JPA-Test/src/main/java/com/guwan/backend/MergeStrategy/JoinBuilder.java

package com.guwan.backend.MergeStrategy;

import jakarta.persistence.EntityManager;
import jakarta.persistence.criteria.*;
import org.springframework.data.jpa.domain.Specification;
import org.springframework.data.jpa.repository.query.QueryUtils;

import java.lang.reflect.Constructor;
import java.util.*;
import java.util.function.Function;
import java.util.stream.Collectors;

/**
 * 自定义连表查询构建器
 * 用于构建复杂的多表连接查询，支持指定返回字段和条件
 */
public class JoinBuilder<T> {
    private final Class<T> rootClass;
    private final Map<Class<?>, JoinInfo> joins = new HashMap<>();
    private final Map<Class<?>, List<Condition>> conditions = new HashMap<>();
    private Map<Class<?>, String[]> selectedFields;
    private Map<String, Object> namedSelections = new LinkedHashMap<>();

    private JoinBuilder(Class<T> rootClass) {
        this.rootClass = rootClass;
    }

    public static <T> JoinBuilder<T> from(Class<T> rootClass) {
        return new JoinBuilder<>(rootClass);
    }

    /**
     * 添加连接表
     * @param joinClass 要连接的表实体类
     * @param sourceField 主表的外键字段
     * @param targetField 连接表的目标字段
     */
    public JoinBuilder<T> join(Class<?> joinClass, String sourceField, String targetField) {
        joins.put(joinClass, new JoinInfo(sourceField, targetField));
        return this;
    }
    
    /**
     * 添加连接表（使用方法引用）
     * @param joinClass 要连接的表实体类
     * @param sourceFieldGetter 主表外键字段的getter方法引用
     * @param targetFieldGetter 连接表目标字段的getter方法引用
     */
    public <J, V> JoinBuilder<T> join(Class<J> joinClass, 
                                     Function<T, V> sourceFieldGetter, 
                                     Function<J, V> targetFieldGetter) {
        String sourceField = getFieldNameFromGetter(sourceFieldGetter);
        String targetField = getFieldNameFromGetter(targetFieldGetter);
        return join(joinClass, sourceField, targetField);
    }

    /**
     * 添加等值条件
     * @param entityClass 实体类
     * @param fieldName 字段名
     * @param value 字段值
     */
    public <V> JoinBuilder<T> equal(Class<?> entityClass, String fieldName, V value) {
        if (!conditions.containsKey(entityClass)) {
            conditions.put(entityClass, new ArrayList<>());
        }
        conditions.get(entityClass).add(new Condition(fieldName, value, Operator.EQUAL));
        return this;
    }
    
    /**
     * 添加等值条件（使用方法引用）
     * @param entityClass 实体类
     * @param fieldGetter 字段的getter方法引用
     * @param value 字段值
     */
    public <E, V> JoinBuilder<T> equal(Class<E> entityClass, Function<E, V> fieldGetter, V value) {
        String fieldName = getFieldNameFromGetter(fieldGetter);
        return equal(entityClass, fieldName, value);
    }

    /**
     * 选择返回的字段
     * @param selectedFields 每个实体类需要返回的字段映射
     */
    public JoinBuilder<T> selectFields(Map<Class<?>, String[]> selectedFields) {
        this.selectedFields = selectedFields;
        return this;
    }
    
    /**
     * 选择返回的字段（使用方法引用）
     * @param fieldGetters 方法引用列表
     */
    @SafeVarargs
    public final <E> JoinBuilder<T> select(Class<E> entityClass, Function<E, ?>... fieldGetters) {
        if (selectedFields == null) {
            selectedFields = new HashMap<>();
        }
        
        String[] fieldNames = Arrays.stream(fieldGetters)
                .map(this::getFieldNameFromGetter)
                .toArray(String[]::new);
        
        selectedFields.put(entityClass, fieldNames);
        return this;
    }
    
    /**
     * 添加一个具有别名的字段选择（优先级高于select方法）
     * @param alias 字段别名
     * @param entityClass 实体类
     * @param fieldGetter 字段的getter方法引用
     */
    public <E, V> JoinBuilder<T> selectAs(String alias, Class<E> entityClass, Function<E, V> fieldGetter) {
        String fieldName = getFieldNameFromGetter(fieldGetter);
        
