teacher-tools/api/source/api_modules/classroom_compliance.d

module api_modules.classroom_compliance;

import handy_httpd;
import handy_httpd.handlers.path_handler;
import d2sqlite3;
import slf4d;
import std.typecons : Nullable;
import std.datetime;
import std.json;
import std.algorithm;
import std.array;

import db;
import data_utils;
import api_modules.auth : User, getUserOrThrow;

struct ClassroomComplianceClass {
    const ulong id;
    const ushort number;
    const string schoolYear;
    const ulong userId;
}

struct ClassroomComplianceStudent {
    const ulong id;
    const string name;
    const ulong classId;
    const ushort deskNumber;
    const bool removed;
}

struct ClassroomComplianceEntry {
    const ulong id;
    const ulong classId;
    const ulong studentId;
    const string date;
    const ulong createdAt;
    const bool absent;
    const string comment;
}

struct ClassroomComplianceEntryPhone {
    const ulong entryId;
    const bool compliant;
}

struct ClassroomComplianceEntryBehavior {
    const ulong entryId;
    const ubyte rating;
}

void registerApiEndpoints(PathHandler handler) {
    const ROOT_PATH = "/api/classroom-compliance";
    
    handler.addMapping(Method.POST, ROOT_PATH ~ "/classes", &createClass);
    handler.addMapping(Method.GET, ROOT_PATH ~ "/classes", &getClasses);
    const CLASS_PATH = ROOT_PATH ~ "/classes/:classId:ulong";
    handler.addMapping(Method.GET, CLASS_PATH, &getClass);
    handler.addMapping(Method.DELETE, CLASS_PATH, &deleteClass);

    handler.addMapping(Method.POST, CLASS_PATH ~ "/students", &createStudent);
    handler.addMapping(Method.GET, CLASS_PATH ~ "/students", &getStudents);
    const STUDENT_PATH = CLASS_PATH ~ "/students/:studentId:ulong";
    handler.addMapping(Method.GET, STUDENT_PATH, &getStudent);
    handler.addMapping(Method.PUT, STUDENT_PATH, &updateStudent);
    handler.addMapping(Method.DELETE, STUDENT_PATH, &deleteStudent);
    handler.addMapping(Method.PUT, STUDENT_PATH ~ "/class", &moveStudentToOtherClass);
    handler.addMapping(Method.GET, STUDENT_PATH ~ "/entries", &getStudentEntries);
    handler.addMapping(Method.GET, STUDENT_PATH ~ "/overview", &getStudentOverview);

    handler.addMapping(Method.GET, CLASS_PATH ~ "/entries", &getEntries);
    handler.addMapping(Method.POST, CLASS_PATH ~ "/entries", &saveEntries);
}

void createClass(ref HttpRequestContext ctx) {
    auto db = getDb();
    User user = getUserOrThrow(ctx, db);
    struct ClassPayload {
        ushort number;
        string schoolYear;
    }
    auto payload = readJsonPayload!(ClassPayload)(ctx);
    const bool classNumberExists = canFind(
        db,
        "SELECT id FROM classroom_compliance_class WHERE number = ? AND school_year = ? AND user_id = ?",
        payload.number,
        payload.schoolYear,
        user.id
    );
    if (classNumberExists) {
        ctx.response.status = HttpStatus.BAD_REQUEST;
        ctx.response.writeBodyString("There is already a class with this number, for the same school year.");
        return;
    }
    auto stmt = db.prepare("INSERT INTO classroom_compliance_class (number, school_year, user_id) VALUES (?, ?, ?)");
    stmt.bindAll(payload.number, payload.schoolYear, user.id);
    stmt.execute();
    ulong classId = db.lastInsertRowid();
    auto newClass = findOne!(ClassroomComplianceClass)(
        db,
        "SELECT * FROM classroom_compliance_class WHERE id = ? AND user_id = ?",
        classId,
        user.id
    ).orElseThrow();
    writeJsonBody(ctx, newClass);
}

