cockpit.js: Series Data Representing series data

Series data consists of values along a continuous (usually time) axis. We can place these in grids which expose a distinct subset of these values. These are the underlying mechanism for displaying metrics data in graphs.

## cockpit.grid()

    grid = cockpit.grid(interval, [beg, end])

Creates a grid object to contain series data.

The `interval` is the granularity of the grid. Usually this is a number of milliseconds, when used with time series data. The `beg` and `end` are the bounds of the grid. If omitted they will be set to zero for an initially empty grid.

If `beg` and/or `end` are negative (including negative zero) then they are interpreted in number of intervals relative to the current time. Thus cockpit.grid(1000, -300, -0) will create a grid for the most recent 5 minutes.

## grid.add()

    row = grid.add(series, path)
    row = grid.add(callback, [early])
    row = grid.add()

Adds a row to the grid. The returned `row` is a Javascript array that will contain series data. The arguments control how the row is populated from the series data. The `row` is a sparse array. Its `row.length` will not match the expected size of the grid, unless and until the row has been completely filled in. The first index of the `row` will contain the data from the series data at the `grid.beg` offset.

When no arguments are passed, an empty row is added, and it is not populated with data.

When called with a `series` and `path` argument then the row will be populated directly with series data. The `series` can either be a series object or an object that has an `obj.series` property. The series interval must match the interval of this grid. If `path` is missing or empty, then the series data is placed into the row directly. Otherwise `path` indicates which part of the series data to place in the row. When `path` is an array, it is used as a set of property names or array indexes to follow into nested series data. When `path` is a dotted string, it is split and used the same way to locate the correct value in nested series data. The exact format of the series data depends on its producer, and relevant paths will be documented there.

If a `callback` function is specified, then it will be invoked to provide series data for the row. The function is invoked as `callback(row, index, count)`, where the `row` is the row to fill in, the `index` is the index to start filling in and `count` is the number of items to fill in. The `this` variable will be set to the grid while invoking the `callback`. The callback is called after other data rows for a given series have been filled in. Callbacks are called in the order added, unless the `early` argument is set to `true`, in which case the callback is called earlier than callbacks without the `early` argument set.

To remove the row use the `grid.remove()` method.

The row will start being populated with data when the `series` produces data. To make this happen right away, use the `grid.sync()` method.

## grid.remove()

    grid.remove(row)

Remove a previously added `row` from the grid. The row will no longer be updated with series data.

## grid.sync()

    grid.sync()

Load or reload data from the series into the rows. This does not clear the rows before populating them. Some data may be populated immediately, others may have to wait until data can be loaded. Internally this function calls `series.load()` for each series.

All rows with callbacks will be invoked to regenerate all the data. The `grid.onnotify` event will be triggered. It is not necessary to call this function after a call of the `grid.move()` method.

## grid.move()

    grid.move(beg[, end])

Move the grid to new `beg` and `end` range. Data will be discarded from the rows and `grid.sync()` will be called to load or reload series data for the new range of offsets.

If `end` is not specified it will be set to `beg`. If `beg` and/or `end` are negative (including negative zero) then they will be set to the number of intervals prior to the current time taken as an interval.

If `beg` and/or `end` are negative (including negative zero) then they are interpreted in number of intervals relative to the current time. Thus cockpit.grid(1000, -300, -0) will create a grid for the most recent 5 minutes.

## grid.walk()

    grid.walk()

Move the grid forward every `grid.interval` milliseconds. To stop moving forward, call `grid.move()`.

## grid.notify()

    grid.notify(index, count)

This function is called to have rows with callbacks recalculate their data. It is not normally necessary to call this function, as it will be invoked automatically when new series data is available or has been loaded. This function triggers the `grid.onnotify` event.

## grid.onnotify

    $(grid).on("notify", function(index, count) { ... });

An event that is triggered when some part of the series data in grid changes. The `index` is the row index where things changed, and the `count` is the length of the data that changed.

## grid.close()

    grid.close()

Close the grid, and stop updating the rows.

## grid.interval

The granularity of the grid. For time series data this is an interval in milliseconds. In order to use a given grid and series together, their interval properties must match.

## grid.beg

The beginning offset of the series data in the grid. Do not set this property directly. Use the grid.move() method instead.

## grid.end

The ending offset of the series data in the grid. Do not set this property directly. Use the grid.move() method instead.

## cockpit.series()

    series = cockpit.series(interval, [cache, fetch])

Create a new sink of series data. This is usually done by producers of series data, and it is rare to invoke this function directly.

The `interval` is the granularity of the series data. For time series data this is an interval in milliseconds. If a `cache` string is specified, series data will be cached across frames for series with the same `cache` cache identifier to load and/or reload.

If a `fetch` callback is specified, then it will be invoked when grids request certain ranges of data. The `fetch` callback is invoked with `function fetch(beg, end) { ... }` range offsets. The series.input() should be called with data retrieved, either immediately or at a later time. The callback may be called multiple times for the same ranges of data. It is up to the callback to determine when or whether it should retrieve the data more than once.

A producer of series data, usually calls this function and creates itself a `obj.series` property containing this series object.

## series.input()

    series.input(beg, items[, mapping])

Send series data into the series sink. Any grids that have added rows based on this series, will have data filled in. The `beg` is the beginning offset of `items`. The `items` are an array one or more series data items.

Producers may wish to provide additional properties that can be used in lookup paths that rows can pull from. This is done in the `mapping` argument. If specified it is a tree of objects. Each sub object should have a property with the name `""` empty string, which will be used as the property name or index in place of the one used in the lookup path.

## series.load()

    series.load(beg, end)

Load data from the series into any grids that have rows based on this series data. Any cached data will be filled in immediately. Any data not cached, will be requested from the producer, if possible, and may arrive at a later time.

The `beg` and `end` denote the range of data to load.

## series.interval

The granularity of the series. For time series data this is an interval in milliseconds. In order to use a given grid and series together, their interval properties must match.

## series.limit

The maximum number of items to cache for loading and/or reloading. You can change this value to a different number. Having a number close to zero will break certain usage of grids, such as `grid.walk()`.