react-native-reanimated/src/reanimated2/interpolation.ts

'use strict';

/**
 * Extrapolation type.
 *
 * @param IDENTITY - Returns the provided value as is.
 * @param CLAMP - Clamps the value to the edge of the output range.
 * @param EXTEND - Predicts the values beyond the output range.
 */
export enum Extrapolation {
  IDENTITY = 'identity',
  CLAMP = 'clamp',
  EXTEND = 'extend',
}

/**
 * Represents the possible values for extrapolation as a string.
 */
type ExtrapolationAsString = 'identity' | 'clamp' | 'extend';

interface InterpolationNarrowedInput {
  leftEdgeInput: number;
  rightEdgeInput: number;
  leftEdgeOutput: number;
  rightEdgeOutput: number;
}

/**
 * Allows to specify extrapolation for left and right edge of the interpolation.
 */
export interface ExtrapolationConfig {
  extrapolateLeft?: Extrapolation | string;
  extrapolateRight?: Extrapolation | string;
}

interface RequiredExtrapolationConfig {
  extrapolateLeft: Extrapolation;
  extrapolateRight: Extrapolation;
}

/**
 * Configuration options for extrapolation.
 */
export type ExtrapolationType =
  | ExtrapolationConfig
  | Extrapolation
  | ExtrapolationAsString
  | undefined;

function getVal(
  type: Extrapolation,
  coef: number,
  val: number,
  leftEdgeOutput: number,
  rightEdgeOutput: number,
  x: number
): number {
  'worklet';

  switch (type) {
    case Extrapolation.IDENTITY:
      return x;
    case Extrapolation.CLAMP:
      if (coef * val < coef * leftEdgeOutput) {
        return leftEdgeOutput;
      }
      return rightEdgeOutput;
    case Extrapolation.EXTEND:
    default:
      return val;
  }
}

function isExtrapolate(value: string): value is Extrapolation {
  'worklet';

  return (
    /* eslint-disable @typescript-eslint/no-unsafe-enum-comparison */
    value === Extrapolation.EXTEND ||
    value === Extrapolation.CLAMP ||
    value === Extrapolation.IDENTITY
    /* eslint-enable @typescript-eslint/no-unsafe-enum-comparison */
  );
}

// validates extrapolations type
// if type is correct, converts it to ExtrapolationConfig
function validateType(type: ExtrapolationType): RequiredExtrapolationConfig {
  'worklet';
  // initialize extrapolationConfig with default extrapolation
  const extrapolationConfig: RequiredExtrapolationConfig = {
    extrapolateLeft: Extrapolation.EXTEND,
    extrapolateRight: Extrapolation.EXTEND,
  };

  if (!type) {
    return extrapolationConfig;
  }

  if (typeof type === 'string') {
    if (!isExtrapolate(type)) {
      throw new Error(
        `[Reanimated] Unsupported value for "interpolate" \nSupported values: ["extend", "clamp", "identity", Extrapolatation.CLAMP, Extrapolatation.EXTEND, Extrapolatation.IDENTITY]\n Valid example:
        interpolate(value, [inputRange], [outputRange], "clamp")`
      );
    }
    extrapolationConfig.extrapolateLeft = type;
    extrapolationConfig.extrapolateRight = type;
    return extrapolationConfig;
  }

  // otherwise type is extrapolation config object
  if (
    (type.extrapolateLeft && !isExtrapolate(type.extrapolateLeft)) ||
    (type.extrapolateRight && !isExtrapolate(type.extrapolateRight))
  ) {
    throw new Error(
      `[Reanimated] Unsupported value for "interpolate" \nSupported values: ["extend", "clamp", "identity", Extrapolatation.CLAMP, Extrapolatation.EXTEND, Extrapolatation.IDENTITY]\n Valid example:
      interpolate(value, [inputRange], [outputRange], {
        extrapolateLeft: Extrapolation.CLAMP,
        extrapolateRight: Extrapolation.IDENTITY
      }})`
    );
  }

