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//! # Example: Server-Initiated Function Call (`callFunction`)
//!
//! Demonstrates how the server can invoke client-side functions via the
//! `callFunction` message, and how the client responds with
//! `functionResponse` or `error` messages.
//!
//! ## What it demonstrates
//! - Sending a `callFunction` message to execute a catalog function
//! - `wantResponse: true` → `drain_outgoing()` returns a `functionResponse`
//! - `wantResponse: false` → silent execution, no outgoing message
//! - Calling an unregistered function → `drain_outgoing()` returns an `error`
//! - Writing the `functionResponse` result back into the data model
//!
//! ## Run
//! ```sh
//! cargo run --example 06_call_function
//! ```
use std::io;
use crossterm::{
event::{self, Event, KeyCode},
execute,
terminal::{disable_raw_mode, enable_raw_mode, EnterAlternateScreen, LeaveAlternateScreen},
};
use ratatui::{
Terminal,
backend::CrosstermBackend,
layout::{Constraint, Direction, Layout},
style::{Color, Style},
text::Line,
widgets::Paragraph,
};
use a2ui::core::catalog::Catalog;
use a2ui::core::message_processor::MessageProcessor;
use a2ui::core::protocol::client_to_server::ClientPayload;
use a2ui::tui::catalogs::basic::{build_basic_catalog, build_basic_registry};
fn main() -> Result<(), Box<dyn std::error::Error>> {
let registry = build_basic_registry();
let render_catalog = Catalog::new("placeholder");
let mut processor = MessageProcessor::new(vec![build_basic_catalog()]);
// Track last outgoing message for display
let mut status_text = String::new();
// ── 1. Create surface with initial data ──────────────────────────────
let create_msg = serde_json::json!({
"version": "v1.0",
"createSurface": {
"surfaceId": "demo",
"catalogId": "https://a2ui.org/specification/v1_0/catalogs/basic/catalog.json",
"dataModel": {
"name": "Alice",
"greeting": "Press 'f' to call a function"
}
}
});
processor.process_message(MessageProcessor::parse_message(&create_msg.to_string())?)?;
// ── 2. Define component tree ────────────────────────────────────────
// The "greeting" Text is bound to /greeting in the data model.
// When we write a functionResponse value there, the UI updates.
let update_msg = serde_json::json!({
"version": "v1.0",
"updateComponents": {
"surfaceId": "demo",
"components": [
{
"id": "root",
"component": "Column",
"children": ["title", "name_display", "divider_1", "greeting", "divider_2", "status"],
"justify": "center",
"align": "stretch"
},
{
"id": "title",
"component": "Text",
"text": "callFunction Demo",
"variant": "h1"
},
{
"id": "name_display",
"component": "Text",
"text": {"path": "/name"},
"variant": "h3"
},
{
"id": "divider_1",
"component": "Divider",
"axis": "horizontal"
},
{
"id": "greeting",
"component": "Text",
"text": {"path": "/greeting"},
"variant": "body"
},
{
"id": "divider_2",
"component": "Divider",
"axis": "horizontal"
},
{
"id": "status",
"component": "Text",
"text": {"path": "/status"},
"variant": "caption"
}
]
}
});
processor.process_message(MessageProcessor::parse_message(&update_msg.to_string())?)?;
// ── 3. Demonstrate callFunction with wantResponse ───────────────────
// The server asks the client to execute "formatString".
// With wantResponse: true, the result comes back via drain_outgoing().
