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

int grep(char pattern[]);

/* grep with graceful buffer overflow */
/* parse and verify arg pattern, pass it to grep */
int main(int argc, char *argv[])
{
    /* verify arg is given */
    if (argc < 2) {
        printf("error: excpected pattern\n");
        return -1;
    }

    char *pattern = argv[1];

    /* verify pattern */
    char c;
    int i;
    for (i = 0; (c = pattern[i]) != '\0'; i++)
        if (c == '\n') {
            printf("error: newline in pattern\n");
            return -2;
        }

    int found = grep(pattern);
    printf("found = %d\n", found);
    return found;
}

void println(void);
int flush_lnbuff(void);
int getch_lnbuff(void);

/* grep: prints lines containing pattern, returns number of matching lines */
int grep(char *pattern)
{
    int found, i, c;
    const int plen = strlen(pattern);

    i = found = 0;

    while ((c = getch_lnbuff()) != EOF)
        if (c != pattern[i])
            i = 0;
        else if (++i == plen) { // found match
            i = 0;
            found++;
            flush_lnbuff();
            println(); 
        }
    return found;
}

/* println: prints next line from stdin
 * prints newline on EOF */
void println()
{
    int c;
    while ((c = getchar()) != EOF && c != '\n')
        putchar(c);
    putchar(c);
}

/* ------------------------ line buffer ---------------------- */

#define LNBUFF_LEN 128

/* the line buffer lenght must be a power of two */
static_assert(!(LNBUFF_LEN % 2), "Line buffer length is not a power of two!");

/* line_buffer: global overflowing line buffer */
struct {
    char self[LNBUFF_LEN];
    unsigned len;
} lnbuff = {.len= 0};

/* LNBUFF_I: current index in line buffer */
#define LNBUFF_I (lnbuff.len & (LNBUFF_LEN - 1))

/* getch_lnbuff: getchar and add it to buffer */
int getch_lnbuff()
{
    int c = getchar();
    
    if (c == EOF || c == '\n') // new line
        lnbuff.len = 0;
    else {
        lnbuff.self[LNBUFF_I] = c;
        lnbuff.len++;
    }

    return c;
}

/* flush_lnbuff: print contents of line buffer, return length */
int flush_lnbuff()
{
    int i;

    /* handle overflowing chars */
    if (lnbuff.len > LNBUFF_LEN) {
        for (i = LNBUFF_LEN; i < lnbuff.len; i++)
            putchar('.');
        for (i = LNBUFF_I; i < LNBUFF_LEN; i++)
            putchar(lnbuff.self[i]);
    }
    /* handle rest of chars */
    for (i = 0; i < LNBUFF_I; i++)
        putchar(lnbuff.self[i]);

    i = lnbuff.len;
    lnbuff.len = 0;
    return i;
}