"""Vectorization pipeline — converts preprocessed binary images to SVG."""

import numpy as np
import potrace


def potrace_trace(
    binary_img: np.ndarray,
    turdsize: int = 2,
    alphamax: float = 1.0,
    opticurve: bool = True,
    opttolerance: float = 0.2,
) -> str:
    """Trace a binary image using Potrace and return an SVG string.

    Args:
        binary_img: 2D numpy array — nonzero pixels are foreground.
        turdsize: Despeckle threshold; curves with enclosed area below this are removed.
        alphamax: Corner detection threshold (0.0 = polygon, 1.3333 = no corners).
        opticurve: Whether to optimize curves by reducing Bezier segments.
        opttolerance: Tolerance for curve optimization.

    Returns:
        Well-formed SVG string.
    """
    if binary_img.ndim != 2:
        raise ValueError(f"Expected 2D binary image, got shape {binary_img.shape}")

    h, w = binary_img.shape

    # Potrace interprets nonzero pixels as foreground.
    # Convert to uint32 — pypotrace needs values that fit in a C int.
    data = (binary_img > 0).astype(np.uint32)

    bmp = potrace.Bitmap(data)
    path = bmp.trace(
        turdsize=turdsize,
        alphamax=alphamax,
        opticurve=int(opticurve),
        opttolerance=opttolerance,
    )

    return _path_to_svg(path, w, h)


def _path_to_svg(path, width: int, height: int) -> str:
    """Convert a potrace Path object to an SVG string."""
    parts = []
    for curve in path:
        sx, sy = curve.start_point
        parts.append(f"M {sx:.3f},{sy:.3f}")
        for segment in curve.segments:
            if segment.is_corner:
                cx, cy = segment.c
                ex, ey = segment.end_point
                parts.append(f"L {cx:.3f},{cy:.3f} L {ex:.3f},{ey:.3f}")
            else:
                c1x, c1y = segment.c1
                c2x, c2y = segment.c2
                ex, ey = segment.end_point
                parts.append(
                    f"C {c1x:.3f},{c1y:.3f} {c2x:.3f},{c2y:.3f} {ex:.3f},{ey:.3f}"
                )
        parts.append("Z")

    d = " ".join(parts)

    return (
        f'<svg xmlns="http://www.w3.org/2000/svg" '
        f'width="{width}" height="{height}" '
        f'viewBox="0 0 {width} {height}">'
        f'<path d="{d}" fill="black" fill-rule="evenodd" stroke="none"/>'
        f"</svg>"
    )