/* This file is part of limb                           https://lila.oss/limb
 * Copyright (C) 2023 Olivier Brunel                          jjk@jjacky.com */
/* SPDX-License-Identifier: GPL-2.0-only */
#include <errno.h>
#include <limb/hasher.h>
#include <limb/patrim.h>
#include <limb/pbkdf2.h>
#include <limb/shldata.h>
#include "shldata.h"

ssize_t
shldata_initr(const char *sce, size_t slen, const char *pwd, size_t plen,
              unsigned *algo, unsigned *iter, shldata_ctx *ctx)
{
    unsigned o;
    const char *salt;
    size_t sltlen;
    ssize_t aadoff;
    int r;

    /* silence warnings */
    salt = NULL;
    sltlen = 0;

    aadoff = -1;
    o = *algo = *iter = 0;
    for (;;) {
        u64 id, u;

        r = patrim_get(&id, &u, sce, slen, o);
        if (r < 0) return (errno = ENODATA, -1);
        if (!patrim_isshldata(id)) {
            /* skip any ID that isn't ours */
            o += r;
            if (patrim_isblob(id))
                o += u;
            continue;
        }
        if (aadoff < 0)
            aadoff = o;
        switch (id) {
            case ID_ALGO:
                *algo = u + 1;
                break;
            case ID_ITER:
                *iter = u;
                break;
            case ID_SALT:
                salt = sce + o + r;
                sltlen = u;
                o += sltlen;
                break;
            case ID_DATA:
                ctx->len = u;
                ctx->done = 0;
                break;
            default:
                return (errno = EINVAL, -1);
        }
        if (id == ID_DATA)
            break;
        o += r;
    }
    if (!*algo || !*iter || !sltlen)
        return (errno = EINVAL, -1);
    --*algo;

    char key[KEY_LEN];
    char nonce[NONCE_LEN] = { 0 };
    pbkdf2(key, sizeof(key), hashers[*algo], pwd, plen, salt, sltlen, *iter);
    ccpl_init(key, nonce, &ctx->ccpl);
    ccpl_aad(sce + aadoff, o - aadoff, &ctx->ccpl);

    /* return offset of begining of encrypted data */
    return o + r;
}