// Copyright 2020-2026 The happyDomain Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// Package checker provides the public types and helpers for writing
// happyDomain checker plugins. It is the stable API surface that all
// external checkers should depend on.
package checker

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

// CheckScopeType represents the scope level of a check target.
type CheckScopeType int

const (
	CheckScopeAdmin CheckScopeType = 0
	CheckScopeUser  CheckScopeType = iota
	CheckScopeDomain
	CheckScopeZone
	CheckScopeService
)

const (
	AutoFillDomainName  = "domain_name"
	AutoFillSubdomain   = "subdomain"
	AutoFillZone        = "zone"
	AutoFillServiceType = "service_type"
	AutoFillService     = "service"

	// AutoFillDiscoveryEntries receives DiscoveryEntry records published by
	// other checkers on the same target. The host does not pre-filter by
	// Type; consumers pick the contracts they understand and ignore the rest.
	AutoFillDiscoveryEntries = "discovery_entries"
)

// CheckTarget identifies the resource a check applies to. Identifiers are
// passed as opaque strings so the SDK stays self-contained and does not
// depend on any happyDomain-specific identifier type. The host is free to
// parse them into its own representation at the boundary.
type CheckTarget struct {
	UserId      string `json:"userId,omitempty"`
	DomainId    string `json:"domainId,omitempty"`
	ServiceId   string `json:"serviceId,omitempty"`
	ServiceType string `json:"serviceType,omitempty"`
}

// Scope returns the most specific scope level of this target.
func (t CheckTarget) Scope() CheckScopeType {
	if t.ServiceId != "" {
		return CheckScopeService
	}
	if t.DomainId != "" {
		return CheckScopeDomain
	}
	return CheckScopeUser
}

// String returns a stable, unambiguous string representation of the target.
// All three fields are always present (even when empty) so that different
// targets never produce the same string.
func (t CheckTarget) String() string {
	return t.UserId + "/" + t.DomainId + "/" + t.ServiceId
}

// CheckerAvailability declares on which scopes a checker can operate.
type CheckerAvailability struct {
	ApplyToDomain    bool     `json:"applyToDomain,omitempty"`
	ApplyToZone      bool     `json:"applyToZone,omitempty"`
	ApplyToService   bool     `json:"applyToService,omitempty"`
	LimitToProviders []string `json:"limitToProviders,omitempty"`
	LimitToServices  []string `json:"limitToServices,omitempty"`
}

// CheckerOptions holds the runtime options for a checker execution.
type CheckerOptions map[string]any

// CheckerOptionField describes a single checker option, used to document
// what configuration the checker accepts. The fields mirror happyDomain's
// generic Field type so that the host can re-export it as a type alias and
// keep using its existing form-rendering code unchanged.
type CheckerOptionField struct {
	// Id is the option identifier (the key in CheckerOptions).
	Id string `json:"id" binding:"required"`

	// Type is the string representation of the option's type
	// (e.g. "string", "number", "uint", "bool").
	Type string `json:"type" binding:"required"`

	// Label is the title shown to the user.
	Label string `json:"label,omitempty"`

	// Placeholder is the placeholder shown in the input.
	Placeholder string `json:"placeholder,omitempty"`

	// Default is the value used when the option is not set by the user.
	Default any `json:"default,omitempty"`

	// Choices holds the available choices for a dropdown option.
	Choices []string `json:"choices,omitempty"`

	// Required indicates whether the option must be filled.
	Required bool `json:"required,omitempty"`

	// Secret indicates that the option holds sensitive information
	// (API keys, tokens, …).
	Secret bool `json:"secret,omitempty"`

	// Hide indicates that the option should be hidden from the user.
	Hide bool `json:"hide,omitempty"`

	// Textarea indicates that a multi-line input should be used.
	Textarea bool `json:"textarea,omitempty"`

	// Description is a help sentence describing the option.
	Description string `json:"description,omitempty"`

	// AutoFill indicates that this option is automatically populated by the
	// host based on execution context (e.g. domain name, service payload).
	AutoFill string `json:"autoFill,omitempty"`

	// NoOverride indicates that once this option is set at a given scope,
	// more specific scopes cannot override its value.
	NoOverride bool `json:"noOverride,omitempty"`
}

// CheckerOptionDocumentation describes a single checker option.
type CheckerOptionDocumentation = CheckerOptionField

// CheckerOptionsDocumentation describes all options a checker accepts, organized by level.
type CheckerOptionsDocumentation struct {
	AdminOpts   []CheckerOptionDocumentation `json:"adminOpts,omitempty"`
	UserOpts    []CheckerOptionDocumentation `json:"userOpts,omitempty"`
	DomainOpts  []CheckerOptionDocumentation `json:"domainOpts,omitempty"`
	ServiceOpts []CheckerOptionDocumentation `json:"serviceOpts,omitempty"`
	RunOpts     []CheckerOptionDocumentation `json:"runOpts,omitempty"`
}

