From 14f1585d9cf8c2e78b893244f1ccde892ad452c8 Mon Sep 17 00:00:00 2001
From: rhijmans <r.hijmans@gmail.com>
Date: Sat, 26 Aug 2023 14:53:14 -0700
Subject: [PATCH] fixes #1261

---
 NAMESPACE  |  2 +-
 R/tiles.R  | 25 +++++++++++++++++++++++++
 man/vrt.Rd |  8 ++++++--
 3 files changed, 32 insertions(+), 3 deletions(-)

diff --git a/NAMESPACE b/NAMESPACE
index 1bd634d55..fade18172 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -18,5 +18,5 @@ S3method(str, SpatRaster)
 S3method(str, SpatExtent)
 S3method(str, SpatGraticule)
 
-export(add_legend, focalMat, gdal, getGDALconfig, graticule, halo, setGDALconfig, map.pal, north, sbar, terraOptions, tmpFiles, makeVRT, mem_info, free_RAM, same.crs, shade, gdalCache, fileBlocksize, vector_layers)
+export(add_legend, focalMat, gdal, getGDALconfig, graticule, halo, setGDALconfig, map.pal, north, sbar, terraOptions, tmpFiles, makeVRT, mem_info, free_RAM, same.crs, shade, gdalCache, fileBlocksize, vector_layers, vrt_tiles)
 
diff --git a/R/tiles.R b/R/tiles.R
index b9b61e4b6..b645a8e07 100644
--- a/R/tiles.R
+++ b/R/tiles.R
@@ -68,3 +68,28 @@ setMethod("vrt", signature(x="character"),
 	}
 )
 
+
+vrt_tiles <- function(x) {
+	if (inherits(x, "SpatRaster")) {
+		x <- sources(x)
+	}
+	if (!inherits(x, "character")) {
+		error("vrt_sources", "x must be a filename (character) or SpatRaster)")
+	}
+	x <- grep(".vrt$", x, ignore.case =TRUE, value=TRUE)
+	if (length(x) == 0) {
+		error("vrt_sources", 'no filenames with extension ".vrt"')	
+	}
+	tiles <- lapply(x, function(f) {
+			v <- readLines(f)
+			v <- v[grep("SourceFilename", v)]
+			s <- strsplit(v, "\"")
+			rel <- sapply(s, \(x) x[2])
+			ff <- strsplit(sapply(s, \(x)x[3]), "<")
+			ff <- gsub(">", "", sapply(ff, \(x) x[1]))
+			ff[rel=="1"] <- file.path(dirname(f), ff[rel=="1"])
+			ff
+		})
+	unlist(tiles)
+}
+
diff --git a/man/vrt.Rd b/man/vrt.Rd
index c858c90ca..c5425624f 100644
--- a/man/vrt.Rd
+++ b/man/vrt.Rd
@@ -4,22 +4,26 @@
 
 \alias{vrt}
 \alias{vrt,character-method}
-
+\alias{vrt_tiles} 
 
 \title{Virtual Raster Dataset}
 
 \description{ 
 Create a Virtual Raster Dataset (VRT) from a collection of file-based raster datasets (tiles). See 
 \href{https://gdal.org/programs/gdalbuildvrt.html}{gdalbuildvrt} for details.
+
+\code{vrt_tiles} returns the filenames of the tiles in a VRT.
 }
 
 \usage{
 \S4method{vrt}{character}(x, filename="", options=NULL, overwrite=FALSE, set_names=FALSE, return_filename=FALSE)
+
+vrt_tiles(filename)
 }
 
 \arguments{
   \item{x}{character. Filenames of raster "tiles". See \code{\link{tiles}}}
-  \item{filename}{character. Output VRT filename}  
+  \item{filename}{character. VRT filename}  
   \item{options}{character. All arguments as separate vector elements. Options as for \href{https://gdal.org/programs/gdalbuildvrt.html}{gdalbuildvrt}}
   \item{overwrite}{logical. Should \code{filename} be overwritten if it exists?}
   \item{set_names}{logical. Add the layer names of the first tile to the vrt?}