www-app-microjournal/htdocs/index.php

<?php declare(strict_types=1);
// Copyright © 2023 Ian Albert
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the “Software”), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.



// --------------------------------------------------------
// -- Begin required configuration ------------------------

/// Absolute path to the journal.db file on your web server. File must be
/// writable by the web server user. THIS FILE SHOULD BE SECURED FROM WEB
/// ACCESS! Otherwise someone can download your journal database if they know
/// the default URL. Options:
///
/// 1. Put journal.db somewhere that isn't under your web directory. (BEST OPTION)
/// 2. Rename journal.db to something randomized, like the output of the
///    `uuidgen` command, so the URL would be too obfuscated to guess.
/// 3. Modify your `.htaccess` to forbid access to .db files. e.g.
///        <Files ~ "\.db$">
///        Order allow,deny
///        Deny from all
///        </Files>
///    This example may or may not work for you. Be sure to test your
///    server configuration!
define('DB_PATH', '/path/to/journal.db');

// URL of this page. You can omit the index.php and just keep the path if you'd
// prefer a cleaner URL.
define('BASE_URL', 'https://example.com/path/index.php');

// -- End required configuration --------------------------
// --------------------------------------------------------






// -- Constants -------------------------------------------

/// For detecting database migrations.
define('SCHEMA_VERSION', '20230107');
define('RECENT_POSTS_PER_PAGE', 50);
define('SESSION_COOKIE_TTL_SECONDS', 14 * 24 * 60 * 60); // 14 days
define('SESSION_COOKIE_NAME', 'journal_token');
/// If a new post matches an existing post created less than this many seconds
/// ago, the new duplicate post will be ignored.
define('DUPLICATE_POST_SECONDS', 10);
define('TIME_ZONE_DEFAULT', 'America/Los_Angeles');
define('TOKEN_BYTES', 16);
define('SESSION_KEY_ERROR', 'error');
define('SESSION_KEY_LAST_ACCESS', 'last_access');
define('SESSION_KEY_POST_BODY', 'post_body');
define('SESSION_KEY_USER_ID', 'user_id');

// -- Core setup ------------------------------------------

session_start();
$_SESSION[SESSION_KEY_LAST_ACCESS] = time(); // keep alive

function handle_error($error_level = E_WARNING, $error_message = '',
		$error_file = '', $error_line = 0, $error_context = null): void {
	$lvl = 'WARNING';
	switch ($error_level) {
		case E_WARNING: case E_USER_WARNING: $lvl = 'WARNING'; break;
		case E_ERROR: case E_USER_ERROR: $lvl = 'ERROR'; break;
		case E_NOTICE: case E_USER_NOTICE: $lvl = 'NOTICE'; break;
	}
	error_log("[{$lvl} - {$error_file}:{$error_line}] {$error_message}", 0);
}
set_error_handler('handle_error');
error_reporting(E_ERROR);

/// Logs a debug message.
function trace(string $message): void {
	// error_log($message, 0);
}

// -- Data classes ----------------------------------------

/// Represents a journal post.
class Post {
	public ?int $post_id;
	public string $body;
	public int $author_id;
	public int $created;
	public ?int $updated;

	function __construct(array $row) {
		$this->post_id = $row['rowid'];
		$this->body = $row['body'];
		$this->author_id = $row['author_id'];
		$this->created = $row['created'];
		$this->updated = $row['updated'];
	}

	/// Normalizes the body of a post.
	private static function normalize_body(string $body): string {
		$s = $body;
		$s = str_replace("\r\n", "\n", $s); // CRLF -> LF
		$s = trim($s);
		return $s;
	}

	/// Creates a new post.
	/// @param string $body    Text content of the journal entry.
	/// @param int $author_id  User ID of the post author.
	/// @param int $created    Unix timestamp of when the post was created.
	public static function create(
			string $body,
			int $author_id,
			int $created): void {
		trace("Creating a post \"{$body}\"");
		$body = self::normalize_body($body);
		if (self::recent_duplicate_exists($body, $author_id, $created)) {
			trace("Same post already created recently. Skipping.");
			return;
		}
		$sql = 'INSERT INTO posts (body, author_id, created) VALUES (:body, :author_id, :created);';
		$args = array(':body' => $body, ':author_id' => $author_id, ':created' => $created);
		Database::query($sql, $args);
	}

	/// Tests if an identical post was created recently. For preventing double
	/// submits.
	/// @param string $body    Text content of the journal entry.
	/// @param int $author_id  User ID of the post author.
	/// @param int $created    Unix timestamp of when the post was created.
	/// @return bool    True if a similar recent post exists, false if not.
	public static function recent_duplicate_exists(
			string $body,
			int $author_id,
			int $created): bool {
		$sql = 'SELECT * FROM posts WHERE body=:body AND author_id=:author_id AND ABS(created - :created) < :seconds LIMIT 1;';
		$args = array(
			':body' => $body,
			':author_id' => $author_id,
			':created' => $created,
			':seconds' => DUPLICATE_POST_SECONDS,
		);
		return sizeof(Database::query($sql, $args)) > 0;
	}

