use crate::hardware::memory_banks::GfxTileBankPoolInstaller;
use crate::model::{AssetEntry, BankStats, BankType, Color, HandleId, LoadStatus, SlotRef, SlotStats, TileBank, TileSize};
use std::collections::HashMap;
use std::sync::{Arc, Mutex, RwLock};
use std::thread;
use std::time::Instant;

/// Resident metadata for a decoded/materialized asset inside a BankPolicy.
#[derive(Debug)]
pub struct ResidentEntry<T> {
    /// The resident, materialized object.
    pub value: Arc<T>,

    /// Resident size in bytes (post-decode). Used for telemetry/budgets.
    pub bytes: usize,

    // /// Pin count (optional): if > 0, entry should not be evicted by policy.
    // pub pins: u32,

    /// Telemetry / profiling fields (optional but useful).
    pub loads: u64,
    pub last_used: Instant,
}

impl<T> ResidentEntry<T> {
    pub fn new(value: Arc<T>, bytes: usize) -> Self {
        Self {
            value,
            bytes,
            // pins: 0,
            loads: 1,
            last_used: Instant::now(),
        }
    }
}

/// Encapsulates the residency and staging policy for a specific type of asset.
/// This is internal to the AssetManager and not visible to peripherals.
pub struct BankPolicy<T> {
    /// Dedup table: asset_id -> resident entry (value + telemetry).
    resident: Arc<RwLock<HashMap<String, ResidentEntry<T>>>>,

    /// Staging area: handle -> value ready to commit.
    staging: Arc<RwLock<HashMap<HandleId, Arc<T>>>>,
}

impl<T> BankPolicy<T> {
    pub fn new() -> Self {
        Self {
            resident: Arc::new(RwLock::new(HashMap::new())),
            staging: Arc::new(RwLock::new(HashMap::new())),
        }
    }

    /// Try get a resident value by asset_id (dedupe path).
    pub fn get_resident(&self, asset_id: &str) -> Option<Arc<T>> {
        let mut map = self.resident.write().unwrap();
        let entry = map.get_mut(asset_id)?;
        entry.last_used = Instant::now();
        Some(Arc::clone(&entry.value))
    }

    /// Insert or reuse a resident entry. Returns the resident Arc<T>.
    pub fn put_resident(&self, asset_id: String, value: Arc<T>, bytes: usize) -> Arc<T> {
        let mut map = self.resident.write().unwrap();
        match map.get_mut(&asset_id) {
            Some(existing) => {
                existing.last_used = Instant::now();
                existing.loads += 1;
                Arc::clone(&existing.value)
            }
            None => {
                let entry = ResidentEntry::new(Arc::clone(&value), bytes);
                map.insert(asset_id, entry);
                value
            }
        }
    }

    /// Place a value into staging for a given handle.
    pub fn stage(&self, handle: HandleId, value: Arc<T>) {
        self.staging.write().unwrap().insert(handle, value);
    }

    /// Take staged value (used by commit path).
    pub fn take_staging(&self, handle: HandleId) -> Option<Arc<T>> {
        self.staging.write().unwrap().remove(&handle)
    }

    pub fn clear(&self) {
        self.resident.write().unwrap().clear();
        self.staging.write().unwrap().clear();
    }
}

pub struct AssetManager {
    assets: Arc<RwLock<HashMap<String, AssetEntry>>>,
    handles: Arc<RwLock<HashMap<HandleId, LoadHandleInfo>>>,
    next_handle_id: Mutex<HandleId>,
    assets_data: Arc<RwLock<Vec<u8>>>,

    /// Narrow hardware interfaces
    gfx_installer: Arc<dyn GfxTileBankPoolInstaller>,

    /// Track what is installed in each hardware slot (for stats/info).
    gfx_slots: Arc<RwLock<[Option<String>; 16]>>,

    /// Residency policy for GFX tile banks.
    gfx_policy: BankPolicy<TileBank>,

    // Commits that are ready to be applied at the next frame boundary.
    pending_commits: Mutex<Vec<HandleId>>,
}

struct LoadHandleInfo {
    _asset_id: String,
    slot: SlotRef,
    status: LoadStatus,
}

impl AssetManager {
    pub fn new(
        assets: Vec<AssetEntry>, 
        assets_data: Vec<u8>, 
        gfx_installer: Arc<dyn GfxTileBankPoolInstaller>,
    ) -> Self {
        let mut asset_map = HashMap::new();
        for entry in assets {
            asset_map.insert(entry.asset_id.clone(), entry);
        }

