/* backend_loader.c — Windows runtime loader for coli_cuda.dll.
 *
 * Why this exists: the engine is built with MinGW-w64 (gcc), but CUDA kernels
 * must be compiled with MSVC + nvcc. We cannot link a CUDA .o into a gcc binary
 * reliably across the MSVC/MinGW ABI, and nvcc requires cl.exe as its host
 * compiler. The clean cross-toolchain split is: build the CUDA backend into a
 * standalone coli_cuda.dll with nvcc+MSVC, then load it here at runtime via
 * LoadLibrary/GetProcAddress. The host (glm.exe) never links cudart directly.
 *
 * On Linux this file is not compiled (the Makefile links backend_cuda.o
 * directly). On Windows, when COLI_CUDA is defined, glm.c calls the
 * coli_cuda_* wrappers below, which forward through function pointers resolved
 * from the DLL at first use. If the DLL is absent, every call safely returns
 * the "not initialized" sentinel (0 / no-op) and the engine falls back to CPU.
 *
 * ABI note: ColiCudaTensor* is opaque to the host (it stores the pointer,
 * never dereferences it), so the MSVC-allocated struct is safe to pass across
 * the boundary as an opaque handle. All scalar types (int, size_t, pointers)
 * agree between MSVC and MinGW-w64 on x86-64.
 */
#ifdef _WIN32

#include <stdio.h>
#include <stddef.h>
#include <windows.h>

#include "backend_cuda.h"

/* Function-pointer typedefs matching each exported symbol. */
typedef int            (*fn_init)(const int *devices, int count);
typedef void           (*fn_shutdown)(void);
typedef int            (*fn_device_count)(void);
typedef int            (*fn_device_at)(int index);
typedef int            (*fn_mem_info)(int device, size_t *free_bytes, size_t *total_bytes);
typedef void           (*fn_stats)(int device, size_t *tensor_count, size_t *tensor_bytes);
typedef void           (*fn_group_stats)(uint64_t *calls, uint64_t *experts, uint64_t *rows,
                                         double *h2d_ms, double *kernel_ms, double *d2h_ms);
typedef int            (*fn_expert_mlp)(ColiCudaTensor *gate, ColiCudaTensor *up,
                                        ColiCudaTensor *down, float *y, const float *x, int S);
typedef int            (*fn_expert_group)(ColiCudaTensor *const *gates, ColiCudaTensor *const *ups,
                                          ColiCudaTensor *const *downs, const int *rows, int count,
                                          float *y, const float *x);
typedef int            (*fn_attention_absorb)(ColiCudaTensor *kv_b, float *ctx, const float *q,
                                              const float *latent, const float *rope, int H, int Q,
                                              int R, int V, int K, int T, float attention_scale);
typedef int            (*fn_tensor_upload)(ColiCudaTensor **tensor, const void *weights,
                                           const float *scales, int fmt, int I, int O, int device);
typedef int            (*fn_matmul)(ColiCudaTensor **tensor, float *y, const float *x,
                                    const void *weights, const float *scales,
                                    int fmt, int S, int I, int O, int device);
typedef void           (*fn_tensor_free)(ColiCudaTensor *tensor);
typedef size_t         (*fn_tensor_bytes)(const ColiCudaTensor *tensor);
typedef int            (*fn_tensor_device)(const ColiCudaTensor *tensor);

/* Resolved pointers, plus a flag so we attempt the load at most once. */
static struct {
    int loaded;        /* 1 = load attempted (success or fail), 0 = not yet */
    int available;     /* 1 = DLL loaded and all symbols resolved */
    HMODULE dll;
    fn_init            init;
    fn_shutdown        shutdown;
    fn_device_count    device_count;
    fn_device_at       device_at;
    fn_mem_info        mem_info;
    fn_stats           stats;
    fn_group_stats     group_stats;
    fn_expert_mlp      expert_mlp;
    fn_expert_group    expert_group;
    fn_attention_absorb attention_absorb;
    fn_tensor_upload   tensor_upload;
    fn_matmul          matmul;
    fn_tensor_free     tensor_free;
    fn_tensor_bytes    tensor_bytes;
    fn_tensor_device   tensor_device;
} g_cuda;

/* Resolve the DLL and all 11 symbols. Returns 1 on success, 0 otherwise.
 * Idempotent: the first call (success or fail) sticks; later calls are no-ops
 * that return the cached result. The engine treats a 0 return as "CUDA
 * unavailable" and falls back to the CPU path without aborting. */
static int coli_cuda_load(void){
    if(g_cuda.loaded) return g_cuda.available;
    g_cuda.loaded = 1;

    /* Search the model directory first (so a DLL shipped next to the model
     * wins), then the engine directory, then the default DLL search path. */
    g_cuda.dll = LoadLibraryA("coli_cuda.dll");
    if(!g_cuda.dll){
        fprintf(stderr, "[CUDA] coli_cuda.dll not found; GPU tier disabled "
                        "(CPU path remains active).\n");
        return 0;
    }

    #define RESOLVE(name, type) \
        /* GetProcAddress returns FARPROC (void(*)(void)); casting it to a   \
         * specific function-pointer type is the standard LoadLibrary idiom. \
         * -Wcast-function-type flags it but it is safe: the DLL exported     \
         * the symbol with extern "C" and the exact signature we expect. */   \
        _Pragma("GCC diagnostic push") \
        _Pragma("GCC diagnostic ignored \"-Wcast-function-type\"") \
        g_cuda.name = (type)GetProcAddress(g_cuda.dll, "coli_cuda_" #name); \
        _Pragma("GCC diagnostic pop") \
        if(!g_cuda.name){ \
            fprintf(stderr, "[CUDA] coli_cuda.dll missing symbol coli_cuda_" #name "\n"); \
            FreeLibrary(g_cuda.dll); g_cuda.dll=NULL; return 0; }

