import random
import re

def filter_initial(letters, wordlist):
    regexp = re.compile(f"[{''.join(letters)}]+")
    return [w for w in wordlist if regexp.fullmatch(w)]

def filter(new_letter, old_letters, wordlist):
    regexp = re.compile(f"[{''.join(old_letters)}]*{new_letter}[{new_letter}{''.join(old_letters)}]*")
    return [w for w in wordlist if regexp.fullmatch(w)]

class WordLottery:
    """This word lottery makes it 20 x less probable
    to again draw a word that had already been drawn previously."""

    def __init__(self, words):
        self.words = words.copy()
        self.sub = None

    def add(self, word):
        self.words.append(word)

    def lots(self):
        if self.sub:
            return len(self.words) + self.sub.lots() / 20
        else:
            return len(self.words)

    def draw(self):
        lots = self.lots()
        r = random.random()
        if r * lots < len(self.words):
            draw_i = random.randrange(0, len(self.words))
            result_word = self.words[draw_i]
            del self.words[draw_i:draw_i+1]
            if not self.sub:
                self.sub = WordLottery([result_word])
            else:
                self.sub.add(result_word)
            return result_word
        else:
            if self.sub:
                return self.sub.draw()
            else:
                raise RuntimeError("This was not supposed to happen. r: {r}, lots: {lots}, self.words: {len(self.words}.")

def write_words(filtered, outdir, outname, words_per_lesson, blanks):
    lottery = WordLottery(filtered)
    with open(f"{outdir}/{outname}", "w") as out:
        for _ in range(0, words_per_lesson):
            out.write(lottery.draw())
            out.write(blanks)
            out.write("\n")

def mk_lessons(wordlist, learn_order, outdir, words_per_lesson = 50, blanks="     "):
    for lesson_name in learn_order.keys():
        if "new_letter" in learn_order[lesson_name]:
            old_letters = learn_order[lesson_name]['old_letters']
            new_letter = learn_order[lesson_name]['new_letter']
            filtered = filter(new_letter, old_letters, wordlist)
        else:
            letters = learn_order[lesson_name]['letters']
            filtered = filter_initial(letters, wordlist)

        if "new_words" in learn_order[lesson_name]:
            if learn_order[lesson_name]["new_words"] != len(filtered):
                raise RuntimeError(f"Lesson {lesson_name}: Wrong word count should: {learn_order[lesson_name]['new_words']} is: {len(filtered)}.")
        for i in range(0, 10):
            write_words(filtered, outdir, f"{lesson_name}_{i}.txt", words_per_lesson, blanks)