//! GPU Temporal Memory.
//!
//! Flat device storage. Pre-allocated segment slab:
//!   n_cells = n_columns * cells_per_column
//!   n_segments_max = n_cells * MAX_SEGMENTS_PER_CELL
//!   n_synapses_max = n_segments_max * MAX_SYN_PER_SEGMENT
//!
//! Defaults (CPU parity targets relaxed on GPU to keep memory tractable):
//!   MAX_SEGMENTS_PER_CELL = 16
//!   MAX_SYN_PER_SEGMENT   = 32
//!
//! At n_cells = 65536:
//!   n_segments_max =  1_048_576   (~1M)
//!   n_synapses_max = 33_554_432   (~33M)
//! Storage:
//!   syn_presyn : u32  × 33M = 128 MB
//!   syn_perm   : i16  × 33M =  64 MB
//!   seg_cell   : u32  ×  1M =   4 MB
//!   seg_syn_n  : u32  ×  1M =   4 MB
//!   misc bitsets etc        ~ <1 MB
//!   -------------------------------
//!   Total per region        ~200 MB
//!
//! Permanences are stored as i16 scaled by 32767 (→ [0, 32767] represents
//! [0.0, 1.0]). inc/dec are provided pre-scaled.

use std::sync::Arc;

use cudarc::driver::{CudaDevice, CudaSlice, DriverError, DeviceRepr, LaunchAsync, LaunchConfig};
use cudarc::nvrtc::Ptx;

/// Packed config struct passed by value to TM kernels to stay under
/// cudarc's 12-tuple launch limit. Layout must match the C-side
/// `TmConfig` struct declared in each kernel.
#[repr(C)]
#[derive(Clone, Copy)]
pub struct TmConfig {
    pub activation_threshold: u32,
    pub learning_threshold: u32,
    pub cells_per_column: u32,
    pub synapses_per_segment: u32,
    pub n_segments: u32,
    pub n_cells: u32,
    pub max_segments_per_cell: u32,
    pub max_new_synapses: u32,
    pub conn_thr_i16: i32,        // i16 widened to i32 for alignment
    pub perm_inc_i16: i32,
    pub perm_dec_i16: i32,
    pub predicted_seg_dec_i16: i32,
    pub initial_perm_i16: i32,
    pub iter_seed: u32,
    pub n_cols: u32,
    pub bits_words: u32,
}

unsafe impl DeviceRepr for TmConfig {}

// Embedded PTX.
const PTX_TM_PREDICT:  &str = include_str!(concat!(env!("HTM_GPU_PTX_DIR"), "/tm_predict.ptx"));
const PTX_TM_ACTIVATE: &str = include_str!(concat!(env!("HTM_GPU_PTX_DIR"), "/tm_activate.ptx"));
const PTX_TM_LEARN:    &str = include_str!(concat!(env!("HTM_GPU_PTX_DIR"), "/tm_learn.ptx"));
const PTX_TM_PUNISH:   &str = include_str!(concat!(env!("HTM_GPU_PTX_DIR"), "/tm_punish.ptx"));
const PTX_TM_GROW:     &str = include_str!(concat!(env!("HTM_GPU_PTX_DIR"), "/tm_grow.ptx"));
const PTX_TM_ANOMALY:  &str = include_str!(concat!(env!("HTM_GPU_PTX_DIR"), "/tm_anomaly.ptx"));
const PTX_TM_RESET:    &str = include_str!(concat!(env!("HTM_GPU_PTX_DIR"), "/tm_reset.ptx"));

