package service

import (
	"context"
	"crypto/sha256"
	"encoding/hex"
	"errors"
	"sort"
	"strings"
	"time"

	"github.com/itworx/pulse/internal/probe"
)

const ContractVersion = "v1"

const (
	CapabilityAvailable        = "available"
	CapabilityUnavailable      = "unavailable"
	CapabilityUnsupported      = "unsupported"
	ConfigurationConfigured    = "configured"
	ConfigurationNotConfigured = "not_configured"
	ConfigurationUnknown       = "unknown"
)

type StatusPolicy struct {
	FreshnessMaxAge time.Duration
	MaxServices     int
	MaxHistory      int
}

func (p StatusPolicy) withDefaults() StatusPolicy {
	if p.FreshnessMaxAge == 0 {
		p.FreshnessMaxAge = 2 * time.Minute
	}
	if p.MaxServices == 0 {
		p.MaxServices = 150
	}
	if p.MaxHistory == 0 {
		p.MaxHistory = 100
	}
	return p
}

func (p StatusPolicy) Validate() error {
	p = p.withDefaults()
	if p.FreshnessMaxAge <= 0 || p.FreshnessMaxAge > 24*time.Hour || p.MaxServices < 1 || p.MaxServices > 1000 || p.MaxHistory < 1 || p.MaxHistory > 500 {
		return errors.New("service status policy is outside safe bounds")
	}
	return nil
}

type ProbeHistory struct {
	ProbeID string
	Results []probe.Result
}

type ProbeConfig struct {
	ID              string `json:"id"`
	Name            string `json:"name"`
	Type            string `json:"type"`
	IntervalSeconds int    `json:"intervalSeconds"`
	TimeoutSeconds  int    `json:"timeoutSeconds"`
	Enabled         bool   `json:"enabled"`
	FollowRedirects bool   `json:"followRedirects"`
	VerifyTLS       bool   `json:"verifyTls"`
	Revision        int64  `json:"revision"`
}

type ServiceInput struct {
	Service           Service
	Probes            []ProbeHistory
	ProbeConfigs      []ProbeConfig
	LatestCertificate *probe.Certificate
}

type ServiceStatus struct {
	ID                    string             `json:"id"`
	EntityID              string             `json:"entityId,omitempty"`
	SourceID              string             `json:"sourceId,omitempty"`
	Name                  string             `json:"name"`
	Description           string             `json:"description"`
	State                 string             `json:"state"`
	Reason                string             `json:"reason,omitempty"`
	LastResultAt          *time.Time         `json:"lastResultAt,omitempty"`
	LastSuccessAt         *time.Time         `json:"lastSuccessAt,omitempty"`
	LastFailureAt         *time.Time         `json:"lastFailureAt,omitempty"`
	ResponseTimeMS        *int               `json:"responseTimeMs,omitempty"`
	AvailabilityPercent   *float64           `json:"availabilityPercent,omitempty"`
	SampleCount           int                `json:"sampleCount"`
	SuccessfulSampleCount int                `json:"successfulSampleCount"`
	History               []probe.Result     `json:"history,omitempty"`
	Probes                []ProbeConfig      `json:"probes,omitempty"`
	Certificate           *probe.Certificate `json:"certificate,omitempty"`
	Revision              int64              `json:"revision"`
	ArchivedAt            *time.Time         `json:"archivedAt,omitempty"`
	CreatedAt             time.Time          `json:"createdAt"`
	UpdatedAt             time.Time          `json:"updatedAt"`
}

type Snapshot struct {
	ContractVersion    string          `json:"contractVersion"`
	ObservedAt         time.Time       `json:"observedAt"`
	CapabilityState    string          `json:"capabilityState"`
	ConfigurationState string          `json:"configurationState"`
	Reason             string          `json:"reason,omitempty"`
	Services           []ServiceStatus `json:"services"`
	Total              int             `json:"total"`
	Events             []Event         `json:"events,omitempty"`
}

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

type UnknownProvider struct {
	Reason string
	Now    func() time.Time
}

func (p UnknownProvider) Snapshot(ctx context.Context) (Snapshot, error) {
	if ctx == nil {
		return Snapshot{}, errors.New("service status context is nil")
	}
	if err := ctx.Err(); err != nil {
		return Snapshot{}, err
	}
	now := time.Now().UTC()
	if p.Now != nil {
		now = p.Now().UTC()
	}
	reason := p.Reason
	if strings.TrimSpace(reason) == "" {
		reason = "source_unavailable"
	}
	return UnknownSnapshot(now, reason), nil
}

func UnknownSnapshot(now time.Time, reason string) Snapshot {
	if now.IsZero() {
		now = time.Now().UTC()
	}
	capability := CapabilityUnavailable
	if reason == "unsupported" {
		capability = CapabilityUnsupported
	}
	return Snapshot{ContractVersion: ContractVersion, ObservedAt: now.UTC(), CapabilityState: capability, ConfigurationState: ConfigurationUnknown, Reason: boundText(reason, 128), Services: []ServiceStatus{}, Total: 0, Events: []Event{}}
}

