use anyhow::{Result, anyhow};
use crossterm::event::{self, Event, KeyCode, KeyEventKind, KeyModifiers};
use ratatui::Terminal;
use ratatui::backend::Backend;
use ratatui::layout::{Constraint, Direction, Layout};
use ratatui::style::{Color, Style};
use ratatui::text::{Line, Span};
use ratatui::widgets::{Block, Borders, Paragraph};
use std::time::Duration;

use crate::app::{self, App, View};
use crate::config::{self, Config};
use crate::emby::Client;
use crate::login::{centered_rect, field_widget};

#[derive(Clone, Copy, PartialEq, Eq)]
enum Field {
    Server,
    User,
    Password,
    AudioLang,
    SubtitleLang,
    VideoOutput,
}

const FIELDS: [Field; 6] = [
    Field::Server,
    Field::User,
    Field::Password,
    Field::AudioLang,
    Field::SubtitleLang,
    Field::VideoOutput,
];

impl Field {
    fn next(self) -> Self {
        let i = FIELDS.iter().position(|f| *f == self).unwrap();
        FIELDS[(i + 1) % FIELDS.len()]
    }
    fn prev(self) -> Self {
        let i = FIELDS.iter().position(|f| *f == self).unwrap();
        FIELDS[(i + FIELDS.len() - 1) % FIELDS.len()]
    }
}

struct Form {
    server: String,
    user: String,
    password: String,
    audio_lang: String,
    subtitle_lang: String,
    video_output: String,
    focus: Field,
    error: Option<String>,
}

impl Form {
    fn from_config(cfg: &Config) -> Self {
        Self {
            server: cfg.server.clone(),
            user: cfg.user.clone(),
            password: cfg.password.clone(),
            audio_lang: cfg.audio_lang.clone().unwrap_or_default(),
            subtitle_lang: cfg.subtitle_lang.clone().unwrap_or_default(),
            video_output: cfg.video_output.clone().unwrap_or_default(),
            focus: Field::Server,
            error: None,
        }
    }

    fn value_mut(&mut self, f: Field) -> &mut String {
        match f {
            Field::Server => &mut self.server,
            Field::User => &mut self.user,
            Field::Password => &mut self.password,
            Field::AudioLang => &mut self.audio_lang,
            Field::SubtitleLang => &mut self.subtitle_lang,
            Field::VideoOutput => &mut self.video_output,
        }
    }
}

/// Open the settings editor. Returns when the user saves or cancels.
/// Mutates `app` in place: applies the new config, re-authenticates if
/// credentials changed, and persists to disk.
pub async fn run<B: Backend>(term: &mut Terminal<B>, app: &mut App) -> Result<()> {
    let mut form = Form::from_config(&app.config);
    loop {
        term.draw(|f| draw(f, &form))?;
        if !event::poll(Duration::from_millis(200))? {
            continue;
        }
        let Event::Key(key) = event::read()? else {
            continue;
        };
        if key.kind != KeyEventKind::Press {
            continue;
        }
        if key.modifiers.contains(KeyModifiers::CONTROL)
            && matches!(key.code, KeyCode::Char('c') | KeyCode::Char('C'))
        {
            return Ok(());
        }
        match key.code {
            KeyCode::Esc => return Ok(()),
            KeyCode::Tab | KeyCode::Down => form.focus = form.focus.next(),
            KeyCode::BackTab | KeyCode::Up => form.focus = form.focus.prev(),
            KeyCode::Enter => match apply(&mut form, app).await {
                Ok(()) => return Ok(()),
                Err(e) => form.error = Some(format!("{e}")),
            },
            KeyCode::Char(c) => form.value_mut(form.focus).push(c),
            KeyCode::Backspace => {
                form.value_mut(form.focus).pop();
            }
            _ => {}
        }
    }
}

async fn apply(form: &mut Form, app: &mut App) -> Result<()> {
    let server = form.server.trim().trim_end_matches('/').to_string();
    let user = form.user.trim().to_string();
    if server.is_empty() {
        form.focus = Field::Server;
        return Err(anyhow!("Server URL required"));
    }
    if !(server.starts_with("http://") || server.starts_with("https://")) {
        form.focus = Field::Server;
        return Err(anyhow!("Server URL must start with http:// or https://"));
    }
    if user.is_empty() {
        form.focus = Field::User;
        return Err(anyhow!("Username required"));
    }
    // Reflect the normalized values back so a successful save shows them on
    // disk and on screen identically.
    form.server = server.clone();
    form.user = user.clone();