	/// Fetches existing posts, newest first.
	/// @param int $user_id       User ID of author to fetch posts for.
	/// @param int $count         Maximum number of posts to return.
	/// @param ?int $before_time  If provided, only posts older than this Unix
	///                           timestamp are returned.
	/// @return array             Three-element tuple - 0: array of Posts,
	///                           1: relative URL to show previous page, or null if none
	///                           2: relative URL to show next page, or null if none
	public static function get_posts(
			int $user_id,
			int $count = RECENT_POSTS_PER_PAGE,
			?string $query = null,
			?int $before_time = null): array {
		$sql = 'SELECT rowid, * FROM posts WHERE author_id=:author_id';
		$args = array(
			':author_id' => $user_id,
			':count' => $count + 1, // to see if there's another page
		);
		if ($before_time) {
			$sql .= ' AND created < :before_time';
			$args[':before_time'] = $before_time;
		}
		$search_where = '';
		if ($query) {
			foreach (explode(' ', $query) as $i => $term) {
				if (strlen($term) == 0) continue;
				$symbol = ":wordpattern{$i}";
				$search_where .= " AND body LIKE $symbol ESCAPE '!'";
				$args[$symbol] = '%' . Database::escape_like($term, '!') . '%';
			}
			$sql .= $search_where;
		}
		$sql .= ' ORDER BY created DESC LIMIT :count;';
		$posts = Database::query_objects('Post', $sql, $args);

		$prev_page = null;
		$next_page = null;
		if (sizeof($posts) > $count) {
			$posts = array_slice($posts, 0, $count);
			$next_page = '?before=' . $posts[array_key_last($posts)]->created;
		}
		if ($before_time) {
			// We're paged forward. Check if there are newer posts.
			$sql = 'SELECT rowid, * FROM posts WHERE author_id=:author_id AND ' .
				'created >= :before_time ' . $search_where . ' ORDER BY created ASC LIMIT :count;';
			// Reusing same $args
			$newer_posts = Database::query_objects('Post', $sql, $args);
			if (sizeof($newer_posts) > $count) {
				$prev_date = $newer_posts[array_key_last($newer_posts)]->created;
				$prev_page = '?before=' . $prev_date;
			} else {
				$prev_page = BASE_URL;
			}
		}
		if ($query) {
			if ($prev_page) {
				$prev_page .= (str_contains($prev_page, '?') ? '&' : '?') .
					'search=' . urlencode($query);
			}
			if ($next_page) {
				$next_page .= (str_contains($next_page, '?') ? '&' : '?') .
					'search=' . urlencode($query);
			}
		}

		return array($posts, $prev_page, $next_page);
	}

	/// Fetches a post by its post ID.
	/// @param int $post_id  ID of the post.
	/// @return ?Post  The Post, or null if not found.
	public static function get_by_id(int $post_id): ?Post {
		$sql = 'SELECT rowid, * FROM posts WHERE rowid=:post_id;';
		$args = array(':post_id' => $post_id);
		return Database::query_object('Post', $sql, $args);
	}

	/// Deletes this post.
	public function delete(): void {
		$sql = 'DELETE FROM posts WHERE rowid=:post_id;';
		$args = array(':post_id' => $this->post_id);
		Database::query($sql, $args);
		$this->post_id = null;
	}

	/// Update text of post.
	public function update(string $new_body): void {
		$new_body = self::normalize_body($new_body);
		$sql = 'UPDATE posts SET body=:body, updated=:updated WHERE rowid=:rowid;';
		$args = array(
			':body' => $new_body,
			':updated' => time(),
			':rowid' => $this->post_id,
		);
		Database::query($sql, $args);
	}
}

/// Represents a user.
class User {
	public static ?User $current = null;

	public int $user_id;
	public string $username;
	public string $password_hash;
	public string $timezone;

	function __construct(array $row) {
		$this->user_id = $row['user_id'];
		$this->username = $row['username'];
		$this->password_hash = $row['password_hash'];
		$this->timezone = $row['timezone'];
	}

	/// Tests if any users exist in the database.
	public static function any_exist(): bool {
		static $has_any = null;
		if ($has_any !== null) return $has_any;
		$rows = Database::query('SELECT * FROM users;');
		$has_any = sizeof($rows) > 0;
		return $has_any;
	}

	/// Fetches a user by their user ID.
	public static function get_by_id(int $user_id): ?User {
		$sql = 'SELECT * FROM users WHERE user_id=:user_id LIMIT 1;';
		$args = array(':user_id' => $user_id);
		return Database::query_object('User', $sql, $args);
	}

	/// Fetches a user by their username.
	public static function get_by_username(string $username): ?User {
		$sql = 'SELECT * FROM users WHERE username=:username LIMIT 1;';
		$args = array(':username' => $username);
		return Database::query_object('User', $sql, $args);
	}

	/// Creates a new user.
	///
	/// @param string $username    Username
	/// @param string $password    Password for the user
	/// @param string $timezone    User's preferred time zone
	public static function create(
			string $username,
			string $password,
			string $timezone): void {
		trace("Creating user {$username}");
		$sql = 'INSERT OR IGNORE INTO users (username, password_hash, timezone) VALUES (:username, :password_hash, :timezone);';
		$args = array(
			':username' => $username,
			':password_hash' => password_hash($password, PASSWORD_DEFAULT),
			':timezone' => $timezone,
		);
		Database::query($sql, $args);
	}

	/// Signs in an existing user and returns their User object, or null if
	/// sign in failed. Sets $_SESSION if successful.
	///
	/// @param string $username  User's username
	/// @param string $password  User's password
	/// @return User object if sign in successful, otherwise null
	public static function sign_in(string $username, string $password): ?User {
		$user = self::get_by_username($username);
		if ($user === null) {
			trace("Login failed. No such user {$username}.");
			fatal_error("Login incorrect.");
			return null;
		}
		if (!password_verify($password, $user->password_hash)) {
			trace("Login failed. Bad password for {$username}.");
			fatal_error("Login incorrect.");
			return null;
		}
		trace("Login succeeded for {$username}.");
		$_SESSION[SESSION_KEY_USER_ID] = $user->user_id;
		self::$current = $user;
		Session::create($user->user_id);
		return $user;
	}

