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

use std::collections::HashSet;

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

use crate::app::state::AppState;
use crate::app::Mode;
use crate::protocol::render_ansi::{BlitEncoder, EncodedBlit};
use crate::protocol::{CursorState, FrameData, RenderEncoding, ServerMessage, TerminalFrame};
use crate::selection::Selection;
use crate::terminal::{TerminalRuntime, TerminalRuntimeRegistry};

/// 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) {
                    crate::render_prof::event("prepare_frame.semantic.skip_current");
                    return None;
                }
                crate::render_prof::event("prepare_frame.semantic.changed");
                Some(PreparedRender::Semantic {
                    message: ServerMessage::Frame(frame),
                })
            }
            Self::TerminalAnsi { blit_encoder, seq } => {
                if blit_encoder.is_current(&frame) {
                    crate::render_prof::event("prepare_frame.ansi.skip_current");
                    return None;
                }
                let mut encoded = blit_encoder.encode(&frame, false);
                crate::render_prof::event("prepare_frame.ansi.changed");
                crate::render_prof::counter("prepare_frame.ansi.bytes", encoded.bytes.len() as u64);
                if encoded.full {
                    crate::render_prof::event("prepare_frame.ansi.full");
                } else {
                    crate::render_prof::event("prepare_frame.ansi.partial");
                }
                insert_graphics_before_sync_end(&mut encoded.bytes, &frame.graphics);
                crate::render_prof::counter(
                    "prepare_frame.graphics.bytes",
                    frame.graphics.len() as u64,
                );
                Some(PreparedRender::TerminalAnsi {
                    message: ServerMessage::Terminal(TerminalFrame {
                        seq: *seq + 1,
                        width: frame.width,
                        height: frame.height,
                        full: encoded.full,
                        bytes: encoded.bytes.clone(),
                    }),
                    frame,
                    encoded: Some(encoded),
                })
            }
        }
    }

    pub(crate) fn last_frame(&self) -> Option<&FrameData> {
        match self {
            Self::Semantic { last_frame } => last_frame.as_ref(),
            Self::TerminalAnsi { blit_encoder, .. } => blit_encoder.last_frame(),
        }
    }

    pub(crate) fn commit_sent_frame(&mut self, prepared: PreparedRender) {
        match (self, prepared) {
            (
                Self::Semantic { last_frame },
                PreparedRender::Semantic {
                    message: ServerMessage::Frame(frame),
                },
            ) => *last_frame = Some(frame),
            (
                Self::TerminalAnsi { blit_encoder, seq },
                PreparedRender::TerminalAnsi {
                    frame,
                    encoded: 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),
        }
    }
}

const SYNC_OUTPUT_END: &[u8] = b"\x1b[?2026l";

fn insert_graphics_before_sync_end(encoded: &mut Vec<u8>, graphics: &[u8]) {
    if graphics.is_empty() {
        return;
    }

    if let Some(sync_end) = rfind_subslice(encoded, SYNC_OUTPUT_END) {
        encoded.splice(sync_end..sync_end, graphics.iter().copied());
    } else {
        encoded.extend_from_slice(graphics);
    }
}

fn rfind_subslice(haystack: &[u8], needle: &[u8]) -> Option<usize> {
    if needle.is_empty() || needle.len() > haystack.len() {
        return None;
    }

    haystack
        .windows(needle.len())
        .rposition(|window| window == needle)
}

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

impl PreparedRender {
    pub(crate) fn message(&self) -> &ServerMessage {
        match self {
            Self::Semantic { message } | Self::TerminalAnsi { message, .. } => message,
        }
    }

    pub(crate) fn into_frame(self) -> Option<FrameData> {
        match self {
            Self::Semantic {
                message: ServerMessage::Frame(frame),
            } => Some(frame),
            Self::TerminalAnsi { frame, .. } => Some(frame),
            _ => None,
        }
    }
}

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,
            shape: 0,
        })
    }
}

