examples: add media-stats-ui plugin

Signed-off-by: NotAShelf <raf@notashelf.dev>
Change-Id: I7c9ccac175440d278fd129dbd53f04d66a6a6964

examples/plugins/media-stats-ui/src/lib.rs

@@ -0,0 +1,101 @@
+//! Media Stats UI - Pinakes plugin
+//!
+//! A UI-only plugin that adds a library statistics dashboard and a tag manager
+//! page. All UI definitions live in `pages/stats.json` and
+//! `pages/tag-manager.json`; this WASM binary provides the minimum lifecycle
+//! surface the host runtime requires.
+//!
+//! This plugin is kind = ["ui_page"]: no media-type, metadata, thumbnail, or
+//! event-handler extension points are needed. The host will never call them,
+//! but exporting them avoids linker warnings if the host performs capability
+//! discovery via symbol inspection.
+
+#![no_std]
+
+extern crate alloc;
+
+use core::alloc::Layout;
+
+#[global_allocator]
+static ALLOC: dlmalloc::GlobalDlmalloc = dlmalloc::GlobalDlmalloc;
+
+#[panic_handler]
+fn panic(_: &core::panic::PanicInfo) -> ! {
+  core::arch::wasm32::unreachable()
+}
+
+// Host functions provided by the Pinakes runtime.
+unsafe extern "C" {
+  // Write a result value back to the host (ptr + byte length).
+  fn host_set_result(ptr: i32, len: i32);
+
+  // Emit a structured log message to the host logger.
+  // `level` mirrors tracing severity: 0=trace 1=debug 2=info 3=warn 4=error
+  fn host_log(level: i32, ptr: i32, len: i32);
+}
+
+/// # Safety
+///
+/// `json` is a valid slice; the host copies the bytes before
+/// returning so there are no lifetime concerns.
+fn set_response(json: &[u8]) {
+  unsafe { host_set_result(json.as_ptr() as i32, json.len() as i32) }
+}
+
+/// # Safety
+///
+///  Same as [`set_response`]
+fn log_info(msg: &[u8]) {
+  unsafe { host_log(2, msg.as_ptr() as i32, msg.len() as i32) }
+}
+
+/// Allocate a buffer for the host to write request data into.
+///
+/// # Returns
+///
+/// The byte offset of the allocation, or -1 on failure.
+///
+/// # Safety
+///
+/// Size is positive; Layout construction cannot fail for align=1.
+#[unsafe(no_mangle)]
+pub extern "C" fn alloc(size: i32) -> i32 {
+  if size <= 0 {
+    return 0;
+  }
+  unsafe {
+    let layout = Layout::from_size_align_unchecked(size as usize, 1);
+    let ptr = alloc::alloc::alloc(layout);
+    if ptr.is_null() { -1 } else { ptr as i32 }
+  }
+}
+
+/// Called once after the plugin is loaded. Returns 0 on success.
+#[unsafe(no_mangle)]
+pub extern "C" fn initialize() -> i32 {
+  log_info(b"media-stats-ui: initialized");
+  0
+}
+
+/// Called before the plugin is unloaded. Returns 0 on success.
+#[unsafe(no_mangle)]
+pub extern "C" fn shutdown() -> i32 {
+  log_info(b"media-stats-ui: shutdown");
+  0
+}
+
+/// # Returns
+///
+/// an empty JSON array; this plugin adds no custom media types.
+#[unsafe(no_mangle)]
+pub extern "C" fn supported_media_types(_ptr: i32, _len: i32) {
+  set_response(b"[]");
+}
+
+/// # Returns
+///
+/// An empty JSON array; this plugin handles no event types.
+#[unsafe(no_mangle)]
+pub extern "C" fn interested_events(_ptr: i32, _len: i32) {
+  set_response(b"[]");
+}