#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>

int main(int argc, char **argv) {
    FILE *fin, *fout;
    int pnm_ver, x_dim, y_dim, max_val = 1;
    int i, j, len, start, width, from, to;

    if (argc != 3 && argc != 4 && argc != 5) {
        fprintf(stderr, "Usage: pnm-select length width [IN.PNM [OUT.PNM]]\n");
        exit(1);
    }

    if (sscanf(argv[1], "%d", &len) != 1 ||  len <= 0) {
        fprintf(stderr, "Incorrect parameter: %s\n", argv[1]);
        exit(1);
    }

    if (sscanf(argv[2], "%d", &width) != 1 ||  width <= 0) {
        fprintf(stderr, "Incorrect parameter: %s\n", argv[2]);
        exit(1);
    }

    if (argc > 3 && strcmp(argv[3], "-")) {
        fin = fopen(argv[3], "rb");
        if (fin == 0) {
            fprintf(stderr, "Can't open %s\n", argv[3]);
            exit(1);
        }
    } else {
        fin = stdin; 
    }

    if (fscanf(fin, "P%d%d%d", &pnm_ver, &x_dim, &y_dim) != 3) {
        fprintf(stderr, "Bad header\n");
        exit(1);
    }
    if (pnm_ver < 1 || pnm_ver > 6 || x_dim <= 0 || y_dim <= 0) {
        fprintf(stderr, "Header parameters are out of range\n");
        exit(1);
    }
    if (pnm_ver == 2 || pnm_ver == 3 || pnm_ver == 5 || pnm_ver == 6) {
        if (fscanf(fin, "%d", &max_val) != 1 ||  max_val <= 0 || max_val > 255) {
            fprintf(stderr, "Bad maximum value\n");
            exit(1);
        }
    }

    if (argc > 4 && strcmp(argv[4], "-")) {
        fout = fopen(argv[4], "wb");
        if (fout == 0) {
            fprintf(stderr, "Can't open %s\n", argv[4]);
            exit(1);
        }
    } else {
        fout = stdout; 
    }

    start = y_dim - len;
    if (start < 0) {
        start = 0;
        len = y_dim;
    }

    if (width >= x_dim) {
        from = 0;
        to = x_dim;
    } else {
        from = (x_dim - width) / 2;
        to = from + width;
    }


    if (fprintf(fout, (pnm_ver == 1 || pnm_ver == 4) ? "P%d\n%d %d\n" : "P%d\n%d %d\n%d\n", pnm_ver, width, len, max_val) < 0) {
      write_error:
        fprintf(stderr, "Error writing output file\n");
        exit(1);
    }

    if (pnm_ver == 1 || pnm_ver == 2) {
        for(j=0; j<y_dim; j++) {
            for(i=0; i<x_dim; i++) {
                int c;
                if (fscanf(fin, "%d", &c) != 1) {
                    fprintf(stderr, "Error reading input file at i=%d, j=%d\n", i, j);
                    exit(1);
                }
                if (j >= start && i >= from && i < to) {
                    if (fprintf(fout, "%d ", c) < 0)
                        goto write_error;
                }
            }
            if (j >= start) {
                if (fprintf(fout, "\n") < 0)
                    goto write_error;
            }
        }
    } else if (pnm_ver == 4) {
        int pack_len = (x_dim + 7)/8;
        int new_pack_len = (width + 7)/8;
        unsigned char *buf = (unsigned char *)malloc(pack_len + 1);
        if (!buf) {
            fprintf(stderr,"malloc(%d) failed\n", pack_len);
            exit(1);
        }
        buf[pack_len] = 0; // for Valgrind
        for(j = 0; j<y_dim; j++) {
            if (fread(buf, 1, pack_len, fin) != pack_len) {
                fprintf(stderr, "Error reading input file\n");
                exit(1);
            }
            if (j >= start) {
                int off = from/8;
                int a = from % 8;
                int b = 8 - a;
                for (i = 0; i < new_pack_len; i++) {
                    buf[i] = (buf[i + off] << a) + (buf[i + off + 1] >> b);
                }
                if(fwrite(buf, 1, new_pack_len, fout) != new_pack_len)
                    goto write_error;
            }
        }
        free(buf);
    } else if (pnm_ver == 5 ) {
        for(j = 0; j<y_dim; j++) {
            for(i = 0; i< x_dim; i++) {
                int c = getc(fin);
                if (c == EOF) {
                    fprintf(stderr, "Error reading input file\n");
                     exit(1);
                }
                if (j >= start && i >= from && i < to) {
                    if (putc(c, fout) == EOF)
                        goto write_error;
                }
            }
        }
    } else {
        fprintf(stderr,"Unsupported PNM type = %d\n", pnm_ver);
        exit(1);
    }
    if (fin != stdin)
        fclose(fin);
    if (fout != stdout)
        fclose(fout);

    return 0;
}