use anyhow::Result;
use ratatui::widgets::ListState;
use std::path::PathBuf;

use crate::config::Config;
use crate::emby::{Client, Item};
use crate::player::Player;

pub const RESUME_VIRTUAL_ID: &str = "__resume__";
pub const RESUME_TITLE: &str = "Continue Watching";

#[derive(Debug, PartialEq, Eq, Clone, Copy)]
pub enum View {
    Libraries,
    Items,
}

#[derive(Debug, Clone)]
pub enum Action {
    Play {
        id: String,
        /// Display title (e.g. "Series — S01E02 — Episode Title").
        title: String,
        /// Resume position from server-side UserData, in Emby ticks (100 ns units).
        start_ticks: i64,
    },
}

pub struct App {
    pub client: Client,
    pub view: View,
    pub libraries: Vec<Item>,
    pub resume: Vec<Item>,
    /// Libraries view list = optional virtual "Continue Watching" entry + libraries.
    pub home_entries: Vec<Item>,
    pub items: Vec<Item>,
    pub list_state: ListState,
    pub current_title: Option<String>,
    pub breadcrumbs: Vec<(String, String)>, // (id, name)
    /// Selected index at each level we navigated away from, so `back` can restore
    /// the cursor where the user left it (e.g. Series → Season → Episode → back
    /// brings you to the same season/series row, not row 0).
    pub selection_stack: Vec<usize>,
    pub status: String,
    /// Live, editable configuration. Mirrors what's on disk; the settings
    /// screen mutates this and persists it through `config_path`.
    pub config: Config,
    /// Where to persist updated settings. `None` when no writable location was
    /// determined (rare; the settings screen will then refuse to save).
    pub config_path: Option<PathBuf>,
}

impl App {
    pub async fn new(
        client: Client,
        config: Config,
        config_path: Option<PathBuf>,
    ) -> Result<Self> {
        let libraries = client.views().await?;
        // Best-effort: don't fail startup if the resume endpoint hiccups.
        let resume = client.resume_items(20).await.unwrap_or_default();

        let home_entries = build_home_entries(&libraries, &resume);

        let mut list_state = ListState::default();
        if !home_entries.is_empty() {
            list_state.select(Some(0));
        }
        let status = format!(
            "Connected as {} · {} libraries · {} in progress",
            client.user_name,
            libraries.len(),
            resume.len()
        );
        Ok(Self {
            client,
            view: View::Libraries,
            libraries,
            resume,
            home_entries,
            items: vec![],
            list_state,
            current_title: None,
            breadcrumbs: vec![],
            selection_stack: vec![],
            status,
            config,
            config_path,
        })
    }

    pub fn current_list(&self) -> &[Item] {
        match self.view {
            View::Libraries => &self.home_entries,
            View::Items => &self.items,
        }
    }

    /// Refresh the Continue Watching list (after playback ends, for example).
    pub async fn refresh_resume(&mut self) {
        if let Ok(resume) = self.client.resume_items(20).await {
            self.resume = resume;
            self.home_entries = build_home_entries(&self.libraries, &self.resume);
        }
    }

    pub fn move_down(&mut self) {
        let len = self.current_list().len();
        if len == 0 {
            return;
        }
        let i = self.list_state.selected().unwrap_or(0);
        self.list_state.select(Some((i + 1).min(len - 1)));
    }

    pub fn move_up(&mut self) {
        let i = self.list_state.selected().unwrap_or(0);
        self.list_state.select(Some(i.saturating_sub(1)));
    }

    pub fn page_down(&mut self) {
        let len = self.current_list().len();
        if len == 0 {
            return;
        }
        let i = self.list_state.selected().unwrap_or(0);
        self.list_state.select(Some((i + 10).min(len - 1)));
    }

    pub fn page_up(&mut self) {
        let i = self.list_state.selected().unwrap_or(0);
        self.list_state.select(Some(i.saturating_sub(10)));
    }

