//! Backtesting Report Generation Module
//!
//! Provides comprehensive markdown report generation for comparing DQN model performance
//! against baseline models. Includes deployment recommendations based on production criteria.
//!
//! # Features
//!
//! - **Markdown Report Generation**: Professional formatted reports with tables
//! - **Production Criteria Validation**: Automated APPROVE/REJECT/REVIEW recommendations
//! - **Baseline Comparison**: Side-by-side comparison with reference model (Trial #35)
//! - **Comprehensive Metrics**: Returns, Sharpe, drawdown, win rate, alpha, trade stats
//!
//! # Usage
//!
//! ```rust
//! use ml_backtesting::report::{BacktestReport, PerformanceMetrics};
//!
//! let new_results = PerformanceMetrics {
//!     total_return_pct: 15.2,
//!     sharpe_ratio: 2.3,
//!     max_drawdown_pct: 12.5,
//!     win_rate: 0.58,
//!     alpha: 3.2,
//!     total_trades: 145,
//!     avg_trade_return_pct: 0.105,
//! };
//!
//! let baseline = Some(PerformanceMetrics {
//!     total_return_pct: 12.1,
//!     sharpe_ratio: 1.8,
//!     max_drawdown_pct: 18.3,
//!     win_rate: 0.52,
//!     alpha: 1.5,
//!     total_trades: 138,
//!     avg_trade_return_pct: 0.088,
//! });
//!
//! let report = BacktestReport {
//!     model_name: "DQN-Wave3-Entropy".to_owned(),
//!     baseline_name: "DQN-Trial35-Baseline".to_owned(),
//!     new_results,
//!     baseline_results: baseline,
//! };
//!
//! let markdown = report.generate_markdown();
//! std::fs::write("backtest_report.md", markdown).unwrap();
//! ```

use chrono::Utc;
use serde::{Deserialize, Serialize};
use std::fmt::Write;

/// Performance metrics for backtesting evaluation
///
/// Simplified metrics struct focused on production criteria validation.
/// Matches the key metrics from `backtesting/src/metrics.rs` but optimized
/// for report generation and comparison purposes.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct PerformanceMetrics {
    /// Total return as percentage (e.g., 15.2 = 15.2%)
    pub total_return_pct: f64,
    /// Sharpe ratio (risk-adjusted return)
    pub sharpe_ratio: f64,
    /// Maximum drawdown as percentage (e.g., 12.5 = 12.5%)
    pub max_drawdown_pct: f64,
    /// Win rate (0.0-1.0, e.g., 0.58 = 58%)
    pub win_rate: f64,
    /// Alpha (excess return vs benchmark, percentage)
    pub alpha: f64,
    /// Total number of trades executed
    pub total_trades: usize,
    /// Average trade return as percentage
    pub avg_trade_return_pct: f64,
}

/// Deployment recommendation structure
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct Recommendation {
    /// Status string (✅ APPROVE, ⚠️ REVIEW, ❌ REJECT)
    pub status: String,
    /// Human-readable reasoning for the recommendation
    pub reasoning: String,
}

/// Complete backtesting report structure
///
/// Compares a new model against an optional baseline and generates
/// deployment recommendations based on production criteria.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct BacktestReport {
    /// Name of the new model being evaluated
    pub model_name: String,
    /// Name of the baseline model for comparison
    pub baseline_name: String,
    /// Performance metrics for the new model
    pub new_results: PerformanceMetrics,
    /// Optional baseline performance metrics (e.g., Trial #35)
    pub baseline_results: Option<PerformanceMetrics>,
}

impl BacktestReport {
    /// Generate comprehensive markdown report
    ///
    /// Creates a professional formatted report with:
    /// - Header with model names and timestamp
    /// - Performance summary table with production criteria
    /// - Baseline comparison table (if baseline provided)
    /// - Deployment recommendation with reasoning
    /// - Trade statistics summary
    ///
    /// # Returns
    ///
    /// A formatted markdown string ready to write to a file
    pub fn generate_markdown(&self) -> String {
        let mut report = String::new();
        
        // Header
        report.push_str("# DQN Backtesting Report\n\n");
        let _w = writeln!(report, "**Model**: {}", self.model_name);
        if self.baseline_results.is_some() {
            let _w = writeln!(report, "**Baseline**: {}", self.baseline_name);
        }
        let _w = write!(report, "**Generated**: {}\n\n", Utc::now().format("%Y-%m-%d %H:%M:%S UTC"));
        
        report.push_str("---\n\n");
        
