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

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);

  // Expenses: debits excluding transfers and investments, split-adjusted
  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(
        CASE
          WHEN ts.share_percent IS NOT NULL THEN COALESCE(t.amount_aud, t.amount) * ts.share_percent / 100
          WHEN o.my_share_percent IS NOT NULL THEN COALESCE(t.amount_aud, t.amount) * o.my_share_percent / 100
          ELSE COALESCE(t.amount_aud, t.amount)
        END
      )::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
    LEFT JOIN transaction_splits ts ON ts.transaction_id = t.id AND ts.participant_id = $1
    JOIN statements s ON s.id = t.statement_id
    WHERE s.owner_id = $1
      AND t.transaction_type IN ('debit', 'fee', 'interest')
      AND COALESCE(o.category_override, t.category) NOT IN ('transfers', 'investment')
      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]
  );

  // Income: credits/payments categorised as income
  const incomeRows = await queryRaw<{
    month: string;
    total_income: number;
    transaction_count: number;
  }>(
    `SELECT
      TO_CHAR(DATE_TRUNC('month', t.transaction_date::date), 'YYYY-MM') as month,
      SUM(COALESCE(t.amount_aud, t.amount))::numeric(12,2) as total_income,
      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 IN ('credit', 'payment')
      AND COALESCE(o.category_override, t.category) = 'income'
      AND t.transaction_date >= $2
      AND t.transaction_date < $3
    GROUP BY 1
    ORDER BY 1 DESC`,
    [user.id, startStr, endStr]
  );

  // Investments: any transaction categorised as investment
  const investmentRows = await queryRaw<{
    month: string;
    total_invested: number;
    transaction_count: number;
  }>(
    `SELECT
      TO_CHAR(DATE_TRUNC('month', t.transaction_date::date), 'YYYY-MM') as month,
      SUM(COALESCE(t.amount_aud, t.amount))::numeric(12,2) as total_invested,
      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 COALESCE(o.category_override, t.category) = 'investment'
      AND t.transaction_date >= $2
      AND t.transaction_date < $3
    GROUP BY 1
    ORDER BY 1 DESC`,
    [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 incomeMap = new Map<string, number>();
  const investMap = 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 incomeRows) incomeMap.set(r.month, Number(r.total_income));
  for (const r of investmentRows) investMap.set(r.month, Number(r.total_invested));

  const allCategories = new Set<string>();
  for (const r of spendRows) allCategories.add(r.category);

  const rows = Array.from(allCategories)
    .sort()
    .map((cat) => {
      const spent: Record<string, number> = {};
      const txCount: Record<string, number> = {};
      for (const m of months) {
        const s = spendMap.get(`${cat}:${m}`);
        const c = countMap.get(`${cat}:${m}`);
        if (s !== undefined) spent[m] = s;
        if (c !== undefined) txCount[m] = c;
      }
      return { category: cat, spent, txCount };
    });

  const totals: Record<string, { spent: number; income: number; investments: number; net: number }> = {};
  for (const m of months) {
    let spent = 0;
    for (const row of rows) spent += row.spent[m] || 0;
    const income = incomeMap.get(m) || 0;
    const investments = investMap.get(m) || 0;
    totals[m] = {
      spent: Math.round(spent * 100) / 100,
      income: Math.round(income * 100) / 100,
      investments: Math.round(investments * 100) / 100,
      net: Math.round((income - spent - investments) * 100) / 100,
    };
  }

  return NextResponse.json({ months, rows, income: Object.fromEntries(incomeMap), investments: Object.fromEntries(investMap), totals });
}