//! SAM 2.1 video object tracker (Hiera backbone) for the Roto Brush.
//!
//! A Rust port of the Hugging Face `transformers` SAM 2 implementation (Apache-2.0; see
//! `NOTICE`). Native only: the crate is empty on wasm32 so L0–L4 still build for the web.
//! Nothing here loads weights unless asked to; weights are never bundled.
//!
//! Modules are added stage by stage, each checked against reference tensors produced by
//! `tools/sam2_reference.py`.
#![cfg(not(target_arch = "wasm32"))]
#![deny(clippy::unwrap_used, clippy::expect_used, clippy::panic, clippy::unimplemented, clippy::todo, clippy::unreachable)]

use std::fmt;

pub mod decoder;
pub mod gpu;
pub mod hiera;
pub mod mask;
pub mod memattn;
pub mod memory;
pub mod model;
pub mod neck;
pub mod nn;
pub mod prompt;
pub mod resize;
pub mod session;
pub mod track;
pub mod weights;

/// Everything that can go wrong in this crate. Never a panic.
#[derive(Debug, Clone, PartialEq)]
pub enum Error {
    /// The weights file is missing a tensor, has the wrong shape, or contains non-finite values.
    Weights(String),
    /// The input (frame size, prompt, frame index) is unusable.
    Input(String),
    /// The work was cancelled by the caller.
    Cancelled,
    /// A time or memory budget was exceeded.
    Budget(String),
    /// A tensor operation failed (shape mismatch, out of memory, device error).
    Compute(String),
}

impl fmt::Display for Error {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Error::Weights(m) => write!(f, "SAM 2 weights: {m}"),
            Error::Input(m) => write!(f, "SAM 2 input: {m}"),
            Error::Cancelled => write!(f, "SAM 2: cancelled"),
            Error::Budget(m) => write!(f, "SAM 2 budget: {m}"),
            Error::Compute(m) => write!(f, "SAM 2 compute: {m}"),
        }
    }
}

impl std::error::Error for Error {}

impl From<candle_core::Error> for Error {
    fn from(e: candle_core::Error) -> Error {
        Error::Compute(e.to_string())
    }
}

pub type Result<T> = std::result::Result<T, Error>;

/// The released SAM 2.1 sizes. Only Tiny is wired up first; the others are configuration.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum Size {
    Tiny,
    Small,
    BasePlus,
    Large,
}

impl Size {
    /// The Hugging Face repository the official weights come from.
    pub fn repo(self) -> &'static str {
        match self {
            Size::Tiny => "facebook/sam2.1-hiera-tiny",
            Size::Small => "facebook/sam2.1-hiera-small",
            Size::BasePlus => "facebook/sam2.1-hiera-base-plus",
            Size::Large => "facebook/sam2.1-hiera-large",
        }
    }

    /// The size a checkpoint is, from its tensors: the width of the patch embedding (96 for Tiny and Small, 112 for
    /// Base+, 144 for Large) and the number of blocks (12 for Tiny, 16 for Small).
    pub fn detect(w: &weights::Weights) -> Result<Size> {
        let width = w.shape("vision_encoder.backbone.patch_embed.projection.weight").and_then(|s| s.first().copied());
        Ok(match width {
            Some(112) => Size::BasePlus,
            Some(144) => Size::Large,
            Some(96) if w.contains("vision_encoder.backbone.blocks.15.layer_norm1.weight") => Size::Small,
            Some(96) => Size::Tiny,
            _ => return Err(Error::Weights("this checkpoint is not a SAM 2.1 Hiera size (patch embedding width)".into())),
        })
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn sizes_name_their_official_repositories() {
        assert_eq!(Size::Tiny.repo(), "facebook/sam2.1-hiera-tiny");
        assert!(Size::Large.repo().ends_with("large"));
    }

    #[test]
    fn configs_match_the_released_sizes() {
        let blocks = |s| hiera::HieraConfig::for_size(s).blocks.iter().sum::<usize>();
        assert_eq!([Size::Tiny, Size::Small, Size::BasePlus, Size::Large].map(blocks), [12, 16, 24, 48]);
        for s in [Size::Tiny, Size::Small, Size::BasePlus, Size::Large] {
            let c = hiera::HieraConfig::for_size(s);
            assert_eq!((c.embed_dims.len(), c.heads.len(), c.windows.len()), (4, 4, 4));
            assert!(c.global_blocks.iter().all(|g| *g < blocks(s)));
        }
    }

    #[test]
    fn size_comes_from_the_patch_embedding_and_depth() {
        use candle_core::{DType, Device, Tensor};
        let make = |width: usize, deep: bool| {
            let mut m = std::collections::HashMap::new();
            m.insert("vision_encoder.backbone.patch_embed.projection.weight".to_string(), Tensor::zeros((width, 3, 7, 7), DType::F32, &Device::Cpu).unwrap());
            if deep {
                m.insert("vision_encoder.backbone.blocks.15.layer_norm1.weight".to_string(), Tensor::zeros(4, DType::F32, &Device::Cpu).unwrap());
            }
            weights::Weights::from_map(m).unwrap()
        };
        assert_eq!(Size::detect(&make(96, false)).unwrap(), Size::Tiny);
        assert_eq!(Size::detect(&make(96, true)).unwrap(), Size::Small);
        assert_eq!(Size::detect(&make(112, false)).unwrap(), Size::BasePlus);
        assert_eq!(Size::detect(&make(144, false)).unwrap(), Size::Large);
        assert!(Size::detect(&make(64, false)).is_err());
        assert!(Size::detect(&weights::Weights::from_map(Default::default()).unwrap()).is_err());
    }

    #[test]
    fn errors_say_what_failed() {
        assert!(Error::Input("empty frame".into()).to_string().contains("empty frame"));
        assert_eq!(Error::Cancelled.to_string(), "SAM 2: cancelled");
    }
}