        // 存储字段信息，稍后在configureSelections处理
        if (selectedFields == null) {
            selectedFields = new HashMap<>();
        }
        if (!selectedFields.containsKey(entityClass)) {
            selectedFields.put(entityClass, new String[0]);
        }
        namedSelections.put(alias, new SelectionInfo(entityClass, fieldName));
        
        return this;
    }

    /**
     * 添加一个具有别名的字段选择（字符串版本）
     * @param alias 字段别名
     * @param entityClass 实体类
     * @param fieldName 字段名称
     */
    public <E> JoinBuilder<T> selectAs(String alias, Class<E> entityClass, String fieldName) {
        // 存储字段信息，稍后在configureSelections处理
        if (selectedFields == null) {
            selectedFields = new HashMap<>();
        }
        if (!selectedFields.containsKey(entityClass)) {
            selectedFields.put(entityClass, new String[0]);
        }
        namedSelections.put(alias, new SelectionInfo(entityClass, fieldName));
        
        return this;
    }
    
    /**
     * 设置实体间字段映射关系的别名，以便对应DTO字段
     * @param dtoClass DTO类
     * @param mappings 字段映射
     */
    @SafeVarargs
    public final <R> JoinBuilder<T> selectDto(Class<R> dtoClass, FieldMapping<R, ?>... mappings) {
        for (FieldMapping<R, ?> mapping : mappings) {
            String dtoFieldName = getFieldNameFromGetter(mapping.getDtoFieldGetter());
            String entityFieldName = getFieldNameFromGetter(mapping.getEntityFieldGetter());
            Class<?> entityClass = mapping.getEntityClass();
            
            // 存储字段信息，稍后在configureSelections处理
            if (selectedFields == null) {
                selectedFields = new HashMap<>();
            }
            if (!selectedFields.containsKey(entityClass)) {
                selectedFields.put(entityClass, new String[0]);
            }
            namedSelections.put(dtoFieldName, new SelectionInfo(entityClass, entityFieldName));
        }
        return this;
    }

    /**
     * 构建规范查询
     * @return Specification<T> 查询规范
     */
    public Specification<T> build() {
        return (root, query, criteriaBuilder) -> {
            // 创建连接关系
            Map<Class<?>, From<?, ?>> joinMap = createJoins(root, query);

            // 应用连表条件和其他条件
            List<Predicate> predicates = applyAllConditions(root, joinMap, criteriaBuilder);

            // 设置查询结果投影
            configureSelections(root, joinMap, query);

            return criteriaBuilder.and(predicates.toArray(new Predicate[0]));
        };
    }
    
    /**
     * 执行查询并返回结果
     * @param entityManager EntityManager实例
     * @return 查询结果列表
     */
    public List<Object[]> execute(EntityManager entityManager) {
        // 创建CriteriaBuilder
        CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
        
        // 创建CriteriaQuery
        CriteriaQuery<Object[]> criteriaQuery = criteriaBuilder.createQuery(Object[].class);
        
        // 设置根实体
        Root<T> root = criteriaQuery.from(rootClass);
        
        // 创建连接关系
        Map<Class<?>, From<?, ?>> fromMap = createJoins(root, criteriaQuery);
        
        // 应用所有条件，包括表之间的连接条件和额外查询条件
        List<Predicate> predicates = applyAllConditions(root, fromMap, criteriaBuilder);
        
        // 添加条件到查询
        if (!predicates.isEmpty()) {
            criteriaQuery.where(criteriaBuilder.and(predicates.toArray(new Predicate[0])));
        }
        
        // 设置查询结果投影
        configureSelections(root, fromMap, criteriaQuery);
        
        // 执行查询并返回结果
        return entityManager.createQuery(criteriaQuery).getResultList();
    }
    
