// Stripped-down primitive printf-style formatting routines,
// used in common by printf, sprintf, fprintf, etc.
// This code is also used by both the kernel and user programs.

#include <inc/types.h>
#include <inc/stdio.h>
#include <inc/string.h>
#include <inc/stdarg.h>
#include <inc/error.h>

/*
 * Space or zero padding and a field width are supported for the numeric
 * formats only.
 *
 * The special format %e takes an integer error code
 * and prints a string describing the error.
 * The integer may be positive or negative,
 * so that -E_NO_MEM and E_NO_MEM are equivalent.
 */

static const char * const error_string[MAXERROR] =
{
	[E_UNSPECIFIED]	= "unspecified error",
	[E_BAD_ENV]	= "bad environment",
	[E_INVAL]	= "invalid parameter",
	[E_NO_MEM]	= "out of memory",
	[E_NO_FREE_ENV]	= "out of environments",
	[E_FAULT]	= "segmentation fault",
};

/*
 * Print a number (base <= 16) in reverse order,
 * using specified putch function and associated pointer putdat.
 */
static void
printnum(void (*putch)(int, void*), void *putdat,
	 unsigned long long num, unsigned base, int width, int padc)
{
	// first recursively print all preceding (more significant) digits
	if (num >= base) {
		printnum(putch, putdat, num / base, base, width - 1, padc);
	} else {
		// print any needed pad characters before first digit
		while (--width > 0)
			putch(padc, putdat);
	}

	// then print this (the least significant) digit
	putch("0123456789abcdef"[num % base], putdat);
}

// Get an unsigned int of various possible sizes from a varargs list,
// depending on the lflag parameter.
static unsigned long long
getuint(va_list *ap, int lflag)
{
	if (lflag >= 2)
		return va_arg(*ap, unsigned long long);
	else if (lflag)
		return va_arg(*ap, unsigned long);
	else
		return va_arg(*ap, unsigned int);
}

// Same as getuint but signed - can't use getuint
// because of sign extension
static long long
getint(va_list *ap, int lflag)
{
	if (lflag >= 2)
		return va_arg(*ap, long long);
	else if (lflag)
		return va_arg(*ap, long);
	else
		return va_arg(*ap, int);
}


// Main function to format and print a string.
void printfmt(void (*putch)(int, void*), void *putdat, const char *fmt, ...);

void
vprintfmt(void (*putch)(int, void*), void *putdat, const char *fmt, va_list ap)
{
	register const char *p;
	register int ch, err;
	unsigned long long num;
	int base, lflag, width, precision, altflag;
	char padc;

	while (1) {
		while ((ch = *(unsigned char *) fmt++) != '%') {    //遍历输入的第一个参数，即输出信息的格式，先把格式字符串中'%'之前的字符一个个输出，因为它们前面没有'%'，所以它们就是要直接显示在屏幕上的
			if (ch == '\0')									//当然中间如果遇到'\0'，代表这个字符串的访问结束
				return;
			putch(ch, putdat);								//调用putch函数，把一个字符ch输出到putdat指针所指向的地址中所存放的值对应的地址处
		}

		// Process a %-escape sequence                      //处理'%'后面的格式化输出
		padc = ' ';											//对齐方式标志位
		width = -1;											//整数部分有效数字位数
		precision = -1;										//小数部分有效数字位数
		lflag = 0;
		altflag = 0;
	reswitch:
		switch (ch = *(unsigned char *) fmt++) {			//根据位于'%'后面的第一个字符进行分情况处理

		// flag to pad on the right
		case '-':											//%后面的'-'代表要进行左对齐输出，右边填空格，如果省略代表右对齐
			padc = '-';										//如果有这个字符代表左对齐，则把对齐方式标志位变为'-'
			goto reswitch;									//处理下一个字符

		// flag to pad with 0's instead of spaces
		case '0':											//0--有0表示进行对齐输出时填0,如省略表示填入空格，并且如果为0，则一定是右对齐
			padc = '0';										//对其方式标志位变为0
			goto reswitch;							

