"""Calibration Engine — Bayesian shrinkage source reliability and weight adjustment.

Computes source reliability scores using Bayesian shrinkage from historical
prediction outcomes, and adjusts evidence weights based on source performance.
Updates the existing source_accuracy table with reliability scores.

Requirements: 8.1, 8.2, 8.3, 8.4, 8.5
"""
from __future__ import annotations

import logging

import asyncpg

logger = logging.getLogger(__name__)


# ---------------------------------------------------------------------------
# Pure functions — testable without a database
# ---------------------------------------------------------------------------


def compute_source_reliability(
    observed_win_rate: float,
    sample_count: int,
    prior_strength: int = 30,
) -> float:
    """Bayesian shrinkage source reliability.

    reliability = 0.5 + (n / (n + prior_strength)) * (observed_win_rate - 0.5)

    Returns value in [0.0, 1.0].
    When n=0, returns 0.5 (prior mean).
    As n→∞, approaches observed_win_rate.
    """
    if sample_count <= 0:
        return 0.5

    shrinkage = sample_count / (sample_count + prior_strength)
    reliability = 0.5 + shrinkage * (observed_win_rate - 0.5)

    # Clamp to [0.0, 1.0] for safety (should already be in range when
    # observed_win_rate is in [0.0, 1.0], but guard against edge cases).
    return max(0.0, min(1.0, reliability))


def compute_adjusted_evidence_weight(
    base_weight: float,
    reliability: float,
) -> float:
    """Adjusted weight = base_weight * (0.5 + reliability), clamped to [0.1, 2.0]."""
    adjusted = base_weight * (0.5 + reliability)
    return max(0.1, min(2.0, adjusted))


# ---------------------------------------------------------------------------
# SQL queries
# ---------------------------------------------------------------------------

# Query v_source_performance to get per-source win rates and sample counts.
# Groups by source, counting total predictions and directional wins.
_SOURCE_PERFORMANCE_SQL = """
SELECT
    source,
    COUNT(*) AS sample_count,
    COUNT(*) FILTER (WHERE direction_correct = TRUE) AS win_count
FROM v_source_performance
WHERE direction_correct IS NOT NULL
GROUP BY source
"""

# Upsert into source_accuracy: update accuracy_ratio and sample_count
# for existing sources, insert new ones.
_UPSERT_SOURCE_ACCURACY_SQL = """
INSERT INTO source_accuracy (source_id, accuracy_ratio, sample_count, last_updated)
VALUES ($1, $2, $3, NOW())
ON CONFLICT (source_id)
DO UPDATE SET
    accuracy_ratio = EXCLUDED.accuracy_ratio,
    sample_count = EXCLUDED.sample_count,
    last_updated = NOW()
"""


# ---------------------------------------------------------------------------
# Database-backed function
# ---------------------------------------------------------------------------


async def update_source_reliabilities(
    pool: asyncpg.Pool,
) -> int:
    """Recompute and store source reliability scores from latest outcomes.

    1. Queries v_source_performance to get per-source win rates and counts
    2. Computes Bayesian shrinkage reliability for each source
    3. Upserts into source_accuracy table (accuracy_ratio = reliability)

    Returns count of sources updated.
    """
    try:
        rows = await pool.fetch(_SOURCE_PERFORMANCE_SQL)
    except Exception:
        logger.exception("Failed to query source performance for reliability update")
        return 0

    if not rows:
        logger.info("No source performance data available for reliability update")
        return 0

    updated = 0

    for row in rows:
        source = row["source"]
        sample_count = row["sample_count"]
        win_count = row["win_count"]

        observed_win_rate = win_count / sample_count if sample_count > 0 else 0.5
        reliability = compute_source_reliability(observed_win_rate, sample_count)

        try:
            await pool.execute(
                _UPSERT_SOURCE_ACCURACY_SQL,
                source,
                reliability,
                sample_count,
            )
            updated += 1
        except Exception:
            logger.exception(
                "Failed to upsert source reliability for source=%s", source
            )

    logger.info("Updated source reliabilities for %d sources", updated)
    return updated