use chrono::{DateTime, Utc};
use std::collections::HashMap;

#[cfg(test)]
use chrono::Duration;

/// Per-task-type expertise tracking for agents with recency bias.
/// Recent performance (last 7 days) weighted 3x higher than historical averages.
#[derive(Debug, Clone)]
pub struct LearningProfile {
    pub agent_id: String,
    pub task_type_expertise: HashMap<String, TaskTypeExpertise>,
    pub last_updated: DateTime<Utc>,
}

/// Task-specific expertise metrics with learning curves.
#[derive(Debug, Clone)]
pub struct TaskTypeExpertise {
    /// Overall success rate (0.0-1.0) including all historical data.
    pub success_rate: f64,
    /// Total number of executions for this task type.
    pub total_executions: u32,
    /// Success rate for last 7 days with recency bias applied.
    /// Recent performance weighted 3x higher than older data.
    pub recent_success_rate: f64,
    /// Average duration in milliseconds.
    pub avg_duration_ms: f64,
    /// Time-series of expertise evolution as (timestamp, success_rate).
    /// Computed by aggregating executions into daily/weekly windows.
    pub learning_curve: Vec<(DateTime<Utc>, f64)>,
    /// Confidence score (0.0-1.0) based on execution count.
    /// Prevents overfitting: min(1.0, total_executions / 20).
    pub confidence: f64,
}

impl LearningProfile {
    /// Create new empty learning profile for agent.
    pub fn new(agent_id: String) -> Self {
        Self {
            agent_id,
            task_type_expertise: HashMap::new(),
            last_updated: Utc::now(),
        }
    }

    /// Add or update expertise for a task type.
    pub fn set_task_type_expertise(&mut self, task_type: String, expertise: TaskTypeExpertise) {
        self.task_type_expertise.insert(task_type, expertise);
        self.last_updated = Utc::now();
    }

    /// Get expertise score for specific task type, default to 0.5 if unknown.
    pub fn get_task_type_score(&self, task_type: &str) -> f64 {
        self.task_type_expertise
            .get(task_type)
            .map(|e| e.success_rate)
            .unwrap_or(0.5)
    }

    /// Get recent success rate for task type (weighted with recency bias).
    /// Returns recent_success_rate if available, falls back to overall success_rate.
    pub fn get_recent_score(&self, task_type: &str) -> f64 {
        self.task_type_expertise
            .get(task_type)
            .map(|e| {
                if e.total_executions >= 5 {
                    e.recent_success_rate
                } else {
                    e.success_rate
                }
            })
            .unwrap_or(0.5)
    }

    /// Get confidence score for task type (0.0-1.0 based on execution count).
    pub fn get_confidence(&self, task_type: &str) -> f64 {
        self.task_type_expertise
            .get(task_type)
            .map(|e| e.confidence)
            .unwrap_or(0.0)
    }
}

impl TaskTypeExpertise {
    /// Create expertise metrics from execution data.
    /// Calculates success_rate, confidence, and applies recency bias.
    pub fn from_executions(executions: Vec<ExecutionData>, _task_type: &str) -> Self {
        if executions.is_empty() {
            return Self {
                success_rate: 0.5,
                total_executions: 0,
                recent_success_rate: 0.5,
                avg_duration_ms: 0.0,
                learning_curve: Vec::new(),
                confidence: 0.0,
            };
        }

        let total_executions = executions.len() as u32;
        let success_count = executions.iter().filter(|e| e.success).count() as u32;
        let success_rate = success_count as f64 / total_executions as f64;

        let total_duration: u64 = executions.iter().map(|e| e.duration_ms).sum();
        let avg_duration_ms = total_duration as f64 / total_executions as f64;

        let recent_success_rate = calculate_recency_weighted_success(&executions);
        let confidence = (total_executions as f64 / 20.0).min(1.0);

        let learning_curve = calculate_learning_curve(&executions);

        Self {
            success_rate,
            total_executions,
            recent_success_rate,
            avg_duration_ms,
            learning_curve,
            confidence,
        }
    }

    /// Update expertise with new execution result.
    pub fn update_with_execution(&mut self, execution: &ExecutionData) {
        let new_count = self.total_executions + 1;
        let new_success_count = (self.success_rate * self.total_executions as f64).round() as u32
            + if execution.success { 1 } else { 0 };
        self.success_rate = new_success_count as f64 / new_count as f64;
        self.total_executions = new_count;
        self.confidence = (new_count as f64 / 20.0).min(1.0);

        let total_duration = self.avg_duration_ms * self.total_executions as f64
            - self.avg_duration_ms
            + execution.duration_ms as f64;
        self.avg_duration_ms = total_duration / new_count as f64;
    }
}

/// Execution data for calculating expertise metrics.
#[derive(Debug, Clone)]
pub struct ExecutionData {
    pub timestamp: DateTime<Utc>,
    pub duration_ms: u64,
    pub success: bool,
}

