matten 0.16.0

//! Shape operations, slicing, and boundary integration methods for `Tensor`
//! (RFC-007, RFC-008, RFC-009). Split from `tensor.rs` per the 300-ELOC guideline.

use crate::{MattenError, Tensor};

impl Tensor {
    // ---- Shape operations (M4 / RFC-007) ------------------------------------

    /// Reshapes the tensor to `new_shape`, returning a new owned tensor.
    ///
    /// The total element count must be unchanged. Data order is preserved
    /// (row-major flat order).
    ///
    /// # Panics
    ///
    /// Panics on element-count mismatch or invalid shape. Use
    /// [`try_reshape`](Tensor::try_reshape) for recoverable construction.
    ///
    /// ```
    /// use matten::Tensor;
    /// let t = Tensor::new(vec![1.0, 2.0, 3.0, 4.0], &[2, 2]);
    /// let flat = t.reshape(&[4]);
    /// assert_eq!(flat.shape(), &[4]);
    /// assert_eq!(flat.as_slice(), &[1.0, 2.0, 3.0, 4.0]);
    /// ```
    #[must_use]
    pub fn reshape(&self, new_shape: &[usize]) -> Tensor {
        crate::reshape::try_reshape_impl(self, new_shape).unwrap_or_else(|e| panic!("{e}"))
    }

    /// Reshapes the tensor, returning an error instead of panicking.
    ///
    /// # Errors
    ///
    /// Returns [`MattenError::Shape`] on element-count mismatch or invalid shape.
    pub fn try_reshape(&self, new_shape: &[usize]) -> Result<Tensor, MattenError> {
        crate::reshape::try_reshape_impl(self, new_shape)
    }

    /// Flattens the tensor to a 1-D tensor, preserving row-major order.
    ///
    /// A scalar (shape `[]`) is returned as shape `[1]`.
    ///
    /// ```
    /// use matten::Tensor;
    /// let t = Tensor::new(vec![1.0, 2.0, 3.0, 4.0], &[2, 2]);
    /// let flat = t.flatten();
    /// assert_eq!(flat.shape(), &[4]);
    /// ```
    #[must_use]
    pub fn flatten(&self) -> Tensor {
        #[cfg(feature = "dynamic")]
        if self.is_dynamic() {
            panic!(
                "matten unsupported error in flatten: dynamic tensors do not support flatten; call try_numeric() first to convert to a numeric tensor"
            );
        }
        let len = self.data.len();
        Tensor {
            data: self.data.clone(),
            shape: vec![len],
            #[cfg(feature = "dynamic")]
            dynamic: None,
        }
    }

    /// Transposes the tensor by reversing the axis order.
    ///
    /// For a rank-2 tensor this swaps rows and columns. For rank > 2 the axis
    /// order is reversed: `[d0, d1, d2] → [d2, d1, d0]`.
    ///
    /// # Panics
    ///
    /// Panics for a rank-0 scalar (no axes to transpose).
    ///
    /// ```
    /// use matten::Tensor;
    /// let m = Tensor::new(vec![1.0, 2.0, 3.0, 4.0, 5.0, 6.0], &[2, 3]);
    /// let mt = m.transpose();
    /// assert_eq!(mt.shape(), &[3, 2]);
    /// assert_eq!(mt.as_slice(), &[1.0, 4.0, 2.0, 5.0, 3.0, 6.0]);
    /// ```
    #[must_use]
    pub fn transpose(&self) -> Tensor {
        let ndim = self.ndim();
        if ndim == 0 {
            panic!("matten shape error in transpose: cannot transpose a scalar (rank 0)");
        }
        let perm: Vec<usize> = (0..ndim).rev().collect();
        crate::reshape::permute_axes(self, &perm)
    }

    /// Alias for [`transpose`](Tensor::transpose).
    #[must_use]
    pub fn t(&self) -> Tensor {
        self.transpose()
    }

    /// Returns a new tensor with `axis1` and `axis2` swapped.
    ///
    /// # Panics
    ///
    /// Panics if either axis is out of range.
    ///
    /// ```
    /// use matten::Tensor;
    /// let t = Tensor::new((1..=24).map(|x| x as f64).collect(), &[2, 3, 4]);
    /// let s = t.swap_axes(0, 2);
    /// assert_eq!(s.shape(), &[4, 3, 2]);
    /// ```
    #[must_use]
    pub fn swap_axes(&self, axis1: usize, axis2: usize) -> Tensor {
        crate::reshape::validate_axes(axis1, axis2, self.ndim(), "swap_axes")
            .unwrap_or_else(|e| panic!("{e}"));
        let mut perm: Vec<usize> = (0..self.ndim()).collect();
        perm.swap(axis1, axis2);
        crate::reshape::permute_axes(self, &perm)
    }

    /// Returns the element at the multidimensional `coord`, or `None` if the
    /// coordinate rank doesn't match or any component is out of bounds.
    ///
    /// ```
    /// use matten::Tensor;
    /// let t = Tensor::new(vec![1.0, 2.0, 3.0, 4.0], &[2, 2]);
    /// assert_eq!(t.get(&[0, 1]), Some(2.0));
    /// assert_eq!(t.get(&[5, 0]), None);
    /// ```
    pub fn get(&self, coord: &[usize]) -> Option<f64> {
        #[cfg(feature = "dynamic")]
        self.panic_if_dynamic("get");
        let flat = crate::shape::coord_to_flat(coord, &self.shape)?;
        self.data.get(flat).copied()
    }

