Add input dialog boxes

This patch implements input dialog boxes.  This required some
refactoring in the dialog backend to allow additional arguments after
the width and the height.

3 files changed, 145 insertions, 26 deletions

diff --git a/src/backends/dialog.rs b/src/backends/dialog.rs
index d50be43..8cde8cc 100644
--- a/src/backends/dialog.rs
+++ b/src/backends/dialog.rs
@@ -5,7 +5,7 @@ use std::io;
 use std::io::Result;
 use std::process;
 
-use crate::Message;
+use crate::{Input, Message};
 
 /// The `dialog` backend.
 ///
@@ -28,20 +28,6 @@ impl Dialog {
         }
     }
 
-    fn execute(&self, args: Vec<&str>) -> Result<process::Output> {
-        let mut args = args;
-        if let Some(ref backtitle) = self.backtitle {
-            args.insert(0, "--backtitle");
-            args.insert(1, backtitle);
-        }
-        println!("{:?}", args);
-        process::Command::new("dialog")
-            .args(args)
-            .stdin(process::Stdio::inherit())
-            .stdout(process::Stdio::inherit())
-            .output()
-    }
-
     /// Sets the backtitle for the dialog boxes.
     ///
     /// The backtitle is displayed on the backdrop, at the top of the screen.
@@ -65,15 +51,31 @@ impl Dialog {
         self.width = width.to_string();
     }
 
-    fn show_box(&self, args: Vec<&str>, title: &Option<String>) -> Result<process::Output> {
-        let mut args = args;
+    fn execute(
+        &self,
+        args: Vec<&str>,
+        post_args: Vec<&str>,
+        title: &Option<String>,
+    ) -> Result<process::Output> {
+        let mut command = process::Command::new("dialog");
+        command.stdin(process::Stdio::inherit());
+        command.stdout(process::Stdio::inherit());
+
+        if let Some(ref backtitle) = self.backtitle {
+            command.arg("--backtitle");
+            command.arg(backtitle);
+        }
         if let Some(ref title) = title {
-            args.insert(0, "--title");
-            args.insert(1, title);
+            command.arg("--title");
+            command.arg(title);
         }
-        args.push(&self.height);
-        args.push(&self.width);
-        self.execute(args)
+
+        command.args(args);
+        command.arg(&self.height);
+        command.arg(&self.width);
+        command.args(post_args);
+
+        command.output()
     }
 }
 
@@ -85,10 +87,47 @@ fn require_success(status: process::ExitStatus) -> Result<()> {
     }
 }
 
