Show remaining character count in SMS app

## Summary

This adds character counter below the “Send” button in SMS conversation. It
uses format XXX/Y where XXX is number of characters that can be added
without splitting the SMS into multiple messages (see article
Concatenated SMS on Wikipedia). Y is number of messages in in current
concatenated SMS. The counter is not visible when insertion of 10 7-bit
or 16-bit (depends on SMS encoding) does not create concatenated SMS.

SMS encoding is automatically guessed. 8-bit encodings are not
supported. If the message contains characters that are not supported by GSM 7-bit
encoding, counter automatically switches to UCS-2.

## Test Plan

Try entering some text that is longer than 150 characters in [GSM 03.38 encoding][1] or 60 characters in UCS-2. Number of remaining characters should be visible below the “Send” button. The character counter should show `0` at exactly 160 or 70 characters. Inserting one character should switch the counter to [Concatenated SMS][2] mode when number of messages is shown.

It should show exactly same number as SMS app in Android.

## Screenshots

These images are in APNG.

![grab.apng](/uploads/21ae23f2fa75c7aca487e61ddce94644/grab.apng)
![grab-cz.apng](/uploads/785e670a8598c5a65a4209f17e75f578/grab-cz.apng)

[1]: https://en.wikipedia.org/w/index.php?oldid=932080074#GSM_7-bit_default_alphabet_and_extension_table_of_3GPP_TS_23.038_/_GSM_03.38
[2]: https://en.wikipedia.org/w/index.php?oldid=943185255#Message_size

smsapp/CMakeLists.txt

@@ -4,6 +4,7 @@ find_package(KF5People)
 
 add_library(kdeconnectsmshelper
 	smshelper.cpp
+	gsmasciimap.cpp
 )
 
 set_target_properties(kdeconnectsmshelper PROPERTIES

smsapp/conversationmodel.cpp

@@ -192,3 +192,21 @@ void ConversationModel::handleConversationLoaded(qint64 threadID, quint64 numMes
     // so we should not be showing a loading indicator
     Q_EMIT loadingFinished();
 }
+
+QString ConversationModel::getCharCountInfo(const QString& message) const
+{
+    SmsCharCount count = SmsHelper::getCharCount(message);
+    
+    if (count.messages > 1) {
+        // Show remaining char count and message count
+        return QString::number(count.remaining) + QLatin1Char('/') + QString::number(count.messages);
+    }
+    if (count.messages == 1 && count.remaining < 10) {
+        // Show only remaining char count
+        return QString::number(count.remaining);
+    }
+    else {
+        // Do not show anything
+        return QString();
+    }
+}

smsapp/conversationmodel.h

@@ -78,6 +78,8 @@ public:
      * TODO: Move to smshelper (or maybe make part of kirigami-addons chat library?)
      */
     Q_INVOKABLE void copyToClipboard(const QString& message) const;
+    
+    Q_INVOKABLE QString getCharCountInfo(const QString& message) const;
 
 Q_SIGNALS:
     void loadingFinished();

