#!/usr/bin/env python3
"""Expand canonical A/B/C poses into the A/B/A/C/A/B/A/C walk cycle."""

from __future__ import annotations

import argparse
from pathlib import Path

from PIL import Image


POSE_SEQUENCE = (0, 1, 0, 2, 0, 1, 0, 2)


def split_equal_columns(image: Image.Image, columns: int) -> list[Image.Image]:
    width, height = image.size
    edges = [round(index * width / columns) for index in range(columns + 1)]
    return [image.crop((edges[index], 0, edges[index + 1], height)) for index in range(columns)]


def expand_pose_triplet(image: Image.Image) -> Image.Image:
    poses = split_equal_columns(image.convert("RGBA"), 3)
    cell_width = max(pose.width for pose in poses)
    cell_height = image.height
    output = Image.new("RGBA", (cell_width * len(POSE_SEQUENCE), cell_height), (0, 0, 0, 0))
    for output_index, pose_index in enumerate(POSE_SEQUENCE):
        pose = poses[pose_index]
        x = output_index * cell_width + (cell_width - pose.width) // 2
        output.alpha_composite(pose, (x, 0))
    return output


def combine_pose_images(paths: list[Path]) -> Image.Image:
    poses = [Image.open(path).convert("RGBA") for path in paths]
    cell_width = max(pose.width for pose in poses)
    cell_height = max(pose.height for pose in poses)
    output = Image.new("RGBA", (cell_width * len(poses), cell_height), (0, 0, 0, 0))
    for index, pose in enumerate(poses):
        x = index * cell_width + (cell_width - pose.width) // 2
        y = (cell_height - pose.height) // 2
        output.alpha_composite(pose, (x, y))
    return output


def main() -> None:
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument("--input", type=Path)
    parser.add_argument("--pose", type=Path, action="append", default=[])
    parser.add_argument("--output", type=Path, required=True)
    args = parser.parse_args()

    if bool(args.input) == bool(args.pose):
        raise ValueError("Use either --input triplet or exactly three --pose images")
    if args.pose:
        if len(args.pose) != 3:
            raise ValueError(f"Expected exactly three --pose images, got {len(args.pose)}")
        for path in args.pose:
            if not path.exists():
                raise FileNotFoundError(f"Canonical pose not found: {path}")
        image = combine_pose_images(args.pose)
    else:
        if args.input is None or not args.input.exists():
            raise FileNotFoundError(f"Pose triplet not found: {args.input}")
        image = Image.open(args.input).convert("RGBA")
    if image.width < 3 or image.height < 1:
        raise ValueError(f"Invalid pose triplet size: {image.size}")

    output = expand_pose_triplet(image)
    args.output.parent.mkdir(parents=True, exist_ok=True)
    output.save(args.output)
    print(args.output)


if __name__ == "__main__":
    main()