package observation

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

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

// PressureRegistry is the durable inventory of material interface pressure.
//
// ArchitectureBlueprint.md section 9 requires deduplication, aggregation,
// cohort segmentation, frequency tracking, severity, confidence, linked
// hypotheses and disposition — and says plainly that pressure may remain
// unresolved on purpose. Not every observed mismatch deserves adaptation.
type PressureRegistry struct {
	store evidence.Store
	iface contract.InterfaceID
	now   func() time.Time
}

// NewPressureRegistry returns a registry backed by the evidence store.
func NewPressureRegistry(store evidence.Store, iface contract.InterfaceID) *PressureRegistry {
	return &PressureRegistry{store: store, iface: iface, now: time.Now}
}

// ErrDismissed reports an attempt to reopen a deliberately closed pressure.
var ErrDismissed = errors.New("pressure was dismissed and will not be reopened automatically")

// pressureID derives a stable identifier from a finding's fingerprint.
//
// Deriving rather than allocating is what makes ingest idempotent: re-running
// analysis over the same window updates one record instead of minting a new one
// on every pass.
func pressureID(iface contract.InterfaceID, fingerprint string) contract.PressureID {
	sum := sha256.Sum256([]byte(string(iface) + "\x00" + fingerprint))
	return contract.PressureID("P-" + hex.EncodeToString(sum[:6]))
}

// Record folds a finding into the registry, creating or updating one pressure.
//
// A finding that matches an existing record extends its window and refreshes
// its counts rather than replacing it: first_seen is evidence about how long
// the interface has had this problem, and overwriting it would erase the age
// that makes a pressure worth prioritizing.
func (r *PressureRegistry) Record(ctx context.Context, f Finding) (contract.FluidPressure, error) {
	id := pressureID(r.iface, f.Fingerprint)

	existing, err := r.Get(ctx, id)
	switch {
	case err == nil:
		if existing.Status == contract.FluidPressureStatusDISMISSED {
			// An operator decided this is not worth acting on. Silently
			// resurrecting it would make the dismissal meaningless.
			return existing, fmt.Errorf("%w: %s", ErrDismissed, id)
		}
		return r.update(ctx, existing, f)
	case errors.Is(err, evidence.ErrNotFound):
		return r.create(ctx, id, f)
	default:
		return contract.FluidPressure{}, err
	}
}

func (r *PressureRegistry) create(ctx context.Context, id contract.PressureID, f Finding) (contract.FluidPressure, error) {
	observations := int64(f.Occurrences)
	consumers := int64(f.Consumers)
	severity := contract.UnitInterval(f.Severity)
	confidence := contract.UnitInterval(f.Confidence)

	p := contract.FluidPressure{
		SchemaVersion:   "0.1",
		ID:              id,
		InterfaceID:     r.iface,
		Class:           f.Class,
		FirstSeen:       f.FirstSeen,
		LastSeen:        f.LastSeen,
		AffectedCohorts: f.Cohorts,
		Frequency: &contract.FluidPressureFrequency{
			Observations:         &observations,
			IndependentConsumers: &consumers,
		},
		Severity:     &severity,
		Confidence:   &confidence,
		Summary:      f.Summary,
		EvidenceRefs: f.Evidence,
		Status:       contract.FluidPressureStatusOPEN,
	}

	if err := r.put(ctx, p); err != nil {
		return contract.FluidPressure{}, err
	}
	if err := r.event(ctx, p, "PRESSURE_OPENED", f.Summary); err != nil {
		return contract.FluidPressure{}, err
	}
	return p, nil
}

func (r *PressureRegistry) update(ctx context.Context, p contract.FluidPressure, f Finding) (contract.FluidPressure, error) {
	if f.FirstSeen.Before(p.FirstSeen) {
		p.FirstSeen = f.FirstSeen
	}
	if f.LastSeen.After(p.LastSeen) {
		p.LastSeen = f.LastSeen
	}

	observations := int64(f.Occurrences)
	consumers := int64(f.Consumers)
	p.Frequency = &contract.FluidPressureFrequency{
		Observations:         &observations,
		IndependentConsumers: &consumers,
	}

	severity := contract.UnitInterval(f.Severity)
	confidence := contract.UnitInterval(f.Confidence)
	p.Severity = &severity
	p.Confidence = &confidence
	p.Summary = f.Summary
	p.AffectedCohorts = mergeCohorts(p.AffectedCohorts, f.Cohorts)
	p.EvidenceRefs = mergeRefs(p.EvidenceRefs, f.Evidence)

	// Fresh evidence for something previously explained means it is back.
	if p.Status == contract.FluidPressureStatusADDRESSED {
		p.Status = contract.FluidPressureStatusOPEN
		if err := r.put(ctx, p); err != nil {
			return contract.FluidPressure{}, err
		}
		return p, r.event(ctx, p, "PRESSURE_REOPENED",
			"new evidence observed after the pressure was marked addressed")
	}

	if err := r.put(ctx, p); err != nil {
		return contract.FluidPressure{}, err
	}
	return p, r.event(ctx, p, "PRESSURE_OBSERVED", f.Summary)
}

// RecordAll folds a batch of findings into the registry.
//
// Dismissed pressures are skipped rather than treated as errors: hitting one
// is the expected outcome of re-analysing a window an operator has already
// triaged.
func (r *PressureRegistry) RecordAll(ctx context.Context, findings []Finding) ([]contract.FluidPressure, error) {
	var out []contract.FluidPressure
	for _, f := range findings {
		p, err := r.Record(ctx, f)
		if errors.Is(err, ErrDismissed) {
			continue
		}
		if err != nil {
			return out, err
		}
		out = append(out, p)
	}
	return out, nil
}