/// Capacity trade-offs for 6 GB VRAM (RTX 3060) shared with the model:
///   n_cells            = 2048 × 32 = 65_536
///   n_segments_max     = n_cells × MAX_SEGMENTS_PER_CELL
///   n_synapses_max     = n_segments_max × MAX_SYN_PER_SEGMENT
///
/// At 4/20 these are 262_144 segments and ~5.2M synapses (~50 MB per region).
/// The training loop runs with `reset_each_forward=True`, so segment counts
/// per window stay well below 32K (typical: ~n_cols new segs per step until
/// the first matching segment is reused; in a 2048-step window that plateaus
/// around ~5K total live segments). The 262K ceiling is generous headroom.
pub const MAX_SEGMENTS_PER_CELL: usize = 4;
pub const MAX_SYN_PER_SEGMENT:   usize = 20;

const PERM_SCALE: f32 = 32767.0;

fn perm_f32_to_i16(x: f32) -> i16 {
    let clamped = x.clamp(0.0, 1.0);
    (clamped * PERM_SCALE).round() as i16
}

pub struct TemporalMemoryGpu {
    dev: Arc<CudaDevice>,

    // Config mirror
    pub n_columns: usize,
    pub cells_per_column: usize,
    pub activation_threshold: u32,
    pub learning_threshold: u32,
    pub initial_perm_i16: i16,
    pub conn_thr_i16: i16,
    pub perm_inc_i16: i16,
    pub perm_dec_i16: i16,
    pub predicted_seg_dec_i16: i16,
    pub max_new_synapse_count: u32,

    // Sizes
    pub n_cells: usize,
    pub n_segments_max: usize,
    pub bits_words: usize,  // n_cells / 32

    // Persistent device buffers
    seg_cell_id:       CudaSlice<u32>,
    seg_syn_count:     CudaSlice<u32>,
    syn_presyn:        CudaSlice<u32>,
    syn_perm:          CudaSlice<i16>,
    cell_seg_count:    CudaSlice<u32>,

    cell_active_bits:     CudaSlice<u32>,
    cell_winner_bits:     CudaSlice<u32>,
    cell_predictive_bits: CudaSlice<u32>,
    prev_active_bits:     CudaSlice<u32>,
    prev_winner_bits:     CudaSlice<u32>,

    col_predicted:         CudaSlice<u8>,
    seg_num_active_conn:   CudaSlice<u32>,
    seg_num_active_pot:    CudaSlice<u32>,
    unpredicted_count:     CudaSlice<u32>,
    burst_cols_flat:       CudaSlice<u32>,
    burst_cols_count:      CudaSlice<u32>,
    col_best_match:        CudaSlice<u32>,

    iter_counter: u32,
}

impl TemporalMemoryGpu {
    pub fn new(
        dev: Arc<CudaDevice>,
        n_columns: usize,
        cells_per_column: usize,
    ) -> Result<Self, DriverError> {
        let n_cells = n_columns * cells_per_column;
        assert!(n_cells % 32 == 0, "n_cells must be divisible by 32 for bitsets");
        let n_segments_max = n_cells * MAX_SEGMENTS_PER_CELL;
        let bits_words = n_cells / 32;

        // Numenta defaults.
        let activation_threshold = 15u32;
        let learning_threshold   = 13u32;
        let initial_perm_i16        = perm_f32_to_i16(0.21);
        let conn_thr_i16            = perm_f32_to_i16(0.50);
        let perm_inc_i16            = perm_f32_to_i16(0.10);
        let perm_dec_i16            = perm_f32_to_i16(0.10);
        let predicted_seg_dec_i16   = perm_f32_to_i16(0.10);
        let max_new_synapse_count   = 20u32;

