use crate::asset::{AssetEntry, BankType};
use crate::cartridge::{
    ASSETS_PA_MAGIC, ASSETS_PA_PRELUDE_SIZE, ASSETS_PA_SCHEMA_VERSION, AssetsPackHeader,
    AssetsPackPrelude, AssetsPayloadSource, Capability, Cartridge, CartridgeDTO, CartridgeError,
    CartridgeManifest,
};
use crate::syscalls::{CapFlags, caps};
use std::collections::HashSet;
use std::fs;
use std::io::{Read, Seek, SeekFrom};
use std::path::Path;

pub struct CartridgeLoader;

impl CartridgeLoader {
    pub fn load(path: impl AsRef<Path>) -> Result<Cartridge, CartridgeError> {
        let path = path.as_ref();
        if !path.exists() {
            return Err(CartridgeError::NotFound);
        }

        if path.is_dir() {
            DirectoryCartridgeLoader::load(path)
        } else if path.extension().is_some_and(|ext| ext == "pmc") {
            PackedCartridgeLoader::load(path)
        } else {
            Err(CartridgeError::InvalidFormat)
        }
    }
}

pub struct DirectoryCartridgeLoader;

impl DirectoryCartridgeLoader {
    pub fn load(path: &Path) -> Result<Cartridge, CartridgeError> {
        let manifest_path = path.join("manifest.json");
        if !manifest_path.exists() {
            return Err(CartridgeError::InvalidManifest);
        }

        let manifest_content =
            fs::read_to_string(manifest_path).map_err(|_| CartridgeError::IoError)?;
        let manifest: CartridgeManifest =
            serde_json::from_str(&manifest_content).map_err(|_| CartridgeError::InvalidManifest)?;

        // Additional validation as per requirements
        if manifest.magic != "PMTU" {
            return Err(CartridgeError::InvalidManifest);
        }
        if manifest.cartridge_version != 1 {
            return Err(CartridgeError::UnsupportedVersion);
        }

        let capabilities = normalize_capabilities(&manifest.capabilities)?;

        let program_path = path.join("program.pbx");
        if !program_path.exists() {
            return Err(CartridgeError::MissingProgram);
        }

        let program = fs::read(program_path).map_err(|_| CartridgeError::IoError)?;

        let assets_pa_path = path.join("assets.pa");
        let (assets, asset_table, preload) = if assets_pa_path.exists() {
            let parsed = parse_assets_pack(&assets_pa_path)?;
            (
                AssetsPayloadSource::from_file(
                    assets_pa_path.clone(),
                    parsed.payload_offset,
                    parsed.payload_len,
                ),
                parsed.header.asset_table,
                parsed.header.preload,
            )
        } else {
            if capabilities & caps::ASSET != 0 {
                return Err(CartridgeError::MissingAssets);
            }

            (AssetsPayloadSource::empty(), Vec::new(), Vec::new())
        };

        let dto = CartridgeDTO {
            app_id: manifest.app_id,
            title: manifest.title,
            app_version: manifest.app_version,
            app_mode: manifest.app_mode,
            capabilities,
            program,
            assets,
            asset_table,
            preload,
        };

        Ok(Cartridge::from(dto))
    }
}

pub struct PackedCartridgeLoader;

impl PackedCartridgeLoader {
    pub fn load(_path: &Path) -> Result<Cartridge, CartridgeError> {
        Err(CartridgeError::InvalidFormat)
    }
}

fn normalize_capabilities(capabilities: &[Capability]) -> Result<CapFlags, CartridgeError> {
    let mut seen = HashSet::new();
    let mut normalized = caps::NONE;

    for capability in capabilities {
        if !seen.insert(*capability) {
            return Err(CartridgeError::InvalidManifest);
        }

        normalized |= match capability {
            Capability::None => caps::NONE,
            Capability::System => caps::SYSTEM,
            Capability::Gfx => caps::GFX,
            Capability::Audio => caps::AUDIO,
            Capability::Fs => caps::FS,
            Capability::Log => caps::LOG,
            Capability::Asset => caps::ASSET,
            Capability::Bank => caps::BANK,
            Capability::All => caps::ALL,
        };
    }

