/*  pgmio.c -- Read and write the pgm image format.
    Written november 12, 2011 by Eric Olson for Math 761
*/

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

void readimage(double x[], int n, char *p) {
    char buf[256];
    FILE *fp;
    printf("Reading %s...\n", p);
    if(!(fp = fopen(p, "r"))) {
        fprintf(stderr, "Can't open %s for read!\n", p);
        exit(1);
    }
    int d, i = 0;
    int stage = 0;
    while(fgets(buf, sizeof(buf), fp)) {
        if(buf[0] == '#')
            continue;
        switch (stage) {
        case 0:;
            if(!strncmp(buf, "P2", 2)) {
                stage++;
                break;
            }
            fprintf(stderr, "Expecting P2 but found %s!\n", buf);
            exit(2);
        case 1:;
            int n1, n2;
            if(sscanf(buf, "%d %d", &n1, &n2) == 2) {
                if(n1 == n && n2 == n) {
                    stage++;
                    break;
                }
            }
            fprintf(stderr, "Expecting %d %d but found %s!\n", n, n, buf);
            exit(3);
        case 2:;
            if(sscanf(buf, "%d", &d) == 1) {
                if(d > 0) {
                    stage++;
                    break;
                }
            }
            fprintf(stderr, "Expecting d>0 but found d=%s!\n", buf);
            exit(4);
        case 3:;
            char *p, *q;
            p = buf;
            for(;;) {
                x[i] = (double) strtol(p, &q, 10) / d;
                if(p < q) {
                    p = q;
                    if(++i == n * n) {
                        fclose(fp);
                        return;
                    }
                } else
                    break;
            }
        }
    }
    fprintf(stderr, "Expecting %d pixels only found %d!\n", n * n, i);
    exit(5);
}

void writeimage(double x[], int n, char *p) {
    FILE *fp;
    printf("Writing %s...\n", p);
    if(!(fp = fopen(p, "w"))) {
        fprintf(stderr, "Can't open %s for write!\n", p);
        exit(6);
    }
    fprintf(fp, "P2\n# Created by writeimage.\n%d %d\n255\n", n, n);
    int i;
    for(i = 0; i < n * n; i++) {
        double r = x[i];
        if(r > 1.0)
            r = 1.0;
        else if(r < 0.0)
            r = 0.0;
        int t = 255 * r + 0.5;
        fprintf(fp, "%d\n", t);
    }
    fclose(fp);
}