From 3a61b7952bb70cf243d3ba6640fdf87e59621544 Mon Sep 17 00:00:00 2001
From: yuming <yuming@baijia.com>
Date: Sat, 15 Aug 2026 17:43:19 +0800
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---
 server/src/atRisk.js       | 66 ++++++++++++++++++++++++++++++++
 server/test/atRisk.test.js | 78 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 144 insertions(+)
 create mode 100644 server/src/atRisk.js
 create mode 100644 server/test/atRisk.test.js

diff --git a/server/src/atRisk.js b/server/src/atRisk.js
new file mode 100644
index 0000000..3a87040
--- /dev/null
+++ b/server/src/atRisk.js
@@ -0,0 +1,66 @@
+/**
+ * 风险预警计算：算出未来一段时间内，有哪些提醒会因额度不足发不出去
+ *
+ * 首页拿这个结果给用户看「谁的提醒有风险」，而不是「还剩几次额度」——
+ * 用户理解不了额度这种抽象概念，但看得懂人名。
+ */
+
+const { getNextOccurrence, daysBetween } = require('./occurrence')
+
+// 预警窗口。太短则提示不及时，太长会拿几个月后的事惊扰用户，两个月是折中。
+const LOOKAHEAD_DAYS = 60
+
+/**
+ * 把一条纪念日展开成未来窗口内的提醒事件
+ * 每条纪念日最多产生两个事件：提前 N 天一个、当天一个
+ */
+function expandEvents(anniv, today = new Date()) {
+  const next = getNextOccurrence(anniv, today)
+  const onDayIn = daysBetween(next, today)
+  const remindDays = anniv.remindDays || 0
+
+  const events = [{
+    anniversaryId: anniv.id,
+    personName: anniv.personName,
+    kind: 'onDay',
+    fireInDays: onDayIn,
+    importance: anniv.importance
+  }]
+
+  if (remindDays > 0) {
+    events.push({
+      anniversaryId: anniv.id,
+      personName: anniv.personName,
+      kind: 'ahead',
+      fireInDays: onDayIn - remindDays,
+      importance: anniv.importance
+    })
+  }
+
+  // 已经过去的（如提前提醒的时点早已过）和超出窗口的都不算
+  return events.filter(e => e.fireInDays >= 0 && e.fireInDays <= LOOKAHEAD_DAYS)
+}
+
+/**
+ * 算出有风险的提醒
+ * 排序用「时间先后」而非重要程度——跨天的额度就是先到先消耗。
+ * 重要程度只在同一天内比较（那部分逻辑在 reminder.js）。
+ */
+function computeAtRisk(anniversaries, balance, today = new Date()) {
+  const events = (anniversaries || [])
+    .filter(a => a && a.remindEnabled)
+    .flatMap(a => expandEvents(a, today))
+    .sort((x, y) => x.fireInDays - y.fireInDays)
+
+  const safeCount = Math.max(0, balance)
+  const atRisk = events.slice(safeCount)
+
+  const names = []
+  for (const e of atRisk) {
+    if (e.personName && !names.includes(e.personName)) names.push(e.personName)
+  }
+
+  return { atRiskCount: atRisk.length, atRiskNames: names }
+}
+
+module.exports = { LOOKAHEAD_DAYS, expandEvents, computeAtRisk }
diff --git a/server/test/atRisk.test.js b/server/test/atRisk.test.js
new file mode 100644
index 0000000..5f38309
--- /dev/null
+++ b/server/test/atRisk.test.js
@@ -0,0 +1,78 @@
+const test = require('node:test')
+const assert = require('node:assert')
+const { expandEvents, computeAtRisk, LOOKAHEAD_DAYS } = require('../src/atRisk')
+
+const TODAY = new Date(2026, 7, 15) // 2026-08-15
+
+// 距今 10 天的公历纪念日，提前 3 天提醒
+const near = {
+  id: 'a1', personName: '张三', remindEnabled: 1, importance: 'high',
+  isLunar: false, solarMonth: 8, solarDay: 25, remindDays: 3
+}
+// 距今 40 天
+const mid = {
+  id: 'a2', personName: '李四', remindEnabled: 1, importance: 'low',
+  isLunar: false, solarMonth: 9, solarDay: 24, remindDays: 7
+}
+
+test('LOOKAHEAD_DAYS 为 60', () => {
+  assert.strictEqual(LOOKAHEAD_DAYS, 60)
+})
+
+test('一条纪念日展开出「当天」和「提前」两个事件', () => {
+  const events = expandEvents(near, TODAY)
+  assert.strictEqual(events.length, 2)
+  const onDay = events.find(e => e.kind === 'onDay')
+  const ahead = events.find(e => e.kind === 'ahead')
+  assert.strictEqual(onDay.fireInDays, 10)
+  assert.strictEqual(ahead.fireInDays, 7)
+})
+
+test('remindDays 为 0 时只有当天事件', () => {
+  const events = expandEvents({ ...near, remindDays: 0 }, TODAY)
+  assert.strictEqual(events.length, 1)
+  assert.strictEqual(events[0].kind, 'onDay')
+})
+
+test('超出 60 天窗口的事件被过滤掉', () => {
+  const far = { ...near, solarMonth: 12, solarDay: 25, remindDays: 3 }
+  assert.strictEqual(expandEvents(far, TODAY).length, 0)
+})
+
+test('提前日已过、当天未到时，只剩当天事件', () => {
+  // 距今 2 天，但提前 7 天的时点早已过去
+  const soon = { ...near, solarMonth: 8, solarDay: 17, remindDays: 7 }
+  const events = expandEvents(soon, TODAY)
+  assert.strictEqual(events.length, 1)
+  assert.strictEqual(events[0].kind, 'onDay')
+})
+
+test('余额足够时没有风险', () => {
+  const r = computeAtRisk([near, mid], 10, TODAY)
+  assert.strictEqual(r.atRiskCount, 0)
+  assert.deepStrictEqual(r.atRiskNames, [])
+})
+
+test('余额为 0 时全部有风险', () => {
+  const r = computeAtRisk([near, mid], 0, TODAY)
+  assert.strictEqual(r.atRiskCount, 4)
+  assert.deepStrictEqual(r.atRiskNames, ['张三', '李四'])
+})
+
+test('按时间先后消耗额度，后面的才有风险', () => {
+  // 张三的两个事件在第 7、10 天，李四的在第 33、40 天
+  const r = computeAtRisk([near, mid], 2, TODAY)
+  assert.strictEqual(r.atRiskCount, 2)
+  assert.deepStrictEqual(r.atRiskNames, ['李四'])
+})
+
+test('人名去重，同一人占两条只出现一次', () => {
+  const r = computeAtRisk([near], 0, TODAY)
+  assert.strictEqual(r.atRiskCount, 2)
+  assert.deepStrictEqual(r.atRiskNames, ['张三'])
+})
+
+test('未开启提醒的纪念日不参与计算', () => {
+  const r = computeAtRisk([{ ...near, remindEnabled: 0 }], 0, TODAY)
+  assert.strictEqual(r.atRiskCount, 0)
+})