//! TUI application state model.
//!
//! Defines the central [`AppState`] struct and the [`Screen`] / [`Focus`] enums
//! that drive the TUI navigation model.  This module holds pure data — no
//! terminal I/O or rendering logic lives here.

use std::fs::OpenOptions;
use std::io::Write;
use std::path::PathBuf;

use crate::models::session::RawEntry;
use crate::parser::discovery::AgentRef;

// ---------------------------------------------------------------------------
// Lightweight display types
// ---------------------------------------------------------------------------

/// Lightweight summary of a session, used in the session-list screen.
///
/// Carries only the fields needed to render the list rows; heavier data
/// (transcript entries, sub-agent details) is loaded on demand when the user
/// navigates into a session.
#[derive(Debug, Clone)]
pub struct SessionListItem {
    /// 8-character prefix of the session UUID (display form).
    pub short_id: String,
    /// Full session UUID (used when resolving to load transcript entries).
    pub full_id: String,
    /// Human-readable date string (e.g. `"2025-03-30 14:22:01"`).
    pub date: String,
    /// Project path recovered from the `cwd` field of the first JSONL line.
    /// Falls back to an empty string when unavailable.
    pub project: String,
    /// Model identifier from the first assistant message (e.g. `"claude-sonnet-4-6"`).
    /// Empty string when no assistant message is present.
    pub model: String,
    /// Total number of user + assistant messages in the session.
    pub msg_count: usize,
    /// Number of sub-agent runs attached to this session.
    pub agent_count: usize,
}

// ---------------------------------------------------------------------------
// Screen enum
// ---------------------------------------------------------------------------

/// The active screen (navigation state) of the TUI.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum Screen {
    /// The session list overview — the TUI's home screen.
    SessionList,
    /// A session transcript view for the given session UUID.
    Transcript {
        /// Full UUID of the session being viewed.
        session_id: String,
    },
    /// A sub-agent transcript view nested under a parent session.
    SubagentTranscript {
        /// Full UUID of the parent session.
        parent_session_id: String,
        /// The agent's UUID (as returned by [`AgentRef::agent_id`]).
        agent_id: String,
    },
}

// ---------------------------------------------------------------------------
// Focus enum
// ---------------------------------------------------------------------------

/// Which panel currently holds keyboard focus on the transcript screen.
///
/// On the session-list screen `Focus` is not meaningful; it is tracked here
/// so the value is preserved when the user navigates back and forth.
#[derive(Debug, Clone, Default, PartialEq, Eq)]
pub enum Focus {
    /// The main chat-log pane (default).
    #[default]
    ChatLog,
    /// The sub-agents side panel (shown when sub-agents are present).
    SubagentsPanel,
    /// The filter input bar at the bottom of the session-list screen.
    FilterInput,
}

// ---------------------------------------------------------------------------
// AppState
// ---------------------------------------------------------------------------

/// Central application state for the TUI.
///
/// All mutable state that drives rendering and event handling lives here.
/// Rendering code reads this struct; event handlers mutate it.
#[derive(Debug)]
pub struct AppState {
    // ── Navigation ──────────────────────────────────────────────────────────
    /// Currently displayed screen.
    pub screen: Screen,

    // ── Session list ────────────────────────────────────────────────────────
    /// All sessions, sorted most-recent-first.  Loaded once at startup.
    pub sessions: Vec<SessionListItem>,
    /// Index of the highlighted row in the session list.
    pub list_selected: usize,

    // ── Transcript ──────────────────────────────────────────────────────────
    /// Parsed JSONL entries for the currently viewed session or sub-agent.
    pub transcript_entries: Vec<RawEntry>,
    /// Vertical scroll offset (lines from the top of the chat log).
    pub transcript_scroll: usize,
    /// Horizontal scroll offset (columns from the left edge of the chat log).
    pub transcript_h_scroll: usize,

    // ── Sub-agents panel ────────────────────────────────────────────────────
    /// Sub-agent references for the currently viewed session.
    pub subagents: Vec<AgentRef>,
    /// Index of the highlighted row in the sub-agents panel.
    pub subagent_selected: usize,

    // ── Focus ───────────────────────────────────────────────────────────────
    /// Which panel currently holds keyboard focus.
    pub focus: Focus,

    // ── Modals ──────────────────────────────────────────────────────────────
    /// Whether the "quit?" confirmation dialog is visible.
    pub show_quit_dialog: bool,
    /// Whether the keyboard-shortcut help overlay is visible.
    pub show_help: bool,

    // ── Filter ──────────────────────────────────────────────────────────────
    /// Text currently being typed in the filter input box.
    pub filter_input: String,
    /// The last successfully applied filter query string.
    /// Empty string means no filter is active.
    pub filter_active: String,
    /// History of previously applied filter queries (most-recent last).
    pub filter_history: Vec<String>,
    /// When browsing history via Up/Down, the current history index.
    /// `None` means the user is not currently browsing history.
    pub filter_history_pos: Option<usize>,

