//! `AppState` — the top-level mutable state of the running TUI.
//!
//! v1 keeps it small on purpose: a list of tabs (each bound to at most one
//! session), an active tab index, focus split between sidebar and pane, the
//! current input mode, and an optional overlay (spawn modal, kill confirm,
//! help, transient toast).
//!
//! v1.5 will replace `Tab::pane: Option<SessionId>` with a split tree.

use uuid::Uuid;

use crate::keymap::Mode;

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum Focus {
    Sidebar,
    Pane,
}

#[derive(Debug, Clone)]
pub struct Tab {
    pub name: String,
    pub pane: Option<Uuid>,
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub enum OverlayKind {
    Spawn,
    KillConfirm(Uuid),
    Help,
    Toast(String),
}

#[derive(Debug)]
pub struct AppState {
    pub tabs: Vec<Tab>,
    pub active_tab_idx: usize,
    pub focus: Focus,
    pub mode: Mode,
    pub sidebar_visible: bool,
    pub sidebar_highlight: Option<Uuid>,
    pub overlay: Option<OverlayKind>,
}

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

impl AppState {
    pub fn new() -> Self {
        Self {
            tabs: vec![Tab {
                name: "1".into(),
                pane: None,
            }],
            active_tab_idx: 0,
            focus: Focus::Sidebar,
            mode: Mode::Normal,
            sidebar_visible: true,
            sidebar_highlight: None,
            overlay: None,
        }
    }

    pub fn active_tab(&self) -> &Tab {
        &self.tabs[self.active_tab_idx]
    }

    pub fn active_tab_mut(&mut self) -> &mut Tab {
        &mut self.tabs[self.active_tab_idx]
    }

    /// Append a new tab and switch to it. Sidebar regains focus so the user
    /// can pick something to attach.
    pub fn new_tab(&mut self) {
        let name = format!("{}", self.tabs.len() + 1);
        self.tabs.push(Tab { name, pane: None });
        self.active_tab_idx = self.tabs.len() - 1;
        self.focus = Focus::Sidebar;
    }

    /// Drop the active tab. No-op if it's the only one — there must always
    /// be at least one tab.
    pub fn close_tab(&mut self) {
        if self.tabs.len() <= 1 {
            return;
        }
        self.tabs.remove(self.active_tab_idx);
        if self.active_tab_idx >= self.tabs.len() {
            self.active_tab_idx = self.tabs.len() - 1;
        }
    }

    pub fn next_tab(&mut self) {
        if self.tabs.is_empty() {
            return;
        }
        self.active_tab_idx = (self.active_tab_idx + 1) % self.tabs.len();
    }

    pub fn prev_tab(&mut self) {
        if self.tabs.is_empty() {
            return;
        }
        self.active_tab_idx = (self.active_tab_idx + self.tabs.len() - 1) % self.tabs.len();
    }

    pub fn goto_tab(&mut self, n: u8) {
        let idx = (n as usize)
            .saturating_sub(1)
            .min(self.tabs.len().saturating_sub(1));
        self.active_tab_idx = idx;
    }

    /// Bind a session to the active tab, move focus into the pane, and
    /// drop straight into Insert mode so keystrokes go to the session
    /// without an extra `i` press. The leader returns to Normal.
    pub fn attach_to_focused(&mut self, session_id: Uuid) {
        self.active_tab_mut().pane = Some(session_id);
        self.focus = Focus::Pane;
        self.mode = Mode::Insert;
    }

    /// Move the sidebar highlight by `delta` (positive = down) within the
    /// given ordered list of selectable session ids. Wraps. No-op on empty.
    pub fn move_sidebar_highlight(&mut self, order: &[Uuid], delta: i32) {
        if order.is_empty() {
            return;
        }
        let len = order.len() as i32;
        let cur = self
            .sidebar_highlight
            .and_then(|id| order.iter().position(|x| *x == id))
            .map(|i| i as i32)
            .unwrap_or(-1);
        let next = (cur + delta).rem_euclid(len) as usize;
        self.sidebar_highlight = Some(order[next]);
    }

    /// Toggle sidebar visibility.
    pub fn toggle_sidebar(&mut self) {
        self.sidebar_visible = !self.sidebar_visible;
        if !self.sidebar_visible {
            self.focus = Focus::Pane;
        }
    }
}