void getClasses(ref HttpRequestContext ctx) {
    auto db = getDb();
    User user = getUserOrThrow(ctx, db);
    auto classes = findAll!(ClassroomComplianceClass)(
        db,
        "SELECT * FROM classroom_compliance_class WHERE user_id = ? ORDER BY school_year DESC, number ASC",
        user.id
    );
    writeJsonBody(ctx, classes);
}

void getClass(ref HttpRequestContext ctx) {
    auto db = getDb();
    User user = getUserOrThrow(ctx, db);
    auto cls = getClassOrThrow(ctx, db, user);
    writeJsonBody(ctx, cls);
}

void deleteClass(ref HttpRequestContext ctx) {
    auto db = getDb();
    User user = getUserOrThrow(ctx, db);
    auto cls = getClassOrThrow(ctx, db, user);
    db.execute("DELETE FROM classroom_compliance_class WHERE id = ? AND user_id = ?", cls.id, user.id);
}

ClassroomComplianceClass getClassOrThrow(ref HttpRequestContext ctx, ref Database db, in User user) {
    ulong classId = ctx.request.getPathParamAs!ulong("classId");
    return findOne!(ClassroomComplianceClass)(
        db,
        "SELECT * FROM classroom_compliance_class WHERE user_id = ? AND id = ?",
        user.id,
        classId
    ).orElseThrow(() => new HttpStatusException(HttpStatus.NOT_FOUND));
}

void createStudent(ref HttpRequestContext ctx) {
    auto db = getDb();
    User user = getUserOrThrow(ctx, db);
    auto cls = getClassOrThrow(ctx, db, user);
    struct StudentPayload {
        string name;
        ushort deskNumber;
        bool removed;
    }
    auto payload = readJsonPayload!(StudentPayload)(ctx);
    bool studentExists = canFind(
        db,
        "SELECT id FROM classroom_compliance_student WHERE name = ? AND class_id = ?",
        payload.name,
        cls.id
    );
    if (studentExists) {
        ctx.response.status = HttpStatus.BAD_REQUEST;
        ctx.response.writeBodyString("A student with that name already exists in this class.");
        return;
    }
    bool deskAlreadyOccupied = payload.deskNumber != 0 && canFind(
        db,
        "SELECT id FROM classroom_compliance_student WHERE class_id = ? AND desk_number = ?",
        cls.id,
        payload.deskNumber
    );
    if (deskAlreadyOccupied) {
        ctx.response.status = HttpStatus.BAD_REQUEST;
        ctx.response.writeBodyString("There is already a student assigned to that desk number.");
    }
    db.execute(
        "INSERT INTO classroom_compliance_student (name, class_id, desk_number, removed) VALUES (?, ?, ?, ?)",
        payload.name, cls.id, payload.deskNumber, payload.removed
    );
    ulong studentId = db.lastInsertRowid();
    auto student = findOne!(ClassroomComplianceStudent)(
        db,
        "SELECT * FROM classroom_compliance_student WHERE id = ?",
        studentId
    ).orElseThrow();
    writeJsonBody(ctx, student);
}

void getStudents(ref HttpRequestContext ctx) {
    auto db = getDb();
    User user = getUserOrThrow(ctx, db);
    auto cls = getClassOrThrow(ctx, db, user);
    auto students = findAll!(ClassroomComplianceStudent)(
        db,
        "SELECT * FROM classroom_compliance_student WHERE class_id = ? ORDER BY name ASC",
        cls.id
    );
    writeJsonBody(ctx, students);
}

void getStudent(ref HttpRequestContext ctx) {
    auto db = getDb();
    User user = getUserOrThrow(ctx, db);
    auto student = getStudentOrThrow(ctx, db, user);
    writeJsonBody(ctx, student);
}

