<?php

namespace RoosterLMS\Community;

use RoosterLMS\Data\Db;
use RoosterLMS\Data\SqlPart;
use RoosterLMS\Data\Transaction;
use RoosterLMS\Domain\DomainError;
use RoosterLMS\Domain\ErrorCode;
use RoosterLMS\I18n\Language;
use RoosterLMS\I18n\Switcher;

defined( 'ABSPATH' ) || exit;

final class Discussions {

	public const MAX_BODY = 10000;

	public const LED = 5;

	public const KSES_TAGS = array(
		'p'          => array(),
		'br'         => array(),
		'strong'     => array(),
		'b'          => array(),
		'em'         => array(),
		'i'          => array(),
		'code'       => array(),
		'pre'        => array(),
		'blockquote' => array(),
		'ul'         => array(),
		'ol'         => array(),
		'li'         => array(),
		'a'          => array(
			'href' => true,
			'rel'  => true,
		),
	);

	public static function clean( string $body ): string {
		$body = trim( wp_kses( $body, self::KSES_TAGS ) );
		return mb_substr( $body, 0, self::MAX_BODY );
	}

	public function post( int $user_id, int $course_id, int $unit_id, int $parent_id, string $body, string $lang = '', bool $asked_private = false ): array {
		if ( $user_id <= 0 ) {
			DomainError::raise( ErrorCode::FORBIDDEN );
		}
		$body = self::clean( $body );
		if ( '' === $body ) {
			DomainError::raise( ErrorCode::INVALID, array( 'reason' => 'body' ) );
		}
		$lang   = Language::normalize( '' !== $lang ? $lang : Switcher::current() );
		$parent = null;
		if ( $parent_id > 0 ) {
			$parent = $this->get( $parent_id );
			if ( null === $parent || 0 !== (int) $parent['parent_id'] || ( $course_id > 0 && (int) $parent['course_id'] !== $course_id ) ) {
				DomainError::raise( ErrorCode::NOT_FOUND, array( 'reason' => 'question' ) );
			}
			$course_id = (int) $parent['course_id'];
			$unit_id   = (int) $parent['unit_id'];
		}
		$staff = CourseFacts::is_staff( $user_id, $course_id );
		if ( ! $staff && ! CourseFacts::is_learner( $user_id, $course_id ) ) {
			DomainError::raise( ErrorCode::FORBIDDEN, array( 'reason' => 'not_member' ) );
		}
		if ( ! CourseFacts::placed( $course_id, $unit_id ) ) {
			DomainError::raise( ErrorCode::NOT_FOUND, array( 'reason' => 'placement' ) );
		}
		$mode = CourseFacts::qa_mode( $course_id );
		if ( 1 === $mode ) {
			DomainError::raise( ErrorCode::FORBIDDEN, array( 'reason' => 'qa_off' ) );
		}
		if ( null !== $parent && ( ( DiscussionState::VISIBLE->value !== (int) $parent['state'] && ! $staff ) || ! $this->can_read( $user_id, $parent ) ) ) {
			DomainError::raise( ErrorCode::NOT_FOUND, array( 'reason' => 'question' ) );
		}
		if ( null === $parent && ! $staff && self::LED === $mode ) {
			DomainError::raise( ErrorCode::FORBIDDEN, array( 'reason' => 'instructor_led' ) );
		}
		if ( null === $parent && $asked_private && ! $staff && ! CourseFacts::qa_private( $course_id ) ) {
			DomainError::raise( ErrorCode::INVALID, array( 'reason' => 'private' ) );
		}
		$private = null !== $parent ? 1 === (int) ( $parent['is_private'] ?? 0 ) : $asked_private && ! $staff;
		if ( ! $staff ) {
			$this->check_rate( $user_id );
		}
		$hold = $private ? 2 : self::hold_mode( $mode );
		$id   = (int) Transaction::run(
			function () use ( $user_id, $course_id, $unit_id, $parent_id, $body, $lang, $staff, $hold, $private ): int {
			$now = Transaction::now();
				if ( $parent_id > 0 ) {
					Db::row( 'SELECT id FROM %i WHERE id = %d FOR UPDATE', Db::table( 'discussions' ), $parent_id );
				}
				$state = DiscussionState::VISIBLE;
				if ( ! $staff && ( 4 === $hold || ( 3 === $hold && ! $this->has_visible( $user_id, $course_id ) ) ) ) {
					$state = DiscussionState::PENDING;
				}
				Db::query(

						'INSERT INTO %i (course_id, unit_id, parent_id, user_id, body, state, is_answer, pinned, reply_count, lang, last_activity_at, created_at, updated_at, is_private) VALUES (%d, %d, %d, %d, %s, %d, 0, 0, 0, %s, %s, %s, %s, %d)',
						Db::table( 'discussions' ),
						$course_id,
						$unit_id,
						$parent_id,
						$user_id,
						$body,
						$state->value,
						$lang,
						$now,
						$now,
						$now,
						$private ? 1 : 0

