"""
Expense prediction model: suggests next expenses based on 6-month history.
- Input: JSON array of 300 expense records
- Output: Top 3 predicted expenses (date, sum, supplier, user)
"""

from datetime import datetime
from collections import defaultdict
import math
import statistics

from sklearn.ensemble import ExtraTreesRegressor, GradientBoostingRegressor, RandomForestRegressor


def _quantile(values: list[float], q: float) -> float:
    """Returns quantile in [0,1] without numpy."""
    if not values:
        return 0.0
    if len(values) == 1:
        return float(values[0])

    data = sorted(float(v) for v in values)
    q = max(0.0, min(1.0, q))
    pos = q * (len(data) - 1)
    lo = int(math.floor(pos))
    hi = int(math.ceil(pos))
    if lo == hi:
        return data[lo]
    weight = pos - lo
    return data[lo] * (1.0 - weight) + data[hi] * weight


def _time_split_xy(X: list[list[float]], y: list[float]) -> tuple[list[list[float]], list[float], list[list[float]], list[float]]:
    """Splits sequence into train/validation by time order (last 20% for validation)."""
    holdout_size = max(1, int(len(X) * 0.2))
    if len(X) - holdout_size >= 5:
        return X[:-holdout_size], y[:-holdout_size], X[-holdout_size:], y[-holdout_size:]
    return X, y, [], []


def _build_candidates(seed: int = 42) -> list[tuple[str, object]]:
    """Returns candidate regressors to compare on validation MAE."""
    return [
        ("rf", RandomForestRegressor(n_estimators=200, min_samples_leaf=3, random_state=seed)),
        ("extra_trees", ExtraTreesRegressor(n_estimators=200, min_samples_leaf=3, random_state=seed)),
        ("gbr", GradientBoostingRegressor(n_estimators=100, max_depth=3, random_state=seed)),
    ]


def _train_global_model(
    samples: list[tuple],
    supplier_to_idx: dict,
    user_to_idx: dict,
    debug: bool = False,
) -> tuple[object | None, float, str]:
    """Trains ONE global model on ALL records.

    Each sample: (date, supplier_id, user_id, amount)
    Features per row: [supplier_idx, user_idx, day, weekday, month,
                       rolling_mean_3 for supplier, rolling_mean_month for supplier]
    Returns: (fitted_model, global_confidence, model_name)
    """
    # Sort all samples by date to build rolling features correctly.
    samples_sorted = sorted(samples, key=lambda s: s[0])

    # Running histories per supplier and per (supplier, user) pair.
    supplier_hist_running: dict = defaultdict(list)
    user_supplier_hist_running: dict = defaultdict(list)
    supplier_last_date: dict = {}
    user_supplier_last_date: dict = {}
    user_supplier_last_sum: dict = {}

    X_all: list[list[float]] = []
    y_all: list[float] = []

    for tx_date, supplier_id, user_id, amount in samples_sorted:
        s_idx = supplier_to_idx.get(supplier_id, -1)
        u_idx = user_to_idx.get(user_id, -1)

        s_hist = supplier_hist_running[supplier_id]
        us_hist = user_supplier_hist_running[(user_id, supplier_id)]

        # Supplier-wide rolling features.
        s_rolling3 = statistics.mean(s_hist[-3:]) if s_hist else amount
        s_rolling_all = statistics.mean(s_hist) if s_hist else amount
        s_median = statistics.median(s_hist) if s_hist else amount

        # User×supplier specific rolling features (strongest signal).
        us_rolling3 = statistics.mean(us_hist[-3:]) if us_hist else s_rolling3
        us_rolling_all = statistics.mean(us_hist) if us_hist else s_rolling_all
        us_median = statistics.median(us_hist) if us_hist else s_median

        last_s_date = supplier_last_date.get(supplier_id)
        last_us_date = user_supplier_last_date.get((user_id, supplier_id))
        us_last_sum = user_supplier_last_sum.get((user_id, supplier_id), us_rolling3)

        s_gap_days = max(0, (tx_date - last_s_date).days) if last_s_date else 0
        us_gap_days = max(0, (tx_date - last_us_date).days) if last_us_date else 0

        X_all.append([
            s_idx,
            u_idx,
            tx_date.day,
            tx_date.weekday(),
            tx_date.month,
            s_rolling3,
            s_rolling_all,
            s_median,
            us_rolling3,
            us_rolling_all,
            us_median,
            us_last_sum,
            s_gap_days,
            us_gap_days,
        ])
        y_all.append(amount)
        s_hist.append(amount)
        us_hist.append(amount)
        supplier_last_date[supplier_id] = tx_date
        user_supplier_last_date[(user_id, supplier_id)] = tx_date
        user_supplier_last_sum[(user_id, supplier_id)] = amount

    if len(X_all) < 10:
        return None, 0.5, "fallback"