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.
#[cfg_attr(not(test), allow(dead_code))]
pub(crate) fn render_virtual(
    app_state: &mut AppState,
    area: Rect,
    resize_panes: bool,
) -> (ratatui::buffer::Buffer, Option<CursorState>) {
    let terminal_runtimes = TerminalRuntimeRegistry::new();
    render_virtual_with_runtime_registry(
        app_state,
        &terminal_runtimes,
        area,
        resize_panes,
        crate::kitty_graphics::HostCellSize::default(),
    )
}

pub(crate) fn render_virtual_with_runtime_registry(
    app_state: &mut AppState,
    terminal_runtimes: &TerminalRuntimeRegistry,
    area: Rect,
    resize_panes: bool,
    cell_size: crate::kitty_graphics::HostCellSize,
) -> (ratatui::buffer::Buffer, Option<CursorState>) {
    let pre_compute_suppresses_focused_terminal_cursor =
        focused_terminal_suppresses_host_cursor(app_state, terminal_runtimes);
    if resize_panes {
        crate::ui::compute_view_with_cell_size(app_state, terminal_runtimes, area, cell_size);
    } else {
        crate::ui::compute_view_without_resizing_panes(app_state, terminal_runtimes, area);
    }
    let suppress_focused_terminal_cursor = pre_compute_suppresses_focused_terminal_cursor
        || focused_terminal_suppresses_host_cursor(app_state, terminal_runtimes);

    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_with_runtime_registry(app_state, terminal_runtimes, frame);
        })
        .expect("render to TestBackend should never fail");

    let buffer = terminal.backend().buffer().clone();
    let cursor = if suppress_focused_terminal_cursor {
        None
    } else {
        focused_terminal_cursor(app_state, terminal_runtimes).or_else(|| {
            (!focused_terminal_owns_host_cursor(app_state, terminal_runtimes))
                .then(|| terminal.backend().rendered_cursor())
                .flatten()
        })
    };

    (buffer, cursor)
}

/// Renders one server-owned terminal directly for `terminal attach` clients.
pub(crate) fn render_terminal_virtual(
    runtime: &crate::terminal::TerminalRuntime,
    area: Rect,
) -> (ratatui::buffer::Buffer, Option<CursorState>) {
    let suppress_cursor = runtime.synchronized_output_active();
    let backend = CursorTrackingBackend::new(area.width, area.height);
    let mut terminal = ratatui::Terminal::new(backend).expect("TestBackend::new should never fail");

    terminal
        .draw(|frame| {
            runtime.render(frame, area, true);
        })
        .expect("render to TestBackend should never fail");

    let buffer = terminal.backend().buffer().clone();
    let cursor = (!suppress_cursor)
        .then(|| runtime.cursor_state(area, true))
        .flatten()
        .map(|cursor| CursorState {
            x: cursor.x,
            y: cursor.y,
            visible: cursor.visible && !crate::ui::pane_is_scrolled_back(runtime),
            shape: cursor.shape,
        })
        .or_else(|| {
            (!suppress_cursor)
                .then(|| terminal.backend().rendered_cursor())
                .flatten()
        });

    (buffer, cursor)
}

pub(crate) fn visible_hyperlinks(
    app_state: &AppState,
    terminal_runtimes: &TerminalRuntimeRegistry,
    final_buffer: Option<&ratatui::buffer::Buffer>,
) -> Vec<((u16, u16), String, String)> {
    let Some(ws_idx) = app_state.active else {
        return Vec::new();
    };
    if app_state.workspaces.get(ws_idx).is_none() {
        return Vec::new();
    }

    let mut links = Vec::new();
    let mut occupied = HashSet::new();
    for info in &app_state.view.pane_infos {
        if let Some(runtime) =
            app_state.runtime_for_pane_in_workspace(terminal_runtimes, ws_idx, info.id)
        {
            for link in runtime.visible_hyperlinks(info.inner_rect) {
                occupied.insert(link.0);
                links.push(link);
            }
            let metrics = app_state.pane_scroll_metrics(terminal_runtimes, info.id);
            for link in plain_url_hyperlinks_for_pane(
                runtime,
                info.id,
                info.inner_rect,
                metrics,
                final_buffer,
            ) {
                if occupied.insert(link.0) {
                    links.push(link);
                }
            }
        }
    }
    links
}