				);
				$id = Db::insert_id();
				if ( $parent_id > 0 ) {
					self::recount( $parent_id );
				}
				return $id;
			}
		);
		if ( ! $staff ) {
			Notices::qa_posted( $course_id, $unit_id, $user_id );
		}
		return (array) $this->get( $id );
	}

	public function edit( int $actor_id, int $id, string $body ): array {
		$row    = $this->require_row( $id );
		$course = (int) $row['course_id'];
		$staff  = CourseFacts::is_staff( $actor_id, $course );
		$own    = (int) $row['user_id'] === $actor_id && $actor_id > 0 && in_array( (int) $row['state'], array( DiscussionState::VISIBLE->value, DiscussionState::PENDING->value ), true );
		if ( ! $own && ! $staff ) {
			DomainError::raise( ErrorCode::FORBIDDEN );
		}
		$mode = $staff ? 0 : CourseFacts::qa_mode( $course );
		if ( 1 === $mode ) {
			DomainError::raise( ErrorCode::FORBIDDEN, array( 'reason' => 'qa_off' ) );
		}
		$body = self::clean( $body );
		if ( '' === $body ) {
			DomainError::raise( ErrorCode::INVALID, array( 'reason' => 'body' ) );
		}
		$hold = 1 !== (int) ( $row['is_private'] ?? 0 ) && in_array( self::hold_mode( $mode ), array( 3, 4 ), true );
		global $wpdb;
		$held = (bool) Transaction::run(
			static function () use ( $id, $body, $hold, $wpdb ): bool {
				$table = Db::table( 'discussions' );
				$now   = Db::row( 'SELECT parent_id, state FROM %i WHERE id = %d FOR UPDATE', $table, $id );
				if ( null === $now ) {
					return false;
				}
				$held = $hold && DiscussionState::VISIBLE->value === (int) $now['state'];
				if ( $held ) {
					Db::query( 'UPDATE %i SET body = %s, state = %d, updated_at = %s WHERE id = %d', $table, $body, DiscussionState::PENDING->value, Transaction::now(), $id );
					if ( (int) $now['parent_id'] > 0 ) {
						self::recount( (int) $now['parent_id'] );
					}
				} else {
					Db::query( 'UPDATE %i SET body = %s, updated_at = %s WHERE id = %d', $table, $body, Transaction::now(), $id );
				}
				return $held;
			}
		);
		if ( $held ) {
			Notices::qa_posted( $course, (int) $row['unit_id'], $actor_id );
		}
		return (array) $this->get( $id );
	}

	public function moderate( int $actor_id, int $id, ?DiscussionState $state, ?bool $pinned = null, ?bool $is_answer = null ): array {
		$row = $this->require_row( $id );
		if ( ! CourseFacts::is_staff( $actor_id, (int) $row['course_id'] ) ) {
			DomainError::raise( ErrorCode::FORBIDDEN );
		}
		$question = 0 === (int) $row['parent_id'];
		if ( ( null !== $pinned && ! $question ) || ( null !== $is_answer && $question ) ) {
			DomainError::raise( ErrorCode::INVALID, array( 'reason' => $question ? 'is_answer' : 'pinned' ) );
		}
		$this->set( $id, $state, $pinned, $is_answer );
		return (array) $this->get( $id );
	}

	public function set( int $id, ?DiscussionState $state, ?bool $pinned = null, ?bool $is_answer = null ): void {
		Transaction::run(
			static function () use ( $id, $state, $pinned, $is_answer ): void {
				global $wpdb;
				$row = Db::row( 'SELECT id, parent_id FROM %i WHERE id = %d FOR UPDATE', Db::table( 'discussions' ), $id );
				if ( null === $row ) {
					return;
				}
				$sets = array();
				if ( null !== $state ) {
					$sets[] = SqlPart::of( 'state = %d', $state->value );
				}
				if ( null !== $pinned ) {
					$sets[] = SqlPart::of( 'pinned = %d', $pinned ? 1 : 0 );
				}
				if ( null !== $is_answer ) {
					$sets[] = SqlPart::of( 'is_answer = %d', $is_answer ? 1 : 0 );
				}
				if ( array() === $sets ) {
					return;
				}
				$sets[] = SqlPart::of( 'updated_at = %s', Transaction::now() );
				Db::query( SqlPart::of( 'UPDATE %i SET ', Db::table( 'discussions' ) )->add( SqlPart::join( ', ', $sets ) )->add( SqlPart::of( ' WHERE id = %d', $id ) ) );
				if ( (int) $row['parent_id'] > 0 && null !== $state ) {
					self::recount( (int) $row['parent_id'] );
				}
			}
		);
	}

