maolan_engine/plugins/

clap.rs

use crate::audio::io::AudioIO;
use crate::midi::io::MidiEvent;
use crate::mutex::UnsafeMutex;
#[cfg(any(
    target_os = "macos",
    target_os = "linux",
    target_os = "freebsd",
    target_os = "openbsd"
))]
use crate::plugins::paths;
use libloading::Library;
use serde::{Deserialize, Serialize};
use std::cell::Cell;
use std::collections::HashMap;
use std::ffi::{CStr, CString, c_char, c_void};
use std::fmt;
use std::path::{Path, PathBuf};
use std::sync::Arc;
use std::sync::atomic::{AtomicU32, Ordering};
use std::time::{Duration, Instant};

#[derive(Clone, Debug, PartialEq)]
pub struct ClapParameterInfo {
    pub id: u32,
    pub name: String,
    pub module: String,
    pub min_value: f64,
    pub max_value: f64,
    pub default_value: f64,
}

#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
pub struct ClapPluginState {
    pub bytes: Vec<u8>,
}

type AudioPortLayout = (Vec<usize>, usize);

#[derive(Clone, Debug, PartialEq, Eq)]
pub struct ClapMidiOutputEvent {
    pub port: usize,
    pub event: MidiEvent,
}

#[derive(Clone, Copy, Debug, Default)]
pub struct ClapTransportInfo {
    pub transport_sample: usize,
    pub playing: bool,
    pub loop_enabled: bool,
    pub loop_range_samples: Option<(usize, usize)>,
    pub bpm: f64,
    pub tsig_num: u16,
    pub tsig_denom: u16,
}

#[derive(Clone, Debug, PartialEq, Eq)]
pub struct ClapGuiInfo {
    pub api: String,
    pub supports_embedded: bool,
}

#[derive(Clone, Copy, Debug)]
struct PendingParamValue {
    param_id: u32,
    value: f64,
}

#[derive(Clone, Copy, Debug)]
pub struct ClapParamUpdate {
    pub param_id: u32,
    pub value: f64,
}

#[derive(Clone, Copy, Debug)]
enum PendingParamEvent {
    Value {
        param_id: u32,
        value: f64,
        frame: u32,
    },
    GestureBegin {
        param_id: u32,
        frame: u32,
    },
    GestureEnd {
        param_id: u32,
        frame: u32,
    },
}

#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
pub struct ClapPluginInfo {
    pub name: String,
    pub path: String,
    pub capabilities: Option<ClapPluginCapabilities>,
}

#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
pub struct ClapPluginCapabilities {
    pub has_gui: bool,
    pub gui_apis: Vec<String>,
    pub supports_embedded: bool,
    pub supports_floating: bool,
    pub has_params: bool,
    pub has_state: bool,
    pub audio_inputs: usize,
    pub audio_outputs: usize,
    pub midi_inputs: usize,
    pub midi_outputs: usize,
}

#[derive(Clone)]
pub struct ClapProcessor {
    path: String,
    name: String,
    sample_rate: f64,
    audio_inputs: Vec<Arc<AudioIO>>,
    audio_outputs: Vec<Arc<AudioIO>>,
    input_port_channels: Vec<usize>,
    output_port_channels: Vec<usize>,
    midi_input_ports: usize,
    midi_output_ports: usize,
    main_audio_inputs: usize,
    main_audio_outputs: usize,
    host_runtime: Arc<HostRuntime>,
    plugin_handle: Arc<PluginHandle>,
    param_infos: Arc<Vec<ClapParameterInfo>>,
    param_values: Arc<UnsafeMutex<HashMap<u32, f64>>>,
    pending_param_events: Arc<UnsafeMutex<Vec<PendingParamEvent>>>,
    pending_param_events_ui: Arc<UnsafeMutex<Vec<PendingParamEvent>>>,
    process_lock: Arc<UnsafeMutex<()>>,
}

impl fmt::Debug for ClapProcessor {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("ClapProcessor")
            .field("path", &self.path)
            .field("name", &self.name)
            .field("audio_inputs", &self.audio_inputs.len())
            .field("audio_outputs", &self.audio_outputs.len())
            .field("input_port_channels", &self.input_port_channels)
            .field("output_port_channels", &self.output_port_channels)
            .field("midi_input_ports", &self.midi_input_ports)
            .field("midi_output_ports", &self.midi_output_ports)
            .field("main_audio_inputs", &self.main_audio_inputs)
            .field("main_audio_outputs", &self.main_audio_outputs)
            .finish()
    }
}

impl ClapProcessor {
    pub fn new(
        sample_rate: f64,
        buffer_size: usize,
        plugin_spec: &str,
        input_count: usize,
        output_count: usize,
    ) -> Result<Self, String> {
        let _thread_scope = HostThreadScope::enter_main();
        let (plugin_path, plugin_id) = split_plugin_spec(plugin_spec);
        let name = Path::new(plugin_path)
            .file_stem()
            .map(|s| s.to_string_lossy().to_string())
            .unwrap_or_else(|| plugin_spec.to_string());
        let host_runtime = Arc::new(HostRuntime::new()?);
        let plugin_handle = Arc::new(PluginHandle::load(
            plugin_path,
            plugin_id,
            host_runtime.clone(),
            sample_rate,
            buffer_size as u32,
        )?);
        let (input_layout_opt, output_layout_opt) = plugin_handle.audio_port_channels();
        let input_port_channels_opt = input_layout_opt.as_ref().map(|(c, _)| c.clone());
        let output_port_channels_opt = output_layout_opt.as_ref().map(|(c, _)| c.clone());
        let discovered_inputs = input_layout_opt.as_ref().map(|(c, _)| c.len());
        let discovered_outputs = output_layout_opt.as_ref().map(|(c, _)| c.len());
        let (discovered_midi_inputs, discovered_midi_outputs) = plugin_handle.note_port_layout();
        let resolved_inputs = discovered_inputs.unwrap_or(input_count);
        let resolved_outputs = discovered_outputs.unwrap_or(output_count);
        let main_audio_inputs = input_layout_opt
            .as_ref()
            .map(|(_, main)| *main)
            .unwrap_or(input_count);
        let main_audio_outputs = output_layout_opt
            .as_ref()
            .map(|(_, main)| *main)
            .unwrap_or(output_count);
        let audio_inputs = (0..resolved_inputs)
            .map(|_| Arc::new(AudioIO::new(buffer_size)))
            .collect();
        let audio_outputs = (0..resolved_outputs)
            .map(|_| Arc::new(AudioIO::new(buffer_size)))
            .collect();
        let param_infos = Arc::new(plugin_handle.parameter_infos());
        let param_values = Arc::new(UnsafeMutex::new(
            plugin_handle.parameter_values(&param_infos),
        ));
        Ok(Self {
            path: plugin_spec.to_string(),
            name,
            sample_rate,
            audio_inputs,
            audio_outputs,
            input_port_channels: input_port_channels_opt
                .unwrap_or_else(|| vec![1; resolved_inputs]),
            output_port_channels: output_port_channels_opt
                .unwrap_or_else(|| vec![1; resolved_outputs]),
            midi_input_ports: discovered_midi_inputs.unwrap_or(0),
            midi_output_ports: discovered_midi_outputs.unwrap_or(0),
            main_audio_inputs,
            main_audio_outputs,
            host_runtime,
            plugin_handle,
            param_infos,
            param_values,
            pending_param_events: Arc::new(UnsafeMutex::new(Vec::new())),
            pending_param_events_ui: Arc::new(UnsafeMutex::new(Vec::new())),
            process_lock: Arc::new(UnsafeMutex::new(())),
        })
    }

    pub fn setup_audio_ports(&self) {
        for port in &self.audio_inputs {
            port.setup();
        }
        for port in &self.audio_outputs {
            port.setup();
        }
    }

    pub fn process_with_audio_io(&self, frames: usize) {
        let _ = self.process_with_midi(frames, &[], ClapTransportInfo::default());
    }

    pub fn process_with_midi(
        &self,
        frames: usize,
        midi_in: &[MidiEvent],
        transport: ClapTransportInfo,
    ) -> Vec<ClapMidiOutputEvent> {
        // CLAP processors are not guaranteed to be re-entrant. Serialize
        // processing per instance to avoid concurrent mutation of plugin state.
        let _process_guard = self.process_lock.lock();
        let started = Instant::now();
        for port in &self.audio_inputs {
            if port.ready() {
                port.process();
            }
        }
        let (processed, processed_midi) = match self.process_native(frames, midi_in, transport) {
            Ok(ok) => ok,
            Err(err) => {
                tracing::warn!(
                    "CLAP process failed for '{}' ({}): {}",
                    self.name,
                    self.path,
                    err
                );
                (false, Vec::new())
            }
        };
        let elapsed = started.elapsed();
        if elapsed > Duration::from_millis(20) {
            tracing::warn!(
                "Slow CLAP process '{}' ({}) took {:.3} ms for {} frames",
                self.name,
                self.path,
                elapsed.as_secs_f64() * 1000.0,
                frames
            );
        }
        if !processed {
            for out in &self.audio_outputs {
                let out_buf = out.buffer.lock();
                out_buf.fill(0.0);
                *out.finished.lock() = true;
            }
        }
        processed_midi
    }

    pub fn parameter_infos(&self) -> Vec<ClapParameterInfo> {
        self.param_infos.as_ref().clone()
    }

    pub fn parameter_values(&self) -> HashMap<u32, f64> {
        self.param_values.lock().clone()
    }

    pub fn set_parameter(&self, param_id: u32, value: f64) -> Result<(), String> {
        self.set_parameter_at(param_id, value, 0)
    }

    pub fn set_parameter_at(&self, param_id: u32, value: f64, frame: u32) -> Result<(), String> {
        let _thread_scope = HostThreadScope::enter_main();
        let Some(info) = self.param_infos.iter().find(|p| p.id == param_id) else {
            return Err(format!("Unknown CLAP parameter id: {param_id}"));
        };
        let clamped = value.clamp(info.min_value, info.max_value);
        self.pending_param_events
            .lock()
            .push(PendingParamEvent::Value {
                param_id,
                value: clamped,
                frame,
            });
        self.pending_param_events_ui
            .lock()
            .push(PendingParamEvent::Value {
                param_id,
                value: clamped,
                frame,
            });
        self.param_values.lock().insert(param_id, clamped);
        Ok(())
    }

    pub fn begin_parameter_edit(&self, param_id: u32) -> Result<(), String> {
        self.begin_parameter_edit_at(param_id, 0)
    }

    pub fn begin_parameter_edit_at(&self, param_id: u32, frame: u32) -> Result<(), String> {
        let _thread_scope = HostThreadScope::enter_main();
        if !self.param_infos.iter().any(|p| p.id == param_id) {
            return Err(format!("Unknown CLAP parameter id: {param_id}"));
        }
        self.pending_param_events
            .lock()
            .push(PendingParamEvent::GestureBegin { param_id, frame });
        self.pending_param_events_ui
            .lock()
            .push(PendingParamEvent::GestureBegin { param_id, frame });
        Ok(())
    }

    pub fn end_parameter_edit(&self, param_id: u32) -> Result<(), String> {
        self.end_parameter_edit_at(param_id, 0)
    }

    pub fn end_parameter_edit_at(&self, param_id: u32, frame: u32) -> Result<(), String> {
        let _thread_scope = HostThreadScope::enter_main();
        if !self.param_infos.iter().any(|p| p.id == param_id) {
            return Err(format!("Unknown CLAP parameter id: {param_id}"));
        }
        self.pending_param_events
            .lock()
            .push(PendingParamEvent::GestureEnd { param_id, frame });
        self.pending_param_events_ui
            .lock()
            .push(PendingParamEvent::GestureEnd { param_id, frame });
        Ok(())
    }

    pub fn snapshot_state(&self) -> Result<ClapPluginState, String> {
        let _thread_scope = HostThreadScope::enter_main();
        self.plugin_handle.snapshot_state()
    }

    pub fn restore_state(&self, state: &ClapPluginState) -> Result<(), String> {
        let _thread_scope = HostThreadScope::enter_main();
        self.plugin_handle.restore_state(state)
    }

    pub fn audio_inputs(&self) -> &[Arc<AudioIO>] {
        &self.audio_inputs
    }

    pub fn audio_outputs(&self) -> &[Arc<AudioIO>] {
        &self.audio_outputs
    }

