feat: add help command

Fixes #206 - Add `--help` command

src/CompilerCli/Argument/ArgumentParserFactory.cs

@@ -24,7 +24,8 @@ public static ArgumentParser Make()
                 new SortedSet<AbstractCliArgument>
                 {
                     new DefaultCliArgument(),
-                    new NoWaitCliArgument()
+                    new NoWaitCliArgument(),
+                    new HelpArgument()
                 }
             );
         }

src/CompilerCli/Cli/CliArguments.cs

@@ -3,5 +3,6 @@
     public class CliArguments
     {
         public bool PauseOnFinish { get; set; } = true;
+        public bool HelpExit { get; set; } = false;
     }
 }

src/CompilerCli/Cli/HelpArgument.cs

@@ -0,0 +1,54 @@
+using System;
+using System.Collections.Generic;
+
+namespace CompilerCli.Cli
+{
+    public class HelpArgument : AbstractCliArgument
+    {
+        public override void Parse(List<string> values, CliArguments cliArguments) {
+            if (values.Count != 0) {
+                throw new ArgumentException("Help flag cannot take any arguments");
+            }
+
+            cliArguments.HelpExit = true;
+        }
+
+        public override string GetSpecifier() {
+            return "--help";
+        }
+
+        public static string GetHelpMessage() {
+            return @"
+usage: CompilerCli.exe [options] --config-file [config-file]
+    Compile the VATSIM-UK Sector File with the specified config file.
+    For more information visit: https://github.com/VATSIM-UK/sector-file-compiler
+
+    options:
+        --config-file       Required. Takes a single argument. Path to a 
+                            compiler configuration JSON file. If this argument 
+                            is specified multiple times, then the compiler will
+                            attempt to merge the configs together.
+        --check-config      If set, only runs the configuration checking step 
+                            to ensure that the compiler config is correct.
+        --lint              If set, only runs the configuration check and 
+                            linting steps.
+        --validate          If set, only runs the configuration check, linting 
+                            and post-validation steps. Does not output files.
+        --skip-validation   If set, the compiler will skip the post-parse 
+                            validation phase of compilation. If running in full
+                            compilation mode, will still produce output.
+        --pretty            If set, ""large"" elements such as SECTOR will have
+                            an extra newline inserted between them, in order to
+                            provide improved readability.
+        --strip-comments    If set, any comments in the input will be removed. 
+                            If an empty line is leftover, it will be discarded.
+        --build-version     Takes a single argument. Specifies the version of 
+                            the build to replace the {VERSION} token in the 
+                            input.
+        --no-wait           Prompts the compiler not to wait for a keypress 
+                            when compilation has finished.
+        --help              Display this help page.
+";
+        }
+    }
+}

src/CompilerCli/CompilerCli.cs

@@ -35,6 +35,11 @@ static int Main(string[] args)
                 return 1;
             }
 
+            if (cliArguments.HelpExit) {
+                output.Write(HelpArgument.GetHelpMessage());
+                return 0;
+            }
+
             int returnCode = SectorFileCompilerFactory.Create(
                 compilerArguments,
                 new List<IEventObserver>() { new ConsoleOutput(output) }

tests/CompilerCliTest/Cli/HelpArgumentTest.cs

@@ -0,0 +1,41 @@
+using CompilerCli.Cli;
+using System;
+using System.Collections.Generic;
+using Xunit;
+
+namespace CompilerCliTest.Cli
+{
+    public class HelpArgumentTest
+    {
+        private CliArguments arguments;
+        private HelpArgument commandLineArgument;
+
+        public HelpArgumentTest() {
+            arguments = new CliArguments();
+            commandLineArgument = new HelpArgument();
+        }
+
+        [Fact]
+        public void TestItSetsHelpExitFlag() {
+            commandLineArgument.Parse(new List<string>(), arguments);
+            Assert.True(arguments.PauseOnFinish);
+        }
+
+        [Fact]
+        public void TestItThrowsExceptionOnTooManyValues() {
+            Assert.Throws<ArgumentException>(
+                () => commandLineArgument.Parse(new List<string>(new[] { "a", "b" }), arguments)
+            );
+        }
+
+        [Fact]
+        public void TestItReturnsASpecifier() {
+            Assert.Equal("--help", commandLineArgument.GetSpecifier());
+        }
+
+        [Fact]
+        public void TestItReturnsAHelpMessage() {
+            Assert.IsType<string>(HelpArgument.GetHelpMessage());
+        }
+    }
+}