import numpy as np
from scipy.spatial.transform import Rotation
from decimal import Decimal

def identity():
    return np.eye(3, 4)


def transform(g: np.ndarray, pts: np.ndarray):
    """ Applies the SE3 transform

    Args:
        g: SE3 transformation matrix of size ([B,] 3/4, 4)
        pts: Points to be transformed ([B,] N, 3)

    Returns:
        transformed points of size (N, 3)
    """
    rot = g[..., :3, :3]  # (3, 3)
    trans = g[..., :3, 3]  # (3)

    transformed = pts[..., :3] @ np.swapaxes(rot, -1, -2) + trans[..., None, :]
    return transformed


def inverse(g: np.ndarray):
    """Returns the inverse of the SE3 transform

    Args:
        g: ([B,] 3/4, 4) transform

    Returns:
        ([B,] 3/4, 4) matrix containing the inverse

    """
    rot = g[..., :3, :3]  # (3, 3)
    trans = g[..., :3, 3]  # (3)

    inv_rot = np.swapaxes(rot, -1, -2)
    inverse_transform = np.concatenate([inv_rot, inv_rot @ -trans[..., None]], axis=-1)
    if g.shape[-2] == 4:
        inverse_transform = np.concatenate([inverse_transform, [[0.0, 0.0, 0.0, 1.0]]], axis=-2)

    return inverse_transform


def concatenate(a: np.ndarray, b: np.ndarray):
    """ Concatenate two SE3 transforms

    Args:
        a: First transform ([B,] 3/4, 4)
        b: Second transform ([B,] 3/4, 4)

    Returns:
        a*b ([B, ] 3/4, 4)

    """

    r_a, t_a = a[..., :3, :3], a[..., :3, 3]
    r_b, t_b = b[..., :3, :3], b[..., :3, 3]

    r_ab = r_a @ r_b
    t_ab = r_a @ t_b[..., None] + t_a[..., None]

    concatenated = np.concatenate([r_ab, t_ab], axis=-1)

    if a.shape[-2] == 4:
        concatenated = np.concatenate([concatenated, [[0.0, 0.0, 0.0, 1.0]]], axis=-2)

    return concatenated


def from_xyzquat(xyzquat):
    """Constructs SE3 matrix from x, y, z, qx, qy, qz, qw

    Args:
        xyzquat: np.array (7,) containing translation and quaterion

    Returns:
        SE3 matrix (4, 4)
    """
    rot = Rotation.from_quat(xyzquat[3:])
    trans = rot.apply(-xyzquat[:3])
    transform = np.concatenate([rot.as_dcm(), trans[:, None]], axis=1)
    transform = np.concatenate([transform, [[0.0, 0.0, 0.0, 1.0]]], axis=0)

    return transform