/* $Id$ */

/* _PDCLIB_scan( const char *, struct _PDCLIB_status_t * )

   This file is part of the Public Domain C Library (PDCLib).
   Permission is granted to use, modify, and / or redistribute at will.
*/

#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h>
#include <stdarg.h>
#include <stdint.h>
#include <ctype.h>
#include <string.h>
#include <stddef.h>
#include <limits.h>

/* Using an integer's bits as flags for both the conversion flags and length
   modifiers.
*/
#define E_suppressed 1<<0
#define E_char       1<<6
#define E_short      1<<7
#define E_long       1<<8
#define E_llong      1<<9
#define E_intmax     1<<10
#define E_size       1<<11
#define E_ptrdiff    1<<12
#define E_intptr     1<<13
#define E_ldouble    1<<14
#define E_unsigned   1<<16


/* Helper macro for assigning a readily converted integer value to the correct
   parameter type, used in a switch on status->flags (see E_* flags above).
   case_cond: combination of the E_* flags above, used for the switch-case
   type:      integer type, used to get the correct type from the parameter
              stack as well as for cast target.
*/
#define ASSIGN_VALUE_TO( case_cond, type ) \
    case case_cond: \
        *( va_arg( status->arg, type * ) ) = (type)( value * sign ); \
        break


/* Helper function to get a character from the string or stream, whatever is
   used for input. When reading from a string, returns EOF on end-of-string
   so that handling of the return value can be uniform for both streams and
   strings.
*/
static int GET( struct _PDCLIB_status_t * status )
{
    int rc;
    if ( status->stream != NULL )
    {
        rc = getc( status->stream );
    }
    else
    {
        rc = ( *status->s == '\0' ) ? EOF : (unsigned char)*((status->s)++);
    }
    if ( rc != EOF )
    {
        ++(status->i);
        ++(status->this);
    }
    return rc;
}


/* Helper function to put a read character back into the string or stream,
   whatever is used for input.
*/
static void UNGET( int c, struct _PDCLIB_status_t * status )
{
    if ( status->stream != NULL )
    {
        ungetc( c, status->stream ); /* TODO: Error? */
    }
    else
    {
        --(status->s);
    }
    --(status->i);
    --(status->this);
}


const char * _PDCLIB_scan( const char * spec, struct _PDCLIB_status_t * status )
{
    /* generic input character */
    int rc;
    const char * orig_spec = spec;
    if ( *(++spec) == '%' )
    {
        /* %% -> match single '%' */
        rc = GET( status );
        switch ( rc )
        {
            case EOF:
                /* input error */
                if ( status->n == 0 )
                {
                    status->n = -1;
                }
                return NULL;
            case '%':
                return ++spec;
            default:
                UNGET( rc, status );
                break;
        }
    }
    /* Initializing status structure */
    status->flags = 0;
    status->base = -1;
    status->this = 0;
    status->width = 0;
    status->prec = 0;

    /* '*' suppresses assigning parsed value to variable */
    if ( *spec == '*' )
    {
        status->flags |= E_suppressed;
        ++spec;
    }

    /* If a width is given, strtol() will return its value. If not given,
       strtol() will return zero. In both cases, endptr will point to the
       rest of the conversion specifier - just what we need.
    */
    char const * prev_spec = spec;
    status->width = (int)strtol( spec, (char**)&spec, 10 );
    if ( spec == prev_spec )
    {
        status->width = SIZE_MAX;
    }

