3 files changed, 127 insertions, 18 deletions

diff --git a/helix-term/src/commands.rs b/helix-term/src/commands.rs
index 55cbf0fe..4a329f28 100644
--- a/helix-term/src/commands.rs
+++ b/helix-term/src/commands.rs
@@ -519,22 +519,37 @@ pub fn append_mode(cx: &mut Context) {
     doc.set_selection(selection);
 }
 
+const COMMAND_LIST: &[&str] = &["write", "open", "quit"];
+
 // TODO: I, A, o and O can share a lot of the primitives.
 pub fn command_mode(cx: &mut Context) {
     let executor = cx.executor;
     let prompt = Prompt::new(
         ":".to_owned(),
-        |_input: &str| {
-            let command_list = vec![
-                "q".to_string(),
-                "o".to_string(),
-                "w".to_string(),
-                // String::from("q"),
-            ];
-            command_list
-                .into_iter()
-                .filter(|command| command.contains(_input))
-                .collect()
+        |input: &str| {
+            // we use .this over split_ascii_whitespace() because we care about empty segments
+            let parts = input.split(' ').collect::<Vec<&str>>();
+
+            // simple heuristic: if there's no space, complete command.
+            // if there's a space, file completion kicks in. We should specialize by command later.
+            if parts.len() <= 1 {
+                COMMAND_LIST
+                    .iter()
+                    .filter(|command| command.contains(input))
+                    .map(|command| std::borrow::Cow::Borrowed(*command))
+                    .collect()
+            } else {
+                let part = parts.last().unwrap();
+                ui::completers::filename(part)
+
+                // TODO
+                // completion needs to be more advanced: need to return starting index for replace
+                // for example, "src/" completion application.rs needs to insert after /, but "hx"
+                // completion helix-core needs to replace the text.
+                //
+                // additionally, completion items could have a info section that would get
+                // displayed in a popup above the prompt when items are tabbed over
+            }
         }, // completion
         move |editor: &mut Editor, input: &str, event: PromptEvent| {
             if event != PromptEvent::Validate {
@@ -544,14 +559,14 @@ pub fn command_mode(cx: &mut Context) {
             let parts = input.split_ascii_whitespace().collect::<Vec<&str>>();
 
             match *parts.as_slice() {
-                ["q"] => {
+                ["q"] | ["quit"] => {
                     editor.tree.remove(editor.view().id);
                     // editor.should_close = true,
                 }
-                ["o", path] => {
+                ["o", path] | ["open", path] => {
                     editor.open(path.into(), executor);
                 }
-                ["w"] => {
+                ["w"] | ["write"] => {
                     // TODO: non-blocking via save() command
                     smol::block_on(editor.view_mut().doc.save());
                 }
diff --git a/helix-term/src/ui/mod.rs b/helix-term/src/ui/mod.rs
index ea1d22ab..1526a210 100644
--- a/helix-term/src/ui/mod.rs
+++ b/helix-term/src/ui/mod.rs
@@ -124,3 +124,79 @@ pub fn buffer_picker(views: &[View], current: usize) -> Picker<(Option<PathBuf>,
     //     },
     // )
 }
+
+pub mod completers {
+    use std::borrow::Cow;
+    // TODO: we could return an iter/lazy thing so it can fetch as many as it needs.
+    pub fn filename(input: &str) -> Vec<Cow<'static, str>> {
+        // Rust's filename handling is really annoying.
+
+        use ignore::WalkBuilder;
+        use std::path::{Path, PathBuf};
+
+        let path = Path::new(input);
+
+        let (dir, file_name) = if input.ends_with('/') {
+            (path.into(), None)
+        } else {
+            let file_name = path
+                .file_name()
+                .map(|file| file.to_str().unwrap().to_owned());
+
+            let path = match path.parent() {
+                Some(path) if !path.as_os_str().is_empty() => path.to_path_buf(),
+                // Path::new("h")'s parent is Some("")...
+                _ => std::env::current_dir().expect("couldn't determine current directory"),
+            };
+
+            (path, file_name)
+        };
+
+        let mut files: Vec<_> = WalkBuilder::new(dir.clone())
+            .max_depth(Some(1))
+            .build()
+            .filter_map(|file| {
+                file.ok().map(|entry| {
+                    let is_dir = entry
+                        .file_type()
+                        .map(|entry| entry.is_dir())
+                        .unwrap_or(false);
+
+                    let mut path = entry.path().strip_prefix(&dir).unwrap().to_path_buf();
+
+                    if is_dir {
+                        path.push("");
+                    }
+                    Cow::from(path.to_str().unwrap().to_string())
+                })
+            }) // TODO: unwrap or skip
+            .filter(|path| !path.is_empty()) // TODO
+            .collect();
+
+        // if empty, return a list of dirs and files in current dir
+        if let Some(file_name) = file_name {
+            use fuzzy_matcher::skim::SkimMatcherV2 as Matcher;
+            use fuzzy_matcher::FuzzyMatcher;
+            use std::cmp::Reverse;
+
+            let matcher = Matcher::default();
+
+            // inefficient, but we need to calculate the scores, filter out None, then sort.
+            let mut matches: Vec<_> = files
+                .into_iter()
+                .filter_map(|file| {
+                    matcher
+                        .fuzzy_match(&file, &file_name)
+                        .map(|score| (file, score))
+                })
+                .collect();
+
+            matches.sort_unstable_by_key(|(_file, score)| Reverse(*score));
+            files = matches.into_iter().map(|(file, _)| file.into()).collect();
+
+            // TODO: complete to longest common match
+        }
+
+        files
+    }
+}
diff --git a/helix-term/src/ui/prompt.rs b/helix-term/src/ui/prompt.rs
index 7228b38c..700bc8a0 100644
--- a/helix-term/src/ui/prompt.rs
+++ b/helix-term/src/ui/prompt.rs
@@ -3,15 +3,16 @@ use crossterm::event::{Event, KeyCode, KeyEvent, KeyModifiers};
 use helix_core::Position;
 use helix_view::Editor;
 use helix_view::Theme;
+use std::borrow::Cow;
 use std::string::String;
 
