<?php

namespace php;

use Exception;
use Monolog\Logger;
use PDO;
use PHPMailer\PHPMailer\Exception as MailerException;
use PHPMailer\PHPMailer\PHPMailer;
use PHPMailer\PHPMailer\SMTP;


/**
 * Queues up mails and sends them when appropriate.
 */
class Mailer
{
    /**
     * @var Logger The logger to use for logging.
     */
    private Logger $logger;
    /**
     * @var array<string, array<string, mixed>> The configuration to use for mailing.
     */
    private array $config;
    /**
     * @var PDO The database connection to interact with.
     */
    private PDO $conn;


    /**
     * Constructs a new mailer.
     *
     * @param array<string, array<string, mixed>> $config the configuration to use for mailing
     * @param Logger $logger the logger to use for logging
     * @param PDO $conn the connection to the email database
     */
    public function __construct(array $config, Logger $logger, PDO $conn)
    {
        $this->logger = $logger;
        $this->config = $config;
        $this->conn = $conn;
    }


    /**
     * Populates the database with the necessary structures for emails.
     *
     * @return void
     */
    public function install(): void
    {
        $this->conn->exec("CREATE TABLE email_tasks(type TEXT NOT NULL,
                                                    recipient TEXT NOT NULL,
                                                    arg1 TEXT NOT NULL DEFAULT(''),
                                                    arg2 TEXT NOT NULL DEFAULT(''),
                                                    PRIMARY KEY (type, recipient, arg1, arg2));");
    }


    /**
     * Queues an email to be sent.
     *
     * @param Email $email the email to queue
     * @return Response a satisfied `Response` if the email was queued, or an unsatisfied `Response` otherwise
     */
    public function queue_email(Email $email): Response
    {
        $stmt = $this->conn->prepare("INSERT OR IGNORE INTO email_tasks (type, recipient, arg1, arg2)
                                      VALUES (:type, :recipient, :arg1, :arg2);");
        $stmt->bindValue(":type", $email->type);
        $stmt->bindValue(":recipient", $email->recipient);
        $stmt->bindValue(":arg1", $email->arg1);
        $stmt->bindValue(":arg2", $email->arg2);

        return $stmt->execute() ? Response::satisfied() : Response::unsatisfied(null);
    }

    /**
     * Sends all emails in the queue.
     *
     * @return void
     */
    public function process_queue(): void
    {
        // Open mailer
        $mailer = new PHPMailer();
        $mailer->IsSMTP();
        $mailer->CharSet = "UTF-8";

        $mailer->SMTPAuth = true;
        $mailer->SMTPDebug = SMTP::DEBUG_OFF;
        $mailer->SMTPKeepAlive = true;
        $mailer->SMTPSecure = PHPMailer::ENCRYPTION_SMTPS;
        $mailer->Host = $this->config["mail"]["host"];
        $mailer->Port = $this->config["mail"]["port"];
        $mailer->Username = $this->config["mail"]["username"];
        $mailer->Password = $this->config["mail"]["password"];
        try {
            $mailer->setFrom($this->config["mail"]["username"], $this->config["mail"]["from_name"]);
        } catch (MailerException $exception) {
            $this->logger->error("Failed to set 'from' address while processing queue.", ["cause" => $exception]);
            $mailer->smtpClose();
        }

        // Get queue
        $stmt = $this->conn->prepare("SELECT type, recipient, arg1, arg2 FROM email_tasks;");
        $stmt->execute();
        $email_tasks = $stmt->fetchAll(PDO::FETCH_ASSOC);

        // Process queue
        $stmt = $this->conn->prepare("DELETE FROM email_tasks
                                      WHERE type=:type AND recipient=:recipient AND arg1=:arg1 AND arg2=:arg2;");
        $stmt->bindParam(":type", $type);
        $stmt->bindParam(":recipient", $recipient);
        $stmt->bindParam(":arg1", $arg1);
        $stmt->bindParam(":arg2", $arg2);
        foreach ($email_tasks as ["type" => $type, "recipient" => $recipient, "arg1" => $arg1, "arg2" => $arg2]) {
            try {
                $email = Email::deserialize($type, $recipient, $arg1, $arg2);
                $mailer->Subject = $email->getSubject();
                $mailer->Body = $email->getBody($this->config);

                try {
                    $mailer->addAddress($recipient);
                    $mailer->send();
                } catch (MailerException $exception) {
                    $this->logger->error(
                        "Failed to send mail.",
                        ["cause" => $exception, "email" => $email]
                    );
                    $mailer->getSMTPInstance()->reset();
                }

