	 * Adds a column to select. This column is not expected to be already mapped to a bean property of the &lt;T&gt; class.
    	 *
    	 * This method might have no purpose for many classes implementing {@link Mapping}.
    	 *
    	 * @param column the column to be read
    	 * @param <O> Java type of the column value
    	 */
    	default <O> void addShadowColumnSelect(Column<T, O> column) {
    		// does nothing by default
    	}

    	void addPropertySetByConstructor(ValueAccessPoint<C> accessor);

    	Map<ReversibleAccessor<C, ?>, Column<T, ?>> getPropertyToColumn();

    	Map<ReversibleAccessor<C, ?>, Column<T, ?>> getReadonlyPropertyToColumn();

    	default ValueAccessPointMap<C, Converter<Object, Object>> getReadConverters() {
    		return new ValueAccessPointMap<>();
    	}

    	default ValueAccessPointMap<C, Converter<Object, Object>> getWriteConverters() {
    		return new ValueAccessPointMap<>();
    	}

    	default Set<Column<T, ?>> getWritableColumns() {
    		return new KeepOrderSet<>(getPropertyToColumn().values());
    	}

    	default Set<Column<T, ?>> getReadonlyColumns() {
    		return new KeepOrderSet<>(getReadonlyPropertyToColumn().values());
    	}

    	/**
    	 * Adds a transformer listener, optional operation
    	 * @param listener the listener to be notified of transformation
    	 */
    	default void addTransformerListener(TransformerListener<C> listener) {
    		// does nothing by default
    	}

    	/**
    	 * Wrapper for {@link Column} placed in an update statement so it can distinguish if it's for the Update or Where part
    	 */
    	class UpwhereColumn<T extends Table<T>> {

    		/**
    		 * Collects all columns from a set of {@link UpwhereColumn}. Helper method.
    		 *
    		 * @param set a non null set
    		 * @return all columns of the set
    		 */
    		public static <T extends Table<T>> Set<Column<T, ?>> getUpdateColumns(Set<? extends UpwhereColumn<T>> set) {
    			Set<Column<T, ?>> updateColumns = new HashSet<>();
    			for (UpwhereColumn<T> upwhereColumn : set) {
    				if (upwhereColumn.update) {
    					updateColumns.add(upwhereColumn.column);
    				}
    			}
    			return updateColumns;
    		}

    		/**
    		 * Collects all columns to be updated (not for the where clause) from a map of {@link UpwhereColumn}. Helper method.
    		 *
    		 * @param map a non null map
    		 * @return all columns to be updated
    		 */
    		public static <T extends Table<T>> Map<Column<T, Object>, ?> getUpdateColumns(Map<? extends UpwhereColumn<T>, ?> map) {
    			Map<Column<T, Object>, Object> updateColumns = new HashMap<>();
    			for (Entry<? extends UpwhereColumn<T>, ?> entry : map.entrySet()) {
    				UpwhereColumn<T> upwhereColumn = entry.getKey();
    				if (upwhereColumn.update) {
    					updateColumns.put(upwhereColumn.column, entry.getValue());
    				}
    			}
    			return updateColumns;
    		}

    		/**
    		 * Collects all columns for the where clause (not for the update clause) from a map of {@link UpwhereColumn}. Helper method.
    		 *
    		 * @param map a non null map
    		 * @return all columns for the where clause
    		 */
    		public static <T extends Table<T>> Map<Column<T, Object>, Object> getWhereColumns(Map<? extends UpwhereColumn<T>, ?> map) {
    			Map<Column<T, Object>, Object> updateColumns = new HashMap<>();
    			for (Entry<? extends UpwhereColumn<T>, ?> entry : map.entrySet()) {
    				UpwhereColumn<T> upwhereColumn = entry.getKey();
    				if (!upwhereColumn.update) {
    					updateColumns.put(upwhereColumn.column, entry.getValue());
    				}
    			}
    			return updateColumns;
    		}

    		private final Column<T, Object> column;
    		private final boolean update;

    		public UpwhereColumn(Column<T, ?> column, boolean update) {
    			this.column = (Column<T, Object>) column;
    			this.update = update;
    		}

    		public Column getColumn() {
    			return column;
    		}

    		public boolean isUpdate() {
    			return update;
    		}

    		/**
    		 * Implemented to distinguish columns of the update clause from those of the where part, because the main purpose of this class is to be put
    		 * in a {@link Map}.
    		 *
    		 * @param obj another object
    		 * @return true if the other object has the same column and has the same target : update or where part
    		 */
    		@Override
    		public boolean equals(Object obj) {
    			if (obj instanceof UpwhereColumn) {
    				UpwhereColumn other = (UpwhereColumn) obj;
    				return this.column.equals(other.column) && this.update == other.update;
    			} else {
    				return false;
    			}
    		}

    		/**
    		 * Based on hash code of the column
    		 * @return column hash code
    		 */
    		@Override
    		public int hashCode() {
    			return this.column.hashCode();
    		}

    		/**
    		 * Overridden to print "U" or "W" according to the purpose of this instance. Simplifies trace and eventual debug.
    		 * @return the column's absolute name, suffixed by "U" or "W" according to the purpose of this instance
    		 */
    		@Override
    		public String toString() {
    			return column.getAbsoluteName() + (update ? " (U)" : " (W)");
    		}
    	}

    	/**
    	 * Contract to provide values of some "unofficial" {@link Column}s out of a mapping strategy at insert and update
    	 * time : those columns are not expected to be one of those mapped by properties but can be discriminator, list
    	 * index, etc...
    	 * <br/>
    	 * An instance may reject to provide a value in some circumstances by overriding {@link #accept(Object)} (which
    	 * returns true by default).
    	 *
    	 * Reader may be interested in getting {@link Column} value in select phase, then he may use
    	 * {@link Mapping#addShadowColumnSelect(Column)}
    	 *
    	 * @param <C> bean type to read value from
    	 * @param <T> table type
    	 * @see #giveValue(Object)
    	 * @see #accept(Object)
    	 */
    	interface ShadowColumnValueProvider<C, T extends Table<T>> {

    		/**
    		 * Made to determine if current column provider must be included to insert / update statement
    		 * @param entity entity being persisted
    		 * @return true if {@link #giveValue(Object)} must be call
    		 */
    		default boolean accept(C entity) {
    			return true;
    		}

    		/**
    		 * Gives the columns to be appended to the insert or update SQL statement.
    		 *
    		 * @return columns to be appended to the insert or update SQL statement.
    		 */
    		Set<Column<T, ?>> getColumns();

    		/**
    		 * Expected to give values to be set in insert or update SQL Statement for given entity
    		 * @param bean the entity that is being persisted
    		 * @return values per {@link Column} (must be same column instances that were given to {@link #getColumns()})
    		 */
    		Map<Column<T, ?>, ?> giveValue(C bean);
    	}
    }