// Package intent implements the FLUID intent store.
//
// ArchitectureBlueprint.md section 27: the system must retain the exact
// interface evolution intent governing each revision, so that a later audit can
// answer whether a change was valid under the intent that existed when it was
// made. An intent document is therefore versioned, content-addressed and
// immutable once recorded.
package intent

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

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

// AuthorityMode is the operational authority granted to the Daimon.
//
// FluidAPIStandards.md section 26 is explicit that these describe authority,
// not maturity: a high-assurance system may deliberately remain at FLUID-2.
type AuthorityMode int

const (
	ModeInstrumented      AuthorityMode = iota // FLUID-0
	ModeAnalytical                             // FLUID-1
	ModeAdvisory                               // FLUID-2
	ModeConstructive                           // FLUID-3
	ModeExperimental                           // FLUID-4
	ModeBoundedAutonomous                      // FLUID-5
	ModeEvolutionary                           // FLUID-6
)

// String renders the canonical FLUID-N form.
func (m AuthorityMode) String() string { return fmt.Sprintf("FLUID-%d", int(m)) }

// Valid reports whether m is a defined mode.
func (m AuthorityMode) Valid() bool { return m >= ModeInstrumented && m <= ModeEvolutionary }

// Allows reports whether this mode permits at least the authority of want.
func (m AuthorityMode) Allows(want AuthorityMode) bool { return m >= want }

var modePattern = regexp.MustCompile(`FLUID-([0-6])\b`)

// Version is one recorded interface evolution intent.
type Version struct {
	// Version is the human-facing label, such as "IEI-7".
	Version string `json:"version"`
	// Digest content-addresses the document. Two intent versions with the same
	// digest are the same intent, whatever they were called.
	Digest contract.Digest `json:"digest"`
	// Document is the full text, retained verbatim. A summary would not settle
	// an audit question about what the intent actually said.
	Document string `json:"document"`
	// Mode is the operational authority the document declares.
	Mode AuthorityMode `json:"mode"`
	// RecordedAt is when this version entered the store.
	RecordedAt time.Time `json:"recorded_at"`
}

// Store holds intent versions and which one is currently active.
type Store struct {
	ev    evidence.Store
	iface contract.InterfaceID
}

// New returns a store backed by ev.
func New(ev evidence.Store, iface contract.InterfaceID) *Store {
	return &Store{ev: ev, iface: iface}
}

var (
	// ErrNotFound reports an unknown intent version.
	ErrNotFound = evidence.ErrNotFound
	// ErrImmutable reports an attempt to change a recorded intent version.
	ErrImmutable = errors.New("a recorded intent version cannot be changed")
	// ErrNoActive reports that no intent has been made active yet.
	ErrNoActive = errors.New("no active interface evolution intent")
)

// activeKey is the record id holding the active-version pointer.
const activeKey = "__active__"

// Digest computes the content address of an intent document.
func Digest(document string) contract.Digest {
	sum := sha256.Sum256([]byte(document))
	return contract.Digest("sha256:" + hex.EncodeToString(sum[:]))
}

// ParseMode extracts the declared authority mode from an intent document.
//
// The template writes the mode as a fenced list of alternatives before it is
// filled in; a document that still contains every mode has not been completed,
// and defaulting it to something permissive would be exactly the wrong failure.
func ParseMode(document string) (AuthorityMode, error) {
	matches := modePattern.FindAllStringSubmatch(document, -1)
	if len(matches) == 0 {
		return 0, errors.New("intent document declares no FLUID-N authority mode")
	}

	seen := map[string]bool{}
	for _, m := range matches {
		seen[m[1]] = true
	}
	if len(seen) > 1 {
		return 0, fmt.Errorf(
			"intent document declares %d different authority modes; the template placeholder has not been resolved",
			len(seen))
	}

	return AuthorityMode(matches[0][1][0] - '0'), nil
}

// Put records an intent version.
//
// Recording the same version twice with identical content is a no-op, which
// makes startup idempotent. Recording it with different content is refused:
// changing what a revision was governed by, after the fact, would break the
// audit question the store exists to answer.
func (s *Store) Put(ctx context.Context, version, document string) (Version, error) {
	if version == "" {
		return Version{}, errors.New("intent version label is required")
	}

	mode, err := ParseMode(document)
	if err != nil {
		return Version{}, fmt.Errorf("intent %s: %w", version, err)
	}

	v := Version{
		Version:    version,
		Digest:     Digest(document),
		Document:   document,
		Mode:       mode,
		RecordedAt: time.Now().UTC(),
	}

	if existing, err := s.Get(ctx, version); err == nil {
		if existing.Digest != v.Digest {
			return Version{}, fmt.Errorf("%w: %s already recorded with digest %s",
				ErrImmutable, version, existing.Digest)
		}
		return existing, nil
	} else if !errors.Is(err, ErrNotFound) {
		return Version{}, err
	}