    pub fn main_audio_input_count(&self) -> usize {
        self.main_audio_inputs
    }

    pub fn main_audio_output_count(&self) -> usize {
        self.main_audio_outputs
    }

    pub fn midi_input_count(&self) -> usize {
        self.midi_input_ports
    }

    pub fn midi_output_count(&self) -> usize {
        self.midi_output_ports
    }

    pub fn path(&self) -> &str {
        &self.path
    }

    pub fn name(&self) -> &str {
        &self.name
    }

    pub fn ui_begin_session(&self) {
        self.host_runtime.begin_ui_session();
    }

    pub fn ui_end_session(&self) {
        self.host_runtime.end_ui_session();
    }

    pub fn ui_should_close(&self) -> bool {
        self.host_runtime.ui_should_close()
    }

    pub fn ui_take_due_timers(&self) -> Vec<u32> {
        self.host_runtime.ui_take_due_timers()
    }

    pub fn ui_take_param_updates(&self) -> Vec<ClapParamUpdate> {
        let pending_ui_events = std::mem::take(self.pending_param_events_ui.lock());
        if pending_ui_events.is_empty() && !self.host_runtime.ui_take_param_flush_requested() {
            return Vec::new();
        }
        let _thread_scope = HostThreadScope::enter_main();
        let updates = self.plugin_handle.flush_params(&pending_ui_events);
        if updates.is_empty() {
            return Vec::new();
        }
        let values = &mut *self.param_values.lock();
        let mut out = Vec::with_capacity(updates.len());
        for update in updates {
            values.insert(update.param_id, update.value);
            out.push(ClapParamUpdate {
                param_id: update.param_id,
                value: update.value,
            });
        }
        out
    }

    pub fn ui_take_state_update(&self) -> Option<ClapPluginState> {
        if !self.host_runtime.ui_take_state_dirty_requested() {
            return None;
        }
        let _thread_scope = HostThreadScope::enter_main();
        self.plugin_handle.snapshot_state().ok()
    }

    pub fn gui_info(&self) -> Result<ClapGuiInfo, String> {
        let _thread_scope = HostThreadScope::enter_main();
        self.plugin_handle.gui_info()
    }

    pub fn gui_create(&self, api: &str, is_floating: bool) -> Result<(), String> {
        let _thread_scope = HostThreadScope::enter_main();
        self.plugin_handle.gui_create(api, is_floating)
    }

    pub fn gui_get_size(&self) -> Result<(u32, u32), String> {
        let _thread_scope = HostThreadScope::enter_main();
        self.plugin_handle.gui_get_size()
    }

    pub fn gui_set_parent_x11(&self, window: usize) -> Result<(), String> {
        let _thread_scope = HostThreadScope::enter_main();
        self.plugin_handle.gui_set_parent_x11(window)
    }

    pub fn gui_show(&self) -> Result<(), String> {
        let _thread_scope = HostThreadScope::enter_main();
        self.plugin_handle.gui_show()
    }

    pub fn gui_hide(&self) {
        let _thread_scope = HostThreadScope::enter_main();
        self.plugin_handle.gui_hide();
    }

    pub fn gui_destroy(&self) {
        let _thread_scope = HostThreadScope::enter_main();
        self.plugin_handle.gui_destroy();
    }

    pub fn gui_on_main_thread(&self) {
        let _thread_scope = HostThreadScope::enter_main();
        self.plugin_handle.on_main_thread();
    }

    pub fn gui_on_timer(&self, timer_id: u32) {
        let _thread_scope = HostThreadScope::enter_main();
        self.plugin_handle.gui_on_timer(timer_id);
    }

    pub fn note_names(&self) -> std::collections::HashMap<u8, String> {
        self.plugin_handle.get_note_names()
    }

    pub fn run_host_callbacks_main_thread(&self) {
        let host_flags = self.host_runtime.take_callback_flags();
        if host_flags.restart {
            let _thread_scope = HostThreadScope::enter_main();
            self.plugin_handle.reset();
        }
        if host_flags.callback {
            let _thread_scope = HostThreadScope::enter_main();
            self.plugin_handle.on_main_thread();
        }
        if host_flags.process {
            // Host already continuously schedules process blocks.
        }
    }

    fn process_native(
        &self,
        frames: usize,
        midi_in: &[MidiEvent],
        transport: ClapTransportInfo,
    ) -> Result<(bool, Vec<ClapMidiOutputEvent>), String> {
        if frames == 0 {
            return Ok((true, Vec::new()));
        }

        let mut in_channel_ptrs: Vec<Vec<*mut f32>> = Vec::with_capacity(self.audio_inputs.len());
        let mut out_channel_ptrs: Vec<Vec<*mut f32>> = Vec::with_capacity(self.audio_outputs.len());
        let mut in_channel_scratch: Vec<Vec<f32>> = Vec::new();
        let mut out_channel_scratch: Vec<Vec<f32>> = Vec::new();
        let mut out_channel_scratch_ranges: Vec<(usize, usize)> =
            Vec::with_capacity(self.audio_outputs.len());
        let mut in_buffers = Vec::with_capacity(self.audio_inputs.len());
        let mut out_buffers = Vec::with_capacity(self.audio_outputs.len());

        for (port_idx, input) in self.audio_inputs.iter().enumerate() {
            let buf = input.buffer.lock();
            let channel_count = self
                .input_port_channels
                .get(port_idx)
                .copied()
                .unwrap_or(1)
                .max(1);
            let mut ptrs = Vec::with_capacity(channel_count);
            ptrs.push(buf.as_ptr() as *mut f32);
            for _ in 1..channel_count {
                in_channel_scratch.push(buf.to_vec());
                let idx = in_channel_scratch.len().saturating_sub(1);
                ptrs.push(in_channel_scratch[idx].as_mut_ptr());
            }
            in_channel_ptrs.push(ptrs);
            in_buffers.push(buf);
        }
        for (port_idx, output) in self.audio_outputs.iter().enumerate() {
            let buf = output.buffer.lock();
            let channel_count = self
                .output_port_channels
                .get(port_idx)
                .copied()
                .unwrap_or(1)
                .max(1);
            let mut ptrs = Vec::with_capacity(channel_count);
            ptrs.push(buf.as_mut_ptr());
            let scratch_start = out_channel_scratch.len();
            for _ in 1..channel_count {
                out_channel_scratch.push(vec![0.0; frames]);
                let idx = out_channel_scratch.len().saturating_sub(1);
                ptrs.push(out_channel_scratch[idx].as_mut_ptr());
            }
            let scratch_end = out_channel_scratch.len();
            out_channel_scratch_ranges.push((scratch_start, scratch_end));
            out_channel_ptrs.push(ptrs);
            out_buffers.push(buf);
        }

        let mut in_audio = Vec::with_capacity(self.audio_inputs.len());
        let mut out_audio = Vec::with_capacity(self.audio_outputs.len());

        for ptrs in &mut in_channel_ptrs {
            in_audio.push(ClapAudioBuffer {
                data32: ptrs.as_mut_ptr(),
                data64: std::ptr::null_mut(),
                channel_count: ptrs.len() as u32,
                latency: 0,
                constant_mask: 0,
            });
        }
        for ptrs in &mut out_channel_ptrs {
            out_audio.push(ClapAudioBuffer {
                data32: ptrs.as_mut_ptr(),
                data64: std::ptr::null_mut(),
                channel_count: ptrs.len() as u32,
                latency: 0,
                constant_mask: 0,
            });
        }

        let pending_params = std::mem::take(self.pending_param_events.lock());
        let (in_events, in_ctx) = input_events_from(
            midi_in,
            &pending_params,
            self.sample_rate,
            transport,
            self.midi_input_ports > 0,
        );
        let out_cap = midi_in
            .len()
            .saturating_add(self.midi_output_ports.saturating_mul(64));
        let (mut out_events, mut out_ctx) = output_events_ctx(out_cap);

        let mut process = ClapProcess {
            steady_time: -1,
            frames_count: frames as u32,
            transport: std::ptr::null(),
            audio_inputs: in_audio.as_mut_ptr(),
            audio_outputs: out_audio.as_mut_ptr(),
            audio_inputs_count: in_audio.len() as u32,
            audio_outputs_count: out_audio.len() as u32,
            in_events: &in_events,
            out_events: &mut out_events,
        };

        let _thread_scope = HostThreadScope::enter_audio();
        let result = self.plugin_handle.process(&mut process);
        drop(in_ctx);
        for output in &self.audio_outputs {
            *output.finished.lock() = true;
        }
        let processed = result?;
        if processed {
            // Downmix multi-channel CLAP output ports into track output buffers.
            for (port_idx, out_buf) in out_buffers.iter_mut().enumerate() {
                let Some((scratch_start, scratch_end)) = out_channel_scratch_ranges.get(port_idx)
                else {
                    continue;
                };
                let scratch_count = scratch_end.saturating_sub(*scratch_start);
                if scratch_count == 0 {
                    continue;
                }
                let ch_count = scratch_count + 1;
                for scratch in &out_channel_scratch[*scratch_start..*scratch_end] {
                    for (dst, src) in out_buf.iter_mut().zip(scratch.iter().take(frames)) {
                        *dst += *src;
                    }
                }
                let inv = 1.0_f32 / ch_count as f32;
                for sample in out_buf.iter_mut().take(frames) {
                    *sample *= inv;
                }
            }
            for update in &out_ctx.param_values {
                self.param_values
                    .lock()
                    .insert(update.param_id, update.value);
            }
            Ok((true, std::mem::take(&mut out_ctx.midi_events)))
        } else {
            Ok((false, Vec::new()))
        }
    }
}

#[repr(C)]
#[derive(Clone, Copy)]
struct ClapVersion {
    major: u32,
    minor: u32,
    revision: u32,
}

const CLAP_VERSION: ClapVersion = ClapVersion {
    major: 1,
    minor: 2,
    revision: 0,
};

#[repr(C)]
struct ClapHost {
    clap_version: ClapVersion,
    host_data: *mut c_void,
    name: *const c_char,
    vendor: *const c_char,
    url: *const c_char,
    version: *const c_char,
    get_extension: Option<unsafe extern "C" fn(*const ClapHost, *const c_char) -> *const c_void>,
    request_restart: Option<unsafe extern "C" fn(*const ClapHost)>,
    request_process: Option<unsafe extern "C" fn(*const ClapHost)>,
    request_callback: Option<unsafe extern "C" fn(*const ClapHost)>,
}

#[repr(C)]
struct ClapPluginEntry {
    clap_version: ClapVersion,
    init: Option<unsafe extern "C" fn(*const ClapHost) -> bool>,
    deinit: Option<unsafe extern "C" fn()>,
    get_factory: Option<unsafe extern "C" fn(*const c_char) -> *const c_void>,
}

#[repr(C)]
struct ClapPluginFactory {
    get_plugin_count: Option<unsafe extern "C" fn(*const ClapPluginFactory) -> u32>,
    get_plugin_descriptor:
        Option<unsafe extern "C" fn(*const ClapPluginFactory, u32) -> *const ClapPluginDescriptor>,
    create_plugin: Option<
        unsafe extern "C" fn(
            *const ClapPluginFactory,
            *const ClapHost,
            *const c_char,
        ) -> *const ClapPlugin,
    >,
}

#[repr(C)]
struct ClapPluginDescriptor {
    clap_version: ClapVersion,
    id: *const c_char,
    name: *const c_char,
    vendor: *const c_char,
    url: *const c_char,
    manual_url: *const c_char,
    support_url: *const c_char,
    version: *const c_char,
    description: *const c_char,
    features: *const *const c_char,
}

#[repr(C)]
struct ClapPlugin {
    desc: *const ClapPluginDescriptor,
    plugin_data: *mut c_void,
    init: Option<unsafe extern "C" fn(*const ClapPlugin) -> bool>,
    destroy: Option<unsafe extern "C" fn(*const ClapPlugin)>,
    activate: Option<unsafe extern "C" fn(*const ClapPlugin, f64, u32, u32) -> bool>,
    deactivate: Option<unsafe extern "C" fn(*const ClapPlugin)>,
    start_processing: Option<unsafe extern "C" fn(*const ClapPlugin) -> bool>,
    stop_processing: Option<unsafe extern "C" fn(*const ClapPlugin)>,
    reset: Option<unsafe extern "C" fn(*const ClapPlugin)>,
    process: Option<unsafe extern "C" fn(*const ClapPlugin, *const ClapProcess) -> i32>,
    get_extension: Option<unsafe extern "C" fn(*const ClapPlugin, *const c_char) -> *const c_void>,
    on_main_thread: Option<unsafe extern "C" fn(*const ClapPlugin)>,
}