// Status represents the result status of a check evaluation.
type Status int

const (
	StatusUnknown Status = iota
	StatusOK
	StatusInfo
	StatusWarn
	StatusCrit
	StatusError
)

// String returns the human-readable name of the status.
func (s Status) String() string {
	switch s {
	case StatusUnknown:
		return "UNKNOWN"
	case StatusOK:
		return "OK"
	case StatusInfo:
		return "INFO"
	case StatusWarn:
		return "WARN"
	case StatusCrit:
		return "CRIT"
	case StatusError:
		return "ERROR"
	default:
		return fmt.Sprintf("Status(%d)", int(s))
	}
}

// CheckState is the result of evaluating a single rule.
type CheckState struct {
	Status  Status         `json:"status"`
	Message string         `json:"message"`
	Code    string         `json:"code,omitempty"`
	Meta    map[string]any `json:"meta,omitempty"`
}

// CheckMetric represents a single metric produced by a check.
type CheckMetric struct {
	Name      string            `json:"name" binding:"required"`
	Value     float64           `json:"value" binding:"required"`
	Unit      string            `json:"unit,omitempty"`
	Labels    map[string]string `json:"labels,omitempty"`
	Timestamp time.Time         `json:"timestamp" binding:"required" format:"date-time"`
}

// ObservationKey identifies a type of observation data.
type ObservationKey = string

// CheckIntervalSpec defines scheduling bounds for a checker.
type CheckIntervalSpec struct {
	Min     time.Duration `json:"min" swaggertype:"integer"`
	Max     time.Duration `json:"max" swaggertype:"integer"`
	Default time.Duration `json:"default" swaggertype:"integer"`
}

// ObservationProvider collects a specific type of data for a target.
type ObservationProvider interface {
	Key() ObservationKey
	Collect(ctx context.Context, opts CheckerOptions) (any, error)
}

// CheckRuleInfo is the JSON-serializable description of a rule, for API/UI listing.
type CheckRuleInfo struct {
	Name        string                       `json:"name"`
	Description string                       `json:"description"`
	Options     *CheckerOptionsDocumentation `json:"options,omitempty"`
}

// CheckRule evaluates observations and produces a CheckState.
type CheckRule interface {
	Name() string
	Description() string
	Evaluate(ctx context.Context, obs ObservationGetter, opts CheckerOptions) CheckState
}

// CheckRuleWithOptions is an optional interface that rules can implement
// to declare their own options documentation for API/UI grouping.
type CheckRuleWithOptions interface {
	CheckRule
	Options() CheckerOptionsDocumentation
}

// ObservationGetter provides access to observation data (used by CheckRule).
// Get unmarshals observation data into dest (like json.Unmarshal).
//
// GetRelated returns observations produced by other checkers on DiscoveryEntry
// records originally published by the current target. It is the core of
// cross-checker composition: a checker that published some entries via its
// DiscoveryPublisher can, during rule evaluation, fetch the latest
// observations that cover those entries and fold them into its own states.
//
// GetRelated returns an empty slice (not an error) when there is nothing
// to relate (no entries originally published, no downstream observation
// yet, no downstream checker registered for the entry type, …). Callers
// handle that as "no related data", typically skipping optional sections.
type ObservationGetter interface {
	Get(ctx context.Context, key ObservationKey, dest any) error
	GetRelated(ctx context.Context, key ObservationKey) ([]RelatedObservation, error)
}

// RelatedObservation is a single observation, produced by some other checker,
// that covers a DiscoveryEntry originally published by the current target.
//
// Data carries the raw JSON payload; consumers parse it according to the
// producer's schema, which they are expected to know via external agreement
// (typically a shared contract package imported by both producer and
// consumer).
type RelatedObservation struct {
	// CheckerID identifies the producer of this observation.
	CheckerID string `json:"checkerId"`

	// Key is the observation key the producer filled.
	Key ObservationKey `json:"key"`

	// Data is the raw JSON payload as persisted by the producer.
	Data json.RawMessage `json:"data"`

	// CollectedAt is when the producer ran its Collect.
	CollectedAt time.Time `json:"collectedAt"`

	// Ref matches DiscoveryEntry.Ref of the entry this observation covers.
	// Opaque to the SDK; meaningful within the producer/consumer contract.
	Ref string `json:"ref"`
}

// CheckAggregator combines multiple CheckStates into a single result.
type CheckAggregator interface {
	Aggregate(states []CheckState) CheckState
}