fn plain_url_hyperlinks_for_pane(
    runtime: &TerminalRuntime,
    pane_id: crate::layout::PaneId,
    area: Rect,
    metrics: Option<crate::pane::ScrollMetrics>,
    final_buffer: Option<&ratatui::buffer::Buffer>,
) -> Vec<((u16, u16), String, String)> {
    if area.width == 0 || area.height == 0 {
        return Vec::new();
    }

    let selection = Selection::line_range(
        pane_id,
        Selection::absolute_row_for_viewport(0, metrics),
        Selection::absolute_row_for_viewport(area.height.saturating_sub(1), metrics),
        area.width.saturating_sub(1),
    );
    let Some(text) = runtime.extract_selection(&selection) else {
        return Vec::new();
    };
    let mut links = Vec::new();
    let cells = crate::app::actions::visible_text_cells(&text, area.width);
    let mut line_start = 0;
    for (byte_idx, ch) in text.char_indices() {
        if ch == '\n' {
            push_plain_url_line_links(
                &mut links,
                &text[line_start..byte_idx],
                line_start,
                &cells,
                area,
            );
            line_start = byte_idx + ch.len_utf8();
        }
    }
    push_plain_url_line_links(&mut links, &text[line_start..], line_start, &cells, area);
    if links.is_empty() {
        return links;
    }
    let pane_buffer = final_buffer.and_then(|_| render_runtime_buffer(runtime, area));
    links
        .into_iter()
        .filter(|((x, y), _, _)| {
            pane_cell_is_visible(
                x.saturating_sub(area.x),
                y.saturating_sub(area.y),
                *x,
                *y,
                pane_buffer.as_ref(),
                final_buffer,
            )
        })
        .collect()
}

fn render_runtime_buffer(runtime: &TerminalRuntime, area: Rect) -> Option<ratatui::buffer::Buffer> {
    let backend = TestBackend::new(area.width, area.height);
    let mut terminal = ratatui::Terminal::new(backend).ok()?;
    terminal
        .draw(|frame| {
            runtime.render(frame, Rect::new(0, 0, area.width, area.height), false);
        })
        .ok()?;
    Some(terminal.backend().buffer().clone())
}

fn push_plain_url_line_links(
    links: &mut Vec<((u16, u16), String, String)>,
    line: &str,
    line_start: usize,
    cells: &[crate::app::actions::VisibleTextCell],
    area: Rect,
) {
    for (start_col, end_col, url) in crate::app::actions::visible_url_spans(line) {
        for cell in cells.iter().filter(|cell| {
            cell.byte_index >= line_start
                && cell.byte_index < line_start + line.len()
                && cell.logical_col >= start_col
                && cell.logical_col <= end_col
                && cell.screen_row < area.height
        }) {
            let x = area.x.saturating_add(cell.screen_col);
            let y = area.y.saturating_add(cell.screen_row);
            links.push(((x, y), cell.ch.to_string(), url.to_owned()));
        }
    }
}

fn pane_cell_is_visible(
    pane_x: u16,
    pane_y: u16,
    frame_x: u16,
    frame_y: u16,
    pane_buffer: Option<&ratatui::buffer::Buffer>,
    final_buffer: Option<&ratatui::buffer::Buffer>,
) -> bool {
    let (Some(pane_buffer), Some(final_buffer)) = (pane_buffer, final_buffer) else {
        return true;
    };
    let Some(pane_cell) = pane_buffer.cell((pane_x, pane_y)) else {
        return false;
    };
    let Some(final_cell) = final_buffer.cell((frame_x, frame_y)) else {
        return false;
    };
    pane_cell.symbol() == final_cell.symbol()
        && pane_cell.fg == final_cell.fg
        && pane_cell.bg == final_cell.bg
        && pane_cell.modifier == final_cell.modifier
}