func BuildSnapshot(now time.Time, inputs []ServiceInput, policy StatusPolicy) (Snapshot, error) {
	policy = policy.withDefaults()
	if err := policy.Validate(); err != nil {
		return Snapshot{}, err
	}
	if now.IsZero() {
		now = time.Now().UTC()
	}
	now = now.UTC()
	if len(inputs) > policy.MaxServices {
		return Snapshot{}, errors.New("service count exceeds bounds")
	}
	statuses := make([]ServiceStatus, 0, len(inputs))
	seen := make(map[string]struct{}, len(inputs))
	for _, input := range inputs {
		if err := input.Service.Validate(); err != nil {
			return Snapshot{}, err
		}
		if _, exists := seen[input.Service.ID]; exists {
			return Snapshot{}, errors.New("duplicate service identity")
		}
		seen[input.Service.ID] = struct{}{}
		status := projectStatus(now, input, policy)
		statuses = append(statuses, status)
	}
	sort.Slice(statuses, func(i, j int) bool { return statuses[i].ID < statuses[j].ID })
	configuration := ConfigurationConfigured
	reason := ""
	if len(statuses) == 0 {
		configuration = ConfigurationNotConfigured
		reason = "no_services_configured"
	}
	return Snapshot{ContractVersion: ContractVersion, ObservedAt: now, CapabilityState: CapabilityAvailable, ConfigurationState: configuration, Reason: reason, Services: statuses, Total: len(statuses), Events: []Event{}}, nil
}

func projectStatus(now time.Time, input ServiceInput, policy StatusPolicy) ServiceStatus {
	status := ServiceStatus{ID: input.Service.ID, EntityID: input.Service.EntityID, SourceID: input.Service.SourceID, Name: input.Service.Name, Description: input.Service.Description, State: StateUnknown, Reason: "no_probe_result", Revision: input.Service.Revision, ArchivedAt: input.Service.ArchivedAt, CreatedAt: input.Service.CreatedAt.UTC(), UpdatedAt: input.Service.UpdatedAt.UTC(), History: make([]probe.Result, 0), Probes: boundProbeConfigs(input.ProbeConfigs), Certificate: boundCertificate(input.LatestCertificate)}
	if len(status.Probes) == 0 {
		status.Reason = "no_probe_configured"
	} else {
		enabled := false
		for _, config := range status.Probes {
			enabled = enabled || config.Enabled
		}
		if !enabled {
			status.Reason = "probes_disabled"
		}
	}
	all := make([]probe.Result, 0)
	for _, history := range input.Probes {
		for _, result := range history.Results {
			if result.ProbeID == "" {
				result.ProbeID = history.ProbeID
			}
			if result.ProbeID == "" || result.ObservedAt.IsZero() {
				continue
			}
			all = append(all, boundResult(result))
		}
	}
	sort.SliceStable(all, func(i, j int) bool {
		if !all[i].ObservedAt.Equal(all[j].ObservedAt) {
			return all[i].ObservedAt.After(all[j].ObservedAt)
		}
		if all[i].ProbeID != all[j].ProbeID {
			return all[i].ProbeID < all[j].ProbeID
		}
		return all[i].ID < all[j].ID
	})
	if len(all) > policy.MaxHistory {
		all = all[:policy.MaxHistory]
	}
	status.History = append(status.History, all...)
	if len(all) == 0 {
		return status
	}
	latest := all[0]
	lastResultAt := latest.ObservedAt.UTC()
	status.LastResultAt = &lastResultAt
	status.State = normalizedState(latest.State)
	status.Reason = latest.ErrorClass
	if status.State == StateUp {
		status.Reason = ""
	} else if status.State == StateDegraded && status.Reason == "" {
		status.Reason = "probe_degraded"
	}
	if now.Sub(latest.ObservedAt) > policy.FreshnessMaxAge || latest.ObservedAt.After(now.Add(time.Minute)) {
		status.State = StateUnknown
		status.Reason = "stale_probe"
	}
	if latest.ResponseTimeMS != nil {
		value := *latest.ResponseTimeMS
		status.ResponseTimeMS = &value
	}
	known := 0
	successful := 0
	for _, result := range all {
		state := normalizedState(result.State)
		switch state {
		case StateUp, StateDegraded:
			known++
			successful++
		case StateDown, StateUnknown:
			known++
		}
		if state == StateUp {
			observed := result.ObservedAt.UTC()
			if status.LastSuccessAt == nil || observed.After(*status.LastSuccessAt) {
				status.LastSuccessAt = &observed
			}
		}
		if state == StateDown || state == StateUnknown {
			observed := result.ObservedAt.UTC()
			if status.LastFailureAt == nil || observed.After(*status.LastFailureAt) {
				status.LastFailureAt = &observed
			}
		}
	}
	status.SampleCount = known
	status.SuccessfulSampleCount = successful
	if known > 0 {
		value := float64(successful) * 100 / float64(known)
		status.AvailabilityPercent = &value
	}
	return status
}