	body, err := json.Marshal(v)
	if err != nil {
		return Version{}, err
	}
	if err := s.ev.PutRecord(ctx, contract.KindIntent, s.key(version), body); err != nil {
		return Version{}, err
	}

	if err := s.ev.AppendEvent(ctx, contract.FluidEvent{
		SchemaVersion: "0.1",
		ID:            contract.EventID("EV-intent-" + string(v.Digest[7:19])),
		OccurredAt:    v.RecordedAt,
		EntityType:    contract.FluidEventEntityTypeIntent,
		EntityID:      version,
		EventType:     "INTENT_RECORDED",
		Actor:         contract.Actor{Type: contract.ActorTypeSystem, ID: "fluid-intent-store"},
		Reason:        fmt.Sprintf("recorded %s at authority mode %s", version, mode),
	}); err != nil {
		return Version{}, err
	}

	return v, nil
}

// Get returns a recorded intent version.
func (s *Store) Get(ctx context.Context, version string) (Version, error) {
	body, err := s.ev.Record(ctx, contract.KindIntent, s.key(version))
	if err != nil {
		return Version{}, err
	}
	var v Version
	if err := json.Unmarshal(body, &v); err != nil {
		return Version{}, fmt.Errorf("decode intent %s: %w", version, err)
	}
	return v, nil
}

// SetActive makes a recorded version the governing intent.
func (s *Store) SetActive(ctx context.Context, version string) error {
	v, err := s.Get(ctx, version)
	if err != nil {
		return fmt.Errorf("cannot activate %s: %w", version, err)
	}

	body, _ := json.Marshal(map[string]string{"version": v.Version, "digest": string(v.Digest)})
	if err := s.ev.PutRecord(ctx, contract.KindIntent, s.key(activeKey), body); err != nil {
		return err
	}

	return s.ev.AppendEvent(ctx, contract.FluidEvent{
		SchemaVersion: "0.1",
		ID:            contract.EventID("EV-intent-active-" + string(v.Digest[7:19])),
		OccurredAt:    time.Now().UTC(),
		EntityType:    contract.FluidEventEntityTypeIntent,
		EntityID:      version,
		EventType:     "INTENT_ACTIVATED",
		Actor:         contract.Actor{Type: contract.ActorTypeSystem, ID: "fluid-intent-store"},
		Reason:        fmt.Sprintf("%s is now the governing intent", version),
	})
}

// Active returns the currently governing intent version.
func (s *Store) Active(ctx context.Context) (Version, error) {
	body, err := s.ev.Record(ctx, contract.KindIntent, s.key(activeKey))
	if errors.Is(err, ErrNotFound) {
		return Version{}, ErrNoActive
	}
	if err != nil {
		return Version{}, err
	}

	var ptr struct {
		Version string `json:"version"`
	}
	if err := json.Unmarshal(body, &ptr); err != nil {
		return Version{}, err
	}
	return s.Get(ctx, ptr.Version)
}

// Bind records that a revision is governed by an intent version.
//
// This is the link Blueprint section 27 requires. It is stored as an event
// rather than as a mutable field so that a revision's governing intent cannot
// be quietly reassigned later.
func (s *Store) Bind(ctx context.Context, rev contract.RevisionID, version string) error {
	v, err := s.Get(ctx, version)
	if err != nil {
		return fmt.Errorf("cannot bind %s: %w", rev, err)
	}

	return s.ev.AppendEvent(ctx, contract.FluidEvent{
		SchemaVersion: "0.1",
		ID:            contract.EventID("EV-bind-" + string(rev) + "-" + version),
		OccurredAt:    time.Now().UTC(),
		EntityType:    contract.FluidEventEntityTypeRevision,
		EntityID:      string(rev),
		EventType:     "INTENT_BOUND",
		Actor:         contract.Actor{Type: contract.ActorTypeSystem, ID: "fluid-intent-store"},
		Inputs:        []string{version},
		Reason:        fmt.Sprintf("%s is governed by %s (%s)", rev, version, v.Digest),
	})
}

// GoverningIntent returns the intent version a revision was bound to.
func (s *Store) GoverningIntent(ctx context.Context, rev contract.RevisionID) (Version, error) {
	events, err := s.ev.Events(ctx, evidence.EventFilter{
		EntityType: contract.KindRevision,
		EntityID:   string(rev),
		EventType:  "INTENT_BOUND",
	})
	if err != nil {
		return Version{}, err
	}
	if len(events) == 0 {
		return Version{}, fmt.Errorf("%w: no intent bound to %s", ErrNotFound, rev)
	}
	// The first binding governs. A later one would be a reassignment, which the
	// audit trail records but must not silently win.
	first := events[0]
	if len(first.Inputs) == 0 {
		return Version{}, fmt.Errorf("binding event %s names no intent version", first.ID)
	}
	return s.Get(ctx, first.Inputs[0])
}

func (s *Store) key(id string) string {
	return string(s.iface) + "/" + strings.TrimSpace(id)
}