    RESOLVE(init,           fn_init)
    RESOLVE(shutdown,       fn_shutdown)
    RESOLVE(device_count,   fn_device_count)
    RESOLVE(device_at,      fn_device_at)
    RESOLVE(mem_info,       fn_mem_info)
    RESOLVE(stats,          fn_stats)
    RESOLVE(group_stats,    fn_group_stats)
    RESOLVE(expert_mlp,     fn_expert_mlp)
    RESOLVE(expert_group,   fn_expert_group)
    RESOLVE(attention_absorb, fn_attention_absorb)
    RESOLVE(tensor_upload,  fn_tensor_upload)
    RESOLVE(matmul,         fn_matmul)
    RESOLVE(tensor_free,    fn_tensor_free)
    RESOLVE(tensor_bytes,   fn_tensor_bytes)
    RESOLVE(tensor_device,  fn_tensor_device)
    #undef RESOLVE

    g_cuda.available = 1;
    return 1;
}

/* ---- Public wrappers: match backend_cuda.h signatures exactly.
 * Each forwards to the resolved pointer; if the DLL never loaded, return the
 * "not initialized" result the engine already handles (init returns 0, matmul
 * returns 0 so the caller marks the tensor cuda_failed and uses CPU). ---- */

int coli_cuda_init(const int *devices, int count){
    if(!coli_cuda_load()) return 0;
    return g_cuda.init(devices, count);
}

void coli_cuda_shutdown(void){
    if(g_cuda.available && g_cuda.shutdown) g_cuda.shutdown();
}

int coli_cuda_device_count(void){
    if(!g_cuda.available) return 0;
    return g_cuda.device_count();
}

int coli_cuda_device_at(int index){
    if(!g_cuda.available) return -1;
    return g_cuda.device_at(index);
}

int coli_cuda_mem_info(int device, size_t *free_bytes, size_t *total_bytes){
    if(!g_cuda.available){ if(free_bytes)*free_bytes=0; if(total_bytes)*total_bytes=0; return 0; }
    return g_cuda.mem_info(device, free_bytes, total_bytes);
}

void coli_cuda_stats(int device, size_t *tensor_count, size_t *tensor_bytes){
    if(!g_cuda.available){ if(tensor_count)*tensor_count=0; if(tensor_bytes)*tensor_bytes=0; return; }
    g_cuda.stats(device, tensor_count, tensor_bytes);
}

void coli_cuda_group_stats(uint64_t *calls, uint64_t *experts, uint64_t *rows,
                           double *h2d_ms, double *kernel_ms, double *d2h_ms){
    if(!g_cuda.available){
        if(calls)*calls=0; if(experts)*experts=0; if(rows)*rows=0;
        if(h2d_ms)*h2d_ms=0; if(kernel_ms)*kernel_ms=0; if(d2h_ms)*d2h_ms=0;
        return;
    }
    g_cuda.group_stats(calls, experts, rows, h2d_ms, kernel_ms, d2h_ms);
}

int coli_cuda_expert_mlp(ColiCudaTensor *gate, ColiCudaTensor *up,
                         ColiCudaTensor *down, float *y, const float *x, int S){
    if(!g_cuda.available) return 0;
    return g_cuda.expert_mlp(gate, up, down, y, x, S);
}

int coli_cuda_expert_group(ColiCudaTensor *const *gates, ColiCudaTensor *const *ups,
                           ColiCudaTensor *const *downs, const int *rows, int count,
                           float *y, const float *x){
    if(!g_cuda.available) return 0;
    return g_cuda.expert_group(gates, ups, downs, rows, count, y, x);
}

int coli_cuda_attention_absorb(ColiCudaTensor *kv_b, float *ctx, const float *q,
                               const float *latent, const float *rope, int H, int Q,
                               int R, int V, int K, int T, float attention_scale){
    if(!g_cuda.available) return 0;
    return g_cuda.attention_absorb(kv_b, ctx, q, latent, rope, H, Q, R, V, K, T, attention_scale);
}

int coli_cuda_tensor_upload(ColiCudaTensor **tensor, const void *weights,
                            const float *scales, int fmt, int I, int O, int device){
    if(!g_cuda.available) return 0;
    return g_cuda.tensor_upload(tensor, weights, scales, fmt, I, O, device);
}

int coli_cuda_matmul(ColiCudaTensor **tensor, float *y, const float *x,
                     const void *weights, const float *scales,
                     int fmt, int S, int I, int O, int device){
    if(!g_cuda.available) return 0;
    return g_cuda.matmul(tensor, y, x, weights, scales, fmt, S, I, O, device);
}

void coli_cuda_tensor_free(ColiCudaTensor *tensor){
    if(g_cuda.available && g_cuda.tensor_free) g_cuda.tensor_free(tensor);
}

size_t coli_cuda_tensor_bytes(const ColiCudaTensor *tensor){
    if(!g_cuda.available) return 0;
    return g_cuda.tensor_bytes(tensor);
}

int coli_cuda_tensor_device(const ColiCudaTensor *tensor){
    if(!g_cuda.available) return -1;
    return g_cuda.tensor_device(tensor);
}

#endif /* _WIN32 */