import json


class CharTokenizer:
    def __init__(self, vocab=None):
        if vocab is None:
            self.itos = []
        else:
            self.itos = list(vocab)
        self.stoi = {ch: i for i, ch in enumerate(self.itos)}

    @classmethod
    def from_text(cls, text):
        return cls(sorted(set(text)))

    @property
    def vocab_size(self):
        return len(self.itos)

    def encode(self, text):
        return [self.stoi[ch] for ch in text if ch in self.stoi]

    def decode(self, ids):
        return "".join(self.itos[i] for i in ids)

    def save(self, path):
        with open(path, "w", encoding="utf-8") as f:
            json.dump(self.itos, f, ensure_ascii=False)

    @classmethod
    def load(cls, path):
        with open(path, encoding="utf-8") as f:
            return cls(json.load(f))