/*
 * File: scanadt.c
 * ---------------
 * This file implements the scanadt.h interface.
 */

#include <stdio.h>
#include <ctype.h>
#include "genlib.h"
#include "strlib.h"
#include "scanadt.h"

/*
 * Type: scannerCDT
 * ----------------
 * This structure is the concrete representation of the type
 * scannerADT, which is exported by this interface.  Its purpose
 * is to maintain the state of the scanner between calls.  The
 * details of the representation are invisible to the client,
 * but consist of the following fields:
 *
 * str          -- Copy of string passed to SetScannerString
 * len          -- Length of string, saved for efficiency
 * cp           -- Current character position in the string
 * savedToken   -- String saved by SaveToken (NULL indicates none)
 * spaceOption  -- Setting of the space option extension
 */

struct scannerCDT {
    string str;
    int len;
    int cp;
    string savedToken;
    spaceOptionT spaceOption;
};

/* Private function prototypes */

static void SkipSpaces(scannerADT scanner);
static int ScanToEndOfIdentifier(scannerADT scanner);

/* Exported entries */

scannerADT NewScanner(void)
{
    scannerADT scanner;

    scanner = New(scannerADT);
    scanner->str = NULL;
    scanner->spaceOption = PreserveSpaces;
    return (scanner);
}

void FreeScanner(scannerADT scanner)
{
    printf("FreeScanner llama a FreeBlock\n");
    if (scanner->str != NULL) FreeBlock(scanner->str);
    FreeBlock(scanner);
}

void SetScannerString(scannerADT scanner, string str)
{
    printf("SetScannerString llama a FreeBlock\n");
    if (scanner->str != NULL) FreeBlock(scanner->str);
    scanner->str = CopyString(str);
    scanner->len = StringLength(str);
    scanner->cp = 0;
    scanner->savedToken = NULL;
}

string ReadToken(scannerADT scanner)
{
    char ch;
    string token;
    int start, finish;

    if (scanner->str == NULL) {
        Error("SetScannerString has not been called");
    }
    if (scanner->savedToken != NULL) {
        token = scanner->savedToken;
        scanner->savedToken = NULL;
        return (token);
    }
    if (scanner->spaceOption == IgnoreSpaces) SkipSpaces(scanner);
    start = finish = scanner->cp;
    if (start >= scanner->len) return (CopyString(""));
    ch = scanner->str[scanner->cp];
    if (isalnum(ch)) {
        finish = ScanToEndOfIdentifier(scanner);
    } else {
        scanner->cp++;
    }
    return (SubString(scanner->str, start, finish));
}

bool MoreTokensExist(scannerADT scanner)
{
    if (scanner->str == NULL) {
        Error("SetScannerString has not been called");
    }
    if (scanner->savedToken != NULL) {
        return (!StringEqual(scanner->savedToken, ""));
    }
    if (scanner->spaceOption == IgnoreSpaces) SkipSpaces(scanner);
    return (scanner->cp < scanner->len);
}

void SaveToken(scannerADT scanner, string token)
{
    if (scanner->str == NULL) {
        Error("SetScannerString has not been called");
    }
    if (scanner->savedToken != NULL) {
        Error("Token has already been saved");
    }
    scanner->savedToken = token;
}

void SetScannerSpaceOption(scannerADT scanner, spaceOptionT option)
{
    scanner->spaceOption = option;
}

spaceOptionT GetScannerSpaceOption(scannerADT scanner)
{
    return (scanner->spaceOption);
}

/* Private functions */

/*
 * Function: SkipSpaces
 * Usage: SkipSpaces(scanner);
 * ---------------------------
 * This function advances the position of the scanner until the
 * current character is not a whitespace character.
 */

static void SkipSpaces(scannerADT scanner)
{
    while (isspace(scanner->str[scanner->cp])) {
        scanner->cp++;
    }
}

/*
 * Function: ScanToEndOfIdentifier
 * Usage: finish = ScanToEndOfIdentifier(scanner);
 * -----------------------------------------------
 * This function advances the position of the scanner until it
 * reaches the end of a sequence of letters or digits that make
 * up an identifier.  The return value is the index of the last
 * character in the identifier; the value of the stored index
 * cp is the first character after that.
 */

static int ScanToEndOfIdentifier(scannerADT scanner)
{
    while (isalnum(scanner->str[scanner->cp])) {
        scanner->cp++;
    }
    return (scanner->cp - 1);
}