/*
    Copyright (C) 2023 Jean Kieffer

    This file is part of FLINT.

    FLINT is free software: you can redistribute it and/or modify it under
    the terms of the GNU Lesser General Public License (LGPL) as published
    by the Free Software Foundation; either version 3 of the License, or
    (at your option) any later version.  See <https://www.gnu.org/licenses/>.
*/

#include "fmpz.h"
#include "acb_theta.h"

static void
sp2gz_fundamental_g2(fmpz_mat_t mat, slong j)
{
    slong g = 2;
    fmpz_mat_t a, b, c, d;

    fmpz_mat_init(a, g, g);
    fmpz_mat_init(b, g, g);
    fmpz_mat_init(c, g, g);
    fmpz_mat_init(d, g, g);

    if (j < 15)
    {
        fmpz_mat_zero(a);
        fmpz_mat_one(c);
        fmpz_mat_neg(b, c);
    }
    if (15 <= j && j < 17)
    {
        fmpz_mat_one(a);
        fmpz_mat_neg(b, a);
    }
    if (17 <= j && j < 19)
    {
        fmpz_mat_zero(b);
        fmpz_one(fmpz_mat_entry(c, 0, 0));
        fmpz_set_si(fmpz_mat_entry(c, 0, 1), -1);
        fmpz_set_si(fmpz_mat_entry(c, 1, 0), -1);
        fmpz_one(fmpz_mat_entry(c, 1, 1));
    }

    switch (j)
    {
        case 0:
            fmpz_mat_zero(d);
            break;
        case 1:
            fmpz_one(fmpz_mat_entry(d, 0, 0));
            break;
        case 2:
            fmpz_set_si(fmpz_mat_entry(d, 0, 0), -1);
            break;
        case 3:
            fmpz_one(fmpz_mat_entry(d, 1, 1));
            break;
        case 4:
            fmpz_set_si(fmpz_mat_entry(d, 1, 1), -1);
            break;
        case 5:
            fmpz_mat_one(d);
            break;
        case 6:
            fmpz_mat_one(d);
            fmpz_mat_neg(d, d);
            break;
        case 7:
            fmpz_set_si(fmpz_mat_entry(d, 0, 0), -1);
            fmpz_one(fmpz_mat_entry(d, 1, 1));
            break;
        case 8:
            fmpz_one(fmpz_mat_entry(d, 0, 0));
            fmpz_set_si(fmpz_mat_entry(d, 1, 1), -1);
            break;
        case 9:
            fmpz_one(fmpz_mat_entry(d, 0, 1));
            fmpz_one(fmpz_mat_entry(d, 1, 0));
            break;
        case 10:
            fmpz_set_si(fmpz_mat_entry(d, 0, 1), -1);
            fmpz_set_si(fmpz_mat_entry(d, 1, 0), -1);
            break;
        case 11:
            fmpz_one(fmpz_mat_entry(d, 0, 0));
            fmpz_one(fmpz_mat_entry(d, 0, 1));
            fmpz_one(fmpz_mat_entry(d, 1, 0));
            break;
        case 12:
            fmpz_set_si(fmpz_mat_entry(d, 0, 0), -1);
            fmpz_set_si(fmpz_mat_entry(d, 0, 1), -1);
            fmpz_set_si(fmpz_mat_entry(d, 1, 0), -1);
            break;
        case 13:
            fmpz_one(fmpz_mat_entry(d, 0, 1));
            fmpz_one(fmpz_mat_entry(d, 1, 0));
            fmpz_one(fmpz_mat_entry(d, 1, 1));
            break;
        case 14:
            fmpz_set_si(fmpz_mat_entry(d, 0, 1), -1);
            fmpz_set_si(fmpz_mat_entry(d, 1, 0), -1);
            fmpz_set_si(fmpz_mat_entry(d, 1, 1), -1);
            break;
        case 15:
            fmpz_one(fmpz_mat_entry(c, 0, 0));
            fmpz_one(fmpz_mat_entry(d, 1, 1));
            break;
        case 16:
            fmpz_one(fmpz_mat_entry(c, 1, 1));
            fmpz_one(fmpz_mat_entry(d, 0, 0));
            break;
        case 17:
            fmpz_mat_one(a);
            fmpz_mat_one(d);
            break;
        default: //case 18:
            fmpz_mat_one(a);
            fmpz_mat_neg(a, a);
            fmpz_mat_set(d, a);
    }

    sp2gz_set_blocks(mat, a, b, c, d);

    fmpz_mat_clear(a);
    fmpz_mat_clear(b);
    fmpz_mat_clear(c);
    fmpz_mat_clear(d);
}

static void
sp2gz_fundamental_gen_1(fmpz_mat_t mat, slong j)
{
    slong g = sp2gz_dim(mat);
    slong k = 0;
    slong cnt = 0;
    slong l, u, v;
    fmpz_mat_t mat_g2;

    fmpz_mat_init(mat_g2, 4, 4);

    while (cnt + (g - 1 - k) <= j/19)
    {
        cnt += g - 1 - k;
        k++;
    }
    l = k + 1 + (j/19 - cnt);
    sp2gz_fundamental_g2(mat_g2, j % 19);

    fmpz_mat_one(mat);
    for (u = 0; u < 2; u++)
    {
        for (v = 0; v < 2; v++)
        {
            fmpz_set(fmpz_mat_entry(mat, k + u * g, k + v * g),
                fmpz_mat_entry(mat_g2, 2 * u, 2 * v));
            fmpz_set(fmpz_mat_entry(mat, k + u * g, l + v * g),
                fmpz_mat_entry(mat_g2, 2 * u, 2 * v + 1));
            fmpz_set(fmpz_mat_entry(mat, l + u * g, k + v * g),
                fmpz_mat_entry(mat_g2, 2 * u + 1, 2 * v));
            fmpz_set(fmpz_mat_entry(mat, l + u * g, l + v * g),
                fmpz_mat_entry(mat_g2, 2 * u + 1, 2 * v + 1));
        }
    }

    fmpz_mat_clear(mat_g2);
}

static void
sp2gz_fundamental_gen_2(fmpz_mat_t mat, slong j)
{
    slong g = sp2gz_dim(mat);
    slong k;

    fmpz_mat_one(mat);

    for (k = g - 1; k >= 0; k--)
    {
        if (j % 2 == 1)
        {
            fmpz_zero(fmpz_mat_entry(mat, k, k));
            fmpz_one(fmpz_mat_entry(mat, k, k + g));
            fmpz_set_si(fmpz_mat_entry(mat, k + g, k), -1);
            fmpz_zero(fmpz_mat_entry(mat, k + g, k + g));
        }
    }
}

void
sp2gz_fundamental(fmpz_mat_t mat, slong j)
{
    slong g = sp2gz_dim(mat);
    slong nb_1 = 19 * ((g * (g - 1))/2);

    if (g == 1)
    {
        sp2gz_j(mat);
    }
    else if (g == 2)
    {
        sp2gz_fundamental_g2(mat, j);
    }
    else if (j < nb_1)
    {
        sp2gz_fundamental_gen_1(mat, j);
    }
    else
    {
        sp2gz_fundamental_gen_2(mat, j - nb_1);
    }
}
