//! Virtual rendering helpers for headless client frame streaming.

use ratatui::backend::{Backend, ClearType, TestBackend, WindowSize};
use ratatui::layout::{Position, Rect, Size};

use crate::app::state::AppState;
use crate::app::Mode;
use crate::client::blit::{BlitEncoder, EncodedBlit};
use crate::server::protocol::{
    CursorState, FrameData, RenderEncoding, ServerMessage, TerminalFrame,
};

/// Per-client render baseline for the negotiated render encoding.
pub(crate) enum ClientRenderState {
    /// Semantic clients compare full frame data and skip identical frames.
    Semantic { last_frame: Option<FrameData> },
    /// Terminal-ANSI clients keep a terminal diff encoder and sequence number.
    TerminalAnsi { blit_encoder: BlitEncoder, seq: u64 },
}

impl ClientRenderState {
    pub(crate) fn new(render_encoding: RenderEncoding) -> Self {
        match render_encoding {
            RenderEncoding::SemanticFrame => Self::Semantic { last_frame: None },
            RenderEncoding::TerminalAnsi => Self::TerminalAnsi {
                blit_encoder: BlitEncoder::new(),
                seq: 0,
            },
        }
    }

    pub(crate) fn reset_baseline(&mut self) {
        match self {
            Self::Semantic { last_frame } => *last_frame = None,
            Self::TerminalAnsi { blit_encoder, .. } => *blit_encoder = BlitEncoder::new(),
        }
    }

    pub(crate) fn reset_semantic_input_baseline(&mut self) {
        if let Self::Semantic { last_frame } = self {
            *last_frame = None;
        }
    }

    pub(crate) fn prepare_frame(&mut self, frame: &FrameData) -> Option<PreparedRender> {
        match self {
            Self::Semantic { last_frame } => {
                if last_frame.as_ref() == Some(frame) {
                    return None;
                }
                Some(PreparedRender {
                    message: ServerMessage::Frame(frame.clone()),
                    encoded: None,
                })
            }
            Self::TerminalAnsi { blit_encoder, seq } => {
                if blit_encoder.is_current(frame) {
                    return None;
                }
                let encoded = blit_encoder.encode(frame, false);
                Some(PreparedRender {
                    message: ServerMessage::Terminal(TerminalFrame {
                        seq: *seq + 1,
                        width: frame.width,
                        height: frame.height,
                        full: encoded.full,
                        bytes: encoded.bytes.clone(),
                    }),
                    encoded: Some(encoded),
                })
            }
        }
    }

    pub(crate) fn note_oversized_frame(&mut self, frame: FrameData) {
        if let Self::Semantic { last_frame } = self {
            *last_frame = Some(frame);
        }
    }

    pub(crate) fn commit_sent_frame(&mut self, frame: FrameData, prepared: PreparedRender) {
        match (self, prepared.encoded) {
            (Self::Semantic { last_frame }, None) => *last_frame = Some(frame),
            (Self::TerminalAnsi { blit_encoder, seq }, Some(encoded)) => {
                blit_encoder.commit(frame, encoded);
                *seq += 1;
            }
            _ => {}
        }
    }

    #[cfg(test)]
    pub(crate) fn terminal_seq(&self) -> Option<u64> {
        match self {
            Self::Semantic { .. } => None,
            Self::TerminalAnsi { seq, .. } => Some(*seq),
        }
    }
}

/// A prepared client render message plus any baseline state needed after send.
pub(crate) struct PreparedRender {
    message: ServerMessage,
    encoded: Option<EncodedBlit>,
}

impl PreparedRender {
    pub(crate) fn message(&self) -> &ServerMessage {
        &self.message
    }
}

struct CursorTrackingBackend {
    inner: TestBackend,
    rendered_cursor: Option<Position>,
}

impl CursorTrackingBackend {
    fn new(width: u16, height: u16) -> Self {
        Self {
            inner: TestBackend::new(width, height),
            rendered_cursor: None,
        }
    }

    fn buffer(&self) -> &ratatui::buffer::Buffer {
        self.inner.buffer()
    }

    fn rendered_cursor(&self) -> Option<CursorState> {
        self.rendered_cursor.map(|pos| CursorState {
            x: pos.x,
            y: pos.y,
            visible: true,
        })
    }
}

