<?php
/**
 * Provides the model class, an abstract interface to a database table
 *
 * @author Camil Staps
 *
 * BusinessAdmin: administrative software for small companies
 * Copyright (C) 2015 Camil Staps (ViviSoft)
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

/**
 * Thrown in Model when a table row could not be found
 */
class ModelNotFoundException extends Exception {
}

/**
 * Thrown in Model when a column cannot be edited
 */
class ModelIllegalAccessException extends Exception {
}

/**
 * Thrown in Model when a call to __set() fails
 */
class ModelSetFailedException extends Exception {
}

/**
 * An abstract interface to a database table
 */
abstract class Model {
	/**
	 * @var string   $table              The database table
	 * @var string[] $protected_columns  Columns that cannot be edited
	 * @var string[] $fillable_columns   Columns that can be edited
	 * @var string   $primary_key        The table's primary key
	 */
	public
		$table             = '',
		$protected_columns = ['id'],
		$fillable_columns  = [],
		$primary_key       = 'id';

	/**
	 * @var PDO $pdo              A PDO instance for database communication
	 * @var mixed[] $data         The column values
	 */
	protected $pdo, $data;

	/**
	 * Create a new instance
	 *
	 * @param PDO $pdo              The PDO class, to access the database
	 * @param int $id               The id of the row to fetch
	 *
	 * @throws PDOException         If something went wrong with the database
	 * @throws ModelNotFoundException If the id could not be found
	 */
	public function __construct($pdo, $id) {
		$this->pdo = $pdo;

		$stmt = $this->pdo->prepare("SELECT * FROM `".$this->table()."` WHERE `{$this->primary_key}`=?");
		$stmt->execute([$id]);
		if ($stmt->rowCount() == 0) {
			throw new ModelNotFoundException("The {$this->table} with id '$id' could not be found.");
		}
		$this->data = $stmt->fetch(PDO::FETCH_ASSOC);
	}

	/**
	 * Set a column value
	 *
	 * @param string $key         The column
	 * @param mixed $value        The value
	 *
	 * @throws PDOException       Database error
	 */
	public function __set($key, $value) {
		if (!in_array($key, $this->fillable_columns)) {
			throw new ModelIllegalAccessException("Column $key cannot be edited.");
		}
		if ($this->data[$key] == $value) {
			return;
		}
		$stmt = $this->pdo->prepare("UPDATE `".$this->table()."` SET `$key`=? WHERE `{$this->primary_key}`=?");
		$stmt->execute([
			$this->mutator($key, $value),
			$this->data[$this->primary_key]
		]);
		if ($stmt->rowCount() != 1) {
			throw new ModelEditFailedException();
		}
		$this->data[$key] = $value;
	}

	/**
	 * Get a column value
	 *
	 * @param string $key         The column
	 *
	 * @return mixed              The value
	 */
	public function __get($key) {
		return $this->accessor($key, $this->data[$key]);
	}

	/**
	 * Post-__get() hook to modify the value
	 *
	 * @param string $key         The column
	 * @param string $value       The value
	 *
	 * @return mixed              The modified value (default: $value)
	 */
	protected function accessor($key, $value) {
		return $value;
	}

	/**
	 * Pre-__set() hook to modify a value
	 *
	 * @param string $key         The column
	 * @param mixed $value        The value
	 *
	 * @return string             The modified value (default: $value casted to string)
	 */
	protected function mutator($key, $value) {
		return (string) $value;
	}

	/**
	 * Delete the row
	 *
	 * @throws PDOException       Database error
	 *
	 * @return bool               True iff the row was really deleted
	 */
	public function delete() {
		$stmt = $this->pdo->prepare("DELETE FROM `{$this->table()}` WHERE `{$this->primary_key}`=?");
		$stmt->execute([$this->data[$this->primary_key]]);
		return $stmt->rowCount() != 0;
	}

	/**
	 * The actual table, after adding prefixes and the like
	 *
	 * @return string The database table
	 */
	private function table() {
		return Constants::db_prefix . $this->table;
	}
}