/**
 * This code is a refactored version of what comes in the
 * ol/control/ScaleLine. It uses much of the same logic but
 * instead of rendering the scale line it returns the metadata
 * for rendering.
 */
import { getPointResolution, METERS_PER_UNIT } from "ol/proj";

/**
 * Units for the scale line. Supported values are `'degrees'`, `'imperial'`,
 * `'nautical'`, `'metric'`, `'us'`.
 * @enum {string}
 */
const Units = {
  DEGREES: "degrees",
  IMPERIAL: "imperial",
  NAUTICAL: "nautical",
  METRIC: "metric",
  US: "us",
};

const LEADING_DIGITS = [1, 2, 5];

const DEFAULT_OPTIONS = {
  minWidth: 64,
  multiplier: 1,
};

export function getScalelineInfo(viewState, units, inOpts = {}) {
  const options = Object.assign({}, DEFAULT_OPTIONS, inOpts);

  const center = viewState.getCenter();
  const projection = viewState.getProjection();
  const pointResolutionUnits = units === Units.DEGREES ? "degrees" : "m";
  if (!projection) {
    return { label: "", width: 0, error: "no-projection" };
  }
  const resolution = viewState.getResolution();
  let pointResolution = getPointResolution(
    projection,
    resolution * options.multiplier,
    center,
    pointResolutionUnits
  );
  if (
    projection.getUnits() !== "degrees" &&
    projection.getMetersPerUnit() &&
    pointResolutionUnits === "m"
  ) {
    pointResolution *= projection.getMetersPerUnit();
  }

  let nominalCount = options.minWidth * pointResolution;
  let suffix = "";
  if (units === Units.DEGREES) {
    const metersPerDegree = METERS_PER_UNIT.degrees;
    if (projection.getUnits() === "degrees") {
      nominalCount *= metersPerDegree;
    } else {
      pointResolution /= metersPerDegree;
    }
    if (nominalCount < metersPerDegree / 60) {
      // seconds
      suffix = "\u2033";
      pointResolution *= 3600;
    } else if (nominalCount < metersPerDegree) {
      // minutes
      suffix = "\u2032";
      pointResolution *= 60;
    } else {
      // degrees
      suffix = "\u00b0";
    }
  } else if (units === Units.IMPERIAL) {
    if (nominalCount < 0.9144) {
      suffix = "in";
      pointResolution /= 0.0254;
    } else if (nominalCount < 1609.344) {
      suffix = "ft";
      pointResolution /= 0.3048;
    } else {
      suffix = "mi";
      pointResolution /= 1609.344;
    }
  } else if (units === Units.NAUTICAL) {
    pointResolution /= 1852;
    suffix = "nm";
  } else if (units === Units.METRIC) {
    if (nominalCount < 0.001) {
      suffix = "μm";
      pointResolution *= 1000000;
    } else if (nominalCount < 1) {
      suffix = "mm";
      pointResolution *= 1000;
    } else if (nominalCount < 1000) {
      suffix = "m";
    } else {
      suffix = "km";
      pointResolution /= 1000;
    }
  } else if (units === Units.US) {
    if (nominalCount < 0.9144) {
      suffix = "in";
      pointResolution *= 39.37;
    } else if (nominalCount < 1609.344) {
      suffix = "ft";
      pointResolution /= 0.30480061;
    } else {
      suffix = "mi";
      pointResolution /= 1609.3472;
    }
  } else {
    return {
      label: "",
      width: 0,
      error: "bad-units",
    };
  }

  let i = 3 * Math.floor(Math.log(options.minWidth * pointResolution) / Math.log(10));
  let count, width;
  while (true) {
    count = LEADING_DIGITS[((i % 3) + 3) % 3] * Math.pow(10, Math.floor(i / 3));
    width = Math.round(count / pointResolution);
    if (isNaN(width)) {
      return {
        label: "",
        width: 0,
        error: "width-is-nan",
      };
    } else if (width >= options.minWidth) {
      break;
    }
    ++i;
  }

  return {
    label: `${count} ${suffix}`,
    width,
  };
}
