// Copyright © SixtyFPS GmbH <info@slint-ui.com>
// SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-Slint-commercial

use crate::lsp_ext::{Health, ServerStatusNotification, ServerStatusParams};
use i_slint_compiler::CompilerConfiguration;
use lsp_types::notification::Notification;
use once_cell::sync::Lazy;
use slint_interpreter::ComponentHandle;
use std::collections::{HashMap, HashSet};
use std::future::Future;
use std::path::{Path, PathBuf};
use std::pin::Pin;
use std::sync::{Arc, Condvar, Mutex};
use std::task::Wake;

#[derive(PartialEq)]
enum RequestedGuiEventLoopState {
    /// The UI event loop hasn't been started yet because no preview has been requested
    Uninitialized,
    /// The LSP thread requested the UI loop to start because a preview was requested,
    /// But the loop hasn't been started yet
    StartLoop,
    /// The Loop is now started so the LSP thread can start posting events
    LoopStated,
    /// The LSP thread requested the application to be terminated
    QuitLoop,
}

static GUI_EVENT_LOOP_NOTIFIER: Lazy<Condvar> = Lazy::new(Condvar::new);
static GUI_EVENT_LOOP_STATE_REQUEST: Lazy<Mutex<RequestedGuiEventLoopState>> =
    Lazy::new(|| Mutex::new(RequestedGuiEventLoopState::Uninitialized));

struct FutureRunner {
    fut: Mutex<Option<Pin<Box<dyn Future<Output = ()>>>>>,
}

/// Safety: the future is only going to be run in the UI thread
unsafe impl Send for FutureRunner {}
/// Safety: the future is only going to be run in the UI thread
unsafe impl Sync for FutureRunner {}

impl Wake for FutureRunner {
    fn wake(self: Arc<Self>) {
        i_slint_core::api::invoke_from_event_loop(move || {
            let waker = self.clone().into();
            let mut cx = std::task::Context::from_waker(&waker);
            let mut fut_opt = self.fut.lock().unwrap();
            if let Some(fut) = &mut *fut_opt {
                match fut.as_mut().poll(&mut cx) {
                    std::task::Poll::Ready(_) => *fut_opt = None,
                    std::task::Poll::Pending => {}
                }
            }
        })
        .unwrap();
    }
}

fn run_in_ui_thread(fut: Pin<Box<dyn Future<Output = ()>>>) {
    // Wake up the main thread to start the event loop, if possible
    {
        let mut state_request = GUI_EVENT_LOOP_STATE_REQUEST.lock().unwrap();
        if *state_request == RequestedGuiEventLoopState::Uninitialized {
            *state_request = RequestedGuiEventLoopState::StartLoop;
            GUI_EVENT_LOOP_NOTIFIER.notify_one();
        }
        // We don't want to call post_event before the loop is properly initialized
        while *state_request == RequestedGuiEventLoopState::StartLoop {
            state_request = GUI_EVENT_LOOP_NOTIFIER.wait(state_request).unwrap();
        }
    }

    Arc::new(FutureRunner { fut: Mutex::new(Some(fut)) }).wake()
}

pub fn start_ui_event_loop() {
    {
        let mut state_requested = GUI_EVENT_LOOP_STATE_REQUEST.lock().unwrap();

        while *state_requested == RequestedGuiEventLoopState::Uninitialized {
            state_requested = GUI_EVENT_LOOP_NOTIFIER.wait(state_requested).unwrap();
        }

        if *state_requested == RequestedGuiEventLoopState::QuitLoop {
            return;
        }

        if *state_requested == RequestedGuiEventLoopState::StartLoop {
            // make sure the backend is initialized
            i_slint_backend_selector::with_platform(|_| Ok(())).unwrap();
            // Send an event so that once the loop is started, we notify the LSP thread that it can send more events
            i_slint_core::api::invoke_from_event_loop(|| {
                let mut state_request = GUI_EVENT_LOOP_STATE_REQUEST.lock().unwrap();
                if *state_request == RequestedGuiEventLoopState::StartLoop {
                    *state_request = RequestedGuiEventLoopState::LoopStated;
                    GUI_EVENT_LOOP_NOTIFIER.notify_one();
                }
            })
            .unwrap();
        }
    }

    i_slint_backend_selector::with_platform(|b| {
        b.set_event_loop_quit_on_last_window_closed(false);
        b.run_event_loop()
    })
    .unwrap();
}

pub fn quit_ui_event_loop() {
    // Wake up the main thread, in case it wasn't woken up earlier. If it wasn't, then don't request
    // a start of the event loop.
    {
        let mut state_request = GUI_EVENT_LOOP_STATE_REQUEST.lock().unwrap();
        *state_request = RequestedGuiEventLoopState::QuitLoop;
        GUI_EVENT_LOOP_NOTIFIER.notify_one();
    }

    let _ = i_slint_core::api::quit_event_loop();

