#include <err.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "query.h"

/*
 * Return an allocated string containing the next query string parameter
 * ("key=value"). The string is truncated to max characters. If truncation
 * occurred, the -1th character of the string is set to 1.
 */
char *
nextparam(enum method method, int max)
{	
	char *buf;
	int i, sz;
	static int j = 0;
	
	/* Return NULL if at end of parameter string. */
	if(method == GET && !query.string[j-1])
		return NULL;
	
#define STEP 256
	
	sz = STEP;
	if(!(buf = malloc(1+sz))) /* Leave space for -1th character. */
		err(1, "malloc");
	
	/*
	 * buf's -1th character is set to 1 if the string
	 * has been truncated (i.e. if input exceeded max).
	 */
	buf++;
	TRUNCATED(buf) = 0;

#define READ(b) (method == GET? \
	(*(b) = query.string[j++]): \
	fread(b, 1, 1, stdin))

	/*
	 * The parameter is read in a rather lopsided loop, treating
	 * the first character specially.
	 */
first:	
	/* Return NULL if at end of parameter string. */
	if(!READ(buf))
		return NULL;
	
	/* Skip empty parameters. */
	if(*buf == '&')
		goto first;
	
	i = 0;
	goto rest;
	
	for(; READ(buf+i); i++){
rest:
		if(buf[i] == '&'){
			buf[i] = 0;
			break;
		}
		if(i+1 > max){
			TRUNCATED(buf) = 1;
			/* Skip ahead to next parameter. */
			while(READ(buf+i+1) && buf[i+1] != '&') ;
			break;
		}
		if(i+1 >= sz){
			sz += STEP;
			/* Remember to adjust for -1th character. */
			if(buf--, buf = realloc(buf, 1+sz), !buf++)
				err(1, "realloc");
		}
	}
	buf[i] = 0;
	
	return buf;
}

/* Fill global query structure from CGI environment variables. */
void
setquery()
{
	query.string = getenv("QUERY_STRING");
	if(!query.string){
		fprintf(stderr, "no QUERY_STRING\n");
		exit(1);
	}
	query.method = strcmp(getenv("REQUEST_METHOD"), "POST")? GET: POST;
}

/*
 * Split parameter string on equals sign and return value portion;
 * return NULL if none found. For example, v = split(p) results in
 * p pointing to the parameter key and v pointing to the value.
 */
char *
split(char *param)
{
	int n;

	n = strcspn(param, "=");
	if(!param[n])
		return NULL;
	param[n] = 0;
	return param+n+1;
}