Get post/page data outside the loop

Question

I'm trying to make a mu-plugin dedicated to make OpenGraph tags for my website, since the current plugin in WP directory arent updated for ages.

But i ran with several headaches trying to get post or page data, something i never tried before.

Using this piece of code:

<?php
/*
    Plugin Name: Open Graph!
    Description: Adiciona tags Open Graph (Facebook) para o site.
    Author: ChronoMania Team
    Version: 1.0
    Author URI: http://chronomania.com.br
*/

function pegarConteudoPost()
{
    if (is_single())
    {
        $texto = apply_filters('the_excerpt', get_post_field('post_excerpt', $post_id));
        if empty($texto)
        {
            $texto = wp_trim_words($post->post_content);
        }
        if empty($texto)
        {
            $texto = get_bloginfo('description');
        }
    }
    elseif (is_page())
    {
        $texto = wp_trim_words($page->post_content);
    }
    else
    {
        $texto = get_bloginfo('description');
    }
    return $texto;
}

function pegaURLAtual()
{
    $link = 'http://' . $_SERVER["HTTP_HOST"] . $_SERVER["REQUEST_URI"];
    return $link;
}

function montaOpenGraph()
{
    echo '<meta property="og:title" content="' . wp_title("", false) . '">';
    echo '<meta property="og:site_name" content="' . get_bloginfo('name') . '">';
    echo '<meta property="og:url" content="' . pegaURLAtual() . '">';
    echo '<meta property="og:description" content="' . pegarConteudoPost() . '">';
    echo '<meta property="og:image" content="' . get_template_directory_uri() . '/img/social/ogp_logo.png">';
    echo '<meta property="og:type" content="article">';
}

// Registrando funções
add_action('wp_head', 'montaOpenGraph');

?>

It gives me error 500. So i managed to trace the error to the function pegarConteudoPost().

As i stated before, i dont have much experience with php (so the jury rig code) and never need to work with data outside the loop, so i dig some code from google and put there, with no results.

Any ideas to how can i make this work?

Answer 1

You're using non-existent variables in your function, $post_id, $post, $page.

Use get_queried_object to get data from the current page.

if( is_single() || is_page() ){
    $this_page = get_queried_object();
    $excerpt = get_post_field( 'post_excerpt', $this_page->ID );
}

Answer 2

After several headaches i managed to solve the issue based on Milo's answer. But i need to add a check if the excerpt returned empty, and if it return empty i need to trim the entire content string to get the desired data.

Final code:

function pegarConteudoPost()
{
    if( is_single() || is_page() )
    {
        $this_page = get_queried_object();
        $excerpt = get_post_field( 'post_excerpt', $this_page->ID );

        if ($excerpt === '')
        {
            $excerpt = wp_trim_words(get_post_field( 'post_content', $this_page->ID ), 55);
        }

        $texto = $excerpt;
    }
    else
    {
        $texto = get_bloginfo('description');
    }
    return $texto;
}