#!/usr/bin/env python3
"""Compose the local-only sprite atlases from the raw asset packs.

Both inputs and outputs are licence-restricted and therefore untracked (see
docs/ASSETS.md), which is why this is a build step rather than a committed file:
anyone with the packs can regenerate, and nobody without them is blocked.

    pip install pillow && python3 tools/build_local_assets.py

The bullet pack's layout is not obvious and cost a wrong guess once:
  * Each of the 8 PNGs is one ANIMATION FRAME, not one sprite sheet.
  * Within a file, a row is a bullet shape and a column is a COLOUR variant.
So animating means cycling files, not walking columns -- walking columns just
cycles through palettes while the shape sits still.

Output is one tidy atlas: 8 frames across, one row per SimConfig.KIND_*.
"""
import os
import sys

try:
    from PIL import Image
except ImportError:
    sys.exit("needs pillow: pip install pillow")

ROOT = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
SRC = os.path.join(ROOT, "assetpacks", "New_All_Fire_Bullet_Pixel_16x16",
                   "All_Fire_Bullet_Pixel_16x16_%02d.png")
OUT = os.path.join(ROOT, "assets", "local", "bullets.png")
CELL = 16
FRAMES = 8

# (source row, source column) per bullet kind, in SimConfig.KIND_* order.
# Column selects the colour: 0 red, 1 orange, 2 amber, 3 gold, 4 bright yellow.
#
# Cells must have EMPTY BORDERS in every frame. Several sprites in this pack
# overflow their 16px cell and bleed into the neighbour below, so a cell picked
# purely by eye can drag in a slice of the sprite above it -- which is exactly
# what put a solid bar across the top of the first "heavy" I chose.
KINDS = [
    ("player_shot",  7, 4),   # small bright-yellow dot
    ("orb",          3, 1),   # round orange orb
    ("needle",       6, 6),   # compact dart, drawn rotated to velocity
    ("heavy",        5, 0),   # larger red ball
]


def main() -> None:
    for f in range(FRAMES):
        if not os.path.exists(SRC % f):
            sys.exit("missing source frame: %s\n"
                     "The raw pack is untracked; see assets/local/README.md."
                     % (SRC % f))
    out = Image.new("RGBA", (CELL * FRAMES, CELL * len(KINDS)), (0, 0, 0, 0))
    for f in range(FRAMES):
        src = Image.open(SRC % f).convert("RGBA")
        for k, (_name, row, col) in enumerate(KINDS):
            box = (col * CELL, row * CELL, (col + 1) * CELL, (row + 1) * CELL)
            out.paste(src.crop(box), (f * CELL, k * CELL))
    os.makedirs(os.path.dirname(OUT), exist_ok=True)
    # Guard the rule the KINDS comment describes, so a future pick that bleeds
    # fails loudly here instead of looking like a rendering bug.
    for k in range(len(KINDS)):
        for f in range(FRAMES):
            for x in range(CELL):
                for y in (0, CELL - 1):
                    if out.getpixel((f * CELL + x, k * CELL + y))[3] > 40:
                        sys.exit("cell for %s bleeds at its border; pick another"
                                 % KINDS[k][0])
    out.save(OUT)
    print("wrote %s (%dx%d): %d kinds x %d frames"
          % (OUT, out.width, out.height, len(KINDS), FRAMES))
    for k, (name, row, col) in enumerate(KINDS):
        print("  row %d = %-12s (source row %2d, colour col %d)" % (k, name, row, col))


if __name__ == "__main__":
    main()