import torch
import cv2
import time

# Dataset constants
BASELINE = 0.191  # Baseline in meters
HEIGHT_ORIGINAL = 1920  # Original image height
HEIGHT_DOWNSCALED = 960  # Downscaled height for disparity


def compute_depth_from_disparity(disparity_map: torch.Tensor) -> torch.Tensor:
    """
    Convert a disparity map to a depth map based on dataset-specific calibration.

    The depth is computed using trigonometric projection:

        depth = B * (sin(theta) / tan(disparity_rad) + cos(theta))

    where:
        - B is the baseline.
        - theta is the vertical angle corresponding to each pixel in the y-grid.
        - disparity_rad is the disparity map scaled to radians.

    Parameters:
        disparity_map (torch.Tensor): Input tensor of shape (bs, 1, h, w) or (bs, h, w).

    Returns:
        torch.Tensor: Depth map of shape (bs, h, w).
    """
    
    # Ensure input is 3D (batch, height, width)
    has_channel_dim = disparity_map.dim() == 4 and disparity_map.shape[1] == 1
    if has_channel_dim:
        disparity_map = disparity_map.squeeze(1)

    bs, height, width = disparity_map.shape

    # Compute y-grid values
    y_grid = (
        torch.arange(512 + 2 * height - 1, 512, step=-2, device=disparity_map.device)
        .unsqueeze(0)
        .unsqueeze(-1)
        .expand(bs, -1, width)
    )

    # Compute angle and disparity in radians
    theta_grid = y_grid * torch.pi / HEIGHT_ORIGINAL
    disparity_map_rad = (torch.pi / HEIGHT_DOWNSCALED) * disparity_map

    # Initialize depth map
    depth_map = torch.zeros_like(disparity_map, dtype=torch.float32)

    # Compute depth only where disparity is valid
    non_zero_disparity = disparity_map != 0
    depth_map[non_zero_disparity] = (
        (torch.sin(theta_grid[non_zero_disparity]) / torch.tan(disparity_map_rad[non_zero_disparity])) 
        + torch.cos(theta_grid[non_zero_disparity])
    ) * BASELINE

    # Restore channel dimension if input had it
    if has_channel_dim:
        depth_map = depth_map.unsqueeze(1)

    return depth_map


def compute_disparity_from_depth(depth_map: torch.Tensor) -> torch.Tensor:
    """
    Convert a depth map to a disparity map based on dataset-specific calibration.

    This function reverses the depth-to-disparity conversion, based on the relationship:

        tan(disparity_rad) = sin(theta) / (depth / B - cos(theta))

    The final disparity in pixel units is then:

        disparity = (H / pi) * atan(tan(disparity_rad))

    where:
        - B is the baseline.
        - theta is the vertical angle corresponding to each pixel in the y-grid.
        - disparity_rad is the angular disparity in radians.

    Parameters:
        depth_map (torch.Tensor): Input tensor of shape (bs, 1, h, w) or (bs, h, w).

    Returns:
        torch.Tensor: Disparity map of shape (bs, h, w).
    """
    
    # Ensure input is 3D (batch, height, width)
    has_channel_dim: bool = depth_map.dim() == 4 and depth_map.shape[1] == 1
    if has_channel_dim:
        depth_map = depth_map.squeeze(1)

    bs, height, width = depth_map.shape

    # Compute y-grid values
    y_grid = (
        torch.arange(512 + 2 * height - 1, 512, step=-2, device=depth_map.device)
        .unsqueeze(0)
        .unsqueeze(-1)
        .expand(bs, -1, width)
    )

    # Compute theta (polar angle)
    theta_grid = y_grid * torch.pi / HEIGHT_ORIGINAL

    # Initialize depth map
    disparity_map = torch.zeros_like(depth_map, dtype=torch.float32)

    # Compute disparity only where depth is valid
    non_zero_depth = depth_map != 0
    tan_disparity_rad = torch.sin(theta_grid[non_zero_depth]) / (
        (depth_map[non_zero_depth] / BASELINE) - torch.cos(theta_grid[non_zero_depth])
    )
    disparity_map_rad = torch.atan(tan_disparity_rad)
    disparity_map[non_zero_depth] = (HEIGHT_DOWNSCALED / torch.pi) * disparity_map_rad

    # Restore channel dimension if input had it
    if has_channel_dim:
        disparity_map = disparity_map.unsqueeze(1)

    return disparity_map


def disp_deg_to_disp_pix(disp_deg: float) -> float:
    """
    Convert a disparity value from degrees to pixels.

    The relationship is:

        disp_pix = (H / 180) * disp_deg

    where:
        - H is the image height specific to the dataset.
        - disp_deg is the disparity value in degrees.

    Parameters:
        disp_deg (float): Disparity in degrees.

    Returns:
        float: Disparity in pixels.
    """
    H_down: int = 960
    return (H_down / 180) * disp_deg



def disp_pix_to_disp_deg(disp_pix: float) -> float:
    """
    Convert a disparity value from pixels to degrees.

    The relationship is:

        disp_deg = (180 / H) * disp_pix

    where:
        - H is the dataset-specific image height.
        - disp_pix is the disparity value in pixels.

    Parameters:
        disp_pix (float): Disparity in pixels.

    Returns:
        float: Disparity in degrees.
    """
    H_down: int = 960
    return (180 / H_down) * disp_pix



def readDepthHelvipad(filename: str) -> tuple[torch.Tensor, torch.Tensor]:
    """
    Read a depth map from a Helvipad dataset file.

    The depth is stored in a 16-bit format and needs to be scaled by 1/256.

    Parameters:
        filename (str): Path to the depth file.

    Returns:
        tuple[torch.Tensor, torch.Tensor]:
            - Depth map tensor (H, W).
            - Validity mask tensor (H, W) indicating valid depth values.
    """
    depth = load_depth_with_infinite_retry(filename) / 256.0
    valid = depth > 0.0
    return depth, valid


def readDisparityHelvipad(filename: str) -> tuple[torch.Tensor, torch.Tensor]:
    """
    Read a disparity map from a Helvipad dataset file.

    The disparity is stored in a 16-bit format and needs to be scaled by 1/2048.

    Parameters:
        filename (str): Path to the disparity file.

    Returns:
        tuple[torch.Tensor, torch.Tensor]:
            - Disparity map tensor (H, W).
            - Validity mask tensor (H, W) indicating valid disparity values.
    """
    disp = load_depth_with_infinite_retry(filename) / 2048.0
    valid = disp > 0.0
    return disp, valid