    // ── Display ─────────────────────────────────────────────────────────────
    /// Whether color coding is enabled in transcript views.
    ///
    /// Initialised from the `NO_COLOR` environment variable: `false` when
    /// `NO_COLOR` is set and non-empty, `true` otherwise.  Can be toggled at
    /// runtime with the `c` key.
    pub color_enabled: bool,

    // ── Lifecycle ───────────────────────────────────────────────────────────
    /// Set to `true` to signal the event loop to exit.
    pub should_quit: bool,
}

impl AppState {
    /// Return the path to the filter history file: `~/.claude/claudbg.tui.history`.
    fn history_file_path() -> Option<PathBuf> {
        let home = std::env::var("HOME").ok()?;
        Some(PathBuf::from(home).join(".claude").join("claudbg.tui.history"))
    }

    /// Load filter history lines from disk.
    ///
    /// Returns an empty vec if the file does not exist or cannot be read.
    fn load_history() -> Vec<String> {
        let Some(path) = Self::history_file_path() else {
            return Vec::new();
        };
        std::fs::read_to_string(&path)
            .unwrap_or_default()
            .lines()
            .filter(|l| !l.trim().is_empty())
            .map(str::to_string)
            .collect()
    }

    /// Append a single query to the history file (open in append mode).
    ///
    /// Does nothing if the history file path cannot be determined.
    pub fn append_history_to_disk(query: &str) {
        let Some(path) = Self::history_file_path() else {
            return;
        };
        // Create parent directory if it doesn't exist.
        if let Some(parent) = path.parent() {
            let _ = std::fs::create_dir_all(parent);
        }
        if let Ok(mut f) = OpenOptions::new().create(true).append(true).open(&path) {
            let _ = writeln!(f, "{query}");
        }
    }

    /// Create a fresh [`AppState`] ready for the session-list screen.
    ///
    /// All data fields are initialised to empty / zero so the TUI can render
    /// immediately; the caller is responsible for populating [`AppState::sessions`]
    /// before the first frame is drawn.
    pub fn new() -> Self {
        // Color is on by default; disabled when NO_COLOR is set and non-empty.
        let color_enabled = std::env::var("NO_COLOR")
            .map(|v| v.is_empty())
            .unwrap_or(true);
        let filter_history = Self::load_history();
        Self {
            screen: Screen::SessionList,
            sessions: Vec::new(),
            list_selected: 0,
            transcript_entries: Vec::new(),
            transcript_scroll: 0,
            transcript_h_scroll: 0,
            subagents: Vec::new(),
            subagent_selected: 0,
            focus: Focus::default(),
            show_quit_dialog: false,
            show_help: false,
            filter_input: String::new(),
            filter_active: String::new(),
            filter_history,
            filter_history_pos: None,
            color_enabled,
            should_quit: false,
        }
    }

    /// Transition to the transcript screen for a session.
    ///
    /// Resets all transcript / sub-agent scroll and selection state so that
    /// the new view starts from the top.  The caller is responsible for
    /// loading [`AppState::transcript_entries`] and [`AppState::subagents`]
    /// after calling this method.
    pub fn enter_transcript(&mut self, session_id: impl Into<String>) {
        self.screen = Screen::Transcript {
            session_id: session_id.into(),
        };
        self.transcript_entries.clear();
        self.transcript_scroll = 0;
        self.transcript_h_scroll = 0;
        self.subagents.clear();
        self.subagent_selected = 0;
        self.focus = Focus::ChatLog;
    }

    /// Transition to the sub-agent transcript screen.
    ///
    /// Resets transcript scroll state.  The caller is responsible for loading
    /// [`AppState::transcript_entries`] for the agent after calling this method.
    pub fn enter_subagent_transcript(
        &mut self,
        parent_session_id: impl Into<String>,
        agent_id: impl Into<String>,
    ) {
        self.screen = Screen::SubagentTranscript {
            parent_session_id: parent_session_id.into(),
            agent_id: agent_id.into(),
        };
        self.transcript_entries.clear();
        self.transcript_scroll = 0;
        self.transcript_h_scroll = 0;
        self.focus = Focus::ChatLog;
    }

    /// Return to the session-list screen.
    ///
    /// Clears transcript and sub-agent data.  The session list and the
    /// previously selected row are preserved so the cursor position is
    /// restored after navigating back.
    pub fn go_back(&mut self) {
        self.screen = Screen::SessionList;
        self.transcript_entries.clear();
        self.transcript_scroll = 0;
        self.transcript_h_scroll = 0;
        self.subagents.clear();
        self.subagent_selected = 0;
        self.focus = Focus::ChatLog;
    }
}

