Add FileSelection dialog type

This patch adds the FileSelection struct representing a file selection
dialog.  It can be displayed using the backend’s show_file_selection
function.

Currently, we only support file open dialogs (i. e.  choosing an
existing file).  Support for save dialogs should be added in the future.

4 files changed, 33 insertions, 3 deletions

diff --git a/src/backends/dialog.rs b/src/backends/dialog.rs
index 8061d98..668cf57 100644
--- a/src/backends/dialog.rs
+++ b/src/backends/dialog.rs
@@ -3,7 +3,7 @@
 
 use std::process;
 
-use crate::{Choice, Error, Input, Message, Password, Question, Result};
+use crate::{Choice, Error, FileSelection, Input, Message, Password, Question, Result};
 
 /// The `dialog` backend.
 ///
@@ -160,4 +160,11 @@ impl super::Backend for Dialog {
         self.execute(args, vec![], &question.title)
             .and_then(|output| get_choice(output.status))
     }
+
+    fn show_file_selection(&self, file_selection: &FileSelection) -> Result<Option<String>> {
+        let dir = file_selection.path_to_string().ok_or("path not valid")?;
+        let args = vec!["--fselect", &dir];
+        self.execute(args, vec![], &file_selection.title)
+            .and_then(get_stderr)
+    }
 }
diff --git a/src/backends/mod.rs b/src/backends/mod.rs
index 1331323..09013b1 100644
--- a/src/backends/mod.rs
+++ b/src/backends/mod.rs
@@ -37,6 +37,9 @@ pub trait Backend {
 
     /// Shows the given question dialog and returns the choice.
     fn show_question(&self, question: &super::Question) -> Result<super::Choice>;
+
+    /// Shows the given file selection dialog and returns the file name.
+    fn show_file_selection(&self, file_selection: &super::FileSelection) -> Result<Option<String>>;
 }
 
 pub(crate) fn is_available(name: &str) -> bool {
diff --git a/src/backends/stdio.rs b/src/backends/stdio.rs
index 9a153df..627714a 100644
--- a/src/backends/stdio.rs
+++ b/src/backends/stdio.rs
@@ -3,7 +3,7 @@
 
 use std::io::{self, Write};
 
-use crate::{Choice, Input, Message, Password, Question, Result};
+use crate::{Choice, FileSelection, Input, Message, Password, Question, Result};
 
 /// The fallback backend using standard input and output.
 ///
@@ -86,4 +86,17 @@ impl super::Backend for Stdio {
         io::stdout().flush()?;
         Ok(parse_choice(&read_input()?))
     }
+
+    fn show_file_selection(&self, file_selection: &FileSelection) -> Result<Option<String>> {
+        let dir = file_selection.path_to_string().ok_or("path not valid")?;
+        print_title(&file_selection.title);
+        print!("{} [{}]: ", file_selection.text, dir);
+        io::stdout().flush()?;
+        let result = read_input()?;
+        if result.starts_with('/') {
+            Ok(Some(result))
+        } else {
+            Ok(Some(dir + &result))
+        }
+    }
 }
diff --git a/src/backends/zenity.rs b/src/backends/zenity.rs
index 0deca0a..4ee7785 100644
--- a/src/backends/zenity.rs
+++ b/src/backends/zenity.rs
@@ -3,7 +3,7 @@
 
 use std::process;
 
-use crate::{Choice, Error, Input, Message, Password, Question, Result};
+use crate::{Choice, Error, FileSelection, Input, Message, Password, Question, Result};
 
 /// The `zenity` backend.
 ///
@@ -163,4 +163,11 @@ impl super::Backend for Zenity {
         self.execute(args, &question.title)
             .and_then(|output| get_choice(output.status))
     }
+
+    fn show_file_selection(&self, file_selection: &FileSelection) -> Result<Option<String>> {
+        let dir = file_selection.path_to_string().ok_or("path not valid")?;
+        let args = vec!["--file-selection", "--filename", &dir];
+        self.execute(args, &file_selection.title)
+            .and_then(get_stdout)
+    }
 }