/*
 * Copyright (C) by Argonne National Laboratory
 *     See COPYRIGHT in top-level directory
 */

#include "adio.h"
#include "adio_extern.h"

void ADIOI_GEN_ReadStrided_naive(ADIO_File fd, void *buf, MPI_Aint count,
                                 MPI_Datatype buftype, int file_ptr_type,
                                 ADIO_Offset offset, ADIO_Status * status, int
                                 *error_code)
{
    /* offset is in units of etype relative to the filetype. */

    ADIOI_Flatlist_node *flat_buf, *flat_file;
    ADIO_Offset size, brd_size, frd_size = 0, req_len, sum;
    int b_index;
    int n_etypes_in_filetype;
    ADIO_Offset n_filetypes, etype_in_filetype;
    ADIO_Offset abs_off_in_filetype = 0;
    MPI_Count bufsize, filetype_size, buftype_size, size_in_filetype;
    ADIO_Offset etype_size;
    MPI_Aint lb, filetype_extent, buftype_extent;
    int buf_count, buftype_is_contig, filetype_is_contig;
    ADIO_Offset userbuf_off;
    ADIO_Offset off, req_off, disp, end_offset = 0, start_off;
    ADIO_Status status1;

    *error_code = MPI_SUCCESS;  /* changed below if error */

    ADIOI_Datatype_iscontig(buftype, &buftype_is_contig);
    ADIOI_Datatype_iscontig(fd->filetype, &filetype_is_contig);

    MPI_Type_size_x(fd->filetype, &filetype_size);
    if (!filetype_size) {
#ifdef HAVE_STATUS_SET_BYTES
        MPIR_Status_set_bytes(status, buftype, 0);
#endif
        *error_code = MPI_SUCCESS;
        return;
    }

    MPI_Type_get_extent(fd->filetype, &lb, &filetype_extent);
    MPI_Type_size_x(buftype, &buftype_size);
    MPI_Type_get_extent(buftype, &lb, &buftype_extent);
    etype_size = fd->etype_size;

    ADIOI_Assert((buftype_size * count) == ((ADIO_Offset) buftype_size * (ADIO_Offset) count));
    bufsize = buftype_size * count;

    /* contiguous in buftype and filetype is handled elsewhere */

    if (!buftype_is_contig && filetype_is_contig) {
        int b_count;
        /* noncontiguous in memory, contiguous in file. */

        flat_buf = ADIOI_Flatten_and_find(buftype);

        off = (file_ptr_type == ADIO_INDIVIDUAL) ? fd->fp_ind : fd->disp + etype_size * offset;

        start_off = off;
        end_offset = off + bufsize - 1;

        /* if atomicity is true, lock (exclusive) the region to be accessed */
        if ((fd->atomicity) && ADIO_Feature(fd, ADIO_LOCKS)) {
            ADIOI_WRITE_LOCK(fd, start_off, SEEK_SET, end_offset - start_off + 1);
        }

        /* for each region in the buffer, grab the data and put it in
         * place
         */
        for (b_count = 0; b_count < count; b_count++) {
            for (b_index = 0; b_index < flat_buf->count; b_index++) {
                userbuf_off = (ADIO_Offset) b_count *(ADIO_Offset) buftype_extent +
                    flat_buf->indices[b_index];
                req_off = off;
                req_len = flat_buf->blocklens[b_index];

                ADIOI_Assert((((ADIO_Offset) (uintptr_t) buf) + userbuf_off) ==
                             (ADIO_Offset) (uintptr_t) ((uintptr_t) buf + userbuf_off));
                ADIOI_Assert(req_len == (int) req_len);
                ADIO_ReadContig(fd,
                                (char *) buf + userbuf_off,
                                req_len,
                                MPI_BYTE, ADIO_EXPLICIT_OFFSET, req_off, &status1, error_code);
                if (*error_code != MPI_SUCCESS)
                    return;

                /* off is (potentially) used to save the final offset later */
                off += flat_buf->blocklens[b_index];
            }
        }

        if ((fd->atomicity) && ADIO_Feature(fd, ADIO_LOCKS)) {
            ADIOI_UNLOCK(fd, start_off, SEEK_SET, end_offset - start_off + 1);
        }

        if (file_ptr_type == ADIO_INDIVIDUAL)
            fd->fp_ind = off;

    }

    else {      /* noncontiguous in file */
        int f_index, st_index = 0;
        ADIO_Offset st_n_filetypes;
        ADIO_Offset st_frd_size;
        int flag;

