<?php
/**
 * The callback key that signs payment notifications: fetched from the Cryptoway project
 * profile, never typed in. Stored with the other settings.
 *
 * @package CryptowayButton
 */

namespace CryptowayButton;

defined( 'ABSPATH' ) || exit;

class CallbackKey {

    public const SETTING = 'callback_key';

    /** When a webhook last asked Cryptoway for a missing key (Unix time). */
    public const OPTION_LAST_ATTEMPT = 'cryptoway_button_callback_key_attempt';

    /** Minimum gap between key fetches started by the public webhook endpoint. */
    public const WEBHOOK_RETRY_GAP = 5 * MINUTE_IN_SECONDS;

    /** Response fields the key may be under. */
    private const FIELDS = [ 'callback_key', 'callback_key_secret', 'callback_secret' ];

    /** The stored key, or an empty string. */
    public static function stored(): string {
        return trim( Settings::get( self::SETTING ) );
    }

    /**
     * Ask Cryptoway for the key and store it, replacing the stored one (a site moved to
     * another project gets that project's key). On failure the stored key is kept.
     *
     * @return array{ok: bool, error: string} error is a readable reason.
     */
    public static function refresh(): array {

        if ( ! Settings::keys_present() ) {
            return [
                'ok'    => false,
                'error' => __( 'Project ID and Secret key are not both saved yet.', 'cryptoway-button' ),
            ];
        }

        $fetched = self::fetch( ApiClient::from_settings() );

        if ( ! $fetched['ok'] ) {
            return [ 'ok' => false, 'error' => $fetched['error'] ];
        }

        if ( self::stored() !== $fetched['key'] ) {
            Settings::set( self::SETTING, $fetched['key'] );
        }

        return [ 'ok' => true, 'error' => '' ];
    }

    /**
     * Ask Cryptoway for the callback key with the given client, without storing it (the
     * settings screen fetches it for keys that are about to be saved).
     *
     * @return array{ok: bool, key: string, error: string}
     */
    public static function fetch( ApiClient $api ): array {
        $profile = $api->get_profile();

        if ( is_wp_error( $profile ) ) {
            return [ 'ok' => false, 'key' => '', 'error' => $profile->get_error_message() ];
        }

        $key = self::read( $profile );

        if ( '' === $key ) {
            return [ 'ok' => false, 'key' => '', 'error' => __( 'the answer does not contain a callback key', 'cryptoway-button' ) ];
        }

        return [ 'ok' => true, 'key' => $key, 'error' => '' ];
    }

    /**
     * The key for an incoming webhook, fetched first when none is stored, at most once
     * per WEBHOOK_RETRY_GAP.
     */
    public static function for_webhook(): string {

        $key = self::stored();

        if ( '' !== $key ) {
            return $key;
        }

        $last = (int) get_option( self::OPTION_LAST_ATTEMPT, 0 );

        if ( $last > 0 && time() - $last < self::WEBHOOK_RETRY_GAP ) {
            return '';
        }

        // Written before the request, so a burst of notifications starts one fetch.
        update_option( self::OPTION_LAST_ATTEMPT, time(), false );

        $result = self::refresh();

        if ( ! $result['ok'] ) {
            Log::write( 'Webhook: could not get the callback key from Cryptoway: ' . $result['error'] );
        }

        return self::stored();
    }

    /** Pull the key out of the profile response. */
    private static function read( $profile ): string {

        if ( ! is_array( $profile ) ) {
            return '';
        }

        // Some endpoints wrap the payload; look one level down as well.
        $candidates = [ $profile ];
        foreach ( [ 'data', 'result', 'user', 'project' ] as $wrapper ) {
            if ( isset( $profile[ $wrapper ] ) && is_array( $profile[ $wrapper ] ) ) {
                $candidates[] = $profile[ $wrapper ];
            }
        }

        foreach ( $candidates as $candidate ) {
            foreach ( self::FIELDS as $field ) {
                if ( isset( $candidate[ $field ] ) && is_string( $candidate[ $field ] ) && '' !== trim( $candidate[ $field ] ) ) {
                    return trim( $candidate[ $field ] );
                }
            }
        }

        return '';
    }
}