#[repr(C)]
struct ClapInputEvents {
    ctx: *const c_void,
    size: Option<unsafe extern "C" fn(*const ClapInputEvents) -> u32>,
    get: Option<unsafe extern "C" fn(*const ClapInputEvents, u32) -> *const ClapEventHeader>,
}

#[repr(C)]
struct ClapOutputEvents {
    ctx: *mut c_void,
    try_push: Option<unsafe extern "C" fn(*const ClapOutputEvents, *const ClapEventHeader) -> bool>,
}

#[repr(C)]
struct ClapEventHeader {
    size: u32,
    time: u32,
    space_id: u16,
    type_: u16,
    flags: u32,
}

const CLAP_CORE_EVENT_SPACE_ID: u16 = 0;
const CLAP_EVENT_NOTE_ON: u16 = 0;
const CLAP_EVENT_NOTE_OFF: u16 = 1;
const CLAP_EVENT_MIDI: u16 = 10;
const CLAP_EVENT_PARAM_VALUE: u16 = 5;
const CLAP_EVENT_PARAM_GESTURE_BEGIN: u16 = 6;
const CLAP_EVENT_PARAM_GESTURE_END: u16 = 7;
const CLAP_EVENT_TRANSPORT: u16 = 9;
const CLAP_TRANSPORT_HAS_TEMPO: u32 = 1 << 0;
const CLAP_TRANSPORT_HAS_BEATS_TIMELINE: u32 = 1 << 1;
const CLAP_TRANSPORT_HAS_SECONDS_TIMELINE: u32 = 1 << 2;
const CLAP_TRANSPORT_HAS_TIME_SIGNATURE: u32 = 1 << 3;
const CLAP_TRANSPORT_IS_PLAYING: u32 = 1 << 4;
const CLAP_TRANSPORT_IS_LOOP_ACTIVE: u32 = 1 << 6;
const CLAP_BEATTIME_FACTOR: i64 = 1_i64 << 31;
const CLAP_SECTIME_FACTOR: i64 = 1_i64 << 31;

#[repr(C)]
struct ClapEventMidi {
    header: ClapEventHeader,
    port_index: u16,
    data: [u8; 3],
}

#[repr(C)]
struct ClapEventNote {
    header: ClapEventHeader,
    note_id: i32,
    port_index: i16,
    channel: i16,
    key: i16,
    velocity: f64,
}

#[repr(C)]
struct ClapEventParamValue {
    header: ClapEventHeader,
    param_id: u32,
    cookie: *mut c_void,
    note_id: i32,
    port_index: i16,
    channel: i16,
    key: i16,
    value: f64,
}

#[repr(C)]
struct ClapEventParamGesture {
    header: ClapEventHeader,
    param_id: u32,
}

#[repr(C)]
struct ClapEventTransport {
    header: ClapEventHeader,
    flags: u32,
    song_pos_beats: i64,
    song_pos_seconds: i64,
    tempo: f64,
    tempo_inc: f64,
    loop_start_beats: i64,
    loop_end_beats: i64,
    loop_start_seconds: i64,
    loop_end_seconds: i64,
    bar_start: i64,
    bar_number: i32,
    tsig_num: u16,
    tsig_denom: u16,
}

#[repr(C)]
struct ClapParamInfoRaw {
    id: u32,
    flags: u32,
    cookie: *mut c_void,
    name: [c_char; 256],
    module: [c_char; 1024],
    min_value: f64,
    max_value: f64,
    default_value: f64,
}

#[repr(C)]
struct ClapPluginParams {
    count: Option<unsafe extern "C" fn(*const ClapPlugin) -> u32>,
    get_info: Option<unsafe extern "C" fn(*const ClapPlugin, u32, *mut ClapParamInfoRaw) -> bool>,
    get_value: Option<unsafe extern "C" fn(*const ClapPlugin, u32, *mut f64) -> bool>,
    value_to_text:
        Option<unsafe extern "C" fn(*const ClapPlugin, u32, f64, *mut c_char, u32) -> bool>,
    text_to_value:
        Option<unsafe extern "C" fn(*const ClapPlugin, u32, *const c_char, *mut f64) -> bool>,
    flush: Option<
        unsafe extern "C" fn(*const ClapPlugin, *const ClapInputEvents, *const ClapOutputEvents),
    >,
}

#[repr(C)]
struct ClapPluginStateExt {
    save: Option<unsafe extern "C" fn(*const ClapPlugin, *const ClapOStream) -> bool>,
    load: Option<unsafe extern "C" fn(*const ClapPlugin, *const ClapIStream) -> bool>,
}

#[repr(C)]
struct ClapAudioPortInfoRaw {
    id: u32,
    name: [c_char; 256],
    flags: u32,
    channel_count: u32,
    port_type: *const c_char,
    in_place_pair: u32,
}

#[repr(C)]
struct ClapPluginAudioPorts {
    count: Option<unsafe extern "C" fn(*const ClapPlugin, bool) -> u32>,
    get: Option<
        unsafe extern "C" fn(*const ClapPlugin, u32, bool, *mut ClapAudioPortInfoRaw) -> bool,
    >,
}

#[repr(C)]
struct ClapNotePortInfoRaw {
    id: u16,
    supported_dialects: u32,
    preferred_dialect: u32,
    name: [c_char; 256],
}

#[repr(C)]
struct ClapPluginNotePorts {
    count: Option<unsafe extern "C" fn(*const ClapPlugin, bool) -> u32>,
    get: Option<
        unsafe extern "C" fn(*const ClapPlugin, u32, bool, *mut ClapNotePortInfoRaw) -> bool,
    >,
}

#[repr(C)]
struct ClapPluginGui {
    is_api_supported: Option<unsafe extern "C" fn(*const ClapPlugin, *const c_char, bool) -> bool>,
    get_preferred_api:
        Option<unsafe extern "C" fn(*const ClapPlugin, *mut *const c_char, *mut bool) -> bool>,
    create: Option<unsafe extern "C" fn(*const ClapPlugin, *const c_char, bool) -> bool>,
    destroy: Option<unsafe extern "C" fn(*const ClapPlugin)>,
    set_scale: Option<unsafe extern "C" fn(*const ClapPlugin, f64) -> bool>,
    get_size: Option<unsafe extern "C" fn(*const ClapPlugin, *mut u32, *mut u32) -> bool>,
    can_resize: Option<unsafe extern "C" fn(*const ClapPlugin) -> bool>,
    get_resize_hints: Option<unsafe extern "C" fn(*const ClapPlugin, *mut c_void) -> bool>,
    adjust_size: Option<unsafe extern "C" fn(*const ClapPlugin, *mut u32, *mut u32) -> bool>,
    set_size: Option<unsafe extern "C" fn(*const ClapPlugin, u32, u32) -> bool>,
    set_parent: Option<unsafe extern "C" fn(*const ClapPlugin, *const ClapWindow) -> bool>,
    set_transient: Option<unsafe extern "C" fn(*const ClapPlugin, *const ClapWindow) -> bool>,
    suggest_title: Option<unsafe extern "C" fn(*const ClapPlugin, *const c_char)>,
    show: Option<unsafe extern "C" fn(*const ClapPlugin) -> bool>,
    hide: Option<unsafe extern "C" fn(*const ClapPlugin) -> bool>,
}

#[repr(C)]
union ClapWindowHandle {
    x11: usize,
    native: *mut c_void,
    cocoa: *mut c_void,
}

#[repr(C)]
struct ClapWindow {
    api: *const c_char,
    handle: ClapWindowHandle,
}

#[repr(C)]
struct ClapPluginTimerSupport {
    on_timer: Option<unsafe extern "C" fn(*const ClapPlugin, u32)>,
}

#[repr(C)]
struct ClapHostThreadCheck {
    is_main_thread: Option<unsafe extern "C" fn(*const ClapHost) -> bool>,
    is_audio_thread: Option<unsafe extern "C" fn(*const ClapHost) -> bool>,
}

#[repr(C)]
struct ClapHostLatency {
    changed: Option<unsafe extern "C" fn(*const ClapHost)>,
}

#[repr(C)]
struct ClapHostTail {
    changed: Option<unsafe extern "C" fn(*const ClapHost)>,
}

#[repr(C)]
struct ClapHostTimerSupport {
    register_timer: Option<unsafe extern "C" fn(*const ClapHost, u32, *mut u32) -> bool>,
    unregister_timer: Option<unsafe extern "C" fn(*const ClapHost, u32) -> bool>,
}

#[repr(C)]
struct ClapHostGui {
    resize_hints_changed: Option<unsafe extern "C" fn(*const ClapHost)>,
    request_resize: Option<unsafe extern "C" fn(*const ClapHost, u32, u32) -> bool>,
    request_show: Option<unsafe extern "C" fn(*const ClapHost) -> bool>,
    request_hide: Option<unsafe extern "C" fn(*const ClapHost) -> bool>,
    closed: Option<unsafe extern "C" fn(*const ClapHost, bool)>,
}

#[repr(C)]
struct ClapHostParams {
    rescan: Option<unsafe extern "C" fn(*const ClapHost, u32)>,
    clear: Option<unsafe extern "C" fn(*const ClapHost, u32, u32)>,
    request_flush: Option<unsafe extern "C" fn(*const ClapHost)>,
}

#[repr(C)]
struct ClapHostState {
    mark_dirty: Option<unsafe extern "C" fn(*const ClapHost)>,
}

#[repr(C)]
struct ClapNoteName {
    name: [c_char; 256],
    port: i16,
    key: i16,
    channel: i16,
}

#[repr(C)]
struct ClapPluginNoteName {
    count: Option<unsafe extern "C" fn(*const ClapPlugin) -> u32>,
    get: Option<unsafe extern "C" fn(*const ClapPlugin, u32, *mut ClapNoteName) -> bool>,
}

#[repr(C)]
struct ClapHostNoteName {
    changed: Option<unsafe extern "C" fn(*const ClapHost)>,
}

#[repr(C)]
struct ClapOStream {
    ctx: *mut c_void,
    write: Option<unsafe extern "C" fn(*const ClapOStream, *const c_void, u64) -> i64>,
}

#[repr(C)]
struct ClapIStream {
    ctx: *mut c_void,
    read: Option<unsafe extern "C" fn(*const ClapIStream, *mut c_void, u64) -> i64>,
}

#[repr(C)]
struct ClapAudioBuffer {
    data32: *mut *mut f32,
    data64: *mut *mut f64,
    channel_count: u32,
    latency: u32,
    constant_mask: u64,
}

#[repr(C)]
struct ClapProcess {
    steady_time: i64,
    frames_count: u32,
    transport: *const c_void,
    audio_inputs: *mut ClapAudioBuffer,
    audio_outputs: *mut ClapAudioBuffer,
    audio_inputs_count: u32,
    audio_outputs_count: u32,
    in_events: *const ClapInputEvents,
    out_events: *mut ClapOutputEvents,
}

enum ClapInputEvent {
    Note(ClapEventNote),
    Midi(ClapEventMidi),
    ParamValue(ClapEventParamValue),
    ParamGesture(ClapEventParamGesture),
    Transport(ClapEventTransport),
}

impl ClapInputEvent {
    fn header_ptr(&self) -> *const ClapEventHeader {
        match self {
            Self::Note(e) => &e.header as *const ClapEventHeader,
            Self::Midi(e) => &e.header as *const ClapEventHeader,
            Self::ParamValue(e) => &e.header as *const ClapEventHeader,
            Self::ParamGesture(e) => &e.header as *const ClapEventHeader,
            Self::Transport(e) => &e.header as *const ClapEventHeader,
        }
    }
}

struct ClapInputEventsCtx {
    events: Vec<ClapInputEvent>,
}

struct ClapOutputEventsCtx {
    midi_events: Vec<ClapMidiOutputEvent>,
    param_values: Vec<PendingParamValue>,
}

struct ClapIStreamCtx<'a> {
    bytes: &'a [u8],
    offset: usize,
}

#[derive(Default, Clone, Copy)]
struct HostCallbackFlags {
    restart: bool,
    process: bool,
    callback: bool,
}