        Self {
            assets: Arc::new(RwLock::new(asset_map)),
            gfx_installer,
            gfx_slots: Arc::new(RwLock::new(std::array::from_fn(|_| None))),
            gfx_policy: BankPolicy::new(),
            handles: Arc::new(RwLock::new(HashMap::new())),
            next_handle_id: Mutex::new(1),
            assets_data: Arc::new(RwLock::new(assets_data)),
            pending_commits: Mutex::new(Vec::new()),
        }
    }

    pub fn initialize_for_cartridge(&self, assets: Vec<AssetEntry>, assets_data: Vec<u8>) {
        self.shutdown();
        let mut asset_map = self.assets.write().unwrap();
        asset_map.clear();
        for entry in assets {
            asset_map.insert(entry.asset_id.clone(), entry);
        }
        *self.assets_data.write().unwrap() = assets_data;
    }

    pub fn load(&self, asset_id: &str, slot: SlotRef) -> Result<HandleId, String> {
        let entry = {
            let assets = self.assets.read().unwrap();
            assets.get(asset_id).ok_or_else(|| format!("Asset not found: {}", asset_id))?.clone()
        };

        if slot.asset_type != entry.bank_type {
            return Err("INCOMPATIBLE_SLOT_KIND".to_string());
        }

        let mut next_id = self.next_handle_id.lock().unwrap();
        let handle_id = *next_id;
        *next_id += 1;

        // Check if already resident
        if let Some(bank) = self.gfx_policy.get_resident(asset_id) {
            // Dedup: already resident
            self.handles.write().unwrap().insert(handle_id, LoadHandleInfo {
                _asset_id: asset_id.to_string(),
                slot,
                status: LoadStatus::READY,
            });
            self.gfx_policy.stage(handle_id, bank);
            return Ok(handle_id);
        }

        // Not resident, start loading
        self.handles.write().unwrap().insert(handle_id, LoadHandleInfo {
            _asset_id: asset_id.to_string(),
            slot,
            status: LoadStatus::PENDING,
        });

        let gfx_policy_resident = Arc::clone(&self.gfx_policy.resident);
        let gfx_policy_staging = Arc::clone(&self.gfx_policy.staging);
        let handles = self.handles.clone();
        let assets_data = self.assets_data.clone();
        let entry_clone = entry.clone();
        let asset_id_clone = asset_id.to_string();

        thread::spawn(move || {
            // Update status to LOADING
            {
                let mut handles_map = handles.write().unwrap();
                if let Some(h) = handles_map.get_mut(&handle_id) {
                    if h.status == LoadStatus::PENDING {
                        h.status = LoadStatus::LOADING;
                    } else {
                        // Might have been canceled
                        return;
                    }
                } else {
                    return;
                }
            }

            // Perform IO and Decode
            let result = Self::perform_load(&entry_clone, assets_data);

            match result {
                Ok(tilebank) => {
                    let bank_arc = Arc::new(tilebank);
                    
                    // Insert or reuse a resident entry (dedup)
                    let resident_arc = {
                        let mut map = gfx_policy_resident.write().unwrap();
                        match map.get_mut(&asset_id_clone) {
                            Some(existing) => {
                                existing.last_used = Instant::now();
                                existing.loads += 1;
                                Arc::clone(&existing.value)
                            }
                            None => {
                                let entry = ResidentEntry::new(Arc::clone(&bank_arc), entry_clone.decoded_size as usize);
                                map.insert(asset_id_clone, entry);
                                bank_arc
                            }
                        }
                    };

                    // Add to staging
                    gfx_policy_staging.write().unwrap().insert(handle_id, resident_arc);

                    // Update status to READY
                    let mut handles_map = handles.write().unwrap();
                    if let Some(h) = handles_map.get_mut(&handle_id) {
                        if h.status == LoadStatus::LOADING {
                            h.status = LoadStatus::READY;
                        }
                    }
                }
                Err(_) => {
                    let mut handles_map = handles.write().unwrap();
                    if let Some(h) = handles_map.get_mut(&handle_id) {
                        h.status = LoadStatus::ERROR;
                    }
                }
            }
        });

