/*
******************************************************************************
*
*   Copyright (C) 1999-2001, International Business Machines
*   Corporation and others.  All Rights Reserved.
*
******************************************************************************
*
*
*  ucnv_io.c:
*  initializes global variables and defines functions pertaining to file
*  access, and name resolution aspect of the library.
*
*   new implementation:
*
*   created on: 1999nov22
*   created by: Markus W. Scherer
*
*   Use the binary cnvalias.icu (created from convrtrs.txt) to work
*   with aliases for converter names.
*
*   Date        Name        Description
*   11/22/1999  markus      Created
*   06/28/2002  grhoten     Major overhaul of the converter alias design.
*                           Now an alias can map to different converters
*                           depending on the specified standard.
*******************************************************************************
*/

#include "unicode/utypes.h"
#include "unicode/putil.h"
#include "unicode/ucnv.h"           /* This file implements ucnv_xXXX() APIs */
#include "unicode/udata.h"

#include "umutex.h"
#include "cstring.h"
#include "cmemory.h"
#include "ucnv_io.h"
#include "uenumimp.h"
#include "ucln_cmn.h"

/* Format of cnvalias.icu -----------------------------------------------------
 *
 * cnvalias.icu is a binary, memory-mappable form of convrtrs.txt.
 * This binary form contains several tables. All indexes are to uint16_t
 * units, and not to the bytes (uint8_t units). Addressing everything on
 * 16-bit boundaries allows us to store more information with small index
 * numbers, which are also 16-bit in size. The majority of the table (except
 * the string table) are 16-bit numbers.
 *
 * First there is the size of the Table of Contents (TOC). The TOC
 * entries contain the size of each section. In order to find the offset
 * you just need to sum up the previous offsets.
 *
 * 1) This section contains a list of converters. This list contains indexes
 * into the string table for the converter name. The index of this list is
 * also used by other sections, which are mentioned later on.
 *
 * 2) This section contains a list of tags. This list contains indexes
 * into the string table for the tag name. The index of this list is
 * also used by other sections, which are mentioned later on.
 *
 * 3) This section contains a list of sorted list of unique aliases. This
 * list contains indexes into the string table for the alias name. The
 * index of this list is also used by other sections, which are mentioned
 * later on.
 *
 * 4) This section contains a list of mapped converter names. Consider this
 * as a table that maps the 3rd section to the 1st section. This list contains
 * indexes into the 1st section. The index of this list is the same index in
 * the 3rd section. There is also some extra information in the high bits of
 * each converter index in this table. Currently it's only used to say that
 * an alias mapped to this converter is ambiguous. See UCNV_CONVERTER_INDEX_MASK
 * and UCNV_AMBIGUOUS_ALIAS_MAP_BIT for more information. This section is
 * the predigested form of the 5th section so that an alias lookup can be fast.
 * 
 * 5) This section contains a 2D array with indexes to the 6th section. This
 * section is the full form of all alias mappings. The column index is the
 * index into the converter list (column header). The row index is the index
 * to tag list (row header). This 2D array is the top part a 3D array. The
 * third dimension is in the 6th section.
 *
 * 6) This is blob of variable length arrays. Each array starts with a size,
 * and is followed by indexes to alias names in the string table. This is
 * the third dimension to the section 5. No other section should be referencing
 * this section.
 *
 * 7) Reserved at this time (There is no information). This _usually_ has a
 * size of 0. Future versions may add more information here.
 *
 * 8) This is the string table. All strings are indexed on an even address.
 * There are two reasons for this. First many chip architectures locate strings
 * faster on even address boundaries. Second, since all indexes are 16-bit
 * numbers, this string table can be 128KB in size instead of 64KB when we
 * only have strings starting on an even address.
 *
 *
 * Here is the concept of section 5 and 6. It's a 3D cube. Each tag
 * has a unique alias among all converters. That same alias can
 * be mentioned in other standards on different converters,
 * but only one alias per tag can be unique.
 *
 *
 *              Converter Names (Usually in TR22 form)
 *           -------------------------------------------.
 *     T    /                                          /|
 *     a   /                                          / |
 *     g  /                                          /  |
 *     s /                                          /   |
 *      /                                          /    |
 *      ------------------------------------------/     |
 *    A |                                         |     |
 *    l |                                         |     |
 *    i |                                         |    /
 *    a |                                         |   /
 *    s |                                         |  /
 *    e |                                         | /
 *    s |                                         |/
 *      -------------------------------------------
 *
 *
 *
 * Here is what it really looks like. It's like swiss cheese.
 * There are holes. Some converters aren't recognized by
 * a standard, or they are really old converters that the
 * standard doesn't recognize anymore.
 *
 *              Converter Names (Usually in TR22 form)
 *           -------------------------------------------.
 *     T    /##########################################/|
 *     a   /     #            #                       /#
 *     g  /  #      ##     ##     ### # ### ### ### #/  
 *     s / #             #####  ####        ##  ## #/#  
 *      / ### # # ##  #  #   #          ### # #   #/##  
 *      ------------------------------------------/# #
 *    A |### # # ##  #  #   #          ### # #   #|# #
 *    l |# # #    #     #               ## #     #|# #
 *    i |# # #    #     #                #       #|#
 *    a |#                                       #|#
 *    s |                                        #|#
 *    e 
 *    s 
 *      
 */

