use std::{
    collections::HashMap,
    fs,
    path::{Path, PathBuf},
    sync::{
        atomic::{AtomicBool, AtomicUsize, Ordering},
        mpsc::{self, RecvError, TryRecvError},
        Arc,
    },
};

use anyhow::Result;

use crate::{audio::Audio, graphics::TextureSink};
use shrooms_vb_core::Sim;
pub use shrooms_vb_core::VBKey;

mod shrooms_vb_core;

pub struct EmulatorBuilder {
    rom: Option<PathBuf>,
    commands: mpsc::Receiver<EmulatorCommand>,
    sim_count: Arc<AtomicUsize>,
    running: Arc<[AtomicBool; 2]>,
    has_game: Arc<[AtomicBool; 2]>,
    linked: Arc<AtomicBool>,
}

#[derive(PartialEq, Eq, Hash, Clone, Copy, Debug)]
pub enum SimId {
    Player1,
    Player2,
}
impl SimId {
    pub const fn values() -> [Self; 2] {
        [Self::Player1, Self::Player2]
    }
    pub const fn to_index(self) -> usize {
        match self {
            Self::Player1 => 0,
            Self::Player2 => 1,
        }
    }
}

impl EmulatorBuilder {
    pub fn new() -> (Self, EmulatorClient) {
        let (queue, commands) = mpsc::channel();
        let builder = Self {
            rom: None,
            commands,
            sim_count: Arc::new(AtomicUsize::new(0)),
            running: Arc::new([AtomicBool::new(false), AtomicBool::new(false)]),
            has_game: Arc::new([AtomicBool::new(false), AtomicBool::new(false)]),
            linked: Arc::new(AtomicBool::new(false)),
        };
        let client = EmulatorClient {
            queue,
            sim_count: builder.sim_count.clone(),
            running: builder.running.clone(),
            has_game: builder.has_game.clone(),
            linked: builder.linked.clone(),
        };
        (builder, client)
    }

    pub fn with_rom(self, path: &Path) -> Self {
        Self {
            rom: Some(path.into()),
            ..self
        }
    }

    pub fn build(self) -> Result<Emulator> {
        let mut emulator = Emulator::new(
            self.commands,
            self.sim_count,
            self.running,
            self.has_game,
            self.linked,
        )?;
        if let Some(path) = self.rom {
            emulator.load_rom(SimId::Player1, &path)?;
        }
        Ok(emulator)
    }
}

pub struct Emulator {
    sims: Vec<Sim>,
    audio: Audio,
    commands: mpsc::Receiver<EmulatorCommand>,
    sim_count: Arc<AtomicUsize>,
    running: Arc<[AtomicBool; 2]>,
    has_game: Arc<[AtomicBool; 2]>,
    linked: Arc<AtomicBool>,
    renderers: HashMap<SimId, TextureSink>,
}

impl Emulator {
    fn new(
        commands: mpsc::Receiver<EmulatorCommand>,
        sim_count: Arc<AtomicUsize>,
        running: Arc<[AtomicBool; 2]>,
        has_game: Arc<[AtomicBool; 2]>,
        linked: Arc<AtomicBool>,
    ) -> Result<Self> {
        Ok(Self {
            sims: vec![],
            audio: Audio::init()?,
            commands,
            sim_count,
            running,
            has_game,
            linked,
            renderers: HashMap::new(),
        })
    }

    pub fn load_rom(&mut self, sim_id: SimId, path: &Path) -> Result<()> {
        let bytes = fs::read(path)?;
        self.reset_sim(sim_id, Some(bytes))?;
        Ok(())
    }

    pub fn start_second_sim(&mut self, rom: Option<PathBuf>) -> Result<()> {
        let bytes = if let Some(path) = rom {
            Some(fs::read(path)?)
        } else {
            self.sims.first().and_then(|s| s.clone_rom())
        };
        self.reset_sim(SimId::Player2, bytes)?;
        self.link_sims();
        Ok(())
    }

    fn reset_sim(&mut self, sim_id: SimId, new_rom: Option<Vec<u8>>) -> Result<()> {
        let index = sim_id.to_index();
        while self.sims.len() <= index {
            self.sims.push(Sim::new());
        }
        self.sim_count.store(self.sims.len(), Ordering::Relaxed);
        let sim = &mut self.sims[index];
        sim.reset();
        if let Some(bytes) = new_rom {
            sim.load_rom(bytes)?;
            self.has_game[index].store(true, Ordering::Release);
        }
        if self.has_game[index].load(Ordering::Acquire) {
            self.running[index].store(true, Ordering::Release);
        }
        Ok(())
    }

    fn link_sims(&mut self) {
        let (first, second) = self.sims.split_at_mut(1);
        let Some(first) = first.first_mut() else {
            return;
        };
        let Some(second) = second.first_mut() else {
            return;
        };
        first.link(second);
        self.linked.store(true, Ordering::Release);
    }

    fn unlink_sims(&mut self) {
        let Some(first) = self.sims.first_mut() else {
            return;
        };
        first.unlink();
        self.linked.store(false, Ordering::Release);
    }

