import java.time.LocalDateTime;
import java.util.*;
import java.util.stream.Collectors;

/**
 * 员工历史记录类 - 负责记录员工的历史变更信息
 * 遵循单一职责原则：只负责员工变更历史的记录和管理
 */
public class EmployeeHistory {
    private final String employeeId;
    private final List<ChangeRecord> historyRecords;
    
    /**
     * 构造函数
     * @param employeeId 员工ID
     */
    public EmployeeHistory(String employeeId) {
        this.employeeId = employeeId;
        this.historyRecords = new ArrayList<>();
    }
    
    /**
     * 记录薪资调整历史
     * @param oldSalary 调整前薪资
     * @param newSalary 调整后薪资
     * @param reason 调整原因
     * @param changedBy 操作人
     */
    public void recordSalaryChange(double oldSalary, double newSalary, String reason, String changedBy) {
        String description = String.format("薪资从 %.2f 调整为 %.2f", oldSalary, newSalary);
        ChangeRecord record = new ChangeRecord(ChangeType.SALARY_ADJUSTMENT, 
                                              description, reason, changedBy);
        historyRecords.add(record);
    }
    
    /**
     * 记录职位变更历史
     * @param oldPosition 原职位
     * @param newPosition 新职位
     * @param reason 变更原因
     * @param changedBy 操作人
     */
    public void recordPositionChange(String oldPosition, String newPosition, String reason, String changedBy) {
        String description = String.format("职位从 '%s' 变更为 '%s'", oldPosition, newPosition);
        ChangeRecord record = new ChangeRecord(ChangeType.POSITION_CHANGE, 
                                              description, reason, changedBy);
        historyRecords.add(record);
    }
    
    /**
     * 记录部门变更历史
     * @param oldDepartment 原部门
     * @param newDepartment 新部门
     * @param reason 变更原因
     * @param changedBy 操作人
     */
    public void recordDepartmentChange(String oldDepartment, String newDepartment, String reason, String changedBy) {
        String description = String.format("部门从 '%s' 变更为 '%s'", oldDepartment, newDepartment);
        ChangeRecord record = new ChangeRecord(ChangeType.DEPARTMENT_CHANGE, 
                                              description, reason, changedBy);
        historyRecords.add(record);
    }
    
    /**
     * 记录员工状态变更历史（在职/离职）
     * @param newStatus 新状态
     * @param reason 变更原因
     * @param changedBy 操作人
     */
    public void recordStatusChange(boolean newStatus, String reason, String changedBy) {
        String description = "状态变更为 " + (newStatus ? "在职" : "离职");
        ChangeRecord record = new ChangeRecord(ChangeType.STATUS_CHANGE, 
                                              description, reason, changedBy);
        historyRecords.add(record);
    }
    
    /**
     * 记录员工基本信息变更历史
     * @param fieldName 变更的字段名
     * @param oldValue 旧值
     * @param newValue 新值
     * @param changedBy 操作人
     */
    public void recordInfoChange(String fieldName, String oldValue, String newValue, String changedBy) {
        String description = String.format("%s 从 '%s' 变更为 '%s'", fieldName, oldValue, newValue);
        ChangeRecord record = new ChangeRecord(ChangeType.INFO_CHANGE, 
                                              description, "信息更新", changedBy);
        historyRecords.add(record);
    }
    
    /**
     * 记录培训完成历史
     * @param courseName 课程名称
     * @param certificateId 证书ID
     * @param score 成绩
     * @param changedBy 操作人
     */
    public void recordTrainingCompletion(String courseName, String certificateId, double score, String changedBy) {
        String description = String.format("完成课程 '%s'，证书ID: %s，成绩: %.2f", 
                                          courseName, certificateId, score);
        ChangeRecord record = new ChangeRecord(ChangeType.TRAINING_COMPLETION, 
                                              description, "培训完成", changedBy);
        historyRecords.add(record);
    }
    
    /**
     * 获取所有历史记录
     * @return 按时间倒序排列的历史记录列表
     */
    public List<ChangeRecord> getAllHistory() {
        List<ChangeRecord> sortedRecords = new ArrayList<>(historyRecords);
        sortedRecords.sort(Comparator.comparing(ChangeRecord::getChangeTime).reversed());
        return sortedRecords;
    }
    
