Working with Jolly Santa’s Outstanding Notes

Note: here’s an article that couldn’t make it to the Perl Advent calendar. Can’t really let it go to waste, now, can I? Merry Xmas, and here’s to happiness and warmth for y’all!

Santa Claus’s workshops, like any other organization working under lot of pressure and chronically undermanned (in this case, quite literally, as no elf stands taller than four feet), are a little bit of a hot, cocoa-scented mess. The workshops’s many systems could be said to be so many special snowflakes, and they bandy information between them with quite an impressive array of protocols and serialization format. Fortunately for everybody, a crack team of develfopers lead by Gluggagaegir make sure that the bedlam remains under relative control.

Their challenge of today is to deal with Santa’s very special short list, available as a JSON document:

{ "good": [ { "rjbs": { "wish": [ "Mark III Ogre", 
"Green Fairy's Vintage Nectar" ] } } , { "miyagawa": { 
"wish": [ "peculiar purple pouch" ] } } ], "bad": [ {
"sawyer": { "reason": 
"wishing things to die is not nice" } } ] }

Typical. Formatting is inexistant, the structure is less than optimal, but at least it’s well-formed. That’s however all Glugg and his cohorts need to be able to leverage App::jt to tame and manipulate the document, straight from the command line.

For example, the first thing they usually do is to pretty-print the JSON so that they can look at it without going blind.

$ jt < shortlist.json
[
{
    "wishlist" : [
        "Mark III Ogre",
        "Green Fairy's Vintage Nectar"
    ],
    "name" : "rjbs",
    "verdict" : "nice"
},
{
    "verdict" : "nice",
    "wishlist" : [
        "peculiar purple pouch"
    ],
    "name" : "miyagawa"
},
{
    "reason" : "wishing things to die is not nice",
    "wishlist" : [
        "hug blanket"
    ],
    "name" : "sawyer",
    "verdict" : "naughty"
}
]

They also can quickly filter entries, and output the data in an easy to manage csv format to send to the other departments.

$ cat shortlist.json                     |     jt --grep '$_{verdict} eq "naughty"' |     jt --field name,reason --csv
name,reason
sawyer,"wishing things to die is not nice"

If push comes to shove, they can even munge the data on the fly. For example, this year the North Pole’s budget is tight, so it’s strictly one gift per person:

$ cat shortlist.json | jt --grep '$_{verdict} eq "nice"' | jt --map '$_{wishlist} = $_{wishlist}[0] '
[
{
    "wishlist" : "Mark III Ogre",
    "verdict" : "nice",
    "name" : "rjbs"
},
{
    "wishlist" : "peculiar purple pouch",
    "name" : "miyagawa",
    "verdict" : "nice"
}
]

JSONPath, it goes without saying, is a non-feature.

$ cat shortlist.json | jt --json-path '$..name'
[
    "rjbs",
    "miyagawa",
    "sawyer"
]

And since it’s all Perl underneath, a clever develfoper even found ways to bend the tool into doing things it wasn’t expected to do. Like only printing a cumulative statement:

$ cat shortlist.json |     jt --silent --map '$::tally{$_{verdict}}++; $::once++ or eval q!END { say join " ", %::tally}!'
naughty 1 nice 2