/******************************************************************************
 * Copyright (c) 2023, Tri Dao.
 ******************************************************************************/
#pragma once

namespace flash {
////////////////////////////////////////////////////////////////////////////////////////////////////

template <bool Varlen = true>
struct BlockInfo {
  template <typename Params>
  __device__ BlockInfo(const Params& params, const int bidb)
      : sum_s_q(!Varlen || params.cu_seqlens_q == nullptr ? -1 : params.cu_seqlens_q[bidb]),
        sum_s_k(!Varlen || params.cu_seqlens_k == nullptr || !params.is_seqlens_k_cumulative ? -1 : params.cu_seqlens_k[bidb]),
        actual_seqlen_q(!Varlen || params.cu_seqlens_q == nullptr ? params.seqlen_q : params.cu_seqlens_q[bidb + 1] - sum_s_q)
        // If is_seqlens_k_cumulative, then seqlen_k is cu_seqlens_k[bidb + 1] - cu_seqlens_k[bidb].
        // Otherwise it's cu_seqlens_k[bidb], i.e., we use cu_seqlens_k to store the sequence lengths of K.
        ,
        seqlen_k_cache(!Varlen || params.cu_seqlens_k == nullptr ? params.seqlen_k : (params.is_seqlens_k_cumulative ? params.cu_seqlens_k[bidb + 1] - sum_s_k : params.cu_seqlens_k[bidb])),
        actual_seqlen_k(seqlen_k_cache + (params.knew_ptr == nullptr ? 0 : params.seqlen_knew)) {
  }

  template <typename index_t>
  inline __device__ index_t q_offset(const index_t batch_stride, const index_t row_stride, const int bidb) const {
    return sum_s_q == -1 ? bidb * batch_stride : uint32_t(sum_s_q) * row_stride;
  }

  template <typename index_t>
  inline __device__ index_t k_offset(const index_t batch_stride, const index_t row_stride, const int bidb) const {
    return sum_s_k == -1 ? bidb * batch_stride : uint32_t(sum_s_k) * row_stride;
  }

  const int sum_s_q;
  const int sum_s_k;
  const int actual_seqlen_q;
  // We have to have seqlen_k_cache declared before actual_seqlen_k, otherwise actual_seqlen_k is set to 0.
  const int seqlen_k_cache;
  const int actual_seqlen_k;
};

////////////////////////////////////////////////////////////////////////////////////////////////////

////////////////////////////////////////////////////////////////////////////////////////////////////
}  // namespace flash
