feat(finance): Phase 6 — Budget & Analytics

Add monthly budgets per category with spend-vs-budget dashboard and 6-month trend table.
Includes upsert budget API, monthly analytics endpoint, inline budget editing, and route auth fixes.

src/app/api/analytics/monthly/route.ts

@@ -0,0 +1,105 @@
+import { NextRequest, NextResponse } from "next/server";
+import { getCurrentUser } from "@/lib/auth";
+import { queryRaw } from "@/lib/db";
+
+export async function GET(req: NextRequest) {
+  const user = await getCurrentUser(req);
+  if (!user) return NextResponse.json({ error: "Unauthorized" }, { status: 403 });
+
+  const { searchParams } = new URL(req.url);
+  const monthCount = Math.min(Math.max(Number(searchParams.get("months") || "6"), 1), 24);
+
+  const now = new Date();
+  const endDate = new Date(now.getFullYear(), now.getMonth() + 1, 1);
+  const startDate = new Date(now.getFullYear(), now.getMonth() - monthCount + 1, 1);
+
+  const startStr = startDate.toISOString().slice(0, 10);
+  const endStr = endDate.toISOString().slice(0, 10);
+
+  const spendRows = await queryRaw<{
+    month: string;
+    category: string;
+    total_spent: number;
+    transaction_count: number;
+  }>(
+    `SELECT
+      TO_CHAR(DATE_TRUNC('month', t.transaction_date::date), 'YYYY-MM') as month,
+      COALESCE(o.category_override, t.category) as category,
+      SUM(t.amount)::numeric(12,2) as total_spent,
+      COUNT(*)::int as transaction_count
+    FROM transactions t
+    LEFT JOIN transaction_overrides o ON o.transaction_id = t.id
+    JOIN statements s ON s.id = t.statement_id
+    WHERE s.owner_id = $1
+      AND t.transaction_type = 'debit'
+      AND t.transaction_date >= $2
+      AND t.transaction_date < $3
+    GROUP BY 1, 2
+    ORDER BY 1 DESC, total_spent DESC`,
+    [user.id, startStr, endStr]
+  );
+
+  const budgetRows = await queryRaw<{ month: string; category: string; amount_limit: number }>(
+    `SELECT TO_CHAR(month, 'YYYY-MM') as month, category, amount_limit::numeric
+     FROM budgets
+     WHERE owner_id = $1 AND month >= $2::date AND month < $3::date`,
+    [user.id, startStr, endStr]
+  );
+
+  // Build month list (most recent first)
+  const months: string[] = [];
+  for (let i = monthCount - 1; i >= 0; i--) {
+    const d = new Date(now.getFullYear(), now.getMonth() - i, 1);
+    months.push(`${d.getFullYear()}-${String(d.getMonth() + 1).padStart(2, "0")}`);
+  }
+  months.reverse();
+
+  const spendMap = new Map<string, number>();
+  const countMap = new Map<string, number>();
+  const budgetMap = new Map<string, number>();
+
+  for (const r of spendRows) {
+    spendMap.set(`${r.category}:${r.month}`, Number(r.total_spent));
+    countMap.set(`${r.category}:${r.month}`, r.transaction_count);
+  }
+  for (const r of budgetRows) {
+    budgetMap.set(`${r.category}:${r.month}`, Number(r.amount_limit));
+  }
+
+  const allCategories = new Set<string>();
+  for (const r of spendRows) allCategories.add(r.category);
+  for (const r of budgetRows) allCategories.add(r.category);
+
+  const rows = Array.from(allCategories)
+    .sort()
+    .map((cat) => {
+      const spent: Record<string, number> = {};
+      const budget: Record<string, number> = {};
+      const txCount: Record<string, number> = {};
+      for (const m of months) {
+        const s = spendMap.get(`${cat}:${m}`);
+        const b = budgetMap.get(`${cat}:${m}`);
+        const c = countMap.get(`${cat}:${m}`);
+        if (s !== undefined) spent[m] = s;
+        if (b !== undefined) budget[m] = b;
+        if (c !== undefined) txCount[m] = c;
+      }
+      return { category: cat, spent, budget, txCount };
+    });
+
+  const totals: Record<string, { spent: number; budget: number }> = {};
+  for (const m of months) {
+    let s = 0;
+    let b = 0;
+    for (const row of rows) {
+      s += row.spent[m] || 0;
+      b += row.budget[m] || 0;
+    }
+    totals[m] = {
+      spent: Math.round(s * 100) / 100,
+      budget: Math.round(b * 100) / 100,
+    };
+  }
+
+  return NextResponse.json({ months, rows, totals });
+}