    /**
     * 创建连接 - 修改为使用from而不是join
     */
    private Map<Class<?>, From<?, ?>> createJoins(Root<T> root, CriteriaQuery<?> query) {
        Map<Class<?>, From<?, ?>> fromMap = new HashMap<>();
        fromMap.put(rootClass, root);
        
        // 对于每个需要连接的表，创建一个单独的From
        for (Map.Entry<Class<?>, JoinInfo> entry : joins.entrySet()) {
            Class<?> joinClass = entry.getKey();
            From<?, ?> joinRoot = query.from(joinClass);
            fromMap.put(joinClass, joinRoot);
        }
        
        return fromMap;
    }
    
    /**
     * 应用所有条件，包括表之间的连接条件和额外查询条件
     */
    private List<Predicate> applyAllConditions(Root<T> root, Map<Class<?>, From<?, ?>> fromMap, CriteriaBuilder criteriaBuilder) {
        List<Predicate> predicates = new ArrayList<>();
        
        // 首先添加表连接条件
        for (Map.Entry<Class<?>, JoinInfo> entry : joins.entrySet()) {
            Class<?> joinClass = entry.getKey();
            JoinInfo joinInfo = entry.getValue();
            
            if (fromMap.containsKey(joinClass)) {
                From<?, ?> joinFrom = fromMap.get(joinClass);
                Predicate joinCondition = criteriaBuilder.equal(
                    root.get(joinInfo.sourceField),
                    joinFrom.get(joinInfo.targetField)
                );
                predicates.add(joinCondition);
            }
        }
        
        // 然后添加普通查询条件
        for (Class<?> entityClass : conditions.keySet()) {
            for (Condition condition : conditions.get(entityClass)) {
                if (fromMap.containsKey(entityClass)) {
                    From<?, ?> from = fromMap.get(entityClass);
                    predicates.add(applyCondition(condition, from, criteriaBuilder));
                }
            }
        }
        
        return predicates;
    }
    
    /**
     * 执行查询并直接映射到DTO对象
     * @param entityManager EntityManager实例
     * @param dtoClass DTO类
     * @param <R> DTO类型
     * @return DTO对象列表
     */
    public <R> List<R> executeAndMap(EntityManager entityManager, Class<R> dtoClass) {
        List<Object[]> results = execute(entityManager);
        return mapToDto(results, dtoClass);
    }
    
    /**
     * 将查询结果映射到DTO对象
     * @param results 查询结果
     * @param dtoClass DTO类
     * @param <R> DTO类型
     * @return DTO对象列表
     */
    public <R> List<R> mapToDto(List<Object[]> results, Class<R> dtoClass) {
        try {
            // 获取所有字段名（顺序与查询结果一致）
            List<String> fieldNames = new ArrayList<>(namedSelections.keySet());
            
            // 获取构造函数
            Class<?>[] paramTypes = new Class[fieldNames.size()];
            Arrays.fill(paramTypes, Object.class);
            Constructor<R> constructor = dtoClass.getDeclaredConstructor(paramTypes);
            
            // 映射结果
            return results.stream()
                    .map(row -> {
                        try {
                            return constructor.newInstance(row);
                        } catch (Exception e) {
                            throw new RuntimeException("Failed to map result to DTO: " + e.getMessage(), e);
                        }
                    })
                    .collect(Collectors.toList());
        } catch (Exception e) {
            throw new RuntimeException("Failed to create DTO mapper: " + e.getMessage(), e);
        }
    }
    
    /**
     * 配置查询结果投影
     */
    private void configureSelections(Root<T> root, Map<Class<?>, From<?, ?>> fromMap, CriteriaQuery<?> query) {
        if (!namedSelections.isEmpty()) {
            // 处理命名选择
            List<Selection<?>> selections = new ArrayList<>();
            
            for (Map.Entry<String, Object> entry : namedSelections.entrySet()) {
                String alias = entry.getKey();
                Object value = entry.getValue();
                
                if (value instanceof SelectionInfo) {
                    SelectionInfo info = (SelectionInfo) value;
                    Path<?> path;
                    
                    if (fromMap.containsKey(info.entityClass)) {
                        path = fromMap.get(info.entityClass).get(info.fieldName);
                        selections.add(path.alias(alias));
                    }
                }
            }
            
            if (!selections.isEmpty()) {
                query.multiselect(selections);
                return;
            }
        }
        