impl Backend for CursorTrackingBackend {
    type Error = std::convert::Infallible;

    fn draw<'a, I>(&mut self, content: I) -> Result<(), Self::Error>
    where
        I: Iterator<Item = (u16, u16, &'a ratatui::buffer::Cell)>,
    {
        self.inner.draw(content)
    }

    fn append_lines(&mut self, n: u16) -> Result<(), Self::Error> {
        self.inner.append_lines(n)
    }

    fn hide_cursor(&mut self) -> Result<(), Self::Error> {
        self.inner.hide_cursor()?;
        self.rendered_cursor = None;
        Ok(())
    }

    fn show_cursor(&mut self) -> Result<(), Self::Error> {
        self.inner.show_cursor()
    }

    fn get_cursor_position(&mut self) -> Result<Position, Self::Error> {
        self.inner.get_cursor_position()
    }

    fn set_cursor_position<P: Into<Position>>(&mut self, position: P) -> Result<(), Self::Error> {
        let position = position.into();
        self.inner.set_cursor_position(position)?;
        self.rendered_cursor = Some(position);
        Ok(())
    }

    fn clear(&mut self) -> Result<(), Self::Error> {
        self.inner.clear()
    }

    fn clear_region(&mut self, clear_type: ClearType) -> Result<(), Self::Error> {
        self.inner.clear_region(clear_type)
    }

    fn size(&self) -> Result<Size, Self::Error> {
        self.inner.size()
    }

    fn window_size(&mut self) -> Result<WindowSize, Self::Error> {
        self.inner.window_size()
    }

    fn flush(&mut self) -> Result<(), Self::Error> {
        self.inner.flush()
    }
}

/// Renders the AppState to an in-memory ratatui Buffer.
///
/// This produces the same output as the monolithic binary's terminal draw,
/// but writes to a `Buffer` instead of stdout. Cursor visibility is captured
/// from explicit frame cursor intent rather than incidental backend state.
pub(crate) fn render_virtual(
    app_state: &mut AppState,
    area: Rect,
    resize_panes: bool,
) -> (ratatui::buffer::Buffer, Option<CursorState>) {
    if resize_panes {
        crate::ui::compute_view(app_state, area);
    } else {
        crate::ui::compute_view_without_resizing_panes(app_state, area);
    }

    let backend = CursorTrackingBackend::new(area.width, area.height);
    let mut terminal = ratatui::Terminal::new(backend).expect("TestBackend::new should never fail");

    terminal
        .draw(|frame| {
            crate::ui::render(app_state, frame);
        })
        .expect("render to TestBackend should never fail");

    let buffer = terminal.backend().buffer().clone();
    let cursor =
        focused_terminal_cursor(app_state).or_else(|| terminal.backend().rendered_cursor());

    (buffer, cursor)
}

pub(crate) fn visible_hyperlinks(app_state: &AppState) -> Vec<((u16, u16), String, String)> {
    let Some(ws_idx) = app_state.active else {
        return Vec::new();
    };
    let Some(tab) = app_state
        .workspaces
        .get(ws_idx)
        .and_then(crate::workspace::Workspace::active_tab)
    else {
        return Vec::new();
    };

    let mut links = Vec::new();
    for info in &app_state.view.pane_infos {
        if let Some(runtime) = tab.runtimes.get(&info.id) {
            links.extend(runtime.visible_hyperlinks(info.inner_rect));
        }
    }
    links
}

fn focused_terminal_cursor(app_state: &AppState) -> Option<CursorState> {
    if app_state.mode != Mode::Terminal {
        return None;
    }

    let ws_idx = app_state.active?;
    let ws = app_state.workspaces.get(ws_idx)?;
    let info = app_state
        .view
        .pane_infos
        .iter()
        .find(|info| info.is_focused)?;
    let rt = ws.runtimes.get(&info.id)?;
    let cursor = rt.cursor_state(info.inner_rect, true)?;
    Some(CursorState {
        x: cursor.x,
        y: cursor.y,
        visible: cursor.visible,
    })
}