	/// Updates self::$current from $_SESSION.
	public static function update_current(): void {
		if (self::any_exist() && array_key_exists(SESSION_KEY_USER_ID, $_SESSION) && is_int($_SESSION[SESSION_KEY_USER_ID])) {
			$id = $_SESSION[SESSION_KEY_USER_ID];
			self::$current = User::get_by_id($id);
		} else {
			self::$current = null;
		}
	}

	public static function sign_out(): void {
		self::$current = null;
		Session::$current?->delete();
		unset($_SESSION[SESSION_KEY_USER_ID]);
	}
}

class Session {
	public static ?Session $current = null;

	public int $rowid;
	public string $token;
	public int $user_id;
	public int $created;
	public int $updated;

	function __construct(array $row) {
		$this->rowid = $row['rowid'];
		$this->token = $row['token'];
		$this->user_id = $row['user_id'];
		$this->created = $row['created'];
		$this->updated = $row['updated'];
	}

	/// Logs in from the journal token cookie if needed.
	public static function check_cookie(): void {
		if (User::$current) return;
		if (!array_key_exists(SESSION_COOKIE_NAME, $_COOKIE)) return;
		$token = $_COOKIE[SESSION_COOKIE_NAME];
		trace("Found token cookie");
		self::$current = self::get_by_token($token);
		if (!self::$current) return;
		$user = User::get_by_id(self::$current->user_id);
		if (!$user) {
			self::$current->delete();
			return;
		}
		trace("Found user from cookie");
		User::$current = $user;
		$_SESSION[SESSION_KEY_USER_ID] = $user->user_id;
		self::$current->touch();
	}

	public static function create(int $user_id): Session {
		$token = bin2hex(random_bytes(TOKEN_BYTES));
		$time = intval(time());
		$sql = 'INSERT INTO sessions (token, user_id, created, updated) ' .
			'VALUES (:token, :user_id, :created, :updated);';
		$args = array(
			':token' => $token,
			':user_id' => $user_id,
			':created' => $time,
			':updated' => $time,
		);
		Database::query($sql, $args);
		$session = self::get_by_token($token);
		$session->touch(false);
		return $session;
	}

	public function touch(bool $update_table = true): void {
		$this->updated = time();
		$secure = str_starts_with(BASE_URL, 'https:');
		$expires = intval(time()) + SESSION_COOKIE_TTL_SECONDS;
		trace('Updating cookie to ' . localized_date_string($expires));
		setcookie(SESSION_COOKIE_NAME, $this->token, $expires, path: '/',
			secure: $secure, httponly: true);
		if ($update_table) {
			$sql = 'UPDATE sessions SET updated=:updated WHERE rowid=:rowid;';
			$args = array(':updated' => $this->updated, ':rowid' => $this->rowid);
			Database::query($sql, $args);
		}
	}

	public static function get_by_token(string $token): ?Session {
		$sql = 'SELECT rowid, * FROM sessions WHERE token=:token LIMIT 1';
		$args = array(':token' => $token);
		return Database::query_object('Session', $sql, $args);
	}

	public static function get_by_user_id(int $user_id): array {
		$sql = 'SELECT rowid, * FROM sessions WHERE user_id=:user_id;';
		$args = array(':user_id' => $user_id);
		return Database::query_objects('Session', $sql, $args);
	}

	public static function delete_all_for_user(int $user_id): void {
		$sql = 'DELETE FROM sessions WHERE user_id=:user_id;';
		$args = array(':user_id' => $user_id);
		Database::query($sql, $args);
	}

	public function delete(): void {
		$sql = 'DELETE FROM sessions WHERE rowid=:rowid;';
		$args = array(':rowid' => $this->rowid);
		Database::query($sql, $args);
		$secure = str_starts_with(BASE_URL, 'https:');
		setcookie(SESSION_COOKIE_NAME, '', 1, path: '/', secure: $secure, httponly: true);
		unset($_COOKIE[SESSION_COOKIE_NAME]);
	}
}

// -- Utility classes -------------------------------------

/// Performs database operations.
class Database {
	/// Tests if the configured database is available.
	public static function exists(): bool {
		return file_exists(DB_PATH);
	}

	/// Tests if the configured database is writable.
	public static function is_writable(): bool {
		return is_writable(DB_PATH);
	}

	/// Tests if the database file is accessible externally by a predictable
	/// URL. If it is, the user should be warned so they can fix its permissions.
	public static function is_accessible_by_web(): bool {
		if (!str_ends_with(DB_PATH, '/journal.db')) return false;
		$ctx = stream_context_create(array(
			'http' => array(
				'timeout' => 1, // shouldn't take long to reach own server
			)
		));
		$journal_url = strip_filename(BASE_URL);
		if (!str_ends_with($journal_url, '/')) $journal_url .= '/';
		$journal_url .= 'journal.db';
		trace("Testing external accessibility of journal URL. This may take a second.");
		return (file_get_contents($journal_url, false, $ctx) !== false);
	}

	/// Performs an SQL query and returns the first row as an object of the
	/// given class. The given class must accept a row array as its only
	/// constructor argument. Adding a "LIMIT 1" clause to the query may help
	/// performance, since only the first result is used.
	///
	/// @param $classname  Class name of the class to use for each result row.
	/// @param $sql        Query to execute.
	/// @param $params     Map of SQL placeholders to values.
	/// @return ?object    Object of given class from first result row, or null
	///                    if no rows matched.
	public static function query_object(string $classname, string $sql, array $params = array()): ?object {
		$objs = self::query_objects($classname, $sql, $params);
		return (sizeof($objs) > 0) ? $objs[0] : null;
	}

