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//! # String Starts With Node
//!
//! A transform node that checks if a string starts with a prefix.
//!
//! ## Ports
//!
//! - **Input**: `"configuration"` - Receives configuration (currently unused, for consistency)
//! - **Input**: `"in"` - Receives string value
//! - **Input**: `"prefix"` - Receives prefix to check for
//! - **Output**: `"out"` - Sends boolean result (true if starts with, false otherwise)
//! - **Output**: `"error"` - Sends errors that occur during processing (e.g., type mismatch)
//!
//! ## Behavior
//!
//! The node checks if a string starts with a prefix and returns a boolean. It supports:
//! - Case-sensitive prefix matching
//! - Error handling: Non-string inputs result in errors sent to the error port
use crate::node::{InputStreams, Node, NodeExecutionError, OutputStreams};
use crate::nodes::common::BaseNode;
use crate::nodes::string::common::string_starts_with;
use async_trait::async_trait;
use futures::stream;
use std::any::Any;
use std::collections::HashMap;
use std::pin::Pin;
use std::sync::Arc;
use tokio_stream::{StreamExt, wrappers::ReceiverStream};
/// Enum to tag input ports
enum InputPort {
/// Input string.
In,
/// Prefix to check.
Prefix,
}
/// A node that checks if a string starts with a prefix.
///
/// The node receives a string value on the "in" port and a prefix on the "prefix" port,
/// then outputs a boolean result to the "out" port.
pub struct StringStartsWithNode {
/// Base node functionality.
pub(crate) base: BaseNode,
}
impl StringStartsWithNode {
/// Creates a new StringStartsWithNode with the given name.
///
/// # Example
///
/// ```rust,no_run
/// use streamweave::nodes::string::StringStartsWithNode;
///
/// let node = StringStartsWithNode::new("starts_with".to_string());
/// // Creates ports: configuration, in, prefix → out, error
/// ```
pub fn new(name: String) -> Self {
Self {
base: BaseNode::new(
name,
vec![
"configuration".to_string(),
"in".to_string(),
"prefix".to_string(),
],
vec!["out".to_string(), "error".to_string()],
),
}
}
}
#[async_trait]
impl Node for StringStartsWithNode {
fn name(&self) -> &str {
self.base.name()
}
fn set_name(&mut self, name: &str) {
self.base.set_name(name);
}
fn input_port_names(&self) -> &[String] {
self.base.input_port_names()
}
fn output_port_names(&self) -> &[String] {
self.base.output_port_names()
}
fn has_input_port(&self, name: &str) -> bool {
self.base.has_input_port(name)
}
fn has_output_port(&self, name: &str) -> bool {
self.base.has_output_port(name)
}
fn execute(
&self,
mut inputs: InputStreams,
) -> Pin<
Box<dyn std::future::Future<Output = Result<OutputStreams, NodeExecutionError>> + Send + '_>,
> {
Box::pin(async move {
// Extract input streams (configuration port is present but unused for now)
let _config_stream = inputs.remove("configuration");
let in_stream = inputs.remove("in").ok_or("Missing 'in' input")?;
let prefix_stream = inputs.remove("prefix").ok_or("Missing 'prefix' input")?;
// Tag streams to distinguish inputs
let in_stream = in_stream.map(|item| (InputPort::In, item));
let prefix_stream = prefix_stream.map(|item| (InputPort::Prefix, item));
// Merge streams
let merged_stream = stream::select(in_stream, prefix_stream);
// Create output streams
let (out_tx, out_rx) = tokio::sync::mpsc::channel(10);
let (error_tx, error_rx) = tokio::sync::mpsc::channel(10);
// Process the merged stream with buffering
let out_tx_clone = out_tx.clone();
let error_tx_clone = error_tx.clone();
tokio::spawn(async move {
let mut merged = merged_stream;
let mut in_buffer: Option<Arc<dyn Any + Send + Sync>> = None;
let mut prefix_buffer: Option<Arc<dyn Any + Send + Sync>> = None;
while let Some((port, item)) = merged.next().await {
match port {
InputPort::In => {
in_buffer = Some(item);
}
InputPort::Prefix => {
prefix_buffer = Some(item);
}
}
// Process when both inputs are available
if let (Some(v), Some(prefix)) = (in_buffer.as_ref(), prefix_buffer.as_ref()) {
match string_starts_with(v, prefix) {
Ok(result) => {
let _ = out_tx_clone.send(result).await;
// Clear buffers after processing
in_buffer = None;
prefix_buffer = None;
}
Err(e) => {
let error_arc = Arc::new(e) as Arc<dyn Any + Send + Sync>;
let _ = error_tx_clone.send(error_arc).await;
// Clear buffers after error
in_buffer = None;
prefix_buffer = None;
}
}
}
}
});
// Convert channels to streams
let mut outputs = HashMap::new();
outputs.insert(
"out".to_string(),
Box::pin(ReceiverStream::new(out_rx))
as Pin<Box<dyn tokio_stream::Stream<Item = Arc<dyn Any + Send + Sync>> + Send>>,
);
outputs.insert(
"error".to_string(),
Box::pin(ReceiverStream::new(error_rx))
as Pin<Box<dyn tokio_stream::Stream<Item = Arc<dyn Any + Send + Sync>> + Send>>,
);
Ok(outputs)
})
}
}