    // Make sure then sender channel gets dropped
    if let Some(cache) = CONTENT_CACHE.get() {
        let mut cache = cache.lock().unwrap();
        cache.sender = None;
    };
}

pub enum PostLoadBehavior {
    ShowAfterLoad,
    DoNothing,
}

pub fn load_preview(
    sender: crate::ServerNotifier,
    component: PreviewComponent,
    post_load_behavior: PostLoadBehavior,
) {
    use std::sync::atomic::{AtomicU32, Ordering};
    static PENDING_EVENTS: AtomicU32 = AtomicU32::new(0);
    if PENDING_EVENTS.load(Ordering::SeqCst) > 0 {
        return;
    }
    PENDING_EVENTS.fetch_add(1, Ordering::SeqCst);
    run_in_ui_thread(Box::pin(async move {
        PENDING_EVENTS.fetch_sub(1, Ordering::SeqCst);
        reload_preview(sender, component, post_load_behavior).await
    }));
}

#[derive(Default, Clone)]
pub struct PreviewComponent {
    /// The file name to preview
    pub path: PathBuf,
    /// The name of the component within that file.
    /// If None, then the last component is going to be shown.
    pub component: Option<String>,

    /// The list of include paths
    pub include_paths: Vec<std::path::PathBuf>,

    /// The style name for the preview
    pub style: String,
}

#[derive(Default)]
struct ContentCache {
    source_code: HashMap<PathBuf, String>,
    dependency: HashSet<PathBuf>,
    current: PreviewComponent,
    sender: Option<crate::ServerNotifier>,
    highlight: Option<(PathBuf, u32)>,
}

static CONTENT_CACHE: once_cell::sync::OnceCell<Mutex<ContentCache>> =
    once_cell::sync::OnceCell::new();

pub fn set_contents(path: &Path, content: String) {
    let mut cache = CONTENT_CACHE.get_or_init(Default::default).lock().unwrap();
    cache.source_code.insert(path.to_owned(), content);
    if cache.dependency.contains(path) {
        let current = cache.current.clone();
        let sender = cache.sender.clone();
        drop(cache);
        if let Some(sender) = sender {
            load_preview(sender, current, PostLoadBehavior::DoNothing);
        }
    }
}

pub fn config_changed(config: &CompilerConfiguration) {
    if let Some(cache) = CONTENT_CACHE.get() {
        let mut cache = cache.lock().unwrap();
        let style = config.style.clone().unwrap_or_default();
        if cache.current.style != style || cache.current.include_paths != config.include_paths {
            cache.current.style = style;
            cache.current.include_paths = config.include_paths.clone();
            let current = cache.current.clone();
            let sender = cache.sender.clone();
            drop(cache);
            if let Some(sender) = sender {
                load_preview(sender, current, PostLoadBehavior::DoNothing);
            }
        }
    };
}

/// If the file is in the cache, returns it.
/// In any was, register it as a dependency
fn get_file_from_cache(path: PathBuf) -> Option<String> {
    let mut cache = CONTENT_CACHE.get_or_init(Default::default).lock().unwrap();
    let r = cache.source_code.get(&path).cloned();
    cache.dependency.insert(path);
    r
}

#[derive(Default)]
struct PreviewState {
    handle: Option<slint_interpreter::ComponentInstance>,
}
thread_local! {static PREVIEW_STATE: std::cell::RefCell<PreviewState> = Default::default();}

async fn reload_preview(
    sender: crate::ServerNotifier,
    preview_component: PreviewComponent,
    post_load_behavior: PostLoadBehavior,
) {
    send_notification(&sender, "Loading Preview…", Health::Ok);

