rssn 0.2.9

//! Bincode-based FFI API for physics sim Schrodinger quantum functions.

use num_complex::Complex;
use serde::Deserialize;

use crate::ffi_apis::common::BincodeBuffer;
use crate::ffi_apis::common::from_bincode_buffer;
use crate::ffi_apis::common::to_bincode_buffer;
use crate::ffi_apis::ffi_api::FfiResult;
use crate::physics::physics_sim::schrodinger_quantum::SchrodingerParameters;
use crate::physics::physics_sim::schrodinger_quantum::{
    self,
};

#[derive(Deserialize)]
struct SchrodingerInput {
    params: SchrodingerParameters,
    initial_psi_re: Vec<f64>,
    initial_psi_im: Vec<f64>,
}

/// Solves the time-dependent Schrödinger equation for quantum wavefunction evolution via bincode serialization.
///
/// The Schrödinger equation iℏ∂ψ/∂t = Ĥψ where Ĥ = -ℏ²∇²/(2m) + V(r) governs quantum
/// mechanical evolution of the wavefunction ψ(r,t) under a potential V. This solver uses
/// the Crank-Nicolson or split-operator method for unitary time evolution.
///
/// # Arguments
///
/// * `buffer` - A bincode-encoded buffer containing `SchrodingerInput` with:
///   - `params`: Schrödinger parameters including:
///     - `n_points`: Number of spatial grid points
///     - `dx`: Spatial discretization step
///     - `dt`: Time step size
///     - `steps`: Number of time steps
///     - `potential`: External potential V(x) values
///   - `initial_psi_re`: Real part of initial wavefunction ψ(x,0)
///   - `initial_psi_im`: Imaginary part of initial wavefunction ψ(x,0)
///
/// # Returns
///
/// A bincode-encoded buffer containing `FfiResult<Vec<f64>, String>` with either:
/// - `ok`: Final probability density |ψ(x,t)|² as a vector
/// - `err`: Error message if computation failed or produced no snapshots
///
/// # Safety
///
/// This function is unsafe because it receives a raw bincode buffer that must be
/// valid and properly encoded.
///
/// # Safety
///
/// This function is unsafe because it dereferences raw pointers as part of the FFI boundary.
/// The caller must ensure:
/// 1. All pointer arguments are valid and point to initialized memory.
/// 2. The memory layout of passed structures matches the expected C-ABI layout.
/// 3. Any pointers returned by this function are managed according to the API's ownership rules.
#[unsafe(no_mangle)]
pub unsafe extern "C" fn rssn_physics_sim_schrodinger_run_bincode(
    buffer: BincodeBuffer
) -> BincodeBuffer {
    let input: SchrodingerInput = match from_bincode_buffer(&buffer) {
        | Some(i) => i,
        | None => {
            return to_bincode_buffer(&FfiResult::<Vec<f64>, String>::err(
                "Invalid Bincode".to_string(),
            ));
        },
    };

    let mut initial_psi: Vec<Complex<f64>> = input
        .initial_psi_re
        .iter()
        .zip(input.initial_psi_im.iter())
        .map(|(&r, &i)| Complex::new(r, i))
        .collect();

    match schrodinger_quantum::run_schrodinger_simulation(&input.params, &mut initial_psi) {
        | Ok(snapshots) => {
            if let Some(final_state) = snapshots.last() {
                to_bincode_buffer(&FfiResult::<Vec<f64>, String>::ok(
                    final_state.clone().into_raw_vec_and_offset().0,
                ))
            } else {
                to_bincode_buffer(&FfiResult::<Vec<f64>, String>::err(
                    "No snapshots".to_string(),
                ))
            }
        },
        | Err(e) => to_bincode_buffer(&FfiResult::<Vec<f64>, String>::err(e)),
    }
}