        /* First we're going to calculate a set of values for use in all
         * the noncontiguous in file cases:
         * start_off - starting byte position of data in file
         * end_offset - last byte offset to be accessed in the file
         * st_n_filetypes - how far into the file we start in terms of
         *                  whole filetypes
         * st_index - index of block in first filetype that we will be
         *            starting in (?)
         * st_frd_size - size of the data in the first filetype block
         *               that we will read (accounts for being part-way
         *               into reading this block of the filetype
         *
         */

        flat_file = ADIOI_Flatten_and_find(fd->filetype);
        disp = fd->disp;

        if (file_ptr_type == ADIO_INDIVIDUAL) {
            start_off = fd->fp_ind;     /* in bytes */
            n_filetypes = -1;
            flag = 0;
            while (!flag) {
                n_filetypes++;
                for (f_index = 0; f_index < flat_file->count; f_index++) {
                    if (disp + flat_file->indices[f_index] +
                        n_filetypes * (ADIO_Offset) filetype_extent +
                        flat_file->blocklens[f_index] >= start_off) {
                        /* this block contains our starting position */

                        st_index = f_index;
                        frd_size = disp + flat_file->indices[f_index] +
                            n_filetypes * (ADIO_Offset) filetype_extent +
                            flat_file->blocklens[f_index] - start_off;
                        flag = 1;
                        break;
                    }
                }
            }
        } else {
            n_etypes_in_filetype = filetype_size / etype_size;
            n_filetypes = offset / n_etypes_in_filetype;
            etype_in_filetype = (int) (offset % n_etypes_in_filetype);
            size_in_filetype = (unsigned) etype_in_filetype *(unsigned) etype_size;

            sum = 0;
            for (f_index = 0; f_index < flat_file->count; f_index++) {
                sum += flat_file->blocklens[f_index];
                if (sum > size_in_filetype) {
                    st_index = f_index;
                    frd_size = sum - size_in_filetype;
                    abs_off_in_filetype = flat_file->indices[f_index] +
                        size_in_filetype - (sum - flat_file->blocklens[f_index]);
                    break;
                }
            }

            /* abs. offset in bytes in the file */
            start_off = disp + n_filetypes * (ADIO_Offset) filetype_extent + abs_off_in_filetype;
        }

        st_frd_size = frd_size;
        st_n_filetypes = n_filetypes;

        /* start_off, st_n_filetypes, st_index, and st_frd_size are
         * all calculated at this point
         */

        /* Calculate end_offset, the last byte-offset that will be accessed.
         * e.g., if start_off=0 and 100 bytes to be read, end_offset=99
         */
        userbuf_off = 0;
        f_index = st_index;
        off = start_off;
        frd_size = MPL_MIN(st_frd_size, bufsize);
        while (userbuf_off < bufsize) {
            userbuf_off += frd_size;
            end_offset = off + frd_size - 1;

            if (f_index < (flat_file->count - 1))
                f_index++;
            else {
                f_index = 0;
                n_filetypes++;
            }

            off = disp + flat_file->indices[f_index] + n_filetypes * (ADIO_Offset) filetype_extent;
            frd_size = MPL_MIN(flat_file->blocklens[f_index], bufsize - (unsigned) userbuf_off);
        }

        /* End of calculations.  At this point the following values have
         * been calculated and are ready for use:
         * - start_off
         * - end_offset
         * - st_n_filetypes
         * - st_index
         * - st_frd_size
         */

        /* if atomicity is true, lock (exclusive) the region to be accessed */
        if ((fd->atomicity) && ADIO_Feature(fd, ADIO_LOCKS)) {
            ADIOI_WRITE_LOCK(fd, start_off, SEEK_SET, end_offset - start_off + 1);
        }

        if (buftype_is_contig && !filetype_is_contig) {
            /* contiguous in memory, noncontiguous in file. should be the
             * most common case.
             */

            userbuf_off = 0;
            f_index = st_index;
            off = start_off;
            n_filetypes = st_n_filetypes;
            frd_size = MPL_MIN(st_frd_size, bufsize);

            /* while there is still space in the buffer, read more data */
            while (userbuf_off < bufsize) {
                if (frd_size) {
                    /* TYPE_UB and TYPE_LB can result in
                     * frd_size = 0. save system call in such cases */
                    req_off = off;
                    req_len = frd_size;

