"""Human-decided entity-merge candidates (Phase 1). Called by server.py routes —
NOT an agent tool. A partner approves (merge) or rejects (keep separate) each
candidate the fuzzy tier surfaced. Approvals apply the merge and record it in
entity_merges (durable, so deterministic resolution respects it); rejections are
remembered so the pair is not re-surfaced. Everything is logged.
"""
import json
import sqlite3
import uuid
from datetime import datetime, timezone


def _now():
    return datetime.now(timezone.utc).replace(tzinfo=None).isoformat() + "Z"


def _conn(db):
    c = sqlite3.connect(db)
    c.row_factory = sqlite3.Row
    c.execute("PRAGMA foreign_keys=ON")
    return c


def _log(c, actor_id, action, target_id, payload):
    c.execute("""INSERT INTO interaction_log
        (id, ts, actor_type, actor_id, action, target_type, target_id, payload, source, created_at)
        VALUES (?,?,?,?,?,?,?,?,?,?)""",
        (str(uuid.uuid4()), _now(), "human", actor_id, action, "canonical_entity", target_id,
         json.dumps(payload) if payload is not None else None, "crm_ui", _now()))


def list_candidates(db, status="pending"):
    c = _conn(db)
    # Only surface candidates whose BOTH sides are still live canonical entities.
    # When entity resolution self-heals (a grid "twin" matched back, so its
    # duplicate entity is soft-deleted), the candidate that paired them becomes
    # moot — hide it instead of asking a human to adjudicate a tombstone.
    rows = [dict(r) for r in c.execute(
        """SELECT mc.* FROM entity_merge_candidates mc
             JOIN canonical_entities a ON a.id = mc.entity_a AND a.deleted_at IS NULL
             JOIN canonical_entities b ON b.id = mc.entity_b AND b.deleted_at IS NULL
            WHERE mc.status=?
            ORDER BY mc.confidence DESC, mc.created_at DESC""", (status,))]
    c.close()
    return {"candidates": rows, "count": len(rows)}


def _apply_merge(c, survivor, loser, confidence, reason):
    """Merge `loser` into `survivor`: record durably, repoint links + relationship
    edges, soft-delete the loser (never hard-delete — guardrail #3)."""
    c.execute("""INSERT INTO entity_merges (merged_id, survivor_id, confidence, reason, created_at)
                 VALUES (?,?,?,?,?)
                 ON CONFLICT(merged_id) DO UPDATE SET survivor_id=excluded.survivor_id,
                     confidence=excluded.confidence, reason=excluded.reason""",
              (loser, survivor, confidence or 0.8, reason, _now()))
    c.execute("UPDATE entity_links SET canonical_id=?, match_kind='fuzzy_merge' WHERE canonical_id=?",
              (survivor, loser))
    # repoint relationship edges (member_of, etc.); OR IGNORE avoids unique clashes,
    # then drop any leftover edges the survivor already had.
    c.execute("UPDATE OR IGNORE relationship_edges SET src_id=? WHERE src_id=?", (survivor, loser))
    c.execute("UPDATE OR IGNORE relationship_edges SET dst_id=? WHERE dst_id=?", (survivor, loser))
    c.execute("DELETE FROM relationship_edges WHERE src_id=? OR dst_id=?", (loser, loser))
    c.execute("UPDATE canonical_entities SET deleted_at=?, updated_at=? WHERE id=?", (_now(), _now(), loser))


def decide(db, candidate_id, decision, decided_by):
    if decision not in ("approve", "reject"):
        return {"error": "bad_decision", "allowed": ["approve", "reject"]}
    c = _conn(db)
    cand = c.execute("SELECT * FROM entity_merge_candidates WHERE id=?", (candidate_id,)).fetchone()
    if not cand:
        c.close()
        return {"error": "not_found", "candidate_id": candidate_id}
    if cand["status"] != "pending":
        c.close()
        return {"error": "already_decided", "status": cand["status"]}

    if decision == "approve":
        _apply_merge(c, cand["entity_a"], cand["entity_b"], cand["confidence"], cand["reason"])
    c.execute("UPDATE entity_merge_candidates SET status=?, decided_by=?, decided_at=? WHERE id=?",
              ("approved" if decision == "approve" else "rejected", decided_by, _now(), candidate_id))
    _log(c, decided_by, f"entity.merge_{decision}d", cand["entity_a"],
         {"survivor": cand["entity_a"], "loser": cand["entity_b"], "names": [cand["name_a"], cand["name_b"]]})
    c.commit()
    c.close()
    return {"id": candidate_id, "decision": decision,
            "merged": (cand["entity_b"] if decision == "approve" else None)}