import json
import mmap
from contextlib import contextmanager


@contextmanager
def read(fname):
    r = Reader(fname)
    try:
        yield r
    finally:
        r.close()


class Reader:
    def __init__(self, fname):
        self.f = open(fname, "r+b")
        self.mmap = mmap.mmap(self.f.fileno(), 0)
        assert int.from_bytes(self.mmap[0:2], byteorder="little") == 0x4D50
        first_entry_idx = 10 + self.metadata_len
        self.root_dir, self.leaves = self.load_directory(
            first_entry_idx, self.root_entries
        )

    def load_directory(self, offset, num_entries):
        directory = {}
        leaves = {}
        for i in range(offset, offset + num_entries * 17, 17):
            z = int.from_bytes(self.mmap[i : i + 1], byteorder="little")
            x = int.from_bytes(self.mmap[i + 1 : i + 4], byteorder="little")
            y = int.from_bytes(self.mmap[i + 4 : i + 7], byteorder="little")
            tile_off = int.from_bytes(self.mmap[i + 7 : i + 13], byteorder="little")
            tile_len = int.from_bytes(self.mmap[i + 13 : i + 17], byteorder="little")
            if z & 0b10000000:
                leaves[(z & 0b01111111, x, y)] = (tile_off, tile_len)
            else:
                directory[(z, x, y)] = (tile_off, tile_len)
        return (directory, leaves)

    def close(self):
        self.f.close()

    @property
    def metadata_len(self):
        return int.from_bytes(self.mmap[4:8], byteorder="little")

    @property
    def metadata(self):
        s = self.mmap[10 : 10 + self.metadata_len]
        return json.loads(s)

    @property
    def version(self):
        return int.from_bytes(self.mmap[2:4], byteorder="little")

    @property
    def root_entries(self):
        return int.from_bytes(self.mmap[8:10], byteorder="little")

    @property
    def leaf_level(self):
        return next(iter(self.leaves))[0]

    def get(self, z, x, y):
        val = self.root_dir.get((z, x, y))
        if val:
            return self.mmap[val[0] : val[0] + val[1]]
        else:
            if len(self.leaves) > 0:
                level_diff = z - self.leaf_level
                leaf = (self.leaf_level, x // (1 << level_diff), y // (1 << level_diff))
                val = self.leaves.get(leaf)
                if val:
                    directory, _ = self.load_directory(val[0], val[1] // 17)
                    val = directory.get((z, x, y))
                    if val:
                        return self.mmap[val[0] : val[0] + val[1]]

    def tiles(self):
        for k, v in self.root_dir.items():
            yield (k, self.mmap[v[0] : v[0] + v[1]])
        for val in self.leaves.values():
            leaf_dir, _ = self.load_directory(val[0], val[1] // 17)
            for k, v in leaf_dir.items():
                yield (k, self.mmap[v[0] : v[0] + v[1]])