#[derive(Clone, Copy)]
struct HostTimer {
    id: u32,
    period: Duration,
    next_tick: Instant,
}

struct HostRuntimeState {
    callback_flags: UnsafeMutex<HostCallbackFlags>,
    timers: UnsafeMutex<Vec<HostTimer>>,
    ui_should_close: AtomicU32,
    ui_active: AtomicU32,
    param_flush_requested: AtomicU32,
    state_dirty_requested: AtomicU32,
    note_names_dirty: AtomicU32,
}

thread_local! {
    static CLAP_HOST_MAIN_THREAD: Cell<bool> = const { Cell::new(true) };
    static CLAP_HOST_AUDIO_THREAD: Cell<bool> = const { Cell::new(false) };
}

struct HostThreadScope {
    main: bool,
    prev: bool,
}

impl HostThreadScope {
    fn enter_main() -> Self {
        let prev = CLAP_HOST_MAIN_THREAD.with(|flag| {
            let prev = flag.get();
            flag.set(true);
            prev
        });
        Self { main: true, prev }
    }

    fn enter_audio() -> Self {
        let prev = CLAP_HOST_AUDIO_THREAD.with(|flag| {
            let prev = flag.get();
            flag.set(true);
            prev
        });
        Self { main: false, prev }
    }
}

impl Drop for HostThreadScope {
    fn drop(&mut self) {
        if self.main {
            CLAP_HOST_MAIN_THREAD.with(|flag| flag.set(self.prev));
        } else {
            CLAP_HOST_AUDIO_THREAD.with(|flag| flag.set(self.prev));
        }
    }
}

struct HostRuntime {
    state: Box<HostRuntimeState>,
    host: ClapHost,
}

impl HostRuntime {
    fn new() -> Result<Self, String> {
        let mut state = Box::new(HostRuntimeState {
            callback_flags: UnsafeMutex::new(HostCallbackFlags::default()),
            timers: UnsafeMutex::new(Vec::new()),
            ui_should_close: AtomicU32::new(0),
            ui_active: AtomicU32::new(0),
            param_flush_requested: AtomicU32::new(0),
            state_dirty_requested: AtomicU32::new(0),
            note_names_dirty: AtomicU32::new(0),
        });
        let host = ClapHost {
            clap_version: CLAP_VERSION,
            host_data: (&mut *state as *mut HostRuntimeState).cast::<c_void>(),
            name: c"Maolan".as_ptr(),
            vendor: c"Maolan".as_ptr(),
            url: c"https://example.invalid".as_ptr(),
            version: c"0.0.1".as_ptr(),
            get_extension: Some(host_get_extension),
            request_restart: Some(host_request_restart),
            request_process: Some(host_request_process),
            request_callback: Some(host_request_callback),
        };
        Ok(Self { state, host })
    }

    fn take_callback_flags(&self) -> HostCallbackFlags {
        let flags = self.state.callback_flags.lock();
        let out = *flags;
        *flags = HostCallbackFlags::default();
        out
    }

    fn begin_ui_session(&self) {
        self.state.ui_should_close.store(0, Ordering::Release);
        self.state.ui_active.store(1, Ordering::Release);
        self.state.param_flush_requested.store(0, Ordering::Release);
        self.state.state_dirty_requested.store(0, Ordering::Release);
        self.state.timers.lock().clear();
    }

    fn end_ui_session(&self) {
        self.state.ui_active.store(0, Ordering::Release);
        self.state.ui_should_close.store(0, Ordering::Release);
        self.state.param_flush_requested.store(0, Ordering::Release);
        self.state.state_dirty_requested.store(0, Ordering::Release);
        self.state.timers.lock().clear();
    }

    fn ui_should_close(&self) -> bool {
        self.state.ui_should_close.load(Ordering::Acquire) != 0
    }

    fn ui_take_due_timers(&self) -> Vec<u32> {
        let now = Instant::now();
        let timers = &mut *self.state.timers.lock();
        let mut due = Vec::new();
        for timer in timers.iter_mut() {
            if now >= timer.next_tick {
                due.push(timer.id);
                timer.next_tick = now + timer.period;
            }
        }
        due
    }

    fn ui_take_param_flush_requested(&self) -> bool {
        self.state.param_flush_requested.swap(0, Ordering::AcqRel) != 0
    }

    fn ui_take_state_dirty_requested(&self) -> bool {
        self.state.state_dirty_requested.swap(0, Ordering::AcqRel) != 0
    }
}

// SAFETY: HostRuntime owns stable CString storage and a CLAP host struct that
// contains raw pointers into that owned storage. The data is immutable after
// construction and safe to share/move across threads.
unsafe impl Send for HostRuntime {}
// SAFETY: See Send rationale above; HostRuntime has no interior mutation.
unsafe impl Sync for HostRuntime {}

struct PluginHandle {
    _library: Library,
    entry: *const ClapPluginEntry,
    plugin: *const ClapPlugin,
}

// SAFETY: PluginHandle only stores pointers/libraries managed by the CLAP ABI.
// Access to plugin processing is synchronized by the engine track scheduling.
unsafe impl Send for PluginHandle {}
// SAFETY: Shared references do not mutate PluginHandle fields directly.
unsafe impl Sync for PluginHandle {}

impl PluginHandle {
    fn load(
        plugin_path: &str,
        plugin_id: Option<&str>,
        host_runtime: Arc<HostRuntime>,
        sample_rate: f64,
        frames: u32,
    ) -> Result<Self, String> {
        let factory_id = c"clap.plugin-factory";

        // SAFETY: We keep `library` alive for at least as long as plugin and entry pointers.
        let library = unsafe { Library::new(plugin_path) }.map_err(|e| e.to_string())?;
        // SAFETY: Symbol name and type follow CLAP ABI (`clap_entry` global variable).
        let entry_ptr = unsafe {
            let sym = library
                .get::<*const ClapPluginEntry>(b"clap_entry\0")
                .map_err(|e| e.to_string())?;
            *sym
        };
        if entry_ptr.is_null() {
            return Err("CLAP entry symbol is null".to_string());
        }
        // SAFETY: entry pointer comes from validated CLAP symbol.
        let entry = unsafe { &*entry_ptr };
        let init = entry
            .init
            .ok_or_else(|| "CLAP entry missing init()".to_string())?;
        let host_ptr = &host_runtime.host as *const ClapHost;
        // SAFETY: Valid host pointer for plugin bundle.
        if unsafe { !init(host_ptr) } {
            return Err(format!("CLAP entry init failed for {plugin_path}"));
        }
        let get_factory = entry
            .get_factory
            .ok_or_else(|| "CLAP entry missing get_factory()".to_string())?;
        // SAFETY: Factory id is a static NUL-terminated C string.
        let factory = unsafe { get_factory(factory_id.as_ptr()) } as *const ClapPluginFactory;
        if factory.is_null() {
            return Err("CLAP plugin factory not found".to_string());
        }
        // SAFETY: factory pointer was validated above.
        let factory_ref = unsafe { &*factory };
        let get_count = factory_ref
            .get_plugin_count
            .ok_or_else(|| "CLAP factory missing get_plugin_count()".to_string())?;
        let get_desc = factory_ref
            .get_plugin_descriptor
            .ok_or_else(|| "CLAP factory missing get_plugin_descriptor()".to_string())?;
        let create = factory_ref
            .create_plugin
            .ok_or_else(|| "CLAP factory missing create_plugin()".to_string())?;

        // SAFETY: factory function pointers are valid CLAP ABI function pointers.
        let count = unsafe { get_count(factory) };
        if count == 0 {
            return Err("CLAP factory returned zero plugins".to_string());
        }
        let mut selected_id = None::<CString>;
        for i in 0..count {
            // SAFETY: i < count.
            let desc = unsafe { get_desc(factory, i) };
            if desc.is_null() {
                continue;
            }
            // SAFETY: descriptor pointer comes from factory.
            let desc = unsafe { &*desc };
            if desc.id.is_null() {
                continue;
            }
            // SAFETY: descriptor id is NUL-terminated per CLAP ABI.
            let id = unsafe { CStr::from_ptr(desc.id) };
            let id_str = id.to_string_lossy();
            if plugin_id.is_none() || plugin_id == Some(id_str.as_ref()) {
                selected_id = Some(
                    CString::new(id_str.as_ref()).map_err(|e| format!("Invalid plugin id: {e}"))?,
                );
                break;
            }
        }
        let selected_id = selected_id.ok_or_else(|| {
            if let Some(id) = plugin_id {
                format!("CLAP descriptor id not found in bundle: {id}")
            } else {
                "CLAP descriptor not found".to_string()
            }
        })?;
        // SAFETY: valid host pointer and plugin id.
        let plugin = unsafe { create(factory, &host_runtime.host, selected_id.as_ptr()) };
        if plugin.is_null() {
            return Err("CLAP factory create_plugin failed".to_string());
        }
        // SAFETY: plugin pointer validated above.
        let plugin_ref = unsafe { &*plugin };
        let plugin_init = plugin_ref
            .init
            .ok_or_else(|| "CLAP plugin missing init()".to_string())?;
        // SAFETY: plugin pointer and function pointer follow CLAP ABI.
        if unsafe { !plugin_init(plugin) } {
            return Err("CLAP plugin init() failed".to_string());
        }
        if let Some(activate) = plugin_ref.activate {
            // SAFETY: plugin pointer and arguments are valid for current engine buffer config.
            if unsafe { !activate(plugin, sample_rate, frames.max(1), frames.max(1)) } {
                return Err("CLAP plugin activate() failed".to_string());
            }
        }
        if let Some(start_processing) = plugin_ref.start_processing {
            // SAFETY: plugin activated above.
            if unsafe { !start_processing(plugin) } {
                return Err("CLAP plugin start_processing() failed".to_string());
            }
        }
        Ok(Self {
            _library: library,
            entry: entry_ptr,
            plugin,
        })
    }

    fn process(&self, process: &mut ClapProcess) -> Result<bool, String> {
        // SAFETY: plugin pointer is valid for lifetime of self.
        let plugin = unsafe { &*self.plugin };
        let Some(process_fn) = plugin.process else {
            return Ok(false);
        };
        // SAFETY: process struct references live buffers for the duration of call.
        let _status = unsafe { process_fn(self.plugin, process as *const _) };
        Ok(true)
    }

    fn reset(&self) {
        // SAFETY: plugin pointer valid during self lifetime.
        let plugin = unsafe { &*self.plugin };
        if let Some(reset) = plugin.reset {
            // SAFETY: function pointer follows CLAP ABI.
            unsafe { reset(self.plugin) };
        }
    }

    fn on_main_thread(&self) {
        // SAFETY: plugin pointer valid during self lifetime.
        let plugin = unsafe { &*self.plugin };
        if let Some(on_main_thread) = plugin.on_main_thread {
            // SAFETY: function pointer follows CLAP ABI.
            unsafe { on_main_thread(self.plugin) };
        }
    }

    fn params_ext(&self) -> Option<&ClapPluginParams> {
        let ext_id = c"clap.params";
        // SAFETY: plugin pointer is valid while self is alive.
        let plugin = unsafe { &*self.plugin };
        let get_extension = plugin.get_extension?;
        // SAFETY: extension id is a valid static C string.
        let ext_ptr = unsafe { get_extension(self.plugin, ext_id.as_ptr()) };
        if ext_ptr.is_null() {
            return None;
        }
        // SAFETY: CLAP guarantees extension pointer layout for requested extension id.
        Some(unsafe { &*(ext_ptr as *const ClapPluginParams) })
    }

    fn state_ext(&self) -> Option<&ClapPluginStateExt> {
        let ext_id = c"clap.state";
        // SAFETY: plugin pointer is valid while self is alive.
        let plugin = unsafe { &*self.plugin };
        let get_extension = plugin.get_extension?;
        // SAFETY: extension id is valid static C string.
        let ext_ptr = unsafe { get_extension(self.plugin, ext_id.as_ptr()) };
        if ext_ptr.is_null() {
            return None;
        }
        // SAFETY: extension pointer layout follows clap.state ABI.
        Some(unsafe { &*(ext_ptr as *const ClapPluginStateExt) })
    }

