from datetime import timedelta
from decimal import Decimal, ROUND_HALF_UP

from django.contrib.auth.models import User
from django.utils import timezone

from .models import StudentProfile


DEMO_STUDENTS = (
    {"name": "Alex", "band": 8.5, "tests": 12, "country": "United Kingdom", "trend": "up"},
    {"name": "Sarah", "band": 8.0, "tests": 10, "country": "Australia", "trend": "up"},
    {"name": "John", "band": 8.0, "tests": 15, "country": "Canada", "trend": "same"},
    {"name": "Emma", "band": 7.5, "tests": 8, "country": "United Kingdom", "trend": "up"},
    {"name": "Daniel", "band": 7.5, "tests": 11, "country": "Germany", "trend": "down"},
    {"name": "Mina", "band": 7.0, "tests": 9, "country": "South Korea", "trend": "up"},
    {"name": "Omar", "band": 7.0, "tests": 7, "country": "United Arab Emirates", "trend": "same"},
    {"name": "Layla", "band": 6.5, "tests": 13, "country": "Turkey", "trend": "up"},
)


def _rounded_half(value):
    return float(
        (Decimal(str(value)) * 2).quantize(Decimal("1"), rounding=ROUND_HALF_UP) / 2
    )


def _objective_band(correct, total):
    if not total:
        return None
    percentage = correct / total
    boundaries = (
        (0.90, 9.0), (0.85, 8.5), (0.80, 8.0), (0.75, 7.5),
        (0.68, 7.0), (0.60, 6.5), (0.52, 6.0), (0.45, 5.5),
        (0.38, 5.0), (0.30, 4.5), (0.22, 4.0), (0, 3.5),
    )
    return next(band for minimum, band in boundaries if percentage >= minimum)


def _attempt_band(attempt, skill="overall"):
    answers = list(attempt.answers.all())
    if skill != "overall":
        answers = [
            answer
            for answer in answers
            if answer.question.section.section_type == skill
        ]
    manual = [answer.manual_score for answer in answers if answer.manual_score is not None]
    objective = [answer for answer in answers if answer.is_correct is not None]
    components = []
    if objective:
        components.append(
            _objective_band(sum(answer.is_correct for answer in objective), len(objective))
        )
    if manual:
        components.append(sum(manual) / len(manual))
    return _rounded_half(sum(components) / len(components)) if components else None


def _period_start(period):
    today = timezone.localdate()
    if period == "week":
        return today - timedelta(days=today.weekday())
    if period == "month":
        return today.replace(day=1)
    return None


def build_leaderboard(period="week", skill="overall", country="", current_user=None):
    start = _period_start(period)
    users = User.objects.filter(studentattempt__is_complete=True).distinct().select_related(
        "studentprofile"
    ).prefetch_related(
        "studentattempt_set__answers__question__section"
    )
    rows = []
    for user in users:
        attempts = [
            attempt
            for attempt in user.studentattempt_set.all()
            if attempt.is_complete
            and attempt.submitted_at
            and (not start or timezone.localdate(attempt.submitted_at) >= start)
        ]
        bands = [
            band for attempt in attempts if (band := _attempt_band(attempt, skill)) is not None
        ]
        if not bands:
            continue
        try:
            profile = user.studentprofile
        except StudentProfile.DoesNotExist:
            profile, _ = StudentProfile.objects.get_or_create(user=user)
        user_country = profile.country or "Not set"
        if country and user_country != country:
            continue
        rows.append(
            {
                "user_id": user.id,
                "name": profile.display_name
                or user.get_full_name()
                or user.username,
                "band": _rounded_half(sum(bands) / len(bands)),
                "tests": len(bands),
                "country": user_country,
                "trend": "up",
                "demo": False,
            }
        )

    if len(rows) < 8:
        used_names = {row["name"].casefold() for row in rows}
        for demo in DEMO_STUDENTS:
            if demo["name"].casefold() not in used_names and (
                not country or demo["country"] == country
            ):
                rows.append({**demo, "user_id": None, "demo": True})

    rows.sort(key=lambda row: (-row["band"], -row["tests"], row["name"].casefold()))
    for index, row in enumerate(rows, start=1):
        row["rank"] = index
        row["initial"] = row["name"][:1].upper()
        row["is_current"] = bool(
            current_user and row["user_id"] == current_user.id
        )
    current_row = next((row for row in rows if row["is_current"]), None)
    countries = sorted(
        {row["country"] for row in rows if row["country"] != "Not set"}
    )
    return rows, current_row, countries