package adminstate

import (
	"context"
	"encoding/hex"
	"encoding/json"
	"errors"
	"net/netip"
	"regexp"
	"strings"
	"time"
	"unicode"
	"unicode/utf8"
)

const (
	MaxIdentifierBytes = 128
	MaxActorIDBytes    = 256
	MaxReasonBytes     = 512
	MaxSourceBytes     = 512
	MaxDefinitions     = 10_000
	MaxPageSize        = 1_000
	SHA256HexBytes     = 64
)

var (
	ErrInvalidCommand = errors.New("invalid admin state command")
	ErrNotFound       = errors.New("admin state resource not found")
	ErrConflict       = errors.New("admin state conflict")
	ErrUnavailable    = errors.New("admin state unavailable")
)

var identifierPattern = regexp.MustCompile(`^[A-Za-z0-9][A-Za-z0-9._-]{0,127}$`)

type Mutator interface {
	SetUpstreamEnabled(context.Context, SetUpstreamCommand) (MutationResult, error)
	SwitchRouting(context.Context, SwitchRoutingCommand) (MutationResult, error)
	CommitConfig(context.Context, CommitConfigCommand) (MutationResult, error)
}

type SnapshotReader interface {
	Snapshot(context.Context) (Snapshot, error)
}

type AuditReader interface {
	ReadAudit(context.Context, AuditQuery) ([]AuditRecord, error)
}

type Outbox interface {
	Claim(context.Context, ClaimCommand) ([]Event, error)
	Acknowledge(context.Context, AcknowledgeCommand) error
}

type Store interface {
	Mutator
	SnapshotReader
	AuditReader
	Outbox
}

type Actor struct {
	ID       string
	SourceIP string
}

type SetUpstreamCommand struct {
	RequestID  string
	Actor      Actor
	OccurredAt time.Time
	Name       string
	Enabled    bool
}

type SwitchRoutingCommand struct {
	RequestID       string
	Actor           Actor
	OccurredAt      time.Time
	Name            string
	ExpectedCurrent string
	Target          string
	Reason          string
}

type CommitConfigCommand struct {
	RequestID     string
	Actor         Actor
	OccurredAt    time.Time
	ConfigVersion string
	Checksum      string
	Source        string
	Upstreams     []UpstreamDefinition
	Routings      []RoutingDefinition
}

type UpstreamDefinition struct {
	Name    string
	Enabled bool
}

type RoutingDefinition struct {
	Name            string
	Enabled         bool
	Upstreams       []string
	CurrentUpstream string
}

type MutationResult struct {
	RequestID string
	Changed   bool
	Revision  uint64
	Message   string
}

type ConfigRevision struct {
	Revision      uint64
	ConfigVersion string
	Checksum      string
	Source        string
	CreatedAt     time.Time
}

type UpstreamState struct {
	Name      string
	Enabled   bool
	Revision  uint64
	UpdatedAt time.Time
}

type RoutingState struct {
	Name            string
	Enabled         bool
	Upstreams       []string
	CurrentUpstream string
	Revision        uint64
	UpdatedAt       time.Time
}

type Snapshot struct {
	Revision  uint64
	Config    *ConfigRevision
	Upstreams []UpstreamState
	Routings  []RoutingState
}

type Action string

const (
	ActionSetUpstream  Action = "set_upstream_enabled"
	ActionSwitchRoute  Action = "switch_routing"
	ActionCommitConfig Action = "commit_config"
)

type AuditRecord struct {
	ID           uint64
	RequestID    string
	Actor        Actor
	Action       Action
	ResourceType string
	ResourceName string
	Changed      bool
	Revision     uint64
	Reason       string
	OccurredAt   time.Time
}

type AuditQuery struct {
	AfterID uint64
	Limit   int
}

type Event struct {
	ID            uint64
	Revision      uint64
	Type          string
	AggregateType string
	AggregateID   string
	Payload       json.RawMessage
	OccurredAt    time.Time
	ClaimedBy     string
	ClaimUntil    *time.Time
	PublishedAt   *time.Time
}

type ClaimCommand struct {
	ConsumerID string
	Now        time.Time
	Limit      int
	Lease      time.Duration
}

type AcknowledgeCommand struct {
	ConsumerID string
	Now        time.Time
	EventIDs   []uint64
}

func validateSetUpstreamCommand(command SetUpstreamCommand) error {
	if err := validateMutationBase(command.RequestID, command.Actor, command.OccurredAt); err != nil ||
		!validIdentifier(command.Name) {
		return ErrInvalidCommand
	}
	return nil
}

func validateSwitchRoutingCommand(command SwitchRoutingCommand) error {
	if err := validateMutationBase(command.RequestID, command.Actor, command.OccurredAt); err != nil ||
		!validIdentifier(command.Name) || !validIdentifier(command.ExpectedCurrent) ||
		!validIdentifier(command.Target) || !validOptionalText(command.Reason, MaxReasonBytes) {
		return ErrInvalidCommand
	}
	return nil
}

func validateCommitConfigCommand(command CommitConfigCommand) error {
	if err := validateMutationBase(command.RequestID, command.Actor, command.OccurredAt); err != nil ||
		!validRequiredText(command.ConfigVersion, MaxIdentifierBytes) ||
		!validSHA256(command.Checksum) || !validRequiredText(command.Source, MaxSourceBytes) ||
		len(command.Upstreams) > MaxDefinitions || len(command.Routings) > MaxDefinitions {
		return ErrInvalidCommand
	}