void updateStudent(ref HttpRequestContext ctx) {
    auto db = getDb();
    User user = getUserOrThrow(ctx, db);
    auto student = getStudentOrThrow(ctx, db, user);
    struct StudentUpdatePayload {
        string name;
        ushort deskNumber;
        bool removed;
    }
    auto payload = readJsonPayload!(StudentUpdatePayload)(ctx);
    // If there is nothing to update, quit.
    if (
        payload.name == student.name
        && payload.deskNumber == student.deskNumber
        && payload.removed == student.removed
    ) return;
    // Check that the new name doesn't already exist.
    bool newNameExists = payload.name != student.name && canFind(
        db,
        "SELECT id FROM classroom_compliance_student WHERE name = ? AND class_id = ?",
        payload.name,
        student.classId
    );
    if (newNameExists) {
        ctx.response.status = HttpStatus.BAD_REQUEST;
        ctx.response.writeBodyString("A student with that name already exists in this class.");
        return;
    }
    // Check that if a new desk number is assigned, that it's not already assigned to anyone else.
    bool newDeskOccupied = payload.deskNumber != 0 && payload.deskNumber != student.deskNumber && canFind(
        db,
        "SELECT id FROM classroom_compliance_student WHERE class_id = ? AND desk_number = ?",
        student.classId,
        payload.deskNumber
    );
    if (newDeskOccupied) {
        ctx.response.status = HttpStatus.BAD_REQUEST;
        ctx.response.writeBodyString("That desk is already assigned to another student.");
        return;
    }
    db.execute(
        "UPDATE classroom_compliance_student SET name = ?, desk_number = ?, removed = ? WHERE id = ?",
        payload.name,
        payload.deskNumber,
        payload.removed,
        student.id
    );
    auto updatedStudent = findOne!(ClassroomComplianceStudent)(
        db,
        "SELECT * FROM classroom_compliance_student WHERE id = ?",
        student.id
    ).orElseThrow();
    writeJsonBody(ctx, updatedStudent);
}

void deleteStudent(ref HttpRequestContext ctx) {
    auto db = getDb();
    User user = getUserOrThrow(ctx, db);
    auto student = getStudentOrThrow(ctx, db, user);
    db.execute(
        "DELETE FROM classroom_compliance_student WHERE id = ? AND class_id = ?",
        student.id,
        student.classId
    );
}

ClassroomComplianceStudent getStudentOrThrow(ref HttpRequestContext ctx, ref Database db, in User user) {
    ulong classId = ctx.request.getPathParamAs!ulong("classId");
    ulong studentId = ctx.request.getPathParamAs!ulong("studentId");
    string query = "
    SELECT s.*
    FROM classroom_compliance_student s
    LEFT JOIN classroom_compliance_class c ON s.class_id = c.id
    WHERE s.id = ? AND s.class_id = ? AND c.user_id = ?
    ";
    return findOne!(ClassroomComplianceStudent)(
        db,
        query,
        studentId,
        classId,
        user.id
    ).orElseThrow(() => new HttpStatusException(HttpStatus.NOT_FOUND));
}

void getEntries(ref HttpRequestContext ctx) {
    auto db = getDb();
    User user = getUserOrThrow(ctx, db);
    auto cls = getClassOrThrow(ctx, db, user);
    // Default to getting entries from the last 5 days.
    SysTime now = Clock.currTime();
    Date toDate = Date(now.year, now.month, now.day);
    Date fromDate = toDate - days(4);
    if (ctx.request.queryParams.contains("to")) {
        try {
            toDate = Date.fromISOExtString(ctx.request.queryParams.getFirst("to").orElse(""));
        } catch (DateTimeException e) {
            ctx.response.status = HttpStatus.BAD_REQUEST;
            ctx.response.writeBodyString("Invalid \"to\" date.");
            return;
        }
    }
    if (ctx.request.queryParams.contains("from")) {
        try {
            fromDate = Date.fromISOExtString(ctx.request.queryParams.getFirst("from").orElse(""));
        } catch (DateTimeException e) {
            ctx.response.status = HttpStatus.BAD_REQUEST;
            ctx.response.writeBodyString("Invalid \"from\" date.");
            return;
        }
    }
    if (fromDate > toDate) {
        ctx.response.status = HttpStatus.BAD_REQUEST;
        ctx.response.writeBodyString("Invalid date range. From-date must be less than or equal to the to-date.");
        return;
    }
    if (toDate - fromDate > days(10)) {
        ctx.response.status = HttpStatus.BAD_REQUEST;
        ctx.response.writeBodyString("Date range is too big. Only ranges of 10 days or less are allowed.");
        return;
    }
    infoF!"Getting entries from %s to %s"(fromDate.toISOExtString(), toDate.toISOExtString());

