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/*
* Course data structures and locking
*
* Copyright (C) 2024 Runxi Yu <https://runxiyu.org>
* SPDX-License-Identifier: BSD-2-Clause
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS "AS IS" AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
package main
import (
"context"
"fmt"
"sync"
)
type coursetypeT string
type courseT struct {
ID int
Selected int
SelectedLock sync.RWMutex
Max int
Title string
Type coursetypeT
Teacher string
Location string
}
/*
* const (
* sport coursetypeT = "Sport"
* enrichment coursetypeT = "Enrichment"
* culture coursetypeT = "Culture"
* )
*/
/*
* The courses are simply stored in a map indexed by the course ID, although
* the course struct itself also contains an ID field. A lock is embedded
* inside the struct; we use a lock here instead of a pointer to a lock as
* it would be easy to forget to initialize the lock when creating the
* struct. However, this means that the struct could not be copied (though
* this should only ever happen during creation anyways), therefore we use a
* pointer to the struct as the value of the map, instead of the struct itself.
*/
var courses map[int](*courseT)
/*
* This RWMutex is only for massive modifications of the course struct, since
* locking it on every write would be inefficient; in normal operation the only
* write that could occur to the courses struct is changing the Selected
* number, which should be handled with courseT.SelectedLock.
*/
var coursesLock sync.RWMutex
/*
* Read course information from the database. This should be called during
* setup. Failure to do so before accessing course information may lead to
* a null pointer dereference.
*/
func setupCourses() error {
coursesLock.Lock()
defer coursesLock.Unlock()
courses = make(map[int](*courseT))
rows, err := db.Query(
context.Background(),
"SELECT id, nmax, title, ctype, teacher, location FROM courses",
)
if err != nil {
return fmt.Errorf("error fetching courses: %w", err)
}
for {
if !rows.Next() {
err := rows.Err()
if err != nil {
return fmt.Errorf("error fetching courses: %w", err)
}
break
}
currentCourse := courseT{} //exhaustruct:ignore
err = rows.Scan(
¤tCourse.ID,
¤tCourse.Max,
¤tCourse.Title,
¤tCourse.Type,
¤tCourse.Teacher,
¤tCourse.Location,
)
if err != nil {
return fmt.Errorf("error fetching courses: %w", err)
}
courses[currentCourse.ID] = ¤tCourse
}
/* TODO: Populate currentCourse.Selected from the database */
return nil
}
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