feat(input): implement IME preedit state machine and cursor area tracker

crates/molotov-core/src/input/ime.rs

@@ -0,0 +1,88 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
+pub struct Rect {
+    pub x: i32,
+    pub y: i32,
+    pub width: i32,
+    pub height: i32,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum ImeState {
+    Inactive,
+    Active,
+}
+
+pub struct ImeManager {
+    state: ImeState,
+    cursor_area: Rect,
+    preedit_text: String,
+    cursor_pos: usize,
+}
+
+impl Default for ImeManager {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl ImeManager {
+    pub fn new() -> Self {
+        Self {
+            state: ImeState::Inactive,
+            cursor_area: Rect::default(),
+            preedit_text: String::new(),
+            cursor_pos: 0,
+        }
+    }
+
+    pub fn is_active(&self) -> bool {
+        self.state == ImeState::Active
+    }
+
+    pub fn start_text_input(&mut self, area: Rect) {
+        self.state = ImeState::Active;
+        self.cursor_area = area;
+        self.preedit_text.clear();
+        self.cursor_pos = 0;
+    }
+
+    pub fn stop_text_input(&mut self) {
+        self.state = ImeState::Inactive;
+        self.preedit_text.clear();
+        self.cursor_pos = 0;
+    }
+
+    pub fn set_cursor_area(&mut self, area: Rect) {
+        self.cursor_area = area;
+    }
+
+    pub fn cursor_area(&self) -> Rect {
+        self.cursor_area
+    }
+
+    pub fn update_preedit(&mut self, text: &str, cursor_pos: usize) {
+        self.preedit_text = text.to_string();
+        self.cursor_pos = cursor_pos.min(self.preedit_text.chars().count());
+    }
+
+    pub fn preedit_text(&self) -> &str {
+        &self.preedit_text
+    }
+
+    pub fn cursor_pos(&self) -> usize {
+        self.cursor_pos
+    }
+
+    pub fn commit_text(&mut self, text: &str) -> String {
+        self.preedit_text.clear();
+        self.cursor_pos = 0;
+        text.to_string()
+    }
+
+    pub fn cancel_composition(&mut self) {
+        self.preedit_text.clear();
+        self.cursor_pos = 0;
+    }
+}

crates/molotov-core/src/input/mod.rs

@@ -0,0 +1,2 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+pub mod ime;

crates/molotov-core/src/lib.rs

@@ -2,6 +2,7 @@
 pub mod audio;
 pub mod dynamic;
 pub mod elf;
+pub mod input;
 pub mod jni;
 pub mod linker;
 pub mod mmap;

crates/molotov-core/tests/ime_preedit_test.rs

@@ -0,0 +1,22 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+use molotov_core::input::ime::{ImeManager, Rect};
+
+#[test]
+fn test_ime_preedit_composition_flow() {
+    let mut ime = ImeManager::new();
+    ime.start_text_input(Rect { x: 100, y: 200, width: 20, height: 24 });
+    assert!(ime.is_active());
+
+    // User types in Japanese IME: preedit string "とうきょう"
+    ime.update_preedit("とうきょう", 4);
+    assert_eq!(ime.preedit_text(), "とうきょう");
+    assert_eq!(ime.cursor_pos(), 4);
+
+    // User selects candidate: commit "東京"
+    let committed = ime.commit_text("東京");
+    assert_eq!(committed, "東京");
+    assert_eq!(ime.preedit_text(), "", "Preedit must clear on commit");
+
+    ime.stop_text_input();
+    assert!(!ime.is_active());
+}