	upstreamNames := make(map[string]struct{}, len(command.Upstreams))
	for _, upstream := range command.Upstreams {
		if !validIdentifier(upstream.Name) {
			return ErrInvalidCommand
		}
		if _, duplicate := upstreamNames[upstream.Name]; duplicate {
			return ErrInvalidCommand
		}
		upstreamNames[upstream.Name] = struct{}{}
	}

	routingNames := make(map[string]struct{}, len(command.Routings))
	for _, routing := range command.Routings {
		if !validIdentifier(routing.Name) || len(routing.Upstreams) == 0 ||
			len(routing.Upstreams) > MaxDefinitions || !validIdentifier(routing.CurrentUpstream) {
			return ErrInvalidCommand
		}
		if _, duplicate := routingNames[routing.Name]; duplicate {
			return ErrInvalidCommand
		}
		routingNames[routing.Name] = struct{}{}
		candidates := make(map[string]struct{}, len(routing.Upstreams))
		for _, upstream := range routing.Upstreams {
			if !validIdentifier(upstream) {
				return ErrInvalidCommand
			}
			if _, exists := upstreamNames[upstream]; !exists {
				return ErrInvalidCommand
			}
			if _, duplicate := candidates[upstream]; duplicate {
				return ErrInvalidCommand
			}
			candidates[upstream] = struct{}{}
		}
		if _, exists := candidates[routing.CurrentUpstream]; !exists {
			return ErrInvalidCommand
		}
	}
	return nil
}

func validateClaimCommand(command ClaimCommand) error {
	if !validIdentifier(command.ConsumerID) || command.Now.IsZero() || command.Limit <= 0 ||
		command.Limit > MaxPageSize || command.Lease <= 0 {
		return ErrInvalidCommand
	}
	return nil
}

func validateAcknowledgeCommand(command AcknowledgeCommand) error {
	if !validIdentifier(command.ConsumerID) || command.Now.IsZero() || len(command.EventIDs) == 0 ||
		len(command.EventIDs) > MaxPageSize {
		return ErrInvalidCommand
	}
	seen := make(map[uint64]struct{}, len(command.EventIDs))
	for _, eventID := range command.EventIDs {
		if eventID == 0 {
			return ErrInvalidCommand
		}
		if _, duplicate := seen[eventID]; duplicate {
			return ErrInvalidCommand
		}
		seen[eventID] = struct{}{}
	}
	return nil
}

func validateAuditQuery(query AuditQuery) error {
	if query.Limit <= 0 || query.Limit > MaxPageSize {
		return ErrInvalidCommand
	}
	return nil
}

func validateMutationBase(requestID string, actor Actor, occurredAt time.Time) error {
	if !validRequiredText(requestID, MaxIdentifierBytes) || !validRequiredText(actor.ID, MaxActorIDBytes) ||
		occurredAt.IsZero() {
		return ErrInvalidCommand
	}
	if actor.SourceIP != "" {
		address, err := netip.ParseAddr(actor.SourceIP)
		if err != nil || !address.IsValid() {
			return ErrInvalidCommand
		}
	}
	return nil
}

func validIdentifier(value string) bool {
	return len(value) <= MaxIdentifierBytes && identifierPattern.MatchString(value)
}

func validSHA256(value string) bool {
	if len(value) != SHA256HexBytes {
		return false
	}
	decoded, err := hex.DecodeString(value)
	return err == nil && len(decoded) == SHA256HexBytes/2
}

func validRequiredText(value string, maximum int) bool {
	return value != "" && validOptionalText(value, maximum)
}

func validOptionalText(value string, maximum int) bool {
	if len(value) > maximum || !utf8.ValidString(value) || strings.TrimSpace(value) != value {
		return false
	}
	for _, character := range value {
		if unicode.IsControl(character) {
			return false
		}
	}
	return true
}

func cloneCommitConfigCommand(command CommitConfigCommand) CommitConfigCommand {
	cloned := command
	cloned.Upstreams = append([]UpstreamDefinition(nil), command.Upstreams...)
	cloned.Routings = make([]RoutingDefinition, len(command.Routings))
	for index, routing := range command.Routings {
		cloned.Routings[index] = routing
		cloned.Routings[index].Upstreams = append([]string(nil), routing.Upstreams...)
	}
	return cloned
}

func cloneSnapshot(snapshot Snapshot) Snapshot {
	cloned := snapshot
	if snapshot.Config != nil {
		config := *snapshot.Config
		cloned.Config = &config
	}
	cloned.Upstreams = append([]UpstreamState(nil), snapshot.Upstreams...)
	cloned.Routings = make([]RoutingState, len(snapshot.Routings))
	for index, routing := range snapshot.Routings {
		cloned.Routings[index] = routing
		cloned.Routings[index].Upstreams = append([]string(nil), routing.Upstreams...)
	}
	return cloned
}

func cloneEvent(event Event) Event {
	cloned := event
	cloned.Payload = append(json.RawMessage(nil), event.Payload...)
	if event.ClaimUntil != nil {
		value := *event.ClaimUntil
		cloned.ClaimUntil = &value
	}
	if event.PublishedAt != nil {
		value := *event.PublishedAt
		cloned.PublishedAt = &value
	}
	return cloned
}

func cloneEvents(events []Event) []Event {
	cloned := make([]Event, len(events))
	for index, event := range events {
		cloned[index] = cloneEvent(event)
	}
	return cloned
}

func cloneAuditRecords(records []AuditRecord) []AuditRecord {
	return append([]AuditRecord(nil), records...)
}