// sampleRow: print color symbols at sampled X positions for a Y range.
// Reads PPM (P6) images. Used to visually inspect specific rows of a
// rendered scene without ever Read'ing the PNG file (which the user has
// banned for context-corruption reasons).

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


static int readToken(FILE *f, char *buf, size_t sz) {
        int c;
        while ((c = fgetc(f)) != EOF) {
                if (c == '#') {
                        while ((c = fgetc(f)) != EOF && c != '\n') {}
                        continue;
                }
                if (!isspace(c)) {
                        break;
                }
        }
        if (c == EOF) {
                return -1;
        }
        size_t i = 0;
        do {
                if (i + 1 >= sz) {
                        return -1;
                }
                buf[i++] = (char)c;
                c = fgetc(f);
        } while (c != EOF && !isspace(c));
        buf[i] = '\0';
        return (int)i;
}


int main(int argc, char **argv) {
        if (argc < 4) {
                fprintf(stderr, "usage: %s img.ppm yStart yEnd [scaleY]\n", argv[0]);
                return 2;
        }
        FILE *f = fopen(argv[1], "rb");
        if (f == NULL) {
                fprintf(stderr, "cannot open %s\n", argv[1]);
                return 1;
        }
        char tok[32];
        if (readToken(f, tok, sizeof(tok)) < 0 || strcmp(tok, "P6") != 0) {
                fprintf(stderr, "not P6\n");
                fclose(f);
                return 1;
        }
        readToken(f, tok, sizeof(tok)); int w = atoi(tok);
        readToken(f, tok, sizeof(tok)); int h = atoi(tok);
        readToken(f, tok, sizeof(tok));
        unsigned char *p = malloc((size_t)w * h * 3);
        if (p == NULL || fread(p, 1, (size_t)w * h * 3, f) != (size_t)w * h * 3) {
                fclose(f);
                free(p);
                return 1;
        }
        fclose(f);
        int yStart = atoi(argv[2]);
        int yEnd   = atoi(argv[3]);
        int scaleY = (argc > 4) ? atoi(argv[4]) : (h / 192);
        int sampleW = (w >= 70) ? 70 : w;
        int xStep   = w / sampleW;
        for (int hy = yStart; hy <= yEnd; hy++) {
                int sy = hy * scaleY + scaleY/2;
                if (sy >= h) {
                        break;
                }
                printf("y=%3d: ", hy);
                for (int sx = 0; sx < w && sx < sampleW * xStep; sx += xStep) {
                        unsigned char *px = &p[((size_t)sy * w + sx) * 3];
                        int r = px[0];
                        int g = px[1];
                        int b = px[2];
                        char c;
                        if (r < 30 && g < 30 && b < 30) {
                                c = '.';
                        } else if (b > r + 30 && b > g + 30) {
                                c = 'B';
                        } else if (g > r + 30 && g > b + 30) {
                                c = 'G';
                        } else if (r > 200 && g > 200 && b > 200) {
                                c = 'W';
                        } else if (r > 100 && b > 100 && g < (r + b) / 4) {
                                c = 'V';
                        } else if (r > 200 && g > 100 && b < 80) {
                                c = 'O';
                        } else if (r > 100 && b > 100) {
                                c = 'M';
                        } else if (g > 100 && b > 100) {
                                c = 'C';
                        } else {
                                c = '?';
                        }
                        putchar(c);
                }
                putchar('\n');
        }
        free(p);
        return 0;
}