//! session.rs — TensorRT ORT session initialisation

use crate::types::DaemonConfig;
use ort::{ExecutionProvider, GraphOptimizationLevel, Session, SessionBuilder};

/// Initialise an ORT session backed by TensorrtExecutionProvider.
///
/// On first call: TRT compiles the FP16 engine (~5 min).
/// Subsequent calls: loads cached .plan file instantly.
pub fn build_trt_session(cfg: &DaemonConfig) -> ort::Result<Session> {
    std::fs::create_dir_all(&cfg.trt_cache_dir)
        .expect("failed to create TRT cache directory");

    let trt_provider = ExecutionProvider::TensorRT(
        ort::TensorRTExecutionProviderOptions::default()
            .with_device_id(0)
            .with_fp16_enable(true)
            .with_engine_cache_enable(true)
            .with_engine_cache_path(&cfg.trt_cache_dir)
            .with_profile_min_shapes(&format!(
                "input_ids:1x16,attention_mask:1x16,token_type_ids:1x16"
            ))
            .with_profile_opt_shapes(&format!(
                "input_ids:{}x128,attention_mask:{}x128,token_type_ids:{}x128",
                cfg.max_batch_size, cfg.max_batch_size, cfg.max_batch_size
            ))
            .with_profile_max_shapes(&format!(
                "input_ids:{}x512,attention_mask:{}x512,token_type_ids:{}x512",
                cfg.max_batch_size, cfg.max_batch_size, cfg.max_batch_size
            )),
    );

    ort::init()
        .with_execution_providers([trt_provider])
        .commit()?;

    SessionBuilder::new()?
        .with_optimization_level(GraphOptimizationLevel::Level3)?
        .with_intra_threads(4)?
        .commit_from_file(&cfg.model_path)
}