	/// Performs an SQL query and returns the result set as an array of objects
	/// of the given class. The given class must accept a row array as its only
	/// constructor argument.
	///
	/// @param $classname  Class name of the class to use for each result row.
	/// @param $sql        Query to execute.
	/// @param $params     Map of SQL placeholders to values.
	/// @return array      Array of records of the given class.
	public static function query_objects(string $classname, string $sql, array $params = array()): array {
		$rows = self::query($sql, $params);
		$objs = array();
		if ($rows !== false) {
			foreach ($rows as $row) {
				$objs[] = new $classname($row);
			}
		}
		return $objs;
	}

	/// Runs a query and returns the complete result. Select queries will return
	/// all rows as an array of row arrays. Insert/update/delete queries will
	/// return a boolean of success.
	///
	/// @param $sql     Query to execute.
	/// @param $params  Map of SQL placeholders to values.
	/// @return array   Array of arrays. The inner arrays contain both indexed
	///                 and named column values.
	public static function query(string $sql, array $params = array()): bool|array {
		$db = new SQLite3(DB_PATH);
		trace('SQL: ' . $sql);
		$stmt = $db->prepare($sql);
		foreach ($params as $name => $value) {
			$type = self::sqlite_type($value);
			$stmt->bindValue($name, $value, $type);
			trace("\tbind {$name} => {$value} ({$type})");
		}
		$result = $stmt->execute();
		if (gettype($result) == 'bool') {
			return $result;
		}
		$rows = array();
		// XXX: Make sure it's a query with results, otherwise fetchArray will
		// cause non-selects (e.g. INSERT) to be executed again.
		if ($result->numColumns()) {
			while ($row = $result->fetchArray()) {
				$rows[] = $row;
			}
		}
		$stmt->close();
		$db->close();
		return $rows;
	}

	/// Returns the closest SQLite3 datatype for the given PHP value.
	private static function sqlite_type($value): int {
		switch (gettype($value)) {
			case 'boolean':
			case 'integer':
				return SQLITE3_INTEGER;
			case 'double':
				return SQLITE3_FLOAT;
			case 'string':
				return SQLITE3_TEXT;
			case 'NULL':
				return SQLITE3_NULL;
			default:
				fatal_error("Bad datatype in sqlite statement");
		}
	}

	/// Escapes a string for use in a LIKE clause.
	/// @param string $value   String to escape.
	/// @param string $escape  Character to use for escaping. Default is !
	/// @return string  Escaped string
	public static function escape_like(string $value, string $escape='!'): string {
		$s = $value;
		$s = str_replace($escape, $escape . $escape, $s); // escape char
		$s = str_replace('%', $escape . '%', $s); // any chars
		$s = str_replace('_', $escape . '_', $s); // one char
		return $s;
	}
}

/// App configuration management. All config is stored in the 'config' table in
/// the sqlite database.
class Config {
	public static function get_is_configured(): bool {
		return self::get_config_value('is_configured', 'bool') ?: false;
	}
	public static function set_is_configured(bool $is_configured): void {
		self::set_config_value('is_configured', $is_configured);
	}
	public static function get_schema_version(): ?string {
		return self::get_config_value('schema_version', 'string');
	}
	public static function set_schema_version(string $schema_version): void {
		self::set_config_value('schema_version', $schema_version);
	}

	/// Fetches a config value from the database, or null if not found.
	private static function get_config_value(string $name, string $type = 'any') {
		$sql = 'SELECT value FROM config WHERE name=:name;';
		$params = array(':name' => $name);
		$rows = Database::query($sql, $params);
		if (sizeof($rows) == 0) return null;
		$value = $rows[0]['value'];
		if ($type != 'any') {
			switch ($type) {
				case 'string': $value = strval($value); break;
				case 'int': $value = intval($value); break;
				case 'bool': $value = boolval($value); break;
			}
		}
		return $value;
	}

	/// Saves a config value to the database.
	private static function set_config_value(string $name, $value): void {
		$args = array(':name' => $name, ':value' => $value);
		Database::query('UPDATE config SET value=:value WHERE name=:name;', $args);
		Database::query('INSERT OR IGNORE INTO config (name, value) VALUES (:name, :value);', $args);
	}
}

// -- Misc utility functions ------------------------------

/// Checks whether the app is setup correctly.
function check_setup(): void {
	// Check user-configurable variables to make sure they aren't default values.
	if (str_contains(BASE_URL, 'example.com') || DB_PATH == '/path/to/journal.db') {
		fatal_error("Journal not configured. Open index.php in an editor and configure the variables at the top of the file.");
	}

	if (!Database::exists()) {
		fatal_error("Database file cannot be found. Check configuration at the top of index.php.");
	}

	if (!Database::is_writable()) {
		$user = trim(shell_exec('whoami'));
		$group = trim(shell_exec('id -gn'));
		fatal_error("Database file exists but is not writable by web server user '{$user}' (user group '{$group}'). Check file permissions.");
	}

	$schema_version = Config::get_schema_version();
	if ($schema_version === null) {
		fatal_error("No schema version in database. Corrupted?");
	}

	if ($schema_version != SCHEMA_VERSION) {
		// TODO: If schema changes, migration paths will go here. For now just fail.
		fatal_error("Unexpected schema version $schema_version.");
	}

	if (Config::get_is_configured()) {
		// Already checked the more expensive tests below, so skip.
		return;
	}

	// If using default database name, make sure it's not accessible from the
	// web. It'd be far too easy to access.
	if (Database::is_accessible_by_web()) {
		fatal_error("Journal database is accessible from the web! Either alter your .htaccess permissions or rename the database with a UUID filename.");
	}