let call_msg = serde_json::json!({
"version": "v1.0",
"functionCallId": "call_1",
"wantResponse": true,
"callFunction": {
"call": "formatString",
"args": { "value": "Hello, ${/name}! Welcome to A2UI." }
}
});
processor.process_message(MessageProcessor::parse_message(&call_msg.to_string())?)?;
// Drain the outgoing messages produced by callFunction
let outgoing = processor.drain_outgoing();
if let Some(msg) = outgoing.first() {
match &msg.payload {
ClientPayload::FunctionResponse(fr) => {
let value = &fr.function_response.value;
// Write the function result into the data model at /greeting
let write_msg = serde_json::json!({
"version": "v1.0",
"updateDataModel": {
"surfaceId": "demo",
"path": "/greeting",
"value": value
}
});
processor.process_message(
MessageProcessor::parse_message(&write_msg.to_string())?,
)?;
status_text = format!(
"functionResponse: call={}, value={}",
fr.function_response.call, value
);
}
ClientPayload::Error(err) => {
status_text = format!("Error: {}", err.error.message);
}
_ => {}
}
}
// Update status text in data model
let status_update = serde_json::json!({
"version": "v1.0",
"updateDataModel": {
"surfaceId": "demo",
"path": "/status",
"value": status_text
}
});
processor.process_message(MessageProcessor::parse_message(&status_update.to_string())?)?;
// ── 4. Interactive loop ─────────────────────────────────────────────
// f: call formatString (with wantResponse) → update greeting
// e: call nonexistent function → see error response
// n: cycle name in data model
enable_raw_mode()?;
let mut stdout = io::stderr();
execute!(stdout, EnterAlternateScreen)?;
let backend = CrosstermBackend::new(io::stderr());
let mut terminal = Terminal::new(backend)?;
let names = ["Alice", "Bob", "Charlie", "Diana"];
let mut name_idx = 0;
let mut call_counter = 1u32;
loop {
terminal.draw(|frame| {
let area = frame.area();
let chunks = Layout::default()
.direction(Direction::Vertical)
.constraints([Constraint::Min(5), Constraint::Length(2)])
.split(area);
if let Some(surface) = processor.model.get_surface("demo") {
let renderer = a2ui::tui::surface::SurfaceRenderer::new(
surface, ®istry, &render_catalog,
);
renderer.render(frame, chunks[0], None);
}
let help = " f: call function e: call invalid n: cycle name q: quit ";
let bar = Paragraph::new(Line::from(help))
.style(Style::default().fg(Color::DarkGray));
frame.render_widget(bar, chunks[1]);
})?;
if event::poll(std::time::Duration::from_millis(100))? {
if let Event::Key(key) = event::read()? {
match key.code {
KeyCode::Char('q') => break,
KeyCode::Char('n') => {
name_idx = (name_idx + 1) % names.len();
let msg = serde_json::json!({
"version": "v1.0",
"updateDataModel": {
"surfaceId": "demo",
"path": "/name",
"value": names[name_idx]
}
});
processor.process_message(
MessageProcessor::parse_message(&msg.to_string())?,
)?;
}
KeyCode::Char('f') => {
// Call formatString with data binding, wantResponse: true
call_counter += 1;
let call_id = format!("call_{}", call_counter);
let call_msg = serde_json::json!({
"version": "v1.0",
"functionCallId": call_id,
"wantResponse": true,
"callFunction": {
"call": "formatString",
"args": { "value": "Hello, ${/name}! The answer is 42." }
}
});
processor.process_message(
MessageProcessor::parse_message(&call_msg.to_string())?,
)?;
let outgoing = processor.drain_outgoing();
let new_status = if let Some(msg) = outgoing.first() {
match &msg.payload {
ClientPayload::FunctionResponse(fr) => {
let value = &fr.function_response.value;
// Write result to data model
let write_msg = serde_json::json!({
"version": "v1.0",
"updateDataModel": {
"surfaceId": "demo",
"path": "/greeting",
"value": value
}
});
processor.process_message(
MessageProcessor::parse_message(&write_msg.to_string())?,
)?;
format!("✓ functionResponse: {}", value)
}
ClientPayload::Error(err) => {
format!("✗ Error: {}", err.error.message)
}
_ => "unknown response".to_string(),
}
} else {
"no response (wantResponse was false)".to_string()
};
let status_update = serde_json::json!({
"version": "v1.0",
"updateDataModel": {
"surfaceId": "demo",
"path": "/status",
"value": new_status
}
});
processor.process_message(
MessageProcessor::parse_message(&status_update.to_string())?,
)?;
}
KeyCode::Char('e') => {
// Call a nonexistent function → should produce an error
call_counter += 1;
let call_id = format!("call_{}", call_counter);
let call_msg = serde_json::json!({
"version": "v1.0",
"functionCallId": call_id,
"wantResponse": true,
"callFunction": {
"call": "thisFunctionDoesNotExist",
"args": {}
}
});
processor.process_message(
MessageProcessor::parse_message(&call_msg.to_string())?,
)?;
let outgoing = processor.drain_outgoing();
if let Some(msg) = outgoing.first() {
match &msg.payload {
ClientPayload::Error(err) => {
let status = format!("✗ Error: {} (code: {})", err.error.message, err.error.code);
let status_update = serde_json::json!({
"version": "v1.0",
"updateDataModel": {
"surfaceId": "demo",
"path": "/status",
"value": status
}
});
processor.process_message(
MessageProcessor::parse_message(&status_update.to_string())?,
)?;
}
other => {
let status = format!("Unexpected response: {:?}", other);
let status_update = serde_json::json!({
"version": "v1.0",
"updateDataModel": {
"surfaceId": "demo",
"path": "/status",
"value": status
}
});
processor.process_message(
MessageProcessor::parse_message(&status_update.to_string())?,
)?;
}
}
}
}
_ => {}
}
}
}
}
disable_raw_mode()?;
execute!(stdout, LeaveAlternateScreen)?;
// Show final state
if let Some(surface) = processor.model.get_surface("demo") {
let dm = surface.data_model.borrow();
println!("Final data model: {}", serde_json::to_string_pretty(&dm.as_value())?);
}
Ok(())
}