From c3f345c7f9139f17ea6945ac372d61a302351142 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Martin=20T=C5=AFma?= <tumic@cbox.cz>
Date: Thu, 31 Dec 2020 14:03:30 +0100
Subject: [PATCH] Added support for ZIPed DEM files

---
 src/data/dem.cpp | 52 ++++++++++++++++++++++++++++++++++++++----------
 src/data/dem.h   |  3 ++-
 2 files changed, 43 insertions(+), 12 deletions(-)

diff --git a/src/data/dem.cpp b/src/data/dem.cpp
index 004156f1..f2ce7f28 100644
--- a/src/data/dem.cpp
+++ b/src/data/dem.cpp
@@ -1,7 +1,21 @@
+/*
+	WARNING: This code uses internal Qt API - the QZipReader class for reading
+	ZIP files - and things may break if Qt changes the API. For Qt5 this is not
+	a problem as we can "see the future" now and there are no changes in all
+	the supported Qt5 versions up to the last one (5.15). In Qt6 the class
+	might change or even disappear in the future, but this is very unlikely
+	as there were no changes for several years and The Qt Company's policy
+	is: "do not invest any resources into any desktop related stuff unless
+	absolutely necessary". There is an issue (QTBUG-3897) since the year 2009 to
+	include the ZIP reader into the public API, which aptly illustrates the
+	effort The Qt Company is willing to make about anything desktop related...
+*/
+
 #include <QtEndian>
 #include <QtMath>
 #include <QDir>
 #include <QFile>
+#include <private/qzipreader_p.h>
 #include "common/coordinates.h"
 #include "dem.h"
 
@@ -55,15 +69,19 @@ static qreal height(const Coordinates &c, const QByteArray *data)
 QString DEM::_dir;
 QCache<DEM::Key, QByteArray> DEM::_data;
 
-QString DEM::fileName(const Key &key)
+QString DEM::baseName(const Key &key)
 {
 	const char ns = (key.lat() >= 0) ? 'N' : 'S';
 	const char ew = (key.lon() >= 0) ? 'E' : 'W';
 
-	QString basename = QString("%1%2%3%4.hgt").arg(ns)
+	return QString("%1%2%3%4.hgt").arg(ns)
 	  .arg(qAbs(key.lat()), 2, 10, QChar('0')).arg(ew)
 	  .arg(qAbs(key.lon()), 3, 10, QChar('0'));
-	return QDir(_dir).absoluteFilePath(basename);
+}
+
+QString DEM::fileName(const QString &baseName)
+{
+	return QDir(_dir).absoluteFilePath(baseName);
 }
 
 void DEM::setDir(const QString &path)
@@ -80,17 +98,29 @@ qreal DEM::elevation(const Coordinates &c)
 
 	QByteArray *ba = _data[k];
 	if (!ba) {
-		QFile file(fileName(k));
-		if (!file.open(QIODevice::ReadOnly)) {
-			qWarning("%s: %s", qPrintable(file.fileName()),
-			  qPrintable(file.errorString()));
-			_data.insert(k, new QByteArray());
-			return NAN;
-		} else {
-			ba = new QByteArray(file.readAll());
+		QString bn(baseName(k));
+		QString fn(fileName(bn));
+		QString zn(fn + ".zip");
+
+		if (QFileInfo::exists(zn)) {
+			QZipReader zip(zn, QIODevice::ReadOnly);
+			ba = new QByteArray(zip.fileData(bn));
 			qreal ele = height(c, ba);
 			_data.insert(k, ba);
 			return ele;
+		} else {
+			QFile file(fn);
+			if (!file.open(QIODevice::ReadOnly)) {
+				qWarning("%s: %s", qPrintable(file.fileName()),
+				  qPrintable(file.errorString()));
+				_data.insert(k, new QByteArray());
+				return NAN;
+			} else {
+				ba = new QByteArray(file.readAll());
+				qreal ele = height(c, ba);
+				_data.insert(k, ba);
+				return ele;
+			}
 		}
 	} else
 		return height(c, ba);
diff --git a/src/data/dem.h b/src/data/dem.h
index 2e4aa0e7..46e25b4e 100644
--- a/src/data/dem.h
+++ b/src/data/dem.h
@@ -27,7 +27,8 @@ private:
 		int _lon, _lat;
 	};
 
-	static QString fileName(const Key &key);
+	static QString baseName(const Key &key);
+	static QString fileName(const QString &baseName);
 
 	static QString _dir;
 	static QCache<Key, QByteArray> _data;