import numpy as np
from PIL import Image


def create_blend_weight(
    height,
    width,
    overlap
):
    """
    Create a smooth 2D blending weight.

    Pixels near the center receive higher weight.
    Pixels near overlapping boundaries receive lower weight.
    """

    if overlap <= 0:
        return np.ones(
            (height, width),
            dtype=np.float32
        )

    # Horizontal weights
    wx = np.ones(width, dtype=np.float32)

    transition = min(overlap, width // 2)

    if transition > 0:

        ramp = np.linspace(
            0.01,
            1.0,
            transition,
            dtype=np.float32
        )

        wx[:transition] = ramp

        wx[-transition:] = ramp[::-1]

    # Vertical weights
    wy = np.ones(height, dtype=np.float32)

    transition = min(overlap, height // 2)

    if transition > 0:

        ramp = np.linspace(
            0.01,
            1.0,
            transition,
            dtype=np.float32
        )

        wy[:transition] = ramp

        wy[-transition:] = ramp[::-1]

    return wy[:, None] * wx[None, :]


def stitch_tiles(
    sr_tiles,
    scale=4,
    original_size=None,
    overlap=32
):
    """
    Stitch overlapping super-resolution tiles.

    Parameters
    ----------
    sr_tiles : list of dictionaries

        Each dictionary must contain:

            image
            x
            y

        where x/y are coordinates in the ORIGINAL image.

    scale : int
        Super-resolution scale factor.

    original_size : tuple
        (width, height) of original image.

    overlap : int
        Overlap in ORIGINAL-image pixels.

    Returns
    -------
    PIL.Image
        Final stitched SR image.
    """

    if not sr_tiles:
        raise ValueError("No SR tiles supplied.")

    if original_size is None:
        raise ValueError(
            "original_size must be provided."
        )

    original_width, original_height = original_size

    output_width = original_width * scale
    output_height = original_height * scale

    # Accumulate weighted RGB values
    canvas = np.zeros(
        (
            output_height,
            output_width,
            3
        ),
        dtype=np.float32
    )

    # Accumulate weights
    weights = np.zeros(
        (
            output_height,
            output_width
        ),
        dtype=np.float32
    )

    sr_overlap = overlap * scale

    for tile_info in sr_tiles:

        image = tile_info["image"]

        if not isinstance(image, Image.Image):
            image = Image.fromarray(image)

        image = image.convert("RGB")

        tile = np.asarray(
            image,
            dtype=np.float32
        )

        tile_height, tile_width = tile.shape[:2]

        # Original-image coordinates → SR coordinates
        x = int(tile_info["x"] * scale)
        y = int(tile_info["y"] * scale)

        # Do not allow the tile to exceed final canvas
        valid_width = min(
            tile_width,
            output_width - x
        )

        valid_height = min(
            tile_height,
            output_height - y
        )

        if valid_width <= 0 or valid_height <= 0:
            continue

        tile = tile[
            :valid_height,
            :valid_width
        ]

        # --------------------------------------------------
        # Build blending weight
        # --------------------------------------------------

        weight = create_blend_weight(
            valid_height,
            valid_width,
            sr_overlap
        )

        # --------------------------------------------------
        # Accumulate
        # --------------------------------------------------

        canvas[
            y:y + valid_height,
            x:x + valid_width
        ] += tile * weight[..., None]

        weights[
            y:y + valid_height,
            x:x + valid_width
        ] += weight

    # ------------------------------------------------------
    # Normalize overlapping pixels
    # ------------------------------------------------------

    weights = np.maximum(
        weights,
        1e-8
    )

    canvas /= weights[..., None]

    canvas = np.clip(
        canvas,
        0,
        255
    ).round().astype(np.uint8)

    return Image.fromarray(
        canvas,
        mode="RGB"
    )