    X_fit, y_fit, X_val, y_val = _time_split_xy(X_all, y_all)
    candidates = _build_candidates()

    best_name = "fallback"
    best_model = None
    best_mae = float("inf")

    for name, model in candidates:
        model.fit(X_fit, y_fit)
        if X_val:
            val_pred = model.predict(X_val)
            mae = statistics.mean([abs(float(p) - float(t)) for p, t in zip(val_pred, y_val)])
        else:
            train_pred = model.predict(X_fit)
            mae = statistics.mean([abs(float(p) - float(t)) for p, t in zip(train_pred, y_fit)])

        if debug:
            print(f"[PREDICT] global model={name}, val_mae={mae:.2f}")

        if mae < best_mae:
            best_mae = mae
            best_name = name
            best_model = model

    if best_model is None:
        return None, 0.5, "fallback"

    baseline_scale = max(1.0, statistics.mean([abs(v) for v in (y_val if y_val else y_fit)]))
    global_conf = math.exp(-(best_mae / baseline_scale))

    if debug:
        print(
            f"[PREDICT] best global model={best_name}, mae={best_mae:.2f}, "
            f"avg_target={baseline_scale:.2f}, global_model_conf={global_conf:.2f}"
        )

    return best_model, max(0.0, min(1.0, global_conf)), best_name


def predict_expenses(expenses: list[dict], target_user_id, debug: bool = False) -> list[dict]:
    if not expenses or len(expenses) < 2:
        if debug:
            print(f"[PREDICT] Not enough records: {len(expenses) if expenses else 0}")
        return []

    # Group by supplier_id (top-3 different suppliers)
    supplier_history = defaultdict(list)
    supplier_freq = defaultdict(int)
    total_records = len(expenses)

    if debug:
        print(f"[PREDICT] Total records received: {total_records}")
        for i, exp in enumerate(expenses):
            print(f"[PREDICT]   [{i+1}] date={exp.get('date')}, sum={exp.get('sum')}, supplier_id={exp.get('supplier_id')}, user_id={exp.get('user_id')}")

    for exp in expenses:
        supplier_id = exp["supplier_id"]
        supplier_history[supplier_id].append(exp)
        supplier_freq[supplier_id] += 1

    if debug:
        print(f"[PREDICT] Unique suppliers: {len(supplier_history)}")
        for supplier_id, count in supplier_freq.items():
            pct = count / total_records * 100
            print(f"[PREDICT]   supplier_id={supplier_id} -> {count} records ({pct:.1f}%)")

    # Select top 10 most popular suppliers by frequency
    candidate_items = sorted(
        supplier_history.items(),
        key=lambda item: supplier_freq[item[0]],
        reverse=True,
    )[:10]

    if debug:
        print(f"[PREDICT] Processing top {len(candidate_items)} suppliers")

    if not candidate_items:
        if debug:
            print("[PREDICT] No suppliers found. Returning empty.")
        return []

    now = datetime.now()

    # Build shared encoders for categorical features.
    supplier_to_idx = {sid: idx for idx, sid in enumerate(supplier_history.keys())}
    user_values = [exp.get("user_id") for exp in expenses if exp.get("user_id") is not None]
    user_to_idx = {uid: idx for idx, uid in enumerate(sorted(set(user_values), key=str))}

    # Collect all valid samples for the global model.
    all_samples: list[tuple] = []
    for exp in expenses:
        try:
            tx_date = datetime.fromisoformat(exp["date"])
            tx_sum = float(exp["sum"])
            tx_supplier = exp["supplier_id"]
            tx_user = exp["user_id"]
            all_samples.append((tx_date, tx_supplier, tx_user, tx_sum))
        except Exception:
            continue

    global_model, global_model_conf, model_name = _train_global_model(
        all_samples, supplier_to_idx, user_to_idx, debug=debug
    )

    # Compute per-supplier and per user×supplier histories for inference features.
    supplier_amounts_sorted: dict = defaultdict(list)
    user_supplier_amounts_sorted: dict = defaultdict(list)
    supplier_last_date: dict = {}
    user_supplier_last_date: dict = {}
    user_supplier_last_sum: dict = {}
    for tx_date, tx_supplier, tx_user, tx_sum in sorted(all_samples, key=lambda s: s[0]):
        supplier_amounts_sorted[tx_supplier].append(tx_sum)
        user_supplier_amounts_sorted[(tx_user, tx_supplier)].append(tx_sum)
        supplier_last_date[tx_supplier] = tx_date
        user_supplier_last_date[(tx_user, tx_supplier)] = tx_date
        user_supplier_last_sum[(tx_user, tx_supplier)] = tx_sum