                $mailer->clearAddresses();
            } catch (Exception $exception) {
                $this->logger->error(
                    "Failed to send mail.",
                    ["cause" => $exception]
                );
                $mailer->getSMTPInstance()->reset();
            }

            $stmt->execute();
        }
    }
}


/**
 * A serializable email that can be queued in a database and can be sent.
 *
 * When serialized, an email is represented by the type of email and two arguments. When deserialized, an email can be
 * constructed from those arguments, and the implementation returns a specific subject and message.
 */
abstract class Email
{
    /**
     * @var string A string identifying the type of email.
     */
    public string $type;
    /**
     * @var string The intended recipient of the email.
     */
    public string $recipient;
    /**
     * @var string The first argument to construct the email.
     */
    public string $arg1 = "";
    /**
     * @var string The second argument to construct the email.
     */
    public string $arg2 = "";


    /**
     * Returns the subject header of the email.
     *
     * @return string the subject header of the email
     */
    public abstract function getSubject(): string;

    /**
     * Returns the body of the email.
     *
     * @param array<string, array<string, mixed>> $config the software configuration
     * @return string the body of the email
     */
    public abstract function getBody(array $config): string;


    /**
     * Deserializes an email back into an instance.
     *
     * Only types of emails that are known can be deserialized.
     *
     * @param string $type the type of email to deserialize
     * @param string $recipient the intended recipient of the email
     * @param string $arg1 the first argument to construct the email
     * @param string $arg2 the second argument to construct the email
     * @return Email a deserialized email
     * @throws Exception if the `type` is not recognized
     */
    public static function deserialize(string $type, string $recipient, string $arg1, string $arg2): Email
    {
        return match ($type) {
            RegisterEmail::TYPE => new RegisterEmail($recipient, $arg1),
            VerifyEmailEmail::TYPE => new VerifyEmailEmail($recipient, $arg1),
            ChangedEmailEmail::TYPE => new ChangedEmailEmail($recipient, $arg1),
            ChangedPasswordEmail::TYPE => new ChangedPasswordEmail($recipient),
            ResetPasswordEmail::TYPE => new ResetPasswordEmail($recipient, $arg1),
            NotifyArticleDeletedEmail::TYPE => new NotifyArticleDeletedEmail($recipient, $arg1),
            NotifyArticleUndeletedEmail::TYPE => new NotifyArticleUndeletedEmail($recipient, $arg1),
            NotifyStatusChangedEmail::TYPE => new NotifyStatusChangedEmail($recipient, $arg1, $arg2),
            default => throw new Exception("Unknown email type $type."),
        };
    }
}

/**
 * An email to be sent to a recently registered user, including instructions for email verification.
 */
class RegisterEmail extends Email
{
    /**
     * A string identifying the type of email.
     */
    public const TYPE = "register";

    /**
     * @var string The token to verify the email address with.
     */
    public string $token;


    /**
     * Constructs an email to be sent to a recently registered user, including instructions for email verification.
     *
     * @param string $recipient the intended recipient of the email
     * @param string $token the token to verify the email address with
     */
    public function __construct(string $recipient, string $token)
    {
        $this->type = self::TYPE;
        $this->recipient = $recipient;

        $this->token = $token;
        $this->arg1 = $token;
    }

    public function getSubject(): string
    {
        return "Welcome to Death Notifier";
    }

    public function getBody(array $config): string
    {
        $base_path = $config["server"]["base_path"];
        $verify_path = "$base_path?action=verify-email&email=" . rawurlencode($this->recipient) . "&token=$this->token";

        return
            "You have successfully created an account with Death Notifier. " .
            "Welcome!" .
            "\n\n" .
            "Until you verify your email address, you will not receive any notifications. " .
            "You can verify your email address by clicking the link below. " .
            "This link will expire after " . UserManager::MINUTES_VALID_VERIFICATION . " minutes." .
            "\n" .
            "Verify: $verify_path" .
            "\n\n" .
            "If you did not create this account, you can delete the account. " .
            "Go to the Death Notifier website, reset your password, log in, and delete the account." .
            "\n\n" .
            $base_path;
    }
}