    // First prepare a list of all students, including ones which don't have any entries.
    ClassroomComplianceStudent[] students = findAll!(ClassroomComplianceStudent)(
        db,
        "SELECT * FROM classroom_compliance_student WHERE class_id = ? ORDER BY name ASC",
        cls.id
    );
    JSONValue[] studentObjects = students.map!((s) {
        JSONValue obj = JSONValue.emptyObject;
        obj.object["id"] = JSONValue(s.id);
        obj.object["deskNumber"] = JSONValue(s.deskNumber);
        obj.object["name"] = JSONValue(s.name);
        obj.object["removed"] = JSONValue(s.removed);
        obj.object["entries"] = JSONValue.emptyObject;
        obj.object["score"] = JSONValue(null);
        return obj;
    }).array;

    const entriesQuery = "
    SELECT
        entry.id,
        entry.date,
        entry.created_at,
        entry.absent,
        entry.comment,
        student.id,
        student.name,
        student.desk_number,
        student.removed,
        phone.compliant,
        behavior.rating
    FROM classroom_compliance_entry entry
    LEFT JOIN classroom_compliance_entry_phone phone
        ON phone.entry_id = entry.id
    LEFT JOIN classroom_compliance_entry_behavior behavior
        ON behavior.entry_id = entry.id
    LEFT JOIN classroom_compliance_student student
        ON student.id = entry.student_id
    WHERE
        entry.class_id = ?
        AND entry.date >= ?
        AND entry.date <= ?
    ORDER BY
        student.id ASC,
        entry.date ASC
    ";
    ResultRange entriesResult = db.execute(entriesQuery, cls.id, fromDate.toISOExtString(), toDate.toISOExtString());
    // Serialize the results into a custom-formatted response object.
    foreach (row; entriesResult) {
        JSONValue entry = JSONValue.emptyObject;
        entry.object["id"] = JSONValue(row.peek!ulong(0));
        entry.object["date"] = JSONValue(row.peek!string(1));
        entry.object["createdAt"] = JSONValue(row.peek!ulong(2));
        entry.object["absent"] = JSONValue(row.peek!bool(3));
        entry.object["comment"] = JSONValue(row.peek!string(4));

        JSONValue phone = JSONValue(null);
        JSONValue behavior = JSONValue(null);
        if (!entry.object["absent"].boolean()) {
            phone = JSONValue.emptyObject;
            phone.object["compliant"] = JSONValue(row.peek!bool(9));
            behavior = JSONValue.emptyObject;
            behavior.object["rating"] = JSONValue(row.peek!ubyte(10));
        }
        entry.object["phone"] = phone;
        entry.object["behavior"] = behavior;
        string dateStr = entry.object["date"].str();

        // Find the student object this entry belongs to, then add it to their list.
        ulong studentId = row.peek!ulong(5);
        bool studentFound = false;
        foreach (idx, studentObj; studentObjects) {
            if (studentObj.object["id"].uinteger == studentId) {
                studentObj.object["entries"].object[dateStr] = entry;
                studentFound = true;
                break;
            }
        }
        if (!studentFound) {
            // The student isn't in our list of original students from the class, so it's a student who's moved to another.
            JSONValue obj = JSONValue.emptyObject;
            obj.object["id"] = JSONValue(studentId);
            obj.object["deskNumber"] = JSONValue(row.peek!ushort(7));
            obj.object["name"] = JSONValue(row.peek!string(6));
            obj.object["removed"] = JSONValue(row.peek!bool(8));
            obj.object["entries"] = JSONValue.emptyObject;
            obj.object["entries"].object[dateStr] = entry;
            obj.object["score"] = JSONValue(null);
            studentObjects ~= obj;
        }
    }