smsapp/gsmasciimap.cpp

@@ -0,0 +1,154 @@
+/**
+ * Copyright (C) 2020 Jiří Wolker <woljiri@gmail.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of
+ * the License or (at your option) version 3 or any later version
+ * accepted by the membership of KDE e.V. (or its successor approved
+ * by the membership of KDE e.V.), which shall act as a proxy
+ * defined in Section 14 of version 3 of the license.
+ *
+ * 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/**
+ * Map used to determine that ASCII character is in GSM 03.38 7-bit alphabet.
+ * 
+ * Only allowed control characters are CR and LF but GSM alphabet has more of them.
+ */
+bool gsm_ascii_map[] = {
+    false, // 0x0, some control char
+    false, // 0x1, some control char
+    false, // 0x2, some control char
+    false, // 0x3, some control char
+    false, // 0x4, some control char
+    false, // 0x5, some control char
+    false, // 0x6, some control char
+    false, // 0x7, some control char
+    false, // 0x8, some control char
+    false, // 0x9, some control char
+    true, // 0xA, LF
+    false, // 0xB, some control char
+    false, // 0xC, some control char
+    true, // 0xD, CR
+    false, // 0xE, some control char
+    false, // 0xF, some control char
+    false, // 0x10, some control char
+    false, // 0x11, some control char
+    false, // 0x12, some control char
+    false, // 0x13, some control char
+    false, // 0x14, some control char
+    false, // 0x15, some control char
+    false, // 0x16, some control char
+    false, // 0x17, some control char
+    false, // 0x18, some control char
+    false, // 0x19, some control char
+    false, // 0x1A, some control char
+    false, // 0x1B, some control char
+    false, // 0x1C, some control char
+    false, // 0x1D, some control char
+    false, // 0x1E, some control char
+    false, // 0x1F, some control char
+    true, // 20, space
+    true, // 21, !
+    true, // 22, "
+    true, // 23, #
+    true, // 24, $
+    true, // 25, %
+    true, // 26, &
+    true, // 27, '
+    true, // 28, (
+    true, // 29, )
+    true, // 2A, *
+    true, // 2B, +
+    true, // 2C, ,
+    true, // 2D, -
+    true, // 2E, .
+    true, // 2F, /
+    true, // 30, 0
+    true, // 31, 1
+    true, // 32, 2
+    true, // 33, 3
+    true, // 34, 4
+    true, // 35, 5
+    true, // 36, 6
+    true, // 37, 7
+    true, // 38, 8
+    true, // 39, 9
+    true, // 3A, :
+    true, // 3B, ;
+    true, // 3C, <
+    true, // 3D, =
+    true, // 3E, >
+    true, // 3F, ?
+    true, // 40, @
+    true, // 41, A
+    true, // 42, B
+    true, // 43, C
+    true, // 44, D
+    true, // 45, E
+    true, // 46, F
+    true, // 47, G
+    true, // 48, H
+    true, // 49, I
+    true, // 4A, J
+    true, // 4B, K
+    true, // 4C, L
+    true, // 4D, M
+    true, // 4E, N
+    true, // 4F, O
+    true, // 50, P
+    true, // 51, Q
+    true, // 52, R
+    true, // 53, S
+    true, // 54, T
+    true, // 55, U
+    true, // 56, V
+    true, // 57, W
+    true, // 58, X
+    true, // 59, Y
+    true, // 5A, Z
+    false, // 5B, [
+    false, // 5C, backslash
+    false, // 5D, ]
+    false, // 5E, ^
+    true, // 5F, _
+    false, // 60, `
+    true, // 61, a
+    true, // 62, b
+    true, // 63, c
+    true, // 64, d
+    true, // 65, e
+    true, // 66, f
+    true, // 67, g
+    true, // 68, h
+    true, // 69, i
+    true, // 6A, j
+    true, // 6B, k
+    true, // 6C, l
+    true, // 6D, m
+    true, // 6E, n
+    true, // 6F, o
+    true, // 70, p
+    true, // 71, q
+    true, // 72, r
+    true, // 73, s
+    true, // 74, t
+    true, // 75, u
+    true, // 76, v
+    true, // 77, w
+    true, // 78, x
+    true, // 79, y
+    true, // 7A, z
+    false, // 7B, {
+    false, // 7C, |
+    false, // 7D, }
+    false, // 7E, ~
+};

smsapp/gsmasciimap.h

@@ -0,0 +1,27 @@
+/**
+ * Copyright (C) 2020 Jiří Wolker <woljiri@gmail.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of
+ * the License or (at your option) version 3 or any later version
+ * accepted by the membership of KDE e.V. (or its successor approved
+ * by the membership of KDE e.V.), which shall act as a proxy
+ * defined in Section 14 of version 3 of the license.
+ *
+ * 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#ifndef GSMASCIIMAP_H
+#define GSMASCIIMAP_H
+
+extern bool gsm_ascii_map[128];
+
+#endif // GSMASCIIMAP_H
+

smsapp/qml/ConversationDisplay.qml

@@ -219,41 +219,50 @@ Kirigami.ScrollablePage
                     }
                 }
             }
+            
+            ColumnLayout {
+                ToolButton {
+                    id: sendButton
+                    Layout.preferredWidth: Kirigami.Units.gridUnit * 2
+                    Layout.preferredHeight: Kirigami.Units.gridUnit * 2
+                    padding: 0
+                    Kirigami.Icon {
+                        source: "document-send"
+                        enabled: sendButton.enabled
+                        isMask: true
+                        smooth: true
+                        anchors.centerIn: parent
+                        width: Kirigami.Units.gridUnit * 1.5
+                        height: width
+                    }
+                    onClicked: {
+                        // don't send empty messages
+                        if (!messageField.text.length) {
+                            return
+                        }
 
