package routingrules

import (
	"fmt"

	"github.com/openmeterio/openmeter/openmeter/ledger"
	"github.com/openmeterio/openmeter/pkg/models"
)

type RoutingRule interface {
	Validate(tx TxView) error
}

type Validator struct {
	Rules []RoutingRule
}

var _ ledger.RoutingValidator = (*Validator)(nil)

func (v Validator) ValidateEntries(entries []ledger.EntryInput) error {
	view, err := NewTxView(entries)
	if err != nil {
		return err
	}

	for _, rule := range v.Rules {
		if err := rule.Validate(view); err != nil {
			return err
		}
	}

	return nil
}

type FuncRule func(tx TxView) error

func (f FuncRule) Validate(tx TxView) error {
	return f(tx)
}

type RequireUniqueSubAccountsRule struct{}

type entryIdentityKey struct {
	subAccountID string
	identityKey  string
}

func (r RequireUniqueSubAccountsRule) Validate(tx TxView) error {
	seen := make(map[entryIdentityKey]struct{}, len(tx.Entries()))
	for _, entry := range tx.Entries() {
		subAccountID := entry.Entry().PostingAddress().SubAccountID()
		identityKey := entry.Entry().IdentityKey()
		key := entryIdentityKey{
			subAccountID: subAccountID,
			identityKey:  identityKey,
		}
		if _, ok := seen[key]; ok {
			return ledger.ErrRoutingRuleViolated.WithAttrs(models.Attributes{
				"reason":         "duplicate_entry_identity",
				"sub_account_id": subAccountID,
				"identity_key":   identityKey,
			})
		}

		seen[key] = struct{}{}
	}

	return nil
}

type AllowedAccountSetsRule struct {
	Sets [][]ledger.AccountType
}

func (r AllowedAccountSetsRule) Validate(tx TxView) error {
	present := tx.AccountTypes()
	if len(present) == 0 {
		return nil
	}

	for _, allowed := range r.Sets {
		if sameAccountTypeSet(present, allowed) {
			return nil
		}
	}

	return ledger.ErrRoutingRuleViolated.WithAttrs(models.Attributes{
		"reason":        "account_type_combination_not_allowed",
		"account_types": present,
	})
}

type RequireFlowDirectionRule struct {
	From ledger.AccountType
	To   ledger.AccountType
}

func (r RequireFlowDirectionRule) Validate(tx TxView) error {
	if !tx.HasAccountTypes(r.From, r.To) {
		return nil
	}

	fromEntries := tx.EntriesOf(r.From)
	toEntries := tx.EntriesOf(r.To)
	if hasMixedSigns(fromEntries) || hasMixedSigns(toEntries) {
		return nil
	}

	for _, entry := range fromEntries {
		if !entry.Amount().IsNegative() {
			if allEntriesPositive(fromEntries) && allEntriesNegative(toEntries) {
				return nil
			}
			return ledger.ErrRoutingRuleViolated.WithAttrs(models.Attributes{
				"reason":       "invalid_flow_direction",
				"account_type": r.From,
				"expected":     "negative_or_positive_if_reversed",
				"target_type":  r.To,
			})
		}
	}

	for _, entry := range toEntries {
		if !entry.Amount().IsPositive() {
			if allEntriesPositive(fromEntries) && allEntriesNegative(toEntries) {
				return nil
			}
			return ledger.ErrRoutingRuleViolated.WithAttrs(models.Attributes{
				"reason":       "invalid_flow_direction",
				"account_type": r.To,
				"expected":     "positive_or_negative_if_reversed",
				"source_type":  r.From,
			})
		}
	}

	return nil
}

func hasMixedSigns(entries []EntryView) bool {
	hasPositive := false
	hasNegative := false

	for _, entry := range entries {
		hasPositive = hasPositive || entry.Amount().IsPositive()
		hasNegative = hasNegative || entry.Amount().IsNegative()
		if hasPositive && hasNegative {
			return true
		}
	}

	return false
}

func allEntriesPositive(entries []EntryView) bool {
	for _, entry := range entries {
		if !entry.Amount().IsPositive() {
			return false
		}
	}

	return len(entries) > 0
}

func allEntriesNegative(entries []EntryView) bool {
	for _, entry := range entries {
		if !entry.Amount().IsNegative() {
			return false
		}
	}