    /**
     * 按变更类型获取历史记录
     * @param changeType 变更类型
     * @return 指定类型的历史记录列表
     */
    public List<ChangeRecord> getHistoryByType(ChangeType changeType) {
        return historyRecords.stream()
                .filter(record -> record.getChangeType() == changeType)
                .sorted(Comparator.comparing(ChangeRecord::getChangeTime).reversed())
                .collect(Collectors.toList());
    }
    
    /**
     * 获取特定时间段内的历史记录
     * @param startTime 开始时间
     * @param endTime 结束时间
     * @return 时间段内的历史记录列表
     */
    public List<ChangeRecord> getHistoryByTimeRange(LocalDateTime startTime, LocalDateTime endTime) {
        return historyRecords.stream()
                .filter(record -> !record.getChangeTime().isBefore(startTime) && 
                                  !record.getChangeTime().isAfter(endTime))
                .sorted(Comparator.comparing(ChangeRecord::getChangeTime).reversed())
                .collect(Collectors.toList());
    }
    
    /**
     * 获取最后N条历史记录
     * @param n 记录数量
     * @return 最近的N条历史记录
     */
    public List<ChangeRecord> getLatestHistory(int n) {
        List<ChangeRecord> sortedRecords = new ArrayList<>(historyRecords);
        sortedRecords.sort(Comparator.comparing(ChangeRecord::getChangeTime).reversed());
        return sortedRecords.stream().limit(n).collect(Collectors.toList());
    }
    
    /**
     * 获取薪资变更次数
     * @return 薪资变更次数
     */
    public int getSalaryChangeCount() {
        return (int) historyRecords.stream()
                .filter(record -> record.getChangeType() == ChangeType.SALARY_ADJUSTMENT)
                .count();
    }
    
    /**
     * 获取职位变更次数
     * @return 职位变更次数
     */
    public int getPositionChangeCount() {
        return (int) historyRecords.stream()
                .filter(record -> record.getChangeType() == ChangeType.POSITION_CHANGE)
                .count();
    }
    
    /**
     * 获取部门变更次数
     * @return 部门变更次数
     */
    public int getDepartmentChangeCount() {
        return (int) historyRecords.stream()
                .filter(record -> record.getChangeType() == ChangeType.DEPARTMENT_CHANGE)
                .count();
    }
    
    /**
     * 获取培训完成次数
     * @return 培训完成次数
     */
    public int getTrainingCompletionCount() {
        return (int) historyRecords.stream()
                .filter(record -> record.getChangeType() == ChangeType.TRAINING_COMPLETION)
                .count();
    }
    
    /**
     * 获取员工ID
     * @return 员工ID
     */
    public String getEmployeeId() {
        return employeeId;
    }
    
    /**
     * 获取历史记录总数
     * @return 历史记录总数
     */
    public int getTotalRecordCount() {
        return historyRecords.size();
    }
    
    /**
     * 变更类型枚举
     */
    public enum ChangeType {
        SALARY_ADJUSTMENT,   // 薪资调整
        POSITION_CHANGE,     // 职位变更
        DEPARTMENT_CHANGE,   // 部门变更
        STATUS_CHANGE,       // 状态变更
        INFO_CHANGE,         // 信息变更
        TRAINING_COMPLETION  // 培训完成
    }
    
    /**
     * 变更记录内部类
     */
    public static class ChangeRecord {
        private final ChangeType changeType;
        private final String description;
        private final String reason;
        private final String changedBy;
        private final LocalDateTime changeTime;
        
        public ChangeRecord(ChangeType changeType, String description, String reason, String changedBy) {
            this.changeType = changeType;
            this.description = description;
            this.reason = reason;
            this.changedBy = changedBy;
            this.changeTime = LocalDateTime.now();
        }
        
        public ChangeType getChangeType() { return changeType; }
        public String getDescription() { return description; }
        public String getReason() { return reason; }
        public String getChangedBy() { return changedBy; }
        public LocalDateTime getChangeTime() { return changeTime; }
        
        @Override
        public String toString() {
            return String.format("[%s] %s | 原因: %s | 操作人: %s | 时间: %s",
                    changeType.name(), description, reason, changedBy, changeTime);
        }
    }
}