use std::ffi::c_void;
use xserv_tensor::{DType, Device, Tensor};

unsafe extern "C" {
    fn launch_gelu_f32(x: *const c_void, out: *mut c_void, n: i32, stream: *mut c_void);
    fn launch_gelu_bf16(x: *const c_void, out: *mut c_void, n: i32, stream: *mut c_void);
    fn launch_silu_f32(x: *const c_void, out: *mut c_void, n: i32, stream: *mut c_void);
    fn launch_silu_bf16(x: *const c_void, out: *mut c_void, n: i32, stream: *mut c_void);
    fn launch_scale_f32(x: *const c_void, out: *mut c_void, scale: f32, n: i32, stream: *mut c_void);
    fn launch_scale_bf16(x: *const c_void, out: *mut c_void, scale: f32, n: i32, stream: *mut c_void);
    fn launch_add_f32(a: *const c_void, b: *const c_void, out: *mut c_void, n: i32, stream: *mut c_void);
    fn launch_add_bf16(a: *const c_void, b: *const c_void, out: *mut c_void, n: i32, stream: *mut c_void);
    fn launch_mul_f32(a: *const c_void, b: *const c_void, out: *mut c_void, n: i32, stream: *mut c_void);
    fn launch_mul_bf16(a: *const c_void, b: *const c_void, out: *mut c_void, n: i32, stream: *mut c_void);
    fn launch_silu_mul_bf16(gate: *const c_void, up: *const c_void, out: *mut c_void, n: i32, stream: *mut c_void);
    fn launch_gpt_oss_glu_bf16(gate_up: *const c_void, out: *mut c_void, n_elements: i32,
                                alpha: f32, limit: f32, stream: *mut c_void);
}

fn dispatch_unary(x: &Tensor, f32_fn: unsafe extern "C" fn(*const c_void, *mut c_void, i32, *mut c_void),
                  bf16_fn: unsafe extern "C" fn(*const c_void, *mut c_void, i32, *mut c_void)) -> Tensor {
    assert!(x.is_contiguous() && matches!(x.device(), Device::Cuda(_)));
    let out = Tensor::empty(x.shape(), x.dtype(), x.device());
    let n = x.numel();
    assert!(n <= i32::MAX as usize, "tensor too large for i32 kernel param ({n} elements)");
    let n = n as i32;
    unsafe {
        match x.dtype() {
            DType::F32 => f32_fn(x.data_ptr() as _, out.data_ptr() as *mut c_void, n, std::ptr::null_mut()),
            DType::BF16 => bf16_fn(x.data_ptr() as _, out.data_ptr() as *mut c_void, n, std::ptr::null_mut()),
            _ => panic!("unsupported dtype"),
        }
    }
    out
}

fn dispatch_binary(a: &Tensor, b: &Tensor,
                   f32_fn: unsafe extern "C" fn(*const c_void, *const c_void, *mut c_void, i32, *mut c_void),
                   bf16_fn: unsafe extern "C" fn(*const c_void, *const c_void, *mut c_void, i32, *mut c_void)) -> Tensor {
    assert_eq!(a.shape(), b.shape());
    assert!(a.is_contiguous() && b.is_contiguous());
    assert!(matches!(a.device(), Device::Cuda(_)));
    assert_eq!(a.dtype(), b.dtype());
    let out = Tensor::empty(a.shape(), a.dtype(), a.device());
    let n = a.numel();
    assert!(n <= i32::MAX as usize, "tensor too large for i32 kernel param ({n} elements)");
    let n = n as i32;
    unsafe {
        match a.dtype() {
            DType::F32 => f32_fn(a.data_ptr() as _, b.data_ptr() as _, out.data_ptr() as *mut c_void, n, std::ptr::null_mut()),
            DType::BF16 => bf16_fn(a.data_ptr() as _, b.data_ptr() as _, out.data_ptr() as *mut c_void, n, std::ptr::null_mut()),
            _ => panic!("unsupported dtype"),
        }
    }
    out
}

pub fn gelu(x: &Tensor) -> Tensor { dispatch_unary(x, launch_gelu_f32, launch_gelu_bf16) }
pub fn silu(x: &Tensor) -> Tensor { dispatch_unary(x, launch_silu_f32, launch_silu_bf16) }

pub fn scale(x: &Tensor, scale_val: f32) -> Tensor {
    assert!(x.is_contiguous() && matches!(x.device(), Device::Cuda(_)));
    let out = Tensor::empty(x.shape(), x.dtype(), x.device());
    let n = x.numel();
    assert!(n <= i32::MAX as usize, "tensor too large for i32 kernel param ({n} elements)");
    let n = n as i32;
    unsafe {
        match x.dtype() {
            DType::F32 => launch_scale_f32(x.data_ptr() as _, out.data_ptr() as *mut c_void, scale_val, n, std::ptr::null_mut()),
            DType::BF16 => launch_scale_bf16(x.data_ptr() as _, out.data_ptr() as *mut c_void, scale_val, n, std::ptr::null_mut()),
            _ => panic!("unsupported dtype for scale"),
        }
    }
    out
}

pub fn add(a: &Tensor, b: &Tensor) -> Tensor { dispatch_binary(a, b, launch_add_f32, launch_add_bf16) }
pub fn mul(a: &Tensor, b: &Tensor) -> Tensor { dispatch_binary(a, b, launch_mul_f32, launch_mul_bf16) }

/// Fused SiLU×Mul: out = silu(gate) * up (BF16 only)
/// Saves one HBM read + one HBM write compared to separate silu + mul.
pub fn silu_mul(gate: &Tensor, up: &Tensor) -> Tensor {
    assert_eq!(gate.shape(), up.shape());
    assert!(gate.is_contiguous() && up.is_contiguous());
    assert!(matches!(gate.device(), Device::Cuda(_)));
    assert_eq!(gate.dtype(), DType::BF16, "silu_mul requires BF16");
    let out = Tensor::empty(gate.shape(), gate.dtype(), gate.device());
    let n = gate.numel();
    assert!(n <= i32::MAX as usize, "tensor too large for i32 kernel param ({n} elements)");
    let n = n as i32;
    unsafe {
        launch_silu_mul_bf16(
            gate.data_ptr() as *const c_void,
            up.data_ptr() as *const c_void,
            out.data_ptr() as *mut c_void,
            n,
            std::ptr::null_mut(),
        );
    }
    out
}

/// gpt-oss fused GLU activation (BF16 only).
/// Input: gate_up [rows, 2*D] with interleaved columns (gate=even, up=odd).
/// Output: [rows, D]
/// Computes: gate.clamp(max=limit) * sigmoid(gate * alpha) * (up.clamp(-limit,limit) + 1)
pub fn gpt_oss_glu(gate_up: &Tensor, alpha: f32, limit: f32) -> Tensor {
    assert!(gate_up.is_contiguous());
    assert!(matches!(gate_up.device(), Device::Cuda(_)));
    assert_eq!(gate_up.dtype(), DType::BF16, "gpt_oss_glu requires BF16");
    assert_eq!(gate_up.ndim(), 2);
    let rows = gate_up.shape()[0];
    let cols = gate_up.shape()[1];
    assert_eq!(cols % 2, 0);
    let d = cols / 2;
    let out = Tensor::empty(&[rows, d], gate_up.dtype(), gate_up.device());
    let n_elements = (rows * d) as i32;
    unsafe {
        launch_gpt_oss_glu_bf16(
            gate_up.data_ptr() as *const c_void,
            out.data_ptr() as *mut c_void,
            n_elements,
            alpha,
            limit,
            std::ptr::null_mut(),
        );
    }
    out
}