	// Everything looks good!
	Config::set_is_configured(true);
}

/// Shows the user an error message and terminates the script. If called from
/// a non-GET request, will first redirec to the main page then display the
/// message.
function fatal_error(string $message): never {
	if ($_SERVER['REQUEST_METHOD'] != 'GET') {
		$_SESSION[SESSION_KEY_ERROR] = $message;
		HTMLPage::redirect_home();
	}
	HTMLPage::render_page_start();
	HTMLPage::render_error($message);
	HTMLPage::render_page_end();
	exit();
}

/// Returns a path or URL without the filename. Result includes trailing /.
function strip_filename(string $path): string {
	$start = 0;
	if (str_starts_with($path, 'http://') || str_starts_with($path, 'https://')) {
		$start = 8;
	}
	$slash = strrpos($path,	'/', $start);
	if ($slash === false) return $path + '/';
	return substr($path, 0, $slash + 1);
}

define('INPUT_TYPE_NONEMPTY', 0x100);
define('INPUT_TYPE_TRIMMED', 0x200);
define('INPUT_TYPE_INT', 0x1 | INPUT_TYPE_TRIMMED | INPUT_TYPE_NONEMPTY);
define('INPUT_TYPE_STRING', 0x2);
define('INPUT_TYPE_USERNAME', 0x4 | INPUT_TYPE_TRIMMED | INPUT_TYPE_NONEMPTY);
/// Validates and casts a form input.
/// @param array $source    Source array, like $_GET or $_POST.
/// @param string $name     Form input variable name.
/// @param int $type        Bit mask of INPUT_TYPE_ constraints.
/// @param bool $required   Whether the value must be present. Will throw error
///                         if value is required and not found.
/// @return Cast value, or null if not required and found
function validate(array $source, string $name, int $type, bool $required = true) {
	if (!array_key_exists($name, $source)) {
		if ($required) {
			fatal_error("Parameter {$name} is required.");
		}
		return null;
	}
	$val = $source[$name];
	if ($type & INPUT_TYPE_TRIMMED) {
		$val = trim($val);
	}
	if (strlen($val) == 0) {
		if ($type & INPUT_TYPE_NONEMPTY) {
			fatal_error("Parameter {$name} cannot be empty.");
		}
	}
	if (($type & INPUT_TYPE_INT) == INPUT_TYPE_INT) {
		if (is_numeric($val)) return intval($val);
		fatal_error("Parameter {$name} must be integer.");
	}
	if (($type & INPUT_TYPE_STRING) == INPUT_TYPE_STRING) {
		return $val;
	}
	if (($type & INPUT_TYPE_USERNAME) == INPUT_TYPE_USERNAME) {
		if (preg_match('/[a-zA-Z0-9_@+-]+/', $val)) return $val;
		fatal_error("Invalid username. Can be letters, numbers, underscores, and dashes, or an email address.");
	}
	return null;
}

function localized_date_string(int $timestamp): string {
	$locale_code = Locale::acceptFromHttp($_SERVER['HTTP_ACCEPT_LANGUAGE']) ?: 'en-US';
	$timezone = User::$current->timezone;
	$formatter = IntlDateFormatter::create(
		$locale_code,
		dateType: IntlDateFormatter::MEDIUM,
		timeType: IntlDateFormatter::MEDIUM,
		timezone: $timezone,
		calendar: IntlDateFormatter::GREGORIAN);
	return $formatter->format($timestamp);
}

// -- HTML renderers --------------------------------------

class HTMLPage {
	public static function render_page_start(): void {
		print(<<<HTML
			<!DOCTYPE html>
			<html>
				<head>
					<title>Microjournal</title>
					<meta charset="UTF-8" />
					<link rel="stylesheet" type="text/css" href="journal.css" />
					<link rel="apple-touch-icon" sizes="58x58" href="apple-touch-icon-58.png" />
					<link rel="apple-touch-icon" sizes="76x76" href="apple-touch-icon-76.png" />
					<link rel="apple-touch-icon" sizes="80x80" href="apple-touch-icon-80.png" />
					<link rel="apple-touch-icon" sizes="87x87" href="apple-touch-icon-87.png" />
					<link rel="apple-touch-icon" sizes="114x114" href="apple-touch-icon-114.png" />
					<link rel="apple-touch-icon" sizes="120x120" href="apple-touch-icon-120.png" />
					<link rel="apple-touch-icon" sizes="152x152" href="apple-touch-icon-152.png" />
					<link rel="apple-touch-icon" sizes="167x167" href="apple-touch-icon-167.png" />
					<link rel="apple-touch-icon" sizes="180x180" href="apple-touch-icon-180.png" />
					<meta name="apple-mobile-web-app-title" content="μJournal" />
					<meta name="apple-mobile-web-app-capable" content="yes" />
					<meta name="theme-color" content="#fff" media="(prefers-color-scheme: light)" />
					<meta name="theme-color" content="#444" media="(prefers-color-scheme: dark)" />
					<meta name="viewport" content="user-scalable=no,width=device-width,viewport-fit=cover" />
					<link rel="icon" sizes="16x16" type="image/png" href="favicon-16.png" />
					<link rel="icon" sizes="32x32" type="image/png" href="favicon-32.png" />
				</head>
				<body>
					<nav>
						<div class="top-nav">
							<span class="title">Microjournal</span>
			HTML
		);
		if (User::$current) {
			print(<<<HTML
							<div class="menu-container">
								<details class="menu">
									<summary class="no-indicator menu-button"><span>☰</span></summary>

