handle environment, ready for stdio communication

.gitignore

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+nimcache
+bin
+src/crvc

crvc.nimble

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+# Package
+
+version          = "0.1.0"
+author           = "Jarrad Hope"
+description   = "Cryptoeconomic Release and Version Control"
+license           = "MIT"
+srcDir              = "src"
+binDir             = "bin"
+bin                   = @["crvc"] # TODO rename to "git-remote-crvc" ?
+
+
+# Dependencies
+
+requires "nim >= 0.19.0"

src/crvc.nim

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+import os, strformat, strutils, rdstdin
+
+const
+  gitEnv = "GIT_DIR"
+  protocol = "crvc"
+
+proc setup(gitEnv: string, protocol: string): (string, string, string, string) =
+  # Checks the Environment and returns the git Working directory, the protocol, the remote and url
+
+  if paramCount() < 2:
+    raise newException(ValueError, fmt"Usage: {getAppFilename()} <remote-name> <url>")
+
+  let
+    remote = paramStr(1) # <remote-name>
+    url = paramStr(2) # <url>
+    gitDir = getEnv(gitEnv)
+
+  # Check if GIT_DIR Environment Variable is set
+  if gitDir.isNilOrWhitespace:
+    raise newException(OSError, fmt"{gitEnv} is not set")
+
+  # Check if the .git directory exists
+  if not existsDir(gitDir):
+    raise newException(OSError, fmt"{gitDir} does not appear to be a git repository")
+
+  # Create our Working Directory if it doesn't exist
+  let path = joinPath(gitDir, protocol, remote)
+  if not existsDir(path):
+    createDir(path)
+  return (gitDir, protocol, remote, url) # I don't like result, too immutable
+
+proc processStdio (env: tuple): void = 
+  # Supports the Git Remote Helper stdio protocol
+  # https://git-scm.com/docs/git-remote-helpers
+  let (gitDir, protocol, remote, url) = env
+
+  while true:
+    var
+      response: string
+      line: string = readLine(stdin) # TODO something better here ? https://nim-lang.org/docs/streams.html
+    # echo line
+
+    # Git sends the remote helper a list of commands on standard input, one per line. 
+    # The first command is always the capabilities command, in response to which the remote helper must print a list of the capabilities it supports followed by a blank line.
+    case line:
+      of "capabilities":
+        response = "capabilities response"
+      of "list":
+        response = "list response"
+      of "export":
+        response = "export response"
+      else:
+        raise newException(IOError, fmt"Unrecognised command: {line}")
+    write(stdout, response)
+
+
+proc bail() {.noconv.} =
+  quit()
+
+when isMainModule:
+  setControlCHook(bail)
+
+  try:
+    processStdio(setup(gitEnv, protocol))
+  except:
+    echo getCurrentExceptionMsg()
+  finally:
+    quit()