    let new_cfg = Config {
        server: server.clone(),
        user: user.clone(),
        password: form.password.clone(),
        audio_lang: trim_to_opt(&form.audio_lang),
        subtitle_lang: trim_to_opt(&form.subtitle_lang),
        video_output: trim_to_opt(&form.video_output),
    };

    let creds_changed = new_cfg.server != app.config.server
        || new_cfg.user != app.config.user
        || new_cfg.password != app.config.password;

    if creds_changed {
        // Re-authenticate against the new endpoint/credentials. On failure
        // we propagate the error so the form stays open and the user can fix
        // the input. The old `Client` stays in place, so the session keeps
        // working if they bail with Esc afterwards.
        let new_client = Client::new(&new_cfg)
            .await
            .map_err(|e| anyhow!("Auth failed: {e}"))?;
        let libraries = new_client.views().await.unwrap_or_default();
        let resume = new_client.resume_items(20).await.unwrap_or_default();
        app.libraries = libraries;
        app.resume = resume;
        app.home_entries = app::build_home_entries(&app.libraries, &app.resume);
        app.view = View::Libraries;
        app.list_state.select(if app.home_entries.is_empty() {
            None
        } else {
            Some(0)
        });
        app.breadcrumbs.clear();
        app.selection_stack.clear();
        app.current_title = None;
        app.client = new_client;
    }

    if let Some(path) = &app.config_path {
        config::save(path, &new_cfg)?;
        app.status = format!("Settings saved to {}", path.display());
    } else {
        app.status = "Settings applied (no writable config path)".into();
    }
    app.config = new_cfg;
    Ok(())
}

fn trim_to_opt(s: &str) -> Option<String> {
    let t = s.trim();
    if t.is_empty() {
        None
    } else {
        Some(t.to_string())
    }
}

fn draw(f: &mut ratatui::Frame, form: &Form) {
    let area = centered_rect(70, 80, f.area());
    let block = Block::default()
        .borders(Borders::ALL)
        .title(" Settings ")
        .border_style(Style::default().fg(Color::Cyan));
    f.render_widget(block.clone(), area);

    let inner = block.inner(area);
    let rows = Layout::default()
        .direction(Direction::Vertical)
        .margin(1)
        .constraints([
            Constraint::Length(1), // hint
            Constraint::Length(3), // server
            Constraint::Length(3), // user
            Constraint::Length(3), // password
            Constraint::Length(3), // audio lang
            Constraint::Length(3), // subtitle lang
            Constraint::Length(3), // video output
            Constraint::Min(1),    // error / help
        ])
        .split(inner);

    let hint = Paragraph::new(Span::styled(
        "Edit configuration. Changing server/user/password reconnects to Emby.",
        Style::default().fg(Color::Gray),
    ));
    f.render_widget(hint, rows[0]);

    f.render_widget(
        field_widget("Server", &form.server, form.focus == Field::Server, false),
        rows[1],
    );
    f.render_widget(
        field_widget("User", &form.user, form.focus == Field::User, false),
        rows[2],
    );
    f.render_widget(
        field_widget(
            "Password",
            &form.password,
            form.focus == Field::Password,
            true,
        ),
        rows[3],
    );
    f.render_widget(
        field_widget(
            "Audio lang (e.g. jpn,eng)",
            &form.audio_lang,
            form.focus == Field::AudioLang,
            false,
        ),
        rows[4],
    );
    f.render_widget(
        field_widget(
            "Subtitle lang (e.g. eng)",
            &form.subtitle_lang,
            form.focus == Field::SubtitleLang,
            false,
        ),
        rows[5],
    );
    f.render_widget(
        field_widget(
            "Video output (gpu/sixel/kitty/drm/tct, blank=mpv default)",
            &form.video_output,
            form.focus == Field::VideoOutput,
            false,
        ),
        rows[6],
    );

    let footer = if let Some(err) = &form.error {
        Line::from(Span::styled(err.clone(), Style::default().fg(Color::Red)))
    } else {
        Line::from(Span::styled(
            "Tab/↓ next · Shift+Tab/↑ prev · Enter save · Esc cancel",
            Style::default().fg(Color::DarkGray),
        ))
    };
    f.render_widget(Paragraph::new(footer), rows[7]);
}