examples/rust_ort_example.rs

// granite-docling ONNX Rust Example with ORT crate
// Demonstrates how to use granite-docling ONNX model in Rust applications

use anyhow::Result;
use ort::{
    execution_providers::ExecutionProvider,
    session::{Session, builder::GraphOptimizationLevel},
    inputs, value::TensorRef,
};
use ndarray::{Array1, Array2, Array4};

/// granite-docling ONNX inference engine
pub struct GraniteDoclingONNX {
    session: Session,
}

impl GraniteDoclingONNX {
    /// Load granite-docling ONNX model
    pub fn new(model_path: &str) -> Result<Self> {
        println!("Loading granite-docling ONNX model from: {}", model_path);

        let session = Session::builder()?
            .with_optimization_level(GraphOptimizationLevel::Level3)?
            .with_execution_providers([
                ExecutionProvider::DirectML,  // Windows ML acceleration
                ExecutionProvider::CUDA,      // NVIDIA acceleration
                ExecutionProvider::CPU,       // Universal fallback
            ])?
            .commit_from_file(model_path)?;

        // Print model information
        println!("Model loaded successfully:");
        for (i, input) in session.inputs()?.iter().enumerate() {
            println!("  Input {}: {} {:?}", i, input.name(), input.input_type());
        }
        for (i, output) in session.outputs()?.iter().enumerate() {
            println!("  Output {}: {} {:?}", i, output.name(), output.output_type());
        }

        Ok(Self { session })
    }

    /// Process document image to DocTags markup
    pub async fn process_document(
        &self,
        document_image: Array4<f32>,  // [batch, channels, height, width]
        prompt: &str,
    ) -> Result<String> {

        println!("Processing document with granite-docling...");

        // Prepare text inputs (simplified tokenization)
        let input_ids = self.tokenize_prompt(prompt)?;
        let attention_mask = Array2::ones((1, input_ids.len()));

        // Convert to required input format
        let input_ids_2d = Array2::from_shape_vec(
            (1, input_ids.len()),
            input_ids.iter().map(|&x| x as i64).collect(),
        )?;

        // Run inference
        let outputs = self.session.run(inputs![
            "pixel_values" => TensorRef::from_array_view(&document_image.view())?,
            "input_ids" => TensorRef::from_array_view(&input_ids_2d.view())?,
            "attention_mask" => TensorRef::from_array_view(&attention_mask.view())?,
        ])?;

        // Extract logits and decode to text
        let logits = outputs["logits"].try_extract_tensor::<f32>()?;
        let tokens = self.decode_logits_to_tokens(&logits)?;
        let doctags = self.detokenize_to_doctags(&tokens)?;

        println!("✅ Document processing complete");
        Ok(doctags)
    }

    /// Simple tokenization (in practice, use proper tokenizer)
    fn tokenize_prompt(&self, prompt: &str) -> Result<Vec<u32>> {
        // Simplified tokenization - in practice, load tokenizer.json
        // and use proper HuggingFace tokenization
        let tokens: Vec<u32> = prompt
            .split_whitespace()
            .enumerate()
            .map(|(i, _)| (i + 1) as u32)
            .collect();

        Ok(tokens)
    }

    /// Decode logits to most likely tokens
    fn decode_logits_to_tokens(&self, logits: &ndarray::ArrayViewD<f32>) -> Result<Vec<u32>> {
        // Find argmax for each position
        let tokens: Vec<u32> = logits
            .axis_iter(ndarray::Axis(2))
            .map(|logit_slice| {
                logit_slice
                    .iter()
                    .enumerate()
                    .max_by(|(_, a), (_, b)| a.partial_cmp(b).unwrap())
                    .map(|(idx, _)| idx as u32)
                    .unwrap_or(0)
            })
            .collect();

        Ok(tokens)
    }

    /// Convert tokens back to DocTags markup
    fn detokenize_to_doctags(&self, tokens: &[u32]) -> Result<String> {
        // In practice, use granite-docling tokenizer to convert tokens → text
        // Then parse the text as DocTags markup

        // Simplified example
        let mock_doctags = format!(
            "<doctag>\n  <text>Document processed with {} tokens</text>\n</doctag>",
            tokens.len()
        );

        Ok(mock_doctags)
    }
}

/// Preprocess document image for granite-docling inference
pub fn preprocess_document_image(image_path: &str) -> Result<Array4<f32>> {
    // Load image and resize to 512x512 (SigLIP2 requirement)
    // Normalize with SigLIP2 parameters
    // Convert to [batch, channels, height, width] format

    // Simplified example - in practice, use image processing library
    let document_image = Array4::zeros((1, 3, 512, 512));

    Ok(document_image)
}

#[tokio::main]
async fn main() -> Result<()> {
    println!("granite-docling ONNX Rust Example");

    // Load granite-docling ONNX model
    let model_path = "granite-docling-258M-onnx/model.onnx";
    let granite_docling = GraniteDoclingONNX::new(model_path)?;

    // Preprocess document image
    let document_image = preprocess_document_image("example_document.png")?;

    // Process document
    let prompt = "Convert this document to DocTags:";
    let doctags = granite_docling.process_document(document_image, prompt).await?;

    println!("Generated DocTags:");
    println!("{}", doctags);

    Ok(())
}

// Cargo.toml dependencies:
/*
[dependencies]
ort = { version = "2.0.0-rc.10", features = ["directml", "cuda", "tensorrt"] }
ndarray = "0.15"
anyhow = "1.0"
tokio = { version = "1.0", features = ["full"] }
*/