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All Rights Reserved.\r\n *\r\n *  Licensed under the Apache License, Version 2.0 (the \"License\"); you may not\r\n *  use this file except in compliance with the License. You may obtain a copy\r\n *  of the License at\r\n *\r\n *      http://www.apache.org/licenses/LICENSE-2.0\r\n *\r\n *  Unless required by applicable law or agreed to in writing, software\r\n *  distributed under the License is distributed on an \"AS IS\" BASIS, WITHOUT\r\n *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the\r\n *  License for the specific language governing permissions and limitations\r\n *  under the License.\r\n */\r\nimport { MotionObservable, } from './observables/proxies';\r\nimport { createPlucker, } from './operators/pluck';\r\nimport { isPoint2D, } from './typeGuards';\r\n// These constants are exported for testing.\r\nexport const MAXIMUM_AGE = 250;\r\nexport const MAXIMUM_INCOMING_DISPATCHES = 5;\r\nconst pluckTimestamp = createPlucker('timestamp');\r\nconst pluckValue = createPlucker('value');\r\nconst pluckX = createPlucker('value.x');\r\nconst pluckY = createPlucker('value.y');\r\n/**\r\n * Computes the velocity of an incoming stream and emits the result. Velocity's\r\n * denominator is in milliseconds; if the incoming stream is measured in pixels,\r\n * the resulting stream will be in pixels / millisecond.\r\n *\r\n * Velocity is computed by watching the trailing 250ms of up to 5 emissions and\r\n * measuring the distance between the longest pair of events moving in the\r\n * current direction.  This approach is more resiliant to anomolous data than a\r\n * simple (nextPosition - prevPosition) / (nextTime - prevTime).\r\n *\r\n * If `pulse$` is supplied, `velocity(pulse$)` will only emit values when\r\n * `pulse$` emits a value.  This is useful for ensuring that velocity is only\r\n * calculated when it will be used.\r\n */\r\nexport function getVelocity$({ value$, pulse$, \r\n    // These values are borrowed from Matthew Bolohan's drag implementation (which\r\n    // presumes the units are \"px / ms\").\r\n    maximumVelocity = 5, defaultVelocity = 1, }) {\r\n    return new MotionObservable((observer) => {\r\n        let records = [];\r\n        const trailingSubscription = value$.timestamp()._slidingWindow({ size: MAXIMUM_INCOMING_DISPATCHES }).subscribe(nextRecords => records = nextRecords);\r\n        const pulseSubscription = pulse$.timestamp().subscribe(({ timestamp: now }) => {\r\n            const recentRecords = records.filter(({ timestamp }) => now - timestamp < MAXIMUM_AGE);\r\n            if (records.length && isPoint2D(records[0].value)) {\r\n                observer.next({\r\n                    x: calculateVelocity({ records: recentRecords, pluckValue: pluckX, pluckTimestamp, maximumVelocity, defaultVelocity }),\r\n                    y: calculateVelocity({ records: recentRecords, pluckValue: pluckY, pluckTimestamp, maximumVelocity, defaultVelocity }),\r\n                });\r\n            }\r\n            else {\r\n                observer.next(calculateVelocity({ records: recentRecords, pluckValue, pluckTimestamp, maximumVelocity, defaultVelocity }));\r\n            }\r\n        });\r\n        return () => {\r\n            trailingSubscription.unsubscribe();\r\n            pulseSubscription.unsubscribe();\r\n        };\r\n    });\r\n}\r\n;\r\n/**\r\n * Computes velocity using the oldest value that's moving in the current\r\n * direction.\r\n *\r\n * It walks backwards over an array of records and makes sure that each segment\r\n * is going in the same direction (incrementing or decrementing) as the last\r\n * segment.  When it detects a change in direction (or has checked the whole\r\n * array), it returns the velocity between the newest value and the oldest\r\n * moving in the same direction.\r\n */\r\nfunction calculateVelocity({ records, pluckValue, pluckTimestamp, maximumVelocity, defaultVelocity }) {\r\n    if (records.length < 2) {\r\n        return 0;\r\n    }\r\n    let velocity = 0;\r\n    // Backing over the array pairwise, `next` is the newer value and `prev` is\r\n    // the older value.  `last` is always the final value.\r\n    const lastIndex = records.length - 1;\r\n    const lastValue = pluckValue(records[lastIndex]);\r\n    const lastTimestamp = pluckTimestamp(records[lastIndex]);\r\n    let prevValue;\r\n    let prevTimestamp;\r\n    let nextValue = lastValue;\r\n    let nextTimestamp = lastTimestamp;\r\n    for (let i = lastIndex - 1; i >= 0; i--) {\r\n        prevValue = pluckValue(records[i]);\r\n        prevTimestamp = pluckTimestamp(records[i]);\r\n        const averageVelocity = (lastValue - prevValue) / (lastTimestamp - prevTimestamp);\r\n        const pairwiseVelocity = (nextValue - prevValue) / (nextTimestamp - prevTimestamp);\r\n        if (velocity !== 0 && pairwiseVelocity > 0 !== velocity > 0) {\r\n            break;\r\n        }\r\n        else {\r\n            velocity = averageVelocity;\r\n        }\r\n        nextValue = prevValue;\r\n        nextTimestamp = prevTimestamp;\r\n    }\r\n    if (Math.abs(velocity) > maximumVelocity) {\r\n        // If there isn't enough data to trust our accuracy (perhaps the main thread\r\n        // was blocked), use the default velocity.\r\n        const direction = velocity / Math.abs(velocity);\r\n        if (records.length < 3) {\r\n            velocity = direction * defaultVelocity;\r\n        }\r\n        else {\r\n            velocity = direction * maximumVelocity;\r\n        }\r\n    }\r\n    return velocity;\r\n}\r\n//# sourceMappingURL=getVelocity$.js.map","dts":{"name":"/Users/brentons/Projects/material-motion-js/packages/core/getVelocity$.d.ts","text":"import { ObservableWithMotionOperators, Point2D } from './types';\r\nexport declare const MAXIMUM_AGE = 250;\r\nexport declare const MAXIMUM_INCOMING_DISPATCHES = 5;\r\nexport declare type GetVelocity$Args<U extends number | Point2D> = {\r\n    value$: ObservableWithMotionOperators<U>;\r\n    pulse$: ObservableWithMotionOperators<any>;\r\n    maximumVelocity?: number;\r\n    defaultVelocity?: number;\r\n};\r\n/**\r\n * Computes the velocity of an incoming stream and emits the result. Velocity's\r\n * denominator is in milliseconds; if the incoming stream is measured in pixels,\r\n * the resulting stream will be in pixels / millisecond.\r\n *\r\n * Velocity is computed by watching the trailing 250ms of up to 5 emissions and\r\n * measuring the distance between the longest pair of events moving in the\r\n * current direction.  This approach is more resiliant to anomolous data than a\r\n * simple (nextPosition - prevPosition) / (nextTime - prevTime).\r\n *\r\n * If `pulse$` is supplied, `velocity(pulse$)` will only emit values when\r\n * `pulse$` emits a value.  This is useful for ensuring that velocity is only\r\n * calculated when it will be used.\r\n */\r\nexport declare function getVelocity$<U extends number | Point2D>({value$, pulse$, maximumVelocity, defaultVelocity}: GetVelocity$Args<U>): ObservableWithMotionOperators<U>;\r\n"}}