open Lacaml.D

module Ds = Determinant_space

type t =
  {
    det_space   : Ds.t ;
    h_matrix    : Mat.t lazy_t ;
    s2_matrix   : Mat.t lazy_t ;
    eigensystem : (Mat.t * Vec.t) lazy_t;
  }

let det_space    t = t.det_space

let h_matrix     t = Lazy.force t.h_matrix

let s2_matrix    t = Lazy.force t.s2_matrix

let eigensystem  t = Lazy.force t.eigensystem 

let eigenvectors t = 
  let (x,_) = eigensystem t in x

let eigenvalues t = 
  let (_,x) = eigensystem t in x

let h_integrals mo_basis = 
  let one_e_ints  = MOBasis.one_e_ints mo_basis
  and two_e_ints  = MOBasis.two_e_ints mo_basis
  in
  ( (fun i j _ -> one_e_ints.{i,j}), 
    (fun i j k l s s' ->
       if s' = Spin.other s then
         ERI.get_phys two_e_ints i j k l
       else
         (ERI.get_phys two_e_ints i j k l) -. 
         (ERI.get_phys two_e_ints i j l k) 
    ) )



let h_ij mo_basis ki kj =
  let integrals =
    List.map (fun f -> f mo_basis)
      [ h_integrals ]
  in
  CIMatrixElement.make integrals ki kj 
  |> List.hd



let make det_space = 
  let ndet = Ds.size det_space in
  let det  = Ds.determinants det_space in
  let mo_basis = Ds.mo_basis det_space in
  let h_matrix = lazy (
    Array.init ndet (fun i -> let ki = det.(i) in
                      Array.init ndet (fun j -> let kj = det.(j) in
                                        h_ij mo_basis ki kj
                                      ))
    |> Mat.of_array
  )
  in
  let s2_matrix = lazy (
    Array.init ndet (fun i -> let ki = det.(i) in
                      Array.init ndet (fun j -> let kj = det.(j) in
                                        CIMatrixElement.make_s2 ki kj
                                      ))
    |> Mat.of_array
  )
  in
  let eigensystem = lazy (
    Lazy.force h_matrix
    |> Util.diagonalize_symm 
  )
  in
  { det_space ; h_matrix ; s2_matrix ; eigensystem }