// Copyright (C) 2022 François Laignel <fengalin@free.fr>
//
// This Source Code Form is subject to the terms of the Mozilla Public License, v2.0.
// If a copy of the MPL was not distributed with this file, You can obtain one at
// <https://mozilla.org/MPL/2.0/>.
//
// SPDX-License-Identifier: MPL-2.0

use futures::future::BoxFuture;
use futures::prelude::*;

use gst::glib;
use gst::prelude::*;
use gst::subclass::prelude::*;
use gst::EventView;

use once_cell::sync::Lazy;

use gstthreadshare::runtime::executor::block_on_or_add_sub_task;
use gstthreadshare::runtime::{prelude::*, PadSink};

use std::sync::{Arc, Mutex};
use std::time::Duration;

use super::super::{Settings, Stats, CAT};

#[derive(Debug, Default)]
struct PadSinkHandlerInner {
    is_flushing: bool,
    is_main_elem: bool,
    last_dts: Option<gst::ClockTime>,
    segment_start: Option<gst::ClockTime>,
    stats: Option<Box<Stats>>,
}

impl PadSinkHandlerInner {
    fn handle_buffer(
        &mut self,
        elem: &super::AsyncMutexSink,
        buffer: gst::Buffer,
    ) -> Result<(), gst::FlowError> {
        if self.is_flushing {
            log_or_trace!(
                CAT,
                self.is_main_elem,
                obj: elem,
                "Discarding {buffer:?} (flushing)"
            );

            return Err(gst::FlowError::Flushing);
        }

        debug_or_trace!(CAT, self.is_main_elem, obj: elem, "Received {buffer:?}");

        let dts = buffer
            .dts()
            .expect("Buffer without dts")
            .checked_sub(self.segment_start.expect("Buffer without Time Segment"))
            .expect("dts before Segment start");

        if let Some(last_dts) = self.last_dts {
            let cur_ts = elem.current_running_time().unwrap();
            let latency: Duration = (cur_ts - dts).into();
            let interval: Duration = (dts - last_dts).into();

            if let Some(stats) = self.stats.as_mut() {
                stats.add_buffer(latency, interval);
            }

            debug_or_trace!(CAT, self.is_main_elem, obj: elem, "o latency {latency:.2?}");
            debug_or_trace!(
                CAT,
                self.is_main_elem,
                obj: elem,
                "o interval {interval:.2?}",
            );
        }

        self.last_dts = Some(dts);

        log_or_trace!(CAT, self.is_main_elem, obj: elem, "Buffer processed");

        Ok(())
    }
}

#[derive(Clone, Debug, Default)]
struct AsyncPadSinkHandler(Arc<futures::lock::Mutex<PadSinkHandlerInner>>);

impl PadSinkHandler for AsyncPadSinkHandler {
    type ElementImpl = AsyncMutexSink;

    fn sink_chain(
        self,
        _pad: gst::Pad,
        elem: super::AsyncMutexSink,
        buffer: gst::Buffer,
    ) -> BoxFuture<'static, Result<gst::FlowSuccess, gst::FlowError>> {
        async move {
            if self.0.lock().await.handle_buffer(&elem, buffer).is_err() {
                return Err(gst::FlowError::Flushing);
            }

            Ok(gst::FlowSuccess::Ok)
        }
        .boxed()
    }

    fn sink_event_serialized(
        self,
        _pad: gst::Pad,
        elem: super::AsyncMutexSink,
        event: gst::Event,
    ) -> BoxFuture<'static, bool> {
        async move {
            match event.view() {
                EventView::Eos(_) => {
                    {
                        let mut inner = self.0.lock().await;
                        debug_or_trace!(CAT, inner.is_main_elem, obj: elem, "EOS");
                        inner.is_flushing = true;
                    }

                    // When each element sends its own EOS message,
                    // it takes ages for the pipeline to process all of them.
                    // Let's just post an error message and let main shuts down
                    // after all streams have posted this message.
                    let _ = elem
                        .post_message(gst::message::Error::new(gst::LibraryError::Shutdown, "EOS"));
                }
                EventView::FlushStop(_) => {
                    self.0.lock().await.is_flushing = false;
                }
                EventView::Segment(evt) => {
                    if let Some(time_seg) = evt.segment().downcast_ref::<gst::ClockTime>() {
                        self.0.lock().await.segment_start = time_seg.start();
                    }
                }
                EventView::SinkMessage(evt) => {
                    let _ = elem.post_message(evt.message());
                }
                _ => (),
            }

            true
        }
        .boxed()
    }

    fn sink_event(self, _pad: &gst::Pad, _imp: &AsyncMutexSink, event: gst::Event) -> bool {
        if let EventView::FlushStart(..) = event.view() {
            block_on_or_add_sub_task(async move { self.0.lock().await.is_flushing = true });
        }

        true
    }
}

impl AsyncPadSinkHandler {
    fn prepare(&self, is_main_elem: bool, stats: Option<Stats>) {
        futures::executor::block_on(async move {
            let mut inner = self.0.lock().await;
            inner.is_main_elem = is_main_elem;
            inner.stats = stats.map(Box::new);
        });
    }

    fn start(&self) {
        futures::executor::block_on(async move {
            let mut inner = self.0.lock().await;

            inner.is_flushing = false;
            inner.last_dts = None;

            if let Some(stats) = inner.stats.as_mut() {
                stats.start();
            }
        });
    }

    fn stop(&self) {
        futures::executor::block_on(async move {
            let mut inner = self.0.lock().await;
            inner.is_flushing = true;
        });
    }
}

