"""
Utilities for loading WAKESET plane slices (unstructured CFD data) 
and interpolating them onto regular 2D grids.
"""

from __future__ import annotations
import re
import numpy as np
import pandas as pd
from pathlib import Path
from scipy.interpolate import LinearNDInterpolator, NearestNDInterpolator

# --- Configuration ---
DEFAULT_GRID_RES: int = 512

# Aliases to map CSV headers to standard names
_COL_ALIASES = {
    "cellnumber": "cell", 
    "x_coordinate": "x", "y_coordinate": "y", "z_coordinate": "z",
    "velocity_magnitude": "velocity_magnitude", 
    "z_velocity": "vz", "y_velocity": "vy", "x_velocity": "vx",
    "total_pressure": "total_pressure",
    "static_pressure": "static_pressure"
}

def process_plane_export(
    filepath: str,
    resolution: int = DEFAULT_GRID_RES,
    fill_value: float = np.nan,
    precision_round: int = 4
):
    """
    Parses unstructured CFD plane exports and interpolates them onto a 
    regular 2D grid (Image format).
    """
    filepath = Path(filepath)
    print(f"Processing Plane: {filepath.name}...")

    # 1. CSV Loading (Handles variable whitespace)
    try:
        df = pd.read_csv(
            filepath, 
            sep=',',                # Comma separator
            skipinitialspace=True,  # Handle " , 1.0"
            engine='c', 
            on_bad_lines='warn'
        )
    except Exception as e:
        print(f"Read failed: {e}")
        return None

    # Normalize columns
    df.columns = [_normalize_col(c) for c in df.columns]
    
    # Ensure coordinates exist
    if not {'x', 'y', 'z'}.issubset(df.columns):
        print(f"Error: Missing coordinate columns. Found: {list(df.columns)}")
        return None

    # 2. Auto-Detect Plane Orientation
    # Look for the axis with the least variance (the flat axis)
    coords = df[['x', 'y', 'z']].values.astype(np.float32)
    spreads = np.ptp(coords, axis=0) # Peak-to-peak (max - min)
    flat_axis_idx = np.argmin(spreads)
    
    axis_names = ['x', 'y', 'z']
    flat_axis_name = axis_names[flat_axis_idx]
    
    # Safety Check: Is it actually a plane?
    if spreads[flat_axis_idx] > 1e-3:
        print(f"Warning: Data does not look planar. Spread in {flat_axis_name} is {spreads[flat_axis_idx]}")

    # 3. Define 2D Projection (U, V)
    # If Plane is X-constant, we map Y->U, Z->V, etc.
    if flat_axis_name == 'x':
        u_col, v_col = 'y', 'z'
    elif flat_axis_name == 'y':
        u_col, v_col = 'x', 'z'
    else: # z
        u_col, v_col = 'x', 'y'
        
    print(f"  -> Orientation: {flat_axis_name}-plane. Projecting {u_col}/{v_col} -> Grid.")

    # 4. Generate Target Grid (Regular Image)
    u_raw = df[u_col].values
    v_raw = df[v_col].values
    
    u_min, u_max = u_raw.min(), u_raw.max()
    v_min, v_max = v_raw.min(), v_raw.max()
    
    # Create the meshgrid
    grid_u_Lin = np.linspace(u_min, u_max, resolution)
    grid_v_Lin = np.linspace(v_min, v_max, resolution)
    grid_u, grid_v = np.meshgrid(grid_u_Lin, grid_v_Lin)
    
    # Flatten targets for interpolation logic
    target_points = np.column_stack((grid_u.ravel(), grid_v.ravel()))
    source_points = np.column_stack((u_raw, v_raw))

    # 5. Vectorized Interpolation
    # We grab all relevant data channels
    channels = [c for c in df.columns if c not in ['x', 'y', 'z', 'cell']]
    source_values = df[channels].values
    
    # LinearNDInterpolator builds a Delaunay triangulation once
    # and interpolates ALL channels simultaneously.
    print(f"  -> Interpolating {len(source_points)} points to {resolution}x{resolution} grid...")
    
    interp = LinearNDInterpolator(source_points, source_values, fill_value=fill_value)
    interpolated_flat = interp(target_points)
    
    # 6. Fallback for Convex Hull Gaps (Optional)
    # LinearND returns NaN for points slightly outside the triangulation (edges).
    # We fill these with Nearest Neighbor to avoid jagged edges.
    if np.isnan(interpolated_flat).any():
        nan_mask = np.isnan(interpolated_flat[:, 0]) # Check first channel
        if np.any(nan_mask):
            # Only train nearest neighbor on valid points
            nn = NearestNDInterpolator(source_points, source_values)
            interpolated_flat[nan_mask] = nn(target_points[nan_mask])

    # 7. Reshape and Store
    plane_data = {
        "meta": {
            "plane_axis": flat_axis_name,
            "plane_value": float(np.median(coords[:, flat_axis_idx])),
            "u_axis": u_col,
            "v_axis": v_col,
            "bounds": [u_min, u_max, v_min, v_max]
        }
    }
    
    for i, col_name in enumerate(channels):
        # Reshape (N*N, ) -> (N, N)
        # Note: We flip ud (up/down) usually to match image coordinates if needed,
        # but here we keep mathematical coordinates.
        plane_data[col_name] = interpolated_flat[:, i].reshape(resolution, resolution)

    return plane_data

def _normalize_col(name: str) -> str:
    clean = re.sub(r"[^a-z0-9]+", "_", name.lower()).strip("_")
    return _COL_ALIASES.get(clean, clean)

if __name__ == "__main__":
    # --- Test ---
    # Update path to a Plane file (VERTPLN or HORZPLN)
    test_file = Path("C:/Users/zacco/Desktop/Files/WAKESET/Test Files/Forward_0100_ms_Angle_00_VERTPLN_ALL")
    
    if not test_file.exists() and test_file.with_suffix(".csv").exists():
        test_file = test_file.with_suffix(".csv")

    if test_file.exists():
        data = process_plane_export(test_file, resolution=512)
        
        if data:
            print("Success!")
            # Access a variable
            grid = data['velocity_magnitude']
            print(f"Output Grid Shape: {grid.shape}")
            print(f"Axis detected: {data['meta']['plane_axis']}")
            
            # Save
            out_path = test_file.with_name(test_file.name + ".npz")
            np.savez_compressed(out_path, **data)
            print(f"Saved to: {out_path}")
    else:
        print(f"File not found: {test_file}")