Add another command for printing out JSON

Sources/CLI/CLI.swift

@@ -7,7 +7,7 @@ struct Tool: ParsableCommand {
     static var configuration = CommandConfiguration(
         commandName: "dotenvy-tool",
         abstract: "Tool for working with dotenv files",
-        subcommands: [Check.self]
+        subcommands: [Check.self, JSON.self]
     )
 }
 
@@ -43,6 +43,49 @@ struct Check: ParsableCommand {
     }
 }
 
+struct JSON: ParsableCommand {
+    static var configuration
+        = CommandConfiguration(
+            abstract: "Convert input to JSON.",
+            discussion: """
+            The input is converted to a JSON object.
+
+            In case of a syntax error, the error is printed to standard error and the
+            command exits with failure code \(ExitCode.failure.rawValue).
+
+            If there are no problems reading the input, the JSON value is printed to
+            standard output and the command exits with \(ExitCode.success.rawValue).
+            """
+        )
+
+    @Argument(help: "Input file. Standard input is used if omitted")
+    var file: FileURL?
+
+    @Flag(help: "Pretty print JSON")
+    var pretty: Bool = false
+
+    func validate() throws {
+        _ = try self.file?.url.checkResourceIsReachable()
+    }
+
+    func run() throws {
+        let string = try readInput(self.file)
+        do {
+            let values = try DotEnvironment.parse(string: string)
+            let json = try JSONSerialization.data(
+                withJSONObject: values,
+                options: self.pretty ? [.prettyPrinted, .sortedKeys] : []
+            )
+            FileHandle.standardOutput.write(json)
+            FileHandle.standardOutput.write(Data("\n".utf8))
+        } catch let error as ParseErrorWithLocation {
+            FileHandle.standardError.write(Data(error.formatError(source: string).utf8))
+            FileHandle.standardError.write(Data("\n".utf8))
+            throw ExitCode.failure
+        }
+    }
+}
+
 struct FileURL: ExpressibleByArgument {
     var url: URL