	return len(entries) > 0
}

type RouteField string

const (
	RouteFieldCurrency                       RouteField = "currency"
	RouteFieldTaxCode                        RouteField = "tax_code"
	RouteFieldTaxBehavior                    RouteField = "tax_behavior"
	RouteFieldFeatures                       RouteField = "features"
	RouteFieldCostBasis                      RouteField = "cost_basis"
	RouteFieldCreditPriority                 RouteField = "credit_priority"
	RouteFieldTransactionAuthorizationStatus RouteField = "transaction_authorization_status"
)

type RequireSameRouteRule struct {
	Left   ledger.AccountType
	Right  ledger.AccountType
	Fields []RouteField
}

func (r RequireSameRouteRule) Validate(tx TxView) error {
	if !tx.HasAccountTypes(r.Left, r.Right) {
		return nil
	}

	return requireMatchingRouteFields(tx.EntriesOf(r.Left), tx.EntriesOf(r.Right), r.Left, r.Right, r.Fields)
}

type RequireTaxDimensionScopeRule struct{}

func (r RequireTaxDimensionScopeRule) Validate(tx TxView) error {
	for _, entry := range tx.Entries() {
		switch entry.AccountType() {
		case ledger.AccountTypeCustomerAccrued, ledger.AccountTypeEarnings:
			if entry.Route().TaxCode == nil && entry.Route().TaxBehavior != nil {
				return ledger.ErrRoutingRuleViolated.WithAttrs(models.Attributes{
					"reason":       "tax_behavior_requires_tax_code_on_accrued_or_earnings",
					"account_type": entry.AccountType(),
				})
			}
		default:
			if entry.Route().TaxCode != nil || entry.Route().TaxBehavior != nil {
				return ledger.ErrRoutingRuleViolated.WithAttrs(models.Attributes{
					"reason":       "tax_dimensions_only_allowed_on_accrued_or_earnings",
					"account_type": entry.AccountType(),
				})
			}
		}
	}

	return nil
}

type RequireFeatureDimensionScopeRule struct{}

func (r RequireFeatureDimensionScopeRule) Validate(tx TxView) error {
	for _, entry := range tx.Entries() {
		if len(entry.Route().Features) == 0 {
			continue
		}

		switch entry.AccountType() {
		case ledger.AccountTypeCustomerFBO, ledger.AccountTypeCustomerReceivable:
			continue
		default:
			return ledger.ErrRoutingRuleViolated.WithAttrs(models.Attributes{
				"reason":       "features_only_allowed_on_fbo_or_receivable",
				"account_type": entry.AccountType(),
			})
		}
	}

	return nil
}

type RequireAccountAuthorizationStatusRule struct {
	WhenHasAccountTypes []ledger.AccountType
	AccountType         ledger.AccountType
	Expected            ledger.TransactionAuthorizationStatus
}

func (r RequireAccountAuthorizationStatusRule) Validate(tx TxView) error {
	if !tx.HasAccountTypes(r.WhenHasAccountTypes...) {
		return nil
	}

	return requireAuthorizationStatus(tx.EntriesOf(r.AccountType), r.AccountType, r.Expected)
}

func sameRouteField(left ledger.Route, right ledger.Route, field RouteField) (bool, error) {
	switch field {
	case RouteFieldCurrency:
		return left.Currency == right.Currency, nil
	case RouteFieldTaxCode:
		return optionalStringEqual(left.TaxCode, right.TaxCode), nil
	case RouteFieldTaxBehavior:
		return optionalTaxBehaviorEqual(left.TaxBehavior, right.TaxBehavior), nil
	case RouteFieldFeatures:
		return stringSliceEqual(left.Features, right.Features), nil
	case RouteFieldCostBasis:
		return optionalDecimalEqual(left.CostBasis, right.CostBasis), nil
	case RouteFieldCreditPriority:
		return optionalIntEqual(left.CreditPriority, right.CreditPriority), nil
	case RouteFieldTransactionAuthorizationStatus:
		return optionalTransactionAuthorizationStatusEqual(left.TransactionAuthorizationStatus, right.TransactionAuthorizationStatus), nil
	default:
		return false, fmt.Errorf("unknown route field: %s", field)
	}
}

type RequireReceivableAuthorizationStageRule struct{}

func (r RequireReceivableAuthorizationStageRule) Validate(tx TxView) error {
	accountTypes := tx.AccountTypes()
	if len(accountTypes) != 1 || accountTypes[0] != ledger.AccountTypeCustomerReceivable {
		return nil
	}

