/**
 * Abstract base class of interpolants over parametric samples.
 *
 * The parameter domain is one dimensional, typically the time or a path
 * along a curve defined by the data.
 *
 * The sample values can have any dimensionality and derived classes may
 * apply special interpretations to the data.
 *
 * This class provides the interval seek in a Template Method, deferring
 * the actual interpolation to derived classes.
 *
 * Time complexity is O(1) for linear access crossing at most two points
 * and O(log N) for random access, where N is the number of positions.
 *
 * References:
 *
 * 		http://www.oodesign.com/template-method-pattern.html
 *
 */

class Interpolant {
	constructor(parameterPositions, sampleValues, sampleSize, resultBuffer) {
		this.parameterPositions = parameterPositions;
		this._cachedIndex = 0;

		this.resultBuffer = resultBuffer !== undefined ? resultBuffer : new sampleValues.constructor(sampleSize);
		this.sampleValues = sampleValues;
		this.valueSize = sampleSize;

		this.settings = null;
		this.DefaultSettings_ = {};
	}

	evaluate(t) {
		const pp = this.parameterPositions;
		let i1 = this._cachedIndex,
			t1 = pp[i1],
			t0 = pp[i1 - 1];

		validate_interval: {
			seek: {
				let right;

				linear_scan: {
					//- See http://jsperf.com/comparison-to-undefined/3
					//- slower code:
					//-
					//- 				if ( t >= t1 || t1 === undefined ) {
					forward_scan: if (!(t < t1)) {
						for (let giveUpAt = i1 + 2; ; ) {
							if (t1 === undefined) {
								if (t < t0) break forward_scan;

								// after end

								i1 = pp.length;
								this._cachedIndex = i1;
								return this.afterEnd_(i1 - 1, t, t0);
							}

							if (i1 === giveUpAt) break; // this loop

							t0 = t1;
							t1 = pp[++i1];

							if (t < t1) {
								// we have arrived at the sought interval
								break seek;
							}
						}

						// prepare binary search on the right side of the index
						right = pp.length;
						break linear_scan;
					}

					//- slower code:
					//-					if ( t < t0 || t0 === undefined ) {
					if (!(t >= t0)) {
						// looping?

						const t1global = pp[1];

						if (t < t1global) {
							i1 = 2; // + 1, using the scan for the details
							t0 = t1global;
						}

						// linear reverse scan

						for (let giveUpAt = i1 - 2; ; ) {
							if (t0 === undefined) {
								// before start

								this._cachedIndex = 0;
								return this.beforeStart_(0, t, t1);
							}

							if (i1 === giveUpAt) break; // this loop

							t1 = t0;
							t0 = pp[--i1 - 1];

							if (t >= t0) {
								// we have arrived at the sought interval
								break seek;
							}
						}

						// prepare binary search on the left side of the index
						right = i1;
						i1 = 0;
						break linear_scan;
					}

					// the interval is valid

					break validate_interval;
				} // linear scan

				// binary search

				while (i1 < right) {
					const mid = (i1 + right) >>> 1;

					if (t < pp[mid]) {
						right = mid;
					} else {
						i1 = mid + 1;
					}
				}

				t1 = pp[i1];
				t0 = pp[i1 - 1];

				// check boundary cases, again

				if (t0 === undefined) {
					this._cachedIndex = 0;
					return this.beforeStart_(0, t, t1);
				}

				if (t1 === undefined) {
					i1 = pp.length;
					this._cachedIndex = i1;
					return this.afterEnd_(i1 - 1, t0, t);
				}
			} // seek

			this._cachedIndex = i1;

			this.intervalChanged_(i1, t0, t1);
		} // validate_interval

		return this.interpolate_(i1, t0, t, t1);
	}

	getSettings_() {
		return this.settings || this.DefaultSettings_;
	}

	copySampleValue_(index) {
		// copies a sample value to the result buffer

		const result = this.resultBuffer,
			values = this.sampleValues,
			stride = this.valueSize,
			offset = index * stride;

		for (let i = 0; i !== stride; ++i) {
			result[i] = values[offset + i];
		}

		return result;
	}

	// Template methods for derived classes:

	interpolate_(/* i1, t0, t, t1 */) {
		throw new Error('call to abstract method');
		// implementations shall return this.resultBuffer
	}

	intervalChanged_(/* i1, t0, t1 */) {
		// empty
	}
}

// ALIAS DEFINITIONS

Interpolant.prototype.beforeStart_ = Interpolant.prototype.copySampleValue_;
Interpolant.prototype.afterEnd_ = Interpolant.prototype.copySampleValue_;

export { Interpolant };