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

// ---------------------------------------------------------------------------
// Tests
// ---------------------------------------------------------------------------

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

    /// `AppState::new()` starts on `Screen::SessionList`.
    #[test]
    fn new_starts_on_session_list() {
        let state = AppState::new();
        assert_eq!(state.screen, Screen::SessionList);
    }

    /// `AppState::new()` starts with empty sessions and zero selection.
    #[test]
    fn new_starts_with_empty_sessions() {
        let state = AppState::new();
        assert!(state.sessions.is_empty());
        assert_eq!(state.list_selected, 0);
    }

    /// `AppState::new()` starts with modals closed.
    #[test]
    fn new_starts_with_modals_closed() {
        let state = AppState::new();
        assert!(!state.show_quit_dialog);
        assert!(!state.show_help);
    }

    /// `enter_transcript` switches to `Screen::Transcript` and resets scroll.
    #[test]
    fn enter_transcript_switches_screen() {
        let mut state = AppState::new();
        state.transcript_scroll = 42;
        state.transcript_h_scroll = 7;
        state.enter_transcript("abc12345-0000-0000-0000-000000000000");
        assert_eq!(
            state.screen,
            Screen::Transcript {
                session_id: "abc12345-0000-0000-0000-000000000000".to_string(),
            }
        );
        assert_eq!(state.transcript_scroll, 0);
        assert_eq!(state.transcript_h_scroll, 0);
    }

    /// `enter_transcript` clears previous transcript entries.
    #[test]
    fn enter_transcript_clears_entries() {
        let mut state = AppState::new();
        // Insert a dummy entry via direct field access (simplest approach).
        state.transcript_entries.push(RawEntry {
            entry_type: Some("user".to_string()),
            session_id: None,
            parent_session_id: None,
            message: None,
            system_message: None,
            cwd: None,
            timestamp: None,
            duration_ms: None,
            extra: Default::default(),
        });
        state.enter_transcript("new-session");
        assert!(state.transcript_entries.is_empty());
    }

    /// `enter_subagent_transcript` sets `Screen::SubagentTranscript`.
    #[test]
    fn enter_subagent_transcript_sets_screen() {
        let mut state = AppState::new();
        state.enter_subagent_transcript("parent-session", "agent-001");
        assert_eq!(
            state.screen,
            Screen::SubagentTranscript {
                parent_session_id: "parent-session".to_string(),
                agent_id: "agent-001".to_string(),
            }
        );
    }

    /// `go_back` returns to `Screen::SessionList` and clears transcript state.
    #[test]
    fn go_back_returns_to_session_list() {
        let mut state = AppState::new();
        state.enter_transcript("some-session");
        state.transcript_scroll = 10;
        state.go_back();
        assert_eq!(state.screen, Screen::SessionList);
        assert_eq!(state.transcript_scroll, 0);
        assert!(state.transcript_entries.is_empty());
    }

    /// `go_back` preserves `list_selected`.
    #[test]
    fn go_back_preserves_list_selected() {
        let mut state = AppState::new();
        state.list_selected = 5;
        state.enter_transcript("some-session");
        state.go_back();
        assert_eq!(state.list_selected, 5);
    }

    /// `Focus::default()` is `ChatLog`.
    #[test]
    fn focus_default_is_chat_log() {
        assert_eq!(Focus::default(), Focus::ChatLog);
    }

    /// `SessionListItem` implements `Debug` and `Clone`.
    #[test]
    fn session_list_item_debug_clone() {
        let item = SessionListItem {
            short_id: "abc12345".to_string(),
            full_id: "abc12345-0000-0000-0000-000000000000".to_string(),
            date: "2025-03-30 14:00:00".to_string(),
            project: "/home/user/project".to_string(),
            model: "claude-sonnet-4-6".to_string(),
            msg_count: 10,
            agent_count: 2,
        };
        let cloned = item.clone();
        assert_eq!(cloned.short_id, item.short_id);
        let _ = format!("{item:?}");
    }

    /// `AppState::new()` enables color when `NO_COLOR` is unset.
    #[test]
    fn new_color_enabled_when_no_color_unset() {
        // Remove NO_COLOR from the environment for this test.
        // SAFETY: single-threaded test; no other threads reading the env.
        unsafe { std::env::remove_var("NO_COLOR") };
        let state = AppState::new();
        assert!(state.color_enabled);
    }

    /// `AppState::new()` disables color when `NO_COLOR` is set to a non-empty value.
    #[test]
    fn new_color_disabled_when_no_color_set() {
        // SAFETY: single-threaded test; no other threads reading the env.
        unsafe { std::env::set_var("NO_COLOR", "1") };
        let state = AppState::new();
        // Restore the environment before asserting so other tests are unaffected.
        unsafe { std::env::remove_var("NO_COLOR") };
        assert!(!state.color_enabled);
    }
}