    fn audio_ports_ext(&self) -> Option<&ClapPluginAudioPorts> {
        let ext_id = c"clap.audio-ports";
        // SAFETY: plugin pointer is valid while self is alive.
        let plugin = unsafe { &*self.plugin };
        let get_extension = plugin.get_extension?;
        // SAFETY: extension id is valid static C string.
        let ext_ptr = unsafe { get_extension(self.plugin, ext_id.as_ptr()) };
        if ext_ptr.is_null() {
            return None;
        }
        // SAFETY: extension pointer layout follows clap.audio-ports ABI.
        Some(unsafe { &*(ext_ptr as *const ClapPluginAudioPorts) })
    }

    fn note_ports_ext(&self) -> Option<&ClapPluginNotePorts> {
        let ext_id = c"clap.note-ports";
        // SAFETY: plugin pointer is valid while self is alive.
        let plugin = unsafe { &*self.plugin };
        let get_extension = plugin.get_extension?;
        // SAFETY: extension id is valid static C string.
        let ext_ptr = unsafe { get_extension(self.plugin, ext_id.as_ptr()) };
        if ext_ptr.is_null() {
            return None;
        }
        // SAFETY: extension pointer layout follows clap.note-ports ABI.
        Some(unsafe { &*(ext_ptr as *const ClapPluginNotePorts) })
    }

    fn note_name_ext(&self) -> Option<&ClapPluginNoteName> {
        let ext_id = c"clap.note-name";
        let plugin = unsafe { &*self.plugin };
        let get_extension = plugin.get_extension?;
        let ext_ptr = unsafe { get_extension(self.plugin, ext_id.as_ptr()) };
        if ext_ptr.is_null() {
            return None;
        }
        Some(unsafe { &*(ext_ptr as *const ClapPluginNoteName) })
    }

    fn get_note_names(&self) -> std::collections::HashMap<u8, String> {
        let mut result = std::collections::HashMap::new();
        let Some(ext) = self.note_name_ext() else {
            eprintln!("[engine] note_name_ext null");
            return result;
        };
        let Some(count_fn) = ext.count else {
            eprintln!("[engine] note_name_ext.count null");
            return result;
        };
        let Some(get_fn) = ext.get else {
            eprintln!("[engine] note_name_ext.get null");
            return result;
        };
        let count = unsafe { count_fn(self.plugin) };
        eprintln!("[engine] note_name_count={count}");
        for i in 0..count {
            let mut nn = ClapNoteName {
                name: [0; 256],
                port: -1,
                key: -1,
                channel: -1,
            };
            if unsafe { get_fn(self.plugin, i, &mut nn) } {
                let name = unsafe {
                    std::ffi::CStr::from_ptr(nn.name.as_ptr())
                        .to_string_lossy()
                        .into_owned()
                };
                if nn.key >= 0 && nn.key <= 127 && !name.is_empty() {
                    result.insert(nn.key as u8, name);
                }
            }
        }
        result
    }

    fn parameter_infos(&self) -> Vec<ClapParameterInfo> {
        let Some(params) = self.params_ext() else {
            return Vec::new();
        };
        let Some(count_fn) = params.count else {
            return Vec::new();
        };
        let Some(get_info_fn) = params.get_info else {
            return Vec::new();
        };
        // SAFETY: function pointers come from plugin extension table.
        let count = unsafe { count_fn(self.plugin) };
        let mut out = Vec::with_capacity(count as usize);
        for idx in 0..count {
            let mut info = ClapParamInfoRaw {
                id: 0,
                flags: 0,
                cookie: std::ptr::null_mut(),
                name: [0; 256],
                module: [0; 1024],
                min_value: 0.0,
                max_value: 1.0,
                default_value: 0.0,
            };
            // SAFETY: info points to valid writable struct.
            if unsafe { !get_info_fn(self.plugin, idx, &mut info as *mut _) } {
                continue;
            }
            out.push(ClapParameterInfo {
                id: info.id,
                name: c_char_buf_to_string(&info.name),
                module: c_char_buf_to_string(&info.module),
                min_value: info.min_value,
                max_value: info.max_value,
                default_value: info.default_value,
            });
        }
        out
    }

    fn parameter_values(&self, infos: &[ClapParameterInfo]) -> HashMap<u32, f64> {
        let mut out = HashMap::new();
        let Some(params) = self.params_ext() else {
            for info in infos {
                out.insert(info.id, info.default_value);
            }
            return out;
        };
        let Some(get_value_fn) = params.get_value else {
            for info in infos {
                out.insert(info.id, info.default_value);
            }
            return out;
        };
        for info in infos {
            let mut value = info.default_value;
            // SAFETY: pointer to stack `value` is valid and param id belongs to plugin metadata.
            if unsafe { !get_value_fn(self.plugin, info.id, &mut value as *mut _) } {
                value = info.default_value;
            }
            out.insert(info.id, value);
        }
        out
    }

    fn flush_params(&self, param_events: &[PendingParamEvent]) -> Vec<PendingParamValue> {
        let Some(params) = self.params_ext() else {
            return Vec::new();
        };
        let Some(flush_fn) = params.flush else {
            return Vec::new();
        };
        let (in_events, _in_ctx) = param_input_events_from(param_events);
        let out_cap = param_events.len().max(32);
        let (out_events, mut out_ctx) = output_events_ctx(out_cap);
        // SAFETY: input/output event wrappers stay valid for duration of flush callback.
        unsafe {
            flush_fn(self.plugin, &in_events, &out_events);
        }
        std::mem::take(&mut out_ctx.param_values)
    }

    fn snapshot_state(&self) -> Result<ClapPluginState, String> {
        let Some(state_ext) = self.state_ext() else {
            return Ok(ClapPluginState { bytes: Vec::new() });
        };
        let Some(save_fn) = state_ext.save else {
            return Ok(ClapPluginState { bytes: Vec::new() });
        };
        let mut bytes = Vec::<u8>::new();
        let mut stream = ClapOStream {
            ctx: (&mut bytes as *mut Vec<u8>).cast::<c_void>(),
            write: Some(clap_ostream_write),
        };
        // SAFETY: stream callbacks reference `bytes` for duration of call.
        if unsafe {
            !save_fn(
                self.plugin,
                &mut stream as *mut ClapOStream as *const ClapOStream,
            )
        } {
            return Err("CLAP state save failed".to_string());
        }
        Ok(ClapPluginState { bytes })
    }

    fn restore_state(&self, state: &ClapPluginState) -> Result<(), String> {
        let Some(state_ext) = self.state_ext() else {
            return Ok(());
        };
        let Some(load_fn) = state_ext.load else {
            return Ok(());
        };
        let mut ctx = ClapIStreamCtx {
            bytes: &state.bytes,
            offset: 0,
        };
        let mut stream = ClapIStream {
            ctx: (&mut ctx as *mut ClapIStreamCtx).cast::<c_void>(),
            read: Some(clap_istream_read),
        };
        // SAFETY: stream callbacks reference `ctx` for duration of call.
        if unsafe {
            !load_fn(
                self.plugin,
                &mut stream as *mut ClapIStream as *const ClapIStream,
            )
        } {
            return Err("CLAP state load failed".to_string());
        }
        Ok(())
    }

    const CLAP_AUDIO_PORT_IS_MAIN: u32 = 1;

    fn audio_port_channels(&self) -> (Option<AudioPortLayout>, Option<AudioPortLayout>) {
        let Some(ext) = self.audio_ports_ext() else {
            return (None, None);
        };
        let Some(count_fn) = ext.count else {
            return (None, None);
        };
        let Some(get_fn) = ext.get else {
            return (None, None);
        };

        let read_ports = |is_input: bool| -> AudioPortLayout {
            let mut channels = Vec::new();
            let mut main_count = 0;
            let count = unsafe { count_fn(self.plugin, is_input) } as usize;
            channels.reserve(count);
            for idx in 0..count {
                let mut info = ClapAudioPortInfoRaw {
                    id: 0,
                    name: [0; 256],
                    flags: 0,
                    channel_count: 1,
                    port_type: std::ptr::null(),
                    in_place_pair: u32::MAX,
                };
                if unsafe { get_fn(self.plugin, idx as u32, is_input, &mut info as *mut _) } {
                    channels.push((info.channel_count as usize).max(1));
                    if info.flags & Self::CLAP_AUDIO_PORT_IS_MAIN != 0 {
                        main_count += 1;
                    }
                }
            }
            (channels, main_count)
        };
        (Some(read_ports(true)), Some(read_ports(false)))
    }

    fn note_port_layout(&self) -> (Option<usize>, Option<usize>) {
        let Some(ext) = self.note_ports_ext() else {
            return (None, None);
        };
        let Some(count_fn) = ext.count else {
            return (None, None);
        };
        // SAFETY: function pointer comes from plugin extension table.
        let in_count = unsafe { count_fn(self.plugin, true) } as usize;
        // SAFETY: function pointer comes from plugin extension table.
        let out_count = unsafe { count_fn(self.plugin, false) } as usize;
        (Some(in_count), Some(out_count))
    }

    fn gui_ext(&self) -> Option<&ClapPluginGui> {
        let ext_id = c"clap.gui";
        let plugin = unsafe { &*self.plugin };
        let get_extension = plugin.get_extension?;
        let ext_ptr = unsafe { get_extension(self.plugin, ext_id.as_ptr()) };
        if ext_ptr.is_null() {
            return None;
        }
        Some(unsafe { &*(ext_ptr as *const ClapPluginGui) })
    }

    fn gui_timer_support_ext(&self) -> Option<&ClapPluginTimerSupport> {
        let ext_id = c"clap.timer-support";
        let plugin = unsafe { &*self.plugin };
        let get_extension = plugin.get_extension?;
        let ext_ptr = unsafe { get_extension(self.plugin, ext_id.as_ptr()) };
        if ext_ptr.is_null() {
            return None;
        }
        Some(unsafe { &*(ext_ptr as *const ClapPluginTimerSupport) })
    }

    fn gui_info(&self) -> Result<ClapGuiInfo, String> {
        let gui = self
            .gui_ext()
            .ok_or_else(|| "CLAP plugin does not expose clap.gui".to_string())?;
        let is_api_supported = gui
            .is_api_supported
            .ok_or_else(|| "CLAP gui.is_api_supported is unavailable".to_string())?;
        for (api, supports_embedded) in [
            ("x11", true),
            ("cocoa", true),
            ("x11", false),
            ("cocoa", false),
        ] {
            let api_c = CString::new(api).map_err(|e| e.to_string())?;
            if unsafe { is_api_supported(self.plugin, api_c.as_ptr(), !supports_embedded) } {
                return Ok(ClapGuiInfo {
                    api: api.to_string(),
                    supports_embedded,
                });
            }
        }
        Err("No supported CLAP GUI API found".to_string())
    }

    fn gui_create(&self, api: &str, is_floating: bool) -> Result<(), String> {
        let gui = self
            .gui_ext()
            .ok_or_else(|| "CLAP plugin does not expose clap.gui".to_string())?;
        let create = gui
            .create
            .ok_or_else(|| "CLAP gui.create is unavailable".to_string())?;
        let api_c = CString::new(api).map_err(|e| e.to_string())?;
        if unsafe { !create(self.plugin, api_c.as_ptr(), is_floating) } {
            return Err("CLAP gui.create failed".to_string());
        }
        Ok(())
    }

    fn gui_get_size(&self) -> Result<(u32, u32), String> {
        let gui = self
            .gui_ext()
            .ok_or_else(|| "CLAP plugin does not expose clap.gui".to_string())?;
        let get_size = gui
            .get_size
            .ok_or_else(|| "CLAP gui.get_size is unavailable".to_string())?;
        let mut width = 0;
        let mut height = 0;
        if unsafe { !get_size(self.plugin, &mut width, &mut height) } {
            return Err("CLAP gui.get_size failed".to_string());
        }
        Ok((width, height))
    }

    fn gui_set_parent_x11(&self, window: usize) -> Result<(), String> {
        let gui = self
            .gui_ext()
            .ok_or_else(|| "CLAP plugin does not expose clap.gui".to_string())?;
        let set_parent = gui
            .set_parent
            .ok_or_else(|| "CLAP gui.set_parent is unavailable".to_string())?;
        let clap_window = ClapWindow {
            api: c"x11".as_ptr(),
            handle: ClapWindowHandle { x11: window },
        };
        if unsafe { !set_parent(self.plugin, &clap_window) } {
            return Err("CLAP gui.set_parent failed".to_string());
        }
        Ok(())
    }

