//! DQN Action Replay Backtesting Binary
//!
//! Runs backtesting by replaying pre-computed DQN actions against historical market data.
//! This is a simplified standalone implementation that simulates trading without the full
//! backtesting infrastructure (to avoid circular dependencies with the backtesting crate).
//!
//! # Features
//! - Loads DQN actions from CSV (exported by evaluate_dqn_main_orchestrator)
//! - Simulates trading with simple position tracking
//! - Computes basic performance metrics (total return, trades, action distribution)
//!
//! # Usage
//! ```bash
//! # Basic usage with defaults
//! cargo run -p ml --example backtest_dqn_replay --release -- \
//!   --actions-csv /tmp/dqn_actions_wave3.csv \
//!   --parquet-file test_data/ES_FUT_unseen.parquet
//!
//! # Custom trading parameters
//! cargo run -p ml --example backtest_dqn_replay --release -- \
//!   --actions-csv /tmp/dqn_actions_wave3.csv \
//!   --parquet-file test_data/ES_FUT_unseen.parquet \
//!   --initial-capital 250000 \
//!   --commission-rate 0.05
//! ```
//!
//! # CSV Format
//! Expected CSV columns: timestamp,action,q_buy,q_sell,q_hold,open,high,low,close,volume
//! Actions: 0=BUY, 1=SELL, 2=HOLD
//!
//! # Output
//! - Console report with detailed metrics
//! - Action distribution analysis
//! - Performance summary (return, trades, PnL)
//!
//! # Design Reference
//! See `/tmp/backtesting_pipeline_design.md` for complete architecture

use anyhow::{Context, Result};
use clap::Parser;
use ml::backtesting::action_loader::load_actions_from_csv;
use ml::data_loaders::parquet_utils::load_parquet_data_with_timestamps;
use std::path::PathBuf;
use tracing::{info, warn};
use tracing_subscriber;

/// CLI arguments for DQN replay backtesting
#[derive(Parser, Debug)]
#[command(
    name = "backtest_dqn_replay",
    about = "Backtest DQN trading decisions via action replay",
    long_about = "Load pre-computed DQN actions from CSV and simulate trading to evaluate performance."
)]
struct Args {
    /// Path to DQN actions CSV (from evaluate_dqn_main_orchestrator)
    #[arg(long, default_value = "/tmp/dqn_actions_wave3.csv")]
    actions_csv: PathBuf,

    /// Path to OHLCV Parquet file (same data used for DQN evaluation)
    #[arg(long, default_value = "test_data/ES_FUT_unseen.parquet")]
    parquet_file: PathBuf,

    /// Initial trading capital (USD)
    #[arg(long, default_value_t = 100000.0)]
    initial_capital: f64,

    /// Commission rate (percentage, e.g., 0.01 = 0.01%)
    #[arg(long, default_value_t = 0.01)]
    commission_rate: f64,

    /// Verbose logging
    #[arg(short, long)]
    verbose: bool,
}

/// Position state for tracking holdings
#[derive(Debug, Clone, Copy, PartialEq)]
enum PositionState {
    Flat,  // No position
    Long,  // Long position
    Short, // Short position
}

/// Trade record for performance tracking
#[derive(Debug, Clone)]
struct Trade {
    entry_price: f64,
    exit_price: f64,
    side: PositionState,
    pnl: f64,
}

/// Simple backtesting simulator
struct SimpleBacktester {
    initial_capital: f64,
    current_capital: f64,
    position: PositionState,
    entry_price: f64,
    commission_rate: f64,
    trades: Vec<Trade>,
    action_counts: [usize; 3], // BUY, SELL, HOLD
}

impl SimpleBacktester {
    fn new(initial_capital: f64, commission_rate: f64) -> Self {
        Self {
            initial_capital,
            current_capital: initial_capital,
            position: PositionState::Flat,
            entry_price: 0.0,
            commission_rate,
            trades: Vec::new(),
            action_counts: [0, 0, 0],
        }
    }