    Ok(normalized)
}

struct ParsedAssetsPack {
    header: AssetsPackHeader,
    payload_offset: u64,
    payload_len: u64,
}

fn parse_assets_pack(path: &Path) -> Result<ParsedAssetsPack, CartridgeError> {
    let mut file = fs::File::open(path).map_err(|_| CartridgeError::IoError)?;
    let mut prelude_bytes = [0_u8; ASSETS_PA_PRELUDE_SIZE];
    file.read_exact(&mut prelude_bytes).map_err(|_| CartridgeError::InvalidFormat)?;

    let prelude =
        AssetsPackPrelude::from_bytes(&prelude_bytes).ok_or(CartridgeError::InvalidFormat)?;

    if prelude.magic != ASSETS_PA_MAGIC || prelude.schema_version != ASSETS_PA_SCHEMA_VERSION {
        return Err(CartridgeError::InvalidFormat);
    }

    let header_start = ASSETS_PA_PRELUDE_SIZE;
    let header_len =
        usize::try_from(prelude.header_len).map_err(|_| CartridgeError::InvalidFormat)?;
    let header_end = header_start.checked_add(header_len).ok_or(CartridgeError::InvalidFormat)?;
    let payload_offset =
        usize::try_from(prelude.payload_offset).map_err(|_| CartridgeError::InvalidFormat)?;
    let file_len = usize::try_from(file.metadata().map_err(|_| CartridgeError::IoError)?.len())
        .map_err(|_| CartridgeError::InvalidFormat)?;

    if payload_offset < header_start || header_end > file_len || payload_offset > file_len {
        return Err(CartridgeError::InvalidFormat);
    }
    if header_end != payload_offset {
        return Err(CartridgeError::InvalidFormat);
    }

    file.seek(SeekFrom::Start(header_start as u64)).map_err(|_| CartridgeError::IoError)?;
    let mut header_bytes = vec![0_u8; header_len];
    file.read_exact(&mut header_bytes).map_err(|_| CartridgeError::InvalidFormat)?;
    let header: AssetsPackHeader =
        serde_json::from_slice(&header_bytes).map_err(|_| CartridgeError::InvalidFormat)?;
    validate_preload(&header.asset_table, &header.preload)?;
    let payload_len =
        u64::try_from(file_len - payload_offset).map_err(|_| CartridgeError::InvalidFormat)?;

    Ok(ParsedAssetsPack { header, payload_offset: prelude.payload_offset, payload_len })
}

fn validate_preload(
    asset_table: &[AssetEntry],
    preload: &[crate::asset::PreloadEntry],
) -> Result<(), CartridgeError> {
    let mut claimed_slots = HashSet::<(BankType, usize)>::new();

    for item in preload {
        let entry = asset_table
            .iter()
            .find(|entry| entry.asset_id == item.asset_id)
            .ok_or(CartridgeError::InvalidFormat)?;

        if !claimed_slots.insert((entry.bank_type, item.slot)) {
            return Err(CartridgeError::InvalidFormat);
        }
    }

    Ok(())
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::asset::{AssetEntry, BankType, PreloadEntry};
    use crate::cartridge::{ASSETS_PA_MAGIC, ASSETS_PA_SCHEMA_VERSION, AssetsPackPrelude};
    use crate::tile_bank::TILE_BANK_PALETTE_COUNT_V1;
    use serde_json::json;
    use std::path::{Path, PathBuf};
    use std::sync::atomic::{AtomicU64, Ordering};
    use std::time::{SystemTime, UNIX_EPOCH};

    static TEST_DIR_COUNTER: AtomicU64 = AtomicU64::new(0);

    struct TestCartridgeDir {
        path: PathBuf,
    }

    impl TestCartridgeDir {
        fn new(manifest: serde_json::Value) -> Self {
            let unique = TEST_DIR_COUNTER.fetch_add(1, Ordering::Relaxed);
            let timestamp = SystemTime::now()
                .duration_since(UNIX_EPOCH)
                .expect("system time must be after unix epoch")
                .as_nanos();
            let path = std::env::temp_dir()
                .join(format!("prometeu-hal-cartridge-loader-{}-{}", timestamp, unique));

            fs::create_dir_all(&path).expect("must create temporary cartridge directory");
            fs::write(
                path.join("manifest.json"),
                serde_json::to_vec_pretty(&manifest).expect("manifest must serialize"),
            )
            .expect("must write manifest.json");
            fs::write(path.join("program.pbx"), [0x01_u8, 0x02, 0x03]).expect("must write program");

