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arrayconnection.js
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arrayconnection.js
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/* @flow */
/**
* Copyright (c) 2015, Facebook, Inc.
* All rights reserved.
*
* This source code is licensed under the BSD-style license found in the
* LICENSE file in the root directory of this source tree. An additional grant
* of patent rights can be found in the PATENTS file in the same directory.
*/
import type {
Connection,
ConnectionArguments,
ConnectionCursor,
} from './connectiontypes';
import {
base64,
unbase64,
} from '../utils/base64.js';
type ArraySliceMetaInfo = {
sliceStart: number;
arrayLength: number;
};
/**
* A simple function that accepts an array and connection arguments, and returns
* a connection object for use in GraphQL. It uses array offsets as pagination,
* so pagination will only work if the array is static.
*/
export function connectionFromArray<T>(
data: Array<T>,
args: ConnectionArguments
): Connection<T> {
return connectionFromArraySlice(
data,
args,
{
sliceStart: 0,
arrayLength: data.length,
}
);
}
/**
* A version of `connectionFromArray` that takes a promised array, and returns a
* promised connection.
*/
export function connectionFromPromisedArray<T>(
dataPromise: Promise<Array<T>>,
args: ConnectionArguments
): Promise<Connection<T>> {
return dataPromise.then(data => connectionFromArray(data, args));
}
/**
* Given a slice (subset) of an array, returns a connection object for use in
* GraphQL.
*
* This function is similar to `connectionFromArray`, but is intended for use
* cases where you know the cardinality of the connection, consider it too large
* to materialize the entire array, and instead wish pass in a slice of the
* total result large enough to cover the range specified in `args`.
*/
export function connectionFromArraySlice<T>(
arraySlice: Array<T>,
args: ConnectionArguments,
meta: ArraySliceMetaInfo
): Connection<T> {
var {after, before, first, last} = args;
var {sliceStart, arrayLength} = meta;
var sliceEnd = sliceStart + arraySlice.length;
var beforeOffset = getOffsetWithDefault(before, arrayLength);
var afterOffset = getOffsetWithDefault(after, -1);
var startOffset = Math.max(
sliceStart - 1,
afterOffset,
-1
) + 1;
var endOffset = Math.min(
sliceEnd,
beforeOffset,
arrayLength
);
if (typeof first === 'number') {
endOffset = Math.min(
endOffset,
startOffset + first
);
}
if (typeof last === 'number') {
startOffset = Math.max(
startOffset,
endOffset - last
);
}
// If supplied slice is too large, trim it down before mapping over it.
var slice = arraySlice.slice(
Math.max(startOffset - sliceStart, 0),
arraySlice.length - (sliceEnd - endOffset)
);
var edges = slice.map((value, index) => ({
cursor: offsetToCursor(startOffset + index),
node: value,
}));
var firstEdge = edges[0];
var lastEdge = edges[edges.length - 1];
var lowerBound = after ? (afterOffset + 1) : 0;
var upperBound = before ? beforeOffset : arrayLength;
return {
edges,
pageInfo: {
startCursor: firstEdge ? firstEdge.cursor : null,
endCursor: lastEdge ? lastEdge.cursor : null,
hasPreviousPage:
typeof last === 'number' ? startOffset > lowerBound : false,
hasNextPage:
typeof first === 'number' ? endOffset < upperBound : false,
},
};
}
/**
* A version of `connectionFromArraySlice` that takes a promised array slice,
* and returns a promised connection.
*/
export function connectionFromPromisedArraySlice<T>(
dataPromise: Promise<Array<T>>,
args: ConnectionArguments,
arrayInfo: ArraySliceMetaInfo
): Promise<Connection<T>> {
return dataPromise.then(
data => connectionFromArraySlice(data, args, arrayInfo)
);
}
var PREFIX = 'arrayconnection:';
/**
* Creates the cursor string from an offset.
*/
export function offsetToCursor(offset: number): ConnectionCursor {
return base64(PREFIX + offset);
}
/**
* Rederives the offset from the cursor string.
*/
export function cursorToOffset(cursor: ConnectionCursor): number {
return parseInt(unbase64(cursor).substring(PREFIX.length), 10);
}
/**
* Return the cursor associated with an object in an array.
*/
export function cursorForObjectInConnection<T>(
data: Array<T>,
object: T
): ?ConnectionCursor {
var offset = data.indexOf(object);
if (offset === -1) {
return null;
}
return offsetToCursor(offset);
}
/**
* Given an optional cursor and a default offset, returns the offset
* to use; if the cursor contains a valid offset, that will be used,
* otherwise it will be the default.
*/
export function getOffsetWithDefault(
cursor?: ?ConnectionCursor,
defaultOffset: number
): number {
if (typeof cursor !== 'string') {
return defaultOffset;
}
var offset = cursorToOffset(cursor);
return isNaN(offset) ? defaultOffset : offset;
}