	public function get( int $id ): ?array {
		return $id > 0 ? Db::row( 'SELECT * FROM %i WHERE id = %d', Db::table( 'discussions' ), $id ) : null;
	}

	public function can_read( int $viewer_id, array $row ): bool {
		$course = (int) $row['course_id'];
		if ( CourseFacts::is_staff( $viewer_id, $course ) ) {
			return true;
		}
		if ( 1 === CourseFacts::qa_mode( $course ) || ! CourseFacts::is_learner( $viewer_id, $course ) ) {
			return false;
		}
		if ( 1 === (int) ( $row['is_private'] ?? 0 ) ) {
			$question = (int) $row['parent_id'] > 0 ? $this->get( (int) $row['parent_id'] ) : $row;
			if ( null === $question || (int) $question['user_id'] !== $viewer_id ) {
				return false;
			}
		}
		$state = (int) $row['state'];
		return DiscussionState::VISIBLE->value === $state || ( DiscussionState::PENDING->value === $state && (int) $row['user_id'] === $viewer_id );
	}

	public function questions( int $viewer_id, int $course_id, int $unit_id, int $page = 1, int $per_page = 20, ?DiscussionState $state = null ): array {
		global $wpdb;
		$per_page = max( 1, min( 100, $per_page ) );
		$where    = SqlPart::of( 'course_id = %d AND parent_id = 0', $course_id );
		if ( $unit_id > 0 ) {
			$where = $where->add( SqlPart::of( ' AND unit_id = %d', $unit_id ) );
		}
		$where = $where->add( $this->state_filter( $viewer_id, $course_id, $state ) );
		if ( ! CourseFacts::is_staff( $viewer_id, $course_id ) ) {
			$where = $where->add( SqlPart::of( ' AND ( is_private = 0 OR user_id = %d )', $viewer_id ) );
		}
		$table = Db::table( 'discussions' );
		$total = (int) Db::value( SqlPart::of( 'SELECT COUNT(*) FROM %i WHERE ', $table )->add( $where ) );
		$rows   = Db::rows( SqlPart::of( 'SELECT * FROM %i WHERE ', $table )->add( $where )->add( SqlPart::of( ' ORDER BY pinned DESC, last_activity_at DESC, id DESC LIMIT %d OFFSET %d', $per_page, ( max( 1, $page ) - 1 ) * $per_page ) ) );
		return array(
			'items' => $this->shape( $rows, $viewer_id ),
			'total' => $total,
		);
	}

	public function thread( int $viewer_id, int $id ): ?array {
		$row = $this->get( $id );
		if ( null !== $row && (int) $row['parent_id'] > 0 ) {
			$row = $this->get( (int) $row['parent_id'] );
		}
		if ( null === $row || ! $this->can_read( $viewer_id, $row ) ) {
			return null;
		}
		global $wpdb;
		$where   = SqlPart::of( 'parent_id = %d', (int) $row['id'] )->add( $this->state_filter( $viewer_id, (int) $row['course_id'], null ) );
		$replies = Db::rows( SqlPart::of( 'SELECT * FROM %i WHERE ', Db::table( 'discussions' ) )->add( $where )->add( ' ORDER BY created_at, id LIMIT 500' ) );
		$shaped  = $this->shape( array_merge( array( $row ), $replies ), $viewer_id );
		return array(
			'question' => $shaped[0],
			'replies'  => array_slice( $shaped, 1 ),
		);
	}

	public function shape( array $rows, int $viewer_id ): array {
		$users = array_values( array_unique( array_filter( array_map( static fn( array $r ): int => (int) $r['user_id'], $rows ) ) ) );
		if ( array() !== $users ) {
			cache_users( $users );
		}
		$out = array();
		foreach ( $rows as $r ) {
			$user  = (int) $r['user_id'];
			$data  = $user > 0 ? get_userdata( $user ) : false;
			$state = DiscussionState::tryFrom( (int) $r['state'] ) ?? DiscussionState::HIDDEN;
			$out[] = array(
				'id'               => (int) $r['id'],
				'course_id'        => (int) $r['course_id'],
				'unit_id'          => (int) $r['unit_id'],
				'parent_id'        => (int) $r['parent_id'],
				'user_id'          => $user,
				'author'           => $data instanceof \WP_User ? (string) $data->display_name : '',
				'body'             => (string) $r['body'],
				'state'            => $state->slug(),
				'is_answer'        => 1 === (int) $r['is_answer'],
				'pinned'           => 1 === (int) $r['pinned'],
				'private'          => 1 === (int) ( $r['is_private'] ?? 0 ),
				'reply_count'      => (int) $r['reply_count'],
				'lang'             => (string) $r['lang'],
				'last_activity_at' => (string) $r['last_activity_at'],
				'created_at'       => (string) $r['created_at'],
				'updated_at'       => (string) $r['updated_at'],
				'own'              => $user > 0 && $user === $viewer_id,
			);
		}
		return $out;
	}