    {
        let mut cache = CONTENT_CACHE.get_or_init(Default::default).lock().unwrap();
        cache.dependency.clear();
        cache.current = preview_component.clone();
    }

    let mut builder = slint_interpreter::ComponentCompiler::default();

    if !preview_component.style.is_empty() {
        builder.set_style(preview_component.style);
    }
    builder.set_include_paths(preview_component.include_paths);

    builder.set_file_loader(|path| {
        let path = path.to_owned();
        Box::pin(async move { get_file_from_cache(path).map(Result::Ok) })
    });

    let compiled = if let Some(mut from_cache) = get_file_from_cache(preview_component.path.clone())
    {
        if let Some(component) = &preview_component.component {
            from_cache =
                format!("{}\nexport component _Preview inherits {} {{ }}\n", from_cache, component);
        }
        builder.build_from_source(from_cache, preview_component.path).await
    } else {
        builder.build_from_path(preview_component.path).await
    };

    notify_diagnostics(builder.diagnostics(), &sender);

    if let Some(compiled) = compiled {
        PREVIEW_STATE.with(|preview_state| {
            let mut preview_state = preview_state.borrow_mut();
            let handle = if let Some(handle) = preview_state.handle.take() {
                let window = handle.window();
                let handle = compiled.create_with_existing_window(window);
                match post_load_behavior {
                    PostLoadBehavior::ShowAfterLoad => handle.show().unwrap(),
                    PostLoadBehavior::DoNothing => {}
                }
                handle
            } else {
                let handle = compiled.create().unwrap();
                handle.show().unwrap();
                handle
            };
            if let Some((path, offset)) =
                CONTENT_CACHE.get().and_then(|c| c.lock().unwrap().highlight.clone())
            {
                handle.highlight(path, offset);
            }
            preview_state.handle = Some(handle);
        });
        send_notification(&sender, "Preview Loaded", Health::Ok);
    } else {
        send_notification(&sender, "Preview not updated", Health::Error);
    }
    CONTENT_CACHE.get_or_init(Default::default).lock().unwrap().sender.replace(sender);
}

fn notify_diagnostics(
    diagnostics: &[slint_interpreter::Diagnostic],
    sender: &crate::ServerNotifier,
) -> Option<()> {
    let mut lsp_diags: HashMap<lsp_types::Url, Vec<lsp_types::Diagnostic>> = Default::default();
    for d in diagnostics {
        if d.source_file().map_or(true, |f| f.is_relative()) {
            continue;
        }
        let uri = lsp_types::Url::from_file_path(d.source_file().unwrap()).unwrap();
        lsp_diags.entry(uri).or_default().push(crate::util::to_lsp_diag(d));
    }

    for (uri, diagnostics) in lsp_diags {
        sender
            .send_notification(
                "textDocument/publishDiagnostics".into(),
                lsp_types::PublishDiagnosticsParams { uri, diagnostics, version: None },
            )
            .ok()?;
    }
    Some(())
}

fn send_notification(sender: &crate::ServerNotifier, arg: &str, health: Health) {
    sender
        .send_notification(
            ServerStatusNotification::METHOD.into(),
            ServerStatusParams { health, quiescent: false, message: Some(arg.into()) },
        )
        .unwrap_or_else(|e| eprintln!("Error sending notification: {:?}", e));
}

/// Highlight the element pointed at the offset in the path.
/// When path is None, remove the highlight.
pub fn highlight(path: Option<PathBuf>, offset: u32) {
    let highlight = path.map(|x| (x, offset));
    let mut cache = CONTENT_CACHE.get_or_init(Default::default).lock().unwrap();

    if cache.highlight == highlight {
        return;
    }
    cache.highlight = highlight;

    if cache.highlight.as_ref().map_or(true, |(path, _)| cache.dependency.contains(path)) {
        run_in_ui_thread(Box::pin(async move {
            PREVIEW_STATE.with(|preview_state| {
                let preview_state = preview_state.borrow();
                if let (Some(cache), Some(handle)) =
                    (CONTENT_CACHE.get(), preview_state.handle.as_ref())
                {
                    if let Some((path, offset)) = cache.lock().unwrap().highlight.clone() {
                        handle.highlight(path, offset);
                    } else {
                        handle.highlight(PathBuf::default(), 0);
                    }
                }
            })
        }))
    }
}