    /* Optional length modifier
       We step one character ahead in any case, and step back only if we find
       there has been no length modifier (or step ahead another character if it
       has been "hh" or "ll").
    */
    switch ( *(spec++) )
    {
        case 'h':
            if ( *spec == 'h' )
            {
                /* hh -> char */
                status->flags |= E_char;
                ++spec;
            }
            else
            {
                /* h -> short */
                status->flags |= E_short;
            }
            break;
        case 'l':
            if ( *spec == 'l' )
            {
                /* ll -> long long */
                status->flags |= E_llong;
                ++spec;
            }
            else
            {
                /* l -> long */
                status->flags |= E_long;
            }
            break;
        case 'j':
            /* j -> intmax_t, which might or might not be long long */
            status->flags |= E_intmax;
            break;
        case 'z':
            /* z -> size_t, which might or might not be unsigned int */
            status->flags |= E_size;
            break;
        case 't':
            /* t -> ptrdiff_t, which might or might not be long */
            status->flags |= E_ptrdiff;
            break;
        case 'L':
            /* L -> long double */
            status->flags |= E_ldouble;
            break;
        default:
            --spec;
            break;
    }

    /* Conversion specifier */

    /* whether valid input had been parsed */
    bool value_parsed = false;

    switch ( *spec )
    {
        case 'd':
            status->base = 10;
            break;
        case 'i':
            status->base = 0;
            break;
        case 'o':
            status->base = 8;
            status->flags |= E_unsigned;
            break;
        case 'u':
            status->base = 10;
            status->flags |= E_unsigned;
            break;
        case 'x':
            status->base = 16;
            status->flags |= E_unsigned;
            break;
        case 'f':
        case 'F':
        case 'e':
        case 'E':
        case 'g':
        case 'G':
        case 'a':
        case 'A':
            break;
        case 'c':
        {
            char * c = va_arg( status->arg, char * );
            /* for %c, default width is one */
            if ( status->width == SIZE_MAX )
            {
                status->width = 1;
            }
            /* reading until width reached or input exhausted */
            while ( ( status->this < status->width ) &&
                    ( ( rc = GET( status ) ) != EOF ) )
            {
                *(c++) = rc;
                value_parsed = true;
            }
            /* width or input exhausted */
            if ( value_parsed )
            {
                ++status->n;
                return ++spec;
            }
            else
            {
                /* input error, no character read */
                if ( status->n == 0 )
                {
                    status->n = -1;
                }
                return NULL;
            }
        }
        case 's':
        {
            char * c = va_arg( status->arg, char * );
            while ( ( status->this < status->width ) && 
                    ( ( rc = GET( status ) ) != EOF ) )
            {
                if ( isspace( rc ) )
                {
                    if ( value_parsed )
                    {
                        /* matching sequence terminated by whitespace */
                        *c = '\0';
                        return spec;
                    }
                    else
                    {
                        /* leading whitespace not counted against width */
                        --(status->this);
                    }
                }
                else
                {
                    value_parsed = true;
                    *(c++) = rc;
                }
            }
            /* width or input exhausted */
            if ( value_parsed )
            {
                *c = '\0';
                ++status->n;
                return ++spec;
            }
            else
            {
                /* input error, no character read */
                if ( status->n == 0 )
                {
                    status->n = -1;
                }
                return NULL;
            }
        }
        case '[':
            // TODO: SOLAR
            break;
        case 'p':
            status->base = 16;
            status->flags |= E_unsigned;
            break;
        case 'n':
        {
            int * val = va_arg( status->arg, int * );
            *val = status->i;
            return ++spec;
        }
        default:
            /* No conversion specifier. Bad conversion. */
            return orig_spec;
    }