/// Calculate success rate with recency bias.
/// Last 7 days weighted 3x higher: weight = 3.0 * e^(-days_ago / 7.0).
fn calculate_recency_weighted_success(executions: &[ExecutionData]) -> f64 {
    if executions.is_empty() {
        return 0.5;
    }

    let now = Utc::now();
    let mut weighted_success = 0.0;
    let mut total_weight = 0.0;

    for execution in executions {
        let days_ago = (now - execution.timestamp).num_days() as f64;
        let weight = if days_ago < 7.0 {
            3.0 * (-days_ago / 7.0).exp()
        } else {
            (-days_ago / 7.0).exp()
        };

        weighted_success += weight * if execution.success { 1.0 } else { 0.0 };
        total_weight += weight;
    }

    if total_weight > 0.0 {
        weighted_success / total_weight
    } else {
        0.5
    }
}

/// Calculate learning curve as time-series of expertise evolution.
/// Groups executions into daily windows and computes success rate per window.
fn calculate_learning_curve(executions: &[ExecutionData]) -> Vec<(DateTime<Utc>, f64)> {
    if executions.is_empty() {
        return Vec::new();
    }

    let mut by_day: HashMap<DateTime<Utc>, (u32, u32)> = HashMap::new();

    for execution in executions {
        let day_start = execution
            .timestamp
            .date_naive()
            .and_hms_opt(0, 0, 0)
            .map(|dt| dt.and_utc())
            .unwrap_or_else(|| execution.timestamp);

        let (total, success) = by_day.entry(day_start).or_insert((0, 0));
        *total += 1;
        if execution.success {
            *success += 1;
        }
    }

    let mut curve: Vec<_> = by_day
        .iter()
        .map(|(day, (total, success))| (*day, *success as f64 / *total as f64))
        .collect();

    curve.sort_by_key(|entry| entry.0);
    curve
}

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

    #[test]
    fn test_learning_profile_creation() {
        let profile = LearningProfile::new("agent-1".to_string());
        assert_eq!(profile.agent_id, "agent-1");
        assert_eq!(profile.task_type_expertise.len(), 0);
    }

    #[test]
    fn test_task_type_expertise_from_executions() {
        let executions = vec![
            ExecutionData {
                timestamp: Utc::now() - Duration::hours(1),
                duration_ms: 100,
                success: true,
            },
            ExecutionData {
                timestamp: Utc::now() - Duration::hours(2),
                duration_ms: 150,
                success: true,
            },
            ExecutionData {
                timestamp: Utc::now() - Duration::hours(3),
                duration_ms: 120,
                success: false,
            },
        ];

        let expertise = TaskTypeExpertise::from_executions(executions, "coding");
        assert_eq!(expertise.total_executions, 3);
        assert!((expertise.success_rate - 2.0 / 3.0).abs() < 0.01);
        assert!((expertise.avg_duration_ms - 123.33).abs() < 1.0);
        assert!((expertise.confidence - 0.15).abs() < 0.01); // 3/20 = 0.15
    }

    #[test]
    fn test_recency_bias_weights_recent_higher() {
        let now = Utc::now();
        let executions = vec![
            ExecutionData {
                timestamp: now - Duration::hours(1),
                duration_ms: 100,
                success: true,
            },
            ExecutionData {
                timestamp: now - Duration::days(8),
                duration_ms: 100,
                success: false,
            },
        ];

        let recent = calculate_recency_weighted_success(&executions);
        assert!(recent > 0.5); // Recent success pulls average up
    }

    #[test]
    fn test_confidence_capped_at_one() {
        let executions = (0..100)
            .map(|i| ExecutionData {
                timestamp: Utc::now() - Duration::hours(i),
                duration_ms: 100,
                success: true,
            })
            .collect();

        let expertise = TaskTypeExpertise::from_executions(executions, "coding");
        assert_eq!(expertise.confidence, 1.0);
    }

    #[test]
    fn test_empty_executions() {
        let expertise = TaskTypeExpertise::from_executions(Vec::new(), "coding");
        assert_eq!(expertise.total_executions, 0);
        assert_eq!(expertise.success_rate, 0.5);
        assert_eq!(expertise.confidence, 0.0);
    }

    #[test]
    fn test_learning_curve_generation() {
        let now = Utc::now();
        let executions = vec![
            ExecutionData {
                timestamp: now - Duration::hours(25),
                duration_ms: 100,
                success: true,
            },
            ExecutionData {
                timestamp: now - Duration::hours(24),
                duration_ms: 100,
                success: true,
            },
            ExecutionData {
                timestamp: now - Duration::hours(1),
                duration_ms: 100,
                success: false,
            },
        ];

        let curve = calculate_learning_curve(&executions);
        assert!(curve.len() > 0);
        // Earlier executions should have lower timestamps
        for i in 1..curve.len() {
            assert!(curve[i - 1].0 <= curve[i].0);
        }
    }
}