tesseract: Use checksums when downloading

Also cache the downloaded files instead of downloading them on each
build.

packages/tesseract/build.sh

@@ -18,13 +18,30 @@ termux_step_post_make_install() {
 	# download english trained data
 	cd "${TERMUX_PREFIX}/share/tessdata"
 	rm -f eng.*
+
+	local checksums
+	declare -A checksums
+	checksums[cube.bigrams]=64adf2cc0b2a6705368aa357224d1a6739035d5fe892cd0cc457016df5b4280f
+	checksums[cube.fold]=2b229895623934b493fe69c51fcc387295d91af8b4e43cc51748b3d269a95eed
+	checksums[cube.lm]=a6f769245b0a55f42a3ce157cd19d96828483c3384c6483433ed83579ea16e36
+	checksums[cube.nn]=8f345f1c19772dd71a5214bc94175ccf647c003ab77e4143fde48f11bf3cb0ef
+	checksums[cube.params]=c2aa2854951bd823d89cc86d53a6d9712a6a885de6fbaf650ff3df48bfed85d7
+	checksums[cube.size]=e5f95de7e2754eb2df03451885277ca4573b3770816043ae2e2f09d1f7232604
+	checksums[cube.word-freq]=8d612bef20ae3052fce0b8650575a80d87c94d772ec6d1f0c6a1ad591586ea44
+	checksums[tesseract_cube.nn]=196bedc8a5bc8c30361c2c9518f648b45b498759cb6041827ff6fbfb8da2a8d1
+	checksums[traineddata]=c0515c9f1e0c79e1069fcc05c2b2f6a6841fb5e1082d695db160333c1154f06d
+
+	mkdir -p $TERMUX_PKG_CACHEDIR/tessdata
+
+	local f
 	for f in cube.{bigrams,fold,lm,nn,params,size,word-freq} tesseract_cube.nn traineddata; do
-		f=eng.$f
 		# From the tessdata README: "These language data files only work with
 		# Tesseract 4. They are based on the sources in tesseract-ocr/langdata on GitHub.
 		# Get language data files for Tesseract 3.04 or 3.05 from the 3.04 tree."
 		termux_download \
-			https://raw.githubusercontent.com/tesseract-ocr/tessdata/3.04.00/$f \
-			$f
+			https://raw.githubusercontent.com/tesseract-ocr/tessdata/3.04.00/eng.$f \
+			$TERMUX_PKG_CACHEDIR/tessdata/eng.$f \
+			${checksums[$f]}
+		cp $TERMUX_PKG_CACHEDIR/tessdata/eng.$f .
 	done
 }