"""Product Knowledge Base service: identity resolution, versioned knowledge, conflicts.

Identity order (operator contract): 1. exact GTIN; 2. strong fingerprint; 3. semantic
fingerprint candidate; 4. unknown. Conflicting knowledge for the same key is kept
side by side and surfaced as KNOWLEDGE_CONFLICT — never picked by majority.
"""
from datetime import datetime, timezone

from sqlalchemy import func as sa_func, select
from ..models import KbKnowledge, KbObservation, KbProduct

EXACT, FINGERPRINT = "EXACT", "FINGERPRINT"
_AUTHORITATIVE = {"OFFICIAL_DATASET", "OPERATOR", "AI_PLUS_OFFICIAL_VALIDATION"}


class KnowledgeBase:
    def __init__(self, session):
        self.session = session

    # ----- identity -----

    def upsert_product(self, fingerprint, gtin=None, normalized_description="", brand=None, unit=None, package_quantity=None, category=None):
        gtin = gtin or None
        product = None
        if gtin:
            product = self.session.scalar(select(KbProduct).where(KbProduct.gtin == gtin))
        if product is None:
            product = self.session.scalar(select(KbProduct).where(KbProduct.fingerprint == fingerprint))
        if product is None:
            product = KbProduct(fingerprint=fingerprint, normalized_description=normalized_description or "")
            self.session.add(product)
        # identity upgrades (never downgrades)
        if gtin and not product.gtin:
            product.gtin = gtin
            product.identity_kind = "GTIN"
        if normalized_description and not product.normalized_description:
            product.normalized_description = normalized_description
        for field, value in (("brand", brand), ("unit", unit), ("package_quantity", package_quantity), ("category", category)):
            if value and not getattr(product, field):
                setattr(product, field, value)
        self.session.flush()
        return product

    def resolve(self, gtin=None, fingerprint=None):
        """Returns (product|None, hit_kind). Cache-first: EXACT (GTIN) beats FINGERPRINT."""
        if gtin:
            product = self.session.scalar(select(KbProduct).where(KbProduct.gtin == gtin))
            if product:
                return product, EXACT
        if fingerprint:
            product = self.session.scalar(select(KbProduct).where(KbProduct.fingerprint == fingerprint))
            if product:
                return product, FINGERPRINT
        return None, None

    # ----- knowledge -----

    def add_knowledge(self, kb_product_id, knowledge_key, value, source, confidence=0.0, evidence=None, model=None, prompt_version=None, dataset_versions=None):
        value = str(value)
        row = self.session.scalar(select(KbKnowledge).where(KbKnowledge.kb_product_id == kb_product_id, KbKnowledge.knowledge_key == knowledge_key, KbKnowledge.value == value))
        if row is None:
            row = KbKnowledge(kb_product_id=kb_product_id, knowledge_key=knowledge_key, value=value, source=source, confidence=confidence, evidence=evidence or {}, model=model, prompt_version=prompt_version, dataset_versions=dataset_versions or {})
            self.session.add(row)
        else:
            # authoritative sources upgrade provenance/confidence of the same value; history preserved
            if source in _AUTHORITATIVE:
                row.source = source
                row.confidence = max(row.confidence, confidence)
                row.evidence = {**row.evidence, **(evidence or {})}
                if dataset_versions:
                    row.dataset_versions = {**row.dataset_versions, **dataset_versions}
            if source == "OFFICIAL_DATASET":
                row.validated_at = datetime.now(timezone.utc)
        self.session.flush()
        return row

    def current_knowledge(self, kb_product_id):
        rows = self.session.scalars(select(KbKnowledge).where(KbKnowledge.kb_product_id == kb_product_id)).all()
        by_key: dict = {}
        for row in rows:
            by_key.setdefault(row.knowledge_key, []).append(row)
        result = {}
        for key, entries in by_key.items():
            values = {entry.value for entry in entries}
            if len(values) > 1:
                result[key] = {"conflict": True, "values": values}
            else:
                best = max(entries, key=lambda entry: entry.confidence)
                result[key] = {"conflict": False, "value": best.value, "source": best.source, "confidence": best.confidence}
        return result

    # ----- observations -----

    def record_observation(self, kb_product_id, tenant_id, company_key, erp_code, database_label, observed_fields, source="ERP_OBSERVATION"):
        row = KbObservation(kb_product_id=kb_product_id, tenant_id=tenant_id, company_key=company_key, erp_code=erp_code, database_label=database_label, observed_fields=observed_fields or {}, source=source)
        self.session.add(row); self.session.flush()
        return row

    def observation_summary(self, kb_product_id):
        rows = self.session.scalars(select(KbObservation).where(KbObservation.kb_product_id == kb_product_id)).all()
        agreement: dict = {}
        for row in rows:
            for field, value in (row.observed_fields or {}).items():
                if value in (None, ""):
                    continue
                bucket = agreement.setdefault(field, {})
                bucket[str(value)] = bucket.get(str(value), 0) + 1
        conflicts = {field: values for field, values in agreement.items() if len(values) > 1}
        return {"observation_count": len(rows), "tenant_count": len({row.tenant_id for row in rows}), "agreement": agreement, "conflicts": conflicts}

    # ----- stats -----

    def stats(self):
        products = self.session.scalar(select(sa_func.count()).select_from(KbProduct)) or 0
        gtin_products = self.session.scalar(select(sa_func.count()).select_from(KbProduct).where(KbProduct.gtin.is_not(None))) or 0
        conflicts = 0
        for product_id in self.session.scalars(select(KbProduct.id)).all():
            knowledge = self.current_knowledge(product_id)
            conflicts += sum(1 for entry in knowledge.values() if entry.get("conflict"))
        fingerprint_products = products - gtin_products
        return {"products": products, "gtin_products": gtin_products, "fingerprint_products": fingerprint_products, "conflicts": conflicts}