-            ToolButton {
+                        // disable the button to prevent sending
-                id: sendButton
+                        // the same message several times
-                Layout.preferredWidth: Kirigami.Units.gridUnit * 2
+                        sendButton.enabled = false
-                Layout.preferredHeight: Kirigami.Units.gridUnit * 2
+
-                padding: 0
+                        // send the message
-                Kirigami.Icon {
+                        if (page.conversationId == page.invalidId) {
-                    source: "document-send"
+                            conversationModel.sendMessageWithoutConversation(messageField.text, page.otherParty)
-                    enabled: sendButton.enabled
+                        } else {
-                    isMask: true
+                            conversationModel.sendReplyToConversation(messageField.text)
-                    smooth: true
+                        }
-                    anchors.centerIn: parent
+                        messageField.text = ""
-                    width: Kirigami.Units.gridUnit * 1.5
+
-                    height: width
+                        // re-enable the button
+                        sendButton.enabled = true
+                    }
                 }
-                onClicked: {
+                
-                    // don't send empty messages
+                
-                    if (!messageField.text.length) {
+                Label {
-                        return
+                    id: "charCount"
-                    }
+                    text: conversationModel.getCharCountInfo(messageField.text)
-
+                    visible: text.length > 0
-                    // disable the button to prevent sending
-                    // the same message several times
-                    sendButton.enabled = false
-
-                    // send the message
-                    if (page.conversationId == page.invalidId) {
-                        conversationModel.sendMessageWithoutConversation(messageField.text, page.otherParty)
-                    } else {
-                        conversationModel.sendReplyToConversation(messageField.text)
-                    }
-                    messageField.text = ""
-
-                    // re-enable the button
-                    sendButton.enabled = true
                 }
             }
         }

smsapp/smscharcount.h

@@ -0,0 +1,50 @@
+/**
+ * Copyright (C) 2020 Jiří Wolker <woljiri@gmail.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of
+ * the License or (at your option) version 3 or any later version
+ * accepted by the membership of KDE e.V. (or its successor approved
+ * by the membership of KDE e.V.), which shall act as a proxy
+ * defined in Section 14 of version 3 of the license.
+ *
+ * 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#ifndef CHARCOUNT_H
+#define CHARCOUNT_H
+
+class SmsCharCount {
+public:
+    /**
+     * Number of octets in current message.
+     */
+    qint32 octets;
+    
+    /**
+     * Bits per character (7, 8 or 16).
+     */
+    qint32 bitsPerChar;
+    
+    /**
+     * Number of chars remaining in current SMS.
+     */
+    qint32 remaining;
+    
+    /**
+     * Count of SMSes in concatenated SMS.
+     */
+    qint32 messages;
+    
+    SmsCharCount(){};
+    ~SmsCharCount(){};
+};
+
+#endif // CHARCOUNT_H

smsapp/smshelper.cpp

@@ -32,6 +32,7 @@
 #include <KPeople/PersonsModel>
 
 #include "interfaces/conversationmessage.h"
+#include "smsapp/gsmasciimap.h"
 
 Q_LOGGING_CATEGORY(KDECONNECT_SMS_SMSHELPER, "kdeconnect.sms.smshelper")
 