                    ADIOI_Assert((((ADIO_Offset) (uintptr_t) buf) + userbuf_off) ==
                                 (ADIO_Offset) (uintptr_t) ((uintptr_t) buf + userbuf_off));
                    ADIOI_Assert(req_len == (int) req_len);
                    ADIO_ReadContig(fd,
                                    (char *) buf + userbuf_off,
                                    req_len,
                                    MPI_BYTE, ADIO_EXPLICIT_OFFSET, req_off, &status1, error_code);
                    if (*error_code != MPI_SUCCESS)
                        return;
                }
                userbuf_off += frd_size;

                if (off + frd_size < disp + flat_file->indices[f_index] +
                    flat_file->blocklens[f_index] + n_filetypes * (ADIO_Offset) filetype_extent) {
                    /* important that this value be correct, as it is
                     * used to set the offset in the fd near the end of
                     * this function.
                     */
                    off += frd_size;
                }
                /* did not reach end of contiguous block in filetype.
                 * no more I/O needed. off is incremented by frd_size.
                 */
                else {
                    if (f_index < (flat_file->count - 1))
                        f_index++;
                    else {
                        f_index = 0;
                        n_filetypes++;
                    }
                    off = disp + flat_file->indices[f_index] +
                        n_filetypes * (ADIO_Offset) filetype_extent;
                    frd_size = MPL_MIN(flat_file->blocklens[f_index],
                                       bufsize - (unsigned) userbuf_off);
                }
            }
        } else {
            ADIO_Offset i_offset, tmp_bufsize = 0;
            /* noncontiguous in memory as well as in file */

            flat_buf = ADIOI_Flatten_and_find(buftype);

            b_index = buf_count = 0;
            i_offset = flat_buf->indices[0];
            f_index = st_index;
            off = start_off;
            n_filetypes = st_n_filetypes;
            frd_size = st_frd_size;
            brd_size = flat_buf->blocklens[0];

            /* while we haven't read size * count bytes, keep going */
            while (tmp_bufsize < bufsize) {
                ADIO_Offset new_brd_size = brd_size, new_frd_size = frd_size;

                size = MPL_MIN(frd_size, brd_size);
                /* keep max of a single read amount <= INT_MAX */
                size = MPL_MIN(size, INT_MAX);

                if (size) {
                    req_off = off;
                    req_len = size;
                    userbuf_off = i_offset;

                    ADIOI_Assert((((ADIO_Offset) (uintptr_t) buf) + userbuf_off) ==
                                 (ADIO_Offset) (uintptr_t) ((uintptr_t) buf + userbuf_off));
                    ADIOI_Assert(req_len == (int) req_len);
                    ADIO_ReadContig(fd,
                                    (char *) buf + userbuf_off,
                                    req_len,
                                    MPI_BYTE, ADIO_EXPLICIT_OFFSET, req_off, &status1, error_code);
                    if (*error_code != MPI_SUCCESS)
                        return;
                }

                if (size == frd_size) {
                    /* reached end of contiguous block in file */
                    if (f_index < (flat_file->count - 1))
                        f_index++;
                    else {
                        f_index = 0;
                        n_filetypes++;
                    }

                    off = disp + flat_file->indices[f_index] +
                        n_filetypes * (ADIO_Offset) filetype_extent;

                    new_frd_size = flat_file->blocklens[f_index];
                    if (size != brd_size) {
                        i_offset += size;
                        new_brd_size -= size;
                    }
                }

                if (size == brd_size) {
                    /* reached end of contiguous block in memory */

                    b_index = (b_index + 1) % flat_buf->count;
                    buf_count++;
                    i_offset = buftype_extent * (buf_count / flat_buf->count) +
                        flat_buf->indices[b_index];
                    new_brd_size = flat_buf->blocklens[b_index];
                    if (size != frd_size) {
                        off += size;
                        new_frd_size -= size;
                    }
                }
                tmp_bufsize += size;
                frd_size = new_frd_size;
                brd_size = new_brd_size;
            }
        }

        /* unlock the file region if we locked it */
        if ((fd->atomicity) && ADIO_Feature(fd, ADIO_LOCKS)) {
            ADIOI_UNLOCK(fd, start_off, SEEK_SET, end_offset - start_off + 1);
        }

        if (file_ptr_type == ADIO_INDIVIDUAL)
            fd->fp_ind = off;
    }   /* end of (else noncontiguous in file) */

    fd->fp_sys_posn = -1;       /* mark it as invalid. */

#ifdef HAVE_STATUS_SET_BYTES
    MPIR_Status_set_bytes(status, buftype, bufsize);
    /* This is a temporary way of filling in status. The right way is to
     * keep track of how much data was actually read and placed in buf
     */
#endif

}
