// Portfolio P&L tracker over a list of position records.
// Each position: {symbol, qty, cost, mark}. Computes per-position and
// total unrealized P&L, market value, and the best/worst performer.
// Shows records, pipe map/filter, sum_by-style reductions over derived fields.

cell PortfolioPnL {
    face {
        signal positions() -> List
        signal enriched() -> List
        signal total_pnl() -> Float
        signal market_value() -> Float
        signal winners() -> List
        signal best() -> List
    }

    on positions() {
        return list(
            Position { symbol: "AAPL", qty: 100, cost: 150.0, mark: 172.0 },
            Position { symbol: "MSFT", qty: 50,  cost: 300.0, mark: 290.0 },
            Position { symbol: "NVDA", qty: 20,  cost: 400.0, mark: 880.0 }
        )
    }

    // attach pnl = qty * (mark - cost) and value = qty * mark to each row
    on enriched() {
        return positions() |> map(p => {
            let pnl = p.qty * (p.mark - p.cost)
            let value = p.qty * p.mark
            p |> with("pnl", pnl) |> with("value", value)
        })
    }

    on total_pnl() {
        let pnls = enriched() |> map(p => p.pnl)
        return sum(pnls)
    }

    on market_value() {
        let vals = enriched() |> map(p => p.value)
        return sum(vals)
    }

    on winners() {
        return enriched() |> filter(p => p.pnl > 0.0)
    }

    on best() {
        return enriched() |> sort_by("pnl", "desc") |> top(1)
    }
}

cell test PortfolioTests {
    rules {
        // AAPL: 100*(172-150)=2200, MSFT: 50*(290-300)=-500, NVDA: 20*480=9600
        assert abs(total_pnl() - 11300.0) < 0.001
        assert abs(market_value() - (17200.0 + 14500.0 + 17600.0)) < 0.001
        // two of three names are up
        assert len(winners()) == 2
        // NVDA is the top performer
        assert best()[0].symbol == "NVDA"
    }
}