        // Performance Summary
        report.push_str("## Performance Summary\n\n");
        report.push_str("| Metric | Value | Target | Status |\n");
        report.push_str("|--------|-------|--------|--------|\n");
        
        let m = &self.new_results;
        
        // Total Return
        let _w = writeln!(
            report,
            "| Total Return | {:.2}% | >0% | {} |",
            m.total_return_pct,
            if m.total_return_pct > 0.0 { "\u{2705}" } else { "\u{274c}" }
        );

        // Sharpe Ratio
        let _w = writeln!(
            report,
            "| Sharpe Ratio | {:.2} | >1.5 | {} |",
            m.sharpe_ratio,
            if m.sharpe_ratio > 1.5 { "\u{2705}" } else { "\u{274c}" }
        );

        // Max Drawdown
        let _w = writeln!(
            report,
            "| Max Drawdown | {:.2}% | <20% | {} |",
            m.max_drawdown_pct,
            if m.max_drawdown_pct < 20.0 { "\u{2705}" } else { "\u{274c}" }
        );

        // Win Rate
        let _w = writeln!(
            report,
            "| Win Rate | {:.1}% | >50% | {} |",
            m.win_rate * 100.0,
            if m.win_rate > 0.50 { "\u{2705}" } else { "\u{274c}" }
        );

        // Alpha
        let _w = writeln!(
            report,
            "| Alpha vs B&H | {:.2}% | >0% | {} |",
            m.alpha,
            if m.alpha > 0.0 { "\u{2705}" } else { "\u{274c}" }
        );
        
        report.push('\n');
        
        // Comparison to baseline (if provided)
        if let Some(baseline) = &self.baseline_results {
            report.push_str("## Comparison to Baseline\n\n");
            report.push_str("| Metric | Baseline | New Model | Change | Direction |\n");
            report.push_str("|--------|----------|-----------|--------|----------|\n");
            
            // Returns comparison
            let return_change = m.total_return_pct - baseline.total_return_pct;
            let return_arrow = if return_change > 0.0 { "\u{2197}\u{fe0f}" } else if return_change < 0.0 { "\u{2198}\u{fe0f}" } else { "\u{2192}" };
            let _w = writeln!(
                report,
                "| Returns | {:.2}% | {:.2}% | {:+.2}% | {} |",
                baseline.total_return_pct, m.total_return_pct, return_change, return_arrow
            );

            // Sharpe comparison
            let sharpe_change = m.sharpe_ratio - baseline.sharpe_ratio;
            let sharpe_arrow = if sharpe_change > 0.0 { "\u{2197}\u{fe0f}" } else if sharpe_change < 0.0 { "\u{2198}\u{fe0f}" } else { "\u{2192}" };
            let _w = writeln!(
                report,
                "| Sharpe | {:.2} | {:.2} | {:+.2} | {} |",
                baseline.sharpe_ratio, m.sharpe_ratio, sharpe_change, sharpe_arrow
            );

            // Drawdown comparison (lower is better)
            let dd_change = m.max_drawdown_pct - baseline.max_drawdown_pct;
            let dd_arrow = if dd_change < 0.0 { "\u{2197}\u{fe0f}" } else if dd_change > 0.0 { "\u{2198}\u{fe0f}" } else { "\u{2192}" };
            let _w = writeln!(
                report,
                "| Drawdown | {:.2}% | {:.2}% | {:+.2}% | {} |",
                baseline.max_drawdown_pct, m.max_drawdown_pct, dd_change, dd_arrow
            );

            // Win Rate comparison
            let wr_change = (m.win_rate - baseline.win_rate) * 100.0;
            let wr_arrow = if wr_change > 0.0 { "\u{2197}\u{fe0f}" } else if wr_change < 0.0 { "\u{2198}\u{fe0f}" } else { "\u{2192}" };
            let _w = writeln!(
                report,
                "| Win Rate | {:.1}% | {:.1}% | {:+.1}% | {} |",
                baseline.win_rate * 100.0, m.win_rate * 100.0, wr_change, wr_arrow
            );

