// Copyright (c) 2022 Marceline Cramer
// SPDX-License-Identifier: LGPL-3.0-or-later

//! This module defines backends for WebAssembly execution.
//!
//! Canary is designed to support multiple WebAssembly runtimes for different
//! purposes. Currently, [wasmtime](https://wasmtime.dev) is the only one
//! implemented, but in the future, [wasm3](https://github.com/wasm3/wasm3)
//! will also be provided.

use std::collections::VecDeque;

use super::*;

pub mod wasmtime;

/// Creates the default WebAssembly backend.
///
/// Currently, only ever creates [wasmtime::WasmtimeBackend].
pub fn make_default_backend() -> anyhow::Result<Box<dyn Backend>> {
    let backend = wasmtime::WasmtimeBackend::new()?;
    Ok(Box::new(backend))
}

/// A WebAssembly runtime backend.
pub trait Backend {
    fn load_module(&self, abi: Arc<ScriptAbi>, module: &[u8]) -> anyhow::Result<Arc<dyn Instance>>;
}

/// An instance of a WebAssembly module.
///
/// All self parameters to this trait's functions are immutable, so the
/// implementation must provide interior mutability. This allows instances
/// to intelligently optimize the execution of their scripts, for example, by
/// allowing the execution of multiple ABI calls from multiple threads when
/// a script supports the WebAssembly multithreading extension.
pub trait Instance {
    /// Binds script data to a Canary panel.
    ///
    /// To "bind" a Canary panel to a Canary script, this function must be
    /// called. It passes the ID of a panel to the script, the name of the
    /// protocol that this panel will be using, plus an initialization
    /// message, and the script returns an integer as userdata. All panel
    /// events will be identified to the script with this userdata as the first
    /// argument.
    ///
    /// The intended usecase for this userdata is to contain a pointer. A
    /// Canary script can allocate some high-level object in memory, and when
    /// a panel is bound, the script will return a pointer to that object as the
    /// userdata. Then, when the runtime calls back into the script, the
    /// userdata will be reinterpreted as a pointer and a method can be called
    /// on that object in memory.
    fn bind_panel(&self, panel: PanelId, protocol: &str, msg: Vec<u8>) -> u32;

    fn update(&self, panel_ud: u32, dt: f32);

    fn draw(&self, panel_ud: u32) -> Vec<DrawCommand>;

    fn on_resize(&self, panel_ud: u32, new_size: Vec2);

    fn on_cursor_event(&self, panel_ud: u32, kind: CursorEventKind, at: Vec2);

    fn on_message(&self, panel_ud: u32, msg: Vec<u8>);
}

#[derive(Default)]
pub struct ScriptAbi {
    draw_cmds: Mutex<Vec<DrawCommand>>,
    font_store: Arc<text::FontStore>,
    font_families: Mutex<HashMap<String, u32>>,
    loaded_fonts: RwLock<Vec<Arc<text::Font>>>,
    text_layouts: RwLock<Slab<text::TextLayout>>,
    message_store: RwLock<Slab<Vec<u8>>>,
    panels: RwLock<Slab<PanelAbi>>,
}

impl ScriptAbi {
    pub fn new(font_store: Arc<text::FontStore>) -> Self {
        Self {
            font_store,
            ..Default::default()
        }
    }

    /// Allocates a new ID and host-side storage for a panel.
    pub fn create_panel(&self) -> PanelId {
        let abi = PanelAbi::default();
        let id = self.panels.write().insert(abi);
        PanelId(id)
    }

    pub fn start_draw(&self) {
        let mut lock = self.draw_cmds.lock();
        lock.clear();
    }

    pub fn draw_indexed(&self, vertices: &[MeshVertex], indices: &[MeshIndex]) {
        self.draw_cmds.lock().push(DrawCommand::Mesh {
            vertices: vertices.to_vec(),
            indices: indices.to_vec(),
        })
    }

    pub fn draw_text_layout(&self, id: u32, offset: Vec2, scale: f32, color: Color) {
        // TODO multiple fonts per layout
        let layouts = self.text_layouts.read();
        let layout = layouts.get(id as usize).unwrap();
        let glyphs = layout.glyphs.as_slice();
        let loaded = self.loaded_fonts.read();
        let font = loaded.get(layout.font_id as usize).unwrap();
        let cmds = font.draw(glyphs, offset, scale, color);
        self.draw_cmds.lock().extend(cmds.into_iter());
    }

    pub fn with_draw_commands(&self, f: impl FnOnce(&[DrawCommand])) {
        f(self.draw_cmds.lock().as_slice());
    }

    pub fn font_load(&self, family: &str) -> u32 {
        let mut family_cache = self.font_families.lock();

        if let Some(cached) = family_cache.get(family) {
            return *cached;
        }

        let font = self.font_store.load_font(family);
        let mut loaded = self.loaded_fonts.write();
        let id = loaded.len() as u32;
        family_cache.insert(family.to_string(), id);
        loaded.push(font);
        id
    }

    pub fn text_layout_new(&self, font_id: u32, text: &str) -> u32 {
        let loaded = self.loaded_fonts.read();
        let font = loaded.get(font_id as usize).unwrap();
        let layout = font.shape(text);
        self.text_layouts.write().insert(layout) as u32
    }

    pub fn text_layout_delete(&self, id: u32) {
        self.text_layouts.write().remove(id as usize);
    }

    pub fn text_layout_get_bounds(&self, id: u32, dst: &mut Rect) {
        let src = self.text_layouts.read().get(id as usize).unwrap().bounds;
        let _ = std::mem::replace(dst, src);
    }

    pub fn message_new(&self, data: Vec<u8>) -> u32 {
        let mut store = self.message_store.write();
        let id = store.insert(data) as u32;
        id
    }

    pub fn message_free(&self, id: u32) {
        let mut store = self.message_store.write();
        store.remove(id as usize);
    }

    pub fn message_get_len(&self, id: u32) -> u32 {
        self.message_store.read().get(id as usize).unwrap().len() as u32
    }

    pub fn message_get_data(&self, id: u32, dst: &mut [u8]) {
        let store = self.message_store.read();
        let src = store.get(id as usize).unwrap();
        dst.copy_from_slice(src);
    }

    pub fn panel_send_message(&self, id: u32, message: Vec<u8>) {
        if let Some(panel) = self.panels.read().get(id as usize) {
            panel.outgoing_messages.write().push_back(message);
        }
    }

    pub fn recv_panel_messages(&self, id: PanelId) -> Vec<Vec<u8>> {
        if let Some(panel) = self.panels.read().get(id.0) {
            panel.outgoing_messages.write().drain(..).collect()
        } else {
            Vec::new()
        }
    }
}

#[derive(Default)]
pub struct PanelAbi {
    outgoing_messages: RwLock<VecDeque<Vec<u8>>>,
}