package com.accounting.util;

import org.junit.jupiter.api.DisplayName;
import org.junit.jupiter.api.Test;

import java.math.BigDecimal;
import java.time.LocalDate;

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertFalse;
import static org.junit.jupiter.api.Assertions.assertTrue;

/**
 * 减重计划计算测试。
 *
 * <p>这块是「设置目标 → 每周该减多少」的核心算术，也是最容易出现
 * 边界问题的地方：同日、超期、目标比起始还重、除零。所以边界用例
 * 写得比正常用例还多。</p>
 */
class WeightPlanCalculatorTest {

    @Test
    @DisplayName("三个月 65→58kg：总减 7kg 分到 13 周，每周 0.54kg")
    void weeklyLossForThreeMonths() {
        LocalDate start = LocalDate.of(2026, 1, 1);
        LocalDate target = LocalDate.of(2026, 4, 1);  // 90 天

        int weeks = WeightPlanCalculator.totalWeeks(start, target);
        assertEquals(13, weeks);

        BigDecimal weekly = WeightPlanCalculator.weeklyLoss(
                new BigDecimal("65"), new BigDecimal("58"), weeks);
        assertEquals(new BigDecimal("0.54"), weekly);
    }

    @Test
    @DisplayName("总天数除不尽 7 时向上取整 —— 少算一周会让每周目标偏轻")
    void roundsUpPartialWeek() {
        // 8 天 = 1 周 + 1 天，应该算 2 周而不是 1 周
        assertEquals(2, WeightPlanCalculator.totalWeeks(
                LocalDate.of(2026, 1, 1), LocalDate.of(2026, 1, 9)));
        // 6 天算 1 周
        assertEquals(1, WeightPlanCalculator.totalWeeks(
                LocalDate.of(2026, 1, 1), LocalDate.of(2026, 1, 7)));
    }

    @Test
    @DisplayName("同日或倒填日期都算 1 周，不除零")
    void sameDayFallsBackToOneWeek() {
        LocalDate day = LocalDate.of(2026, 1, 1);

        assertEquals(1, WeightPlanCalculator.totalWeeks(day, day));
        // 目标日期早于开始日期也不该崩
        assertEquals(1, WeightPlanCalculator.totalWeeks(day, day.minusDays(5)));

        // 1 周减 7kg 是个荒谬的值，但必须是个数、不能是异常
        assertEquals(new BigDecimal("7.00"), WeightPlanCalculator.weeklyLoss(
                new BigDecimal("65"), new BigDecimal("58"), 1));
    }

    @Test
    @DisplayName("目标比起始还重时每周应减为 0，不能是负数")
    void gainingWeightGivesZeroNotNegative() {
        // 负数会让进度条宽度算反、也会让「每周应减」显示成 -0.5kg
        assertEquals(BigDecimal.ZERO, WeightPlanCalculator.weeklyLoss(
                new BigDecimal("58"), new BigDecimal("65"), 13));
        assertEquals(BigDecimal.ZERO, WeightPlanCalculator.weeklyLoss(
                new BigDecimal("60"), new BigDecimal("60"), 13));
    }

    @Test
    @DisplayName("理想体重曲线：第 0 周是起始体重，最后一周落在目标上")
    void idealCurveEndsAtTarget() {
        BigDecimal start = new BigDecimal("65");
        BigDecimal target = new BigDecimal("58");
        BigDecimal weekly = new BigDecimal("0.54");

        assertEquals(new BigDecimal("65.0"),
                WeightPlanCalculator.idealWeightAt(start, target, weekly, 0));

        // 第 13 周：65 - 0.54*13 = 57.98，低于目标 58 → 应该钉在 58
        assertEquals(new BigDecimal("58"),
                WeightPlanCalculator.idealWeightAt(start, target, weekly, 13));
    }

    @Test
    @DisplayName("理想体重不会跌破目标 —— 否则参照线会穿到目标下方")
    void idealWeightNeverGoesBelowTarget() {
        BigDecimal target = new BigDecimal("58");
        // 刻意给一个过大的每周减重
        BigDecimal ideal = WeightPlanCalculator.idealWeightAt(
                new BigDecimal("65"), target, new BigDecimal("2.0"), 10);
        assertEquals(target, ideal);
    }

    @Test
    @DisplayName("时间进度：未开始 0、进行中在 0~1、超期封顶 1.0")
    void timeProgressIsClamped() {
        LocalDate start = LocalDate.of(2026, 1, 1);
        LocalDate target = LocalDate.of(2026, 1, 11);  // 10 天

        // 还没开始
        assertEquals(0.0, WeightPlanCalculator.timeProgress(start, target,
                LocalDate.of(2025, 12, 20)));
        // 正中间
        assertEquals(0.5, WeightPlanCalculator.timeProgress(start, target,
                LocalDate.of(2026, 1, 6)), 0.001);
        // 已超期：封顶 1.0，不是 1.5 —— 进度条宽度不能溢出
        assertEquals(1.0, WeightPlanCalculator.timeProgress(start, target,
                LocalDate.of(2026, 3, 1)));
    }

    @Test
    @DisplayName("每周超过 1kg 会被标记成不健康")
    void flagsUnhealthyPace() {
        // 65→58 只用 3 周 = 每周 2.33kg
        BigDecimal weekly = WeightPlanCalculator.weeklyLoss(
                new BigDecimal("65"), new BigDecimal("58"), 3);
        assertTrue(weekly.compareTo(WeightPlanCalculator.HEALTHY_WEEKLY_LOSS_KG) > 0);

        // 正常节奏不该被标
        BigDecimal healthy = WeightPlanCalculator.weeklyLoss(
                new BigDecimal("65"), new BigDecimal("58"), 13);
        assertFalse(healthy.compareTo(WeightPlanCalculator.HEALTHY_WEEKLY_LOSS_KG) > 0);
    }
}