    fn gui_show(&self) -> Result<(), String> {
        let gui = self
            .gui_ext()
            .ok_or_else(|| "CLAP plugin does not expose clap.gui".to_string())?;
        let show = gui
            .show
            .ok_or_else(|| "CLAP gui.show is unavailable".to_string())?;
        if unsafe { !show(self.plugin) } {
            return Err("CLAP gui.show failed".to_string());
        }
        Ok(())
    }

    fn gui_hide(&self) {
        if let Some(gui) = self.gui_ext()
            && let Some(hide) = gui.hide
        {
            unsafe { hide(self.plugin) };
        }
    }

    fn gui_destroy(&self) {
        if let Some(gui) = self.gui_ext()
            && let Some(destroy) = gui.destroy
        {
            unsafe { destroy(self.plugin) };
        }
    }

    fn gui_on_timer(&self, timer_id: u32) {
        if let Some(timer_ext) = self.gui_timer_support_ext()
            && let Some(on_timer) = timer_ext.on_timer
        {
            unsafe { on_timer(self.plugin, timer_id) };
        }
    }
}

impl Drop for PluginHandle {
    fn drop(&mut self) {
        // SAFETY: pointers were obtained from valid CLAP entry and plugin factory.
        unsafe {
            if !self.plugin.is_null() {
                let plugin = &*self.plugin;
                if let Some(stop_processing) = plugin.stop_processing {
                    stop_processing(self.plugin);
                }
                if let Some(deactivate) = plugin.deactivate {
                    deactivate(self.plugin);
                }
                if let Some(destroy) = plugin.destroy {
                    destroy(self.plugin);
                }
            }
            if !self.entry.is_null() {
                let entry = &*self.entry;
                if let Some(deinit) = entry.deinit {
                    deinit();
                }
            }
        }
    }
}

static HOST_THREAD_CHECK_EXT: ClapHostThreadCheck = ClapHostThreadCheck {
    is_main_thread: Some(host_is_main_thread),
    is_audio_thread: Some(host_is_audio_thread),
};
static HOST_LATENCY_EXT: ClapHostLatency = ClapHostLatency {
    changed: Some(host_latency_changed),
};
static HOST_TAIL_EXT: ClapHostTail = ClapHostTail {
    changed: Some(host_tail_changed),
};
static HOST_TIMER_EXT: ClapHostTimerSupport = ClapHostTimerSupport {
    register_timer: Some(host_timer_register),
    unregister_timer: Some(host_timer_unregister),
};
static HOST_GUI_EXT: ClapHostGui = ClapHostGui {
    resize_hints_changed: Some(host_gui_resize_hints_changed),
    request_resize: Some(host_gui_request_resize),
    request_show: Some(host_gui_request_show),
    request_hide: Some(host_gui_request_hide),
    closed: Some(host_gui_closed),
};
static HOST_PARAMS_EXT: ClapHostParams = ClapHostParams {
    rescan: Some(host_params_rescan),
    clear: Some(host_params_clear),
    request_flush: Some(host_params_request_flush),
};
static HOST_STATE_EXT: ClapHostState = ClapHostState {
    mark_dirty: Some(host_state_mark_dirty),
};
static HOST_NOTE_NAME_EXT: ClapHostNoteName = ClapHostNoteName {
    changed: Some(host_note_name_changed),
};
static NEXT_TIMER_ID: AtomicU32 = AtomicU32::new(1);

fn host_runtime_state(host: *const ClapHost) -> Option<&'static HostRuntimeState> {
    if host.is_null() {
        return None;
    }
    let state_ptr = unsafe { (*host).host_data as *const HostRuntimeState };
    if state_ptr.is_null() {
        return None;
    }
    Some(unsafe { &*state_ptr })
}

unsafe extern "C" fn host_get_extension(
    _host: *const ClapHost,
    _extension_id: *const c_char,
) -> *const c_void {
    if _extension_id.is_null() {
        return std::ptr::null();
    }
    // SAFETY: extension id is expected to be a valid NUL-terminated string.
    let id = unsafe { CStr::from_ptr(_extension_id) }.to_string_lossy();
    match id.as_ref() {
        "clap.host.thread-check" => {
            (&HOST_THREAD_CHECK_EXT as *const ClapHostThreadCheck).cast::<c_void>()
        }
        "clap.host.latency" => (&HOST_LATENCY_EXT as *const ClapHostLatency).cast::<c_void>(),
        "clap.host.tail" => (&HOST_TAIL_EXT as *const ClapHostTail).cast::<c_void>(),
        "clap.host.timer-support" => {
            (&HOST_TIMER_EXT as *const ClapHostTimerSupport).cast::<c_void>()
        }
        "clap.host.gui" => host_runtime_state(_host)
            .filter(|state| state.ui_active.load(Ordering::Acquire) != 0)
            .map(|_| (&HOST_GUI_EXT as *const ClapHostGui).cast::<c_void>())
            .unwrap_or(std::ptr::null()),
        "clap.host.params" => host_runtime_state(_host)
            .filter(|state| state.ui_active.load(Ordering::Acquire) != 0)
            .map(|_| (&HOST_PARAMS_EXT as *const ClapHostParams).cast::<c_void>())
            .unwrap_or(std::ptr::null()),
        "clap.host.state" => host_runtime_state(_host)
            .filter(|state| state.ui_active.load(Ordering::Acquire) != 0)
            .map(|_| (&HOST_STATE_EXT as *const ClapHostState).cast::<c_void>())
            .unwrap_or(std::ptr::null()),
        "clap.host.note-name" => (&HOST_NOTE_NAME_EXT as *const ClapHostNoteName).cast::<c_void>(),
        _ => std::ptr::null(),
    }
}

unsafe extern "C" fn host_request_process(_host: *const ClapHost) {
    if let Some(state) = host_runtime_state(_host) {
        state.callback_flags.lock().process = true;
    }
}

unsafe extern "C" fn host_request_callback(_host: *const ClapHost) {
    if let Some(state) = host_runtime_state(_host) {
        state.callback_flags.lock().callback = true;
    }
}

unsafe extern "C" fn host_request_restart(_host: *const ClapHost) {
    if let Some(state) = host_runtime_state(_host) {
        state.callback_flags.lock().restart = true;
    }
}

unsafe extern "C" fn host_note_name_changed(_host: *const ClapHost) {
    if let Some(state) = host_runtime_state(_host) {
        state.note_names_dirty.store(1, Ordering::Release);
    }
}

unsafe extern "C" fn host_is_main_thread(_host: *const ClapHost) -> bool {
    CLAP_HOST_MAIN_THREAD.with(Cell::get)
}

unsafe extern "C" fn host_is_audio_thread(_host: *const ClapHost) -> bool {
    CLAP_HOST_AUDIO_THREAD.with(Cell::get)
}

unsafe extern "C" fn host_latency_changed(_host: *const ClapHost) {}

unsafe extern "C" fn host_tail_changed(_host: *const ClapHost) {}

unsafe extern "C" fn host_timer_register(
    _host: *const ClapHost,
    _period_ms: u32,
    timer_id: *mut u32,
) -> bool {
    if timer_id.is_null() {
        return false;
    }
    let id = NEXT_TIMER_ID.fetch_add(1, Ordering::Relaxed);
    if let Some(state) = host_runtime_state(_host) {
        let period_ms = _period_ms.max(1);
        state.timers.lock().push(HostTimer {
            id,
            period: Duration::from_millis(period_ms as u64),
            next_tick: Instant::now() + Duration::from_millis(period_ms as u64),
        });
    }
    // SAFETY: timer_id points to writable u32 provided by plugin.
    unsafe {
        *timer_id = id;
    }
    true
}

unsafe extern "C" fn host_timer_unregister(_host: *const ClapHost, _timer_id: u32) -> bool {
    if let Some(state) = host_runtime_state(_host) {
        state.timers.lock().retain(|timer| timer.id != _timer_id);
    }
    true
}

unsafe extern "C" fn host_gui_resize_hints_changed(_host: *const ClapHost) {}

unsafe extern "C" fn host_gui_request_resize(
    _host: *const ClapHost,
    _width: u32,
    _height: u32,
) -> bool {
    true
}

unsafe extern "C" fn host_gui_request_show(_host: *const ClapHost) -> bool {
    true
}

unsafe extern "C" fn host_gui_request_hide(_host: *const ClapHost) -> bool {
    if let Some(state) = host_runtime_state(_host) {
        if state.ui_active.load(Ordering::Acquire) != 0 {
            state.ui_should_close.store(1, Ordering::Release);
        }
        true
    } else {
        false
    }
}

unsafe extern "C" fn host_gui_closed(_host: *const ClapHost, _was_destroyed: bool) {
    if let Some(state) = host_runtime_state(_host)
        && state.ui_active.load(Ordering::Acquire) != 0
    {
        state.ui_should_close.store(1, Ordering::Release);
    }
}

unsafe extern "C" fn host_params_rescan(_host: *const ClapHost, _flags: u32) {}

unsafe extern "C" fn host_params_clear(_host: *const ClapHost, _param_id: u32, _flags: u32) {}

unsafe extern "C" fn host_params_request_flush(_host: *const ClapHost) {
    if let Some(state) = host_runtime_state(_host) {
        state.param_flush_requested.store(1, Ordering::Release);
        state.callback_flags.lock().callback = true;
    }
}

unsafe extern "C" fn host_state_mark_dirty(_host: *const ClapHost) {
    if let Some(state) = host_runtime_state(_host) {
        state.state_dirty_requested.store(1, Ordering::Release);
        state.callback_flags.lock().callback = true;
    }
}

unsafe extern "C" fn input_events_size(_list: *const ClapInputEvents) -> u32 {
    if _list.is_null() {
        return 0;
    }
    // SAFETY: ctx points to ClapInputEventsCtx owned by process_native.
    let ctx = unsafe { (*_list).ctx as *const ClapInputEventsCtx };
    if ctx.is_null() {
        return 0;
    }
    // SAFETY: ctx is valid during process callback lifetime.
    unsafe { (*ctx).events.len() as u32 }
}

unsafe extern "C" fn input_events_get(
    _list: *const ClapInputEvents,
    _index: u32,
) -> *const ClapEventHeader {
    if _list.is_null() {
        return std::ptr::null();
    }
    // SAFETY: ctx points to ClapInputEventsCtx owned by process_native.
    let ctx = unsafe { (*_list).ctx as *const ClapInputEventsCtx };
    if ctx.is_null() {
        return std::ptr::null();
    }
    // SAFETY: ctx is valid during process callback lifetime.
    let events = unsafe { &(*ctx).events };
    let Some(event) = events.get(_index as usize) else {
        return std::ptr::null();
    };
    event.header_ptr()
}

unsafe extern "C" fn output_events_try_push(
    _list: *const ClapOutputEvents,
    _event: *const ClapEventHeader,
) -> bool {
    if _list.is_null() || _event.is_null() {
        return false;
    }
    // SAFETY: ctx points to ClapOutputEventsCtx owned by process_native.
    let ctx = unsafe { (*_list).ctx as *mut ClapOutputEventsCtx };
    if ctx.is_null() {
        return false;
    }
    // SAFETY: event pointer is valid for callback lifetime.
    let header = unsafe { &*_event };
    if header.space_id != CLAP_CORE_EVENT_SPACE_ID {
        return false;
    }
    match header.type_ {
        CLAP_EVENT_MIDI => {
            if (header.size as usize) < std::mem::size_of::<ClapEventMidi>() {
                return false;
            }
            // SAFETY: validated type/size above.
            let midi = unsafe { &*(_event as *const ClapEventMidi) };
            // SAFETY: ctx pointer is valid and uniquely owned during processing.
            unsafe {
                (*ctx).midi_events.push(ClapMidiOutputEvent {
                    port: midi.port_index as usize,
                    event: MidiEvent::new(header.time, midi.data.to_vec()),
                });
            }
            true
        }
        CLAP_EVENT_PARAM_VALUE => {
            if (header.size as usize) < std::mem::size_of::<ClapEventParamValue>() {
                return false;
            }
            // SAFETY: validated type/size above.
            let param = unsafe { &*(_event as *const ClapEventParamValue) };
            // SAFETY: ctx pointer is valid and uniquely owned during processing.
            unsafe {
                (*ctx).param_values.push(PendingParamValue {
                    param_id: param.param_id,
                    value: param.value,
                });
            }
            true
        }
        _ => false,
    }
}