typedef struct UAliasContext {
    uint32_t stanardNum;
    uint32_t convNum;
    uint32_t listIdx;
} UAliasContext;

static const char DATA_NAME[] = "cnvalias";
static const char DATA_TYPE[] = "icu";

static UDataMemory *aliasData=NULL;

static const uint16_t *converterList = NULL;
static const uint16_t *tagList = NULL;
static const uint16_t *aliasList = NULL;
static const uint16_t *untaggedConvArray = NULL;
static const uint16_t *taggedAliasArray = NULL;
static const uint16_t *taggedAliasLists = NULL;
static const uint16_t *stringTable = NULL;

static uint32_t converterListNum;
static uint32_t tagListNum;
static uint32_t aliasListNum;
static uint32_t untaggedConvArraySize;
static uint32_t taggedAliasArraySize;
static uint32_t taggedAliasListsSize;
static uint32_t stringTableSize;

static const char **availableConverters = NULL;
static uint16_t availableConverterCount = 0;

static char defaultConverterNameBuffer[UCNV_MAX_CONVERTER_NAME_LENGTH + 1]; /* +1 for NULL */
static const char *defaultConverterName = NULL;

#define GET_STRING(idx) (const char *)(stringTable + (idx))
#define NUM_RESERVED_TAGS 2

static UBool U_CALLCONV
isAcceptable(void *context,
             const char *type, const char *name,
             const UDataInfo *pInfo) {
    return (UBool)(
        pInfo->size>=20 &&
        pInfo->isBigEndian==U_IS_BIG_ENDIAN &&
        pInfo->charsetFamily==U_CHARSET_FAMILY &&
        pInfo->dataFormat[0]==0x43 &&   /* dataFormat="CvAl" */
        pInfo->dataFormat[1]==0x76 &&
        pInfo->dataFormat[2]==0x41 &&
        pInfo->dataFormat[3]==0x6c &&
        pInfo->formatVersion[0]==3);
}

static UBool
haveAliasData(UErrorCode *pErrorCode) {
    if(pErrorCode==NULL || U_FAILURE(*pErrorCode)) {
        return FALSE;
    }

    /* load converter alias data from file if necessary */
    if(aliasData==NULL) {
        UDataMemory *data = NULL;
        const uint16_t *table = NULL;
        uint32_t tableStart;
        uint32_t currOffset;
        uint32_t reservedSize1;

        data = udata_openChoice(NULL, DATA_TYPE, DATA_NAME, isAcceptable, NULL, pErrorCode);
        if(U_FAILURE(*pErrorCode)) {
            return FALSE;
        }

        table = (const uint16_t *)udata_getMemory(data);

        tableStart      = ((const uint32_t *)(table))[0];
        if (tableStart < 8) {
            *pErrorCode = U_INVALID_FORMAT_ERROR;
            return FALSE;
        }

        umtx_lock(NULL);
        if(aliasData==NULL) {
            aliasData = data;
            data=NULL;