    // Find scores for each student for this timeframe.
    Optional!double[ulong] scores = getScores(db, cls.id, fromDate, toDate);
    foreach (studentId, score; scores) {
        JSONValue scoreValue = score.isNull ? JSONValue(null) : JSONValue(score.value);
        bool studentFound = false;
        foreach (studentObj; studentObjects) {
            if (studentObj.object["id"].uinteger == studentId) {
                studentObj.object["score"] = scoreValue;
                studentFound = true;
                break;
            }
        }
        if (!studentFound) {
            throw new Exception("Failed to find student.");
        }
    }

    JSONValue response = JSONValue.emptyObject;
    // Provide the list of dates that we're providing data for, to make it easier for the frontend.
    response.object["dates"] = JSONValue.emptyArray;
    
    // Also fill in "null" for any students that don't have an entry on one of these days.
    Date d = fromDate;
    while (d <= toDate) {
        string dateStr = d.toISOExtString();
        response.object["dates"].array ~= JSONValue(dateStr);
        foreach (studentObj; studentObjects) {
            if (dateStr !in studentObj.object["entries"].object) {
                studentObj.object["entries"].object[dateStr] = JSONValue(null);
            }
        }
        d += days(1);
    }
    response.object["students"] = JSONValue(studentObjects);

    string jsonStr = response.toJSON();
    ctx.response.writeBodyString(jsonStr, "application/json");
}

void saveEntries(ref HttpRequestContext ctx) {
    auto db = getDb();
    User user = getUserOrThrow(ctx, db);
    auto cls = getClassOrThrow(ctx, db, user);
    JSONValue bodyContent = ctx.request.readBodyAsJson();
    db.begin();
    try {
        foreach (JSONValue studentObj; bodyContent.object["students"].array) {
            ulong studentId = studentObj.object["id"].integer();
            JSONValue entries = studentObj.object["entries"];
            foreach (string dateStr, JSONValue entry; entries.object) {
                if (entry.isNull) {
                    deleteEntry(db, cls.id, studentId, dateStr);
                    continue;
                }

                Optional!ClassroomComplianceEntry existingEntry = findOne!(ClassroomComplianceEntry)(
                    db,
                    "SELECT * FROM classroom_compliance_entry WHERE class_id = ? AND student_id = ? AND date = ?",
                    cls.id, studentId, dateStr
                );

                ulong entryId = entry.object["id"].integer();
                bool creatingNewEntry = entryId == 0;

                if (creatingNewEntry) {
                    if (!existingEntry.isNull) {
                        ctx.response.status = HttpStatus.BAD_REQUEST;
                        ctx.response.writeBodyString("Cannot create a new entry when one already exists.");
                        return;
                    }

                    insertNewEntry(db, cls.id, studentId, dateStr, entry);
                } else {
                    if (existingEntry.isNull) {
                        ctx.response.status = HttpStatus.BAD_REQUEST;
                        ctx.response.writeBodyString("Cannot update an entry which doesn't exist.");
                        return;
                    }
                    updateEntry(db, cls.id, studentId, dateStr, entryId, entry);
                }
            }
        }
        db.commit();
    } catch (HttpStatusException e) {
        db.rollback();
        ctx.response.status = e.status;
        ctx.response.writeBodyString(e.message);
    } catch (JSONException e) {
        db.rollback();
        ctx.response.status = HttpStatus.BAD_REQUEST;
        ctx.response.writeBodyString("Invalid JSON payload.");
        warn(e);
    } catch (Exception e) {
        db.rollback();
        ctx.response.status = HttpStatus.INTERNAL_SERVER_ERROR;
        ctx.response.writeBodyString("An internal server error occurred: " ~ e.msg);
        error(e);
    }
}

private void deleteEntry(
    ref Database db,
    ulong classId,
    ulong studentId,
    string dateStr
) {
    db.execute(
        "DELETE FROM classroom_compliance_entry WHERE class_id = ? AND student_id = ? AND date = ?",
        classId,
        studentId,
        dateStr
    );
    infoF!"Deleted entry for student %s on %s"(studentId, dateStr);
}