/**
 * An email to help a user verify their email address.
 */
class VerifyEmailEmail extends Email
{
    /**
     * A string identifying the type of email.
     */
    public const TYPE = "verify-email";

    /**
     * @var string The token to verify the email address with.
     */
    public string $token;


    /**
     * Constructs an email to help a user verify their email address.
     *
     * @param string $recipient the intended recipient of the email
     * @param string $token the token to verify the email address with
     */
    public function __construct(string $recipient, string $token)
    {
        $this->type = self::TYPE;
        $this->recipient = $recipient;

        $this->token = $token;
        $this->arg1 = $token;
    }


    public function getSubject(): string
    {
        return "Verify your email address";
    }

    public function getBody(array $config): string
    {
        $base_path = $config["server"]["base_path"];
        $verify_path = "$base_path?action=verify-email&email=" . rawurlencode($this->recipient) . "&token=$this->token";

        return
            "You requested a new verification link for your Death Notifier account. " .
            "You can verify your email address by clicking the link below. " .
            "This link will expire after " . UserManager::MINUTES_VALID_VERIFICATION . " minutes. " .
            "Until you verify your email address, you will not receive any notifications." .
            "\n" .
            "Verify: $verify_path" .
            "\n\n" .
            $base_path;
    }
}

/**
 * An email informing a user that their email has been changed, and needs verification.
 */
class ChangedEmailEmail extends Email
{
    /**
     * A string identifying the type of email.
     */
    public const TYPE = "changed-email";

    /**
     * @var string The token to verify the email address with.
     */
    public string $token;


    /**
     * Constructs an email informing a user that their email has been changed, and needs verification.
     *
     * @param string $recipient the intended recipient of the email
     * @param string $token the token to verify the email address with
     */
    public function __construct(string $recipient, string $token)
    {
        $this->type = self::TYPE;
        $this->recipient = $recipient;

        $this->token = $token;
        $this->arg1 = $token;
    }


    public function getSubject(): string
    {
        return "Verify your new email address";
    }

    public function getBody(array $config): string
    {
        $base_path = $config["server"]["base_path"];
        $verify_path = "$base_path?action=verify-email&email=" . rawurlencode($this->recipient) . "&token=$this->token";

        return
            "You changed the email address of your Death Notifier account. " .
            "Until you verify your email address, you will not receive any notifications. " .
            "You can verify your new email address by clicking the link below. " .
            "This link will expire after " . UserManager::MINUTES_VALID_VERIFICATION . " minutes." .
            "\n" .
            "Verify: $verify_path" .
            "\n\n" .
            $base_path;
    }
}

/**
 * An email informing a user that their password has been changed.
 */
class ChangedPasswordEmail extends Email
{
    /**
     * A string identifying the type of email.
     */
    public const TYPE = "changed-password";


    /**
     * Constructs an email informing a user that their email has been changed, and needs verification.
     *
     * @param string $recipient the intended recipient of the email
     */
    public function __construct(string $recipient)
    {
        $this->type = self::TYPE;
        $this->recipient = $recipient;
    }


    public function getSubject(): string
    {
        return "Your password has been changed";
    }

    public function getBody(array $config): string
    {
        $base_path = $config["server"]["base_path"];

        return
            "You changed the password of your Death Notifier account." .
            "\n\n" .
            "If you did not change the password of your account, go to the Death Notifier website and use the forgot " .
            "password option to change your password back." .
            "\n\n" .
            $base_path;
    }
}

/**
 * An email to help a user reset their password.
 */
class ResetPasswordEmail extends Email
{
    /**
     * A string identifying the type of email.
     */
    public const TYPE = "reset-password";

    /**
     * @var string The token to reset the password with.
     */
    public string $token;


    /**
     * Constructs an email to help a user reset their password.
     *
     * @param string $recipient the intended recipient of the email
     * @param string $token the token to reset the password with
     */
    public function __construct(string $recipient, string $token)
    {
        $this->type = self::TYPE;
        $this->recipient = $recipient;

        $this->token = $token;
        $this->arg1 = $token;
    }


    public function getSubject(): string
    {
        return "Reset your password";
    }

    public function getBody(array $config): string
    {
        $base_path = $config["server"]["base_path"];
        $verify_path =
            "$base_path?action=reset-password&email=" . rawurlencode($this->recipient) . "&token=$this->token";

        return
            "You requested a password reset link for your Death Notifier account. " .
            "You can choose a new password by clicking the link below. " .
            "This link expires after " . UserManager::MINUTES_VALID_PASSWORD_RESET . " minutes." .
            "\n" .
            "Reset password: $verify_path" .
            "\n\n" .
            "If you did not request a new password, you can safely ignore this message." .
            "\n\n" .
            $base_path;
    }
}