            Self { path }
        }

        fn path(&self) -> &Path {
            &self.path
        }

        fn write_assets_pa(
            &self,
            asset_table: Vec<AssetEntry>,
            preload: Vec<PreloadEntry>,
            payload: &[u8],
        ) {
            let header = serde_json::to_vec(&AssetsPackHeader { asset_table, preload })
                .expect("assets header must serialize");
            let payload_offset = (ASSETS_PA_PRELUDE_SIZE + header.len()) as u64;
            let prelude = AssetsPackPrelude {
                magic: ASSETS_PA_MAGIC,
                schema_version: ASSETS_PA_SCHEMA_VERSION,
                header_len: header.len() as u32,
                payload_offset,
                flags: 0,
                reserved: 0,
                header_checksum: 0,
            };

            let mut bytes = prelude.to_bytes().to_vec();
            bytes.extend_from_slice(&header);
            bytes.extend_from_slice(payload);
            fs::write(self.path.join("assets.pa"), bytes).expect("must write assets.pa");
        }
    }

    impl Drop for TestCartridgeDir {
        fn drop(&mut self) {
            let _ = fs::remove_dir_all(&self.path);
        }
    }

    fn manifest_with_capabilities(capabilities: Option<Vec<&str>>) -> serde_json::Value {
        let mut manifest = json!({
            "magic": "PMTU",
            "cartridge_version": 1,
            "app_id": 1001,
            "title": "Example",
            "app_version": "1.0.0",
            "app_mode": "Game"
        });

        if let Some(capabilities) = capabilities {
            manifest["capabilities"] = json!(capabilities);
        }

        manifest
    }

    #[test]
    fn load_without_capabilities_defaults_to_none() {
        let dir = TestCartridgeDir::new(manifest_with_capabilities(None));

        let cartridge = DirectoryCartridgeLoader::load(dir.path()).expect("cartridge must load");

        assert_eq!(cartridge.capabilities, caps::NONE);
    }

    #[test]
    fn load_with_single_capability_normalizes_to_flag() {
        let dir = TestCartridgeDir::new(manifest_with_capabilities(Some(vec!["gfx"])));

        let cartridge = DirectoryCartridgeLoader::load(dir.path()).expect("cartridge must load");

        assert_eq!(cartridge.capabilities, caps::GFX);
    }

    #[test]
    fn load_with_multiple_capabilities_combines_flags() {
        let dir = TestCartridgeDir::new(manifest_with_capabilities(Some(vec!["gfx", "audio"])));

        let cartridge = DirectoryCartridgeLoader::load(dir.path()).expect("cartridge must load");

        assert_eq!(cartridge.capabilities, caps::GFX | caps::AUDIO);
    }

    #[test]
    fn load_with_all_capability_normalizes_to_all_flags() {
        let dir = TestCartridgeDir::new(manifest_with_capabilities(Some(vec!["all"])));
        dir.write_assets_pa(vec![], vec![], &[]);

        let cartridge = DirectoryCartridgeLoader::load(dir.path()).expect("cartridge must load");

        assert_eq!(cartridge.capabilities, caps::ALL);
    }

    #[test]
    fn load_with_none_capability_keeps_zero_flags() {
        let dir = TestCartridgeDir::new(manifest_with_capabilities(Some(vec!["none"])));

        let cartridge = DirectoryCartridgeLoader::load(dir.path()).expect("cartridge must load");

        assert_eq!(cartridge.capabilities, caps::NONE);
    }

    #[test]
    fn load_with_duplicate_capabilities_fails() {
        let dir = TestCartridgeDir::new(manifest_with_capabilities(Some(vec!["gfx", "gfx"])));

        let error = DirectoryCartridgeLoader::load(dir.path()).unwrap_err();

        assert!(matches!(error, CartridgeError::InvalidManifest));
    }

    #[test]
    fn load_with_unknown_capability_fails() {
        let dir = TestCartridgeDir::new(manifest_with_capabilities(Some(vec!["network"])));

        let error = DirectoryCartridgeLoader::load(dir.path()).unwrap_err();

        assert!(matches!(error, CartridgeError::InvalidManifest));
    }

    #[test]
    fn load_with_legacy_input_capability_fails() {
        let dir = TestCartridgeDir::new(manifest_with_capabilities(Some(vec!["input"])));

        let error = DirectoryCartridgeLoader::load(dir.path()).unwrap_err();

        assert!(matches!(error, CartridgeError::InvalidManifest));
    }

    fn test_asset_entry(offset: u64, size: u64) -> AssetEntry {
        AssetEntry {
            asset_id: 7,
            asset_name: "tiles".to_string(),
            bank_type: BankType::TILES,
            offset,
            size,
            decoded_size: 16 * 16 + (TILE_BANK_PALETTE_COUNT_V1 as u64 * 16 * 2),
            codec: "NONE".to_string(),
            metadata: json!({
                "tile_size": 16,
                "width": 16,
                "height": 16,
                "palette_count": TILE_BANK_PALETTE_COUNT_V1
            }),
        }
    }