  Object.assign(extrapolationConfig, type);
  return extrapolationConfig;
}

function internalInterpolate(
  x: number,
  narrowedInput: InterpolationNarrowedInput,
  extrapolationConfig: RequiredExtrapolationConfig
) {
  'worklet';
  const { leftEdgeInput, rightEdgeInput, leftEdgeOutput, rightEdgeOutput } =
    narrowedInput;
  if (rightEdgeInput - leftEdgeInput === 0) {
    return leftEdgeOutput;
  }
  const progress = (x - leftEdgeInput) / (rightEdgeInput - leftEdgeInput);
  const val = leftEdgeOutput + progress * (rightEdgeOutput - leftEdgeOutput);
  const coef = rightEdgeOutput >= leftEdgeOutput ? 1 : -1;

  if (coef * val < coef * leftEdgeOutput) {
    return getVal(
      extrapolationConfig.extrapolateLeft,
      coef,
      val,
      leftEdgeOutput,
      rightEdgeOutput,
      x
    );
  } else if (coef * val > coef * rightEdgeOutput) {
    return getVal(
      extrapolationConfig.extrapolateRight,
      coef,
      val,
      leftEdgeOutput,
      rightEdgeOutput,
      x
    );
  }

  return val;
}

/**
 * Lets you map a value from one range to another using linear interpolation.
 *
 * @param value - A number from the `input` range that is going to be mapped to the `output` range.
 * @param inputRange - An array of numbers specifying the input range of the interpolation.
 * @param outputRange - An array of numbers specifying the output range of the interpolation.
 * @param extrapolate - determines what happens when the `value` goes beyond the `input` range. Defaults to `Extrapolation.EXTEND` - {@link ExtrapolationType}.
 * @returns A mapped value within the output range.
 * @see https://docs.swmansion.com/react-native-reanimated/docs/utilities/interpolate
 */
export function interpolate(
  x: number,
  inputRange: readonly number[],
  outputRange: readonly number[],
  type?: ExtrapolationType
): number {
  'worklet';
  if (inputRange.length < 2 || outputRange.length < 2) {
    throw new Error(
      '[Reanimated] Interpolation input and output ranges should contain at least two values.'
    );
  }

  const extrapolationConfig = validateType(type);
  const length = inputRange.length;
  const narrowedInput: InterpolationNarrowedInput = {
    leftEdgeInput: inputRange[0],
    rightEdgeInput: inputRange[1],
    leftEdgeOutput: outputRange[0],
    rightEdgeOutput: outputRange[1],
  };
  if (length > 2) {
    if (x > inputRange[length - 1]) {
      narrowedInput.leftEdgeInput = inputRange[length - 2];
      narrowedInput.rightEdgeInput = inputRange[length - 1];
      narrowedInput.leftEdgeOutput = outputRange[length - 2];
      narrowedInput.rightEdgeOutput = outputRange[length - 1];
    } else {
      for (let i = 1; i < length; ++i) {
        if (x <= inputRange[i]) {
          narrowedInput.leftEdgeInput = inputRange[i - 1];
          narrowedInput.rightEdgeInput = inputRange[i];
          narrowedInput.leftEdgeOutput = outputRange[i - 1];
          narrowedInput.rightEdgeOutput = outputRange[i];
          break;
        }
      }
    }
  }

  return internalInterpolate(x, narrowedInput, extrapolationConfig);
}

/**
 * Lets you limit a value within a specified range.
 *
 * @param value - A number that will be returned as long as the provided value is in range between `min` and `max`.
 * @param min - A number which will be returned when provided `value` is lower than `min`.
 * @param max - A number which will be returned when provided `value` is higher than `max`.
 * @returns A number between min and max bounds.
 * @see https://docs.swmansion.com/react-native-reanimated/docs/utilities/clamp/
 */
export function clamp(value: number, min: number, max: number) {
  'worklet';
  return Math.min(Math.max(value, min), max);
}