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

    let ws_idx = app_state.active?;
    let info = app_state
        .view
        .pane_infos
        .iter()
        .find(|info| info.is_focused)?;
    if !app_state.pane_exposes_host_cursor(ws_idx, info.id) {
        return None;
    }
    let rt = app_state.runtime_for_pane_in_workspace(terminal_runtimes, ws_idx, info.id)?;
    if rt.synchronized_output_active() {
        return None;
    }
    let scrolled_back = crate::ui::pane_is_scrolled_back(rt);
    // Determine whether the IME-anchor reveal applies to this focused pane.
    // The master switch must be on, and either no agent filter is configured
    // (apply to any pane) or the focused pane's detected agent matches the
    // allow-list. A configured list with no valid entries reveals nothing.
    let reveal = app_state.reveal_hidden_cursor_for_cjk_ime
        && (!app_state.cjk_ime_agent_filter_configured || {
            let detected = app_state
                .workspaces
                .get(ws_idx)
                .and_then(|ws| ws.terminal_id(info.id))
                .and_then(|tid| app_state.terminals.get(tid))
                .and_then(|t| t.detected_agent);
            detected.is_some_and(|agent| app_state.cjk_ime_agents.contains(&agent))
        });

    if let Some(cursor) = rt.cursor_state(info.inner_rect, true) {
        // When the reveal applies, expose the cursor anchor regardless of the
        // pane's `?25l` request so macOS IMEs keep tracking the candidate
        // window when TUIs paint their own cursor. Scrollback suppression
        // still applies.
        let visible = if reveal {
            !scrolled_back
        } else {
            cursor.visible && !scrolled_back
        };
        Some(CursorState {
            x: cursor.x,
            y: cursor.y,
            visible,
            shape: if reveal && visible {
                app_state.cjk_ime_cursor_shape
            } else {
                cursor.shape
            },
        })
    } else if reveal && !scrolled_back {
        // cursor_state() returned None — the viewport has no cursor position
        // (can happen with complex TUIs). Fall back to the pane's top-left so
        // the outer terminal still exposes a cursor anchor for IME tracking.
        Some(CursorState {
            x: info.inner_rect.x,
            y: info.inner_rect.y,
            visible: true,
            shape: app_state.cjk_ime_cursor_shape,
        })
    } else {
        None
    }
}

fn focused_terminal_owns_host_cursor(
    app_state: &AppState,
    terminal_runtimes: &TerminalRuntimeRegistry,
) -> bool {
    if app_state.mode != Mode::Terminal {
        return false;
    }

    let Some(ws_idx) = app_state.active else {
        return false;
    };
    let Some(info) = app_state
        .view
        .pane_infos
        .iter()
        .find(|info| info.is_focused)
    else {
        return false;
    };
    if !app_state.pane_exposes_host_cursor(ws_idx, info.id) {
        return false;
    }

    app_state
        .runtime_for_pane_in_workspace(terminal_runtimes, ws_idx, info.id)
        .is_some()
}

fn focused_terminal_suppresses_host_cursor(
    app_state: &AppState,
    terminal_runtimes: &TerminalRuntimeRegistry,
) -> bool {
    if app_state.mode != Mode::Terminal {
        return false;
    }

    let Some(ws_idx) = app_state.active else {
        return false;
    };
    let Some(info) = app_state
        .view
        .pane_infos
        .iter()
        .find(|info| info.is_focused)
    else {
        return false;
    };
    if !app_state.pane_exposes_host_cursor(ws_idx, info.id) {
        return false;
    }

    app_state
        .runtime_for_pane_in_workspace(terminal_runtimes, ws_idx, info.id)
        .is_some_and(crate::terminal::TerminalRuntime::synchronized_output_active)
}