        // 如果没有命名选择或处理失败，回退到原来的处理方式
        if (selectedFields != null && !selectedFields.isEmpty()) {
            List<Selection<?>> selections = new ArrayList<>();
            
            // 添加根实体的选择字段
            if (selectedFields.containsKey(rootClass)) {
                for (String field : selectedFields.get(rootClass)) {
                    selections.add(root.get(field));
                }
            }
            
            // 添加关联实体的选择字段
            for (Class<?> entityClass : selectedFields.keySet()) {
                if (entityClass != rootClass && fromMap.containsKey(entityClass)) {
                    From<?, ?> from = fromMap.get(entityClass);
                    for (String field : selectedFields.get(entityClass)) {
                        selections.add(from.get(field));
                    }
                }
            }
            
            if (!selections.isEmpty()) {
                query.multiselect(selections);
            }
        }
    }

    private <X> Predicate applyCondition(Condition condition, From<?, X> from, CriteriaBuilder criteriaBuilder) {
        switch (condition.operator) {
            case EQUAL:
                return criteriaBuilder.equal(from.get(condition.fieldName), condition.value);
            // 可以添加更多操作符支持，如LIKE, IN, GREATER_THAN等
            default:
                throw new UnsupportedOperationException("Unsupported operator: " + condition.operator);
        }
    }
    
    /**
     * 从getter方法引用中提取属性名
     */
    private <E, R> String getFieldNameFromGetter(Function<E, R> getter) {
        // 直接尝试从方法引用的toString中获取
        try {
            String methodRef = getter.toString();
            if (methodRef.contains("::")) {
                // 处理方法引用格式: com.example.Entity::getName
                String methodName = methodRef.substring(methodRef.lastIndexOf("::") + 2);
                return extractFieldNameFromMethod(methodName);
            } else if (methodRef.contains("->")) {
                // 处理Lambda表达式格式: (Entity e) -> e.getName()
                String methodCall = methodRef.substring(methodRef.indexOf("->") + 2).trim();
                String methodName = methodCall.substring(methodCall.lastIndexOf(".") + 1);
                if (methodName.endsWith(")")) {
                    methodName = methodName.substring(0, methodName.indexOf("("));
                }
                return extractFieldNameFromMethod(methodName);
            }
        } catch (Exception ignored) {
            // 忽略异常，尝试下一种方法
        }
        
        try {
            String getterName = getter.getClass().getName();
            if (getterName.contains("$$Lambda$")) {
                // 处理Lambda表达式
                if (getterName.contains("get")) {
                    // 尝试从名称中提取字段名
                    int getIndex = getterName.lastIndexOf("get");
                    if (getIndex >= 0 && getIndex + 3 < getterName.length()) {
                        String fieldName = getterName.substring(getIndex + 3);
                        if (fieldName.indexOf('$') > 0) {
                            fieldName = fieldName.substring(0, fieldName.indexOf('$'));
                        }
                        return fieldName.substring(0, 1).toLowerCase() + fieldName.substring(1);
                    }
                }
            }
        } catch (Exception ignored) {
            // 忽略异常，fallback到基于字符串的方法
        }
        
        // Fallback到基于字符串的方法
        String methodReference = getter.toString();
        return getFieldNameFromGetterString(methodReference);
    }
    
