import java.time.LocalDate;
import java.time.Period;
import java.util.*;
import java.util.stream.Collectors;

/**
 * 员工统计类 - 负责生成复杂的统计报告
 * 遵循单一职责原则：只负责员工数据的统计分析逻辑
 */
public class EmployeeStatistics {
    
    /**
     * 计算员工薪资总额
     * @param employees 员工列表
     * @return 薪资总额
     */
    public double calculateTotalSalary(List<Employee> employees) {
        return employees.stream()
                .mapToDouble(Employee::getSalary)
                .sum();
    }
    
    /**
     * 计算员工平均薪资
     * @param employees 员工列表
     * @return 平均薪资
     */
    public double calculateAverageSalary(List<Employee> employees) {
        if (employees.isEmpty()) {
            return 0;
        }
        return calculateTotalSalary(employees) / employees.size();
    }
    
    /**
     * 获取最高薪资
     * @param employees 员工列表
     * @return 最高薪资
     */
    public double getMaxSalary(List<Employee> employees) {
        if (employees.isEmpty()) {
            return 0;
        }
        return employees.stream()
                .mapToDouble(Employee::getSalary)
                .max()
                .orElse(0);
    }
    
    /**
     * 获取最低薪资
     * @param employees 员工列表
     * @return 最低薪资
     */
    public double getMinSalary(List<Employee> employees) {
        if (employees.isEmpty()) {
            return 0;
        }
        return employees.stream()
                .mapToDouble(Employee::getSalary)
                .min()
                .orElse(0);
    }
    
    /**
     * 计算部门薪资分布
     * @param employees 员工列表
     * @return 部门薪资分布映射（部门 -> 薪资统计）
     */
    public Map<String, DepartmentSalaryStats> calculateDepartmentSalaryDistribution(List<Employee> employees) {
        return employees.stream()
                .collect(Collectors.groupingBy(Employee::getDepartment))
                .entrySet().stream()
                .collect(Collectors.toMap(
                        Map.Entry::getKey,
                        entry -> {
                            List<Employee> deptEmployees = entry.getValue();
                            double totalSalary = deptEmployees.stream().mapToDouble(Employee::getSalary).sum();
                            double avgSalary = deptEmployees.isEmpty() ? 0 : totalSalary / deptEmployees.size();
                            double maxSalary = deptEmployees.stream().mapToDouble(Employee::getSalary).max().orElse(0);
                            double minSalary = deptEmployees.stream().mapToDouble(Employee::getSalary).min().orElse(0);
                            return new DepartmentSalaryStats(totalSalary, avgSalary, maxSalary, minSalary, deptEmployees.size());
                        }
                ));
    }
    
    /**
     * 计算员工年龄分布
     * @param employees 员工列表
     * @return 年龄分布映射（年龄段 -> 人数）
     */
    public Map<String, Long> calculateAgeDistribution(List<Employee> employees) {
        return employees.stream()
                .collect(Collectors.groupingBy(
                        e -> {
                            int age = e.getAge();
                            if (age < 25) return "25岁以下";
                            else if (age < 35) return "25-34岁";
                            else if (age < 45) return "35-44岁";
                            else if (age < 55) return "45-54岁";
                            else return "55岁以上";
                        },
                        Collectors.counting()
                ));
    }
    
    /**
     * 计算员工司龄分布
     * @param employees 员工列表
     * @return 司龄分布映射（司龄段 -> 人数）
     */
    public Map<String, Long> calculateTenureDistribution(List<Employee> employees) {
        return employees.stream()
                .collect(Collectors.groupingBy(
                        e -> {
                            int tenure = e.getTenure();
                            if (tenure < 1) return "不足1年";
                            else if (tenure < 3) return "1-2年";
                            else if (tenure < 5) return "3-4年";
                            else if (tenure < 10) return "5-9年";
                            else return "10年以上";
                        },
                        Collectors.counting()
                ));
    }
    
    /**
     * 计算部门人数分布
     * @param employees 员工列表
     * @return 部门人数分布映射（部门 -> 人数）
     */
    public Map<String, Long> calculateDepartmentHeadcount(List<Employee> employees) {
        return employees.stream()
                .collect(Collectors.groupingBy(Employee::getDepartment, Collectors.counting()));
    }
    
    /**
     * 获取指定年份入职的员工数
     * @param employees 员工列表
     * @param year 年份
     * @return 该年份入职的员工数
     */
    public long getHireCountByYear(List<Employee> employees, int year) {
        return employees.stream()
                .filter(e -> e.getHireDate().getYear() == year)
                .count();
    }
    
    /**
     * 计算性别分布（如果Employee类中有性别属性）
     * 这里作为示例，假设Employee类有gender属性
     * @param employees 员工列表
     * @return 性别分布映射（性别 -> 人数）
     */
    // 由于Employee类中没有性别属性，此方法作为示例保留
    public Map<String, Long> calculateGenderDistribution(List<Employee> employees) {
        // 实际实现需要在Employee类中添加gender属性
        System.out.println("注意：Employee类中暂未添加性别属性，无法计算性别分布");
        return new HashMap<>();
    }
    
    /**
     * 获取薪资排名前N的员工
     * @param employees 员工列表
     * @param n 数量
     * @return 薪资最高的N名员工
     */
    public List<Employee> getTopNSalaryEmployees(List<Employee> employees, int n) {
        if (n <= 0) {
            throw new IllegalArgumentException("N必须为正整数");
        }
        
        return employees.stream()
                .sorted(Comparator.comparingDouble(Employee::getSalary).reversed())
                .limit(n)
                .collect(Collectors.toList());
    }
    
    /**
     * 计算在职率
     * @param employees 员工列表
     * @return 在职率（百分比）
     */
    public double calculateActiveRate(List<Employee> employees) {
        if (employees.isEmpty()) {
            return 0;
        }
        long activeCount = employees.stream()
                .filter(Employee::isActive)
                .count();
        return (double) activeCount / employees.size() * 100;
    }
    
    /**
     * 部门薪资统计内部类
     */
    public static class DepartmentSalaryStats {
        private final double totalSalary;
        private final double averageSalary;
        private final double maxSalary;
        private final double minSalary;
        private final int headcount;
        
        public DepartmentSalaryStats(double totalSalary, double averageSalary, 
                                   double maxSalary, double minSalary, int headcount) {
            this.totalSalary = totalSalary;
            this.averageSalary = averageSalary;
            this.maxSalary = maxSalary;
            this.minSalary = minSalary;
            this.headcount = headcount;
        }
        
        public double getTotalSalary() { return totalSalary; }
        public double getAverageSalary() { return averageSalary; }
        public double getMaxSalary() { return maxSalary; }
        public double getMinSalary() { return minSalary; }
        public int getHeadcount() { return headcount; }
        
        @Override
        public String toString() {
            return "部门薪资统计{" +
                   "总薪资= " + totalSalary +
                   ", 平均薪资= " + String.format("%.2f", averageSalary) +
                   ", 最高薪资= " + maxSalary +
                   ", 最低薪资= " + minSalary +
                   ", 人数= " + headcount +
                   "}";
        }
    }
}