									<ul>
										<li><a href="?search">Search</a></li>
										<li class="menu-divider"></li>
										<li class="logout-item destructive"><a href="?logout">Log out</a></li>
									</ul>
								</details>
							</div>
				HTML
			);
		}
		print(<<<HTML
						</div>
					</nav>
					<div class="content">
			HTML
		);
	}

	public static function render_page_end(): void {
		print(<<<HTML
					</div>
				</body>
			</html>
			HTML
		);
	}

	public static function render_error_if_needed(): void {
		if (array_key_exists(SESSION_KEY_ERROR, $_SESSION)) {
			$e = $_SESSION[SESSION_KEY_ERROR];
			unset($_SESSION[SESSION_KEY_ERROR]);
			self::render_error($e);
		}
	}

	public static function render_error(string $message): void {
		print("<div class=\"error\">" . htmlentities($message) . "</div>\n");
	}

	public static function render_post_form(): void {
		$action = 'post';
		$verb = 'Post';
		$body = '';
		if ($edit_id = validate($_GET, 'edit', INPUT_TYPE_INT, required: false)) {
			if ($post = Post::get_by_id($edit_id)) {
				$body = $post->body;
				$action = 'edit';
				$verb = 'Update';
			} else {
				unset($edit_id);
			}
		} elseif (array_key_exists(SESSION_KEY_POST_BODY, $_SESSION)) {
			$body = $_SESSION[SESSION_KEY_POST_BODY];
			unset($_SESSION[SESSION_KEY_POST_BODY]);
		}
		$body_html = htmlentities($body);
		print(<<<HTML
			<form id="post-form" method="POST">
				<div class="text-container"><textarea name="body" placeholder="Your journal post here…">$body_html</textarea></div>
				<input type="hidden" name="action" value="{$action}" />
			HTML
		);
		if ($edit_id) {
			print("<input type=\"hidden\" name=\"edit_id\" value=\"{$edit_id}\" />");
		}
		print(<<<HTML
				<div class="submit-post"><input type="submit" value="{$verb}" /></div>
			</form>
			HTML
		);
	}

	public static function render_recent_posts(): void {
		$query = validate($_GET, 'search', INPUT_TYPE_STRING | INPUT_TYPE_TRIMMED, required: false);
		$before = validate($_GET, 'before', INPUT_TYPE_INT, required: false);
		[ $posts, $prev_url, $next_url ] = Post::get_posts(User::$current->user_id, query: $query, before_time: $before);
		print("<div class=\"post-container\">\n");
		if ($prev_url !== null) {
			print("<div class=\"previous\"><a href=\"{$prev_url}\">Previous</a></div>\n");
		}
		foreach ($posts as $post) {
			self::render_post($post);
		}
		if ($next_url !== null) {
			print("<div class=\"next\"><a href=\"{$next_url}\">Next</a></div>\n");
		}
		print("</div>\n");
	}

	/// Encodes a post body as HTML. Inserts linebreaks and paragraph tags.
	private static function post_body_html(string $body): string {
		$html_p_start = "<p>";
		$html_p_end = "</p>\n";
		$html_newline = "<br/>\n";
		$body_html = htmlentities($body);
		// Single newlines are turned into linebreaks.
		$body_html = str_replace("\n", $html_newline, $body_html);
		// Pairs of newlines are turned into paragraph separators.
		$body_html = $html_p_start .
			str_replace($html_newline . $html_newline,
				$html_p_end . $html_p_start,
				$body_html) .
			$html_p_end;
		return $body_html;
	}

	public static function render_post(Post $post): void {
		$body_html = Markdown::markdown_to_html($post->body);
		$date = localized_date_string($post->created);
		print(<<<HTML
			<div class="post">
				<article>
					<div class="post-body">{$body_html}</div>
					<div class="post-footer">
						<footer class="secondary-text">
							<div class="post-date">
								Posted {$date}
			HTML
		);
		if ($post->updated && $post->updated != $post->created) {
			print('<br/>(updated ' . localized_date_string($post->updated) . ')');
		}
		print(<<<HTML
							</div>
							<details class="post-actions menu">
								<summary class="no-indicator menu-button"><span>actions</span></summary>

								<ul>
									<li><a href="?edit={$post->post_id}">Edit</a></li>
									<li class="menu-divider"></li>
									<li class="post-action-delete destructive"><a href="?delete={$post->post_id}">Delete</a></li>
								</ul>
							</details>
						</footer>
					</div>
				</article>
			</div>
			HTML
		);
	}

	public static function render_search_form(): void {
		$q = validate($_GET, 'search', INPUT_TYPE_STRING | INPUT_TYPE_TRIMMED, required: false);
		$q_html = htmlentities($q);
		$cancel = BASE_URL;
		print(<<<HTML
			<form id="search-form" method="GET">
				<div>
					<label for="search">Search:</label>
					<input type="text" name="search" id="search" value="{$q_html}" autocapitalize="off" />
					<input type="submit" value="Search" />
					<a href="{$cancel}">Cancel</a>
				</div>
			</form>
			HTML
		);
	}

	public static function render_sign_in_form(): void {
		print(<<<HTML
			<form id="signin-form" method="POST">
				<div>
					<label for="username">Username:</label>
					<input type="text" name="username" id="username" autocapitalize="off" autocorrect="off" />
				</div>
				<div>
					<label for="password">Password:</label>
					<input type="password" name="password" id="password" />
				</div>
				<input type="hidden" name="action" value="signin" />
				<input type="submit" value="Sign in" />
			</form>
			HTML
		);
	}

	public static function render_setup_form(): void {
		print(<<<HTML
			<div class="important">Journal is not setup. Please create a username and password to secure your data.</div>
			<form id="setup-form" method="POST">
				<div>
					<label for="username">Username:</label>
					<input type="text" id="username" name="username" autocapitalize="off" autocorrect="off" />
				</div>
				<div>
					<label for="password">Password:</label>
					<input type="password" id="password" name="password" />
				</div>
				<div>
					<label for="timezone">Time zone:</label>
					<select name="timezone" id="timezone">
			HTML
		);
		foreach (DateTimeZone::listIdentifiers() as $timezone) {
			print("<option value=\"" . htmlentities($timezone) . "\"");
			if ($timezone == TIME_ZONE_DEFAULT) {
				print(" selected=\"selected\"");
			}
			print(">" . htmlentities($timezone) . "</option>\n");
		}
		print(<<<HTML
					</select></div>
				<input type="hidden" name="action" value="createaccount" />
				<div><input type="submit" value="Create account" /></div>
			</form>
			HTML
		);
	}

