import { BBI } from './bbi.ts'

import type { RequestOptions } from './types.ts'

/**
 * Parser for BigWig files. Inherits `getHeader`, `getFeatures`,
 * `getFeaturesMulti`, `getFeaturesAsArrays`, and `getFeaturesAsArraysMulti`
 * from `BBI`.
 *
 * Supports zoom levels — pass `opts.scale` or `opts.basesPerSpan` to
 * automatically select the appropriate pre-computed zoom level.
 */
export class BigWig extends BBI {
  /**
   * Retrieves a BlockView of a specific zoomLevel
   *
   * @param scale - number
   *
   * @param opts - An object containing basesPerSpan (e.g. pixels per basepair)
   * or scale used to infer the zoomLevel to use
   */
  protected async getView(scale: number, opts?: RequestOptions) {
    const { zoomLevels, refsByName, uncompressBufSize } =
      await this.getHeader(opts)
    const basesPerPx = 1 / scale
    const maxLevel = zoomLevels.length - 1

    for (let i = maxLevel; i >= 0; i -= 1) {
      const zh = zoomLevels[i]!
      if (zh.reductionLevel <= 2 * basesPerPx) {
        return this.getOrCreateBlockView(
          refsByName,
          zh.indexOffset,
          uncompressBufSize,
          'summary',
        )
      }
    }
    return this.getUnzoomedView(opts)
  }
}