        // Allocate buffers.
        let seg_cell_id_host: Vec<u32> = vec![u32::MAX; n_segments_max];
        let seg_cell_id = dev.htod_sync_copy(&seg_cell_id_host)?;
        let seg_syn_count = dev.alloc_zeros::<u32>(n_segments_max)?;
        let syn_presyn = dev.alloc_zeros::<u32>(n_segments_max * MAX_SYN_PER_SEGMENT)?;
        let syn_perm = dev.alloc_zeros::<i16>(n_segments_max * MAX_SYN_PER_SEGMENT)?;
        let cell_seg_count = dev.alloc_zeros::<u32>(n_cells)?;

        let cell_active_bits     = dev.alloc_zeros::<u32>(bits_words)?;
        let cell_winner_bits     = dev.alloc_zeros::<u32>(bits_words)?;
        let cell_predictive_bits = dev.alloc_zeros::<u32>(bits_words)?;
        let prev_active_bits     = dev.alloc_zeros::<u32>(bits_words)?;
        let prev_winner_bits     = dev.alloc_zeros::<u32>(bits_words)?;

        let col_predicted       = dev.alloc_zeros::<u8>(n_columns)?;
        let seg_num_active_conn = dev.alloc_zeros::<u32>(n_segments_max)?;
        let seg_num_active_pot  = dev.alloc_zeros::<u32>(n_segments_max)?;
        let unpredicted_count   = dev.alloc_zeros::<u32>(1)?;
        // Bursting columns for one step bounded by n_columns.
        let burst_cols_flat   = dev.alloc_zeros::<u32>(n_columns)?;
        let burst_cols_count  = dev.alloc_zeros::<u32>(1)?;
        let col_best_match    = dev.alloc_zeros::<u32>(n_columns)?;

        // Load PTX modules.
        let modules = [
            ("htm_tm_predict",  PTX_TM_PREDICT,  "tm_predict"),
            ("htm_tm_activate", PTX_TM_ACTIVATE, "tm_activate"),
            ("htm_tm_learn",    PTX_TM_LEARN,    "tm_learn_reinforce"),
            ("htm_tm_punish",   PTX_TM_PUNISH,   "tm_punish"),
            ("htm_tm_grow",     PTX_TM_GROW,     "tm_grow"),
            ("htm_tm_anomaly",  PTX_TM_ANOMALY,  "tm_anomaly"),
            ("htm_tm_reset",    PTX_TM_RESET,    "tm_reset_step"),
        ];
        for (modname, ptx, fnname) in modules {
            if dev.get_func(modname, fnname).is_none() {
                dev.load_ptx(Ptx::from_src(ptx), modname, &[fnname])?;
            }
        }

        Ok(Self {
            dev,
            n_columns,
            cells_per_column,
            activation_threshold,
            learning_threshold,
            initial_perm_i16,
            conn_thr_i16,
            perm_inc_i16,
            perm_dec_i16,
            predicted_seg_dec_i16,
            max_new_synapse_count,
            n_cells,
            n_segments_max,
            bits_words,
            seg_cell_id,
            seg_syn_count,
            syn_presyn,
            syn_perm,
            cell_seg_count,
            cell_active_bits,
            cell_winner_bits,
            cell_predictive_bits,
            prev_active_bits,
            prev_winner_bits,
            col_predicted,
            seg_num_active_conn,
            seg_num_active_pot,
            unpredicted_count,
            burst_cols_flat,
            burst_cols_count,
            col_best_match,
            iter_counter: 0,
        })
    }

    // --- Fused-path accessors ---
    pub fn seg_cell_id_accessor(&self) -> &CudaSlice<u32> { &self.seg_cell_id }
    pub fn seg_syn_count_accessor(&self) -> &CudaSlice<u32> { &self.seg_syn_count }
    pub fn syn_presyn_accessor(&self) -> &CudaSlice<u32> { &self.syn_presyn }
    pub fn syn_perm_accessor(&self) -> &CudaSlice<i16> { &self.syn_perm }
    pub fn cell_seg_count_accessor(&self) -> &CudaSlice<u32> { &self.cell_seg_count }