fn input_events_from(
    midi_events: &[MidiEvent],
    param_events: &[PendingParamEvent],
    sample_rate: f64,
    transport: ClapTransportInfo,
    has_note_ports: bool,
) -> (ClapInputEvents, Box<ClapInputEventsCtx>) {
    let mut events = Vec::with_capacity(midi_events.len() + param_events.len() + 1);
    let bpm = transport.bpm.max(1.0);
    let sample_rate = sample_rate.max(1.0);
    let seconds = transport.transport_sample as f64 / sample_rate;
    let song_pos_seconds = (seconds * CLAP_SECTIME_FACTOR as f64) as i64;
    let beats = seconds * (bpm / 60.0);
    let song_pos_beats = (beats * CLAP_BEATTIME_FACTOR as f64) as i64;
    let mut flags = CLAP_TRANSPORT_HAS_TEMPO
        | CLAP_TRANSPORT_HAS_BEATS_TIMELINE
        | CLAP_TRANSPORT_HAS_SECONDS_TIMELINE
        | CLAP_TRANSPORT_HAS_TIME_SIGNATURE;
    if transport.playing {
        flags |= CLAP_TRANSPORT_IS_PLAYING;
    }
    let (loop_start_seconds, loop_end_seconds, loop_start_beats, loop_end_beats) =
        if transport.loop_enabled {
            if let Some((loop_start, loop_end)) = transport.loop_range_samples {
                flags |= CLAP_TRANSPORT_IS_LOOP_ACTIVE;
                let ls_sec = loop_start as f64 / sample_rate;
                let le_sec = loop_end as f64 / sample_rate;
                let ls_beats = ls_sec * (bpm / 60.0);
                let le_beats = le_sec * (bpm / 60.0);
                (
                    (ls_sec * CLAP_SECTIME_FACTOR as f64) as i64,
                    (le_sec * CLAP_SECTIME_FACTOR as f64) as i64,
                    (ls_beats * CLAP_BEATTIME_FACTOR as f64) as i64,
                    (le_beats * CLAP_BEATTIME_FACTOR as f64) as i64,
                )
            } else {
                (0, 0, 0, 0)
            }
        } else {
            (0, 0, 0, 0)
        };
    let ts_num = transport.tsig_num.max(1);
    let ts_denom = transport.tsig_denom.max(1);
    let beats_per_bar = ts_num as f64 * (4.0 / ts_denom as f64);
    let bar_number = if beats_per_bar > 0.0 {
        (beats / beats_per_bar).floor().max(0.0) as i32
    } else {
        0
    };
    let bar_start_beats = (bar_number as f64 * beats_per_bar * CLAP_BEATTIME_FACTOR as f64) as i64;
    events.push(ClapInputEvent::Transport(ClapEventTransport {
        header: ClapEventHeader {
            size: std::mem::size_of::<ClapEventTransport>() as u32,
            time: 0,
            space_id: CLAP_CORE_EVENT_SPACE_ID,
            type_: CLAP_EVENT_TRANSPORT,
            flags: 0,
        },
        flags,
        song_pos_beats,
        song_pos_seconds,
        tempo: bpm,
        tempo_inc: 0.0,
        loop_start_beats,
        loop_end_beats,
        loop_start_seconds,
        loop_end_seconds,
        bar_start: bar_start_beats,
        bar_number,
        tsig_num: ts_num,
        tsig_denom: ts_denom,
    }));
    for event in midi_events {
        if event.data.is_empty() {
            continue;
        }
        let mut data = [0_u8; 3];
        let bytes = event.data.len().min(3);
        data[..bytes].copy_from_slice(&event.data[..bytes]);
        let status = data[0];
        let is_note_on = (0x90..=0x9F).contains(&status);
        let is_note_off = (0x80..=0x8F).contains(&status);
        if has_note_ports && (is_note_on || is_note_off) {
            let channel = (status & 0x0F) as i16;
            let key = data.get(1).copied().unwrap_or(0).min(127) as i16;
            let velocity_byte = data.get(2).copied().unwrap_or(0);
            let velocity = if is_note_on && velocity_byte == 0 {
                // Note-on with velocity 0 is conventionally note-off.
                events.push(ClapInputEvent::Note(ClapEventNote {
                    header: ClapEventHeader {
                        size: std::mem::size_of::<ClapEventNote>() as u32,
                        time: event.frame,
                        space_id: CLAP_CORE_EVENT_SPACE_ID,
                        type_: CLAP_EVENT_NOTE_OFF,
                        flags: 0,
                    },
                    note_id: -1,
                    port_index: 0,
                    channel,
                    key,
                    velocity: 0.0,
                }));
                continue;
            } else {
                (velocity_byte as f64 / 127.0).clamp(0.0, 1.0)
            };
            events.push(ClapInputEvent::Note(ClapEventNote {
                header: ClapEventHeader {
                    size: std::mem::size_of::<ClapEventNote>() as u32,
                    time: event.frame,
                    space_id: CLAP_CORE_EVENT_SPACE_ID,
                    type_: if is_note_on {
                        CLAP_EVENT_NOTE_ON
                    } else {
                        CLAP_EVENT_NOTE_OFF
                    },
                    flags: 0,
                },
                note_id: -1,
                port_index: 0,
                channel,
                key,
                velocity,
            }));
        } else {
            events.push(ClapInputEvent::Midi(ClapEventMidi {
                header: ClapEventHeader {
                    size: std::mem::size_of::<ClapEventMidi>() as u32,
                    time: event.frame,
                    space_id: CLAP_CORE_EVENT_SPACE_ID,
                    type_: CLAP_EVENT_MIDI,
                    flags: 0,
                },
                port_index: 0,
                data,
            }));
        }
    }
    for param in param_events {
        match *param {
            PendingParamEvent::Value {
                param_id,
                value,
                frame,
            } => events.push(ClapInputEvent::ParamValue(ClapEventParamValue {
                header: ClapEventHeader {
                    size: std::mem::size_of::<ClapEventParamValue>() as u32,
                    time: frame,
                    space_id: CLAP_CORE_EVENT_SPACE_ID,
                    type_: CLAP_EVENT_PARAM_VALUE,
                    flags: 0,
                },
                param_id,
                cookie: std::ptr::null_mut(),
                note_id: -1,
                port_index: -1,
                channel: -1,
                key: -1,
                value,
            })),
            PendingParamEvent::GestureBegin { param_id, frame } => {
                events.push(ClapInputEvent::ParamGesture(ClapEventParamGesture {
                    header: ClapEventHeader {
                        size: std::mem::size_of::<ClapEventParamGesture>() as u32,
                        time: frame,
                        space_id: CLAP_CORE_EVENT_SPACE_ID,
                        type_: CLAP_EVENT_PARAM_GESTURE_BEGIN,
                        flags: 0,
                    },
                    param_id,
                }))
            }
            PendingParamEvent::GestureEnd { param_id, frame } => {
                events.push(ClapInputEvent::ParamGesture(ClapEventParamGesture {
                    header: ClapEventHeader {
                        size: std::mem::size_of::<ClapEventParamGesture>() as u32,
                        time: frame,
                        space_id: CLAP_CORE_EVENT_SPACE_ID,
                        type_: CLAP_EVENT_PARAM_GESTURE_END,
                        flags: 0,
                    },
                    param_id,
                }))
            }
        }
    }
    events.sort_by_key(|event| match event {
        ClapInputEvent::Note(e) => e.header.time,
        ClapInputEvent::Midi(e) => e.header.time,
        ClapInputEvent::ParamValue(e) => e.header.time,
        ClapInputEvent::ParamGesture(e) => e.header.time,
        ClapInputEvent::Transport(e) => e.header.time,
    });
    let mut ctx = Box::new(ClapInputEventsCtx { events });
    let list = ClapInputEvents {
        ctx: (&mut *ctx as *mut ClapInputEventsCtx).cast::<c_void>(),
        size: Some(input_events_size),
        get: Some(input_events_get),
    };
    (list, ctx)
}

fn param_input_events_from(
    param_events: &[PendingParamEvent],
) -> (ClapInputEvents, Box<ClapInputEventsCtx>) {
    let mut events = Vec::with_capacity(param_events.len());
    for param in param_events {
        match *param {
            PendingParamEvent::Value {
                param_id,
                value,
                frame,
            } => events.push(ClapInputEvent::ParamValue(ClapEventParamValue {
                header: ClapEventHeader {
                    size: std::mem::size_of::<ClapEventParamValue>() as u32,
                    time: frame,
                    space_id: CLAP_CORE_EVENT_SPACE_ID,
                    type_: CLAP_EVENT_PARAM_VALUE,
                    flags: 0,
                },
                param_id,
                cookie: std::ptr::null_mut(),
                note_id: -1,
                port_index: -1,
                channel: -1,
                key: -1,
                value,
            })),
            PendingParamEvent::GestureBegin { param_id, frame } => {
                events.push(ClapInputEvent::ParamGesture(ClapEventParamGesture {
                    header: ClapEventHeader {
                        size: std::mem::size_of::<ClapEventParamGesture>() as u32,
                        time: frame,
                        space_id: CLAP_CORE_EVENT_SPACE_ID,
                        type_: CLAP_EVENT_PARAM_GESTURE_BEGIN,
                        flags: 0,
                    },
                    param_id,
                }))
            }
            PendingParamEvent::GestureEnd { param_id, frame } => {
                events.push(ClapInputEvent::ParamGesture(ClapEventParamGesture {
                    header: ClapEventHeader {
                        size: std::mem::size_of::<ClapEventParamGesture>() as u32,
                        time: frame,
                        space_id: CLAP_CORE_EVENT_SPACE_ID,
                        type_: CLAP_EVENT_PARAM_GESTURE_END,
                        flags: 0,
                    },
                    param_id,
                }))
            }
        }
    }
    events.sort_by_key(|event| match event {
        ClapInputEvent::Note(e) => e.header.time,
        ClapInputEvent::Midi(e) => e.header.time,
        ClapInputEvent::ParamValue(e) => e.header.time,
        ClapInputEvent::ParamGesture(e) => e.header.time,
        ClapInputEvent::Transport(e) => e.header.time,
    });
    let mut ctx = Box::new(ClapInputEventsCtx { events });
    let list = ClapInputEvents {
        ctx: (&mut *ctx as *mut ClapInputEventsCtx).cast::<c_void>(),
        size: Some(input_events_size),
        get: Some(input_events_get),
    };
    (list, ctx)
}

fn output_events_ctx(capacity: usize) -> (ClapOutputEvents, Box<ClapOutputEventsCtx>) {
    let mut ctx = Box::new(ClapOutputEventsCtx {
        midi_events: Vec::with_capacity(capacity),
        param_values: Vec::with_capacity(capacity / 2),
    });
    let list = ClapOutputEvents {
        ctx: (&mut *ctx as *mut ClapOutputEventsCtx).cast::<c_void>(),
        try_push: Some(output_events_try_push),
    };
    (list, ctx)
}

fn c_char_buf_to_string<const N: usize>(buf: &[c_char; N]) -> String {
    let bytes = buf
        .iter()
        .take_while(|&&b| b != 0)
        .map(|&b| b as u8)
        .collect::<Vec<u8>>();
    String::from_utf8_lossy(&bytes).to_string()
}

fn split_plugin_spec(spec: &str) -> (&str, Option<&str>) {
    if let Some((path, id)) = spec.split_once("::")
        && !id.trim().is_empty()
    {
        return (path, Some(id.trim()));
    }
    (spec, None)
}

unsafe extern "C" fn clap_ostream_write(
    stream: *const ClapOStream,
    buffer: *const c_void,
    size: u64,
) -> i64 {
    if stream.is_null() || buffer.is_null() {
        return -1;
    }
    // SAFETY: ctx is initialized by snapshot_state and valid during callback.
    let ctx = unsafe { (*stream).ctx as *mut Vec<u8> };
    if ctx.is_null() {
        return -1;
    }
    let n = (size as usize).min(isize::MAX as usize);
    // SAFETY: source pointer is valid for `n` bytes per caller contract.
    let src = unsafe { std::slice::from_raw_parts(buffer.cast::<u8>(), n) };
    // SAFETY: ctx points to writable Vec<u8>.
    unsafe {
        (*ctx).extend_from_slice(src);
    }
    n as i64
}