		// width field										//遇到指定输出位数标志
		case '1':
		case '2':
		case '3':
		case '4':
		case '5':
		case '6':
		case '7':
		case '8':
		case '9':
			for (precision = 0; ; ++fmt) {					//把遇到的位数字符串转换为真实的位数，比如输入的'%40'，代表有效位数为40位，下面的循环就是把precesion的值设置为40
				precision = precision * 10 + ch - '0';
				ch = *fmt;
				if (ch < '0' || ch > '9')
					break;
			}
			goto process_precision;							//跳转到process_precistion子过程

		case '*':											//*--代表有效数字的位数也是由输入参数指定的，比如printf("%*.*f", 10, 2, n)，其中10,2就是用来指定显示的有效数字位数的
			precision = va_arg(ap, int);
			goto process_precision;

		case '.':											//如果遇到'.'，代表有小数字段
			if (width < 0)									//代表有小数点，但是小数点前面并没有数字，比如'%.6f'这种情况，此时代表整数部分全部显示
				width = 0;			
			goto reswitch;

		case '#':
			altflag = 1;
			goto reswitch;

		process_precision:									//处理输出精度，把width字段赋值为刚刚计算出来的precision值，所以width应该是整数部分的有效数字位数
			if (width < 0)
				width = precision, precision = -1;
			goto reswitch;

		// long flag (doubled for long long)				
		case 'l':											//如果遇到'l'，代表应该是输入long类型，如果有两个'l'代表long long
			lflag++;										//此时把lflag++
			goto reswitch;

		// character
		case 'c':											//如果是'c'代表显示一个字符
			putch(va_arg(ap, int), putdat);					//调用输出一个字符到内存的函数putch
			break;

		// error message
		case 'e':
			err = va_arg(ap, int);
			if (err < 0)
				err = -err;
			if (err >= MAXERROR || (p = error_string[err]) == NULL)
				printfmt(putch, putdat, "error %d", err);
			else
				printfmt(putch, putdat, "%s", p);
			break;

		// string
		case 's':
			if ((p = va_arg(ap, char *)) == NULL)
				p = "(null)";
			if (width > 0 && padc != '-')
				for (width -= strnlen(p, precision); width > 0; width--)
					putch(padc, putdat);
			for (; (ch = *p++) != '\0' && (precision < 0 || --precision >= 0); width--)
				if (altflag && (ch < ' ' || ch > '~'))
					putch('?', putdat);
				else
					putch(ch, putdat);
			for (; width > 0; width--)
				putch(' ', putdat);
			break;

		// (signed) decimal
		case 'd':
			num = getint(&ap, lflag);
			if ((long long) num < 0) {
				putch('-', putdat);
				num = -(long long) num;
			}
			base = 10;
			goto number;

		// unsigned decimal
		case 'u':
			num = getuint(&ap, lflag);
			base = 10;
			goto number;

		// (unsigned) octal
		case 'o':
			// Replace this with your code.
			putch('0', putdat);
			num = getuint(&ap, lflag);
			base = 8;
			goto number;
		// pointer
		case 'p':
			putch('0', putdat);
			putch('x', putdat);
			num = (unsigned long long)
				(uintptr_t) va_arg(ap, void *);
			base = 16;
			goto number;

		// (unsigned) hexadecimal
		case 'x':
			num = getuint(&ap, lflag);
			base = 16;
		number:
			printnum(putch, putdat, num, base, width, padc);
			break;

		// escaped '%' character
		case '%':
			putch(ch, putdat);
			break;

		// unrecognized escape sequence - just print it literally
		default:
			putch('%', putdat);
			for (fmt--; fmt[-1] != '%'; fmt--)
				/* do nothing */;
			break;
		}
	}
}

void
printfmt(void (*putch)(int, void*), void *putdat, const char *fmt, ...)
{
	va_list ap;

	va_start(ap, fmt);
	vprintfmt(putch, putdat, fmt, ap);
	va_end(ap);
}

struct sprintbuf {
	char *buf;
	char *ebuf;
	int cnt;
};

static void
sprintputch(int ch, struct sprintbuf *b)
{
	b->cnt++;
	if (b->buf < b->ebuf)
		*b->buf++ = ch;
}

int
vsnprintf(char *buf, int n, const char *fmt, va_list ap)
{
	struct sprintbuf b = {buf, buf+n-1, 0};

	if (buf == NULL || n < 1)
		return -E_INVAL;

	// print the string to the buffer
	vprintfmt((void*)sprintputch, &b, fmt, ap);

	// null terminate the buffer
	*b.buf = '\0';

	return b.cnt;
}

int
snprintf(char *buf, int n, const char *fmt, ...)
{
	va_list ap;
	int rc;

	va_start(ap, fmt);
	rc = vsnprintf(buf, n, fmt, ap);
	va_end(ap);

	return rc;
}