<?php

namespace DeliciousBrains\WPMDB\Pro\Transfers\Files;

class IncrementalSizeController implements SizeControllerInterface {
	/**
	 * Current segment index.
	 *
	 * @var int
	 */
	private $currentSegment;

	/**
	 * Max payload size value in bytes.
	 *
	 * @var int
	 */
	private $max;

	/**
	 * The default fallback payload size in bytes.
	 *
	 * @var int
	 */
	private $fallback;

	/**
	 * Array of byte values that represent various payload sizes.
	 *
	 * @var array
	 */
	private $seekArray;

	/**
	 * Failure retry count.
	 *
	 * @var int
	 */
	private $retry;

	/**
	 * Initializes the default values for all the required properties.
	 *
	 * @param int $max
	 * @param int $fallback
	 * @param int $initialSize
	 * @param int $retryCount
	 *
	 * @return void
	 */
	public function initialize( $max, $fallback, $initialSize = null, $retryCount = 5 ) {
		$this->currentSegment = 0;
		$this->max            = $max;
		$this->fallback       = $fallback;
		$this->retry          = $retryCount;

		$this->initialize_seek_array( $initialSize );
	}

	/**
	 * increments in the segment size if the seek array has further segments
	 * and returns the actual segment size.
	 *
	 * @return int
	 */
	public function step_up_size() {
		if ( array_key_exists( $this->currentSegment + 1, $this->seekArray ) ) {
			++$this->currentSegment;
		}

		return $this->get_current_size();
	}

	/**
	 * Decrements the segment size if the seek array has lower values,
	 * or defaults to 0 if it doesn't, and  returns the actual segment size.
	 *
	 * @param int $steps
	 *
	 * @return int
	 */
	public function step_down_size( $steps = 1 ) {
		if ( array_key_exists( $this->currentSegment - 1, $this->seekArray ) ) {
			$newSegment = $this->currentSegment - $steps;
			if ( array_key_exists( $newSegment, $this->seekArray ) ) {
				$this->currentSegment = $newSegment;
			} else {
				$this->currentSegment = 0;
			}
		}

		return $this->get_current_size();
	}

	/**
	 * Returns current segment's actual size in bytes.
	 *
	 * @return int
	 */
	public function get_current_size() {
		return $this->seekArray[ $this->currentSegment ];
	}

	/**
	 * Returns the fallback size in bytes.
	 *
	 * @return int
	 */
	public function get_fallback_size() {
		return $this->fallback;
	}

	/**
	 * Initializes a seek array with different segments values, these sizes are used to set up and step down
	 * the payload size during HP mode migration.
	 *
	 * The first element of the seek array is the fallback size, then every other element is 20% larger of its
	 * predecessor. The last element of the array is the $max value.
	 *
	 * @param int $initialSize
	 *
	 * @return void
	 */
	private function initialize_seek_array( $initialSize = null ) {
		$this->seekArray = [ $this->fallback ];
		$target          = 0;
		$i               = 0;
		while ( $target < $this->max ) {
			$last_entry = end( $this->seekArray );
			$new_value  = (int) round( ( ( $last_entry / 100 ) * 20 ) + $last_entry );

			if ( $new_value > $this->max ) {
				$new_value = $this->max;
			}

			$target = $new_value;
			$i++;

			$this->seekArray[] = $new_value;
			if ( $new_value === $initialSize ) {
				$this->currentSegment = $i;
			}

			if ( $initialSize === null ) {
				$this->currentSegment = 1;
			}
		}
	}

	/**
	 * Returns true of the current segment size equals the max payload size.
	 *
	 * @return bool
	 */
	public function is_at_max_size() {
		return $this->currentSegment === count( $this->seekArray ) - 1;
	}
}