    /// Process a single action
    fn process_action(&mut self, action: usize, price: f64) {
        // Track action distribution
        if action <= 2 {
            self.action_counts[action] += 1;
        }

        match action {
            0 => self.handle_buy(price),  // BUY
            1 => self.handle_sell(price), // SELL
            2 => {},                      // HOLD - no action
            _ => warn!("Invalid action: {}", action),
        }
    }

    fn handle_buy(&mut self, price: f64) {
        match self.position {
            PositionState::Flat => {
                // Open long position
                self.position = PositionState::Long;
                self.entry_price = price;
                let commission = self.current_capital * (self.commission_rate / 100.0);
                self.current_capital -= commission;
            },
            PositionState::Short => {
                // Close short position
                let pnl = (self.entry_price - price) / self.entry_price * self.initial_capital;
                let commission = self.current_capital * (self.commission_rate / 100.0);
                self.current_capital += pnl - commission;

                self.trades.push(Trade {
                    entry_price: self.entry_price,
                    exit_price: price,
                    side: PositionState::Short,
                    pnl: pnl - commission,
                });

                // Open long position
                self.position = PositionState::Long;
                self.entry_price = price;
            },
            PositionState::Long => {
                // Already long, hold
            },
        }
    }

    fn handle_sell(&mut self, price: f64) {
        match self.position {
            PositionState::Flat => {
                // Open short position
                self.position = PositionState::Short;
                self.entry_price = price;
                let commission = self.current_capital * (self.commission_rate / 100.0);
                self.current_capital -= commission;
            },
            PositionState::Long => {
                // Close long position
                let pnl = (price - self.entry_price) / self.entry_price * self.initial_capital;
                let commission = self.current_capital * (self.commission_rate / 100.0);
                self.current_capital += pnl - commission;

                self.trades.push(Trade {
                    entry_price: self.entry_price,
                    exit_price: price,
                    side: PositionState::Long,
                    pnl: pnl - commission,
                });

                // Open short position
                self.position = PositionState::Short;
                self.entry_price = price;
            },
            PositionState::Short => {
                // Already short, hold
            },
        }
    }

    /// Close any open position at final price
    fn finalize(&mut self, final_price: f64) {
        if self.position != PositionState::Flat {
            let pnl = match self.position {
                PositionState::Long => {
                    (final_price - self.entry_price) / self.entry_price * self.initial_capital
                },
                PositionState::Short => {
                    (self.entry_price - final_price) / self.entry_price * self.initial_capital
                },
                PositionState::Flat => 0.0,
            };

            let commission = self.current_capital * (self.commission_rate / 100.0);
            self.current_capital += pnl - commission;

            self.trades.push(Trade {
                entry_price: self.entry_price,
                exit_price: final_price,
                side: self.position,
                pnl: pnl - commission,
            });
        }
    }

    /// Get performance metrics
    fn get_metrics(&self) -> PerformanceMetrics {
        let total_return = (self.current_capital - self.initial_capital) / self.initial_capital;
        let total_trades = self.trades.len();
        let winning_trades = self.trades.iter().filter(|t| t.pnl > 0.0).count();
        let win_rate = if total_trades > 0 {
            winning_trades as f64 / total_trades as f64
        } else {
            0.0
        };

        PerformanceMetrics {
            total_return,
            final_capital: self.current_capital,
            total_pnl: self.current_capital - self.initial_capital,
            total_trades,
            win_rate,
            action_counts: self.action_counts,
        }
    }
}

/// Performance metrics summary
#[derive(Debug)]
struct PerformanceMetrics {
    total_return: f64,
    final_capital: f64,
    total_pnl: f64,
    total_trades: usize,
    win_rate: f64,
    action_counts: [usize; 3],
}

fn main() -> Result<()> {
    let args = Args::parse();