func boundProbeConfigs(configs []ProbeConfig) []ProbeConfig {
	bounded := append([]ProbeConfig(nil), configs...)
	sort.SliceStable(bounded, func(i, j int) bool {
		if bounded[i].ID != bounded[j].ID {
			return bounded[i].ID < bounded[j].ID
		}
		return bounded[i].Name < bounded[j].Name
	})
	if len(bounded) > 100 {
		bounded = bounded[:100]
	}
	for index := range bounded {
		bounded[index].ID = boundText(bounded[index].ID, 64)
		bounded[index].Name = boundText(bounded[index].Name, 160)
		bounded[index].Type = boundText(bounded[index].Type, 16)
		if bounded[index].IntervalSeconds < 0 {
			bounded[index].IntervalSeconds = 0
		}
		if bounded[index].TimeoutSeconds < 0 {
			bounded[index].TimeoutSeconds = 0
		}
	}
	return bounded
}
func boundResult(result probe.Result) probe.Result {
	result.ObservedAt = result.ObservedAt.UTC()
	result.CompletedAt = result.CompletedAt.UTC()
	result.ErrorClass = boundText(result.ErrorClass, 64)
	result.ErrorMessage = boundText(result.ErrorMessage, 256)
	if result.ResponseTimeMS != nil && *result.ResponseTimeMS < 0 {
		result.ResponseTimeMS = nil
	}
	if result.Attributes != nil {
		keys := make([]string, 0, len(result.Attributes))
		for key := range result.Attributes {
			keys = append(keys, key)
		}
		sort.Strings(keys)
		if len(keys) > 16 {
			keys = keys[:16]
		}
		bounded := make(map[string]any, len(keys))
		for _, key := range keys {
			bounded[boundText(key, 64)] = boundAttribute(result.Attributes[key])
		}
		result.Attributes = bounded
	}
	if result.Certificate != nil {
		result.Certificate = boundCertificate(result.Certificate)
	}
	return result
}

func boundCertificate(value *probe.Certificate) *probe.Certificate {
	if value == nil {
		return nil
	}
	certificate := *value
	certificate.ID = boundText(certificate.ID, 128)
	certificate.ServiceID = boundText(certificate.ServiceID, 128)
	certificate.EndpointID = boundText(certificate.EndpointID, 128)
	certificate.ObservedAt = certificate.ObservedAt.UTC()
	if certificate.ExpiresAt != nil {
		expiresAt := certificate.ExpiresAt.UTC()
		certificate.ExpiresAt = &expiresAt
	}
	certificate.Issuer = boundText(certificate.Issuer, 256)
	certificate.Subject = boundText(certificate.Subject, 256)
	certificate.VerificationState = boundText(certificate.VerificationState, 32)
	return &certificate
}

func boundAttribute(value any) any {
	switch typed := value.(type) {
	case string:
		return boundText(typed, 256)
	case bool, int, int32, int64, float32, float64, nil:
		return typed
	default:
		return "[redacted]"
	}
}
func normalizedState(state string) string {
	switch state {
	case StateUp, StateDegraded, StateDown, StateUnknown:
		return state
	default:
		return StateUnknown
	}
}

func boundText(value string, max int) string {
	value = strings.TrimSpace(value)
	if len(value) > max {
		return value[:max]
	}
	return value
}

type Event struct {
	ID         string    `json:"id"`
	Type       string    `json:"type"`
	ServiceID  string    `json:"serviceId"`
	FromState  string    `json:"fromState"`
	ToState    string    `json:"toState"`
	Reason     string    `json:"reason,omitempty"`
	OccurredAt time.Time `json:"occurredAt"`
}

func TransitionEvents(previous, current Snapshot) []Event {
	previousByID := make(map[string]ServiceStatus, len(previous.Services))
	for _, item := range previous.Services {
		previousByID[item.ID] = item
	}
	events := make([]Event, 0)
	for _, item := range current.Services {
		before, exists := previousByID[item.ID]
		if !exists || before.State == item.State {
			continue
		}
		eventType := "service.state_changed"
		if item.State == StateDown {
			eventType = "service.down"
		} else if item.State == StateUp && (before.State == StateDown || before.State == StateUnknown) {
			eventType = "service.recovered"
		}
		eventTime := current.ObservedAt.UTC()
		event := Event{Type: eventType, ServiceID: item.ID, FromState: before.State, ToState: item.State, Reason: boundText(item.Reason, 128), OccurredAt: eventTime}
		digest := sha256.Sum256([]byte(item.ID + "\x00" + before.State + "\x00" + item.State + "\x00" + eventTime.Format(time.RFC3339Nano)))
		event.ID = hex.EncodeToString(digest[:])
		events = append(events, event)
	}
	sort.Slice(events, func(i, j int) bool { return events[i].ServiceID < events[j].ServiceID })
	return events
}