    pub async fn activate(&mut self) -> Result<Option<Action>> {
        let Some(i) = self.list_state.selected() else {
            return Ok(None);
        };
        match self.view {
            View::Libraries => {
                let Some(entry) = self.home_entries.get(i).cloned() else {
                    return Ok(None);
                };
                // Remember which library/virtual entry was selected for restore on back.
                self.selection_stack.clear();
                self.selection_stack.push(i);
                if entry.id == RESUME_VIRTUAL_ID {
                    self.items = self.resume.clone();
                    self.view = View::Items;
                    self.breadcrumbs.clear();
                    self.breadcrumbs
                        .push((RESUME_VIRTUAL_ID.into(), RESUME_TITLE.into()));
                    self.current_title = Some(RESUME_TITLE.into());
                    self.list_state
                        .select(if self.items.is_empty() { None } else { Some(0) });
                    self.status = format!("{}: {} items", RESUME_TITLE, self.items.len());
                    return Ok(None);
                }
                self.status = format!("Loading {}...", entry.name);
                self.items = self.client.items(&entry.id).await?;
                self.view = View::Items;
                self.breadcrumbs.clear();
                self.breadcrumbs
                    .push((entry.id.clone(), entry.name.clone()));
                self.current_title = Some(entry.name.clone());
                self.list_state
                    .select(if self.items.is_empty() { None } else { Some(0) });
                self.status = format!("{}: {} items", entry.name, self.items.len());
                Ok(None)
            }
            View::Items => {
                let Some(item) = self.items.get(i).cloned() else {
                    return Ok(None);
                };
                if item.is_folder {
                    // Remember position in this folder before drilling down.
                    self.selection_stack.push(i);
                    self.status = format!("Loading {}...", item.name);
                    self.items = self.client.items(&item.id).await?;
                    self.breadcrumbs.push((item.id.clone(), item.name.clone()));
                    self.current_title = Some(item.name.clone());
                    self.list_state
                        .select(if self.items.is_empty() { None } else { Some(0) });
                    self.status = format!("{}: {} items", item.name, self.items.len());
                    Ok(None)
                } else {
                    let start_ticks = item
                        .user_data
                        .as_ref()
                        .map(|ud| ud.position_ticks)
                        .unwrap_or(0);
                    let title = item.display_title();
                    Ok(Some(Action::Play {
                        id: item.id,
                        title,
                        start_ticks,
                    }))
                }
            }
        }
    }

    pub async fn back(&mut self) -> Result<()> {
        if self.view != View::Items {
            return Ok(());
        }
        // Pop the current breadcrumb (current folder)
        self.breadcrumbs.pop();
        let restore = self.selection_stack.pop();
        if let Some((parent_id, parent_name)) = self.breadcrumbs.last().cloned() {
            if parent_id == RESUME_VIRTUAL_ID {
                self.items = self.resume.clone();
            } else {
                self.items = self.client.items(&parent_id).await?;
            }
            self.current_title = Some(parent_name.clone());
            self.list_state.select(restore_selection(restore, self.items.len()));
            self.status = format!("{}: {} items", parent_name, self.items.len());
        } else {
            self.view = View::Libraries;
            self.current_title = None;
            self.items.clear();
            self.list_state
                .select(restore_selection(restore, self.home_entries.len()));
            self.status = format!(
                "{} libraries · {} in progress",
                self.libraries.len(),
                self.resume.len()
            );
        }
        Ok(())
    }

    pub fn play(&mut self, action: &Action) -> Result<()> {
        match action {
            Action::Play {
                id,
                title,
                start_ticks,
            } => {
                let url = self.client.stream_url(id);
                self.status = format!("Playing {title}...");
                let start_seconds = (*start_ticks as f64) / 10_000_000.0;
                let reporter = self.client.reporter(id.clone());
                let mut player = Player::new(
                    self.config.audio_lang.as_deref(),
                    self.config.subtitle_lang.as_deref(),
                )?;
                let r = player.play_blocking(&url, title, start_seconds, Some(&reporter));
                self.status = match &r {
                    Ok(_) => format!("Finished: {title}"),
                    Err(e) => format!("Playback error: {e}"),
                };
                r
            }
        }
    }

    pub fn breadcrumb_path(&self) -> String {
        if self.breadcrumbs.is_empty() {
            "Libraries".into()
        } else {
            self.breadcrumbs
                .iter()
                .map(|(_, n)| n.as_str())
                .collect::<Vec<_>>()
                .join(" / ")
        }
    }
}

/// Clamp the remembered selection to the current list size. Returns None if
/// the list is empty (so no row is highlighted).
fn restore_selection(saved: Option<usize>, len: usize) -> Option<usize> {
    if len == 0 {
        return None;
    }
    Some(saved.unwrap_or(0).min(len - 1))
}

pub(crate) fn build_home_entries(libraries: &[Item], resume: &[Item]) -> Vec<Item> {
    let mut entries: Vec<Item> = Vec::with_capacity(libraries.len() + 1);
    if !resume.is_empty() {
        entries.push(Item {
            id: RESUME_VIRTUAL_ID.into(),
            name: format!("{RESUME_TITLE} ({})", resume.len()),
            item_type: "Collection".into(),
            is_folder: true,
            ..Item::default()
        });
    }
    entries.extend(libraries.iter().cloned());
    entries
}