/**
 * An email to inform a user that a tracked article has been deleted.
 */
class NotifyArticleDeletedEmail extends Email
{
    /**
     * A string identifying the type of email.
     */
    public const TYPE = "notify-article-deleted";

    /**
     * @var string The name of the article that was deleted.
     */
    public string $name;


    /**
     * Constructs an email to inform a user that a tracked article has been deleted.
     *
     * @param string $recipient the intended recipient of the email
     * @param string $name the name of the article that was deleted
     */
    public function __construct(string $recipient, string $name)
    {
        $this->type = self::TYPE;
        $this->recipient = $recipient;

        $this->name = $name;
        $this->arg1 = $name;
    }


    public function getSubject(): string
    {
        return "$this->name article has been deleted";
    }

    public function getBody(array $config): string
    {
        $base_path = $config["server"]["base_path"];

        return
            "The Wikipedia article about $this->name has been deleted. " .
            "Death Notifier is now unable to send you a notification if $this->name dies. " .
            "If the Wikipedia article is ever re-created, Death Notifier will automatically resume tracking this " .
            "article, and you will receive another notification." .
            "\n\n" .
            "You are receiving this message because of the preferences in your Death Notifier account. " .
            "To unsubscribe from these messages, go to the Death Notifier website, log in, and change your email " .
            "preferences." .
            "\n\n" .
            $base_path;
    }
}

/**
 * An email to inform a user that a tracked article has been re-created.
 */
class NotifyArticleUndeletedEmail extends Email
{
    /**
     * A string identifying the type of email.
     */
    public const TYPE = "notify-article-undeleted";

    /**
     * @var string The name of the article that was re-created.
     */
    public string $name;


    /**
     * Constructs an email to inform a user that a tracked article has been re-created.
     *
     * @param string $recipient the intended recipient of the email
     * @param string $name the name of the article that was re-created
     */
    public function __construct(string $recipient, string $name)
    {
        $this->type = self::TYPE;
        $this->recipient = $recipient;

        $this->name = $name;
        $this->arg1 = $name;
    }


    public function getSubject(): string
    {
        return "$this->name article has been re-created";
    }

    public function getBody(array $config): string
    {
        $base_path = $config["server"]["base_path"];

        return
            "The Wikipedia article about $this->name has been re-created. " .
            "Death Notifier will once again track the article and notify you if $this->name dies." .
            "\n\n" .
            "You are receiving this message because of the preferences in your Death Notifier account. " .
            "To unsubscribe from these messages, go to the Death Notifier website, log in, and change your email " .
            "preferences." .
            "\n\n" .
            $base_path;
    }
}

/**
 * An email to inform a user a tracker person's status has changed.
 */
class NotifyStatusChangedEmail extends Email
{
    /**
     * A string identifying the type of email.
     */
    public const TYPE = "notify-status-changed";

    /**
     * @var string The name of the person whose status has changed.
     */
    public string $name;
    /**
     * @var string The new status of the person.
     */
    public string $new_status;


    /**
     * Constructs an email to inform a user someone has died.
     *
     * @param string $recipient the intended recipient of the email
     * @param string $name the name of the person who died
     * @param string $new_status the new status of the person
     */
    public function __construct(string $recipient, string $name, string $new_status)
    {
        $this->type = self::TYPE;
        $this->recipient = $recipient;

        $this->name = $name;
        $this->arg1 = $name;

        $this->new_status = $new_status;
        $this->arg2 = $new_status;
    }


    public function getSubject(): string
    {
        return "$this->name may be $this->new_status";
    }

    public function getBody(array $config): string
    {
        $base_path = $config["server"]["base_path"];

        return
            "Someone has edited Wikipedia to state that $this->name is $this->new_status. " .
            "For more information, read their Wikipedia article at " .
            "https://en.wikipedia.org/wiki/" . rawurlencode($this->name) .
            "\n\n" .
            "You are receiving this message because of the preferences in your Death Notifier account. " .
            "To unsubscribe from these messages, go to the Death Notifier website, log in, and change your email " .
            "preferences." .
            "\n\n" .
            $base_path;
    }
}