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

    #[test]
    fn new_app_starts_with_one_empty_tab_focused_on_sidebar() {
        let state = AppState::new();
        assert_eq!(state.tabs.len(), 1);
        assert_eq!(state.tabs[0].pane, None);
        assert_eq!(state.focus, Focus::Sidebar);
        assert_eq!(state.mode, Mode::Normal);
        assert!(state.sidebar_visible);
        assert!(state.overlay.is_none());
    }

    #[test]
    fn new_tab_extends_and_focuses() {
        let mut state = AppState::new();
        state.new_tab();
        assert_eq!(state.tabs.len(), 2);
        assert_eq!(state.active_tab_idx, 1);
        assert_eq!(state.focus, Focus::Sidebar);
    }

    #[test]
    fn close_tab_keeps_at_least_one() {
        let mut state = AppState::new();
        state.close_tab();
        assert_eq!(state.tabs.len(), 1);
        state.new_tab();
        state.close_tab();
        assert_eq!(state.tabs.len(), 1);
    }

    #[test]
    fn close_tab_advances_when_last_is_closed() {
        let mut state = AppState::new();
        state.new_tab();
        state.new_tab();
        assert_eq!(state.active_tab_idx, 2);
        state.close_tab();
        assert_eq!(state.tabs.len(), 2);
        assert_eq!(state.active_tab_idx, 1);
    }

    #[test]
    fn next_prev_tab_wraps() {
        let mut state = AppState::new();
        state.new_tab();
        state.new_tab();
        state.active_tab_idx = 0;
        state.next_tab();
        assert_eq!(state.active_tab_idx, 1);
        state.next_tab();
        assert_eq!(state.active_tab_idx, 2);
        state.next_tab();
        assert_eq!(state.active_tab_idx, 0);
        state.prev_tab();
        assert_eq!(state.active_tab_idx, 2);
    }

    #[test]
    fn goto_tab_uses_one_based_clamp() {
        let mut state = AppState::new();
        state.new_tab();
        state.new_tab();
        state.goto_tab(1);
        assert_eq!(state.active_tab_idx, 0);
        state.goto_tab(2);
        assert_eq!(state.active_tab_idx, 1);
        state.goto_tab(99);
        // Clamped to last available tab.
        assert_eq!(state.active_tab_idx, state.tabs.len() - 1);
    }

    #[test]
    fn move_sidebar_highlight_walks_order_and_wraps() {
        let mut state = AppState::new();
        let a = Uuid::from_u128(1);
        let b = Uuid::from_u128(2);
        let c = Uuid::from_u128(3);
        let order = vec![a, b, c];

        // No prior highlight + delta +1 lands on first item.
        state.move_sidebar_highlight(&order, 1);
        assert_eq!(state.sidebar_highlight, Some(a));

        state.move_sidebar_highlight(&order, 1);
        assert_eq!(state.sidebar_highlight, Some(b));
        state.move_sidebar_highlight(&order, 1);
        assert_eq!(state.sidebar_highlight, Some(c));
        // Wraps forward.
        state.move_sidebar_highlight(&order, 1);
        assert_eq!(state.sidebar_highlight, Some(a));
        // Wraps backward.
        state.move_sidebar_highlight(&order, -1);
        assert_eq!(state.sidebar_highlight, Some(c));
    }

    #[test]
    fn move_sidebar_highlight_is_noop_on_empty_order() {
        let mut state = AppState::new();
        state.move_sidebar_highlight(&[], 1);
        assert_eq!(state.sidebar_highlight, None);
    }

    #[test]
    fn attach_binds_focuses_pane_and_enters_insert_mode() {
        let mut state = AppState::new();
        let sid = Uuid::from_u128(7);
        state.attach_to_focused(sid);
        assert_eq!(state.tabs[0].pane, Some(sid));
        assert_eq!(state.focus, Focus::Pane);
        // The user expects to type into the session right away; the leader
        // (default ctrl-a) is the way back.
        assert_eq!(state.mode, Mode::Insert);
    }

    #[test]
    fn toggle_sidebar_moves_focus_to_pane_when_hiding() {
        let mut state = AppState::new();
        state.toggle_sidebar();
        assert!(!state.sidebar_visible);
        assert_eq!(state.focus, Focus::Pane);
        state.toggle_sidebar();
        assert!(state.sidebar_visible);
        // Doesn't force focus back; sidebar shown but focus stays where it was.
        assert_eq!(state.focus, Focus::Pane);
    }
}