    // Initialize logging
    if args.verbose {
        tracing_subscriber::fmt()
            .with_max_level(tracing::Level::DEBUG)
            .init();
    } else {
        tracing_subscriber::fmt()
            .with_max_level(tracing::Level::INFO)
            .init();
    }

    info!("=== DQN Action Replay Backtesting ===");
    info!("Actions CSV: {}", args.actions_csv.display());
    info!("Parquet file: {}", args.parquet_file.display());
    info!("Initial capital: ${}", args.initial_capital);
    info!("Commission rate: {}%", args.commission_rate);

    // Step 1: Load DQN actions from CSV
    info!("Loading DQN actions from CSV...");
    let actions = load_actions_from_csv(&args.actions_csv).map_err(|e| {
        anyhow::anyhow!(
            "Failed to load actions from {}: {}",
            args.actions_csv.display(),
            e
        )
    })?;
    info!("Loaded {} DQN actions", actions.len());

    // Step 2: Load OHLCV data from Parquet
    info!("Loading OHLCV data from Parquet...");
    let (_features, timestamps, ohlcv_bars) =
        load_parquet_data_with_timestamps(&args.parquet_file, 0).with_context(|| {
            format!(
                "Failed to load Parquet data from {}",
                args.parquet_file.display()
            )
        })?;
    info!("Loaded {} OHLCV bars", ohlcv_bars.len());

    // Validate alignment
    if actions.is_empty() {
        anyhow::bail!("No actions loaded from CSV");
    }
    if ohlcv_bars.is_empty() {
        anyhow::bail!("No OHLCV data loaded from Parquet");
    }
    if actions.len() > ohlcv_bars.len() {
        anyhow::bail!(
            "Action count ({}) exceeds OHLCV bars ({}). Warmup mismatch?",
            actions.len(),
            ohlcv_bars.len()
        );
    }

    info!(
        "Data time range: {} to {}",
        timestamps.first().unwrap(),
        timestamps.last().unwrap()
    );

    // Step 3: Run backtest simulation
    info!("Running backtest simulation...");
    let mut backtester = SimpleBacktester::new(args.initial_capital, args.commission_rate);

    for (i, action_record) in actions.iter().enumerate() {
        if i < ohlcv_bars.len() {
            let bar = &ohlcv_bars[i];
            backtester.process_action(action_record.action as usize, bar.close);
        }
    }

    // Close any open position at final price
    if !ohlcv_bars.is_empty() {
        backtester.finalize(ohlcv_bars.last().unwrap().close);
    }

    // Step 4: Print results
    let metrics = backtester.get_metrics();

    info!("");
    info!("=== Backtesting Complete ===");
    info!("Total actions processed: {}", actions.len());
    info!("");
    info!("Action Distribution:");
    info!(
        "  BUY:  {} ({:.1}%)",
        metrics.action_counts[0],
        100.0 * (metrics.action_counts[0] as f64) / (actions.len() as f64)
    );
    info!(
        "  SELL: {} ({:.1}%)",
        metrics.action_counts[1],
        100.0 * (metrics.action_counts[1] as f64) / (actions.len() as f64)
    );
    info!(
        "  HOLD: {} ({:.1}%)",
        metrics.action_counts[2],
        100.0 * (metrics.action_counts[2] as f64) / (actions.len() as f64)
    );
    info!("");
    info!("Performance Metrics:");
    info!("  Total trades: {}", metrics.total_trades);
    info!("  Win rate: {:.2}%", metrics.win_rate * 100.0);
    info!("  Total return: {:.2}%", metrics.total_return * 100.0);
    info!("  Final capital: ${:.2}", metrics.final_capital);
    info!("  Total PnL: ${:.2}", metrics.total_pnl);

    // Warn if 0% BUY signals
    if metrics.action_counts[0] == 0 {
        info!("");
        warn!("⚠️  WARNING: 0% BUY signals detected!");
        warn!("   This may indicate a model bias or specific market conditions.");
        warn!("   Review /tmp/backtesting_pipeline_design.md for interpretation guidance.");
    }

    Ok(())
}