            converterListNum        = ((const uint32_t *)(table))[1];
            tagListNum              = ((const uint32_t *)(table))[2];
            aliasListNum            = ((const uint32_t *)(table))[3];
            untaggedConvArraySize   = ((const uint32_t *)(table))[4];
            taggedAliasArraySize    = ((const uint32_t *)(table))[5];
            taggedAliasListsSize    = ((const uint32_t *)(table))[6];
            reservedSize1           = ((const uint32_t *)(table))[7];   /* reserved */
            stringTableSize         = ((const uint32_t *)(table))[8];

            currOffset = tableStart * (sizeof(uint32_t)/sizeof(uint16_t)) + (sizeof(uint32_t)/sizeof(uint16_t));
            converterList = table + currOffset;

            currOffset += converterListNum;
            tagList = table + currOffset;

            currOffset += tagListNum;
            aliasList = table + currOffset;

            currOffset += aliasListNum;
            untaggedConvArray = table + currOffset;

            currOffset += untaggedConvArraySize;
            taggedAliasArray = table + currOffset;

            /* aliasLists is a 1's based array, but it has a padding character */
            currOffset += taggedAliasArraySize;
            taggedAliasLists = table + currOffset;

            currOffset += taggedAliasListsSize;
            /* reserved */

            currOffset += reservedSize1;
            stringTable = table + currOffset;

        }
        umtx_unlock(NULL);

        /* if a different thread set it first, then close the extra data */
        if(data!=NULL) {
            udata_close(data); /* NULL if it was set correctly */
        }
    }

    return TRUE;
}

static UBool
isAlias(const char *alias, UErrorCode *pErrorCode) {
    if(alias==NULL) {
        *pErrorCode=U_ILLEGAL_ARGUMENT_ERROR;
        return FALSE;
    } else if(*alias==0) {
        return FALSE;
    } else {
        return TRUE;
    }
}

UBool 
ucnv_io_cleanup()
{
    if (aliasData) {
        udata_close(aliasData);
        aliasData = NULL;
    }

    ucnv_io_flushAvailableConverterCache();

    converterListNum        = 0;
    tagListNum              = 0;
    aliasListNum            = 0;
    untaggedConvArraySize   = 0;
    taggedAliasArraySize    = 0;
    taggedAliasListsSize    = 0;
    stringTableSize         = 0;

    converterList = NULL;
    tagList = NULL;
    aliasList = NULL;
    untaggedConvArray = NULL;
    taggedAliasArray = NULL;
    taggedAliasLists = NULL;
    stringTable = NULL;

    defaultConverterName = NULL;
    defaultConverterNameBuffer[0] = 0;

    return TRUE;                   /* Everything was cleaned up */
}


static uint32_t getTagNumber(const char *tagname) {
    if (tagList) {
        uint32_t tagNum;
        for (tagNum = 0; tagNum < tagListNum; tagNum++) {
            if (!uprv_stricmp(GET_STRING(tagList[tagNum]), tagname)) {
                return tagNum;
            }
        }
    }

    return UINT32_MAX;
}

/**
 * Do a fuzzy compare of a two converter/alias names.  The comparison
 * is case-insensitive.  It also ignores the characters '-', '_', and
 * ' ' (dash, underscore, and space).  Thus the strings "UTF-8",
 * "utf_8", and "Utf 8" are exactly equivalent.
 * 
 * This is a symmetrical (commutative) operation; order of arguments
 * is insignificant.  This is an important property for sorting the
 * list (when the list is preprocessed into binary form) and for
 * performing binary searches on it at run time.
 * 
 * @param name1 a converter name or alias, zero-terminated
 * @param name2 a converter name or alias, zero-terminated
 * @return 0 if the names match, or a negative value if the name1
 * lexically precedes name2, or a positive value if the name1
 * lexically follows name2.
 */
U_CAPI int U_EXPORT2
ucnv_compareNames(const char *name1, const char *name2) {
    int rc;
    char c1, c2;

    for (;;) {
        /* Ignore delimiters '-', '_', and ' ' */
        while ((c1 = *name1) == '-' || c1 == '_' || c1 == ' ') {
            ++name1;
        }
        while ((c2 = *name2) == '-' || c2 == '_' || c2 == ' ') {
            ++name2;
        }

