package spool

import (
	"bytes"
	"context"
	"database/sql"
	"errors"
	"fmt"

	"github.com/rvbox/rvbox/internal/domain"
)

var (
	ErrIntegrityCheck        = errors.New("client spool SQLite integrity check failed")
	ErrQuotaCounterMismatch  = errors.New("client spool quota counter mismatch")
	ErrStoredPayloadChecksum = errors.New("client spool stored payload checksum mismatch")
)

type RecoveryReport struct {
	EventsChecked  uint64
	ScriptsChecked uint64
}

// Check verifies state that SQLite's own structural check cannot express. The
// daemon runs it asynchronously during startup and exposes failure as dirty
// local health; it never invents a replacement identity or counter value.
func (store *Store) Check(ctx context.Context) (RecoveryReport, error) {
	if store == nil || store.db == nil {
		return RecoveryReport{}, sql.ErrConnDone
	}
	if err := quickCheck(ctx, store.db); err != nil {
		return RecoveryReport{}, err
	}
	if err := checkQuotaCounters(ctx, store.db); err != nil {
		return RecoveryReport{}, err
	}
	return checkPayloads(ctx, store.db, store.maxScriptBytes)
}

func quickCheck(ctx context.Context, database *sql.DB) error {
	rows, err := database.QueryContext(ctx, `PRAGMA quick_check(100)`)
	if err != nil {
		return fmt.Errorf("%w: query failed", ErrIntegrityCheck)
	}
	defer rows.Close()
	count := 0
	for rows.Next() {
		var result string
		if err := rows.Scan(&result); err != nil {
			return fmt.Errorf("%w: unreadable result", ErrIntegrityCheck)
		}
		count++
		if result != "ok" {
			return fmt.Errorf("%w: %s", ErrIntegrityCheck, result)
		}
	}
	if err := rows.Err(); err != nil || count != 1 {
		return fmt.Errorf("%w: incomplete result", ErrIntegrityCheck)
	}
	return nil
}

func checkQuotaCounters(ctx context.Context, database *sql.DB) error {
	var invalid int
	err := database.QueryRowContext(ctx, `SELECT count(*) FROM commands AS c
WHERE c.total_charged_bytes != c.base_charged_bytes +
  COALESCE((SELECT sum(charged_bytes) FROM events WHERE issue_uuid = c.issue_uuid), 0) +
  COALESCE((SELECT charged_bytes FROM scripts WHERE issue_uuid = c.issue_uuid), 0)
OR c.output_charged_bytes !=
  COALESCE((SELECT sum(charged_bytes) FROM events WHERE issue_uuid = c.issue_uuid AND output = 1), 0)`).Scan(&invalid)
	if err != nil {
		return err
	}
	var stored, computed uint64
	if err := database.QueryRowContext(ctx, `SELECT client_total_charged_bytes, COALESCE((SELECT sum(total_charged_bytes) FROM commands), 0) FROM spool_counters WHERE singleton = 1`).Scan(&stored, &computed); err != nil {
		return err
	}
	if invalid != 0 || stored != computed {
		return ErrQuotaCounterMismatch
	}
	return nil
}

func checkPayloads(ctx context.Context, database *sql.DB, maxScriptBytes uint64) (RecoveryReport, error) {
	var report RecoveryReport
	rows, err := database.QueryContext(ctx, `SELECT issue_uuid, payload, payload_sha256 FROM events ORDER BY issue_uuid, local_ordinal`)
	if err != nil {
		return report, err
	}
	for rows.Next() {
		var owner, payload, digest []byte
		if err := rows.Scan(&owner, &payload, &digest); err != nil {
			_ = rows.Close()
			return report, err
		}
		computed := immutableDigest(payload)
		if _, valid := copiedUUID(owner); !valid || len(digest) != 32 || !bytes.Equal(computed[:], digest) {
			_ = rows.Close()
			return report, ErrStoredPayloadChecksum
		}
		report.EventsChecked++
	}
	if err := rows.Close(); err != nil {
		return report, err
	}
	scripts, err := database.QueryContext(ctx, `SELECT issue_uuid, received_raw_bytes, stored_bytes, stored_data FROM scripts ORDER BY issue_uuid`)
	if err != nil {
		return report, err
	}
	defer scripts.Close()
	for scripts.Next() {
		var owner, stored []byte
		var received, storedBytes uint64
		if err := scripts.Scan(&owner, &received, &storedBytes, &stored); err != nil {
			return report, err
		}
		if _, valid := copiedUUID(owner); !valid || storedBytes != uint64(len(stored)) {
			return report, ErrScriptState
		}
		if _, err := decompressScript(stored, received, maxScriptBytes); err != nil {
			return report, err
		}
		report.ScriptsChecked++
	}
	return report, scripts.Err()
}

// copiedUUID is intentionally kept here to make a corrupted BLOB type obvious
// at the recovery boundary rather than relying on SQLite's dynamic conversions.
func copiedUUID(value []byte) (domain.UUID, bool) {
	var result domain.UUID
	if len(value) != len(result) {
		return result, false
	}
	copy(result[:], value)
	return result, validUUID(result)
}