	/// Redirects to the main page. Used after operation requests. Terminates
	/// the script.
	public static function redirect_home(): never {
		header("Location: " . BASE_URL, true, 302); // 302 = found/moved temporarily
		exit();
	}
}

class HTMLBlock {
	public HTMLBlockType $type;
	public int $indent;
	public string $content_markdown;

	function __construct(HTMLBlockType $type, int $indent, string $content_markdown) {
		$this->type = $type;
		$this->indent = $indent;
		$this->content_markdown = $content_markdown;
	}
}

enum HTMLBlockType {
	case Plain;
	case ListItem;
	case BlockQuote;
	case Preformatted;
	case H1;
	case H2;
	case H3;
	case H4;
	case H5;
	case H6;
}

class Markdown {
	/// Converts one line of markdown to HTML.
	/// @param string $markdown  Markdown string
	/// @return string  HTML
	public static function line_markdown_to_html(string $markdown): string {
		$html = htmlentities($markdown);
		// Explicit URL [label](URL)
		$html = preg_replace('|\[(.*?)\]\((.*?)\)|',
			'<a referrerpolicy="no-referrer" target="_new" href="$2">$1</a>', $html);
		// Implicit URL
		$html = preg_replace('|(?<!href=")(http(?:s)?://)(\S+[^\s\.,\?!:;"\'\)])|',
			'<a referrerpolicy="no-referrer" target="_new" href="$1$2">$2</a>', $html);
		// Italic
		$html = preg_replace('/__(\S|\S.*?)__/', '<em>$1</em>', $html);
		// Bold
		$html = preg_replace('/\*\*(\S|\S.*?\S)\*\*/', '<strong>$1</strong>', $html);
		// Strikethrough
		$html = preg_replace('/~~(\S|\S.*?\S)~~/', '<strike>$1</strike>', $html);
		// Code
		$html = preg_replace('/`(\S|\S.*?\S)`/', '<code>$1</code>', $html);
		return $html;
	}

	/// Converts markdown into an array of HTMLBlocks.
	/// @param string $markdown  Markdown string
	/// @return array  Array of HTMLBlocks
	private static function markdown_to_blocks(string $markdown): array {
		$prefix_to_linetype = array(
			'*' => HTMLBlockType::ListItem,
			'-' => HTMLBlockType::ListItem,
			'+' => HTMLBlockType::ListItem,
			'>' => HTMLBlockType::BlockQuote,
			'######' => HTMLBlockType::H6,
			'#####' => HTMLBlockType::H5,
			'####' => HTMLBlockType::H4,
			'###' => HTMLBlockType::H3,
			'##' => HTMLBlockType::H2,
			'#' => HTMLBlockType::H1,
		);
		$blocks = array();
		foreach (explode("\n", $markdown) as $line) {
			$trimmed_line = trim($line);
			$indent = intval(round((strlen($line) - strlen($trimmed_line)) / 4));
			$block_type = HTMLBlockType::Plain;
			$block_content = $trimmed_line;
			foreach ($prefix_to_linetype as $prefix => $type) {
				if ($trimmed_line == $prefix ||
					str_starts_with($trimmed_line, $prefix . ' ')) {
					$block_content = substr($trimmed_line, strlen($prefix));
					$block_type = $type;
					break;
				}
			}
			$blocks[] = new HTMLBlock($block_type, $indent, $block_content);
		}
		return $blocks;
	}

	/// Converts markdown to HTML
	public static function markdown_to_html(string $markdown): string {
		return self::blocks_to_html(self::markdown_to_blocks($markdown));
	}

