2 files changed, 44 insertions, 3 deletions

diff --git a/readme.md b/readme.md
index 55d0546..be2587c 100644
--- a/readme.md
+++ b/readme.md
@@ -17,10 +17,13 @@ Building this project requires Nim and Nimble version 0.19.0 or later.
 Usage
 -----
 
+```
+Usage: gziplike <compress|decompress> <input file> <output file>
+```
+
 Compression and decompression are done using the `compress` and `decompress` commands repsectively.
 
-The input stream is read from the standard input.
-The result is outputted to the standard output.
+Paths to the input and output files are given as second and third arguments respectively.
 
 
 License
diff --git a/src/main.nim b/src/main.nim
index dbf331f..8f0536c 100644
--- a/src/main.nim
+++ b/src/main.nim
@@ -14,5 +14,43 @@
 # You should have received a copy of the GNU Affero General Public License
 # along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
+import os, streams, sugar
+import bitreader, bitwriter, streamblock
+
+proc transform(operation: (BitReader, BitWriter) -> void, input, output: string) =
+  let inputStream = openFileStream(input, fmRead)
+  defer: inputStream.close()
+  let outputStream = openFileStream(output, fmWrite)
+  defer: outputStream.close()
+  operation(inputStream.bitReader(), outputStream.bitWriter())
+
+proc compress(bitReader: BitReader, bitWriter: BitWriter) =
+  while not bitReader.atEnd():
+    let streamBlock = streamblock.readRaw(bitReader)
+    streamBlock.writeSerialisedTo(bitWriter)
+  bitWriter.flush()
+
+proc decompress(bitReader: BitReader, bitWriter: BitWriter) =
+  var hasMore = true
+  while hasMore:
+    let streamBlock = streamblock.readSerialised(bitReader)
+    streamBlock.writeRawTo(bitWriter)
+    hasMore = not streamBlock.isLast()
+  bitWriter.flush()
+
+proc printUsage(output: File) =
+  output.writeLine("Usage: " & paramStr(0) & " <compress|decompress> <input file> <output file>")
+
 when isMainModule:
-  echo("Hello, World!")
+  if paramCount() != 3:
+    stderr.writeLine("Error: invalid argument count.")
+    printUsage(stderr)
+    quit(1)
+
+  case paramStr(1):
+    of "compress": compress.transform(paramStr(2), paramStr(3))
+    of "decompress": decompress.transform(paramStr(2), paramStr(3))
+    else:
+      stderr.writeLine("Error: invalid operation.")
+      printUsage(stderr)
+      quit(1)