    # Predict amount for each selected supplier.
    predictions = []

    for supplier_id, _records in candidate_items:
        s_hist = supplier_amounts_sorted.get(supplier_id, [])
        us_hist = user_supplier_amounts_sorted.get((target_user_id, supplier_id), [])

        avg_amount = statistics.mean(s_hist) if s_hist else 0.0

        s_rolling3 = statistics.mean(s_hist[-3:]) if s_hist else avg_amount
        s_rolling_all = avg_amount
        s_median = statistics.median(s_hist) if s_hist else avg_amount

        us_rolling3 = statistics.mean(us_hist[-3:]) if us_hist else s_rolling3
        us_rolling_all = statistics.mean(us_hist) if us_hist else s_rolling_all
        us_median = statistics.median(us_hist) if us_hist else s_median

        last_s_date = supplier_last_date.get(supplier_id)
        last_us_date = user_supplier_last_date.get((target_user_id, supplier_id))
        us_last_sum = user_supplier_last_sum.get((target_user_id, supplier_id), us_rolling3)
        s_gap_days = max(0, (now - last_s_date).days) if last_s_date else 0
        us_gap_days = max(0, (now - last_us_date).days) if last_us_date else s_gap_days

        next_features = [[
            supplier_to_idx.get(supplier_id, -1),
            user_to_idx.get(target_user_id, -1),
            now.day,
            now.weekday(),
            now.month,
            s_rolling3,
            s_rolling_all,
            s_median,
            us_rolling3,
            us_rolling_all,
            us_median,
            us_last_sum,
            s_gap_days,
            us_gap_days,
        ]]

        if global_model is not None:
            predicted_amount = float(global_model.predict(next_features)[0])

            # Local confidence: disagreement between trees.
            if hasattr(global_model, "estimators_"):
                tree_preds = [float(tree.predict(next_features)[0]) for tree in global_model.estimators_]
                tree_std = statistics.stdev(tree_preds) if len(tree_preds) > 1 else 0.0
                amount_scale = max(1.0, abs(predicted_amount))
                local_model_conf = math.exp(-(tree_std / amount_scale))
            else:
                local_model_conf = 0.7

            model_conf = (0.6 * global_model_conf) + (0.4 * local_model_conf)
            model_conf = max(0.0, min(1.0, model_conf))
        else:
            predicted_amount = avg_amount
            model_conf = 0.5

        # Calibrate prediction toward robust historical center for this user/supplier.
        # This usually stabilizes noisy forecasts and reduces MAE on small histories.
        us_count = len(us_hist)
        w_user_hist = min(1.0, us_count / 8.0)
        robust_center = (w_user_hist * us_median) + ((1.0 - w_user_hist) * s_median)
        blend_weight = 0.7 if global_model is not None else 0.0
        predicted_amount = (blend_weight * predicted_amount) + ((1.0 - blend_weight) * robust_center)

        # Clamp into realistic historical range to avoid extreme outputs.
        hist_for_bounds = us_hist if len(us_hist) >= 5 else s_hist
        if hist_for_bounds:
            lower_bound = _quantile(hist_for_bounds, 0.1)
            upper_bound = _quantile(hist_for_bounds, 0.9)
            predicted_amount = max(lower_bound, min(predicted_amount, upper_bound))

        next_predicted_date = now.strftime("%Y-%m-%d")
        predicted_user = target_user_id

        amount_std = statistics.stdev(s_hist) if len(s_hist) > 1 else 0
        consistency = max(0, 1 - (amount_std / avg_amount)) if avg_amount > 0 else 0.5
        frequency_score = min(supplier_freq[supplier_id] / total_records, 1.0)
        confidence = (0.4 * consistency) + (0.3 * frequency_score) + (0.3 * model_conf)

        if debug:
            print(
                f"[PREDICT] supplier_id={supplier_id}, user_id={predicted_user} | "
                f"avg_amount={avg_amount:.2f}, s_rolling3={s_rolling3:.2f}, "
                f"us_rolling3={us_rolling3:.2f}, pred_sum={predicted_amount:.2f}, "
                f"target_date={next_predicted_date}, "
                f"us_count={us_count}, us_gap={us_gap_days}d, "
                f"consistency={consistency:.2f}, freq_score={frequency_score:.2f}, "
                f"model={model_name if global_model is not None else 'fallback'}, "
                f"model_conf={model_conf:.2f}, confidence={confidence:.2f}"
            )

        predictions.append({
            "date": next_predicted_date,
            "sum": round(max(0.0, predicted_amount), 2),
            "supplier_id": supplier_id,
            "user_id": predicted_user,
            "show": True,
            "confidence": round(confidence, 2)
        })

    # Return all selected suppliers sorted by frequency desc.
    result = sorted(
        predictions,
        key=lambda x: supplier_freq.get(x["supplier_id"], 0),
        reverse=True,
    )

    if debug:
        print(f"[PREDICT] Final top {len(result)} predictions:")
        for i, p in enumerate(result, 1):
            print(f"[PREDICT]   #{i}: supplier_id={p['supplier_id']}, user_id={p['user_id']}, date={p['date']}, sum={p['sum']}, confidence={p['confidence']}")

    return result