// https://en.wikipedia.org/wiki/Program-specific_information

import type {BufferIterator} from '../../iterator/buffer-iterator';
import type {TransportStreamPATBox, TransportStreamSdtBox} from './boxes';
import {discardRestOfPacket} from './discard-rest-of-packet';

export type TransportStreamProgramAssociationTableEntry = {
	type: 'transport-stream-program-association-table';
	programNumber: number;
	programMapIdentifier: number;
};

const parsePatTable = (
	iterator: BufferIterator,
	tableId: number,
): TransportStreamPATBox => {
	iterator.getUint16(); // table ID extension
	iterator.startReadingBits();
	iterator.getBits(7); // reserved
	iterator.getBits(1); // current / next indicator;
	const sectionNumber = iterator.getBits(8);
	const lastSectionNumber = iterator.getBits(8);
	if (tableId !== 0) {
		throw new Error('Invalid table ID: ' + tableId);
	}

	const tables: TransportStreamProgramAssociationTableEntry[] = [];
	for (let i = sectionNumber; i <= lastSectionNumber; i++) {
		const programNumber = iterator.getBits(16); // program number
		iterator.getBits(3); // reserved
		const programMapIdentifier = iterator.getBits(13); // program map PID

		tables.push({
			type: 'transport-stream-program-association-table',
			programNumber,
			programMapIdentifier,
		});
	}

	iterator.stopReadingBits();

	return {
		type: 'transport-stream-pat-box',
		tableId: tableId.toString(16),
		pat: tables,
	};
};

export const parsePat = (iterator: BufferIterator): TransportStreamPATBox => {
	iterator.startReadingBits();

	const tableId = iterator.getBits(8);
	iterator.getBits(1); // syntax indicator
	iterator.getBits(1); // private bit
	iterator.getBits(4);
	const sectionLength = iterator.getBits(10);
	if (sectionLength > 1021) {
		throw new Error('Invalid section length');
	}

	iterator.stopReadingBits();

	const tables = parsePatTable(iterator, tableId);
	discardRestOfPacket(iterator);
	return tables;
};

export const parseSdt = (iterator: BufferIterator): TransportStreamSdtBox => {
	iterator.startReadingBits();
	iterator.getBits(8); // table ID
	iterator.getBits(1); // section syntax indicator
	iterator.getBits(1); // private bit
	iterator.getBits(2); // reserved
	const sectionLength = iterator.getBits(12);
	iterator.stopReadingBits();
	iterator.discard(sectionLength);
	discardRestOfPacket(iterator);

	return {
		type: 'transport-stream-sdt-box',
	};
};