<?php
namespace Strikewise\Migration;

defined( 'ABSPATH' ) || exit;

/**
 * Turns point-in-time price snapshots into Strikewise history intervals.
 * Pure PHP, unit-tested.
 */
final class Timeline {

	/**
	 * @param OmnibusSnapshot[] $snapshots Any order.
	 * @param int|null          $end       Where Strikewise's own history begins; null = the last price is still valid.
	 * @return array<int,array{from:int,to:int|null,snapshot:OmnibusSnapshot}>
	 */
	public static function build( array $snapshots, ?int $end ): array {
		if ( null !== $end ) {
			// Strikewise's own records are authoritative from where they start.
			$snapshots = array_filter(
				$snapshots,
				static function ( OmnibusSnapshot $s ) use ( $end ) {
					return $s->timestamp < $end;
				}
			);
		}

		// Stable sort: of several records with the same second, the last one wins.
		$snapshots = array_values( $snapshots );
		$order     = array_keys( $snapshots );
		usort(
			$order,
			static function ( $a, $b ) use ( $snapshots ) {
				return array( $snapshots[ $a ]->timestamp, $a ) <=> array( $snapshots[ $b ]->timestamp, $b );
			}
		);

		// Collapse records of the same second, keeping the last.
		$by_second = array();
		foreach ( $order as $index ) {
			$by_second[ $snapshots[ $index ]->timestamp ] = $snapshots[ $index ];
		}
		$sorted = array_values( $by_second );

		// Merge consecutive records with the same price.
		$changes = array();
		foreach ( $sorted as $snapshot ) {
			$previous = end( $changes );
			if ( false === $previous || ! $previous->same_price_as( $snapshot ) ) {
				$changes[] = $snapshot;
			}
		}

		$intervals = array();
		$count     = count( $changes );
		foreach ( $changes as $i => $snapshot ) {
			$to          = $i + 1 < $count ? $changes[ $i + 1 ]->timestamp : $end;
			$intervals[] = array(
				'from'     => $snapshot->timestamp,
				'to'       => $to,
				'snapshot' => $snapshot,
			);
		}

		return $intervals;
	}
}