        /* If we reach the ends of both strings then they match */
        if ((c1|c2)==0) {
            return 0;
        }
        
        /* Case-insensitive comparison */
        rc = (int)(unsigned char)uprv_tolower(c1) -
             (int)(unsigned char)uprv_tolower(c2);
        if (rc != 0) {
            return rc;
        }
        ++name1;
        ++name2;
    }
}

/*
 * search for an alias
 * return the converter number index for converterList
 */
static uint32_t
findConverter(const char *alias, UErrorCode *pErrorCode) {
    uint32_t mid, start, limit;
    int result;

    /* do a binary search for the alias */
    start = 0;
    limit = untaggedConvArraySize - 1;
    mid = limit;

    /* Once mid == 0 we've already checked the 0'th element and we can stop */
    while (start <= limit && mid != 0) {
        mid = (uint32_t)((start + limit + 1) / 2);    /* +1 is to round properly */
        result = ucnv_compareNames(alias, GET_STRING(aliasList[mid]));

        if (result < 0) {
            limit = mid-1;
        } else if (result > 0) {
            start = mid+1;
        } else {
            /* Since the gencnval tool folds duplicates into one entry,
             * this alias in aliasList is unique, but different standards
             * may map an alias to different converters.
             */
            if (untaggedConvArray[mid] & UCNV_AMBIGUOUS_ALIAS_MAP_BIT) {
                *pErrorCode = U_AMBIGUOUS_ALIAS_WARNING;
            }
            return untaggedConvArray[mid] & UCNV_CONVERTER_INDEX_MASK;
        }
    }

    return UINT32_MAX;
}

U_CFUNC const char *
ucnv_io_getConverterName(const char *alias, UErrorCode *pErrorCode) {
    if(haveAliasData(pErrorCode) && isAlias(alias, pErrorCode)) {
        uint32_t convNum = findConverter(alias, pErrorCode);
        if (convNum < converterListNum) {
            return GET_STRING(converterList[convNum]);
        }
        /* else converter not found */
    }
    return NULL;
}

static int32_t U_CALLCONV
ucnv_io_countStandardAliases(UEnumeration *enumerator, UErrorCode *pErrorCode) {
    int32_t value = 0;
    UAliasContext *myContext = (UAliasContext *)(enumerator->context);
    uint32_t listOffset = taggedAliasArray[myContext->stanardNum*converterListNum + myContext->convNum];

    if (listOffset) {
        value = taggedAliasLists[listOffset];
    }
    return value;
}

static const char* U_CALLCONV
ucnv_io_nextStandardAliases(UEnumeration *enumerator,
                            int32_t* resultLength,
                            UErrorCode *pErrorCode)
{
    UAliasContext *myContext = (UAliasContext *)(enumerator->context);
    uint32_t listOffset = taggedAliasArray[myContext->stanardNum*converterListNum + myContext->convNum];

    if (listOffset) {
        uint32_t listCount = taggedAliasLists[listOffset];
        const uint16_t *currList = taggedAliasLists + listOffset + 1;

        if (myContext->listIdx < listCount) {
            return GET_STRING(currList[myContext->listIdx++]);
        }
    }
    /* Either we accessed a zero length list, or we enumerated too far. */
    *pErrorCode = U_INDEX_OUTOFBOUNDS_ERROR;
    return NULL;
}

static void U_CALLCONV
ucnv_io_resetStandardAliases(UEnumeration *enumerator, UErrorCode *pErrorCode) {
    ((UAliasContext *)(enumerator->context))->listIdx = 0;
}

static void U_CALLCONV
ucnv_io_closeUEnumeration(UEnumeration *enumerator) {
    uprv_free(enumerator->context);
    uprv_free(enumerator);
}

/* Enumerate the aliases for the specified converter and standard tag */
static const UEnumeration gEnumAliases = {
    NULL,
    ucnv_io_closeUEnumeration,
    ucnv_io_countStandardAliases,
    NULL,
    ucnv_io_nextStandardAliases,
    ucnv_io_resetStandardAliases
};