    if ( status->base != -1 )
    {
        /* integer conversion */
        uintmax_t value = 0;         /* absolute value read */
        bool prefix_parsed = false;
        int sign = 0;
        while ( ( status->this < status->width ) &&
                ( ( rc = GET( status ) ) != EOF ) )
        {
            if ( isspace( rc ) )
            {
                if ( sign )
                {
                    /* matching sequence terminated by whitespace */
                    UNGET( rc, status );
                    break;
                }
                else
                {
                    /* leading whitespace not counted against width */
                    status->this--;
                }
            }
            else if ( ! sign )
            {
                /* no sign parsed yet */
                switch ( rc )
                {
                    case '-':
                        sign = -1;
                        break;
                    case '+':
                        sign = 1;
                        break;
                    default:
                        /* not a sign; put back character */
                        sign = 1;
                        UNGET( rc, status );
                        break;
                }
            }
            else if ( ! prefix_parsed )
            {
                /* no prefix (0x... for hex, 0... for octal) parsed yet */
                prefix_parsed = true;
                if ( rc != '0' )
                {
                    /* not a prefix; if base not yet set, set to decimal */
                    if ( status->base == 0 )
                    {
                        status->base = 10;
                    }
                    UNGET( rc, status );
                }
                else
                {
                    /* starts with zero, so it might be a prefix. */
                    /* check what follows next (might be 0x...) */
                    if ( ( status->this < status->width ) &&
                         ( ( rc = GET( status ) ) != EOF ) )
                    {
                        if ( tolower( rc ) == 'x' )
                        {
                            /* 0x... would be prefix for hex base... */
                            if ( ( status->base == 0 ) ||
                                 ( status->base == 16 ) )
                            {
                                status->base = 16;
                            }
                            else
                            {
                                /* ...unless already set to other value */
                                UNGET( rc, status );
                                value_parsed = true;
                            }
                        }
                        else
                        {
                            /* 0... but not 0x.... would be octal prefix */
                            UNGET( rc, status );
                            if ( status->base == 0 )
                            {
                                status->base = 8;
                            }
                            /* in any case we have read a zero */
                            value_parsed = true;
                        }
                    }
                    else
                    {
                        /* failed to read beyond the initial zero */
                        value_parsed = true;
                        break;
                    }
                }
            }
            else
            {
                char * digitptr = memchr( _PDCLIB_digits, tolower( rc ), status->base );
                if ( digitptr == NULL )
                {
                    /* end of input item */
                    UNGET( rc, status );
                    break;
                }
                value *= status->base;
                value += digitptr - _PDCLIB_digits;
                value_parsed = true;
            }
        }
        /* width or input exhausted, or non-matching character */
        if ( ! value_parsed )
        {
            /* out of input before anything could be parsed - input error */
            /* FIXME: if first character does not match, value_parsed is not set - but it is NOT an input error */
            if ( ( status->n == 0 ) && ( rc == EOF ) )
            {
                status->n = -1;
            }
            return NULL;
        }
        /* convert value to target type and assign to parameter */
        switch ( status->flags & ( E_char | E_short | E_long | E_llong |
                                   E_intmax | E_size | E_ptrdiff |
                                   E_unsigned ) )
        {
            ASSIGN_VALUE_TO( E_char, char );
            ASSIGN_VALUE_TO( E_char | E_unsigned, unsigned char );
            ASSIGN_VALUE_TO( E_short, short );
            ASSIGN_VALUE_TO( E_short | E_unsigned, unsigned short );
            ASSIGN_VALUE_TO( 0, int );
            ASSIGN_VALUE_TO( E_unsigned, unsigned int );
            ASSIGN_VALUE_TO( E_long, long );
            ASSIGN_VALUE_TO( E_long | E_unsigned, unsigned long );
            ASSIGN_VALUE_TO( E_llong, long long );
            ASSIGN_VALUE_TO( E_llong | E_unsigned, unsigned long long );
            ASSIGN_VALUE_TO( E_intmax, intmax_t );
            ASSIGN_VALUE_TO( E_intmax | E_unsigned, uintmax_t );
            ASSIGN_VALUE_TO( E_size, size_t );
            /* ASSIGN_VALUE_TO( E_size | E_unsigned, unsigned size_t ); */
            ASSIGN_VALUE_TO( E_ptrdiff, ptrdiff_t );
            /* ASSIGN_VALUE_TO( E_ptrdiff | E_unsigned, unsigned ptrdiff_t ); */
            default:
                puts( "UNSUPPORTED SCANF FLAG COMBINATION" );
                return NULL; /* behaviour unspecified */
        }
        ++(status->n);
        return ++spec;
    }
    /* TODO: Floats. */
    return NULL;
}


#ifdef TEST
#include <_PDCLIB_test.h>
#include <limits.h>


 
int main( void )
{
    /* Testing covered by fscanf.c */
    return TEST_RESULTS;
}

#endif