    /**
     * 从getter方法字符串中提取属性名
     */
    private String getFieldNameFromGetterString(String methodReference) {
        // 方法引用的格式通常是：类名::get字段名 或 Lambda表达式
        if (methodReference.contains("::")) {
            // 处理方法引用格式: com.example.Entity::getName
            String methodName = methodReference.substring(methodReference.lastIndexOf("::") + 2);
            return extractFieldNameFromMethod(methodName);
        } else if (methodReference.contains("->")) {
            // 处理Lambda表达式格式: (Entity e) -> e.getName()
            String methodCall = methodReference.substring(methodReference.indexOf("->") + 2).trim();
            String methodName = methodCall.substring(methodCall.lastIndexOf(".") + 1);
            if (methodName.endsWith(")")) {
                methodName = methodName.substring(0, methodName.indexOf("("));
            }
            return extractFieldNameFromMethod(methodName);
        }
        
        // 无法识别的格式，返回原始字符串
        return methodReference;
    }
    
    /**
     * 从方法名中提取字段名
     */
    private String extractFieldNameFromMethod(String methodName) {
        if (methodName.startsWith("get") && methodName.length() > 3) {
            // getName -> name (首字母小写)
            String fieldName = methodName.substring(3);
            return fieldName.substring(0, 1).toLowerCase() + fieldName.substring(1);
        } else if (methodName.startsWith("is") && methodName.length() > 2) {
            // isActive -> active (首字母小写)
            String fieldName = methodName.substring(2);
            return fieldName.substring(0, 1).toLowerCase() + fieldName.substring(1);
        }
        return methodName;
    }
    
    /**
     * 首字母大写
     */
    private String capitalize(String str) {
        if (str == null || str.isEmpty()) {
            return str;
        }
        return str.substring(0, 1).toUpperCase() + str.substring(1);
    }

    private enum Operator {
        EQUAL
        // 可以添加更多操作符支持，如LIKE, IN, GREATER_THAN等
    }

    private static class Condition {
        private final String fieldName;
        private final Object value;
        private final Operator operator;

        Condition(String fieldName, Object value, Operator operator) {
            this.fieldName = fieldName;
            this.value = value;
            this.operator = operator;
        }
    }
    
    /**
     * 连接信息
     */
    private static class JoinInfo {
        private final String sourceField;
        private final String targetField;
        
        JoinInfo(String sourceField, String targetField) {
            this.sourceField = sourceField;
            this.targetField = targetField;
        }
    }
    
    /**
     * 选择字段信息
     */
    private static class SelectionInfo {
        private final Class<?> entityClass;
        private final String fieldName;
        
        SelectionInfo(Class<?> entityClass, String fieldName) {
            this.entityClass = entityClass;
            this.fieldName = fieldName;
        }
    }
    
    /**
     * 字段映射定义，用于DTO映射
     */
    public static class FieldMapping<D, E> {
        private final Function<D, ?> dtoFieldGetter;
        private final Function<E, ?> entityFieldGetter;
        private final Class<E> entityClass;
        
        private FieldMapping(Function<D, ?> dtoFieldGetter, Function<E, ?> entityFieldGetter, Class<E> entityClass) {
            this.dtoFieldGetter = dtoFieldGetter;
            this.entityFieldGetter = entityFieldGetter;
            this.entityClass = entityClass;
        }
        
        public static <D, E, V> FieldMapping<D, E> of(Function<D, V> dtoFieldGetter, Function<E, V> entityFieldGetter) {
            // 通过反射或其他方式获取entityClass
            Class<E> entityClass = null;
            try {
                // 尝试从方法引用中提取类信息
                String methodRef = entityFieldGetter.toString();
                if (methodRef.contains("::")) {
                    String className = methodRef.substring(0, methodRef.indexOf("::"));
                    entityClass = (Class<E>) Class.forName(className);
                }
            } catch (Exception e) {
                // 忽略异常，entityClass将在运行时确定
            }
            
            return new FieldMapping<>(dtoFieldGetter, entityFieldGetter, entityClass);
        }
        
        public Function<D, ?> getDtoFieldGetter() {
            return dtoFieldGetter;
        }
        
        public Function<E, ?> getEntityFieldGetter() {
            return entityFieldGetter;
        }
        
        public Class<?> getEntityClass() {
            return entityClass;
        }
    }
}