import { BiquadFilter, createHighpassFilter, createHighshelfFilter } from './BiquadFilter.js';

export class KWeightingFilter {
	readonly highShelfFilter: BiquadFilter
	readonly highPassFilter: BiquadFilter

	constructor(
		public readonly sampleRate: number,
		public readonly useStandard44100Filters = false) {

		if (useStandard44100Filters) {
			// These parameter values are taken from ITU-R BS.1770-2
			// and designed only for a 44100 Hz sample rate:
			this.highShelfFilter = new BiquadFilter({
				b0: 1.53512485958697,
				b1: -2.69169618940638,
				b2: 1.19839281085285,
				a1: -1.69065929318241,
				a2: 0.73248077421585,
			})

			this.highPassFilter = new BiquadFilter({
				b0: 1.0,
				b1: -2.0,
				b2: 1.0,
				a1: -1.99004745483398,
				a2: 0.99007225036621,
			})
		} else {
			this.highShelfFilter = createHighshelfFilter(sampleRate, 2000.0, 4.0)
			this.highPassFilter = createHighpassFilter(sampleRate, 1.5, 0.01)
		}
	}

	process(sample: number): number {
		let outputSample = sample

		outputSample = this.highShelfFilter.filter(outputSample)
		outputSample = this.highPassFilter.filter(outputSample)

		return outputSample
	}
}