Swift xsd:duration Parser Extensions
This set of extensions allows us to easily parse duration values, as expressed in XML documents that expect their duration values to be in the standard xsd:duration format.
What Problem Does This Solve?
The duration format has a number of ways that it can be expressed, and this set of extensions should allow us to deal with all of them. It will be most useful integrated into an XML parser. It will read a duration from a String instance, and return a DateComponents instance, representing the duration in that String. You can also do the reverse, and take a DateComponents instance, and express it as a properly-formatted xsd:duration String.
It should work fine for osx, tvOS and iOS. It only depends on the Swift Foundation library.
This requires Swift Version 4.0 or above (tested with 4.2).
WHERE TO GET
Include the Source in Your Project
This is a simple source file; not a module.
To use this, simply add the RVS_ParseXMLDuration/RVS_ParseXMLDuration.swift file to your project; copying it wherever you want.
The String variant will return an optional DateComponents result (a parsed string), and the DateComponents variant will return an optional String (a properly-formatted xsd:duration string).
All the rest of the stuff is for testing, validating and sharing.
A Few Rules:
The string is formatted as
The first character MUST be a
"P", and any negative sign must PRECEDE the
Any time (hours, minutes, seconds), MUST be preceded by a
"T". This either starts the time, or separates it from a date.
P2Y6M5DT12H35M30S is 2 years, 6 months, 5 days, 12 hours, 35 minutes and 30 seconds.
For our purposes, when a unit is not specified, we don't include it at all in the DateComponents. If the unit is specified, but is a zero (0), then we specify that unit as zero in the DateComponents.
Not much to show, really. The parser is ridiculously easy to use.
Parsing From A String:
Each part is composed of 1 or more decimal digits, immediately succeeded by "Y" (years), "M" (months or minutes), "D" (days), "H" (hours), or "S" (seconds). Seconds can be expressed as a decimal. All other numbers are integers.
let durationComponents1 = "P2Y6M5DT12H35M30.123S".asXMLDuration // DateComponents(year: 2, month: 6, day: 5, hour: 12, minute: 35, second: 30, nanosecond: 1230000000)
You can have more than 59 minutes or 23 hours.
let durationComponents2 = "PT168H120M".asXMLDuration // DateComponents(hour: 168, minute: 120)
In order to have a negative duration, the first character must be a minus sign, and ALL components in the result will be negative.
let durationComponents3 = "-P2M4DT10M5.23S".asXMLDuration // DateComponents(month: -2, day: -4, minute: -10, second: -5, nanosecond: -2300000000)
Delivering A String From A DateComponents Instance:
Zero (or unspecified) components are not included in the resultant String.
let durationString1 = DateComponents(year: 0, day: 1, hour: 1, minute: 0, second: 1, nanosecond: 0).asXMLDuration // "P1DT1H1S"
Note that fractional seconds are expressed as seconds and nanoseconds.
let durationString2 = DateComponents(year: 1, month: 1, day: 1, hour: 1, minute: 1, second: 1, nanosecond: 1000000000).asXMLDuration // "P1Y1M1DT1H1M1.1S"
In order to specify a negative duration, ALL components must be negative.
let durationString3 = DateComponents(year: -1, month: -1, day: -1, hour: -1, minute: -1, second: -1, nanosecond: -1000000000).asXMLDuration // "-P1Y1M1DT1H1M1.1S"
There are no dependencies to use RVS_ParseXMLDuration in your project. In order to test it and run it in the module project, you should use CocoaPods to install SwiftLint, although that is not required. It's just good practice.
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