use anyhow::Result;
use notify::Watcher;
use rand::Rng;
use std::{
    fs::{self, File},
    io::{Read, Seek as _, SeekFrom, Write as _},
    path::{Path, PathBuf},
    sync::{Arc, atomic::AtomicBool},
};

use crate::emulator::{SimId, game_info::GameInfo, shrooms_vb_util::rom_from_isx};

pub struct Cart {
    pub file_path: PathBuf,
    pub rom: Vec<u8>,
    sram_file: File,
    pub sram: Vec<u8>,
    pub info: Arc<GameInfo>,
    watcher: Option<notify::RecommendedWatcher>,
    changed: Arc<AtomicBool>,
}

impl Cart {
    pub fn load(file_path: &Path, sim_id: SimId, watch: bool) -> Result<Self> {
        let rom = fs::read(file_path)?;
        let (rom, info) = try_parse_isx(file_path, &rom)
            .or_else(|| try_parse_elf(file_path, &rom))
            .unwrap_or_else(|| (rom, GameInfo::empty(file_path)));

        let mut sram_file = File::options()
            .read(true)
            .write(true)
            .create(true)
            .truncate(false)
            .open(sram_path(file_path, sim_id))?;

        let sram = if sram_file.metadata()?.len() == 0 {
            // new SRAM file, randomize the contents
            let mut sram = vec![0; 16 * 1024];
            let mut rng = rand::rng();
            for dst in sram.iter_mut().step_by(2) {
                *dst = rng.random();
            }
            sram
        } else {
            let mut sram = Vec::with_capacity(16 * 1024);
            sram_file.read_to_end(&mut sram)?;
            sram
        };

        let changed = Arc::new(AtomicBool::new(false));
        let watcher = if watch {
            build_watcher(file_path, changed.clone())
        } else {
            None
        };

        Ok(Cart {
            file_path: file_path.to_path_buf(),
            rom,
            sram_file,
            sram,
            info: Arc::new(info),
            watcher,
            changed,
        })
    }

    pub fn save_sram(&mut self) -> Result<()> {
        self.sram_file.seek(SeekFrom::Start(0))?;
        self.sram_file.write_all(&self.sram)?;
        Ok(())
    }

    pub fn changed(&self) -> bool {
        self.changed.load(std::sync::atomic::Ordering::Relaxed)
    }

    pub fn is_watching(&self) -> bool {
        self.watcher.is_some()
    }

    pub fn restart_watching(&mut self) {
        self.changed = Arc::new(AtomicBool::new(false));
        if let Some(mut watcher) = self.watcher.take() {
            let _ = watcher.unwatch(&self.file_path);
        };
        self.watcher = build_watcher(&self.file_path, self.changed.clone());
    }

    pub fn stop_watching(&mut self) {
        self.changed = Arc::new(AtomicBool::new(false));
        self.watcher = None;
    }
}

fn build_watcher(file_path: &Path, changed: Arc<AtomicBool>) -> Option<notify::RecommendedWatcher> {
    let file_path = file_path.to_path_buf();
    let mut watcher =
        notify::recommended_watcher(move |event: Result<notify::Event, notify::Error>| {
            let Ok(e) = event else {
                return;
            };
            let modified = !matches!(
                e.kind,
                notify::EventKind::Access(_)
                    | notify::EventKind::Modify(notify::event::ModifyKind::Metadata(_))
            );
            if modified {
                changed.store(true, std::sync::atomic::Ordering::Relaxed);
            }
        })
        .ok()?;
    watcher
        .watch(&file_path, notify::RecursiveMode::NonRecursive)
        .ok()?;
    Some(watcher)
}

fn try_parse_isx(file_path: &Path, data: &[u8]) -> Option<(Vec<u8>, GameInfo)> {
    let rom = rom_from_isx(data)?;
    let info = GameInfo::from_isx(file_path, data);
    Some((rom, info))
}

fn try_parse_elf(file_path: &Path, data: &[u8]) -> Option<(Vec<u8>, GameInfo)> {
    use object::read::elf::FileHeader;
    let program = match object::FileKind::parse(data).ok()? {
        object::FileKind::Elf32 => {
            let header = object::elf::FileHeader32::parse(data).ok()?;
            parse_elf_program(header, data)?
        }
        object::FileKind::Elf64 => {
            let header = object::elf::FileHeader64::parse(data).ok()?;
            parse_elf_program(header, data)?
        }
        _ => return None,
    };
    let info = GameInfo::from_elf(file_path, data).unwrap_or_else(|_| GameInfo::empty(file_path));
    Some((program, info))
}

fn parse_elf_program<Elf: object::read::elf::FileHeader<Endian = object::Endianness>>(
    header: &Elf,
    data: &[u8],
) -> Option<Vec<u8>> {
    use object::read::elf::ProgramHeader;
    let endian = header.endian().ok()?;
    let mut bytes = vec![];
    let mut pstart = None;
    for phdr in header.program_headers(endian, data).ok()? {
        let pma = phdr.p_paddr(endian).into();
        if pma < 0x07000000 || phdr.p_filesz(endian).into() == 0 {
            continue;
        }
        let start = pstart.unwrap_or(pma);
        pstart = Some(start);
        bytes.resize((pma - start) as usize, 0);
        let data = phdr.data(endian, data).ok()?;
        bytes.extend_from_slice(data);
    }
    Some(bytes)
}

fn sram_path(file_path: &Path, sim_id: SimId) -> PathBuf {
    match sim_id {
        SimId::Player1 => file_path.with_extension("p1.sram"),
        SimId::Player2 => file_path.with_extension("p2.sram"),
    }
}