private void insertNewEntry(
    ref Database db,
    ulong classId,
    ulong studentId,
    string dateStr,
    JSONValue payload
) {
    ulong createdAt = getUnixTimestampMillis();
    bool absent = payload.object["absent"].boolean;
    string comment = payload.object["comment"].str;
    if (comment is null) comment = "";
    db.execute(
        "INSERT INTO classroom_compliance_entry
        (class_id, student_id, date, created_at, absent, comment)
        VALUES (?, ?, ?, ?, ?, ?)",
        classId, studentId, dateStr, createdAt, absent, comment
    );
    if (!absent) {
        ulong entryId = db.lastInsertRowid();
        if ("phone" !in payload.object || payload.object["phone"].type != JSONType.object) {
            throw new HttpStatusException(HttpStatus.BAD_REQUEST, "Missing phone data.");
        }
        if ("behavior" !in payload.object || payload.object["behavior"].type != JSONType.object) {
            throw new HttpStatusException(HttpStatus.BAD_REQUEST, "Missing behavior data.");
        }
        bool phoneCompliance = payload.object["phone"].object["compliant"].boolean;
        db.execute(
            "INSERT INTO classroom_compliance_entry_phone (entry_id, compliant)
            VALUES (?, ?)",
            entryId, phoneCompliance
        );
        ubyte behaviorRating = cast(ubyte) payload.object["behavior"].object["rating"].integer;
        db.execute(
            "INSERT INTO classroom_compliance_entry_behavior (entry_id, rating)
            VALUES (?, ?)",
            entryId, behaviorRating
        );
    }
    infoF!"Created new entry for student %d: %s"(studentId, payload);
}

private void updateEntry(
    ref Database db,
    ulong classId,
    ulong studentId,
    string dateStr,
    ulong entryId,
    JSONValue obj
) {
    bool absent = obj.object["absent"].boolean;
    string comment = obj.object["comment"].str;
    if (comment is null) comment = "";
    db.execute(
        "UPDATE classroom_compliance_entry
        SET absent = ?, comment = ?
        WHERE class_id = ? AND student_id = ? AND date = ? AND id = ?",
        absent, comment,
        classId, studentId, dateStr, entryId
    );
    if (absent) {
        db.execute(
            "DELETE FROM classroom_compliance_entry_phone WHERE entry_id = ?",
            entryId
        );
        db.execute(
            "DELETE FROM classroom_compliance_entry_behavior WHERE entry_id = ?",
            entryId
        );
    } else {
        bool phoneCompliant = obj.object["phone"].object["compliant"].boolean;
        bool phoneDataExists = canFind(
            db,
            "SELECT * FROM classroom_compliance_entry_phone WHERE entry_id = ?",
            entryId
        );

        if (phoneDataExists) {
            db.execute(
                "UPDATE classroom_compliance_entry_phone
                SET compliant = ?
                WHERE entry_id = ?",
                phoneCompliant,
                entryId
            );
        } else {
            db.execute(
                "INSERT INTO classroom_compliance_entry_phone (entry_id, compliant)
                VALUES (?, ?)",
                entryId, phoneCompliant
            );
        }

        ubyte behaviorRating = cast(ubyte) obj.object["behavior"].object["rating"].integer;
        bool behaviorDataExists = canFind(
            db,
            "SELECT * FROM classroom_compliance_entry_behavior WHERE entry_id = ?",
            entryId
        );
        if (behaviorDataExists) {
            db.execute(
                "UPDATE classroom_compliance_entry_behavior
                SET rating = ?
                WHERE entry_id = ?",
                behaviorRating,
                entryId
            );
        } else {
            db.execute(
                "INSERT INTO classroom_compliance_entry_behavior (entry_id, rating)
                VALUES (?, ?)",
                entryId, behaviorRating
            );
        }
    }
    infoF!"Updated entry %d"(entryId);
}

Optional!double[ulong] getScores(
    ref Database db,
    ulong classId,
    Date fromDate,
    Date toDate
) {
    infoF!"Getting scores from %s to %s"(fromDate.toISOExtString(), toDate.toISOExtString());