    #[test]
    fn load_with_asset_capability_requires_assets_pa() {
        let dir = TestCartridgeDir::new(manifest_with_capabilities(Some(vec!["asset"])));

        let error = DirectoryCartridgeLoader::load(dir.path()).unwrap_err();

        assert!(matches!(error, CartridgeError::MissingAssets));
    }

    #[test]
    fn load_without_asset_capability_accepts_missing_assets_pa() {
        let dir = TestCartridgeDir::new(manifest_with_capabilities(Some(vec!["gfx"])));

        let cartridge = DirectoryCartridgeLoader::load(dir.path()).expect("cartridge must load");

        assert!(cartridge.assets.is_empty());
        assert!(cartridge.asset_table.is_empty());
        assert!(cartridge.preload.is_empty());
    }

    #[test]
    fn load_reads_asset_table_and_preload_from_assets_pa_header() {
        let dir = TestCartridgeDir::new(manifest_with_capabilities(Some(vec!["asset"])));
        let payload = vec![1_u8, 2, 3, 4];
        dir.write_assets_pa(
            vec![test_asset_entry(0, payload.len() as u64)],
            vec![PreloadEntry { asset_id: 7, slot: 2 }],
            &payload,
        );

        let cartridge = DirectoryCartridgeLoader::load(dir.path()).expect("cartridge must load");

        let slice = cartridge
            .assets
            .open_slice(0, payload.len() as u64)
            .expect("payload slice must open")
            .read_all()
            .expect("payload slice must read");
        assert_eq!(slice, payload);
        assert_eq!(cartridge.asset_table.len(), 1);
        assert_eq!(cartridge.asset_table[0].asset_name, "tiles");
        assert_eq!(cartridge.preload.len(), 1);
        assert_eq!(cartridge.preload[0].asset_id, 7);
        assert_eq!(cartridge.preload[0].slot, 2);
    }

    #[test]
    fn load_rejects_preload_with_missing_asset_id() {
        let dir = TestCartridgeDir::new(manifest_with_capabilities(Some(vec!["asset"])));
        dir.write_assets_pa(
            vec![test_asset_entry(0, 4)],
            vec![PreloadEntry { asset_id: 999, slot: 2 }],
            &[1_u8, 2, 3, 4],
        );

        let error = DirectoryCartridgeLoader::load(dir.path()).unwrap_err();

        assert!(matches!(error, CartridgeError::InvalidFormat));
    }

    #[test]
    fn load_rejects_preload_slot_clash_per_bank_type() {
        let dir = TestCartridgeDir::new(manifest_with_capabilities(Some(vec!["asset"])));
        let asset_table = vec![
            test_asset_entry(0, 4),
            AssetEntry {
                asset_id: 8,
                asset_name: "other_tiles".to_string(),
                bank_type: BankType::TILES,
                offset: 4,
                size: 4,
                decoded_size: 16 * 16 + (TILE_BANK_PALETTE_COUNT_V1 as u64 * 16 * 2),
                codec: "NONE".to_string(),
                metadata: json!({
                    "tile_size": 16,
                    "width": 16,
                    "height": 16,
                    "palette_count": TILE_BANK_PALETTE_COUNT_V1
                }),
            },
        ];
        let preload =
            vec![PreloadEntry { asset_id: 7, slot: 2 }, PreloadEntry { asset_id: 8, slot: 2 }];
        dir.write_assets_pa(asset_table, preload, &[1_u8, 2, 3, 4, 5, 6, 7, 8]);

        let error = DirectoryCartridgeLoader::load(dir.path()).unwrap_err();

        assert!(matches!(error, CartridgeError::InvalidFormat));
    }

    #[test]
    fn load_rejects_invalid_assets_pa_prelude() {
        let dir = TestCartridgeDir::new(manifest_with_capabilities(Some(vec!["asset"])));
        fs::write(dir.path().join("assets.pa"), b"not-a-valid-pack").expect("must write assets.pa");

        let error = DirectoryCartridgeLoader::load(dir.path()).unwrap_err();

        assert!(matches!(error, CartridgeError::InvalidFormat));
    }

    #[test]
    fn load_rejects_invalid_assets_pa_header_json() {
        let dir = TestCartridgeDir::new(manifest_with_capabilities(Some(vec!["asset"])));
        let prelude = AssetsPackPrelude {
            magic: ASSETS_PA_MAGIC,
            schema_version: ASSETS_PA_SCHEMA_VERSION,
            header_len: 4,
            payload_offset: (ASSETS_PA_PRELUDE_SIZE + 4) as u64,
            flags: 0,
            reserved: 0,
            header_checksum: 0,
        };
        let mut bytes = prelude.to_bytes().to_vec();
        bytes.extend_from_slice(b"{no}");
        fs::write(dir.path().join("assets.pa"), bytes).expect("must write assets.pa");

        let error = DirectoryCartridgeLoader::load(dir.path()).unwrap_err();

        assert!(matches!(error, CartridgeError::InvalidFormat));
    }
}