// Get returns one pressure record.
func (r *PressureRegistry) Get(ctx context.Context, id contract.PressureID) (contract.FluidPressure, error) {
	body, err := r.store.Record(ctx, contract.KindPressure, string(id))
	if err != nil {
		return contract.FluidPressure{}, err
	}
	var doc contract.PressureDocument
	if err := json.Unmarshal(body, &doc); err != nil {
		return contract.FluidPressure{}, fmt.Errorf("decode pressure %s: %w", id, err)
	}
	return doc.FluidPressure, nil
}

// List returns pressures, optionally filtered by status.
func (r *PressureRegistry) List(ctx context.Context, status contract.FluidPressureStatus) ([]contract.FluidPressure, error) {
	records, err := r.store.Records(ctx, contract.KindPressure)
	if err != nil {
		return nil, err
	}

	out := make([]contract.FluidPressure, 0, len(records))
	for _, body := range records {
		var doc contract.PressureDocument
		if err := json.Unmarshal(body, &doc); err != nil {
			continue
		}
		if status != "" && doc.FluidPressure.Status != status {
			continue
		}
		out = append(out, doc.FluidPressure)
	}

	// Most severe first: the registry is a work queue as much as an inventory.
	sort.Slice(out, func(i, j int) bool {
		si, sj := unit(out[i].Severity), unit(out[j].Severity)
		if si != sj {
			return si > sj
		}
		return out[i].ID < out[j].ID
	})
	return out, nil
}

// SetStatus moves a pressure through its lifecycle.
//
// Transitions are recorded as events rather than only as a field, so a
// dismissal can be traced to whoever made it and why.
func (r *PressureRegistry) SetStatus(ctx context.Context, id contract.PressureID, status contract.FluidPressureStatus, actor contract.Actor, reason string) error {
	if !status.Valid() {
		return fmt.Errorf("unknown pressure status %q", status)
	}
	if reason == "" {
		// A status change with no reason is not auditable, and dismissals
		// without a reason are how a registry quietly loses its evidence.
		return errors.New("a status change requires a reason")
	}

	p, err := r.Get(ctx, id)
	if err != nil {
		return err
	}
	previous := p.Status
	p.Status = status

	if err := r.put(ctx, p); err != nil {
		return err
	}
	return r.eventBy(ctx, p, "PRESSURE_STATUS_CHANGED", actor,
		fmt.Sprintf("%s -> %s: %s", previous, status, reason))
}

// LinkHypothesis records that a hypothesis addresses this pressure.
func (r *PressureRegistry) LinkHypothesis(ctx context.Context, id contract.PressureID, h contract.HypothesisID) error {
	if err := contract.RequireKind(string(h), contract.KindHypothesis); err != nil {
		return err
	}

	p, err := r.Get(ctx, id)
	if err != nil {
		return err
	}
	for _, existing := range p.LinkedHypotheses {
		if existing == h {
			return nil
		}
	}
	p.LinkedHypotheses = append(p.LinkedHypotheses, h)
	if p.Status == contract.FluidPressureStatusOPEN {
		p.Status = contract.FluidPressureStatusANALYZING
	}

	if err := r.put(ctx, p); err != nil {
		return err
	}
	return r.event(ctx, p, "PRESSURE_HYPOTHESIS_LINKED", fmt.Sprintf("linked %s", h))
}

func (r *PressureRegistry) put(ctx context.Context, p contract.FluidPressure) error {
	body, err := json.Marshal(contract.PressureDocument{FluidPressure: p})
	if err != nil {
		return err
	}
	return r.store.PutRecord(ctx, contract.KindPressure, string(p.ID), body)
}

func (r *PressureRegistry) event(ctx context.Context, p contract.FluidPressure, kind, reason string) error {
	return r.eventBy(ctx, p, kind,
		contract.Actor{Type: contract.ActorTypeSystem, ID: "fluid-pressure-engine"}, reason)
}

func (r *PressureRegistry) eventBy(ctx context.Context, p contract.FluidPressure, kind string, actor contract.Actor, reason string) error {
	return r.store.AppendEvent(ctx, contract.FluidEvent{
		SchemaVersion: "0.1",
		ID:            contract.EventID(fmt.Sprintf("EV-%s-%d", p.ID, r.now().UnixNano())),
		OccurredAt:    r.now().UTC(),
		EntityType:    contract.FluidEventEntityTypePressure,
		EntityID:      string(p.ID),
		EventType:     kind,
		Actor:         actor,
		Reason:        reason,
		EvidenceRefs:  p.EvidenceRefs,
	})
}

func unit(v *contract.UnitInterval) float64 {
	if v == nil {
		return 0
	}
	return float64(*v)
}

func mergeCohorts(a, b []contract.CohortID) []contract.CohortID {
	seen := map[contract.CohortID]struct{}{}
	var out []contract.CohortID
	for _, list := range [][]contract.CohortID{a, b} {
		for _, c := range list {
			if _, ok := seen[c]; ok {
				continue
			}
			seen[c] = struct{}{}
			out = append(out, c)
		}
	}
	sort.Slice(out, func(i, j int) bool { return out[i] < out[j] })
	return out
}

func mergeRefs(a, b []contract.EvidenceRef) []contract.EvidenceRef {
	seen := map[contract.EvidenceRef]struct{}{}
	var out []contract.EvidenceRef
	for _, list := range [][]contract.EvidenceRef{a, b} {
		for _, s := range list {
			if _, ok := seen[s]; ok {
				continue
			}
			seen[s] = struct{}{}
			out = append(out, s)
		}
	}
	sort.Slice(out, func(i, j int) bool { return out[i] < out[j] })
	return out
}