	public function delete_course( int $course_id ): int {
		return $this->delete_where( 'course_id', $course_id );
	}

	public function delete_unit( int $unit_id ): int {
		return $this->delete_where( 'unit_id', $unit_id );
	}

	public function delete_user( int $user_id ): int {
		if ( $user_id <= 0 ) {
			return 0;
		}
		return (int) Transaction::run(
			static function () use ( $user_id ): int {
			$table   = Db::table( 'discussions' );
				$parents = array_map( 'intval', Db::col( 'SELECT DISTINCT parent_id FROM %i WHERE user_id = %d AND parent_id > 0', $table, $user_id ) );
				$own     = array_map( 'intval', Db::col( 'SELECT id FROM %i WHERE user_id = %d AND parent_id = 0', $table, $user_id ) );
				$n       = 0;
				foreach ( array_chunk( $own, 500 ) as $chunk ) {
					$n += Db::query( 'DELETE FROM %i WHERE parent_id IN (' . implode( ',', array_fill( 0, count( $chunk ), '%d' ) ) . ')', array_merge( array( $table ), $chunk ) );
				}
				$n += Db::query( 'DELETE FROM %i WHERE user_id = %d', $table, $user_id );
				foreach ( array_diff( $parents, $own ) as $parent ) {
					self::recount( $parent );
				}
				return $n;
			}
		);
	}

	public static function recount( int $question_id ): void {
		$table = Db::table( 'discussions' );
		Db::query(

				'UPDATE %i q SET q.reply_count = ( SELECT x.n FROM ( SELECT LEAST( COUNT(*), 65535 ) AS n FROM %i r WHERE r.parent_id = %d AND r.state = %d ) x ), q.last_activity_at = GREATEST( q.created_at, COALESCE( ( SELECT y.m FROM ( SELECT MAX( r2.created_at ) AS m FROM %i r2 WHERE r2.parent_id = %d AND r2.state = %d ) y ), q.created_at ) ) WHERE q.id = %d',
				$table,
				$table,
				$question_id,
				DiscussionState::VISIBLE->value,
				$table,
				$question_id,
				DiscussionState::VISIBLE->value,
				$question_id

		);
	}

	private function check_rate( int $user_id ): void {
		$limit = (int) CommunitySettings::get( 'qa_rate_limit' );
		if ( $limit <= 0 ) {
			return;
		}
		$since = gmdate( 'Y-m-d H:i:s', \RoosterLMS\Core\Clock::timestamp() - HOUR_IN_SECONDS );
		$n     = (int) Db::value( 'SELECT COUNT(*) FROM %i WHERE user_id = %d AND created_at > %s', Db::table( 'discussions' ), $user_id, $since );
		if ( $n >= $limit ) {
			DomainError::raise( ErrorCode::INVALID, array( 'reason' => 'rate_limit' ) );
		}
	}

	public static function hold_mode( int $mode ): int {
		if ( self::LED !== $mode ) {
			return $mode;
		}
		$site = (int) CommunitySettings::get( 'qa_mode' );
		return 3 === $site || 4 === $site ? $site : 2;
	}

	private function has_visible( int $user_id, int $course_id ): bool {
		return null !== Db::value( 'SELECT 1 FROM %i WHERE user_id = %d AND course_id = %d AND state = %d LIMIT 1', Db::table( 'discussions' ), $user_id, $course_id, DiscussionState::VISIBLE->value );
	}

	private function state_filter( int $viewer_id, int $course_id, ?DiscussionState $state ): SqlPart {
		global $wpdb;
		if ( CourseFacts::is_staff( $viewer_id, $course_id ) ) {
			return null !== $state ? SqlPart::of( ' AND state = %d', $state->value ) : SqlPart::of( ' AND state <> %d', DiscussionState::TRASHED->value );
		}
		if ( 1 === CourseFacts::qa_mode( $course_id ) ) {
			return SqlPart::of( ' AND 1 = 0' );
		}
		return SqlPart::of( ' AND ( state = %d OR ( state = %d AND user_id = %d ) )', DiscussionState::VISIBLE->value, DiscussionState::PENDING->value, $viewer_id );
	}

	private function require_row( int $id ): array {
		$row = $this->get( $id );
		if ( null === $row ) {
			DomainError::raise( ErrorCode::NOT_FOUND );
		}
		return $row;
	}

	private function delete_where( string $column, int $id ): int {
		if ( $id <= 0 ) {
			return 0;
		}
		$n = 0;
		do {
			$gone = Db::query( 'DELETE FROM %i WHERE %i = %d LIMIT 1000', Db::table( 'discussions' ), $column, $id );
			$n   += $gone;
		} while ( $gone >= 1000 );
		return $n;
	}
}