1 files changed, 224 insertions, 0 deletions
diff --git a/backend/wsm.go b/backend/wsm.go
new file mode 100644
index 0000000..5f271ff
--- /dev/null
+++ b/backend/wsm.go
@@ -0,0 +1,224 @@
+/*
+ * WebSocket message handlers
+ *
+ * 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"
+	"errors"
+	"fmt"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/coder/websocket"
+	"github.com/jackc/pgx/v5"
+	"github.com/jackc/pgx/v5/pgconn"
+)
+
+func messageHello(ctx context.Context, c *websocket.Conn, reportError reportErrorT, mar []string, userID string, session string) error {
+	_, _ = mar, session
+
+	select {
+	case <-ctx.Done():
+		return fmt.Errorf("context done when handling hello: %w", ctx.Err())
+	default:
+	}
+
+	rows, err := db.Query(
+		ctx,
+		"SELECT courseid FROM choices WHERE userid = $1",
+		userID,
+	)
+	if err != nil {
+		return reportError("error fetching choices")
+	}
+	courseIDs, err := pgx.CollectRows(rows, pgx.RowTo[string])
+	if err != nil {
+		return reportError("error collecting choices")
+	}
+
+	err = writeText(ctx, c, "HI :"+strings.Join(courseIDs, ","))
+	if err != nil {
+		return fmt.Errorf("error replying to HELLO: %w", err)
+	}
+
+	return nil
+}
+
+func messageChooseCourse(ctx context.Context, c *websocket.Conn, reportError reportErrorT, mar []string, userID string, session string, userCourseGroups *userCourseGroupsT) error {
+	_ = session
+
+	select {
+	case <-ctx.Done():
+		return fmt.Errorf("context done when handling choose: %w", ctx.Err())
+	default:
+	}
+
+	if len(mar) != 2 {
+		return reportError("Invalid number of arguments for Y")
+	}
+	_courseID, err := strconv.ParseInt(mar[1], 10, strconv.IntSize)
+	if err != nil {
+		return reportError("Course ID must be an integer")
+	}
+	courseID := int(_courseID)
+	course := getCourseByID(courseID)
+
+	if course == nil {
+		return reportError("nil course")
+	}
+
+	err = func() (returnedError error) { /* Named returns so I could modify them in defer */
+		tx, err := db.Begin(ctx)
+		if err != nil {
+			return reportError("Database error while beginning transaction")
+		}
+		defer func() {
+			err := tx.Rollback(ctx)
+			if err != nil && (!errors.Is(err, pgx.ErrTxClosed)) {
+				returnedError = reportError("Database error while rolling back transaction in defer block")
+				return
+			}
+		}()
+
+		_, err = tx.Exec(
+			ctx,
+			"INSERT INTO choices (seltime, userid, courseid) VALUES ($1, $2, $3)",
+			time.Now().UnixMicro(),
+			userID,
+			courseID,
+		)
+		if err != nil {
+			var pgErr *pgconn.PgError
+			if errors.As(err, &pgErr) && pgErr.Code == pgErrUniqueViolation {
+				err := writeText(ctx, c, "Y "+mar[1])
+				if err != nil {
+					return fmt.Errorf("error reaffirming course choice: %w", err)
+				}
+				return nil
+			}
+			return reportError("Database error while inserting course choice")
+		}
+
+		ok := func() bool {
+			course.SelectedLock.Lock()
+			defer course.SelectedLock.Unlock()
+			if course.Selected < course.Max {
+				course.Selected++
+				return true
+			}
+			return false
+		}()
+
+		if ok {
+			go propagateSelectedUpdate(courseID)
+			err := tx.Commit(ctx)
+			if err != nil {
+				go course.decrementSelectedAndPropagate()
+				return reportError("Database error while committing transaction")
+			}
+			var thisCourseGroup courseGroupT
+			func() {
+				coursesLock.RLock()
+				defer coursesLock.RUnlock()
+				thisCourseGroup = courses[courseID].Group
+			}()
+			if (*userCourseGroups)[thisCourseGroup] {
+				go course.decrementSelectedAndPropagate()
+				return reportError("inconsistent user course groups")
+			}
+			(*userCourseGroups)[thisCourseGroup] = true
+			err = writeText(ctx, c, "Y "+mar[1])
+			if err != nil {
+				return fmt.Errorf("error affirming course choice: %w", err)
+			}
+		} else {
+			err := tx.Rollback(ctx)
+			if err != nil {
+				return reportError("Database error while rolling back transaction due to course limit")
+			}
+			err = writeText(ctx, c, "R "+mar[1]+" :Full")
+			if err != nil {
+				return fmt.Errorf("error rejecting course choice: %w", err)
+			}
+		}
+		return nil
+	}()
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+func messageUnchooseCourse(ctx context.Context, c *websocket.Conn, reportError reportErrorT, mar []string, userID string, session string, userCourseGroups *userCourseGroupsT) error {
+	_ = session
+
+	select {
+	case <-ctx.Done():
+		return fmt.Errorf("context done when handling unchoose: %w", 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 := getCourseByID(courseID)
+
+	if course == nil {
+		return reportError("nil course")
+	}
+
+	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 {
+		go course.decrementSelectedAndPropagate()
+		var thisCourseGroup courseGroupT
+		func() {
+			coursesLock.RLock()
+			defer coursesLock.RUnlock()
+			thisCourseGroup = courses[courseID].Group
+		}()
+		if !(*userCourseGroups)[thisCourseGroup] {
+			return reportError("inconsistent user course groups")
+		}
+		(*userCourseGroups)[thisCourseGroup] = false
+	}
+
+	err = writeText(ctx, c, "N "+mar[1])
+	if err != nil {
+		return fmt.Errorf("error replying that course has been deselected: %w", err)
+	}
+
+	return nil
+}