@@ -274,3 +275,139 @@ QIcon SmsHelper::getIconForAddresses(const QList<ConversationAddress>& addresses
     // around randomly (based on how the data came to us from Android)
     return combineIcons(icons);
 }
+
+SmsCharCount SmsHelper::getCharCount(const QString& message)
+{
+    const int remainingWhenEmpty = 160;
+    const int septetsInSingleSms = 160;
+    const int septetsInSingleConcatSms = 153;
+    const int charsInSingleUcs2Sms = 70;
+    const int charsInSingleConcatUcs2Sms = 67;
+
+    SmsCharCount count;
+    bool enc7bit = true; // 7-bit is used when true, UCS-2 if false
+    quint32 septets = 0; // GSM encoding character count (characters in extension are counted as 2 chars)
+    int length = message.length();
+    
+    // Count characters and detect encoding
+    for (int i = 0; i < length; i++) {
+        QChar ch = message[i];
+        
+        if (isInGsmAlphabet(ch)) {
+            septets++;
+        }
+        else if (isInGsmAlphabetExtension(ch)) {
+            septets += 2;
+        }
+        else {
+            enc7bit = false;
+            break;
+        }
+    }
+    
+    if (length == 0) {
+        count.bitsPerChar = 7;
+        count.octets = 0;
+        count.remaining = remainingWhenEmpty;
+        count.messages = 1;
+    }
+    else if (enc7bit) {
+        count.bitsPerChar = 7;
+        count.octets = (septets * 7 + 6) / 8;
+        if (septets > septetsInSingleSms) {
+            count.messages = (septetsInSingleConcatSms - 1 + septets) / septetsInSingleConcatSms;
+            count.remaining = (septetsInSingleConcatSms * count.messages - septets) % septetsInSingleConcatSms;
+        }
+        else {
+            count.messages = 1;
+            count.remaining = (septetsInSingleSms - septets) % septetsInSingleSms;
+        }
+    }
+    else {
+        count.bitsPerChar = 16;
+        count.octets = length * 2; // QString should be in UTF-16
+        if (length > charsInSingleUcs2Sms) {
+            count.messages = (charsInSingleConcatUcs2Sms - 1 + length) / charsInSingleConcatUcs2Sms;
+            count.remaining = (charsInSingleConcatUcs2Sms * count.messages - length) % charsInSingleConcatUcs2Sms;
+        }
+        else {
+            count.messages = 1;
+            count.remaining = (charsInSingleUcs2Sms - length) % charsInSingleUcs2Sms;
+        }
+    }
+    
+    return count;
+}
+
+bool SmsHelper::isInGsmAlphabet(const QChar& ch)
+{
+    wchar_t unicode = ch.unicode();
+    
+    if ((unicode & ~0x7f) == 0) { // If the character is ASCII
+        // use map
+        return gsm_ascii_map[unicode];
+    }
+    else {
+        switch (unicode) {
+            case 0xa1: // “¡”
+            case 0xa7: // “§”
+            case 0xbf: // “¿”
+            case 0xa4: // “¤”
+            case 0xa3: // “£”
+            case 0xa5: // “¥”
+            case 0xe0: // “à”
+            case 0xe5: // “å”
+            case 0xc5: // “Å”
+            case 0xe4: // “ä”
+            case 0xc4: // “Ä”
+            case 0xe6: // “æ”
+            case 0xc6: // “Æ”
+            case 0xc7: // “Ç”
+            case 0xe9: // “é”
+            case 0xc9: // “É”
+            case 0xe8: // “è”
+            case 0xec: // “ì”
+            case 0xf1: // “ñ”
+            case 0xd1: // “Ñ”
+            case 0xf2: // “ò”
+            case 0xf5: // “ö”
+            case 0xd6: // “Ö”
+            case 0xf8: // “ø”
+            case 0xd8: // “Ø”
+            case 0xdf: // “ß”
+            case 0xf9: // “ù”
+            case 0xfc: // “ü”
+            case 0xdc: // “Ü”
+            case 0x393: // “Γ”
+            case 0x394: // “Δ”
+            case 0x398: // “Θ”
+            case 0x39b: // “Λ”
+            case 0x39e: // “Ξ”
+            case 0x3a0: // “Π”
+            case 0x3a3: // “Σ”
+            case 0x3a6: // “Φ”
+            case 0x3a8: // “Ψ”
+            case 0x3a9: // “Ω”
+                return true;
+        }
+    }
+    return false;
+}
+
+bool SmsHelper::isInGsmAlphabetExtension(const QChar& ch)
+{
+    wchar_t unicode = ch.unicode();
+    switch (unicode) {
+        case '{':
+        case '}':
+        case '|':
+        case '\\':
+        case '^':
+        case '[':
+        case ']':
+        case '~':
+        case 0x20ac: // Euro sign
+            return true;
+    }
+    return false;
+}

smsapp/smshelper.h

@@ -30,6 +30,7 @@
 #include "interfaces/conversationmessage.h"
 
 #include "kdeconnectsms_export.h"
+#include "smsapp/smscharcount.h"
 
 Q_DECLARE_LOGGING_CATEGORY(KDECONNECT_SMS_SMSHELPER)
 
@@ -106,7 +107,17 @@ public:
      * Get the data for all persons currently stored on device
      */
     static QList<QSharedPointer<KPeople::PersonData>> getAllPersons();
-
+    
+    /**
+     * Get SMS character count status of SMS. It contains number of remaining characters
+     * in current SMS (automatically selects 7-bit, 8-bit or 16-bit mode), octet count and
+     * number of messages in concatenated SMS.
+     */
+    static SmsCharCount getCharCount(const QString& message);
+    
+    static bool isInGsmAlphabet(const QChar& ch);
+    static bool isInGsmAlphabetExtension(const QChar& ch);
+    
 private:
     SmsHelper(){};
     ~SmsHelper(){};