//! Task decomposition — breaks complex tasks into smaller subtasks.

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

/// Decomposes a complex task into smaller, actionable subtasks.
pub struct Decomposer {
    /// Maximum depth of decomposition.
    #[allow(dead_code)]
    max_depth: usize,
}

impl Decomposer {
    /// Create a new decomposer.
    pub fn new() -> Self {
        Self { max_depth: 3 }
    }

    /// Decompose a task into subtasks using heuristics.
    ///
    /// In production, this would use the LLM to intelligently break down
    /// tasks. For now, it uses a simple heuristic based on the description.
    pub fn decompose(&self, task: &Task) -> KanbanResult<Vec<Task>> {
        let mut subtasks = Vec::new();

        // Heuristic: if the task mentions "and" or lists, create subtasks
        let description_lower = task.description.to_lowercase();

        if description_lower.contains(" and ") {
            subtasks.push(self.make_subtask(task, &format!("Part 1 of: {}", task.title), 1));
            subtasks.push(self.make_subtask(task, &format!("Part 2 of: {}", task.title), 2));
        }

        if description_lower.contains("first") || description_lower.contains("step 1") {
            subtasks.push(self.make_subtask(task, &format!("Step 1: {}", task.title), 1));
        }

        if description_lower.contains("second") || description_lower.contains("step 2") {
            subtasks.push(self.make_subtask(task, &format!("Step 2: {}", task.title), 2));
        }

        // If no specific decomposition found, create a default 3-part split
        if subtasks.is_empty() && task.description.len() > 100 {
            subtasks.push(self.make_subtask(task, &format!("Research: {}", task.title), 1));
            subtasks.push(self.make_subtask(task, &format!("Implement: {}", task.title), 2));
            subtasks.push(self.make_subtask(task, &format!("Verify: {}", task.title), 3));
        }

        Ok(subtasks)
    }

    /// Create a single subtask.
    fn make_subtask(&self, parent: &Task, title: &str, _index: usize) -> Task {
        Task {
            id: Uuid::new_v4(),
            title: title.to_string(),
            description: format!("Subtask of '{}': {}", parent.title, parent.description),
            priority: parent.priority,
            status: TaskStatus::Backlog,
            assigned_agent: None,
            created_at: chrono::Utc::now(),
            updated_at: chrono::Utc::now(),
            subtasks: Vec::new(),
            dependencies: vec![parent.id],
            tags: parent.tags.clone(),
        }
    }
}

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

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

    #[test]
    fn test_decompose_simple() {
        let decomposer = Decomposer::new();
        let task = Task {
            id: Uuid::new_v4(),
            title: "Build feature".to_string(),
            description: "Implement the login system and add tests".to_string(),
            priority: Priority::High,
            status: TaskStatus::Backlog,
            assigned_agent: None,
            created_at: chrono::Utc::now(),
            updated_at: chrono::Utc::now(),
            subtasks: Vec::new(),
            dependencies: Vec::new(),
            tags: Vec::new(),
        };
        let subtasks = decomposer.decompose(&task).unwrap();
        assert!(subtasks.len() >= 2);
    }

    #[test]
    fn test_decompose_short_description() {
        let decomposer = Decomposer::new();
        let task = Task {
            id: Uuid::new_v4(),
            title: "Simple task".to_string(),
            description: "Do the thing".to_string(),
            priority: Priority::Low,
            status: TaskStatus::Backlog,
            assigned_agent: None,
            created_at: chrono::Utc::now(),
            updated_at: chrono::Utc::now(),
            subtasks: Vec::new(),
            dependencies: Vec::new(),
            tags: Vec::new(),
        };
        let subtasks = decomposer.decompose(&task).unwrap();
        assert!(subtasks.is_empty()); // too short to decompose
    }
}