category-home-page.php

<?php
/*
 * Plugin Name: Category Home Page
 * Plugin URI: trepmal.com
 * Description:
 * Version:
 * Author: Kailey Lampert
 * Author URI: kaileylampert.com
 * License: GPLv2 or later
 * License URI: http://www.gnu.org/licenses/gpl-2.0.html
 * TextDomain: category-home-page
 * DomainPath:
 * Network:
 */

$category_home_page = new Category_Home_Page();

class Category_Home_Page {

	function __construct() {
		add_action( 'admin_init',    array( $this, 'admin_init' ) );
		add_action( 'pre_get_posts', array( $this, 'pre_get_posts' ) );
	}

	function admin_init() {
		register_setting( 'reading', 'chp_category_home_page', 'intval' );
		register_setting( 'reading', 'chp_disable_archive', 'intval' );
		register_setting( 'reading', 'chp_use_category_template', 'intval' );
		add_settings_field( '_category_home_page', '<label for="chp_category_home_page">'. __( 'Category for Home Page' , 'category-home-page' ) .'</label>' , array( $this, '_form_field' ) , 'reading', 'default' );
	}

	function _form_field() {

		$category = get_option( 'chp_category_home_page', '' );

		$dropdown = true;
		if ( $dropdown ) {
			wp_dropdown_categories( array(
				'orderby'          => 'name',
				'id'               => 'chp_category_home_page',
				'name'             => 'chp_category_home_page',
				'hide_empty'       => false,
				'show_option_none' => __( 'None', 'category-home-page' ),
				'selected'         => intval( $category ),
			) );
		} else {
			echo '<input type="text" name="chp_category_home_page" value="'. esc_attr( $category ) .'" /> '. __( 'Category ID (-1 to disable)', 'category-home-page' );
		}

		echo '<p>';
		$disable = get_option( 'chp_disable_archive', 0 );
		echo '<input type="hidden" name="chp_disable_archive" value="0" />';
		echo '<label><input type="checkbox" name="chp_disable_archive" value="1" '. checked( $disable, 1, false ) .' /> '. __( 'Disable default archive page', 'category-home-page' ) .'</label>';

		$template = get_option( 'chp_use_category_template', 0 );
		echo ' <input type="hidden" name="chp_use_category_template" value="0" />';
		echo '<label><input type="checkbox" name="chp_use_category_template" value="1" '. checked( $template, 1, false ) .' /> '. __( 'Use category template', 'category-home-page' ) .'</label>';
		echo '</p>';
	}

	function pre_get_posts( $query ) {
		if ( is_admin() ) return;
		if ( ! $query->is_main_query() ) return;

		if ( -1 == ( $category = get_option( 'chp_category_home_page', -1 ) ) ) return;

		if ( $query->is_category( $category ) && get_option( 'chp_disable_archive', 0 ) ) {
			status_header( 404 );
			$query->set_404();
		}

		if ( is_home() ) {
			$query->set( 'cat', $category );
			if ( get_option( 'chp_use_category_template', 0 ) ) {
				$query->is_home = false;
				$query->is_category = true;
			}
		}
	}
}