ferrum-quantization 0.8.1

//! `WeightLoader` trait — unified interface for loading tensor/linear weights
//! into a specific backend.
//!
//! Implementations (landing in Phase B):
//!   - `SafeTensorsLoader` — reads `.safetensors` files, returns `DenseLinear`
//!     unless `quantize_config.json` indicates GPTQ/AWQ, in which case it
//!     returns `GptqLinear` / `AwqLinear`.
//!   - `GgufLoader` — reads `.gguf` files, returns `GgufLinear`.
//!
//! The trait is generic over `B: Backend` so the loader can materialise
//! tensors directly into backend-native buffers (zero-copy on Apple Silicon
//! shared memory, dtoh/htod for CUDA, etc.).

use ferrum_kernels::{backend::Backend, MarlinExpertStack};
use ferrum_types::{FerrumError, Result};

use crate::config::QuantConfig;
use crate::traits::Linear;

pub trait WeightLoader<B: Backend>: Send + Sync {
    /// Load a single tensor by fully qualified name
    /// (e.g. `"model.embed_tokens.weight"`).
    fn load_tensor(&self, name: &str) -> Result<B::Buffer>;

    /// Load a projection as a `Linear<B>`. The concrete implementation
    /// (DenseLinear / GptqLinear / AwqLinear / GgufLinear) depends on the
    /// loader's file format and quant config.
    ///
    /// `name` is the module path without the `.weight` suffix, e.g.
    /// `"model.layers.0.self_attn.qkv_proj"`.
    fn load_linear(&self, name: &str) -> Result<Box<dyn Linear<B>>>;

    /// Whether a tensor with this name exists in the source.
    fn has_tensor(&self, name: &str) -> bool;

    /// Quantization metadata (parsed from `quantize_config.json` or a GGUF header).
    /// `None` means the source is dense.
    fn quant_config(&self) -> Option<&QuantConfig>;

    /// Load per-expert GPTQ projections into one backend-native stacked expert
    /// tile. Backends/loaders that do not expose native stacked GPTQ return an
    /// explicit unsupported error.
    fn load_stacked_gptq_experts(
        &self,
        expert_prefix_fmt: &str,
        num_experts: usize,
        proj_names: &[&str],
    ) -> Result<(std::sync::Arc<dyn MarlinExpertStack<B>>, usize, usize)> {
        let _ = (expert_prefix_fmt, num_experts, proj_names);
        Err(FerrumError::unsupported(
            "load_stacked_gptq_experts not implemented for this weight loader",
        ))
    }
}

/// Adapter that prepends a fixed prefix to every tensor name before
/// delegating to an underlying loader.
///
/// Use case: a single safetensors file contains a sub-model (e.g.
/// Qwen3-TTS stores the Talker LM under `talker.model.*`) and we want
/// to reuse a backbone loader like `LlamaFamilyModel::new` that
/// expects bare `model.*` names. Wrapping with
/// `PrefixedLoader { inner, prefix: "talker." }` lets the backbone
/// code stay prefix-agnostic.
pub struct PrefixedLoader<'a, B: Backend> {
    inner: &'a dyn WeightLoader<B>,
    prefix: String,
}

impl<'a, B: Backend> PrefixedLoader<'a, B> {
    pub fn new(inner: &'a dyn WeightLoader<B>, prefix: impl Into<String>) -> Self {
        Self {
            inner,
            prefix: prefix.into(),
        }
    }
}

impl<'a, B: Backend> WeightLoader<B> for PrefixedLoader<'a, B> {
    fn load_tensor(&self, name: &str) -> Result<B::Buffer> {
        self.inner.load_tensor(&format!("{}{}", self.prefix, name))
    }

    fn load_linear(&self, name: &str) -> Result<Box<dyn Linear<B>>> {
        self.inner.load_linear(&format!("{}{}", self.prefix, name))
    }

    fn has_tensor(&self, name: &str) -> bool {
        self.inner.has_tensor(&format!("{}{}", self.prefix, name))
    }

    fn quant_config(&self) -> Option<&QuantConfig> {
        self.inner.quant_config()
    }

    fn load_stacked_gptq_experts(
        &self,
        expert_prefix_fmt: &str,
        num_experts: usize,
        proj_names: &[&str],
    ) -> Result<(std::sync::Arc<dyn MarlinExpertStack<B>>, usize, usize)> {
        self.inner.load_stacked_gptq_experts(
            &format!("{}{}", self.prefix, expert_prefix_fmt),
            num_experts,
            proj_names,
        )
    }
}