class PolicyEngine:

    def __init__(self, db):
        self.db = db

        self.rules = []
        self.overrides = {}

    # -----------------------------
    # REGISTER RULE
    # -----------------------------
    def add_rule(self, rule):
        self.rules.append(rule)

    # -----------------------------
    # SET LIVE OVERRIDE
    # -----------------------------
    def set_override(self, key, value):
        self.overrides[key] = value

    # -----------------------------
    # CLEAR OVERRIDE
    # -----------------------------
    def clear_override(self, key):
        if key in self.overrides:
            del self.overrides[key]

    # -----------------------------
    # APPLY POLICY TO NODE SELECTION
    # -----------------------------
    def evaluate(self, action, target, node):

        score_modifier = 0

        # -----------------------------
        # APPLY STATIC RULES
        # -----------------------------
        for rule in self.rules:
            score_modifier += rule.apply(action, target, node)

        # -----------------------------
        # APPLY HEURISTICS
        # -----------------------------
        score_modifier += self._heuristics(action, target, node)

        # -----------------------------
        # APPLY OVERRIDES
        # -----------------------------
        score_modifier += self._overrides(action, target, node)

        return score_modifier

    # -----------------------------
    # HEURISTICS (LEARNING LAYER)
    # -----------------------------
    def _heuristics(self, action, target, node):

        score = 0

        history = self.db.events

        # simple heuristic: prefer nodes that succeeded before
        success_count = 0

        for session_id in history:
            for event in history[session_id]:
                if event["type"] == "action_end":
                    if (
                        event["data"]["action"] == action["name"]
                        and event["data"]["state"] == "done"
                        and event["data"].get("node") == node["name"]
                    ):
                        success_count += 1

        score += success_count * 2

        return score

    # -----------------------------
    # LIVE OVERRIDES
    # -----------------------------
    def _overrides(self, action, target, node):

        score = 0

        # force node
        forced = self.overrides.get("force_node")

        if forced and node["name"] == forced:
            score += 1000

        # avoid node
        avoid = self.overrides.get("avoid_node")

        if avoid and node["name"] == avoid:
            score -= 1000

        return score