//! Per-cell backtest output writers + summary statistics.
//!
//! See docs/superpowers/specs/2026-05-18-real-lob-integration-design.md §7
//! "Output artifacts".
//!
//!   summary.json    top-level stats (Sharpe, drawdown, profit factor, etc.)
//!   trades.csv      per-trade audit log
//!   pnl_curve.bin   binary float32 cumulative P&L at each event timestamp
//!
//! Annualisation uses the non-overlapping convention per
//! `pearl_phase1d4_backtest_cost_edge_frontier`: σ_ann = σ_trade × √825
//! (K=6000 holding period, 250 trading days = ~825 non-overlapping trades/yr).

use anyhow::{Context, Result};
use serde::{Deserialize, Serialize};
use std::io::Write;
use std::path::Path;

use crate::order::TradeRecord;

/// Top-level per-cell summary. Serialised to summary.json.
#[derive(Clone, Debug, Default, Serialize, Deserialize)]
pub struct Summary {
    pub total_pnl_usd: f32,
    pub sharpe_ann: f32,
    pub sortino_ann: f32,
    pub max_drawdown_usd: f32,
    /// X16: max drawdown as a fraction of starting capital. Computed
    /// in compute_summary using STARTING_CAPITAL_USD ($35k per project
    /// convention; see memory `project_ml_alpha_starting_capital`).
    /// Range [0.0, 1.0]; 0.20 = 20% drawdown.
    pub max_drawdown_pct: f32,
    pub calmar: f32,
    pub n_trades: u64,
    pub win_rate: f32,
    pub avg_win_usd: f32,
    pub avg_loss_usd: f32,
    pub profit_factor: f32,
    pub total_fees_usd: f32,
    /// Fraction of decision points where any backtest held a non-flat
    /// position. Populated by the harness if it tracks bars-in-position;
    /// 0.0 placeholder when unmeasured.
    pub exposure_pct: f32,
    /// Downsampled per-horizon Kelly cap trace (entries × N_HORIZONS).
    /// Empty if the harness doesn't record per-decision Kelly caps;
    /// when populated, used by aggregate/diagnostics.
    #[serde(default)]
    pub kelly_cap_history_sample: Vec<Vec<f32>>,
}

/// Non-overlapping annualisation factor (√825) per
/// `pearl_phase1d4_backtest_cost_edge_frontier.md`. Pinned here so
/// `aggregate` reads from the same constant if it ever recomputes.
pub const ANNUALISATION_SQRT_FACTOR: f32 = 28.722_815;

/// X16: starting capital in USD used as the base for max_drawdown_pct.
/// $35k is the project's chosen base for ES single-contract analysis
/// — realistic for a small-account ES trader (margin ~$15k initial,
/// ~$20k headroom for adverse moves before a margin call). See memory
/// `project_ml_alpha_starting_capital`.
pub const STARTING_CAPITAL_USD: f32 = 35_000.0;

/// Convert TradeRecord fixed-point USD ×100 to plain USD float.
#[inline]
fn fp_to_usd(fp: i32) -> f32 {
    fp as f32 / 100.0
}

/// Compute summary statistics from the per-cell trade log + cumulative
/// P&L curve (USD). The curve is sampled at every event; the harness
/// passes the same vector it serialises to pnl_curve.bin.
pub fn compute_summary(records: &[TradeRecord], pnl_curve_usd: &[f32]) -> Summary {
    if records.is_empty() {
        return Summary {
            total_pnl_usd: 0.0,
            n_trades: 0,
            ..Default::default()
        };
    }

    let n_trades = records.len() as u64;
    let mut wins = 0u64;
    let mut losses = 0u64;
    let mut win_sum = 0.0f32;
    let mut loss_sum = 0.0f32;
    let mut total_fees = 0.0f32;
    let mut per_trade_returns: Vec<f32> = Vec::with_capacity(records.len());
    for r in records {
        let p = fp_to_usd(r.realised_pnl_usd_fp);
        total_fees += fp_to_usd(r.fees_usd_fp);
        per_trade_returns.push(p);
        if p > 0.0 {
            wins += 1;
            win_sum += p;
        } else if p < 0.0 {
            losses += 1;
            loss_sum += -p;
        }
    }

    let total_pnl_usd: f32 = per_trade_returns.iter().sum();
    let win_rate = wins as f32 / n_trades as f32;
    let avg_win = if wins > 0 { win_sum / wins as f32 } else { 0.0 };
    let avg_loss = if losses > 0 { loss_sum / losses as f32 } else { 0.0 };
    let profit_factor = if loss_sum > 0.0 {
        win_sum / loss_sum
    } else if win_sum > 0.0 {
        f32::INFINITY
    } else {
        0.0
    };

