"""Per-prediction model certainty — the glass-box "how sure is ESM-2?" signal.

Every ΔLL score answers "is this substitution favorable?" — but not "how much
should I trust that call?". This module adds the second axis, honestly: it
measures how SHARP ESM-2's amino-acid distribution is at each position. A
well-conserved position where the model overwhelmingly prefers one residue
(low entropy) is one it's confident about; a flexible position where many
residues are near-equiprobable (high entropy) is one where any single call is
a weaker signal — and we say so rather than hide it.

Crucially this is NOT calibrated against wet-lab outcomes (we don't claim it
is): it's the model's own posterior confidence, surfaced instead of buried.
The bench-calibrated axis is the separate active-learning / calibration work.

Cost is zero extra compute: softmax is shift-invariant, so the full
per-position posterior over the 20 amino acids is recoverable from the ΔLL
table we already computed — ``p(a) ∝ exp(ΔLL_a)`` with ``ΔLL_wt = 0`` — no
extra ESM-2 forward pass.
"""
from __future__ import annotations

import math
import re
from typing import Dict, Optional, Sequence, Tuple

import numpy as np

# 20 canonical AAs; H_max is the entropy of a uniform posterior over them.
_N_AA = 20
_H_MAX = math.log(_N_AA)

_LABEL_RE = re.compile(r"^([A-Za-z])(\d+)([A-Za-z*])$")   # "F76Y"


def _entropy_confidence(delta_lls: Sequence[float]) -> float:
    """Confidence in [0,1] for one position from its 19 mutant ΔLLs.

    Reconstruct the posterior p(a) ∝ exp(ΔLL_a) (wt's ΔLL is 0 by definition),
    then confidence = 1 - H(p)/H_max. 1.0 = the model is certain (one residue
    dominates); 0.0 = maximally uncertain (flat over all 20)."""
    vals = np.asarray(list(delta_lls) + [0.0], dtype=np.float64)   # + implicit WT
    vals = vals - vals.max()                     # numerically-stable softmax
    p = np.exp(vals)
    p = p / p.sum()
    nz = p[p > 0]
    h = float(-(nz * np.log(nz)).sum())
    conf = 1.0 - h / _H_MAX
    return float(min(1.0, max(0.0, conf)))


def position_confidence_from_scores(scores_df) -> Dict[int, float]:
    """position (0-indexed) -> confidence in [0,1], from the long-format ΔLL
    DataFrame (columns: position, delta_ll, ...). Positions with fewer than a
    near-complete substitution set are still scored on whatever is present."""
    out: Dict[int, float] = {}
    if scores_df is None or len(scores_df) == 0:
        return out
    for pos, group in scores_df.groupby("position"):
        out[int(pos)] = _entropy_confidence([float(x) for x in group["delta_ll"].values])
    return out


def _parse_positions(mutations: str) -> list:
    """'V60L,F76Y' -> [('V60L', 59), ('F76Y', 75)] (label, 0-indexed pos)."""
    out = []
    for tok in re.split(r"[,\s;]+", (mutations or "").strip()):
        m = _LABEL_RE.match(tok.strip())
        if not m:
            continue
        pos = int(m.group(2)) - 1
        if pos >= 0:
            out.append((tok.strip(), pos))
    return out


def variant_confidence(
    mutations: str, pos_conf: Dict[int, float],
) -> Tuple[Optional[float], str]:
    """Overall confidence for a variant = the WEAKEST-LINK of its mutated
    positions (one uncertain position honestly undermines the whole call).
    Returns (confidence or None if no scorable position, weakest-site label)."""
    sites = _parse_positions(mutations)
    scored = [(lbl, pos_conf[pos]) for (lbl, pos) in sites if pos in pos_conf]
    if not scored:
        return (None, "")
    weakest_label, weakest = min(scored, key=lambda t: t[1])
    return (round(weakest, 4), weakest_label)


def attach_confidence(rows: list, pos_conf: Dict[int, float]) -> list:
    """In-place: add ``Confidence`` (0-1, weakest-link) and
    ``Confidence_Weakest`` (the label of the least-certain changed residue) to
    each variant row dict that has a ``Mutations_AA``. WT / mutation-less rows
    get Confidence = None. Returns the same list for chaining."""
    for r in rows:
        if not isinstance(r, dict):
            continue
        muts = str(r.get("Mutations_AA", "") or "")
        if not muts:
            r["Confidence"] = None
            r["Confidence_Weakest"] = ""
            continue
        conf, weakest = variant_confidence(muts, pos_conf)
        r["Confidence"] = conf
        r["Confidence_Weakest"] = weakest
    return rows