        Ok(handle_id)
    }

    fn perform_load(entry: &AssetEntry, assets_data: Arc<RwLock<Vec<u8>>>) -> Result<TileBank, String> {
        if entry.codec != "RAW" {
            return Err(format!("Unsupported codec: {}", entry.codec));
        }

        let assets_data = assets_data.read().unwrap();
        
        let start = entry.offset as usize;
        let end = start + entry.size as usize;
        
        if end > assets_data.len() {
            return Err("Asset offset/size out of bounds".to_string());
        }

        let buffer = &assets_data[start..end];

        // Decode TILEBANK metadata
        let tile_size_val = entry.metadata.get("tile_size").and_then(|v| v.as_u64()).ok_or("Missing tile_size")?;
        let width = entry.metadata.get("width").and_then(|v| v.as_u64()).ok_or("Missing width")? as usize;
        let height = entry.metadata.get("height").and_then(|v| v.as_u64()).ok_or("Missing height")? as usize;

        let tile_size = match tile_size_val {
            8 => TileSize::Size8,
            16 => TileSize::Size16,
            32 => TileSize::Size32,
            _ => return Err(format!("Invalid tile_size: {}", tile_size_val)),
        };

        let pixel_data_size = width * height;
        if buffer.len() < pixel_data_size + 2048 {
            return Err("Buffer too small for TILEBANK".to_string());
        }

        let pixel_indices = buffer[0..pixel_data_size].to_vec();
        let palette_data = &buffer[pixel_data_size..pixel_data_size + 2048];

        let mut palettes = [[Color::BLACK; 16]; 64];
        for p in 0..64 {
            for c in 0..16 {
                let offset = (p * 16 + c) * 2;
                let color_raw = u16::from_le_bytes([palette_data[offset], palette_data[offset + 1]]);
                palettes[p][c] = Color(color_raw);
            }
        }

        Ok(TileBank {
            tile_size,
            width,
            height,
            pixel_indices,
            palettes,
        })
    }

    pub fn status(&self, handle: HandleId) -> LoadStatus {
        self.handles.read().unwrap().get(&handle).map(|h| h.status).unwrap_or(LoadStatus::ERROR)
    }

    pub fn commit(&self, handle: HandleId) {
        let mut handles_map = self.handles.write().unwrap();
        if let Some(h) = handles_map.get_mut(&handle) {
            if h.status == LoadStatus::READY {
                self.pending_commits.lock().unwrap().push(handle);
            }
        }
    }

    pub fn cancel(&self, handle: HandleId) {
        let mut handles_map = self.handles.write().unwrap();
        if let Some(h) = handles_map.get_mut(&handle) {
            match h.status {
                LoadStatus::PENDING | LoadStatus::LOADING | LoadStatus::READY => {
                    h.status = LoadStatus::CANCELED;
                }
                _ => {}
            }
        }
        self.gfx_policy.take_staging(handle);
    }

    pub fn apply_commits(&self) {
        let mut pending = self.pending_commits.lock().unwrap();
        let mut handles = self.handles.write().unwrap();

        for handle_id in pending.drain(..) {
            if let Some(h) = handles.get_mut(&handle_id) {
                if h.status == LoadStatus::READY {
                    if let Some(bank) = self.gfx_policy.take_staging(handle_id) {
                        if h.slot.asset_type == BankType::TILES {
                            self.gfx_installer.install_tilebank(h.slot.index, bank);
                            
                            // Update internal tracking of what's in the slot
                            let mut slots = self.gfx_slots.write().unwrap();
                            if h.slot.index < slots.len() {
                                slots[h.slot.index] = Some(h._asset_id.clone());
                            }
                        }
                        h.status = LoadStatus::COMMITTED;
                    }
                }
            }
        }
    }

    pub fn bank_info(&self, kind: BankType) -> BankStats {
        match kind {
            BankType::TILES => {
                let mut used_bytes = 0;
                {
                    let resident = self.gfx_policy.resident.read().unwrap();
                    for entry in resident.values() {
                        used_bytes += entry.bytes;
                    }
                }

                let mut inflight_bytes = 0;
                {
                    let staging = self.gfx_policy.staging.read().unwrap();
                    let assets = self.assets.read().unwrap();
                    let handles = self.handles.read().unwrap();
                    
                    for (handle_id, _) in staging.iter() {
                        if let Some(h) = handles.get(handle_id) {
                            if let Some(entry) = assets.get(&h._asset_id) {
                                inflight_bytes += entry.decoded_size as usize;
                            }
                        }
                    }
                }

