//! Diagnostics — task tracking, bottlenecks, and performance metrics.

use std::collections::HashMap;

use chrono::{DateTime, Utc};
use gyandoot_core::{KanbanResult, Task, TaskStatus};
use uuid::Uuid;

/// A diagnostic snapshot of the Kanban system.
#[derive(Debug, Clone)]
pub struct KanbanDiagnostics {
    pub total_tasks: usize,
    pub backlog_count: usize,
    pub in_progress_count: usize,
    pub done_count: usize,
    pub blocked_count: usize,
    pub average_completion_time_ms: Option<f64>,
    pub bottlenecks: Vec<String>,
    pub timestamp: DateTime<Utc>,
}

/// Tracks task lifecycle and produces diagnostic information.
pub struct Diagnostics {
    task_timings: HashMap<Uuid, TaskTiming>,
    bottlenecks: Vec<String>,
}

#[derive(Debug, Clone)]
struct TaskTiming {
    created_at: DateTime<Utc>,
    started_at: Option<DateTime<Utc>>,
    completed_at: Option<DateTime<Utc>>,
    status_changes: Vec<(DateTime<Utc>, TaskStatus)>,
}

impl Diagnostics {
    /// Create a new diagnostics tracker.
    pub fn new() -> Self {
        Self {
            task_timings: HashMap::new(),
            bottlenecks: Vec::new(),
        }
    }

    /// Record a task creation.
    pub fn record_creation(&mut self, task_id: Uuid) {
        self.task_timings.insert(
            task_id,
            TaskTiming {
                created_at: Utc::now(),
                started_at: None,
                completed_at: None,
                status_changes: vec![(Utc::now(), TaskStatus::Backlog)],
            },
        );
    }

    /// Record a task status change.
    pub fn record_status_change(&mut self, task_id: &Uuid, new_status: TaskStatus) {
        if let Some(timing) = self.task_timings.get_mut(task_id) {
            timing.status_changes.push((Utc::now(), new_status.clone()));

            if new_status == TaskStatus::InProgress && timing.started_at.is_none() {
                timing.started_at = Some(Utc::now());
            }

            if new_status == TaskStatus::Done {
                timing.completed_at = Some(Utc::now());
            }
        }
    }

    /// Generate a diagnostics snapshot for a set of tasks.
    pub fn analyze(&self, tasks: &[Task]) -> KanbanResult<KanbanDiagnostics> {
        let total = tasks.len();
        let backlog = tasks.iter().filter(|t| t.status == TaskStatus::Backlog).count();
        let in_progress = tasks.iter().filter(|t| t.status == TaskStatus::InProgress).count();
        let done = tasks.iter().filter(|t| t.status == TaskStatus::Done).count();
        let blocked = tasks.iter().filter(|t| t.status == TaskStatus::Blocked).count();

        // Calculate average completion time
        let completion_times: Vec<f64> = self
            .task_timings
            .values()
            .filter_map(|t| {
                let start = t.started_at?;
                let end = t.completed_at?;
                Some((end - start).num_milliseconds() as f64)
            })
            .collect();

        let avg_completion = if completion_times.is_empty() {
            None
        } else {
            Some(completion_times.iter().sum::<f64>() / completion_times.len() as f64)
        };

        Ok(KanbanDiagnostics {
            total_tasks: total,
            backlog_count: backlog,
            in_progress_count: in_progress,
            done_count: done,
            blocked_count: blocked,
            average_completion_time_ms: avg_completion,
            bottlenecks: self.bottlenecks.clone(),
            timestamp: Utc::now(),
        })
    }

    /// Add a bottleneck warning.
    pub fn report_bottleneck(&mut self, description: String) {
        self.bottlenecks.push(description);
    }
}

impl Default for Diagnostics {
    fn default() -> Self {
        Self::new()
    }
}

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

    #[test]
    fn test_diagnostics_tracking() {
        let mut diagnostics = Diagnostics::new();
        let task_id = Uuid::new_v4();
        diagnostics.record_creation(task_id);
        diagnostics.record_status_change(&task_id, TaskStatus::InProgress);
        diagnostics.record_status_change(&task_id, TaskStatus::Done);

        let tasks = vec![Task {
            id: task_id,
            title: "Test".to_string(),
            description: String::new(),
            priority: gyandoot_core::Priority::Low,
            status: TaskStatus::Done,
            assigned_agent: None,
            created_at: Utc::now(),
            updated_at: Utc::now(),
            subtasks: Vec::new(),
            dependencies: Vec::new(),
            tags: Vec::new(),
        }];

        let report = diagnostics.analyze(&tasks).unwrap();
        assert_eq!(report.total_tasks, 1);
        assert_eq!(report.done_count, 1);
    }
}