    // Per-trade Sharpe + Sortino.
    let mean = total_pnl_usd / n_trades as f32;
    let var: f32 = per_trade_returns
        .iter()
        .map(|p| (p - mean).powi(2))
        .sum::<f32>()
        / n_trades as f32;
    let std_dev = var.sqrt().max(1e-9);
    let sharpe_per_trade = mean / std_dev;
    let sharpe_ann = sharpe_per_trade * ANNUALISATION_SQRT_FACTOR;

    let downside_var: f32 = per_trade_returns
        .iter()
        .filter_map(|p| if *p < mean { Some((p - mean).powi(2)) } else { None })
        .sum::<f32>()
        / n_trades as f32;
    let downside_std = downside_var.sqrt().max(1e-9);
    let sortino_per_trade = mean / downside_std;
    let sortino_ann = sortino_per_trade * ANNUALISATION_SQRT_FACTOR;

    // Max drawdown from the cumulative P&L curve.
    let (max_drawdown_usd, _peak_at_dd) = if pnl_curve_usd.is_empty() {
        (0.0, 0.0)
    } else {
        let mut peak = pnl_curve_usd[0];
        let mut dd = 0.0f32;
        let mut peak_at_dd = peak;
        for &v in pnl_curve_usd {
            if v > peak {
                peak = v;
            }
            let cur_dd = peak - v;
            if cur_dd > dd {
                dd = cur_dd;
                peak_at_dd = peak;
            }
        }
        (dd, peak_at_dd)
    };

    let calmar = if max_drawdown_usd > 0.0 {
        total_pnl_usd / max_drawdown_usd
    } else if total_pnl_usd > 0.0 {
        f32::INFINITY
    } else {
        0.0
    };

    let max_drawdown_pct = max_drawdown_usd.abs() / STARTING_CAPITAL_USD;
    Summary {
        total_pnl_usd,
        sharpe_ann,
        sortino_ann,
        max_drawdown_usd,
        max_drawdown_pct,
        calmar,
        n_trades,
        win_rate,
        avg_win_usd: avg_win,
        avg_loss_usd: avg_loss,
        profit_factor,
        total_fees_usd: total_fees,
        exposure_pct: 0.0, // populated by harness if it tracks this
        kelly_cap_history_sample: Vec::new(),
    }
}

/// Write `summary.json` to the given path.
pub fn write_summary(path: &Path, s: &Summary) -> Result<()> {
    let f = std::fs::File::create(path)
        .with_context(|| format!("create {}", path.display()))?;
    serde_json::to_writer_pretty(f, s).context("write summary.json")?;
    Ok(())
}

/// Write `trades.csv` to the given path. Side is rendered "buy"/"sell"
/// from the sign of `size_lots`; price columns are converted from
/// fixed-point ×100 ticks back to float-tick values for human readability.
pub fn write_trades_csv(path: &Path, records: &[TradeRecord]) -> Result<()> {
    let mut f = std::fs::File::create(path)
        .with_context(|| format!("create {}", path.display()))?;
    writeln!(
        f,
        "entry_ts_ns,exit_ts_ns,side,size_lots,entry_px_ticks,exit_px_ticks,fees_usd,realised_pnl_usd,strategy_id,horizon_idx"
    )?;
    for r in records {
        let side = if r.size_lots > 0 { "buy" } else { "sell" };
        let entry_px = r.entry_px_ticks as f32 / 100.0;
        let exit_px = r.exit_px_ticks as f32 / 100.0;
        writeln!(
            f,
            "{},{},{},{},{:.2},{:.2},{:.2},{:.2},{},{}",
            r.entry_ts_ns,
            r.exit_ts_ns,
            side,
            r.size_lots.abs(),
            entry_px,
            exit_px,
            fp_to_usd(r.fees_usd_fp),
            fp_to_usd(r.realised_pnl_usd_fp),
            r.strategy_id,
            r.horizon_idx,
        )?;
    }
    Ok(())
}