	negativeEntries, positiveEntries := entriesBySign(tx.EntriesOf(ledger.AccountTypeCustomerReceivable))

	if len(negativeEntries) == 0 || len(positiveEntries) == 0 {
		return ledger.ErrRoutingRuleViolated.WithAttrs(models.Attributes{
			"reason":       "receivable_authorization_transition_requires_both_sides",
			"account_type": ledger.AccountTypeCustomerReceivable,
		})
	}

	if allEntriesHaveAuthorizationStatus(negativeEntries, ledger.TransactionAuthorizationStatusAuthorized) &&
		allEntriesHaveAuthorizationStatus(positiveEntries, ledger.TransactionAuthorizationStatusOpen) {
		return requireMatchingRouteFields(
			negativeEntries,
			positiveEntries,
			ledger.AccountTypeCustomerReceivable,
			ledger.AccountTypeCustomerReceivable,
			[]RouteField{
				RouteFieldCurrency,
				RouteFieldTaxCode,
				RouteFieldFeatures,
				RouteFieldCostBasis,
				RouteFieldCreditPriority,
			},
		)
	}

	if allEntriesHaveAuthorizationStatus(negativeEntries, ledger.TransactionAuthorizationStatusOpen) &&
		allEntriesHaveAuthorizationStatus(positiveEntries, ledger.TransactionAuthorizationStatusOpen) {
		if err := requireKnownToUnknownCostBasisTranslationEitherDirection(
			negativeEntries,
			positiveEntries,
			ledger.AccountTypeCustomerReceivable,
			[]RouteField{
				RouteFieldCurrency,
				RouteFieldTaxCode,
				RouteFieldCreditPriority,
				RouteFieldTransactionAuthorizationStatus,
			},
		); err != nil {
			return err
		}

		return nil
	}

	return ledger.ErrRoutingRuleViolated.WithAttrs(models.Attributes{
		"reason":       "unsupported_receivable_same_account_transition",
		"account_type": ledger.AccountTypeCustomerReceivable,
	})
}

type RequireAccruedCostBasisTranslationRule struct{}

func (r RequireAccruedCostBasisTranslationRule) Validate(tx TxView) error {
	accountTypes := tx.AccountTypes()
	if len(accountTypes) != 1 || accountTypes[0] != ledger.AccountTypeCustomerAccrued {
		return nil
	}

	negativeEntries, positiveEntries := entriesBySign(tx.EntriesOf(ledger.AccountTypeCustomerAccrued))
	if len(negativeEntries) == 0 || len(positiveEntries) == 0 {
		return ledger.ErrRoutingRuleViolated.WithAttrs(models.Attributes{
			"reason":       "accrued_cost_basis_translation_requires_both_sides",
			"account_type": ledger.AccountTypeCustomerAccrued,
		})
	}

	return requireKnownToUnknownCostBasisTranslationEitherDirection(
		negativeEntries,
		positiveEntries,
		ledger.AccountTypeCustomerAccrued,
		[]RouteField{
			RouteFieldCurrency,
			RouteFieldTaxCode,
			RouteFieldTaxBehavior,
		},
	)
}

type RequireFBOCostBasisTranslationRule struct{}

func (r RequireFBOCostBasisTranslationRule) Validate(tx TxView) error {
	accountTypes := tx.AccountTypes()
	if len(accountTypes) != 1 || accountTypes[0] != ledger.AccountTypeCustomerFBO {
		return nil
	}

	negativeEntries, positiveEntries := entriesBySign(tx.EntriesOf(ledger.AccountTypeCustomerFBO))
	if len(negativeEntries) == 0 || len(positiveEntries) == 0 {
		return ledger.ErrRoutingRuleViolated.WithAttrs(models.Attributes{
			"reason":       "fbo_cost_basis_translation_requires_both_sides",
			"account_type": ledger.AccountTypeCustomerFBO,
		})
	}

	return requireKnownToUnknownCostBasisTranslationEitherDirection(
		positiveEntries,
		negativeEntries,
		ledger.AccountTypeCustomerFBO,
		[]RouteField{
			RouteFieldCurrency,
			RouteFieldFeatures,
			RouteFieldCreditPriority,
		},
	)
}

