package store

import (
	"context"
	"errors"
	"fmt"
	"sort"
	"strings"
	"time"

	"github.com/tech/sendico/billing/fees/storage"
	"github.com/tech/sendico/billing/fees/storage/model"
	dmath "github.com/tech/sendico/pkg/decimal"
	"github.com/tech/sendico/pkg/db/repository"
	"github.com/tech/sendico/pkg/db/repository/builder"
	ri "github.com/tech/sendico/pkg/db/repository/index"
	"github.com/tech/sendico/pkg/merrors"
	"github.com/tech/sendico/pkg/mlogger"
	m "github.com/tech/sendico/pkg/model"
	"github.com/tech/sendico/pkg/mservice"
	"go.mongodb.org/mongo-driver/bson/primitive"
	"go.mongodb.org/mongo-driver/mongo"
	"go.uber.org/zap"
)

type plansStore struct {
	logger mlogger.Logger
	repo   repository.Repository
}

// NewPlans constructs a Mongo-backed PlansStore.
func NewPlans(logger mlogger.Logger, db *mongo.Database) (storage.PlansStore, error) {
	repo := repository.CreateMongoRepository(db, mservice.FeePlans)

	// Index for organisation lookups.
	orgIndex := &ri.Definition{
		Keys: []ri.Key{
			{Field: m.OrganizationRefField, Sort: ri.Asc},
			{Field: "effectiveFrom", Sort: ri.Desc},
		},
	}
	if err := repo.CreateIndex(orgIndex); err != nil {
		logger.Error("failed to ensure fee plan organization index", zap.Error(err))
		return nil, err
	}

	// Unique index for plan versions (per organisation + effectiveFrom).
	uniqueIndex := &ri.Definition{
		Keys: []ri.Key{
			{Field: m.OrganizationRefField, Sort: ri.Asc},
			{Field: "effectiveFrom", Sort: ri.Asc},
		},
		Unique: true,
	}
	if err := repo.CreateIndex(uniqueIndex); err != nil {
		logger.Error("failed to ensure fee plan uniqueness index", zap.Error(err))
		return nil, err
	}

	// Recommended index to speed up active-plan lookups (org/global + active + dates).
	activeIndex := &ri.Definition{
		Keys: []ri.Key{
			{Field: m.OrganizationRefField, Sort: ri.Asc},
			{Field: "active", Sort: ri.Asc},
			{Field: "effectiveFrom", Sort: ri.Asc},
			{Field: "effectiveTo", Sort: ri.Asc},
		},
	}
	if err := repo.CreateIndex(activeIndex); err != nil {
		logger.Warn("failed to ensure fee plan active index", zap.Error(err))
	}

	return &plansStore{
		logger: logger.Named("plans"),
		repo:   repo,
	}, nil
}

func (p *plansStore) Create(ctx context.Context, plan *model.FeePlan) error {
	if err := validatePlan(plan); err != nil {
		return err
	}
	if err := p.ensureNoOverlap(ctx, plan); err != nil {
		return err
	}

	if err := p.repo.Insert(ctx, plan, nil); err != nil {
		if errors.Is(err, merrors.ErrDataConflict) {
			return storage.ErrDuplicateFeePlan
		}
		p.logger.Warn("failed to create fee plan", zap.Error(err))
		return err
	}
	return nil
}

func (p *plansStore) Update(ctx context.Context, plan *model.FeePlan) error {
	if plan == nil || plan.GetID() == nil || plan.GetID().IsZero() {
		return merrors.InvalidArgument("plansStore: invalid fee plan reference")
	}
	if err := validatePlan(plan); err != nil {
		return err
	}
	if err := p.ensureNoOverlap(ctx, plan); err != nil {
		return err
	}

	if err := p.repo.Update(ctx, plan); err != nil {
		p.logger.Warn("failed to update fee plan", zap.Error(err))
		return err
	}
	return nil
}

func (p *plansStore) Get(ctx context.Context, planRef primitive.ObjectID) (*model.FeePlan, error) {
	if planRef.IsZero() {
		return nil, merrors.InvalidArgument("plansStore: zero plan reference")
	}
	result := &model.FeePlan{}
	if err := p.repo.Get(ctx, planRef, result); err != nil {
		if errors.Is(err, merrors.ErrNoData) {
			return nil, storage.ErrFeePlanNotFound
		}
		return nil, err
	}
	return result, nil
}

func (p *plansStore) GetActivePlan(ctx context.Context, orgRef primitive.ObjectID, at time.Time) (*model.FeePlan, error) {
	// Compatibility shim: prefer org plan, fall back to global; allow zero org to mean global.
	if orgRef.IsZero() {
		return p.FindActiveGlobalPlan(ctx, at)
	}

	plan, err := p.FindActiveOrgPlan(ctx, orgRef, at)
	if err == nil {
		return plan, nil
	}
	if errors.Is(err, storage.ErrFeePlanNotFound) {
		return p.FindActiveGlobalPlan(ctx, at)
	}
	return nil, err
}

func (p *plansStore) FindActiveOrgPlan(ctx context.Context, orgRef primitive.ObjectID, at time.Time) (*model.FeePlan, error) {
	if orgRef.IsZero() {
		return nil, merrors.InvalidArgument("plansStore: zero organization reference")
	}
	query := repository.Query().Filter(repository.OrgField(), orgRef)
	return p.findActivePlan(ctx, query, at)
}

func (p *plansStore) FindActiveGlobalPlan(ctx context.Context, at time.Time) (*model.FeePlan, error) {
	globalQuery := repository.Query().Or(
		repository.Exists(repository.OrgField(), false),
		repository.Query().Filter(repository.OrgField(), nil),
	)
	return p.findActivePlan(ctx, globalQuery, at)
}