U_CAPI UEnumeration *
ucnv_openStandardNames(const char *convName,
                            const char *standard,
                            UErrorCode *pErrorCode)
{
    UEnumeration *myEnum = NULL;
    if (haveAliasData(pErrorCode) && isAlias(convName, pErrorCode)) {
        uint32_t convNum = findConverter(convName, pErrorCode);
        uint32_t tagNum = getTagNumber(standard);
        if (tagNum < (tagListNum - NUM_RESERVED_TAGS) && convNum < converterListNum) {
            UAliasContext *myContext;

            myEnum = uprv_malloc(sizeof(UEnumeration));
            if (myEnum == NULL) {
                *pErrorCode = U_MEMORY_ALLOCATION_ERROR;
                return NULL;
            }
            uprv_memcpy(myEnum, &gEnumAliases, sizeof(UEnumeration));
            myContext = uprv_malloc(sizeof(UAliasContext));
            if (myContext == NULL) {
                *pErrorCode = U_MEMORY_ALLOCATION_ERROR;
                uprv_free(myEnum);
                return NULL;
            }
            myEnum->context = myContext;
            myContext->stanardNum = tagNum;
            myContext->convNum = convNum;
            myContext->listIdx = 0;
        }
        /* else converter or tag not found */
    }
    return myEnum;
}

U_CFUNC uint16_t
ucnv_io_countAliases(const char *alias, UErrorCode *pErrorCode) {
    if(haveAliasData(pErrorCode) && isAlias(alias, pErrorCode)) {
        uint32_t convNum = findConverter(alias, pErrorCode);
        if (convNum < converterListNum) {
            /* tagListNum - 1 is the ALL tag */
            int32_t listOffset = taggedAliasArray[(tagListNum - 1)*converterListNum + convNum];

            if (listOffset) {
                return taggedAliasLists[listOffset];
            }
            /* else this shouldn't happen. internal program error */
        }
        /* else converter not found */
    }
    return 0;
}

U_CFUNC uint16_t
ucnv_io_getAliases(const char *alias, uint16_t start, const char **aliases, UErrorCode *pErrorCode) {
    if(haveAliasData(pErrorCode) && isAlias(alias, pErrorCode)) {
        uint32_t currAlias;
        uint32_t convNum = findConverter(alias, pErrorCode);
        if (convNum < converterListNum) {
            /* tagListNum - 1 is the ALL tag */
            int32_t listOffset = taggedAliasArray[(tagListNum - 1)*converterListNum + convNum];

            if (listOffset) {
                uint32_t listCount = taggedAliasLists[listOffset];
                /* +1 to skip listCount */
                const uint16_t *currList = taggedAliasLists + listOffset + 1;

                for (currAlias = start; currAlias < listCount; currAlias++) {
                    aliases[currAlias] = GET_STRING(currList[currAlias]);
                }
            }
            /* else this shouldn't happen. internal program error */
        }
        /* else converter not found */
    }
    return 0;
}

U_CFUNC const char *
ucnv_io_getAlias(const char *alias, uint16_t n, UErrorCode *pErrorCode) {
    if(haveAliasData(pErrorCode) && isAlias(alias, pErrorCode)) {
        uint32_t convNum = findConverter(alias, pErrorCode);
        if (convNum < converterListNum) {
            /* tagListNum - 1 is the ALL tag */
            int32_t listOffset = taggedAliasArray[(tagListNum - 1)*converterListNum + convNum];

            if (listOffset) {
                uint32_t listCount = taggedAliasLists[listOffset];
                /* +1 to skip listCount */
                const uint16_t *currList = taggedAliasLists + listOffset + 1;

                if (n < listCount)  {
                    return GET_STRING(currList[n]);
                }
                *pErrorCode = U_INDEX_OUTOFBOUNDS_ERROR;
            }
            /* else this shouldn't happen. internal program error */
        }
        /* else converter not found */
    }
    return NULL;
}