func entriesBySign(entries []EntryView) ([]EntryView, []EntryView) {
	negativeEntries := make([]EntryView, 0, len(entries))
	positiveEntries := make([]EntryView, 0, len(entries))

	for _, entry := range entries {
		switch {
		case entry.Amount().IsNegative():
			negativeEntries = append(negativeEntries, entry)
		case entry.Amount().IsPositive():
			positiveEntries = append(positiveEntries, entry)
		}
	}

	return negativeEntries, positiveEntries
}

func requireAuthorizationStatus(entries []EntryView, accountType ledger.AccountType, expected ledger.TransactionAuthorizationStatus) error {
	for _, entry := range entries {
		if entry.Route().TransactionAuthorizationStatus == nil || *entry.Route().TransactionAuthorizationStatus != expected {
			return ledger.ErrRoutingRuleViolated.WithAttrs(models.Attributes{
				"reason":                           "transaction_authorization_status_mismatch",
				"account_type":                     accountType,
				"expected_transaction_auth_status": expected,
			})
		}
	}

	return nil
}

func allEntriesHaveAuthorizationStatus(entries []EntryView, expected ledger.TransactionAuthorizationStatus) bool {
	for _, entry := range entries {
		if entry.Route().TransactionAuthorizationStatus == nil || *entry.Route().TransactionAuthorizationStatus != expected {
			return false
		}
	}

	return true
}

func requireKnownToUnknownCostBasisTranslation(knownEntries, unknownEntries []EntryView, accountType ledger.AccountType, fields []RouteField) error {
	for _, entry := range knownEntries {
		if entry.Route().CostBasis == nil {
			return ledger.ErrRoutingRuleViolated.WithAttrs(models.Attributes{
				"reason":       "known_cost_basis_required",
				"account_type": accountType,
			})
		}
	}

	for _, entry := range unknownEntries {
		if entry.Route().CostBasis != nil {
			return ledger.ErrRoutingRuleViolated.WithAttrs(models.Attributes{
				"reason":       "unknown_cost_basis_required",
				"account_type": accountType,
			})
		}
	}

	return requireMatchingRouteFields(knownEntries, unknownEntries, accountType, accountType, fields)
}

func requireKnownToUnknownCostBasisTranslationEitherDirection(leftEntries, rightEntries []EntryView, accountType ledger.AccountType, fields []RouteField) error {
	if err := requireKnownToUnknownCostBasisTranslation(leftEntries, rightEntries, accountType, fields); err == nil {
		return nil
	}

	return requireKnownToUnknownCostBasisTranslation(rightEntries, leftEntries, accountType, fields)
}

func requireMatchingRouteFields(leftEntries, rightEntries []EntryView, leftType, rightType ledger.AccountType, fields []RouteField) error {
	for _, left := range leftEntries {
		matched, err := hasMatchingRouteFields(left, rightEntries, fields)
		if err != nil {
			return err
		}
		if !matched {
			return ledger.ErrRoutingRuleViolated.WithAttrs(models.Attributes{
				"reason":     "route_field_mismatch",
				"left_type":  leftType,
				"right_type": rightType,
				"fields":     fields,
			})
		}
	}

	for _, right := range rightEntries {
		matched, err := hasMatchingRouteFields(right, leftEntries, fields)
		if err != nil {
			return err
		}
		if !matched {
			return ledger.ErrRoutingRuleViolated.WithAttrs(models.Attributes{
				"reason":     "route_field_mismatch",
				"left_type":  leftType,
				"right_type": rightType,
				"fields":     fields,
			})
		}
	}

	return nil
}

func hasMatchingRouteFields(entry EntryView, candidates []EntryView, fields []RouteField) (bool, error) {
	for _, candidate := range candidates {
		matches := true
		for _, field := range fields {
			same, err := sameRouteField(entry.Route(), candidate.Route(), field)
			if err != nil {
				return false, err
			}
			if !same {
				matches = false
				break
			}
		}
		if matches {
			return true, nil
		}
	}

	return false, nil
}

func sameAccountTypeSet(left []ledger.AccountType, right []ledger.AccountType) bool {
	if len(left) != len(right) {
		return false
	}

	index := make(map[ledger.AccountType]struct{}, len(left))
	for _, item := range left {
		index[item] = struct{}{}
	}

	for _, item := range right {
		if _, ok := index[item]; !ok {
			return false
		}
	}

	return true
}