Add --output-format argument

This patch adds the --output-format argument that makes it possible to
select a format for the data that nitrocli prints to stdout.  Currently,
the only supported format is text output, i. e. a human-readable
representation.

TODO: man page, changelog

3 files changed, 56 insertions, 13 deletions

diff --git a/src/args.rs b/src/args.rs
index f54025e..758af8c 100644
--- a/src/args.rs
+++ b/src/args.rs
@@ -16,6 +16,9 @@ pub struct Args {
   /// Disables the cache for all secrets.
   #[structopt(long, global = true)]
   pub no_cache: bool,
+  /// Selects the output format.
+  #[structopt(long, global = true, possible_values = &OutputFormat::all_str())]
+  pub output_format: Option<OutputFormat>,
   #[structopt(subcommand)]
   pub cmd: Command,
 }
@@ -68,6 +71,26 @@ impl<'de> serde::Deserialize<'de> for DeviceModel {
   }
 }
 
+Enum! {
+  /// The format for the nitrocli output.
+  OutputFormat, [
+    Text => "text",
+  ]
+}
+
+impl<'de> serde::Deserialize<'de> for OutputFormat {
+  fn deserialize<D>(deserializer: D) -> Result<OutputFormat, D::Error>
+  where
+    D: serde::Deserializer<'de>,
+  {
+    use serde::de::Error as _;
+    use std::str::FromStr as _;
+
+    let s = String::deserialize(deserializer)?;
+    OutputFormat::from_str(&s).map_err(D::Error::custom)
+  }
+}
+
 Command! {
   /// A top-level command for nitrocli.
   Command, [
diff --git a/src/config.rs b/src/config.rs
index aceda38..b96d071 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -32,6 +32,8 @@ pub struct Config {
   #[merge(strategy = merge::num::overwrite_zero)]
   #[serde(default)]
   pub verbosity: u8,
+  /// The output format.
+  pub output_format: Option<args::OutputFormat>,
 }
 
 impl Config {
@@ -57,6 +59,9 @@ impl Config {
     if args.verbose > 0 {
       self.verbosity = args.verbose;
     }
+    if args.output_format.is_some() {
+      self.output_format = args.output_format;
+    }
   }
 }
 
diff --git a/src/output.rs b/src/output.rs
index 77fb93b..7c85a82 100644
--- a/src/output.rs
+++ b/src/output.rs
@@ -7,19 +7,28 @@
 
 use std::fmt;
 
+use crate::args;
 use crate::Context;
 
 /// A trait for objects that can be printed as nitrocli’s output.
 pub trait Output {
-  /// Formats this object as a string that can be printed to the standard output.
-  fn format(&self) -> anyhow::Result<String>;
+  /// Formats this object using the given output format.
+  fn format(&self, format: args::OutputFormat) -> anyhow::Result<String>;
 
-  /// Prints this object to the output set in the given context.
+  /// Prints this object to the output set in the given context using the output format set in the
+  /// context configuration.
   ///
   /// The default implementation for this method prints the return value of `format` to
   /// `ctx.stdout`.
   fn print(&self, ctx: &mut Context<'_>) -> anyhow::Result<()> {
-    println!(ctx, "{}", self.format()?.trim_end()).map_err(From::from)
+    println!(
+      ctx,
+      "{}",
+      self
+        .format(ctx.config.output_format.unwrap_or(args::OutputFormat::Text))?
+        .trim_end()
+    )
+    .map_err(From::from)
   }
 }
 
@@ -54,8 +63,10 @@ impl<T: fmt::Display> Value<T> {
 }
 
 impl<T: fmt::Display> Output for Value<T> {
-  fn format(&self) -> anyhow::Result<String> {
-    Ok(self.0.to_string())
+  fn format(&self, format: args::OutputFormat) -> anyhow::Result<String> {
+    match format {
+      args::OutputFormat::Text => Ok(self.0.to_string()),
+    }
   }
 }
 
@@ -77,13 +88,17 @@ impl<T: TableItem> Table<T> {
 }
 
 impl<T: TableItem> Output for Table<T> {
-  fn format(&self) -> anyhow::Result<String> {
-    if self.items.is_empty() {
-      Ok(self.empty_message.clone())
-    } else {
-      let headers = T::headers().into_iter().map(ToOwned::to_owned).collect();
-      let values = self.items.iter().map(TableItem::values);
-      Ok(print_table(headers, values))
+  fn format(&self, format: args::OutputFormat) -> anyhow::Result<String> {
+    match format {
+      args::OutputFormat::Text => {
+        if self.items.is_empty() {
+          Ok(self.empty_message.clone())
+        } else {
+          let headers = T::headers().into_iter().map(ToOwned::to_owned).collect();
+          let values = self.items.iter().map(TableItem::values);
+          Ok(print_table(headers, values))
+        }
+      }
     }
   }
 }