bstore-j/src/main/java/com/reliancy/dbo/Ordering.java

package com.reliancy.dbo;

import java.util.ArrayList;
import java.util.List;

/**
 * Ordering specification for multiple fields.
 * 
 * <p>This class manages an ordered list of field/direction pairs for sorting.
 * It supports chaining methods to build complex ordering specifications.
 * 
 * <p>Example usage:
 * <pre>{@code
 * Ordering ordering = new Ordering("name ASC, created DESC", entity)
 *     .orderBy(Field.by("status"))
 *     .orderBy(Field.by("priority"), false);
 * }</pre>
 */
public class Ordering {
    private static class FieldOrder {
        Field field;
        boolean ascending;
        
        FieldOrder(Field field, boolean ascending) {
            this.field = field;
            this.ascending = ascending;
        }
    }
    
    private ArrayList<FieldOrder> orders = new ArrayList<>();
    
    /**
     * Creates an empty Ordering.
     */
    public Ordering() {
    }
    
    /**
     * Creates an Ordering from a string specification.
     * 
     * @param str String in format "field1 ASC, field2 DESC, ..." or "field1, field2, ..."
     * @param entity Entity to resolve field names
     */
    public Ordering(String str, Entity entity) {
        fromString(str, entity);
    }
    
    /**
     * Creates an Ordering with a single field.
     * 
     * @param field Field to order by
     * @param ascending true for ascending, false for descending
     */
    public Ordering(Field field, boolean ascending) {
        orderBy(field, ascending);
    }
    
    /**
     * Parses a string specification and adds to this ordering.
     * 
     * @param str String in format "field1 ASC, field2 DESC, ..." or "field1, field2, ..."
     * @param entity Entity to resolve field names
     * @return this for chaining
     */
    public Ordering fromString(String str, Entity entity) {
        if (str == null || str.trim().isEmpty()) {
            return this;
        }
        String[] parts = str.split(",");
        for (String part : parts) {
            part = part.trim();
            if (part.isEmpty()) continue;
            if (!part.contains(" ")) part = part + " ASC";
            String[] fieldParts = part.split("\\s+");
            Field field = entity.getField(fieldParts[0]);
            if (field == null) {
                throw new IllegalArgumentException("Field " + fieldParts[0] + " not found in entity " + entity.getName());
            }
            boolean ascending = fieldParts.length > 1 && fieldParts[1].equalsIgnoreCase("ASC");
            orderBy(field, ascending);
        }
        return this;
    }
    
    /**
     * Clears all ordering specifications.
     * 
     * @return this for chaining
     */
    public Ordering clear() {
        orders.clear();
        return this;
    }
    
    /**
     * Adds a field to order by (ascending by default).
     * 
     * @param field Field to order by
     * @return this for chaining
     */
    public Ordering orderBy(Field field) {
        return orderBy(field, true);
    }
    
    /**
     * Adds a field to order by with specified direction.
     * 
     * @param field Field to order by
     * @param ascending true for ascending, false for descending
     * @return this for chaining
     */
    public Ordering orderBy(Field field, boolean ascending) {
        if (field != null) {
            orders.add(new FieldOrder(field, ascending));
        }
        return this;
    }
    
    /**
     * Gets the number of ordering specifications.
     * 
     * @return number of fields in this ordering
     */
    public int size() {
        return orders.size();
    }
    
    /**
     * Gets the field at the specified index.
     * 
     * @param index index of the field
     * @return Field at the index
     */
    public Field getField(int index) {
        return orders.get(index).field;
    }
    
    /**
     * Gets whether the field at the specified index is ascending.
     * 
     * @param index index of the field
     * @return true if ascending, false if descending
     */
    public boolean isAscending(int index) {
        return orders.get(index).ascending;
    }
    
    /**
     * Gets all fields in this ordering.
     * 
     * @return list of fields
     */
    public List<Field> getFields() {
        List<Field> fields = new ArrayList<>();
        for (FieldOrder fo : orders) {
            fields.add(fo.field);
        }
        return fields;
    }
    
    /**
     * Checks if this ordering is empty.
     * 
     * @return true if no fields are specified
     */
    public boolean isEmpty() {
        return orders.isEmpty();
    }
    
    @Override
    public String toString() {
        if (orders.isEmpty()) {
            return "";
        }
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < orders.size(); i++) {
            if (i > 0) sb.append(", ");
            FieldOrder fo = orders.get(i);
            sb.append(fo.field.getName()).append(fo.ascending ? " ASC" : " DESC");
        }
        return sb.toString();
    }
    
    // Static factory methods for backward compatibility and convenience
    
    /**
     * Creates an Ordering with a single ascending field.
     * 
     * @param field Field to order by
     * @return new Ordering instance
     */
    public static Ordering ascending(Field field) {
        return new Ordering(field, true);
    }
    
    /**
     * Creates an Ordering with a single descending field.
     * 
     * @param field Field to order by
     * @return new Ordering instance
     */
    public static Ordering descending(Field field) {
        return new Ordering(field, false);
    }
    
    /**
     * Creates an Ordering with a single ascending field.
     * 
     * @param field Field to order by
     * @return new Ordering instance
     */
    public static Ordering by(Field field) {
        return new Ordering(field, true);
    }
    
}