            // Alpha comparison
            let alpha_change = m.alpha - baseline.alpha;
            let alpha_arrow = if alpha_change > 0.0 { "\u{2197}\u{fe0f}" } else if alpha_change < 0.0 { "\u{2198}\u{fe0f}" } else { "\u{2192}" };
            let _w = writeln!(
                report,
                "| Alpha | {:.2}% | {:.2}% | {:+.2}% | {} |",
                baseline.alpha, m.alpha, alpha_change, alpha_arrow
            );
            
            report.push('\n');
        }
        
        // Trade Statistics
        report.push_str("## Trade Statistics\n\n");
        report.push_str("| Metric | Value |\n");
        report.push_str("|--------|-------|\n");
        let _w = writeln!(report, "| Total Trades | {} |", m.total_trades);
        let _w = writeln!(report, "| Avg Trade Return | {:.3}% |", m.avg_trade_return_pct);
        let _w = writeln!(report, "| Win Rate | {:.2}% |", m.win_rate * 100.0);

        if let Some(baseline) = &self.baseline_results {
            let trade_diff = m.total_trades as i64 - baseline.total_trades as i64;
            let _w = writeln!(report, "| Trades vs Baseline | {:+} |", trade_diff);
        }
        
        report.push('\n');
        
        // Deployment Recommendation
        report.push_str("## Deployment Recommendation\n\n");
        let recommendation = self.get_recommendation();
        let _w = write!(report, "**Status**: {}\n\n", recommendation.status);
        let _w = write!(report, "{}\n\n", recommendation.reasoning);
        
        // Production Criteria Summary
        report.push_str("### Production Criteria Checklist\n\n");
        let criteria_passed = self.count_criteria_passed();
        let _w = writeln!(report, "- **Criteria Passed**: {}/5", criteria_passed);
        let _w = writeln!(report, "- **Total Return**: {} ({:.2}% > 0%)",
            if m.total_return_pct > 0.0 { "\u{2705} PASS" } else { "\u{274c} FAIL" },
            m.total_return_pct
        );
        let _w = writeln!(report, "- **Sharpe Ratio**: {} ({:.2} > 1.5)",
            if m.sharpe_ratio > 1.5 { "\u{2705} PASS" } else { "\u{274c} FAIL" },
            m.sharpe_ratio
        );
        let _w = writeln!(report, "- **Max Drawdown**: {} ({:.2}% < 20%)",
            if m.max_drawdown_pct < 20.0 { "\u{2705} PASS" } else { "\u{274c} FAIL" },
            m.max_drawdown_pct
        );
        let _w = writeln!(report, "- **Win Rate**: {} ({:.1}% > 50%)",
            if m.win_rate > 0.50 { "\u{2705} PASS" } else { "\u{274c} FAIL" },
            m.win_rate * 100.0
        );
        let _w = writeln!(report, "- **Alpha vs B&H**: {} ({:.2}% > 0%)",
            if m.alpha > 0.0 { "\u{2705} PASS" } else { "\u{274c} FAIL" },
            m.alpha
        );
        
        report.push('\n');
        
        // Footer
        report.push_str("---\n\n");
        report.push_str("*Report generated automatically by Foxhunt ML Evaluation Framework*\n");
        
        report
    }
    
    /// Count how many production criteria are passed
    ///
    /// # Returns
    ///
    /// Number of criteria passed (0-5)
    fn count_criteria_passed(&self) -> usize {
        let m = &self.new_results;
        [
            m.total_return_pct > 0.0,
            m.sharpe_ratio > 1.5,
            m.max_drawdown_pct < 20.0,
            m.win_rate > 0.50,
            m.alpha > 0.0,
        ]
        .iter()
        .filter(|&&x| x)
        .count()
    }
    
    /// Generate deployment recommendation based on production criteria
    ///
    /// # Recommendation Logic
    ///
    /// - **APPROVE (4-5 criteria)**: Model is production-ready
    /// - **REVIEW (2-3 criteria)**: Marginal performance, needs review
    /// - **REJECT (0-1 criteria)**: Not production-ready
    ///
    /// # Returns
    ///
    /// A `Recommendation` with status and reasoning
    pub fn get_recommendation(&self) -> Recommendation {
        let m = &self.new_results;
        let passes = self.count_criteria_passed();
        
        if passes >= 4 {
            Recommendation {
                status: "\u{2705} APPROVE - Ready for Production".to_owned(),
                reasoning: format!(
                    "Model passes {}/5 production criteria. Strong performance with {:.2}% return, {:.2} Sharpe ratio, and {:.1}% win rate. \
                    Risk is acceptable with {:.2}% max drawdown. Model demonstrates profitability with {:.2}% alpha vs buy-and-hold. \
                    \n\n**Action**: Proceed with production deployment after final validation.",
                    passes,
                    m.total_return_pct,
                    m.sharpe_ratio,
                    m.win_rate * 100.0,
                    m.max_drawdown_pct,
                    m.alpha
                ),
            }
        } else if passes >= 2 {
            Recommendation {
                status: "\u{26a0}\u{fe0f} REVIEW - Marginal Performance".to_owned(),
                reasoning: format!(
                    "Model passes {}/5 production criteria. Performance is marginal and requires careful review. \
                    \n\n**Concerns**:\n{}
                    \n**Action**: Conduct detailed risk assessment and consider additional testing before deployment.",
                    passes,
                    self.generate_concerns_list()
                ),
            }
        } else {
            Recommendation {
                status: "\u{274c} REJECT - Not Production Ready".to_owned(),
                reasoning: format!(
                    "Model only passes {}/5 production criteria. Performance is insufficient for production deployment. \
                    \n\n**Critical Issues**:\n{}
                    \n**Action**: Do not deploy. Retrain model with improved hyperparameters or different architecture.",
                    passes,
                    self.generate_concerns_list()
                ),
            }
        }
    }
    
