use nesemu::prelude::*;
use nesemu::{
    AudioOutput, HostConfig, InputProvider, JOYPAD_BUTTONS_COUNT, NullAudio, NullInput, NullVideo,
    RuntimeError, VideoOutput,
};

#[derive(Clone, Copy)]
struct Fnv1a64 {
    state: u64,
}

impl Fnv1a64 {
    const OFFSET_BASIS: u64 = 0xcbf2_9ce4_8422_2325;
    const PRIME: u64 = 0x0000_0100_0000_01b3;

    const fn new() -> Self {
        Self {
            state: Self::OFFSET_BASIS,
        }
    }

    fn update(&mut self, bytes: &[u8]) {
        for &b in bytes {
            self.state ^= u64::from(b);
            self.state = self.state.wrapping_mul(Self::PRIME);
        }
    }

    const fn finish(self) -> u64 {
        self.state
    }
}

fn nrom_test_rom() -> Vec<u8> {
    let mut rom = vec![0u8; 16 + 16 * 1024 + 8 * 1024];
    rom[0..4].copy_from_slice(b"NES\x1A");
    rom[4] = 1;
    rom[5] = 1;

    let prg_offset = 16;
    let reset_vec = prg_offset + 0x3FFC;
    rom[reset_vec] = 0x00;
    rom[reset_vec + 1] = 0x80;

    rom[prg_offset] = 0xEA;
    rom[prg_offset + 1] = 0x4C;
    rom[prg_offset + 2] = 0x00;
    rom[prg_offset + 3] = 0x80;
    rom
}

struct FixedInput;

impl InputProvider for FixedInput {
    fn poll_buttons(&mut self) -> [bool; JOYPAD_BUTTONS_COUNT] {
        [true, false, false, false, false, false, false, false]
    }
}

#[derive(Default)]
struct CountingVideo {
    frames: usize,
    last_hash: u64,
}

impl VideoOutput for CountingVideo {
    fn present_rgba(&mut self, frame: &[u8], _width: usize, _height: usize) {
        self.frames = self.frames.saturating_add(1);
        let mut hasher = Fnv1a64::new();
        hasher.update(frame);
        self.last_hash = hasher.finish();
    }
}

struct CountingAudio {
    samples: usize,
    hash: u64,
}

impl Default for CountingAudio {
    fn default() -> Self {
        Self {
            samples: 0,
            hash: Fnv1a64::new().finish(),
        }
    }
}

impl AudioOutput for CountingAudio {
    fn push_samples(&mut self, samples: &[f32]) {
        self.samples = self.samples.saturating_add(samples.len());
        let mut hasher = Fnv1a64 { state: self.hash };
        for sample in samples {
            hasher.update(&sample.to_le_bytes());
        }
        self.hash = hasher.finish();
    }
}

#[test]
fn public_api_load_run_input_frame_flow() {
    let rom = nrom_test_rom();
    let runtime = NesRuntime::from_rom_bytes(&rom).expect("runtime init");
    let mut host = RuntimeHostLoop::with_config(runtime, HostConfig::new(48_000, false));

    let mut input = FixedInput;
    let mut video = CountingVideo::default();
    let mut audio = CountingAudio::default();

    let first = host
        .run_frame_unpaced(&mut input, &mut video, &mut audio)
        .expect("frame 1");
    let second = host
        .run_frame_unpaced(&mut input, &mut video, &mut audio)
        .expect("frame 2");

    assert_eq!(first.frame_number, 1);
    assert_eq!(second.frame_number, 2);
    assert_eq!(video.frames, 2);
    assert!(audio.samples > 0);
}

#[test]
fn public_api_invalid_state_is_reported() {
    let rom = nrom_test_rom();
    let mut runtime = NesRuntime::from_rom_bytes(&rom).expect("runtime init");
    runtime.run_until_frame_complete().expect("frame");

    let mut state = runtime.save_state();
    state[0] ^= 0xFF;

    let err = runtime
        .load_state(&state)
        .expect_err("must reject bad state");
    assert!(matches!(err, RuntimeError::InvalidState(_)));
}

#[test]
fn public_api_headless_client_loop_smoke_1000_frames() {
    let rom = nrom_test_rom();
    let runtime = NesRuntime::from_rom_bytes(&rom).expect("runtime init");
    let mut host = RuntimeHostLoop::with_config(runtime, HostConfig::new(48_000, false));

    let total_samples = host
        .run_frames_unpaced(1_000, &mut NullInput, &mut NullVideo, &mut NullAudio)
        .expect("run frames");

    assert_eq!(host.runtime().frame_number(), 1_000);
    assert!(total_samples > 0);
}

#[test]
fn public_api_client_pause_resume_contract() {
    let rom = nrom_test_rom();
    let runtime = NesRuntime::from_rom_bytes(&rom).expect("runtime init");
    let mut client = ClientRuntime::with_config(runtime, HostConfig::new(48_000, false));

    let mut input = FixedInput;
    let mut video = CountingVideo::default();
    let mut audio = CountingAudio::default();

    client.pause();
    let skipped = client
        .tick(&mut input, &mut video, &mut audio)
        .expect("tick");
    assert!(skipped.is_none());

    let stepped = client
        .step_frame(&mut input, &mut video, &mut audio)
        .expect("step");
    assert_eq!(stepped.frame_number, 1);

    client.resume();
    let ticked = client
        .tick(&mut input, &mut video, &mut audio)
        .expect("tick")
        .expect("running tick");
    assert_eq!(ticked.frame_number, 2);
}

#[test]
fn public_api_audio_timing_within_expected_drift() {
    let rom = nrom_test_rom();
    let runtime = NesRuntime::from_rom_bytes(&rom).expect("runtime init");
    let mode = runtime.video_mode();
    let mut host = RuntimeHostLoop::with_config(runtime, HostConfig::new(48_000, false));

    let total_samples = host
        .run_frames_unpaced(1_200, &mut NullInput, &mut NullVideo, &mut NullAudio)
        .expect("run frames");

    let expected = ((host.runtime().frame_number() as f64) * 48_000.0 / mode.frame_hz()).round();
    let drift_pct = ((total_samples as f64 - expected).abs() / expected) * 100.0;

    assert!(
        drift_pct <= 2.5,
        "audio drift too high: {drift_pct:.3}% (samples={total_samples}, expected={expected:.0})"
    );
}

#[test]
fn public_api_regression_hashes_for_reference_rom() {
    let rom = nrom_test_rom();
    let runtime = NesRuntime::from_rom_bytes(&rom).expect("runtime init");
    let mut host = RuntimeHostLoop::with_config(runtime, HostConfig::new(48_000, false));

    let mut input = FixedInput;
    let mut video = CountingVideo::default();
    let mut audio = CountingAudio::default();

    host.run_frames_unpaced(120, &mut input, &mut video, &mut audio)
        .expect("run frames");

    let expected_frame_hash = 0x42d1_20e3_54e0_a325_u64;
    let expected_audio_hash = 0xa075_8dd6_adea_e775_u64;

    assert_eq!(
        video.last_hash, expected_frame_hash,
        "update expected frame hash to 0x{:016x}",
        video.last_hash
    );
    assert_eq!(
        audio.hash, expected_audio_hash,
        "update expected audio hash to 0x{:016x}",
        audio.hash
    );
}