    /// Returns the element at flat row-major `index`, or `None` if out of bounds.
    ///
    /// This is the flat-index companion to [`get`](Tensor::get). The index
    /// follows the same row-major layout as [`as_slice`](Tensor::as_slice).
    ///
    /// ```
    /// use matten::Tensor;
    /// let t = Tensor::new(vec![1.0, 2.0, 3.0, 4.0], &[2, 2]);
    /// assert_eq!(t.get_flat(1), Some(2.0));
    /// assert_eq!(t.get_flat(10), None);
    /// ```
    pub fn get_flat(&self, index: usize) -> Option<f64> {
        #[cfg(feature = "dynamic")]
        self.panic_if_dynamic("get_flat");
        self.data.get(index).copied()
    }

    // ---- Slicing (M4 / RFC-008) ---------------------------------------------

    /// Starts a slice builder for this tensor. The builder is the canonical
    /// slicing API; [`slice_str`](Tensor::slice_str) is a convenience wrapper.
    ///
    /// ```
    /// use matten::Tensor;
    /// let t = Tensor::new(vec![1.0,2.0,3.0,4.0,5.0,6.0], &[2, 3]);
    /// let row = t.slice().index(0).all().build().unwrap();
    /// assert_eq!(row.as_slice(), &[1.0, 2.0, 3.0]);
    /// ```
    pub fn slice(&self) -> crate::slice::SliceBuilder<'_> {
        crate::slice::SliceBuilder::new(self)
    }

    /// Slices this tensor using a NumPy-like string specification.
    ///
    /// This is a convenience wrapper over the builder API. It always returns
    /// `Result` and never panics on malformed input.
    ///
    /// # Errors
    ///
    /// Returns [`MattenError::Slice`] for any parse or bounds error.
    ///
    /// ```
    /// use matten::Tensor;
    /// let t = Tensor::new(vec![1.0,2.0,3.0,4.0,5.0,6.0], &[2, 3]);
    /// let top = t.slice_str("0, :").unwrap();
    /// assert_eq!(top.as_slice(), &[1.0, 2.0, 3.0]);
    /// ```
    pub fn slice_str(&self, spec: &str) -> Result<Tensor, MattenError> {
        let specs = crate::slice::parse_slice_str(spec)?;
        crate::slice::execute_slice(self, &specs, "slice_str")
    }
}

// ---- Boundary integration (M5 / RFC-009) --------------------------------

impl Tensor {
    /// Parses a JSON string into a `Tensor`.
    ///
    /// Accepts the canonical `{"shape":[…],"data":[…]}` object form and the
    /// convenience nested-array form (rank 1 and 2). Returns
    /// [`MattenError::Parse`] for any error; never panics.
    ///
    /// ```
    /// use matten::Tensor;
    ///
    /// // Canonical object form
    /// let t = Tensor::from_json(r#"{"shape":[2,2],"data":[1.0,2.0,3.0,4.0]}"#).unwrap();
    /// assert_eq!(t.shape(), &[2, 2]);
    ///
    /// // Nested-array convenience form
    /// let t = Tensor::from_json("[[1.0,2.0],[3.0,4.0]]").unwrap();
    /// assert_eq!(t.shape(), &[2, 2]);
    /// ```
    #[cfg(feature = "json")]
    pub fn from_json(input: &str) -> Result<Tensor, MattenError> {
        crate::parse::json::from_json_str(input)
    }

    /// Parses a CSV string into a `Tensor` with shape `[rows, cols]`.
    ///
    /// All fields must be valid `f64` values. Returns [`MattenError::Parse`]
    /// for ragged rows or non-numeric fields; never panics.
    ///
    /// ```
    /// use matten::Tensor;
    ///
    /// let t = Tensor::from_csv("1.0,2.0\n3.0,4.0\n").unwrap();
    /// assert_eq!(t.shape(), &[2, 2]);
    /// assert_eq!(t.as_slice(), &[1.0, 2.0, 3.0, 4.0]);
    /// ```
    #[cfg(feature = "csv")]
    pub fn from_csv(input: &str) -> Result<Tensor, MattenError> {
        crate::parse::csv::from_csv_str(input)
    }

    /// Loads and parses a JSON file into a `Tensor`.
    ///
    /// Returns [`MattenError::Io`] for file errors, [`MattenError::Parse`] for
    /// parse errors.
    ///
    /// # Errors
    ///
    /// Returns an error if the file cannot be read or the content is invalid.
    #[cfg(feature = "json")]
    pub fn load_json(path: impl AsRef<std::path::Path>) -> Result<Tensor, MattenError> {
        let path = path.as_ref();
        let content = std::fs::read_to_string(path).map_err(|e| MattenError::Io {
            path: path.to_path_buf(),
            source: e,
        })?;
        crate::parse::json::from_json_str(&content)
    }

    /// Loads and parses a CSV file into a `Tensor` with shape `[rows, cols]`.
    ///
    /// Returns [`MattenError::Io`] for file errors, [`MattenError::Parse`] for
    /// parse errors.
    ///
    /// # Errors
    ///
    /// Returns an error if the file cannot be read or the content is invalid.
    #[cfg(feature = "csv")]
    pub fn load_csv(path: impl AsRef<std::path::Path>) -> Result<Tensor, MattenError> {
        let path = path.as_ref();
        let content = std::fs::read_to_string(path).map_err(|e| MattenError::Io {
            path: path.to_path_buf(),
            source: e,
        })?;
        crate::parse::csv::from_csv_str(&content)
    }
}