                BankStats {
                    total_bytes: 16 * 1024 * 1024,
                    used_bytes,
                    free_bytes: (16usize * 1024 * 1024).saturating_sub(used_bytes),
                    inflight_bytes,
                    slot_count: 16,
                }
            }
        }
    }

    pub fn slot_info(&self, slot: SlotRef) -> SlotStats {
        match slot.asset_type {
            BankType::TILES => {
                let slots = self.gfx_slots.read().unwrap();
                let asset_id = slots.get(slot.index).and_then(|s| s.clone());
                
                let bytes = if let Some(id) = &asset_id {
                    self.gfx_policy.resident.read().unwrap()
                        .get(id)
                        .map(|entry| entry.bytes)
                        .unwrap_or(0)
                } else {
                    0
                };

                SlotStats {
                    asset_id,
                    generation: 0,
                    resident_bytes: bytes,
                }
            }
        }
    }
    
    pub fn shutdown(&self) {
        self.gfx_policy.clear();
        self.handles.write().unwrap().clear();
        self.pending_commits.lock().unwrap().clear();
        self.gfx_slots.write().unwrap().fill(None);
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::hardware::memory_banks::{GfxTileBankPoolAccess, MemoryBanks};

    #[test]
    fn test_asset_loading_flow() {
        let banks = Arc::new(MemoryBanks::new());
        let gfx_installer = Arc::clone(&banks) as Arc<dyn GfxTileBankPoolInstaller>;

        let mut data = vec![1u8; 256];
        data.extend_from_slice(&[0u8; 2048]);

        let asset_entry = AssetEntry {
            asset_id: "test_tiles".to_string(),
            bank_type: BankType::TILES,
            offset: 0,
            size: data.len() as u64,
            decoded_size: data.len() as u64,
            codec: "RAW".to_string(),
            metadata: serde_json::json!({
                "tile_size": 16,
                "width": 16,
                "height": 16
            }),
        };

        let am = AssetManager::new(vec![asset_entry], data, gfx_installer);
        let slot = SlotRef::gfx(0);
        
        let handle = am.load("test_tiles", slot).expect("Should start loading");
        
        let mut status = am.status(handle);
        let start = Instant::now();
        while status != LoadStatus::READY && start.elapsed().as_secs() < 5 {
            thread::sleep(std::time::Duration::from_millis(10));
            status = am.status(handle);
        }
        
        assert_eq!(status, LoadStatus::READY);
        
        {
            let staging = am.gfx_policy.staging.read().unwrap();
            assert!(staging.contains_key(&handle));
        }

        am.commit(handle);
        am.apply_commits();
        
        assert_eq!(am.status(handle), LoadStatus::COMMITTED);
        assert!(banks.tilebank_slot(0).is_some());
    }

    #[test]
    fn test_asset_dedup() {
        let banks = Arc::new(MemoryBanks::new());
        let gfx_installer = Arc::clone(&banks) as Arc<dyn GfxTileBankPoolInstaller>;

        let mut data = vec![1u8; 256];
        data.extend_from_slice(&[0u8; 2048]);

        let asset_entry = AssetEntry {
            asset_id: "test_tiles".to_string(),
            bank_type: BankType::TILES,
            offset: 0,
            size: data.len() as u64,
            decoded_size: data.len() as u64,
            codec: "RAW".to_string(),
            metadata: serde_json::json!({
                "tile_size": 16,
                "width": 16,
                "height": 16
            }),
        };

        let am = AssetManager::new(vec![asset_entry], data, gfx_installer);
        
        let handle1 = am.load("test_tiles", SlotRef::gfx(0)).unwrap();
        let start = Instant::now();
        while am.status(handle1) != LoadStatus::READY && start.elapsed().as_secs() < 5 {
            thread::sleep(std::time::Duration::from_millis(10));
        }
        
        let handle2 = am.load("test_tiles", SlotRef::gfx(1)).unwrap();
        assert_eq!(am.status(handle2), LoadStatus::READY);

        let staging = am.gfx_policy.staging.read().unwrap();
        let bank1 = staging.get(&handle1).unwrap();
        let bank2 = staging.get(&handle2).unwrap();
        assert!(Arc::ptr_eq(bank1, bank2));
    }
}