qdate - A Wrapper for Erlang Date/Time Management

Purpose

Erlang Date and Time management is rather primitive, but improving.

dh_date, of which ec_date in erlware_commons is a huge step towards formatting and parsing dates in a way that compares nicely with PHP's date and strtotime functions.

Unfortunately, ec_date doesn't deal with timezones, but conveniently, the project erlang_localtime does.

It is the express purpose of this qdate package to bring together the benefits of ec_date and erlang_localtime, as well as extending the capabilities of both to provide for other needed tools found in a single module.

qdate will provide, under the roof of a single module date and time formatting and parsing from and into:

Formatting Strings
Erlang Date Format
Erlang Now Format
Unixtime integers

All while doing so by allowing you to either set a timezone by some arbitrary key or by using the current process's Pid is the key.

Further, while ec_date doesn't support PHP's timezone characters (e, I, O, P, and T, Z), qdate will handle them for us.

Exported Functions:

Conversion Functions

to_string(FormatString, Date) - "FormatString" is a string that follows the date function formatting rules. Date is any date, in almost any common format
to_string(FormatString) - Formats the current time
to_date(Date) - converts any date/time format to Erlang date format.
to_now(Date) - converts any date/time format to Erlang now format.
to_unixtime(Date) - converts any date/time format to a unixtime integer

Conversion Functions provided for API compatibility with `ec_date`

parse/1 - Same as to_date(Date)
nparse/1 - Same as to_now(Date)
format/1 - Same as to_string/1
format/2 - Same as to_string/2

Timezone Functions

set_timezone(Key, TZ) - Set the timezone to TZ for the key Key
set_timezone(TZ) - Sets the timezone, and uses the Pid from self() as the Key. Also links the process for removal from the record when the Pid dies.
get_timezone(Key) - Gets the timezone assigned to Key
get_timezone() - Gets the timezone using self() as the Key
clear_timezone(Key) - Removes the timezone record associated with Key.
clear_timezone() - Removes the timezone record using self() as Key. This function is not necessary for cleanup, most of the time, since if Key is a Pid, the qdate server will automatically clean up when the Pid dies.

Note: If no timezone is set, then anything relying on the timezone will default to GMT.

Example:

Calling qdate:format will allow single-line re-encoding of a date.

Say we wanted to convert the date and time from "12/31/2013 8:15pm" to something like "2013-12-31 (16:15:00)":

Using just ec_date, you would do it like this:

	OldDate = "12/31/2013 8:15pm",

   Date = ec_date:parse(OldDate),
   NewString = ec_date:format("Y-m-d (H:i:s)",Date).

With the new method, you could do it simply and clearly with one line:

	NewString = qdate:format("Y-m-d (H:i:s)",OldDate).

The nice thing about it this though, is that OldDate can be any date format, and it will figure it out. It can be any of the following:

Erlang Date Format: {{Y,M,D},{H,M,S}}
Erlang Now Format: {MegaSecs, Secs, MicroSecs}
Date String: "2013-12-31 08:15pm"
Integer Unix Timestamp: 1388448000

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