/* 
 * MIME header support by Akinori ITO
 */

#include <sys/types.h>
#include "Str.h"

#define LINELEN 4096

#define MIME_ENCODED_LINE_LIMIT	80
#define MIME_ENCODED_WORD_LENGTH_OFFSET 18
#define MIME_ENCODED_WORD_LENGTH_ESTIMATION(x) \
	(((x)+2)*4/3+MIME_ENCODED_WORD_LENGTH_OFFSET)
#define MIME_DECODED_WORD_LENGTH_ESTIMATION(x) \
	(((x)-MIME_ENCODED_WORD_LENGTH_OFFSET)/4*3)
#define J_CHARSET "ISO-2022-JP"

#define BAD_BASE64 255

static
unsigned char
c2e(char x)
{
    if ('A' <= x && x <= 'Z')
	return (x) - 'A';
    if ('a' <= x && x <= 'z')
	return (x) - 'a' + 26;
    if ('0' <= x && x <= '9')
	return (x) - '0' + 52;
    if (x == '+')
	return 62;
    if (x == '/')
	return 63;
    return BAD_BASE64;
}

static
int
ha2d(char x, char y)
{
    int r = 0;

    if ('0' <= x && x <= '9')
	r = x - '0';
    else if ('A' <= x && x <= 'F')
	r = x - 'A' + 10;
    else if ('a' <= x && x <= 'f')
	r = x - 'a' + 10;

    r <<= 4;

    if ('0' <= y && y <= '9')
	r += y - '0';
    else if ('A' <= y && y <= 'F')
	r += y - 'A' + 10;
    else if ('a' <= y && y <= 'f')
	r += y - 'a' + 10;

    return r;

}

Str
decodeB(char **ww)
{
    unsigned char c[4];
    char *wp = *ww;
    char d[3];
    int i, n_pad;
    Str ap = Strnew_size(strlen(wp));

    n_pad = 0;
    while (1) {
	for (i = 0; i < 4; i++) {
	    c[i] = *(wp++);
	    if (*wp == '\0' || *wp == '?') {
		i++;
		for (; i < 4; i++) {
		    c[i] = '=';
		}
		break;
	    }
	}
	if (c[3] == '=') {
	    n_pad++;
	    c[3] = 'A';
	    if (c[2] == '=') {
		n_pad++;
		c[2] = 'A';
	    }
	}
	for (i = 0; i < 4; i++) {
	    c[i] = c2e(c[i]);
	    if (c[i] == BAD_BASE64) {
		*ww = wp;
		return ap;
	    }
	}
	d[0] = ((c[0] << 2) | (c[1] >> 4));
	d[1] = ((c[1] << 4) | (c[2] >> 2));
	d[2] = ((c[2] << 6) | c[3]);
	for (i = 0; i < 3 - n_pad; i++) {
	    Strcat_char(ap, d[i]);
	}
	if (n_pad || *wp == '\0' || *wp == '?')
	    break;
    }
    *ww = wp;
    return ap;
}

/* RFC2047 (4.2. The "Q" encoding) */
Str
decodeQ(char **ww)
{
    char *w = *ww;
    Str a = Strnew_size(strlen(w));

    for (; *w != '\0' && *w != '?'; w++) {
	if (*w == '=') {
	    w++;
	    Strcat_char(a, ha2d(*w, *(w + 1)));
	    w++;
	}
	else if (*w == '_') {
	    Strcat_char(a, ' ');
	}
	else
	    Strcat_char(a, *w);
    }
    *ww = w;
    return a;
}

/* RFC2045 (6.7. Quoted-Printable Content-Transfer-Encoding) */
Str
decodeQP(char **ww)
{
    char *w = *ww;
    Str a = Strnew_size(strlen(w));

    for (; *w != '\0'; w++) {
	if (*w == '=') {
	    w++;
	    if (*w == '\n' || *w == '\r' || *w == ' ' || *w == '\t') {
		while (*w != '\n' && *w != '\0')
		    w++;
		if (*w == '\0')
		    break;
	    }
	    else {
		if (*w == '\0' || *(w + 1) == '\0')
		    break;
		Strcat_char(a, ha2d(*w, *(w + 1)));
		w++;
	    }
	}
	else
	    Strcat_char(a, *w);
    }
    *ww = w;
    return a;
}

Str
decodeWord(char **ow)
{
    char charset[32];
    char *p, *w = *ow;
    char method;
    Str a = Strnew();

    if (*w != '=' || *(w + 1) != '?')
	goto convert_fail;
    w += 2;
    for (p = charset; *w != '?'; w++) {
	if (*w == '\0')
	    goto convert_fail;
	*(p++) = *w;
    }
    *p = '\0';
    if (strcasecmp(charset, J_CHARSET) != 0) {
	/* NOT ISO-2022-JP encoding ... don't convert */
	goto convert_fail;
    }
    w++;
    method = *(w++);
    if (*w != '?')
	goto convert_fail;
    w++;
    p = w;
    switch (method) {
    case 'B':
	a = decodeB(&w);
	break;
    case 'Q':
	a = decodeQ(&w);
	break;
    default:
	goto convert_fail;
    }
    if (p == w)
	goto convert_fail;
    if (*w == '?') {
	w++;
	if (*w == '=')
	    w++;
    }
    *ow = w;
    return a;

  convert_fail:
    return Strnew();
}

/* 
 * convert MIME encoded string to the original one
 */
Str
decodeMIME(char *orgstr)
{
    char *org = orgstr;
    char *org0, *p;
    Str cnv = Strnew_size(strlen(orgstr));

    while (*org) {
	if (*org == '=' && *(org + 1) == '?') {
	  nextEncodeWord:
	    p = org;
	    Strcat(cnv, decodeWord(&org));
	    if (org == p) {	/* Convert failure */
		Strcat_charp(cnv, org);
		return cnv;
	    }
	    org0 = org;
	  SPCRLoop:
	    switch (*org0) {
	    case ' ':
	    case '\t':
	    case '\n':
	    case '\r':
		org0++;
		goto SPCRLoop;
	    case '=':
		if (org0[1] == '?') {
		    org = org0;
		    goto nextEncodeWord;
		}
	    default:
		break;
	    }
	}
	else
	    Strcat_char(cnv, *(org++));
    }
    return cnv;
}

/* encoding */

static char Base64Table[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";

Str
encodeB(char *a)
{
    unsigned char d[3];
    unsigned char c1, c2, c3, c4;
    int i, n_pad;
    Str w = Strnew();

    while (1) {
	if (*a == '\0')
	    break;
	n_pad = 0;
	d[1] = d[2] = 0;
	for (i = 0; i < 3; i++) {
	    d[i] = a[i];
	    if (a[i] == '\0') {
		n_pad = 3 - i;
		break;
	    }
	}
	c1 = d[0] >> 2;
	c2 = (((d[0] << 4) | (d[1] >> 4)) & 0x3f);
	if (n_pad == 2) {
	    c3 = c4 = 64;
	}
	else if (n_pad == 1) {
	    c3 = ((d[1] << 2) & 0x3f);
	    c4 = 64;
	}
	else {
	    c3 = (((d[1] << 2) | (d[2] >> 6)) & 0x3f);
	    c4 = (d[2] & 0x3f);
	}
	Strcat_char(w, Base64Table[c1]);
	Strcat_char(w, Base64Table[c2]);
	Strcat_char(w, Base64Table[c3]);
	Strcat_char(w, Base64Table[c4]);
	if (n_pad)
	    break;
	a += 3;
    }
    return w;
}