"""Rules for student contributions. Pure, so every rule is unit-tested."""
import os
from datetime import datetime, timedelta
from typing import Optional, Sequence

ALLOWED_EXT = (".pdf", ".pptx", ".docx")
MAX_BYTES = 20 * 1024 * 1024  # the bot can only read files up to 20 MB (needed for duplicate checks + stamping)
BLOCK_AFTER_REJECTIONS = 3
REJECTION_WINDOW_DAYS = 14
BLOCK_DAYS = 7
SPARSE_COURSE_FILES = 3  # a course with fewer files than this counts as "wanted"
BADGES = ((15, "gold"), (5, "silver"), (1, "bronze"))  # approved files needed -> badge
REJECT_REASONS = ("duplicate", "quality", "notallowed")


def check_file(file_name: Optional[str], size: Optional[int]) -> Optional[str]:
    """None = fine, else a reason code ('ext' | 'size')."""
    if os.path.splitext(file_name or "")[1].lower() not in ALLOWED_EXT:
        return "ext"
    if size is None or size > MAX_BYTES:
        return "size"
    return None


def blocked_until(rejected_at: Sequence[datetime], now: datetime) -> Optional[datetime]:
    """3 rejections inside 14 days -> no new submissions for 7 days after the last one."""
    recent = sorted(d for d in rejected_at if d >= now - timedelta(days=REJECTION_WINDOW_DAYS))
    if len(recent) < BLOCK_AFTER_REJECTIONS:
        return None
    until = recent[-1] + timedelta(days=BLOCK_DAYS)
    return until if until > now else None


def eligibility(
    *, active_days: int, min_days: int, pending: int, pending_limit: int, today: int, daily_limit: int,
    blocked: Optional[datetime],
) -> Optional[str]:
    """None = may submit, else a reason code."""
    if active_days < min_days:
        return "new"
    if blocked is not None:
        return "blocked"
    if pending >= pending_limit:
        return "pending"
    if today >= daily_limit:
        return "daily"
    return None


def badge_for(approved: int) -> Optional[str]:
    for needed, tier in BADGES:
        if approved >= needed:
            return tier
    return None


def next_badge(approved: int) -> Optional[tuple[int, str]]:
    """(files still needed, tier) for the next badge, or None at the top."""
    for needed, tier in reversed(BADGES):
        if approved < needed:
            return needed - approved, tier
    return None


def reward(
    *, rewarded_this_week: int, course_files_before: int, xp: int, bonus: int, weekly_cap: int
) -> tuple[int, int]:
    """(XP, bonus XP). Nothing once the weekly cap is used; the bonus is for courses that are short of material."""
    if rewarded_this_week >= weekly_cap:
        return 0, 0
    return xp, (bonus if course_files_before < SPARSE_COURSE_FILES else 0)