+fn get_stderr(output: process::Output) -> Result<Option<String>> {
+    if output.status.success() {
+        String::from_utf8(output.stderr)
+            .map(|s| Some(s))
+            .map_err(|_| {
+                io::Error::new(io::ErrorKind::Other, "Input contained invalid UTF-8 bytes")
+            })
+    } else {
+        if let Some(code) = output.status.code() {
+            match code {
+                0 => Ok(None),
+                1 => Ok(None),
+                -1 => Ok(None),
+                _ => Err(io::Error::new(
+                    io::ErrorKind::Other,
+                    "Could not execute dialog",
+                )),
+            }
+        } else {
+            Err(io::Error::new(
+                io::ErrorKind::Other,
+                "dialog was terminated by a signal",
+            ))
+        }
+    }
+}
+
 impl super::Backend for Dialog {
+    fn show_input(&self, input: &Input) -> Result<Option<String>> {
+        let args = vec!["--inputbox", &input.text];
+        let mut post_args: Vec<&str> = Vec::new();
+        if let Some(ref default) = input.default {
+            post_args.push(default);
+        }
+        self.execute(args, post_args, &input.title)
+            .and_then(get_stderr)
+    }
+
     fn show_message(&self, message: &Message) -> Result<()> {
         let args = vec!["--msgbox", &message.text];
-        self.show_box(args, &message.title)
+        self.execute(args, vec![], &message.title)
             .and_then(|output| require_success(output.status))
             .map(|_| ())
     }
diff --git a/src/backends/mod.rs b/src/backends/mod.rs
index c316307..1abb8d1 100644
--- a/src/backends/mod.rs
+++ b/src/backends/mod.rs
@@ -17,6 +17,9 @@ use std::io::Result;
 /// [`default_backend`]: ../function.default_backend.html
 /// [`show_with`]: ../trait.DialogBox.html#method.show_with
 pub trait Backend {
+    /// Shows the given input dialog and returns the input.
+    fn show_input(&self, input: &super::Input) -> Result<Option<String>>;
+
     /// Shows the given message dialog.
     fn show_message(&self, message: &super::Message) -> Result<()>;
 }
diff --git a/src/lib.rs b/src/lib.rs
index 67bef2d..0c9d9f9 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -7,6 +7,7 @@
 //!
 //! The `dialog` crate can be used to display different types of dialog boxes.  The supported types
 //! are:
+//! - [`Input`][]: a text input dialog
 //! - [`Message`][]: a simple message box
 //!
 //! These dialog boxes can be displayed using various backends:
@@ -45,8 +46,24 @@
 //!     .expect("Could not display dialog box");
 //! ```
 //!
-//! [`Message`]: struct.Message.html
+//! Query a string from the user:
+//!
+//! ```no_run
+//! use dialog::DialogBox;
+//!
+//! let name = dialog::Input::new("Please enter your name")
+//!     .title("Name")
+//!     .show()
+//!     .expect("Could not display dialog box");
+//! match name {
+//!     Some(name) => println!("Hello {}!", name),
+//!     None => println!("Hello stranger!"),
+//! };
+//! ```
+//!
 //! [`Dialog`]: backends/struct.Dialog.html
+//! [`Input`]: struct.Input.html
+//! [`Message`]: struct.Message.html
 //! [`default_backend`]: fn.default_backend.html
 //! [`show`]: trait.DialogBox.html#method.show
 //! [`show_with`]: trait.DialogBox.html#method.show_with
@@ -69,14 +86,14 @@ pub trait DialogBox {
     /// The type of the data returned by the dialog box.
     type Output;
 
-    /// Shows this dialog box using the default backend.
+    /// Shows this dialog box using the default backend and returns the output.
     ///
     /// `box.show()` is a shorthand for `box.show_with(&default_backend())`.
     fn show(&self) -> Result<Self::Output> {
         self.show_with(&default_backend())
     }
 
-    /// Shows this dialog box using the given backend.
+    /// Shows this dialog box using the given backend and returns the output.
     fn show_with(&self, backend: &impl backends::Backend) -> Result<Self::Output>;
 }
 
@@ -126,6 +143,66 @@ impl DialogBox for Message {
     }
 }
 
+/// A dialog box with a text input field.
+///
+/// This dialog box displays a text and an input field.  It returns the text entered by the user or
+/// `None` if the user cancelled the dialog.
+///
+/// # Example
+///
+/// ```no_run
+/// use dialog::DialogBox;
+///
+/// let name = dialog::Input::new("Please enter your name")
+///     .title("Name")
+///     .show()
+///     .expect("Could not display dialog box");
+/// match name {
+///     Some(name) => println!("Hello {}!", name),
+///     None => println!("Hello stranger!"),
+/// };
+/// ```
+pub struct Input {
+    text: String,
+    title: Option<String>,
+    default: Option<String>,
+}
+
+impl Input {
+    /// Creates a new input dialog box with the given text.
+    pub fn new(text: impl Into<String>) -> Input {
+        Input {
+            text: text.into(),
+            title: None,
+            default: None,
+        }
+    }
+
+    /// Sets the title of this input box.
+    ///
+    /// This method returns a reference to `self` to enable chaining.
+    pub fn title(&mut self, title: impl Into<String>) -> &mut Input {
+        self.title = Some(title.into());
+        self
+    }
+
+    /// Sets the default value of this input box.
+    ///
+    /// This method returns a reference to `self` to enable chaining.
+    pub fn default(&mut self, default: impl Into<String>) -> &mut Input {
+        self.default = Some(default.into());
+        self
+    }
+}
+
+impl DialogBox for Input {
+    type Output = Option<String>;
+
+    fn show_with(&self, backend: &impl backends::Backend) -> Result<Self::Output> {
+        backend.show_input(self)
+    }
+}
+
 /// Creates a new instance of the default backend.
 ///
 /// The current implementation always returns a [`Dialog`][] instance.