<?php
/**
 * Parses a typed latitude/longitude pair.
 *
 * @package Mapsemble
 */

namespace Mapsemble\Geo;

/**
 * Pure: returns error codes, not messages, so it needs no WordPress; the
 * meta box and its script translate them. A comma decimal is what a Dutch or
 * Spanish keyboard produces, so it is accepted — but only as the one decimal
 * mark, never alongside a dot, where it would be a thousands separator.
 *
 * Input format — the meta box script mirrors this exactly, and both are
 * tested against tests/fixtures/coordinate-input.json:
 *
 * 1. Normalise each field: U+00A0 (no-break space), U+202F (narrow no-break
 *    space) and U+FEFF (byte-order mark) become a plain space; U+2212 (minus
 *    sign, as pasted from web pages) becomes "-".
 * 2. Trim each field of exactly " \t\n\r\x0B" (space, tab, LF, CR, VT) at
 *    both ends. Nothing else is whitespace: NUL, for one, is not.
 * 3. Both fields empty: {status: empty}. Exactly one empty: error "half".
 * 4. Comma rule, per field: if it contains no "." and exactly one ",", that
 *    comma becomes ".". Otherwise it is left alone (and so fails step 5).
 * 5. Each field must then match ^[+-]?([0-9]+(\.[0-9]*)?|\.[0-9]+) up to
 *    the very end of the string (\z in PCRE, whose $ would allow a final
 *    newline; plain $ in JavaScript) — ASCII digits only; no exponent, hex,
 *    Infinity/NaN, separators or inner spaces. If either field fails: error
 *    "not_number".
 * 6. The value is that decimal as a float; -0 is read as 0.
 * 7. Latitude outside -90..90 (inclusive): error "lat_range"; then longitude
 *    outside -180..180 (inclusive): error "lng_range".
 *
 * Errors are reported in that order (half, not_number on either field,
 * lat_range, lng_range), and only the first applies.
 */
final class CoordinateInput {

	/**
	 * Characters treated as a plain space before trimming.
	 */
	private const SPACES = array( "\u{00A0}", "\u{202F}", "\u{FEFF}" );

	/**
	 * The one set of characters trimmed from both ends.
	 */
	private const TRIM = " \t\n\r\x0B";

	/**
	 * Parses a pair.
	 *
	 * @param string $lat Latitude as typed.
	 * @param string $lng Longitude as typed.
	 * @return array{status: 'empty'}|array{status: 'valid', lat: float, lng: float}|array{status: 'invalid', error: 'half'|'not_number'|'lat_range'|'lng_range'}
	 */
	public static function parse( string $lat, string $lng ): array {
		$lat = self::normalise( $lat );
		$lng = self::normalise( $lng );
		if ( '' === $lat && '' === $lng ) {
			return array( 'status' => 'empty' );
		}
		if ( '' === $lat || '' === $lng ) {
			return self::invalid( 'half' );
		}
		$lat_value = self::number( $lat );
		$lng_value = self::number( $lng );
		if ( null === $lat_value || null === $lng_value ) {
			return self::invalid( 'not_number' );
		}
		if ( $lat_value < -90.0 || $lat_value > 90.0 ) {
			return self::invalid( 'lat_range' );
		}
		if ( $lng_value < -180.0 || $lng_value > 180.0 ) {
			return self::invalid( 'lng_range' );
		}
		return array(
			'status' => 'valid',
			'lat'    => $lat_value,
			'lng'    => $lng_value,
		);
	}

	/**
	 * Steps 1 and 2: unify look-alike characters, then trim.
	 *
	 * @param string $raw Field as typed.
	 */
	private static function normalise( string $raw ): string {
		$raw = str_replace( self::SPACES, ' ', $raw );
		$raw = str_replace( "\u{2212}", '-', $raw );
		return trim( $raw, self::TRIM );
	}

	/**
	 * Steps 4 to 6: one number, dot or comma decimal, plain notation only.
	 *
	 * @param string $raw Normalised, non-empty field.
	 */
	private static function number( string $raw ): ?float {
		if ( false === strpos( $raw, '.' ) && 1 === substr_count( $raw, ',' ) ) {
			$raw = str_replace( ',', '.', $raw );
		}
		if ( 1 !== preg_match( '/^[+-]?([0-9]+(\.[0-9]*)?|\.[0-9]+)\z/', $raw ) ) {
			return null;
		}
		$value = (float) $raw;
		// -0.0 == 0.0, so this turns negative zero into plain zero.
		return 0.0 === $value ? 0.0 : $value;
	}

	/**
	 * An invalid result.
	 *
	 * @param 'half'|'not_number'|'lat_range'|'lng_range' $error Error code.
	 * @return array{status: 'invalid', error: 'half'|'not_number'|'lat_range'|'lng_range'}
	 */
	private static function invalid( string $error ): array {
		return array(
			'status' => 'invalid',
			'error'  => $error,
		);
	}
}