U_CFUNC uint16_t
ucnv_io_countStandards(UErrorCode *pErrorCode) {
    if (haveAliasData(pErrorCode)) {
        /* Don't include the empty list */
        return (uint16_t)(tagListNum - NUM_RESERVED_TAGS);
    }

    return 0;
}

U_CAPI const char * U_EXPORT2
ucnv_getStandard(uint16_t n, UErrorCode *pErrorCode) {
    if (haveAliasData(pErrorCode)) {
        if (n < tagListNum - NUM_RESERVED_TAGS) {
            return GET_STRING(tagList[n]);
        }
        *pErrorCode = U_INDEX_OUTOFBOUNDS_ERROR;
    }

    return NULL;
}

U_CAPI const char * U_EXPORT2
ucnv_getStandardName(const char *alias, const char *standard, UErrorCode *pErrorCode) {
    if (haveAliasData(pErrorCode) && isAlias(alias, pErrorCode)) {
        uint32_t idx;
        uint32_t listOffset;
        uint32_t convNum;
        uint32_t tagNum = getTagNumber(standard);
        UErrorCode myErr = U_ZERO_ERROR;

        /* Make a quick guess. Hopefully they used a TR22 canonical alias. */
        convNum = findConverter(alias, &myErr);

        if (tagNum < (tagListNum - NUM_RESERVED_TAGS) && convNum < converterListNum) {
            if (myErr == U_AMBIGUOUS_ALIAS_WARNING) {
                /* Uh Oh! They used an ambiguous alias.
                   Hopefully the standard knows the alias.
                   This may take a while.
                */
                for (idx = 0; idx < converterListNum; idx++) {
                    listOffset = taggedAliasArray[tagNum*converterListNum + idx];
                    if (listOffset) {
                        uint32_t currAlias;
                        uint32_t listCount = taggedAliasLists[listOffset];
                        /* +1 to skip listCount */
                        const uint16_t *currList = taggedAliasLists + listOffset + 1;
                        for (currAlias = 0; currAlias < listCount; currAlias++) {
                            if (currList[currAlias]
                                && ucnv_compareNames(alias, GET_STRING(currList[currAlias]))==0)
                            {
                                if (currList[0]) {
                                    return GET_STRING(currList[0]);
                                }
                                else {
                                    /* Someone screwed up the alias table. */
                                    return NULL;
                                }
                            }
                        }
                    }
                }
                /* The standard doesn't know about the alias */
                *pErrorCode = U_AMBIGUOUS_ALIAS_WARNING;
            }
            listOffset = taggedAliasArray[tagNum*converterListNum + convNum];
            if (listOffset && taggedAliasLists[listOffset + 1]) {
                return GET_STRING(taggedAliasLists[listOffset + 1]);
            }
            /* else no default name */
        }
        /* else converter or tag not found */
    }

    return NULL;
}

void
ucnv_io_flushAvailableConverterCache() {
    if (availableConverters) {
        umtx_lock(NULL);
        availableConverterCount = 0;
        uprv_free((char **)availableConverters);
        availableConverters = NULL;
        umtx_unlock(NULL);
    }
}

static UBool haveAvailableConverterList(UErrorCode *pErrorCode) {
    if (availableConverters == NULL) {
        uint16_t idx;
        uint16_t localConverterCount;
        UErrorCode status;
        const char *converterName;
        const char **localConverterList;

        if (!haveAliasData(pErrorCode)) {
            return FALSE;
        }

        /* We can't have more than "*converterTable" converters to open */
        localConverterList = (const char **) uprv_malloc(converterListNum * sizeof(char*));
        if (!localConverterList) {
            *pErrorCode = U_MEMORY_ALLOCATION_ERROR;
            return FALSE;
        }

        localConverterCount = 0;

        for (idx = 0; idx < converterListNum; idx++) {
            status = U_ZERO_ERROR;
            converterName = GET_STRING(converterList[idx]);
            ucnv_close(ucnv_open(converterName, &status));
            if (U_SUCCESS(status)) {
                localConverterList[localConverterCount++] = converterName;
            }
        }

        umtx_lock(NULL);
        if (availableConverters == NULL) {
            availableConverters = localConverterList;
            availableConverterCount = localConverterCount;
        }
        else {
            uprv_free((char **)localConverterList);
        }
        umtx_unlock(NULL);
    }
    return TRUE;
}