    /// Hard reset — clear everything (predictive + active + segments).
    pub fn reset(&mut self) -> Result<(), DriverError> {
        // Restore "unused" sentinel in seg_cell_id.
        let unused_host: Vec<u32> = vec![u32::MAX; self.n_segments_max];
        self.dev.htod_sync_copy_into(&unused_host, &mut self.seg_cell_id)?;
        self.dev.memset_zeros(&mut self.seg_syn_count)?;
        self.dev.memset_zeros(&mut self.cell_seg_count)?;
        self.dev.memset_zeros(&mut self.cell_active_bits)?;
        self.dev.memset_zeros(&mut self.cell_winner_bits)?;
        self.dev.memset_zeros(&mut self.cell_predictive_bits)?;
        self.dev.memset_zeros(&mut self.prev_active_bits)?;
        self.dev.memset_zeros(&mut self.prev_winner_bits)?;
        self.dev.memset_zeros(&mut self.col_best_match)?;
        self.iter_counter = 0;
        Ok(())
    }

    fn build_cfg(&self) -> TmConfig {
        TmConfig {
            activation_threshold: self.activation_threshold,
            learning_threshold: self.learning_threshold,
            cells_per_column: self.cells_per_column as u32,
            synapses_per_segment: MAX_SYN_PER_SEGMENT as u32,
            n_segments: self.n_segments_max as u32,
            n_cells: self.n_cells as u32,
            max_segments_per_cell: MAX_SEGMENTS_PER_CELL as u32,
            max_new_synapses: self.max_new_synapse_count,
            conn_thr_i16: self.conn_thr_i16 as i32,
            perm_inc_i16: self.perm_inc_i16 as i32,
            perm_dec_i16: self.perm_dec_i16 as i32,
            predicted_seg_dec_i16: self.predicted_seg_dec_i16 as i32,
            initial_perm_i16: self.initial_perm_i16 as i32,
            iter_seed: self.iter_counter,
            n_cols: self.n_columns as u32,
            bits_words: self.bits_words as u32,
        }
    }

    /// Run one TM step on the GPU. Takes the SP active-column mask (u8, already
    /// on device) and writes `anomaly_out[t_slot]`.
    pub fn step(
        &mut self,
        sp_active_mask: &CudaSlice<u8>,
        anomaly_out: &mut CudaSlice<f32>,
        t_slot: u32,
        learn: bool,
    ) -> Result<(), DriverError> {
        let n_cells = self.n_cells;
        let n_cols = self.n_columns;

        let predict_fn  = self.dev.get_func("htm_tm_predict",  "tm_predict").unwrap();
        let activate_fn = self.dev.get_func("htm_tm_activate", "tm_activate").unwrap();
        let learn_fn    = self.dev.get_func("htm_tm_learn",    "tm_learn_reinforce").unwrap();
        let punish_fn   = self.dev.get_func("htm_tm_punish",   "tm_punish").unwrap();
        let grow_fn     = self.dev.get_func("htm_tm_grow",     "tm_grow").unwrap();
        let anom_fn     = self.dev.get_func("htm_tm_anomaly",  "tm_anomaly").unwrap();
        let reset_fn    = self.dev.get_func("htm_tm_reset",    "tm_reset_step").unwrap();

        self.iter_counter = self.iter_counter.wrapping_add(1);
        let cfg_val = self.build_cfg();

        // 0. Per-step reset.
        let reset_words = self.bits_words.max(n_cols);
        let reset_cfg = LaunchConfig {
            grid_dim: (((reset_words + 255) / 256) as u32, 1, 1),
            block_dim: (256, 1, 1),
            shared_mem_bytes: 0,
        };
        unsafe {
            reset_fn.clone().launch(
                reset_cfg,
                (
                    &mut self.cell_active_bits,
                    &mut self.cell_winner_bits,
                    &mut self.cell_predictive_bits,
                    &mut self.prev_active_bits,
                    &mut self.prev_winner_bits,
                    &mut self.col_predicted,
                    &mut self.unpredicted_count,
                    &mut self.burst_cols_count,
                    &mut self.col_best_match,
                    self.bits_words as u32,
                    n_cols as u32,
                ),
            )?;
        }

