/*****************************************************************************

NAME:
   qp.c -- decode quoted printable text

AUTHOR:
   David Relson <relson@osagesoftware.com>

******************************************************************************/

#include "common.h"

#include "qp.h"

/* Local Variables */

static byte qp_xlate2045[256];
static byte qp_xlate2047[256];

static int hex_to_bin(byte c) {
    switch (c) {
	case '0': return 0;
	case '1': return 1;
	case '2': return 2;
	case '3': return 3;
	case '4': return 4;
	case '5': return 5;
	case '6': return 6;
	case '7': return 7;
	case '8': return 8;
	case '9': return 9;
	case 'a': case 'A': return 10;
	case 'b': case 'B': return 11;
	case 'c': case 'C': return 12;
	case 'd': case 'D': return 13;
	case 'e': case 'E': return 14;
	case 'f': case 'F': return 15;
	default: return -1;
    }
}

/* Function Prototypes  */

static int qp_eol_check(byte *s, byte *e);

/* Function Definitions  */

uint qp_decode(word_t *word, qp_mode mode)
{
    uint size = word->leng;
    byte *s = word->u.text;	/* src */
    byte *d = word->u.text;	/* dst */
    byte *e = s + size;		/* end */

    while (s < e)
    {
	byte ch = *s++;
	int x, y;
	switch (ch) {
	    case '=':
		if (mode == RFC2045) {
		    int c = qp_eol_check(s, e);
		    if (c != 0) {
			/* continuation line, trailing = */
			s += c;
			continue;
		    }
		}
		if (s + 2 <= e && 
			(y = hex_to_bin(s[0])) >= 0 && (x = hex_to_bin(s[1])) >= 0) {
		    /* encoded character */
		    ch = (byte) (y << 4 | x);
		    s += 2;
		}
		break;
	    case '_':
		if (mode == RFC2047)
		    ch = ' ';
		break;
	}
	*d++ = ch;
    }
    /* do not stuff NUL byte here:
     * if there was one, it has been copied! */
    return d - word->u.text;
}

/* rfc2047 - QP    [!->@-~]+
*/

static void qp_init(void)
{
    unsigned i;
    static bool first = true;

    if (!first)
	return;
    first = false;

    for (i = 33; i <= 126; i ++) {
	qp_xlate2045[i] = qp_xlate2047[i] = (byte) i;
    }

    qp_xlate2045[(unsigned char)'\t'] = '\t';	/* HTAB */
    qp_xlate2045[(unsigned char)' ']  = ' ';	/* SP */
    qp_xlate2045[(unsigned char)'=']  = 0;	/* illegal */

    qp_xlate2047[(unsigned char)'_']  = ' ';	/* SP */
    qp_xlate2047[(unsigned char)'=']  = 0;	/* illegal */
    qp_xlate2047[(unsigned char)'?']  = 0;	/* illegal */

    return;
}

bool qp_validate(const word_t *word, qp_mode mode)
{
    uint i;
    const byte *qp_xlate = mode == RFC2047 ? qp_xlate2047 : qp_xlate2045;

    qp_init();

    for (i = 0; i < word->leng; i += 1) {
	byte b = word->u.text[i];
	byte v = qp_xlate[b];
	if (v == 0)
	    switch (b) {
		case '=': /* allowed in encoded words,
			     but must be encoded */
		    break;
		default:
		    return false;
	    }
    }

    return true;
}

static int qp_eol_check(byte *s, byte *e)
{
    if (s + 1 <= e) {
	/* test for LF */
	if (s[0] == '\n')
	{
	    /* only LF */
	    return 1;
	}

	if (s[0] == '\r'
		&& s + 2 <= e && s[1] == '\n')
	    /* CR LF */
	    return 2;
    }

    return 0;
}