package store

import (
	"context"
	"crypto/sha256"
	"database/sql"
	"encoding/binary"
	"errors"
	"time"

	rvboxv1 "github.com/rvbox/rvbox/gen/go/rvbox/v1"
	"github.com/rvbox/rvbox/internal/domain"
)

var ErrSignalDeliveryUnavailable = errors.New("signal delivery is unavailable for this command state")

type SignalInput struct {
	IssueUUID   domain.UUID
	ClientID    string
	RequestUUID domain.UUID
	Signal      rvboxv1.SignalKind
	Hash        [32]byte
	OccurredAt  time.Time
}

type SignalResult struct {
	CommandRevision uint64
	Duplicate       bool
	Cancelled       bool
}

// SignalCommand applies the only locally-completable signal operation: a
// queued command can be cancelled before dispatch. For dispatched/accepted/
// running work the revisioned remote delivery path is intentionally not
// claimed until a live session control queue is available.
func (store *Store) SignalCommand(ctx context.Context, input SignalInput) (SignalResult, error) {
	if input.IssueUUID == (domain.UUID{}) || input.ClientID == "" || input.RequestUUID == (domain.UUID{}) || input.Signal < rvboxv1.SignalKind_SIGNAL_HUP || input.Signal > rvboxv1.SignalKind_SIGNAL_USR2 || input.Hash == [32]byte{} || input.OccurredAt.IsZero() {
		return SignalResult{}, errors.New("invalid signal request")
	}
	store.writeMu.Lock()
	defer store.writeMu.Unlock()
	database, err := store.openDatabase()
	if err != nil {
		return SignalResult{}, err
	}
	method := "signal_command"
	target := input.IssueUUID.String()
	if existing, found, lookupErr := lookupControlMutation(ctx, database, input.RequestUUID, method, target, input.Hash); lookupErr != nil {
		return SignalResult{}, lookupErr
	} else if found {
		if len(existing) != 8 {
			return SignalResult{}, ErrInvalidSegmentRecord
		}
		return SignalResult{CommandRevision: binary.BigEndian.Uint64(existing), Duplicate: true}, nil
	}
	tx, err := database.BeginTx(ctx, nil)
	if err != nil {
		return SignalResult{}, err
	}
	defer tx.Rollback()
	var lifecycle uint32
	var revision uint64
	err = tx.QueryRowContext(ctx, `SELECT lifecycle, revision FROM commands WHERE issue_uuid = ? AND client_id = ?`, input.IssueUUID[:], input.ClientID).Scan(&lifecycle, &revision)
	if errors.Is(err, sql.ErrNoRows) {
		return SignalResult{}, ErrCommandNotFound
	}
	if err != nil {
		return SignalResult{}, err
	}
	if lifecycle != uint32(rvboxv1.CommandLifecycle_COMMAND_QUEUED) {
		return SignalResult{}, ErrSignalDeliveryUnavailable
	}
	if revision == ^uint64(0) {
		return SignalResult{}, errors.New("command revision exhausted")
	}
	nextRevision := revision + 1
	if _, err := tx.ExecContext(ctx, `UPDATE commands SET lifecycle = ?, terminal_time = ?, revision = ? WHERE issue_uuid = ? AND client_id = ? AND lifecycle = ? AND revision = ?`, rvboxv1.CommandLifecycle_COMMAND_CANCELLED, input.OccurredAt.UTC().UnixNano(), nextRevision, input.IssueUUID[:], input.ClientID, rvboxv1.CommandLifecycle_COMMAND_QUEUED, revision); err != nil {
		return SignalResult{}, err
	}
	result := make([]byte, 8)
	binary.BigEndian.PutUint64(result, nextRevision)
	_, err = tx.ExecContext(ctx, `INSERT INTO control_mutations (request_uuid, method, owner_kind, owner_id, target, immutable_sha256, assigned_revision, result, created_at) VALUES (?, ?, 'command', ?, ?, ?, ?, ?, ?)`, input.RequestUUID[:], method, input.IssueUUID.String(), target, input.Hash[:], nextRevision, result, input.OccurredAt.UTC().UnixNano())
	if err != nil {
		return SignalResult{}, err
	}
	// Keep a compact audit digest; command text/stdin is never copied to the
	// audit payload.
	auditPayload := []byte{byte(input.Signal)}
	auditHash := sha256.Sum256(auditPayload)
	_, err = tx.ExecContext(ctx, `INSERT INTO audit_events (occurred_at, source, action, outcome, compression, payload, raw_bytes, stored_bytes, sha256) VALUES (?, 'control', ?, 'success', 1, ?, ?, ?, ?)`, input.OccurredAt.UTC().UnixNano(), method, auditPayload, len(auditPayload), len(auditPayload), auditHash[:])
	if err != nil {
		return SignalResult{}, err
	}
	if err := tx.Commit(); err != nil {
		return SignalResult{}, err
	}
	return SignalResult{CommandRevision: nextRevision, Cancelled: true}, nil
}