// Package evidence implements the FLUID evidence store.
//
// ArchitectureBlueprint.md section 26 requires append-only history, with
// mutable summary views derived from immutable events. Auditability is a core
// invariant (FluidAPIStandards.md section 25): the store must be able to answer
// what changed, why, on what evidence, and how the prior state is restored.
package evidence

import (
	"context"
	"errors"
	"time"

	"github.com/tegwick/fluid-core/internal/contract"
)

// Store is the append-only evidence log plus the queries built on it.
//
// Nothing in this interface updates or deletes. That is deliberate: history
// that can be rewritten is not evidence, and Blueprint section 28.1 gives the
// evidence writer permission to append but not to revise.
type Store interface {
	// AppendEvent records a lifecycle transition.
	AppendEvent(context.Context, contract.FluidEvent) error
	// Events returns matching events in occurrence order.
	Events(context.Context, EventFilter) ([]contract.FluidEvent, error)

	// WriteTelemetry records a normalized interaction event.
	WriteTelemetry(context.Context, contract.FluidTelemetry) error
	// Telemetry returns matching telemetry in occurrence order.
	Telemetry(context.Context, TelemetryFilter) ([]contract.FluidTelemetry, error)

	// PutRecord stores or supersedes a FLUID record (pressure, hypothesis,
	// revision, experiment, feedback, backend requirement).
	//
	// Records are summary state derived from events; the event log remains the
	// authority. A record may be rewritten, an event may not.
	PutRecord(ctx context.Context, kind contract.EntityKind, id string, body []byte) error
	// Record returns one stored record.
	Record(ctx context.Context, kind contract.EntityKind, id string) ([]byte, error)
	// Records returns every record of a kind, ordered by id.
	Records(ctx context.Context, kind contract.EntityKind) (map[string][]byte, error)

	Close() error
}

// ErrNotFound reports a record or event that does not exist.
var ErrNotFound = errors.New("not found")

// ErrImmutable reports an attempt to rewrite history.
var ErrImmutable = errors.New("evidence events are append-only")

// EventFilter narrows an event query. Zero values mean "no constraint".
type EventFilter struct {
	EntityType contract.EntityKind
	EntityID   string
	EventType  string
	Since      time.Time
	Until      time.Time
	Limit      int
}

// TelemetryFilter narrows a telemetry query.
type TelemetryFilter struct {
	InterfaceID contract.InterfaceID
	Revision    contract.RevisionID
	Experiment  contract.ExperimentID
	Cohort      contract.CohortID
	Kind        contract.FluidTelemetryKind
	Since       time.Time
	Until       time.Time
	Limit       int
}