"""Source accuracy tracker for historical prediction accuracy per source.

Tracks per-source accuracy metrics (fraction of correct directional calls)
used by the probabilistic scoring pipeline to weight source credibility.
Accuracy data is stored in the ``source_accuracy`` database table and
fetched in batch at the start of each aggregation cycle.

Requirements: 4.1, 4.2, 4.3, 4.4, 4.5
"""
from __future__ import annotations

import logging
from dataclasses import dataclass
from datetime import datetime, timezone

import asyncpg

logger = logging.getLogger(__name__)


@dataclass
class SourceAccuracy:
    """Per-source historical prediction accuracy.

    Attributes:
        source_id: Unique identifier for the signal source.
        accuracy_ratio: Fraction of correct directional calls, in [0, 1].
        sample_count: Number of signals with known outcomes.
        last_updated: Timestamp of the most recent accuracy update.
    """

    source_id: str
    accuracy_ratio: float
    sample_count: int
    last_updated: datetime

    @property
    def accuracy_factor(self) -> float:
        """Multiplicative factor for credibility weight.

        Returns 1.0 (neutral) when sample_count < 10.
        Otherwise scales linearly from 0.5 (0% accuracy) to 1.5
        (100% accuracy).  Corrupted accuracy_ratio values outside
        [0, 1] are clamped before computing the factor.
        """
        if self.sample_count < 10:
            return 1.0
        clamped = max(0.0, min(1.0, self.accuracy_ratio))
        return 0.5 + clamped


async def fetch_source_accuracy(
    pool: asyncpg.Pool,
    source_ids: list[str],
) -> dict[str, SourceAccuracy]:
    """Fetch accuracy metrics for a batch of sources.

    Queries the ``source_accuracy`` table for all requested *source_ids*
    in a single round-trip.  Returns a mapping from source_id to its
    :class:`SourceAccuracy` record.

    When the database is unreachable or the query fails, returns an empty
    dict so that callers fall back to the neutral accuracy factor of 1.0.
    """
    if not source_ids:
        return {}

    try:
        rows = await pool.fetch(
            """
            SELECT source_id, accuracy_ratio, sample_count, last_updated
            FROM source_accuracy
            WHERE source_id = ANY($1::varchar[])
            """,
            source_ids,
        )
    except Exception:
        logger.warning(
            "Failed to fetch source accuracy; defaulting to neutral factor",
            exc_info=True,
        )
        return {}

    result: dict[str, SourceAccuracy] = {}
    for row in rows:
        sid = row["source_id"]
        ratio = row["accuracy_ratio"]
        # Clamp corrupted accuracy_ratio to [0.0, 1.0]
        ratio = max(0.0, min(1.0, float(ratio)))
        result[sid] = SourceAccuracy(
            source_id=sid,
            accuracy_ratio=ratio,
            sample_count=int(row["sample_count"]),
            last_updated=row["last_updated"],
        )
    return result


async def update_source_accuracy(
    pool: asyncpg.Pool,
    source_id: str,
    realized_outcomes: list[tuple[str, float]],
) -> None:
    """Update accuracy metrics for a source from realized price outcomes.

    Each element of *realized_outcomes* is a ``(predicted_direction,
    actual_7d_return)`` pair.  A prediction is considered correct when:

    * ``predicted_direction`` is ``"bullish"`` and ``actual_7d_return > 0``
    * ``predicted_direction`` is ``"bearish"`` and ``actual_7d_return < 0``

    Neutral predictions and zero returns are excluded from the accuracy
    calculation.

    The function upserts the ``source_accuracy`` row, merging the new
    outcomes with any existing sample count and accuracy ratio.
    """
    if not realized_outcomes:
        return

    # Count correct directional calls from the new outcomes.
    correct = 0
    total = 0
    for predicted_direction, actual_return in realized_outcomes:
        direction = predicted_direction.lower()
        if direction not in ("bullish", "bearish"):
            continue
        if actual_return == 0.0:
            continue
        total += 1
        if direction == "bullish" and actual_return > 0:
            correct += 1
        elif direction == "bearish" and actual_return < 0:
            correct += 1

    if total == 0:
        return

    now = datetime.now(timezone.utc)

    try:
        await pool.execute(
            """
            INSERT INTO source_accuracy (source_id, accuracy_ratio, sample_count, last_updated)
            VALUES ($1, $2, $3, $4)
            ON CONFLICT (source_id) DO UPDATE SET
                accuracy_ratio = (
                    source_accuracy.accuracy_ratio * source_accuracy.sample_count
                    + $2 * $3
                ) / NULLIF(source_accuracy.sample_count + $3, 0),
                sample_count = source_accuracy.sample_count + $3,
                last_updated = $4
            """,
            source_id,
            correct / total,
            total,
            now,
        )
    except Exception:
        logger.warning(
            "Failed to update source accuracy for %s; continuing with stale data",
            source_id,
            exc_info=True,
        )