    /// Generate list of concerns for models not passing all criteria
    ///
    /// # Returns
    ///
    /// Markdown-formatted list of failed criteria
    fn generate_concerns_list(&self) -> String {
        let m = &self.new_results;
        let mut concerns = Vec::new();
        
        if m.total_return_pct <= 0.0 {
            concerns.push(format!("- \u{274c} Negative total return ({:.2}%)", m.total_return_pct));
        }
        if m.sharpe_ratio <= 1.5 {
            concerns.push(format!("- \u{274c} Low Sharpe ratio ({:.2} < 1.5)", m.sharpe_ratio));
        }
        if m.max_drawdown_pct >= 20.0 {
            concerns.push(format!("- \u{274c} Excessive drawdown ({:.2}% > 20%)", m.max_drawdown_pct));
        }
        if m.win_rate <= 0.50 {
            concerns.push(format!("- \u{274c} Poor win rate ({:.1}% < 50%)", m.win_rate * 100.0));
        }
        if m.alpha <= 0.0 {
            concerns.push(format!("- \u{274c} Negative alpha ({:.2}%)", m.alpha));
        }
        
        if concerns.is_empty() {
            "- No critical issues identified".to_owned()
        } else {
            concerns.join("\n")
        }
    }
}

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

    #[test]
    fn test_report_generation_approve() {
        let report = BacktestReport {
            model_name: "DQN-Test-Model".to_owned(),
            baseline_name: "DQN-Baseline".to_owned(),
            new_results: PerformanceMetrics {
                total_return_pct: 15.2,
                sharpe_ratio: 2.3,
                max_drawdown_pct: 12.5,
                win_rate: 0.58,
                alpha: 3.2,
                total_trades: 145,
                avg_trade_return_pct: 0.105,
            },
            baseline_results: None,
        };

        let markdown = report.generate_markdown();
        
        assert!(markdown.contains("# DQN Backtesting Report"));
        assert!(markdown.contains("DQN-Test-Model"));
        assert!(markdown.contains("✅ APPROVE"));
        assert!(markdown.contains("5/5"));
    }

    #[test]
    fn test_report_generation_reject() {
        let report = BacktestReport {
            model_name: "DQN-Poor-Model".to_owned(),
            baseline_name: "DQN-Baseline".to_owned(),
            new_results: PerformanceMetrics {
                total_return_pct: -5.2,
                sharpe_ratio: 0.8,
                max_drawdown_pct: 35.0,
                win_rate: 0.42,
                alpha: -2.1,
                total_trades: 120,
                avg_trade_return_pct: -0.043,
            },
            baseline_results: None,
        };

        let markdown = report.generate_markdown();
        
        assert!(markdown.contains("❌ REJECT"));
        assert!(markdown.contains("0/5"));
    }

    #[test]
    fn test_baseline_comparison() {
        let report = BacktestReport {
            model_name: "DQN-New".to_owned(),
            baseline_name: "DQN-Trial35".to_owned(),
            new_results: PerformanceMetrics {
                total_return_pct: 18.5,
                sharpe_ratio: 2.5,
                max_drawdown_pct: 10.2,
                win_rate: 0.62,
                alpha: 4.5,
                total_trades: 150,
                avg_trade_return_pct: 0.123,
            },
            baseline_results: Some(PerformanceMetrics {
                total_return_pct: 12.1,
                sharpe_ratio: 1.8,
                max_drawdown_pct: 18.3,
                win_rate: 0.52,
                alpha: 1.5,
                total_trades: 138,
                avg_trade_return_pct: 0.088,
            }),
        };

        let markdown = report.generate_markdown();

        assert!(markdown.contains("Comparison to Baseline"));
        assert!(markdown.contains("DQN-Trial35"));
        assert!(markdown.contains("+6.40%")); // Return improvement (18.5 - 12.1 = 6.4)
    }
}