 pub struct Prompt {
     pub prompt: String,
     pub line: String,
     pub cursor: usize,
-    pub completion: Vec<String>,
+    pub completion: Vec<Cow<'static, str>>,
     pub completion_selection_index: Option<usize>,
-    completion_fn: Box<dyn FnMut(&str) -> Vec<String>>,
+    completion_fn: Box<dyn FnMut(&str) -> Vec<Cow<'static, str>>>,
     callback_fn: Box<dyn FnMut(&mut Editor, &str, PromptEvent)>,
 }
 
@@ -28,7 +29,7 @@ pub enum PromptEvent {
 impl Prompt {
     pub fn new(
         prompt: String,
-        mut completion_fn: impl FnMut(&str) -> Vec<String> + 'static,
+        mut completion_fn: impl FnMut(&str) -> Vec<Cow<'static, str>> + 'static,
         callback_fn: impl FnMut(&mut Editor, &str, PromptEvent) + 'static,
     ) -> Prompt {
         Prompt {
@@ -83,7 +84,19 @@ impl Prompt {
         let index =
             self.completion_selection_index.map(|i| i + 1).unwrap_or(0) % self.completion.len();
         self.completion_selection_index = Some(index);
-        self.line = self.completion[index].clone();
+
+        let item = &self.completion[index];
+
+        // replace the last arg
+        if let Some(pos) = self.line.rfind(' ') {
+            self.line.replace_range(pos + 1.., item);
+        } else {
+            // need toowned_clone_into nightly feature to reuse allocation
+            self.line = item.to_string();
+        }
+
+        self.move_end();
+        // TODO: recalculate completion when completion item is accepted, (Enter)
     }
     pub fn exit_selection(&mut self) {
         self.completion_selection_index = None;
@@ -175,9 +188,14 @@ impl Component for Prompt {
         )));
 
         match event {
+            // char or shift char
             KeyEvent {
                 code: KeyCode::Char(c),
                 modifiers: KeyModifiers::NONE,
+            }
+            | KeyEvent {
+                code: KeyCode::Char(c),
+                modifiers: KeyModifiers::SHIFT,
             } => {
                 self.insert_char(c);
                 (self.callback_fn)(cx.editor, &self.line, PromptEvent::Update);