    pub fn stop_second_sim(&mut self) {
        self.renderers.remove(&SimId::Player2);
        self.sims.truncate(1);
        self.sim_count.store(self.sims.len(), Ordering::Relaxed);
        self.running[SimId::Player2.to_index()].store(false, Ordering::Release);
        self.has_game[SimId::Player2.to_index()].store(false, Ordering::Release);
        self.linked.store(false, Ordering::Release);
    }

    pub fn run(&mut self) {
        let mut eye_contents = vec![0u8; 384 * 224 * 2];
        let mut audio_samples = vec![];
        loop {
            let p1_running = self.running[SimId::Player1.to_index()].load(Ordering::Acquire);
            let p2_running = self.running[SimId::Player2.to_index()].load(Ordering::Acquire);
            let mut idle = p1_running || p2_running;
            if p1_running && p2_running {
                Sim::emulate_many(&mut self.sims);
            } else if p1_running {
                self.sims[SimId::Player1.to_index()].emulate();
            } else if p2_running {
                self.sims[SimId::Player2.to_index()].emulate();
            }

            for sim_id in SimId::values() {
                let Some(renderer) = self.renderers.get_mut(&sim_id) else {
                    continue;
                };
                let Some(sim) = self.sims.get_mut(sim_id.to_index()) else {
                    continue;
                };
                if sim.read_pixels(&mut eye_contents) {
                    idle = false;
                    if renderer.queue_render(&eye_contents).is_err() {
                        self.renderers.remove(&sim_id);
                    }
                }
            }
            let weight = 1.0 / self.sims.len() as f32;
            for sim in self.sims.iter_mut() {
                sim.read_samples(&mut audio_samples, weight);
            }
            if !audio_samples.is_empty() {
                idle = false;
                self.audio.update(&audio_samples);
                audio_samples.clear();
            }
            if idle {
                // The game is paused, and we have output all the video/audio we have.
                // Block the thread until a new command comes in.
                match self.commands.recv() {
                    Ok(command) => self.handle_command(command),
                    Err(RecvError) => {
                        return;
                    }
                }
            }
            loop {
                match self.commands.try_recv() {
                    Ok(command) => self.handle_command(command),
                    Err(TryRecvError::Empty) => {
                        break;
                    }
                    Err(TryRecvError::Disconnected) => {
                        return;
                    }
                }
            }
        }
    }

    fn handle_command(&mut self, command: EmulatorCommand) {
        match command {
            EmulatorCommand::SetRenderer(sim_id, renderer) => {
                self.renderers.insert(sim_id, renderer);
            }
            EmulatorCommand::LoadGame(sim_id, path) => {
                if let Err(error) = self.load_rom(sim_id, &path) {
                    eprintln!("error loading rom: {}", error);
                }
            }
            EmulatorCommand::StartSecondSim(path) => {
                if let Err(error) = self.start_second_sim(path) {
                    eprintln!("error starting second sim: {}", error);
                }
            }
            EmulatorCommand::StopSecondSim => {
                self.stop_second_sim();
            }
            EmulatorCommand::Pause => {
                for sim in SimId::values() {
                    self.running[sim.to_index()].store(false, Ordering::Release);
                }
            }
            EmulatorCommand::Resume => {
                for sim_id in SimId::values() {
                    let index = sim_id.to_index();
                    if self.has_game[index].load(Ordering::Acquire) {
                        self.running[index].store(true, Ordering::Relaxed);
                    }
                }
            }
            EmulatorCommand::Link => {
                self.link_sims();
            }
            EmulatorCommand::Unlink => {
                self.unlink_sims();
            }
            EmulatorCommand::Reset(sim_id) => {
                if let Err(error) = self.reset_sim(sim_id, None) {
                    eprintln!("error resetting sim: {}", error);
                }
            }
            EmulatorCommand::SetKeys(sim_id, keys) => {
                if let Some(sim) = self.sims.get_mut(sim_id.to_index()) {
                    sim.set_keys(keys);
                }
            }
        }
    }
}

#[derive(Debug)]
pub enum EmulatorCommand {
    SetRenderer(SimId, TextureSink),
    LoadGame(SimId, PathBuf),
    StartSecondSim(Option<PathBuf>),
    StopSecondSim,
    Pause,
    Resume,
    Link,
    Unlink,
    Reset(SimId),
    SetKeys(SimId, VBKey),
}

#[derive(Clone)]
pub struct EmulatorClient {
    queue: mpsc::Sender<EmulatorCommand>,
    sim_count: Arc<AtomicUsize>,
    running: Arc<[AtomicBool; 2]>,
    has_game: Arc<[AtomicBool; 2]>,
    linked: Arc<AtomicBool>,
}

impl EmulatorClient {
    pub fn has_player_2(&self) -> bool {
        self.sim_count.load(Ordering::Acquire) == 2
    }
    pub fn is_running(&self, sim_id: SimId) -> bool {
        self.running[sim_id.to_index()].load(Ordering::Acquire)
    }
    pub fn has_game(&self, sim_id: SimId) -> bool {
        self.has_game[sim_id.to_index()].load(Ordering::Acquire)
    }
    pub fn are_sims_linked(&self) -> bool {
        self.linked.load(Ordering::Acquire)
    }
    pub fn send_command(&self, command: EmulatorCommand) {
        if let Err(err) = self.queue.send(command) {
            eprintln!(
                "could not send command {:?} as emulator is shut down",
                err.0
            );
        }
    }
}