#!/usr/bin/env python3

# Copyright 2018-2019 Abdulkadir Furkan Şanlı

# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at

#     http://www.apache.org/licenses/LICENSE-2.0

# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

import sqlite3
import time
from os import name
from sys import exit

# Windows has standard library getch, use that.
if name == "nt":
    from msvcrt import getch
else:
    from getch import getch


def connect_database(file):
    """Get database connection object.

    Connect to SQLite database and return a connection object.

    :param file: SQLite database
    """
    conn = sqlite3.connect(file)
    return conn


def get_data(conn):
    """Get student data.

    Request student ID.  Return tuple (id, class, other) with valid
    student ID, corresponding class number and "other" subject IDs.

    :param conn: Connection object
    """
    try:
        id = int(input("\nPlease enter student ID: "))

        cur = conn.cursor()
        cur.execute("""
            SELECT id, student_class, other
            FROM students
            WHERE id = ?
            """, (id,))
        data = cur.fetchone()

        if data is not None:
            data = list(data)  # SQLite returns tuples.
            data[2] = data[2].split()
        else:
            raise ValueError

        return data
    except ValueError:
        print("\nInvalid ID, try again.")
        return get_data(conn)


def select_final_time(conn, day, data):
    """Select student finishing time.

    Returns ending time (type struct_time) of final lesson student must
    attend on given day, or None if no lessons.

    :param conn: Connection object
    :param day: current weekday, lowercase str
    :param data: student data tuple returned by get_data
    """
    cur = conn.cursor()
    # Select finishing time of IB lessons.
    cur.execute("""
        SELECT end_time
        FROM timetable
            INNER JOIN students ON g1 = lesson_id
                OR g2 = lesson_id
                OR g3 = lesson_id
                OR g4 = lesson_id
                OR g5 = lesson_id
                OR g6 = lesson_id
        WHERE id = ?
            AND day = ?
            AND lesson_class = ?
        ORDER BY end_time DESC
        LIMIT 1
        """, (data[0], day, data[1]))  # Queries return None if no matches.
    ib_finish = cur.fetchone()
    if ib_finish is not None:
        ib_finish = parse_time_string(ib_finish[0])

    # Select finishing time of other lessons.
    others = []
    for subject in data[2]:
        cur.execute("""
            SELECT end_time
            FROM timetable
                INNER JOIN students ON ? = lesson_id
            WHERE id = ?
                AND day = ?
                AND lesson_class = ?
            ORDER BY end_time DESC
            LIMIT 1
            """, (subject, data[0], day, data[1]))
        subject_finish = cur.fetchone()
        if subject_finish is not None:
            others.append(parse_time_string(subject_finish[0]))
    if not others:
        others_finish = None
    else:
        others_finish = max(others)

    if ib_finish is not None and others_finish is not None:
        if ib_finish > others_finish:
            finish = ib_finish
        else:
            finish = others_finish
    elif ib_finish is not None:
        finish = ib_finish
    elif others_finish is not None:
        finish = others_finish
    else:
        finish = None

    return finish


def parse_time_string(timestring):
    """Convert time string to tuple.

    Parses given 24h time string of format "HH:MM" into the struct_time
    object provided by library time.

    :param timestring: time string "HH:MM"
    """
    structtime = time.strptime(timestring, "%H:%M")
    return structtime


def clear(finish_time):
    """Return clearance message.

    Compare the current time with finishing time and return relevant
    clearance message.

    :param finish_time: finishing time, struct_time object
    """
    current_time = parse_time_string(time.strftime("%H:%M"))
    if finish_time == None:
        message = "Student has no lessons today, clear to leave."
    elif finish_time < current_time:
        message = "Student has finished for today, clear to leave."
    else:
        message = "Student still has lessons, clearance not granted."
    return message


def exit_sequence():
    """Initiate exit sequence.

    Asks user to enter character, and exits program if X is pressed.
    """
    print("Press X to exit.")
    key = getch()
    if isinstance(key, bytes):
        # msvcrt.getch returns type bytes, decode into str.
        key = key.decode()
    if key.upper() == "X":
        exit()


def main():
    print("ib-clearance")
    print("Copyright 2018-2019 Abdulkadir Furkan Şanlı")

    conn = connect_database("database.db")

    while True:
        student_data = get_data(conn)
        day = time.strftime("%A").lower()
        finish_time = select_final_time(conn, day, student_data)

        print("\n" + clear(finish_time) + "\n")

        exit_sequence()


if __name__ == "__main__":
    main()