// ReportContext carries both the primary observation payload and any
// observations produced by other checkers that cover the same discovery
// entries. Hosts build a ReportContext and hand it to reporter methods.
//
// The method set is deliberately tiny: a single primary payload (Data) and
// a query for related observations by key (Related). Hosts return nil from
// Related when there is nothing to relate; reporters must tolerate that.
type ReportContext interface {
	Data() json.RawMessage
	Related(key ObservationKey) []RelatedObservation
}

// NewReportContext returns a ReportContext backed by a primary payload and
// a pre-resolved map of related observations by key. The SDK's /report HTTP
// handler uses this to wrap ExternalReportRequest contents; hosts and tests
// can use it whenever they already have the related observations in memory.
//
// Passing a nil or empty related map is fine; Related(key) will then return
// nil, just like StaticReportContext.
func NewReportContext(data json.RawMessage, related map[ObservationKey][]RelatedObservation) ReportContext {
	return fixedReportContext{data: data, related: related}
}

// StaticReportContext is a shorthand for NewReportContext(data, nil): a
// ReportContext with a primary payload and no related observations.
// Intended for tests and ad-hoc callers that have no lineage to supply.
func StaticReportContext(data json.RawMessage) ReportContext {
	return fixedReportContext{data: data}
}

type fixedReportContext struct {
	data    json.RawMessage
	related map[ObservationKey][]RelatedObservation
}

func (f fixedReportContext) Data() json.RawMessage { return f.data }
func (f fixedReportContext) Related(key ObservationKey) []RelatedObservation {
	if f.related == nil {
		return nil
	}
	return f.related[key]
}

// CheckerHTMLReporter is an optional interface that observation providers can
// implement to render their stored data as a full HTML document (for iframe embedding).
// Detect support with a type assertion: _, ok := provider.(CheckerHTMLReporter)
//
// The ReportContext carries the primary observation payload plus any
// downstream observations produced on DiscoveryEntry records this checker
// published. Implementations that do not need related observations can
// simply consume ctx.Data().
type CheckerHTMLReporter interface {
	GetHTMLReport(ctx ReportContext) (string, error)
}

// CheckerMetricsReporter is an optional interface that observation providers can
// implement to extract time-series metrics from their stored data.
// Detect support with a type assertion: _, ok := provider.(CheckerMetricsReporter)
//
// As with CheckerHTMLReporter, the ReportContext exposes related
// observations for cross-checker composition.
type CheckerMetricsReporter interface {
	ExtractMetrics(ctx ReportContext, collectedAt time.Time) ([]CheckMetric, error)
}

// CheckerDefinitionProvider is an optional interface that observation providers can
// implement to expose their checker definition. Used by the SDK server to serve
// /definition and /evaluate endpoints without requiring a separate argument.
// Detect support with a type assertion: _, ok := provider.(CheckerDefinitionProvider)
type CheckerDefinitionProvider interface {
	// Definition returns the checker definition for this provider.
	Definition() *CheckerDefinition
}

// CheckerDefinition is the complete definition of a checker, registered via init().
type CheckerDefinition struct {
	ID              string                      `json:"id"`
	Name            string                      `json:"name"`
	Version         string                      `json:"version,omitempty"`
	Availability    CheckerAvailability         `json:"availability"`
	Options         CheckerOptionsDocumentation `json:"options"`
	RulesInfo       []CheckRuleInfo             `json:"rules"`
	Rules           []CheckRule                 `json:"-"`
	Aggregator      CheckAggregator             `json:"-"`
	Interval        *CheckIntervalSpec          `json:"interval,omitempty"`
	HasHTMLReport   bool                        `json:"has_html_report,omitempty"`
	HasMetrics      bool                        `json:"has_metrics,omitempty"`
	ObservationKeys []ObservationKey            `json:"observationKeys,omitempty"`
}

// BuildRulesInfo populates RulesInfo from the Rules slice.
func (d *CheckerDefinition) BuildRulesInfo() {
	d.RulesInfo = make([]CheckRuleInfo, len(d.Rules))
	for i, rule := range d.Rules {
		info := CheckRuleInfo{
			Name:        rule.Name(),
			Description: rule.Description(),
		}
		if rwo, ok := rule.(CheckRuleWithOptions); ok {
			opts := rwo.Options()
			info.Options = &opts
		}
		d.RulesInfo[i] = info
	}
}

// OptionsValidator is an optional interface that checkers (or their rules/providers)
// can implement to perform domain-specific validation of checker options.
type OptionsValidator interface {
	ValidateOptions(opts CheckerOptions) error
}

// ExternalCollectRequest is sent to POST /collect on a remote checker endpoint.
type ExternalCollectRequest struct {
	Key     ObservationKey `json:"key"`
	Target  CheckTarget    `json:"target"`
	Options CheckerOptions `json:"options"`
}