    // First populate all students with an initial "null" score.
    Optional!double[ulong] scores;
    ResultRange studentsResult = db.execute(
        "SELECT id FROM classroom_compliance_student WHERE class_id = ?",
        classId
    );
    foreach (row; studentsResult) {
        scores[row.peek!ulong(0)] = Optional!double.empty;
    }

    const query = "
    SELECT
        e.student_id,
        COUNT(e.id) AS entry_count,
        SUM(e.absent) AS absence_count,
        SUM(NOT p.compliant) AS phone_noncompliance_count,
        SUM(b.rating = 3) AS behavior_good,
        SUM(b.rating = 2) AS behavior_mediocre,
        SUM(b.rating = 1) AS behavior_poor
    FROM classroom_compliance_entry e
    LEFT JOIN classroom_compliance_entry_phone p
        ON p.entry_id = e.id
    LEFT JOIN classroom_compliance_entry_behavior b
        ON b.entry_id = e.id
    WHERE
        e.date >= ?
        AND e.date <= ?
        AND e.class_id = ?
    GROUP BY e.student_id
    ";
    ResultRange result = db.execute(
        query,
        fromDate.toISOExtString(),
        toDate.toISOExtString(),
        classId
    );
    foreach (row; result) {
        ulong studentId = row.peek!ulong(0);
        uint entryCount = row.peek!uint(1);
        uint absenceCount = row.peek!uint(2);
        uint phoneNonComplianceCount = row.peek!uint(3);
        uint behaviorGoodCount = row.peek!uint(4);
        uint behaviorMediocreCount = row.peek!uint(5);
        uint behaviorPoorCount = row.peek!uint(6);
        scores[studentId] = calculateScore(
            entryCount,
            absenceCount,
            phoneNonComplianceCount,
            behaviorGoodCount,
            behaviorMediocreCount,
            behaviorPoorCount
        );
    }
    return scores;
}

private Optional!double calculateScore(
    uint entryCount,
    uint absenceCount,
    uint phoneNonComplianceCount,
    uint behaviorGoodCount,
    uint behaviorMediocreCount,
    uint behaviorPoorCount
) {
    if (
        entryCount == 0
        || entryCount <= absenceCount
    ) return Optional!double.empty;

    const uint presentCount = entryCount - absenceCount;

    // Phone subscore:
    uint phoneCompliantCount;
    if (presentCount < phoneNonComplianceCount) {
        phoneCompliantCount = 0;
    } else {
        phoneCompliantCount = presentCount - phoneNonComplianceCount;
    }
    double phoneScore = phoneCompliantCount / cast(double) presentCount;

    // Behavior subscore:
    double behaviorScore = (
        behaviorGoodCount * 1.0
        + behaviorMediocreCount * 0.5
        + behaviorPoorCount * 0
    ) / cast(double) presentCount;

    double score = 0.3 * phoneScore + 0.7 * behaviorScore;
    return Optional!double.of(score);
}

void moveStudentToOtherClass(ref HttpRequestContext ctx) {
    auto db = getDb();
    User user = getUserOrThrow(ctx, db);
    auto student = getStudentOrThrow(ctx, db, user);
    struct Payload {
        ulong classId;
    }
    Payload payload = readJsonPayload!(Payload)(ctx);
    if (payload.classId == student.classId) {
        return; // Quit if the student is already in the desired class.
    }
    // Check that the desired class exists, and belongs to the user.
    bool newClassIdValid = canFind(
        db,
        "SELECT id FROM classroom_compliance_class WHERE user_id = ? and id = ?",
        user.id, payload.classId
    );
    if (!newClassIdValid) {
        ctx.response.status = HttpStatus.BAD_REQUEST;
        ctx.response.writeBodyString("Invalid class was selected.");
        return;
    }
    // All good, so update the student's class to the desired one, and reset their desk.
    db.execute(
        "UPDATE classroom_compliance_student SET class_id = ?, desk_number = 0 WHERE id = ?",
        payload.classId,
        student.id
    );
    // We just return 200 OK, no response body.
}

void getStudentEntries(ref HttpRequestContext ctx) {
    auto db = getDb();
    User user = getUserOrThrow(ctx, db);
    auto student = getStudentOrThrow(ctx, db, user);

