Songs And Charts

Tachi structures its song and chart data in a specific manner in order to avoid copying properties all over the place.

---

Songs

Songs look like this:

{
    "title": "5.1.1.",
    "artist": "dj nagureo",
    "id": 1,
    "firstVersion": "0",
    "alt-titles": [],
    "search-titles": [],
    "data": {
        "genre": "PIANO AMBIENT"
    }
}

They're relatively small documents, and contain some metadata.

Depending on the game, the data prop will contain game-specific properties (i.e. not all games have song genres!)

Songs, however, don't contain any information about their charts. The charts are what people actually play.

In short, songs are just a collection of metadata that parents a chart document!

---

Chart Documents

Chart Documents MUST belong to a song. In the below chart, songID refers to the above song document:

{
    "chartID": "c2311194e3897ddb5745b1760d2c0141f933e683",
    "difficulty": "ANOTHER",
    "songID": 1,
    "playtype": "SP",
    "levelNum": 10,
    "level": "10",
    "data": {
        "inGameID": 1000,
        "notecount": 786,
    },
    "isPrimary": true,
    "versions": [
        "27-omni",
        "26-omni",
        "27",
        "26",
        "inf",
        "16-cs",
        "12-cs",
        "10-cs",
        "8-cs",
        "7-cs",
        "bmus"
    ]
}

Songs can have multiple charts, but charts can only have one song.

Primary

Sometimes, games like to rechart things and release them under the exact same song. Sometimes, they even do this under the exact same internal songID!

A 'Primary' chart refers to a chart that is the current variant of that chart for this game. Non-Primary charts are not eligible for any rating calculations, nor do they contribute to profile rating.

To check if a chart is primary or not, the isPrimary property handles that.

For example:

{
    "chartID": "103ff8bb004e1a8a005f808c025c3feb",
    "difficulty": "ANOTHER",
    "songID": 1,
    "playtype": "SP",
    "levelNum": 5,
    "level": "5",
    "data": {
        "inGameID": 1000,
        "notecount": 433
    },
    "isPrimary": false,
    "versions": [
        "1"
    ]
}

Notice that the chartID is different, and isPrimary is set to false.

Even though this chart is "5.1.1 (SP ANOTHER)", it isn't the primary chart for this songID + playtype + difficulty.

For the UI, Tachi will hide non-primary charts by default. Realistically, they only exist to support legacy scores without having to throw them away when a rechart occurs.