package lottery

import (
	"context"
	"encoding/json"
	"fmt"
	"strings"
)

// 门槛规则类型常量。前端展示时可依据这些 key 组装本地化提示。
const (
	RuleTypeHasSubscription  = "has_subscription"  // 需要有活跃订阅（可带 min_days_remaining）
	RuleTypeSubscriptionType = "subscription_type" // 订阅套餐必须在 plan_ids 中
	RuleTypeInviteCount      = "invite_count"      // 邀请人数 ≥ min（可带 window_days，由 ContextBuilder 预算）
	RuleTypeTotalRecharge    = "total_recharge"    // 累计充值 ≥ min_usdt
	RuleTypeRegisterDays     = "register_days"     // 注册天数 ≥ min
	RuleTypeUserTag          = "user_tag"          // 用户标签命中 tags[] 中任一
)

const (
	OpAND = "AND"
	OpOR  = "OR"
)

// defaultEvaluator 是 RuleEvaluator 的开箱实现。
type defaultEvaluator struct{}

// NewRuleEvaluator 返回默认门槛评估器。
func NewRuleEvaluator() RuleEvaluator { return &defaultEvaluator{} }

func (e *defaultEvaluator) Evaluate(_ context.Context, tree *EligibilityRule, rc RuleContext) (bool, []UnmetReason, error) {
	if tree == nil {
		return true, nil, nil
	}
	unmet := make([]UnmetReason, 0, 4)
	passed, err := e.evalNode(tree, rc, &unmet)
	if err != nil {
		return false, nil, err
	}
	return passed, unmet, nil
}

func (e *defaultEvaluator) evalNode(node *EligibilityRule, rc RuleContext, unmet *[]UnmetReason) (bool, error) {
	if node == nil {
		return true, nil
	}
	// 聚合节点
	if node.Op != "" {
		return e.evalGroup(node, rc, unmet)
	}
	// 叶子节点
	if node.Type == "" {
		return true, nil
	}
	return e.evalLeaf(node, rc, unmet)
}

func (e *defaultEvaluator) evalGroup(node *EligibilityRule, rc RuleContext, unmet *[]UnmetReason) (bool, error) {
	op := strings.ToUpper(node.Op)
	if len(node.Children) == 0 {
		return true, nil
	}
	switch op {
	case OpAND:
		allPassed := true
		for _, child := range node.Children {
			ok, err := e.evalNode(child, rc, unmet)
			if err != nil {
				return false, err
			}
			if !ok {
				allPassed = false
			}
		}
		return allPassed, nil
	case OpOR:
		// OR 只收集内部未通过项到一个临时篮子；若整体通过则不冒泡出去。
		anyPassed := false
		local := make([]UnmetReason, 0, len(node.Children))
		for _, child := range node.Children {
			ok, err := e.evalNode(child, rc, &local)
			if err != nil {
				return false, err
			}
			if ok {
				anyPassed = true
			}
		}
		if !anyPassed {
			*unmet = append(*unmet, local...)
		}
		return anyPassed, nil
	default:
		return false, fmt.Errorf("unknown group op %q", node.Op)
	}
}

func (e *defaultEvaluator) evalLeaf(node *EligibilityRule, rc RuleContext, unmet *[]UnmetReason) (bool, error) {
	switch node.Type {
	case RuleTypeHasSubscription:
		return e.evalHasSubscription(node, rc, unmet)
	case RuleTypeSubscriptionType:
		return e.evalSubscriptionType(node, rc, unmet)
	case RuleTypeInviteCount:
		return e.evalInviteCount(node, rc, unmet)
	case RuleTypeTotalRecharge:
		return e.evalTotalRecharge(node, rc, unmet)
	case RuleTypeRegisterDays:
		return e.evalRegisterDays(node, rc, unmet)
	case RuleTypeUserTag:
		return e.evalUserTag(node, rc, unmet)
	default:
		return false, fmt.Errorf("unknown leaf rule type %q", node.Type)
	}
}