    const query = "
    SELECT
        e.id,
        e.date,
        e.created_at,
        e.absent,
        e.comment,
        p.compliant,
        b.rating
    FROM classroom_compliance_entry e
    LEFT JOIN classroom_compliance_entry_phone p
        ON p.entry_id = e.id
    LEFT JOIN classroom_compliance_entry_behavior b
        ON b.entry_id = e.id
    WHERE
        e.student_id = ?
    ORDER BY e.date DESC
    ";
    JSONValue response = JSONValue.emptyArray;
    foreach (row; db.execute(query, student.id)) {
        JSONValue e = JSONValue.emptyObject;
        bool absent = row.peek!bool(3);
        e.object["id"] = JSONValue(row.peek!ulong(0));
        e.object["date"] = JSONValue(row.peek!string(1));
        e.object["createdAt"] = JSONValue(row.peek!ulong(2));
        e.object["absent"] = JSONValue(absent);
        e.object["comment"] = JSONValue(row.peek!string(4));
        if (absent) {
            e.object["phone"] = JSONValue(null);
            e.object["behavior"] = JSONValue(null);
        } else {
            JSONValue phone = JSONValue.emptyObject;
            phone.object["compliant"] = JSONValue(row.peek!bool(5));
            e.object["phone"] = phone;
            JSONValue behavior = JSONValue.emptyObject;
            behavior.object["rating"] = JSONValue(row.peek!ubyte(6));
            e.object["behavior"] = behavior;
        }
        response.array ~= e;
    }
    ctx.response.writeBodyString(response.toJSON(), "application/json");
}

void getStudentOverview(ref HttpRequestContext ctx) {
    auto db = getDb();
    User user = getUserOrThrow(ctx, db);
    auto student = getStudentOrThrow(ctx, db, user);
    
    const ulong entryCount = findOne!ulong(
        db,
        "SELECT COUNT(*) FROM classroom_compliance_entry WHERE student_id = ?",
        student.id
    ).orElse(0);
    if (entryCount == 0) {
        ctx.response.status = HttpStatus.NOT_FOUND;
        ctx.response.writeBodyString("No entries for this student.");
        return;
    }
    const ulong absenceCount = findOne!ulong(
        db,
        "SELECT COUNT(*) FROM classroom_compliance_entry WHERE student_id = ? AND absent = true",
        student.id
    ).orElse(0);
    const ulong phoneNoncomplianceCount = findOne!ulong(
        db,
        "
        SELECT COUNT(*)
        FROM classroom_compliance_entry_phone p
        LEFT JOIN classroom_compliance_entry e
            ON e.id = p.entry_id
        WHERE p.compliant = false AND e.student_id = ?
        ",
        student.id
    ).orElse(0);
    const behaviorCountQuery = "
    SELECT COUNT(*)
    FROM classroom_compliance_entry_behavior b
    LEFT JOIN classroom_compliance_entry e
        ON e.id = b.entry_id
    WHERE e.student_id = ? AND b.rating = ?
    ";

    const ulong behaviorGoodCount = findOne!ulong(db, behaviorCountQuery, student.id, 3).orElse(0);
    const ulong behaviorMediocreCount = findOne!ulong(db, behaviorCountQuery, student.id, 2).orElse(0);
    const ulong behaviorPoorCount = findOne!ulong(db, behaviorCountQuery, student.id, 1).orElse(0);
    
    // Calculate derived statistics.
    const ulong attendanceCount = entryCount - absenceCount;
    double attendanceRate = attendanceCount / cast(double) entryCount;
    double phoneComplianceRate = (attendanceCount - phoneNoncomplianceCount) / cast(double) attendanceCount;
    double behaviorScore = (
        behaviorGoodCount * 1.0 +
        behaviorMediocreCount * 0.5
    ) / attendanceCount;
    
    JSONValue response = JSONValue.emptyObject;
    response.object["attendanceRate"] = JSONValue(attendanceRate);
    response.object["phoneComplianceRate"] = JSONValue(phoneComplianceRate);
    response.object["behaviorScore"] = JSONValue(behaviorScore);
    response.object["entryCount"] = JSONValue(entryCount);
    ctx.response.writeBodyString(response.toJSON(), "application/json");
}