var _ storage.PlansStore = (*plansStore)(nil)

func (p *plansStore) findActivePlan(ctx context.Context, orgQuery builder.Query, at time.Time) (*model.FeePlan, error) {
	limit := int64(2)
	query := orgQuery.
		Filter(repository.Field("active"), true).
		Comparison(repository.Field("effectiveFrom"), builder.Lte, at).
		Sort(repository.Field("effectiveFrom"), false).
		Limit(&limit)

	query = query.And(
		repository.Query().Or(
			repository.Query().Filter(repository.Field("effectiveTo"), nil),
			repository.Query().Comparison(repository.Field("effectiveTo"), builder.Gte, at),
		),
	)

	var plans []*model.FeePlan
	decoder := func(cursor *mongo.Cursor) error {
		target := &model.FeePlan{}
		if err := cursor.Decode(target); err != nil {
			return err
		}
		plans = append(plans, target)
		return nil
	}

	if err := p.repo.FindManyByFilter(ctx, query, decoder); err != nil {
		if errors.Is(err, merrors.ErrNoData) {
			return nil, storage.ErrFeePlanNotFound
		}
		return nil, err
	}

	if len(plans) == 0 {
		return nil, storage.ErrFeePlanNotFound
	}
	if len(plans) > 1 {
		return nil, storage.ErrConflictingFeePlans
	}
	return plans[0], nil
}

func validatePlan(plan *model.FeePlan) error {
	if plan == nil {
		return merrors.InvalidArgument("plansStore: nil fee plan")
	}
	if len(plan.Rules) == 0 {
		return merrors.InvalidArgument("plansStore: fee plan must contain at least one rule")
	}
	if plan.Active && plan.EffectiveTo != nil && plan.EffectiveTo.Before(plan.EffectiveFrom) {
		return merrors.InvalidArgument("plansStore: effectiveTo cannot be before effectiveFrom")
	}

	// Ensure unique priority per (trigger, appliesTo) combination.
	seen := make(map[string]struct{})
	for _, rule := range plan.Rules {
		if strings.TrimSpace(rule.Percentage) != "" {
			if _, err := dmath.RatFromString(rule.Percentage); err != nil {
				return merrors.InvalidArgument("plansStore: invalid rule percentage")
			}
		}
		if strings.TrimSpace(rule.FixedAmount) != "" {
			if _, err := dmath.RatFromString(rule.FixedAmount); err != nil {
				return merrors.InvalidArgument("plansStore: invalid rule fixed amount")
			}
		}
		if strings.TrimSpace(rule.MinimumAmount) != "" {
			if _, err := dmath.RatFromString(rule.MinimumAmount); err != nil {
				return merrors.InvalidArgument("plansStore: invalid rule minimum amount")
			}
		}
		if strings.TrimSpace(rule.MaximumAmount) != "" {
			if _, err := dmath.RatFromString(rule.MaximumAmount); err != nil {
				return merrors.InvalidArgument("plansStore: invalid rule maximum amount")
			}
		}

		appliesKey := normalizeAppliesTo(rule.AppliesTo)
		priorityKey := fmt.Sprintf("%s|%d|%s", rule.Trigger, rule.Priority, appliesKey)
		if _, ok := seen[priorityKey]; ok {
			return merrors.InvalidArgument("plansStore: duplicate priority for trigger/appliesTo")
		}
		seen[priorityKey] = struct{}{}
	}
	return nil
}

func normalizeAppliesTo(applies map[string]string) string {
	if len(applies) == 0 {
		return ""
	}
	keys := make([]string, 0, len(applies))
	for k := range applies {
		keys = append(keys, k)
	}
	sort.Strings(keys)
	parts := make([]string, 0, len(keys))
	for _, k := range keys {
		parts = append(parts, k+"="+applies[k])
	}
	return strings.Join(parts, ",")
}

func (p *plansStore) ensureNoOverlap(ctx context.Context, plan *model.FeePlan) error {
	if plan == nil || !plan.Active {
		return nil
	}

	orgQuery := repository.Query()
	if plan.OrganizationRef.IsZero() {
		orgQuery = repository.Query().Or(
			repository.Exists(repository.OrgField(), false),
			repository.Query().Filter(repository.OrgField(), nil),
		)
	} else {
		orgQuery = repository.Query().Filter(repository.OrgField(), plan.OrganizationRef)
	}

	maxTime := time.Date(9999, 12, 31, 23, 59, 59, 0, time.UTC)
	newFrom := plan.EffectiveFrom
	newTo := maxTime
	if plan.EffectiveTo != nil {
		newTo = *plan.EffectiveTo
	}

	query := orgQuery.
		Filter(repository.Field("active"), true).
		Comparison(repository.Field("effectiveFrom"), builder.Lte, newTo).
		And(repository.Query().Or(
			repository.Query().Filter(repository.Field("effectiveTo"), nil),
			repository.Query().Comparison(repository.Field("effectiveTo"), builder.Gte, newFrom),
		))

	if id := plan.GetID(); id != nil && !id.IsZero() {
		query = query.And(repository.Query().Comparison(repository.IDField(), builder.Ne, *id))
	}

	limit := int64(1)
	query = query.Limit(&limit)

	var overlapFound bool
	decoder := func(cursor *mongo.Cursor) error {
		overlapFound = true
		return nil
	}

	if err := p.repo.FindManyByFilter(ctx, query, decoder); err != nil {
		if errors.Is(err, merrors.ErrNoData) {
			return nil
		}
		return err
	}
	if overlapFound {
		return storage.ErrConflictingFeePlans
	}
	return nil
}