#include "pg_bikram_sambat.h"

PG_FUNCTION_INFO_V1(ad_to_bs);

/*
    This function basically only:
     - accepts the argument
     - converts it to date values (only for validation)
     - performs validation (by calling adToBs itself)
     - returns it (the argument itself)
     - the actual conversion happens in the bs_date_out function because the SQL function that makes use of this function has a return type 'bs_date'

    So where does the conversion happen:
    - if this function is used in an INSERT statement, no conversion needs to happen since we are basically storing int32 AD dates for bs_date type
    - if this function is used in a SELECT statement, the bs_date_out conversion function will handle the conversion from AD to BS

    Why not make use of the bs_date_out function in the `CREATE FUNCTION ad_to_bs` statement then?
    - because the bs_date_out function returns a cstring/text which is:
        - fine for SELECT statements
        - but not correct for INSERT statements

    If the date validation happens in the bs_date_out function, why do it here in this ad_to_bs function as well?
    - because the bs_date_out function only gets called for SELECT statements,
    - for INSERT statements that may make use of this ad_to_bs function, validation will not happen otherwise
*/
Datum ad_to_bs(PG_FUNCTION_ARGS)
{
    DateADT adDate = PG_GETARG_DATEADT(0);
    int year, month, day;

    j2date(adDate + POSTGRES_EPOCH_JDATE, &year, &month, &day);
    adToBs(year, month, day); // done in order to trigger all of the valdations

    PG_RETURN_INT32((int32)adDate);
}

PG_FUNCTION_INFO_V1(bs_date_to_char);

Datum bs_date_to_char(PG_FUNCTION_ARGS)
{
    BSDateADT date = PG_GETARG_INT32(0);
    text *fmtStrArg = PG_GETARG_TEXT_PP(1);
    char *fmtStrC = text_to_cstring(fmtStrArg);

    DateParts bsDate;
    char *formattedDate;
    text *returnText;

    int year, month, day;
    j2date(date + POSTGRES_EPOCH_JDATE, &year, &month, &day);
    bsDate = adToBs(year, month, day);

    formattedDate = extractDateWithFmtStr(&bsDate, fmtStrC, NULL);
    returnText = cstring_to_text(formattedDate);

    pfree(fmtStrC);
    pfree(formattedDate);
    /*
        # Why not pfree(fmtStrArg) (We do pfree fmtStrC though)
          - it is an input argument
          - never pfree() an input argument passived via PG_GETARG
          - because these memory addresses are managed by the executor
          - only pfree() memory that we explicitly allocate (e.g., the result of text_to_cstring())
    */

    PG_RETURN_TEXT_P(returnText);
}

PG_FUNCTION_INFO_V1(bs_date_to_char_lang);
/*
    - similar to the bs_date_to_char function but this also supports Devanagari output
    Example: SELECT to_char(bs_date_value, 'YYYY/MM/DD', 'dev')
*/
Datum bs_date_to_char_lang(PG_FUNCTION_ARGS)
{
    BSDateADT date = PG_GETARG_INT32(0);
    text *fmtStrArg = PG_GETARG_TEXT_PP(1);
    text *lang = PG_GETARG_TEXT_PP(2);

    char *fmtStrC = text_to_cstring(fmtStrArg);
    char *langC = text_to_cstring(lang);

    DateParts bsDate;
    char *formattedDate;
    text *returnText;

    int year, month, day;
    j2date(date + POSTGRES_EPOCH_JDATE, &year, &month, &day);
    bsDate = adToBs(year, month, day);

    formattedDate = extractDateWithFmtStr(&bsDate, fmtStrC, langC);
    returnText = cstring_to_text(formattedDate);

    pfree(fmtStrC);
    pfree(langC);
    pfree(formattedDate);
    /*
        # Why not pfree(fmtStrArg) (We do pfree fmtStrC though)
          - it is an input argument
          - never pfree() an input argument passived via PG_GETARG
          - because these memory addresses are managed by the executor
          - only pfree() memory that we explicitly allocate (e.g., the result of text_to_cstring())
    */
    PG_RETURN_TEXT_P(returnText);
}

PG_FUNCTION_INFO_V1(current_bs_date);
/*
    This function basically only:
     - gets the current transaction timestamp (by making use of GetCurrentTimestamp() from PostgreSQL utils/timestamp.h)
     - extracts the year, month and date from it (by making use of timestamp2tm())
     - performs validation (by calling adToBs itself)
     - gets the Julian day value from the year, month and date
     - returns the Julian day int
     - the actual conversion happens in the bs_date_out function because the SQL function that makes use of this function has a return type 'bs_date'
*/
Datum current_bs_date(PG_FUNCTION_ARGS)
{
    /*
        GetCurrentTimestamp() returns the current time (int64 representation) at the start of the transaction
        - meaning, multiple calls to this function 'current_bs_date' within the same transaction will return consistent result
        - which is why we prefer this instead of using the builtin C time() and localtime_r() functions based implementation
    */
    TimestampTz now = GetCurrentTimestamp();

    /*
        the only variable we're concerned with here is 'tm'
        all of the other variables are passed (instead of NULL) because
        timestamp2tm is a low-level C function that unconditionally
        attempts to write the results to the memory addresses (passed as arguments)
        Dereferencing a NULL pointer to write a value would cause segmentatino fault, which would crash the entire PostgreSQL backend process
    */
    int tz;
    struct pg_tm tm;
    fsec_t fsec;
    const char *tzn;
    DateADT adDate;

    if (timestamp2tm(now, &tz, &tm, &fsec, &tzn, NULL) != 0) // timestamp2tm returns 0 on success
        ereport(ERROR, (errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE), errmsg("timestamp out of range")));

    /*
        subtracting the Postgres Epoch (2000-01-01) to match the internal DateADT representation.
    */
    adDate = date2j(tm.tm_year, tm.tm_mon, tm.tm_mday) - POSTGRES_EPOCH_JDATE;
    adToBs(tm.tm_year, tm.tm_mon, tm.tm_mday); // done in order to trigger all of the valdations

    PG_RETURN_INT32(adDate);
}