// ---- 单条规则 -------------------------------------------------------------

func (e *defaultEvaluator) evalHasSubscription(node *EligibilityRule, rc RuleContext, unmet *[]UnmetReason) (bool, error) {
	var params struct {
		MinDaysRemaining int64 `json:"min_days_remaining"`
	}
	if len(node.Params) > 0 {
		if err := json.Unmarshal(node.Params, &params); err != nil {
			return false, fmt.Errorf("has_subscription params: %w", err)
		}
	}
	if !rc.HasActiveSubscription {
		*unmet = append(*unmet, UnmetReason{
			Rule: RuleTypeHasSubscription,
			Hint: "需要有活跃订阅",
		})
		return false, nil
	}
	if params.MinDaysRemaining > 0 {
		got := rc.SubscriptionExpiresIn / 86400
		if got < params.MinDaysRemaining {
			*unmet = append(*unmet, UnmetReason{
				Rule:     RuleTypeHasSubscription,
				Hint:     fmt.Sprintf("订阅剩余天数不足，还差 %d 天", params.MinDaysRemaining-got),
				Current:  got,
				Required: params.MinDaysRemaining,
			})
			return false, nil
		}
	}
	return true, nil
}

func (e *defaultEvaluator) evalSubscriptionType(node *EligibilityRule, rc RuleContext, unmet *[]UnmetReason) (bool, error) {
	var params struct {
		PlanIds []int64 `json:"plan_ids"`
	}
	if err := json.Unmarshal(node.Params, &params); err != nil {
		return false, fmt.Errorf("subscription_type params: %w", err)
	}
	want := make(map[int64]struct{}, len(params.PlanIds))
	for _, id := range params.PlanIds {
		want[id] = struct{}{}
	}
	for _, id := range rc.SubscriptionPlanIds {
		if _, ok := want[id]; ok {
			return true, nil
		}
	}
	*unmet = append(*unmet, UnmetReason{
		Rule: RuleTypeSubscriptionType,
		Hint: "订阅类型不符合活动要求",
	})
	return false, nil
}

func (e *defaultEvaluator) evalInviteCount(node *EligibilityRule, rc RuleContext, unmet *[]UnmetReason) (bool, error) {
	var params struct {
		Min        int64 `json:"min"`
		WindowDays int64 `json:"window_days,omitempty"`
	}
	if err := json.Unmarshal(node.Params, &params); err != nil {
		return false, fmt.Errorf("invite_count params: %w", err)
	}
	if rc.InviteCount >= params.Min {
		return true, nil
	}
	*unmet = append(*unmet, UnmetReason{
		Rule:     RuleTypeInviteCount,
		Hint:     fmt.Sprintf("还需邀请 %d 人（%d/%d）", params.Min-rc.InviteCount, rc.InviteCount, params.Min),
		Current:  rc.InviteCount,
		Required: params.Min,
	})
	return false, nil
}

func (e *defaultEvaluator) evalTotalRecharge(node *EligibilityRule, rc RuleContext, unmet *[]UnmetReason) (bool, error) {
	var params struct {
		MinUSDT int64 `json:"min_usdt"`
	}
	if err := json.Unmarshal(node.Params, &params); err != nil {
		return false, fmt.Errorf("total_recharge params: %w", err)
	}
	if rc.TotalRechargeUSDT >= params.MinUSDT {
		return true, nil
	}
	*unmet = append(*unmet, UnmetReason{
		Rule:     RuleTypeTotalRecharge,
		Hint:     fmt.Sprintf("累计充值不足，还差 %d USDT", params.MinUSDT-rc.TotalRechargeUSDT),
		Current:  rc.TotalRechargeUSDT,
		Required: params.MinUSDT,
	})
	return false, nil
}

func (e *defaultEvaluator) evalRegisterDays(node *EligibilityRule, rc RuleContext, unmet *[]UnmetReason) (bool, error) {
	var params struct {
		Min int64 `json:"min"`
	}
	if err := json.Unmarshal(node.Params, &params); err != nil {
		return false, fmt.Errorf("register_days params: %w", err)
	}
	if rc.RegisterDays >= params.Min {
		return true, nil
	}
	*unmet = append(*unmet, UnmetReason{
		Rule:     RuleTypeRegisterDays,
		Hint:     fmt.Sprintf("注册天数不足，还差 %d 天", params.Min-rc.RegisterDays),
		Current:  rc.RegisterDays,
		Required: params.Min,
	})
	return false, nil
}

func (e *defaultEvaluator) evalUserTag(node *EligibilityRule, rc RuleContext, unmet *[]UnmetReason) (bool, error) {
	var params struct {
		Tags []string `json:"tags"`
	}
	if err := json.Unmarshal(node.Params, &params); err != nil {
		return false, fmt.Errorf("user_tag params: %w", err)
	}
	want := make(map[string]struct{}, len(params.Tags))
	for _, t := range params.Tags {
		want[t] = struct{}{}
	}
	for _, t := range rc.UserTags {
		if _, ok := want[t]; ok {
			return true, nil
		}
	}
	*unmet = append(*unmet, UnmetReason{
		Rule: RuleTypeUserTag,
		Hint: "用户标签不符合活动要求",
	})
	return false, nil
}