// ExternalCollectResponse is returned by POST /collect on a remote checker endpoint.
type ExternalCollectResponse struct {
	Data    json.RawMessage  `json:"data,omitempty"`
	Entries []DiscoveryEntry `json:"entries,omitempty"`
	Error   string           `json:"error,omitempty"`
}

// DiscoveryEntry is a single "thing worth probing" declared by a checker as a
// by-product of its collection, intended to be consumed by other checkers
// without having to re-parse raw observations.
//
// The SDK treats Payload as an opaque byte string: producer and consumer
// checkers agree on a schema through a separate contract (typically a small
// shared Go package imported by both). This keeps the SDK free of
// protocol-specific concepts; new entry families (TLS endpoint, HTTP probe,
// ACME challenge, DNSSEC key, …) can appear without touching it.
//
// Entries are ingested by happyDomain into a separate index. Each new
// collection from the same source atomically replaces the set of entries
// previously published for the same (producer, target) pair.
type DiscoveryEntry struct {
	// Type names the contract Payload follows, e.g. "tls.endpoint" or
	// "http.probe". Producers and consumers match on this string; the SDK
	// does not interpret it. Stick to a reverse-DNS-ish convention so that
	// independent contracts do not collide.
	Type string `json:"type"`

	// Ref is a stable per-entry identifier chosen by the producer. The host
	// uses it to dedupe entries across repeated collections and to link
	// related observations back to this entry (RelatedObservation.Ref). Two
	// producers may reuse the same Ref space; the host namespaces them by
	// (producer, target).
	Ref string `json:"ref"`

	// Payload is the entry-specific data, in the format defined by the
	// contract named in Type. Opaque to the SDK.
	Payload json.RawMessage `json:"payload"`
}

// DiscoveryPublisher is an optional interface an ObservationProvider can
// co-implement to declare DiscoveryEntry records derived from the value it
// just collected.
//
// The host invokes DiscoverEntries immediately after Collect, passing the
// native Go value returned by Collect (no JSON round-trip). Implementations
// should therefore type-assert data to their concrete collection type and
// marshal each contract payload themselves.
type DiscoveryPublisher interface {
	DiscoverEntries(data any) ([]DiscoveryEntry, error)
}

// ExternalEvaluateRequest is sent to POST /evaluate on a remote checker endpoint.
type ExternalEvaluateRequest struct {
	Observations map[ObservationKey]json.RawMessage `json:"observations"`
	Options      CheckerOptions                     `json:"options"`
	EnabledRules map[string]bool                    `json:"enabledRules,omitempty"`
}

// ExternalEvaluateResponse is returned by POST /evaluate on a remote checker endpoint.
type ExternalEvaluateResponse struct {
	States []CheckState `json:"states"`
	Error  string       `json:"error,omitempty"`
}

// ExternalReportRequest is sent to POST /report on a remote checker endpoint.
//
// Related carries observations produced by other checkers on DiscoveryEntry
// records originally published by the target of this report, that is, the
// cross-checker lineage that ObservationGetter.GetRelated would expose in
// the in-process path. The host composes it before making the HTTP request;
// when absent, the remote checker receives a context that reports no
// related observations (equivalent to StaticReportContext).
type ExternalReportRequest struct {
	Key     ObservationKey                          `json:"key"`
	Data    json.RawMessage                         `json:"data"`
	Related map[ObservationKey][]RelatedObservation `json:"related,omitempty"`
}

// HealthResponse is returned by GET /health on a remote checker endpoint.
// It carries lightweight runtime signals so a scheduler can pick the least
// busy worker among a set of equivalent checker instances.
//
// LoadAvg mirrors /proc/loadavg semantics: it is the 1, 5, 15-minute
// exponentially weighted moving average of the InFlight request count,
// sampled every 5 seconds. Divide by NumCPU to estimate saturation.
type HealthResponse struct {
	// Status is a coarse liveness indicator. Currently always "ok";
	// "degraded" is reserved for future use.
	Status string `json:"status"`

	// Uptime is the number of (fractional) seconds since the server started.
	Uptime float64 `json:"uptime_seconds"`

	// NumCPU is the value of runtime.NumCPU() on this worker.
	NumCPU int `json:"num_cpu"`

	// InFlight is the number of work requests (/collect, /evaluate, /report)
	// currently being processed. /health and /definition are not counted.
	InFlight int64 `json:"inflight"`

	// TotalRequests is the cumulative number of work requests served since
	// the server started. /health and /definition are not counted.
	TotalRequests uint64 `json:"total_requests"`

	// LoadAvg holds the 1, 5, 15-minute EWMAs of InFlight.
	LoadAvg [3]float64 `json:"loadavg"`
}