1 files changed, 136 insertions, 0 deletions
diff --git a/wsmsg_unchoose.go b/wsmsg_unchoose.go
new file mode 100644
index 0000000..07cb18b
--- /dev/null
+++ b/wsmsg_unchoose.go
@@ -0,0 +1,136 @@
+/*
+ * Handle the "N" message for unchoosing a course
+ *
+ * Copyright (C) 2024  Runxi Yu <https://runxiyu.org>
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero 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 Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package main
+
+import (
+	"context"
+	"fmt"
+	"strconv"
+	"sync/atomic"
+
+	"github.com/coder/websocket"
+)
+
+func messageUnchooseCourse(
+	ctx context.Context,
+	c *websocket.Conn,
+	reportError reportErrorT,
+	mar []string,
+	userID string,
+	session string,
+	userCourseGroups *userCourseGroupsT,
+) error {
+	_ = session
+
+	if atomic.LoadUint32(&state) != 2 {
+		err := writeText(ctx, c, "E :Course selections are not open")
+		if err != nil {
+			return fmt.Errorf(
+				"%w: %w",
+				errCannotSend,
+				err,
+			)
+		}
+		return nil
+	}
+
+	select {
+	case <-ctx.Done():
+		return fmt.Errorf(
+			"%w: %w",
+			errContextCancelled,
+			ctx.Err(),
+		)
+	default:
+	}
+
+	if len(mar) != 2 {
+		return reportError("Invalid number of arguments for N")
+	}
+	_courseID, err := strconv.ParseInt(mar[1], 10, strconv.IntSize)
+	if err != nil {
+		return reportError("Course ID must be an integer")
+	}
+	courseID := int(_courseID)
+
+	_course, ok := courses.Load(courseID)
+	if !ok {
+		return reportError("no such course")
+	}
+	course, ok := _course.(*courseT)
+	if !ok {
+		panic("courses map has non-\"*courseT\" items")
+	}
+	if course == nil {
+		return reportError("couse is nil")
+	}
+
+	ct, err := db.Exec(
+		ctx,
+		"DELETE FROM choices WHERE userid = $1 AND courseid = $2",
+		userID,
+		courseID,
+	)
+	if err != nil {
+		return reportError(
+			"Database error while deleting course choice",
+		)
+	}
+
+	if ct.RowsAffected() != 0 {
+		err := course.decrementSelectedAndPropagate(ctx, c)
+		if err != nil {
+			return fmt.Errorf(
+				"%w: %w",
+				errCannotSend,
+				err,
+			)
+		}
+
+		_course, ok := courses.Load(courseID)
+		if !ok {
+			return reportError("no such course")
+		}
+		course, ok := _course.(*courseT)
+		if !ok {
+			panic("courses map has non-\"*courseT\" items")
+		}
+		if course == nil {
+			return reportError("couse is nil")
+		}
+
+		if _, ok := (*userCourseGroups)[course.Group]; !ok {
+			return reportError("inconsistent user course groups")
+		}
+		delete(*userCourseGroups, course.Group)
+	}
+
+	err = writeText(ctx, c, "N "+mar[1])
+	if err != nil {
+		return fmt.Errorf(
+			"%w: %w",
+			errCannotSend,
+			err,
+		)
+	}
+
+	return nil
+}