"Fuzzy" search of Mediawiki Commons categories

Question

I am developing an app that lets smartphone users upload a picture to Wikimedia Commons. The user must categorize the picture by typing Commons category names. Typing on a smartphone is slow/painful/erratic, and category names are not obvious, so the app should do its best to guess what category the user is trying to find.

QUESTION: Is there an API that takes a string, and returns 1~10 Commons category names that fuzzy-match the beginning of the string?

Requirements:

• Response of the server must be very fast (as-you-type)
• Free, as there is no budget for the app
• Scalability should not be a problem for now, less than 5 concurrent users at any one time

For instance, Category:Power plants in New Zealand‎ should be found even if the typed string is:

• Power plants in New Z (as-you-type)
• power plants in new zealand (lowercase)
• Power plants in New-Zealand (dash instead of space)
• Power plant in New Zealand (singular)
• Pwer plants in New Zeland (typo - ideally)
• New Zeland power plant (word order - ideally)

Answer 1

First variant: MediaWiki API for Commons with search query for pages of type "Category" (srnamespace=14), maximum 10 results (srlimit=10), and searched string your_string:

https://commons.wikimedia.org/w/api.php?action=query&list=search&srwhat=text&srenablerewrites=1&srnamespace=14&srlimit=10&srsearch=your_string

Second variant: MediaWiki API for Commons with opensearch for maximum 10 results (limit=10), and searched string your_string:

https://commons.wikimedia.org/w/api.php?action=opensearch&limit=10&suggest=1&search=Category:your_string

For your example:

• Power plants in New Z returns the desired category on 1st place for the second variant
• power plants in new zealand returns the desired category on 1st place for both variants
• Power plants in New-Zealand returns the desired category on 4th place for the first variant
• Power plant in New Zealand returns the desired category on 4th place for the first variant
• Pwer plants in New Zeland and New Zeland power plant returns suggestion for the first variant

I couldn't find something better, so if you want you can make some combination of these two variants or you can do compromise and will use one of them.