1 files changed, 86 insertions, 0 deletions
diff --git a/packages/opencode/src/project/vcs.ts b/packages/opencode/src/project/vcs.ts
new file mode 100644
index 000000000..153583564
--- /dev/null
+++ b/packages/opencode/src/project/vcs.ts
@@ -0,0 +1,86 @@
+import { $ } from "bun"
+import { watch, type FSWatcher } from "fs"
+import path from "path"
+import z from "zod"
+import { Log } from "@/util/log"
+import { Bus } from "@/bus"
+import { Instance } from "./instance"
+
+const log = Log.create({ service: "vcs" })
+
+export namespace Vcs {
+  export const Event = {
+    Changed: Bus.event(
+      "vcs.changed",
+      z.object({
+        branch: z.string().optional(),
+      }),
+    ),
+  }
+
+  async function currentBranch() {
+    return $`git rev-parse --abbrev-ref HEAD`
+      .quiet()
+      .nothrow()
+      .cwd(Instance.worktree)
+      .text()
+      .then((x) => x.trim())
+      .catch(() => undefined)
+  }
+
+  const state = Instance.state(
+    async () => {
+      if (Instance.project.vcs !== "git") {
+        return { branch: async () => undefined, watcher: undefined }
+      }
+      let current = await currentBranch()
+      log.info("initialized", { branch: current })
+
+      const gitDir = await $`git rev-parse --git-dir`
+        .quiet()
+        .nothrow()
+        .cwd(Instance.worktree)
+        .text()
+        .then((x) => x.trim())
+        .catch(() => undefined)
+      if (!gitDir) {
+        log.warn("failed to resolve git directory")
+        return { branch: async () => current, watcher: undefined }
+      }
+
+      const gitHead = path.join(gitDir, "HEAD")
+      let watcher: FSWatcher | undefined
+      // we should probably centralize file watching (see watcher.ts)
+      // but parcel still marked experimental rn
+      try {
+        watcher = watch(gitHead, async () => {
+          const next = await currentBranch()
+          if (next !== current) {
+            log.info("branch changed", { from: current, to: next })
+            current = next
+            Bus.publish(Event.Changed, { branch: next })
+          }
+        })
+        log.info("watching", { path: gitHead })
+      } catch (e) {
+        log.warn("failed to watch git HEAD", { error: e })
+      }
+
+      return {
+        branch: async () => current,
+        watcher,
+      }
+    },
+    async (state) => {
+      state.watcher?.close()
+    },
+  )
+
+  export async function init() {
+    return state()
+  }
+
+  export async function branch() {
+    return await state().then((s) => s.branch())
+  }
+}