        // 1. Predict (grid = n_cells; each block iterates its cell's segments).
        let predict_cfg = LaunchConfig {
            grid_dim: (n_cells as u32, 1, 1),
            block_dim: (32, 1, 1),
            shared_mem_bytes: 0,
        };
        unsafe {
            predict_fn.clone().launch(
                predict_cfg,
                (
                    &self.seg_cell_id,
                    &self.seg_syn_count,
                    &self.syn_presyn,
                    &self.syn_perm,
                    &self.prev_active_bits,
                    &mut self.cell_predictive_bits,
                    &mut self.col_predicted,
                    &mut self.seg_num_active_conn,
                    &mut self.seg_num_active_pot,
                    &mut self.col_best_match,
                    &self.cell_seg_count,
                    cfg_val,
                ),
            )?;
        }

        // 2. Activate.
        let activate_cfg = LaunchConfig {
            grid_dim: (((n_cols + 255) / 256) as u32, 1, 1),
            block_dim: (256, 1, 1),
            shared_mem_bytes: 0,
        };
        unsafe {
            activate_fn.clone().launch(
                activate_cfg,
                (
                    sp_active_mask,
                    &self.col_predicted,
                    &self.cell_predictive_bits,
                    &mut self.cell_active_bits,
                    &mut self.cell_winner_bits,
                    &mut self.unpredicted_count,
                    &mut self.burst_cols_flat,
                    &mut self.burst_cols_count,
                    cfg_val,
                ),
            )?;
        }

        // 3. Anomaly.
        let anom_cfg = LaunchConfig {
            grid_dim: (1, 1, 1),
            block_dim: (256, 1, 1),
            shared_mem_bytes: 0,
        };
        unsafe {
            anom_fn.clone().launch(
                anom_cfg,
                (
                    sp_active_mask,
                    &self.unpredicted_count,
                    anomaly_out,
                    t_slot,
                    n_cols as u32,
                ),
            )?;
        }

        if learn {
            // 4. Reinforce (grid = n_cells).
            let learn_cfg = LaunchConfig {
                grid_dim: (n_cells as u32, 1, 1),
                block_dim: (32, 1, 1),
                shared_mem_bytes: 0,
            };
            unsafe {
                learn_fn.clone().launch(
                    learn_cfg,
                    (
                        &self.seg_cell_id,
                        &self.seg_syn_count,
                        &self.syn_presyn,
                        &mut self.syn_perm,
                        &self.seg_num_active_conn,
                        &self.prev_active_bits,
                        sp_active_mask,
                        &self.col_predicted,
                        &self.cell_seg_count,
                        cfg_val,
                    ),
                )?;
            }

            // 5. Punish.
            unsafe {
                punish_fn.clone().launch(
                    learn_cfg,
                    (
                        &self.seg_cell_id,
                        &self.seg_syn_count,
                        &self.syn_presyn,
                        &mut self.syn_perm,
                        &self.seg_num_active_pot,
                        &self.prev_active_bits,
                        sp_active_mask,
                        &self.cell_seg_count,
                        cfg_val,
                    ),
                )?;
            }

            // 6. Grow.
            let grow_cfg = LaunchConfig {
                grid_dim: (n_cols as u32, 1, 1),
                block_dim: (32, 1, 1),
                shared_mem_bytes: 0,
            };
            unsafe {
                grow_fn.clone().launch(
                    grow_cfg,
                    (
                        &mut self.seg_cell_id,
                        &mut self.seg_syn_count,
                        &mut self.syn_presyn,
                        &mut self.syn_perm,
                        &mut self.cell_seg_count,
                        &self.burst_cols_flat,
                        &self.burst_cols_count,
                        &self.prev_winner_bits,
                        &self.prev_active_bits,
                        &self.col_best_match,
                        cfg_val,
                    ),
                )?;
            }
        }

        Ok(())
    }
}