U_CFUNC uint16_t
ucnv_io_countAvailableConverters(UErrorCode *pErrorCode) {
    if (haveAvailableConverterList(pErrorCode)) {
        return availableConverterCount;
    }
    return 0;
}

U_CFUNC const char *
ucnv_io_getAvailableConverter(uint16_t n, UErrorCode *pErrorCode) {
    if (haveAvailableConverterList(pErrorCode)) {
        if (n < availableConverterCount) {
            return availableConverters[n];
        }
        *pErrorCode = U_INDEX_OUTOFBOUNDS_ERROR;
    }
    return NULL;
}

U_CFUNC void
ucnv_io_fillAvailableConverters(const char **aliases, UErrorCode *pErrorCode) {
    if (haveAvailableConverterList(pErrorCode)) {
        uint16_t count = 0;
        while (count < availableConverterCount) {
            *aliases++=availableConverters[count++];
        }
    }
}

U_CFUNC uint16_t
ucnv_io_countAvailableAliases(UErrorCode *pErrorCode) {
    if (haveAliasData(pErrorCode)) {
        return (uint16_t)aliasListNum;
    }
    return 0;
}

/* default converter name --------------------------------------------------- */

/*
 * In order to be really thread-safe, the get function would have to take
 * a buffer parameter and copy the current string inside a mutex block.
 * This implementation only tries to be really thread-safe while
 * setting the name.
 * It assumes that setting a pointer is atomic.
 */

U_CFUNC const char *
ucnv_io_getDefaultConverterName() {
    /* local variable to be thread-safe */
    const char *name=defaultConverterName;
    if(name==NULL) {
        const char *codepage = uprv_getDefaultCodepage();
        if(codepage!=NULL) {
            UErrorCode errorCode=U_ZERO_ERROR;
            name=ucnv_io_getConverterName(codepage, &errorCode);
            if(U_FAILURE(errorCode) || name==NULL) {
                name=codepage;
            }
        }

        /* if the name is there, test it out */
        if(name != NULL) {
            UErrorCode errorCode = U_ZERO_ERROR;
            UConverter *cnv = ucnv_open(name, &errorCode);
            if(U_FAILURE(errorCode) || (cnv == NULL)) {
                /* Panic time, let's use a fallback. */
#if (U_CHARSET_FAMILY == U_ASCII_FAMILY) 
                name = "US-ASCII";
                /* there is no 'algorithmic' converter for EBCDIC */
#elif defined(OS390)
                name = "ibm-1047-s390";
#else
                name = "ibm-37";
#endif
            }
            ucnv_close(cnv);
        }

        if(name != NULL) {
            umtx_lock(NULL);
            /* Did find a name. And it works.*/
            defaultConverterName=name;
            umtx_unlock(NULL);
        }
    }

    return name;
}

U_CFUNC void
ucnv_io_setDefaultConverterName(const char *converterName) {
    if(converterName==NULL) {
        /* reset to the default codepage */
        defaultConverterName=NULL;
    } else {
        UErrorCode errorCode=U_ZERO_ERROR;
        const char *name=ucnv_io_getConverterName(converterName, &errorCode);
        if(U_SUCCESS(errorCode) && name!=NULL) {
            defaultConverterName=name;
        } else {
            /* do not set the name if the alias lookup failed and it is too long */
            int32_t length=(int32_t)(uprv_strlen(converterName));
            if(length<sizeof(defaultConverterNameBuffer)) {
                /* it was not found as an alias, so copy it - accept an empty name */
                UBool didLock;
                if(defaultConverterName==defaultConverterNameBuffer) {
                    umtx_lock(NULL);
                    didLock=TRUE;
                } else {
                    didLock=FALSE;
                }
                uprv_memcpy(defaultConverterNameBuffer, converterName, length);
                defaultConverterNameBuffer[length]=0;
                defaultConverterName=defaultConverterNameBuffer;
                if(didLock) {
                    umtx_unlock(NULL);
                }
            }
        }
    }
}

/*
 * Hey, Emacs, please set the following:
 *
 * Local Variables:
 * indent-tabs-mode: nil
 * End:
 *
 */