// SPDX-License-Identifier: GPL-3.0-or-later
// src/active_state.rs
//
// Pure navigation state: tracks which session and item are currently active.

use anyhow::{Context, Result};
use uuid::Uuid;

use crate::workspace::model::{Item, Session, Workspace};

/// Tracks the active session and item selection.
///
/// `ActiveState` does not own or store a `Workspace`. All methods that need
/// workspace data receive it as a parameter. This keeps navigation state
/// cleanly separated from domain data.
#[derive(Debug, Clone)]
pub struct ActiveState {
    active_session: Option<Uuid>,
    active_item: Option<usize>,
}

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

impl ActiveState {
    #[must_use]
    pub fn new() -> Self {
        Self {
            active_session: None,
            active_item: None,
        }
    }

    /// Clear all navigation state.
    pub fn reset(&mut self) {
        self.active_session = None;
        self.active_item = None;
    }

    pub fn select_session(&mut self, workspace: &Workspace, name: &str) -> Result<()> {
        let session = workspace.session_by_name(name)?;
        if self.active_session == Some(session.id) {
            return Ok(());
        }
        self.active_session = Some(session.id);
        self.active_item = if session.items.is_empty() {
            None
        } else {
            Some(0)
        };
        Ok(())
    }

    pub fn select_session_by_id(&mut self, workspace: &Workspace, id: Uuid) -> Result<()> {
        if self.active_session == Some(id) {
            return Ok(());
        }
        let session = workspace.session(id)?;
        self.active_session = Some(session.id);
        self.active_item = if session.items.is_empty() {
            None
        } else {
            Some(0)
        };
        Ok(())
    }

    pub fn clear_session(&mut self) {
        self.active_session = None;
        self.active_item = None;
    }

    pub fn select_item(&mut self, workspace: &Workspace, index: usize) -> Result<()> {
        let session = self.require_active_session(workspace)?;
        if index >= session.items.len() {
            anyhow::bail!(
                "Item index {index} out of range (session {:?} has {} items)",
                session.name,
                session.items.len()
            );
        }
        self.active_item = Some(index);
        Ok(())
    }

    pub fn next_item(&mut self, workspace: &Workspace) {
        let count = self.item_count(workspace);
        if let Some(idx) = self.active_item {
            if idx + 1 < count {
                self.active_item = Some(idx + 1);
            }
        }
    }

    pub fn previous_item(&mut self) {
        if let Some(idx) = self.active_item {
            if idx > 0 {
                self.active_item = Some(idx - 1);
            }
        }
    }

    /// Adjust the item cursor after an item was removed from the active session.
    pub fn adjust_after_remove(&mut self, workspace: &Workspace) {
        let count = self.item_count(workspace);
        self.active_item = if count == 0 {
            None
        } else {
            Some(self.active_item.unwrap_or(0).min(count - 1))
        };
    }

    /// Point the item cursor to the last item in the active session.
    pub fn select_last_item(&mut self, workspace: &Workspace) {
        let count = self.item_count(workspace);
        self.active_item = if count == 0 { None } else { Some(count - 1) };
    }

    // -- Read-only accessors --

    #[must_use]
    pub fn active_session_id(&self) -> Option<Uuid> {
        self.active_session
    }

    #[must_use]
    pub fn active_item_index(&self) -> Option<usize> {
        self.active_item
    }

    /// Returns the active session from the workspace.
    #[must_use]
    pub fn active_session<'a>(&self, workspace: &'a Workspace) -> Option<&'a Session> {
        let id = self.active_session?;
        workspace.session(id).ok()
    }

    /// Returns the active item from the active session.
    #[must_use]
    pub fn active_item<'a>(&self, workspace: &'a Workspace) -> Option<&'a Item> {
        let session = self.active_session(workspace)?;
        let idx = self.active_item?;
        session.items.get(idx)
    }

    /// Returns the UUID of the active item.
    #[must_use]
    pub fn active_item_id(&self, workspace: &Workspace) -> Option<Uuid> {
        self.active_item(workspace).map(|i| i.id)
    }

    // Private helpers

    fn require_active_session<'a>(&self, workspace: &'a Workspace) -> Result<&'a Session> {
        let id = self.active_session.context("No active session")?;
        workspace.session(id)
    }

    fn item_count(&self, workspace: &Workspace) -> usize {
        self.active_session(workspace).map_or(0, |s| s.items.len())
    }
}