#[derive(Debug)]
pub struct AsyncMutexSink {
    sink_pad: PadSink,
    sink_pad_handler: AsyncPadSinkHandler,
    settings: Mutex<Settings>,
}

impl AsyncMutexSink {
    fn prepare(&self) -> Result<(), gst::ErrorMessage> {
        let settings = self.settings.lock().unwrap();
        debug_or_trace!(CAT, settings.is_main_elem, imp: self, "Preparing");
        let stats = if settings.logs_stats {
            Some(Stats::new(
                settings.max_buffers,
                settings.push_period + settings.context_wait / 2,
            ))
        } else {
            None
        };

        self.sink_pad_handler.prepare(settings.is_main_elem, stats);
        debug_or_trace!(CAT, settings.is_main_elem, imp: self, "Prepared");

        Ok(())
    }

    fn stop(&self) -> Result<(), gst::ErrorMessage> {
        let is_main_elem = self.settings.lock().unwrap().is_main_elem;
        debug_or_trace!(CAT, is_main_elem, imp: self, "Stopping");
        self.sink_pad_handler.stop();
        debug_or_trace!(CAT, is_main_elem, imp: self, "Stopped");

        Ok(())
    }

    fn start(&self) -> Result<(), gst::ErrorMessage> {
        let is_main_elem = self.settings.lock().unwrap().is_main_elem;
        debug_or_trace!(CAT, is_main_elem, imp: self, "Starting");
        self.sink_pad_handler.start();
        debug_or_trace!(CAT, is_main_elem, imp: self, "Started");

        Ok(())
    }
}

#[glib::object_subclass]
impl ObjectSubclass for AsyncMutexSink {
    const NAME: &'static str = "TsStandaloneAsyncMutexSink";
    type Type = super::AsyncMutexSink;
    type ParentType = gst::Element;

    fn with_class(klass: &Self::Class) -> Self {
        let sink_pad_handler = AsyncPadSinkHandler::default();
        Self {
            sink_pad: PadSink::new(
                gst::Pad::from_template(&klass.pad_template("sink").unwrap()),
                sink_pad_handler.clone(),
            ),
            sink_pad_handler,
            settings: Default::default(),
        }
    }
}

impl ObjectImpl for AsyncMutexSink {
    fn properties() -> &'static [glib::ParamSpec] {
        static PROPERTIES: Lazy<Vec<glib::ParamSpec>> = Lazy::new(Settings::properties);
        PROPERTIES.as_ref()
    }

    fn set_property(&self, id: usize, value: &glib::Value, pspec: &glib::ParamSpec) {
        self.settings.lock().unwrap().set_property(id, value, pspec);
    }

    fn property(&self, id: usize, pspec: &glib::ParamSpec) -> glib::Value {
        self.settings.lock().unwrap().property(id, pspec)
    }

    fn constructed(&self) {
        self.parent_constructed();

        let obj = self.obj();
        obj.add_pad(self.sink_pad.gst_pad()).unwrap();
        obj.set_element_flags(gst::ElementFlags::SINK);
    }
}

impl GstObjectImpl for AsyncMutexSink {}

impl ElementImpl for AsyncMutexSink {
    fn metadata() -> Option<&'static gst::subclass::ElementMetadata> {
        static ELEMENT_METADATA: Lazy<gst::subclass::ElementMetadata> = Lazy::new(|| {
            gst::subclass::ElementMetadata::new(
                "Thread-sharing standalone test async mutex sink",
                "Sink/Test",
                "Thread-sharing standalone test async mutex sink",
                "François Laignel <fengalin@free.fr>",
            )
        });

        Some(&*ELEMENT_METADATA)
    }

    fn pad_templates() -> &'static [gst::PadTemplate] {
        static PAD_TEMPLATES: Lazy<Vec<gst::PadTemplate>> = Lazy::new(|| {
            let caps = gst::Caps::new_any();

            let sink_pad_template = gst::PadTemplate::new(
                "sink",
                gst::PadDirection::Sink,
                gst::PadPresence::Always,
                &caps,
            )
            .unwrap();

            vec![sink_pad_template]
        });

        PAD_TEMPLATES.as_ref()
    }

    fn change_state(
        &self,
        transition: gst::StateChange,
    ) -> Result<gst::StateChangeSuccess, gst::StateChangeError> {
        gst::trace!(CAT, imp: self, "Changing state {transition:?}");

        match transition {
            gst::StateChange::NullToReady => {
                self.prepare().map_err(|err| {
                    self.post_error_message(err);
                    gst::StateChangeError
                })?;
            }
            gst::StateChange::ReadyToPaused => {
                self.start().map_err(|_| gst::StateChangeError)?;
            }
            gst::StateChange::PausedToReady => {
                self.stop().map_err(|_| gst::StateChangeError)?;
            }
            _ => (),
        }

        self.parent_change_state(transition)
    }
}