	/// Converts an array of HTMLBlocks to HTML.
	private static function blocks_to_html(array $blocks): string {
		$html = '';
		$last_block = null;
		$tag_stack = array(); // stack of end tag strings for current open blocks
		foreach ($blocks as $block) {
			$is_empty = strlen($block->content_markdown) == 0;
			$is_last_empty = strlen($last_block?->content_markdown ?? '') == 0;
			$is_same_block = $block->type == $last_block?->type;
			if (!$is_same_block && sizeof($tag_stack) > 0) {
				foreach (array_reverse($tag_stack) as $tag) {
					$html .= $tag;
				}
				$tag_stack = array();
			}
			switch ($block->type) {
				case HTMLBlockType::Plain:
					if ($is_empty) {
						if ($is_last_empty) {
							// ignore two consecutive empty lines
						} else {
							$html .= array_pop($tag_stack);
						}
					} elseif ($is_last_empty) {
						$html .= "<p>" . self::line_markdown_to_html($block->content_markdown);
						$tag_stack[] = "</p>\n\n";
					} else {
						$html .= "<br/>\n" . self::line_markdown_to_html($block->content_markdown);
					}
					break;
				case HTMLBlockType::ListItem:
					if (!$is_same_block) {
						foreach (array_reverse($tag_stack) as $tag) {
							$html .= $tag;
						}
						$tag_stack = array();
						for ($i = 0; $i <= $block->indent; $i++) {
							$html .= "<ul>\n";
							$html .= "<li>";
							$tag_stack[] = "</ul>\n";
							$tag_stack[] = "</li>\n";
						}
						$html .= self::line_markdown_to_html($block->content_markdown);
					} elseif ($block->indent == $last_block->indent) {
						$html .= "</li>\n";
						$html .= "<li>" . self::line_markdown_to_html($block->content_markdown);
					} elseif ($block->indent > $last_block->indent) {
						// Deeper indent level
						for ($i = $last_block->indent; $i < $block->indent; $i++) {
							$html .= "<ul>\n<li>" . self::line_markdown_to_html($block->content_markdown);
							$tag_stack[] = "</ul>\n";
							$tag_stack[] = "</li>\n";
						}
					} elseif ($block->indent < $last_block->indent) {
						// Shallower indent level
						for ($i = $block->indent; $i < $last_block->indent; $i++) {
							$html .= array_pop($tag_stack);
							$html .= array_pop($tag_stack);
						}
						$html .= "</li>\n";
						$html .= "<li>" . self::line_markdown_to_html($block->content_markdown);
					}
					break;
				case HTMLBlockType::BlockQuote:
					if ($is_same_block) {
						$html .= "<br/>\n";
					} else {
						$html .= "<blockquote>";
						$tag_stack[] = "</blockquote>\n\n";
					}
					$html .= self::line_markdown_to_html($block->content_markdown);
					break;
				case HTMLBlockType::Preformatted:
					if ($is_same_block) {
						$html .= "\n";
					} else {
						$html .= "<pre>";
						$tag_stack[] = "</pre>\n\n";
					}
					$html .= htmlentities($block->content_markdown);
					break;
				case HTMLBlockType::H1:
					$html .= '<h1>' . self::line_markdown_to_html($block->content_markdown) . "</h1>\n\n";
					break;
				case HTMLBlockType::H2:
					$html .= '<h2>' . self::line_markdown_to_html($block->content_markdown) . "</h2>\n\n";
					break;
				case HTMLBlockType::H3:
					$html .= '<h3>' . self::line_markdown_to_html($block->content_markdown) . "</h3>\n\n";
					break;
				case HTMLBlockType::H4:
					$html .= '<h4>' . self::line_markdown_to_html($block->content_markdown) . "</h4>\n\n";
					break;
				case HTMLBlockType::H5:
					$html .= '<h5>' . self::line_markdown_to_html($block->content_markdown) . "</h5>\n\n";
					break;
				case HTMLBlockType::H6:
					$html .= '<h6>' . self::line_markdown_to_html($block->content_markdown) . "</h6>\n\n";
					break;
			}
			$last_block = $block;
		}
		if (sizeof($tag_stack) > 0) {
			foreach (array_reverse($tag_stack) as $tag) {
				$html .= $tag;
			}
		}
		return $html;
	}
}

// -- Main logic ------------------------------------------

check_setup();
Session::check_cookie();
User::update_current();
switch ($_SERVER['REQUEST_METHOD']) {
	case 'GET':
		if (array_key_exists('logout', $_GET)) {
			User::sign_out();
			HTMLPage::redirect_home();
		}
		HTMLPage::render_page_start();
		HTMLPage::render_error_if_needed();
		if (User::$current) {
			if ($delete_id = validate($_GET, 'delete', INPUT_TYPE_INT, required: false)) {
				Post::get_by_id($delete_id)?->delete();
				HTMLPage::redirect_home();
			}
			if (array_key_exists('search', $_GET)) {
				HTMLPage::render_search_form();
			} else {
				HTMLPage::render_post_form();
			}
			HTMLPage::render_recent_posts();
		} elseif (User::any_exist()) {
			HTMLPage::render_sign_in_form();
		} else {
			HTMLPage::render_setup_form();
		}
		HTMLPage::render_page_end();
		exit();
	case 'POST':
		$nonempty_str_type = INPUT_TYPE_STRING | INPUT_TYPE_NONEMPTY | INPUT_TYPE_TRIMMED;
		$password_type = INPUT_TYPE_STRING | INPUT_TYPE_NONEMPTY;
		switch ($_POST['action']) {
			case 'post':
				$body = validate($_POST, 'body', $nonempty_str_type);
				$author = User::$current->user_id;
				$created = time();
				if (!User::$current) {
					// Not logged in. Save body for populating once they sign in.
					$_SESSION[SESSION_KEY_POST_BODY] = $body;
					fatal_error('Please sign in to post.');
				}
				Post::create($body, $author, $created);
				break;
			case 'edit':
				$body = validate($_POST, 'body', $nonempty_str_type);
				$edit_id = validate($_POST, 'edit_id', INPUT_TYPE_INT);
				if (!User::$current) {
					// Not logged in. Save body for populating once they sign in.
					fatal_error('Please sign in to edit.');
				}
				Post::get_by_id($edit_id)?->update($body);
				break;
			case 'createaccount':
				$username = validate($_POST, 'username', INPUT_TYPE_USERNAME);
				$password = validate($_POST, 'password', $password_type);
				$timezone = validate($_POST, 'timezone', $nonempty_str_type);
				User::create($username, $password, $timezone);
				break;
			case 'signin':
				$username = validate($_POST, 'username', INPUT_TYPE_USERNAME);
				$password = validate($_POST, 'password', $password_type);
				User::sign_in($username, $password);
				break;
			case 'signout':
				User::sign_out();
				break;
			default:
				trace('Invalid POST action: ' . ($_POST['action'] ?: 'null'));
				http_response_code(400);
				exit(1);
		}
		HTMLPage::redirect_home();
	default:
		trace("Invalid request method: " . $_SERVER['REQUEST_METHOD']);
		http_response_code(405);
		exit(1);
}
?>