/// Write the cumulative P&L curve as a packed binary float32 array.
pub fn write_pnl_curve_bin(path: &Path, curve_usd: &[f32]) -> Result<()> {
    let mut f = std::fs::File::create(path)
        .with_context(|| format!("create {}", path.display()))?;
    let bytes: &[u8] = bytemuck::cast_slice(curve_usd);
    f.write_all(bytes).context("write pnl_curve.bin")?;
    Ok(())
}

#[cfg(test)]
mod tests {
    use super::*;

    fn trade(entry_ts: u64, exit_ts: u64, size: i32, pnl_fp: i32) -> TradeRecord {
        TradeRecord {
            entry_ts_ns: entry_ts,
            exit_ts_ns: exit_ts,
            entry_px_ticks: 550_000,
            exit_px_ticks: 550_500,
            size_lots: size,
            fees_usd_fp: 0,
            realised_pnl_usd_fp: pnl_fp,
            horizon_idx: 4,
            strategy_id: 0,
            _pad: [0; 2],
        }
    }

    #[test]
    fn empty_records_summary_is_zero() {
        let s = compute_summary(&[], &[]);
        assert_eq!(s.n_trades, 0);
        assert_eq!(s.total_pnl_usd, 0.0);
        assert_eq!(s.profit_factor, 0.0);
    }

    #[test]
    fn three_wins_one_loss_summary() {
        let recs = vec![
            trade(1_000_000_000, 2_000_000_000, 1, 5000),  // +$50
            trade(3_000_000_000, 4_000_000_000, 1, 7500),  // +$75
            trade(5_000_000_000, 6_000_000_000, -1, -2500), // -$25
            trade(7_000_000_000, 8_000_000_000, 1, 10000), // +$100
        ];
        // Cumulative pnl curve sampled at trade-close events.
        let curve = vec![0.0, 50.0, 125.0, 100.0, 200.0];
        let s = compute_summary(&recs, &curve);
        assert_eq!(s.n_trades, 4);
        assert!((s.total_pnl_usd - 200.0).abs() < 0.01);
        assert!((s.win_rate - 0.75).abs() < 0.01);
        assert!((s.avg_win_usd - 75.0).abs() < 0.01);
        assert!((s.avg_loss_usd - 25.0).abs() < 0.01);
        assert!((s.profit_factor - (225.0 / 25.0)).abs() < 0.01);
        // Drawdown of $25 from peak $125 to trough $100.
        assert!((s.max_drawdown_usd - 25.0).abs() < 0.01);
    }

    #[test]
    fn write_then_read_pnl_curve_bin_roundtrip() {
        let dir = tempfile::tempdir().expect("tmpdir");
        let path = dir.path().join("pnl_curve.bin");
        let curve = vec![0.0f32, 10.0, 25.5, -3.25, 100.125];
        write_pnl_curve_bin(&path, &curve).unwrap();
        let raw = std::fs::read(&path).unwrap();
        let read_back: Vec<f32> = bytemuck::cast_slice(&raw).to_vec();
        assert_eq!(read_back, curve);
    }

    #[test]
    fn write_summary_then_parse_back() {
        let dir = tempfile::tempdir().expect("tmpdir");
        let path = dir.path().join("summary.json");
        let s = Summary {
            total_pnl_usd: 123.45,
            sharpe_ann: 1.5,
            n_trades: 7,
            win_rate: 0.6,
            ..Default::default()
        };
        write_summary(&path, &s).unwrap();
        let raw = std::fs::read_to_string(&path).unwrap();
        let back: Summary = serde_json::from_str(&raw).unwrap();
        assert!((back.total_pnl_usd - 123.45).abs() < 0.01);
        assert_eq!(back.n_trades, 7);
    }

    #[test]
    fn write_trades_csv_header_and_one_row() {
        let dir = tempfile::tempdir().expect("tmpdir");
        let path = dir.path().join("trades.csv");
        let recs = vec![trade(1_000_000_000, 2_000_000_000, 3, 12345)];
        write_trades_csv(&path, &recs).unwrap();
        let s = std::fs::read_to_string(&path).unwrap();
        assert!(s.contains("entry_ts_ns,exit_ts_ns,side"));
        assert!(s.contains("1000000000,2000000000,buy,3"));
        assert!(s.contains("123.45")); // $123.45 from fp 12345
    }
}