unsafe extern "C" fn clap_istream_read(
    stream: *const ClapIStream,
    buffer: *mut c_void,
    size: u64,
) -> i64 {
    if stream.is_null() || buffer.is_null() {
        return -1;
    }
    // SAFETY: ctx is initialized by restore_state and valid during callback.
    let ctx = unsafe { (*stream).ctx as *mut ClapIStreamCtx<'_> };
    if ctx.is_null() {
        return -1;
    }
    // SAFETY: ctx points to valid read context.
    let ctx = unsafe { &mut *ctx };
    let remaining = ctx.bytes.len().saturating_sub(ctx.offset);
    if remaining == 0 {
        return 0;
    }
    let n = remaining.min(size as usize);
    // SAFETY: destination pointer is valid for `n` bytes per caller contract.
    let dst = unsafe { std::slice::from_raw_parts_mut(buffer.cast::<u8>(), n) };
    dst.copy_from_slice(&ctx.bytes[ctx.offset..ctx.offset + n]);
    ctx.offset += n;
    n as i64
}

pub fn list_plugins() -> Vec<ClapPluginInfo> {
    list_plugins_with_capabilities(false)
}

pub fn list_plugins_with_capabilities(scan_capabilities: bool) -> Vec<ClapPluginInfo> {
    let mut roots = default_clap_search_roots();

    if let Ok(extra) = std::env::var("CLAP_PATH") {
        for p in std::env::split_paths(&extra) {
            if !p.as_os_str().is_empty() {
                roots.push(p);
            }
        }
    }

    let mut out = Vec::new();
    for root in roots {
        collect_clap_plugins(&root, &mut out, scan_capabilities);
    }

    out.sort_by_key(|a| a.name.to_lowercase());
    out.dedup_by(|a, b| a.path.eq_ignore_ascii_case(&b.path));
    out
}

fn collect_clap_plugins(root: &Path, out: &mut Vec<ClapPluginInfo>, scan_capabilities: bool) {
    let Ok(entries) = std::fs::read_dir(root) else {
        return;
    };
    for entry in entries.flatten() {
        let path = entry.path();
        let Ok(ft) = entry.file_type() else {
            continue;
        };
        if ft.is_dir() {
            collect_clap_plugins(&path, out, scan_capabilities);
            continue;
        }

        if path
            .extension()
            .is_some_and(|ext| ext.eq_ignore_ascii_case("clap"))
        {
            let infos = scan_bundle_descriptors(&path, scan_capabilities);
            if infos.is_empty() {
                let name = path
                    .file_stem()
                    .map(|s| s.to_string_lossy().to_string())
                    .unwrap_or_else(|| path.to_string_lossy().to_string());
                out.push(ClapPluginInfo {
                    name,
                    path: path.to_string_lossy().to_string(),
                    capabilities: None,
                });
            } else {
                out.extend(infos);
            }
        }
    }
}

fn scan_bundle_descriptors(path: &Path, scan_capabilities: bool) -> Vec<ClapPluginInfo> {
    let path_str = path.to_string_lossy().to_string();
    let factory_id = c"clap.plugin-factory";
    let host_runtime = match HostRuntime::new() {
        Ok(runtime) => runtime,
        Err(_) => return Vec::new(),
    };
    // SAFETY: path points to plugin module file.
    let library = match unsafe { Library::new(path) } {
        Ok(lib) => lib,
        Err(_) => return Vec::new(),
    };
    // SAFETY: symbol is CLAP entry pointer.
    let entry_ptr = unsafe {
        match library.get::<*const ClapPluginEntry>(b"clap_entry\0") {
            Ok(sym) => *sym,
            Err(_) => return Vec::new(),
        }
    };
    if entry_ptr.is_null() {
        return Vec::new();
    }
    // SAFETY: entry pointer validated above.
    let entry = unsafe { &*entry_ptr };
    let Some(init) = entry.init else {
        return Vec::new();
    };
    let host_ptr = &host_runtime.host;
    // SAFETY: valid host pointer.
    if unsafe { !init(host_ptr) } {
        return Vec::new();
    }
    let mut out = Vec::new();
    if let Some(get_factory) = entry.get_factory {
        // SAFETY: static factory id.
        let factory = unsafe { get_factory(factory_id.as_ptr()) } as *const ClapPluginFactory;
        if !factory.is_null() {
            // SAFETY: factory pointer validated above.
            let factory_ref = unsafe { &*factory };
            if let (Some(get_count), Some(get_desc)) = (
                factory_ref.get_plugin_count,
                factory_ref.get_plugin_descriptor,
            ) {
                // SAFETY: function pointer from plugin.
                let count = unsafe { get_count(factory) };
                for i in 0..count {
                    // SAFETY: i < count.
                    let desc = unsafe { get_desc(factory, i) };
                    if desc.is_null() {
                        continue;
                    }
                    // SAFETY: descriptor pointer from plugin factory.
                    let desc = unsafe { &*desc };
                    if desc.id.is_null() || desc.name.is_null() {
                        continue;
                    }
                    // SAFETY: CLAP descriptor strings are NUL-terminated.
                    let id = unsafe { CStr::from_ptr(desc.id) }
                        .to_string_lossy()
                        .to_string();
                    // SAFETY: CLAP descriptor strings are NUL-terminated.
                    let name = unsafe { CStr::from_ptr(desc.name) }
                        .to_string_lossy()
                        .to_string();

                    let capabilities = if scan_capabilities {
                        scan_plugin_capabilities(factory_ref, factory, &host_runtime.host, &id)
                    } else {
                        None
                    };

                    out.push(ClapPluginInfo {
                        name,
                        path: format!("{path_str}::{id}"),
                        capabilities,
                    });
                }
            }
        }
    }
    // SAFETY: deinit belongs to entry and is valid after init.
    if let Some(deinit) = entry.deinit {
        unsafe { deinit() };
    }
    out
}

fn scan_plugin_capabilities(
    factory: &ClapPluginFactory,
    factory_ptr: *const ClapPluginFactory,
    host: &ClapHost,
    plugin_id: &str,
) -> Option<ClapPluginCapabilities> {
    let create = factory.create_plugin?;

    let id_cstring = CString::new(plugin_id).ok()?;
    // SAFETY: valid factory, host, and id pointers.
    let plugin = unsafe { create(factory_ptr, host, id_cstring.as_ptr()) };
    if plugin.is_null() {
        return None;
    }

    // SAFETY: plugin pointer validated above.
    let plugin_ref = unsafe { &*plugin };
    let plugin_init = plugin_ref.init?;

    // SAFETY: plugin pointer and function pointer follow CLAP ABI.
    if unsafe { !plugin_init(plugin) } {
        return None;
    }

    let mut capabilities = ClapPluginCapabilities {
        has_gui: false,
        gui_apis: Vec::new(),
        supports_embedded: false,
        supports_floating: false,
        has_params: false,
        has_state: false,
        audio_inputs: 0,
        audio_outputs: 0,
        midi_inputs: 0,
        midi_outputs: 0,
    };

    // Check for extensions
    if let Some(get_extension) = plugin_ref.get_extension {
        // Check GUI extension
        let gui_ext_id = c"clap.gui";
        // SAFETY: extension id is valid static C string.
        let gui_ptr = unsafe { get_extension(plugin, gui_ext_id.as_ptr()) };
        if !gui_ptr.is_null() {
            capabilities.has_gui = true;
            // SAFETY: CLAP guarantees extension pointer layout for requested extension id.
            let gui = unsafe { &*(gui_ptr as *const ClapPluginGui) };

            // Check which GUI APIs are supported
            if let Some(is_api_supported) = gui.is_api_supported {
                for api in ["x11", "cocoa"] {
                    if let Ok(api_cstr) = CString::new(api) {
                        // Check embedded mode
                        // SAFETY: valid plugin and API string pointers.
                        if unsafe { is_api_supported(plugin, api_cstr.as_ptr(), false) } {
                            capabilities.gui_apis.push(format!("{} (embedded)", api));
                            capabilities.supports_embedded = true;
                        }
                        // Check floating mode
                        // SAFETY: valid plugin and API string pointers.
                        if unsafe { is_api_supported(plugin, api_cstr.as_ptr(), true) } {
                            if !capabilities.supports_embedded {
                                capabilities.gui_apis.push(format!("{} (floating)", api));
                            }
                            capabilities.supports_floating = true;
                        }
                    }
                }
            }
        }

        // Check params extension
        let params_ext_id = c"clap.params";
        // SAFETY: extension id is valid static C string.
        let params_ptr = unsafe { get_extension(plugin, params_ext_id.as_ptr()) };
        capabilities.has_params = !params_ptr.is_null();

        // Check state extension
        let state_ext_id = c"clap.state";
        // SAFETY: extension id is valid static C string.
        let state_ptr = unsafe { get_extension(plugin, state_ext_id.as_ptr()) };
        capabilities.has_state = !state_ptr.is_null();

        // Check audio-ports extension
        let audio_ports_ext_id = c"clap.audio-ports";
        // SAFETY: extension id is valid static C string.
        let audio_ports_ptr = unsafe { get_extension(plugin, audio_ports_ext_id.as_ptr()) };
        if !audio_ports_ptr.is_null() {
            // SAFETY: CLAP guarantees extension pointer layout for requested extension id.
            let audio_ports = unsafe { &*(audio_ports_ptr as *const ClapPluginAudioPorts) };
            if let Some(count_fn) = audio_ports.count {
                // SAFETY: function pointer comes from plugin extension table.
                capabilities.audio_inputs = unsafe { count_fn(plugin, true) } as usize;
                // SAFETY: function pointer comes from plugin extension table.
                capabilities.audio_outputs = unsafe { count_fn(plugin, false) } as usize;
            }
        }

        // Check note-ports extension
        let note_ports_ext_id = c"clap.note-ports";
        // SAFETY: extension id is valid static C string.
        let note_ports_ptr = unsafe { get_extension(plugin, note_ports_ext_id.as_ptr()) };
        if !note_ports_ptr.is_null() {
            // SAFETY: CLAP guarantees extension pointer layout for requested extension id.
            let note_ports = unsafe { &*(note_ports_ptr as *const ClapPluginNotePorts) };
            if let Some(count_fn) = note_ports.count {
                // SAFETY: function pointer comes from plugin extension table.
                capabilities.midi_inputs = unsafe { count_fn(plugin, true) } as usize;
                // SAFETY: function pointer comes from plugin extension table.
                capabilities.midi_outputs = unsafe { count_fn(plugin, false) } as usize;
            }
        }
    }

    // Clean up plugin instance
    if let Some(destroy) = plugin_ref.destroy {
        // SAFETY: plugin pointer is valid.
        unsafe { destroy(plugin) };
    }

    Some(capabilities)
}

fn default_clap_search_roots() -> Vec<PathBuf> {
    let mut roots = Vec::new();

    #[cfg(target_os = "macos")]
    {
        paths::push_macos_audio_plugin_roots(&mut roots, "CLAP");
    }

    #[cfg(any(target_os = "linux", target_os = "freebsd", target_os = "openbsd"))]
    {
        paths::push_unix_plugin_roots(&mut roots, "clap");
    }

    roots
}

#[cfg(test)]
mod tests {
    use super::collect_clap_plugins;
    use std::fs;
    use std::path::PathBuf;
    use std::time::{SystemTime, UNIX_EPOCH};

    #[cfg(unix)]
    fn make_symlink(src: &PathBuf, dst: &PathBuf) {
        std::os::unix::fs::symlink(src, dst).expect("should create symlink");
    }

    #[cfg(unix)]
    #[test]
    fn collect_clap_plugins_includes_symlinked_clap_files() {
        let nanos = SystemTime::now()
            .duration_since(UNIX_EPOCH)
            .expect("time should be valid")
            .as_nanos();
        let root = std::env::temp_dir().join(format!(
            "maolan-clap-symlink-test-{}-{nanos}",
            std::process::id()
        ));
        fs::create_dir_all(&root).expect("should create temp dir");

        let target_file = root.join("librural_modeler.so");
        fs::write(&target_file, b"not a real clap binary").expect("should create target file");
        let clap_link = root.join("RuralModeler.clap");
        make_symlink(&PathBuf::from("librural_modeler.so"), &clap_link);

        let mut out = Vec::new();
        collect_clap_plugins(&root, &mut out, false);

        assert!(
            out.iter()
                .any(|info| info.path == clap_link.to_string_lossy()),
            "scanner should include symlinked .clap files"
        );

        fs::remove_dir_all(&root).expect("should remove temp dir");
    }
}