#include <grass/config.h>
#include <stdlib.h>
#include <string.h>
#include <grass/gis.h>
#include <grass/raster.h>
#include "tinf.h"

CELL select_dir(CELL i)
{
    CELL dir[256] = {
        0,   1,   2,   2,   4,   1,   2,   2,   8,   1,   8,   2,   8,   4,
        4,   2,   16,  16,  16,  2,   16,  4,   4,   2,   8,   8,   8,   8,
        8,   8,   8,   4,   32,  1,   2,   2,   4,   4,   2,   2,   32,  8,
        8,   2,   8,   8,   4,   4,   32,  32,  32,  32,  16,  32,  4,   2,
        16,  16,  16,  16,  8,   16,  8,   8,   64,  64,  64,  1,   64,  1,
        2,   2,   64,  64,  8,   2,   8,   8,   4,   2,   16,  64,  64,  2,
        16,  64,  2,   2,   16,  8,   8,   8,   8,   8,   8,   4,   32,  64,
        32,  1,   32,  32,  32,  2,   32,  32,  32,  2,   32,  8,   4,   4,
        32,  32,  32,  32,  32,  32,  32,  32,  32,  32,  16,  16,  16,  16,
        8,   8,   128, 128, 128, 1,   4,   1,   2,   2,   128, 128, 2,   1,
        8,   4,   4,   2,   16,  128, 2,   1,   4,   128, 2,   1,   8,   128,
        8,   1,   8,   8,   4,   2,   32,  128, 1,   1,   128, 128, 2,   1,
        32,  128, 32,  1,   8,   128, 4,   2,   32,  32,  32,  1,   32,  128,
        32,  1,   16,  16,  16,  1,   16,  16,  8,   4,   128, 128, 128, 128,
        128, 128, 2,   1,   128, 128, 128, 1,   128, 128, 4,   2,   64,  128,
        128, 1,   128, 128, 128, 1,   8,   128, 8,   1,   8,   8,   8,   2,
        64,  128, 64,  128, 64,  128, 64,  128, 32,  64,  64,  128, 64,  64,
        64,  1,   32,  64,  64,  128, 64,  64,  64,  128, 32,  32,  32,  64,
        32,  32,  16,  128};

    return dir[i];
}

void flink(int i, int j, int nl, int ns, CELL *p1, CELL *p2, CELL *p3,
           int *active, int *goagain)
{
    CELL bitmask[8] = {1, 2, 4, 8, 16, 32, 64, 128};
    CELL outflow, cwork, c[8];
    int k;

    cwork = p2[j];
    if (Rast_is_c_null_value(p2 + j) || cwork >= 0 || cwork == -256)
        return;
    cwork = -cwork;

    for (k = 7; k >= 0; k--) {
        c[k] = 0;
        if (cwork >= bitmask[k]) {
            c[k] = 1;
            cwork -= bitmask[k];
        }
    }

    outflow = 0;

    /* There's no need to resolve directions at cells adjacent to null cells,
     * as those directions will be resolved before we get here */
    /* look one row back */
    cwork = p1[j - 1];
    if (cwork > 0 && cwork != 4 && c[6])
        outflow += 64;
    cwork = p1[j];
    if (cwork > 0 && cwork != 8 && c[7])
        outflow += 128;
    cwork = p1[j + 1];
    if (cwork > 0 && cwork != 16 && c[0])
        outflow += 1;

    /* look at this row */
    cwork = p2[j - 1];
    if (cwork > 0 && cwork != 2 && c[5])
        outflow += 32;
    cwork = p2[j + 1];
    if (cwork > 0 && cwork != 32 && c[1])
        outflow += 2;

    /* look one row forward */
    cwork = p3[j - 1];
    if (cwork > 0 && cwork != 1 && c[4])
        outflow += 16;
    cwork = p3[j];
    if (cwork > 0 && cwork != 128 && c[3])
        outflow += 8;
    cwork = p3[j + 1];
    if (cwork > 0 && cwork != 64 && c[2])
        outflow += 4;

    if (outflow == 0) {
        *active = 1;
    }
    else {
        *goagain = 1;
        p2[j] = select_dir(outflow);
    }
    return;
}

void resolve(int fd, int nl, struct band3 *bnd)
{
    CELL cvalue;
    int *active;
    int offset, isz, i, j, pass, activity, goagain, done;

    active = (int *)G_calloc(nl, sizeof(int));

    isz = sizeof(CELL);

    /* select a direction when there are multiple non-flat links */
    lseek(fd, bnd->sz, SEEK_SET);
    for (i = 1; i < nl - 1; i += 1) {
        read(fd, bnd->b[0], bnd->sz);
        for (j = 1; j < bnd->ns - 1; j += 1) {
            offset = j * isz;
            if (Rast_is_c_null_value((void *)(bnd->b[0] + offset)))
                continue;
            memcpy(&cvalue, bnd->b[0] + offset, isz);
            if (cvalue > 0)
                cvalue = select_dir(cvalue);
            memcpy(bnd->b[0] + offset, &cvalue, isz);
        }
        lseek(fd, -bnd->sz, SEEK_CUR);
        write(fd, bnd->b[0], bnd->sz);
    }

    pass = 0;
    for (i = 1; i < nl - 1; i += 1)
        active[i] = 1;

    /* select a direction when there are multiple flat links */
    do {
        done = 1;
        pass += 1;

        activity = 0;

        lseek(fd, 0, SEEK_SET);
        advance_band3(fd, bnd);
        advance_band3(fd, bnd);
        for (i = 1; i < nl - 1; i++) {
            lseek(fd, (off_t)(i + 1) * bnd->sz, SEEK_SET);
            advance_band3(fd, bnd);

            if (!active[i])
                continue;

            done = 0;
            active[i] = 0;
            do {
                goagain = 0;
                for (j = 1; j < bnd->ns - 1; j += 1) {
                    flink(i, j, nl, bnd->ns, (void *)bnd->b[0],
                          (void *)bnd->b[1], (void *)bnd->b[2], &active[i],
                          &goagain);
                    if (goagain)
                        activity = 1;
                }
            } while (goagain);

            lseek(fd, (off_t)i * bnd->sz, SEEK_SET);
            write(fd, bnd->b[1], bnd->sz);
        }

        if (!activity) {
            done = 1;
            continue;
        }

        activity = 0;

        lseek(fd, (off_t)(nl - 1) * bnd->sz, SEEK_SET);
        retreat_band3(fd, bnd);
        retreat_band3(fd, bnd);
        for (i = nl - 2; i >= 1; i -= 1) {
            lseek(fd, (off_t)(i - 1) * bnd->sz, SEEK_SET);
            retreat_band3(fd, bnd);

            if (!active[i])
                continue;

            done = 0;
            active[i] = 0;
            do {
                goagain = 0;
                for (j = 1; j < bnd->ns - 1; j++) {
                    flink(i, j, nl, bnd->ns, (void *)bnd->b[0],
                          (void *)bnd->b[1], (void *)bnd->b[2], &active[i],
                          &goagain);
                    if (goagain)
                        activity = 1;
                }
            } while (goagain);

            lseek(fd, (off_t)i * bnd->sz, SEEK_SET);
            write(fd, bnd->b[1], bnd->sz);
        }

        if (!activity) {
            done = 1;
        }

    } while (!done);

    G_free(active);

    return;
}
