package filescan

import (
	"bytes"
	"context"
	"errors"
	"io"
	"log/slog"
	"os"
	"path/filepath"

	"github.com/ultisuite/ulti-backend/internal/orgpolicy"
	"github.com/ultisuite/ulti-backend/internal/virustotal"
)

const memoryBufferLimit = 32 * 1024 * 1024

// Result holds scan outcome for persistence.
type Result struct {
	Status string // clean | skipped
}

// PolicyLoader supplies org file policies at runtime.
type PolicyLoader interface {
	FilePolicies(ctx context.Context) (orgpolicy.FilePolicies, error)
	ScanEnabled(ctx context.Context) (bool, string, error)
}

// Scanner coordinates org policy and VirusTotal scanning.
type Scanner struct {
	policies PolicyLoader
	logger   *slog.Logger
}

func NewScanner(policies PolicyLoader, logger *slog.Logger) *Scanner {
	if logger == nil {
		logger = slog.Default()
	}
	return &Scanner{policies: policies, logger: logger}
}

// ScanReader reads all bytes from r (up to maxBytes), optionally scans, returns data for storage.
func (s *Scanner) ScanReader(ctx context.Context, filename string, r io.Reader, size int64) ([]byte, Result, error) {
	fp, err := s.policies.FilePolicies(ctx)
	if err != nil {
		return nil, Result{}, err
	}

	maxBytes := fp.MaxUploadBytes
	if maxBytes <= 0 {
		maxBytes = 512 * 1024 * 1024
	}
	if maxBytes > virustotalMaxBytes() {
		maxBytes = virustotalMaxBytes()
	}

	data, err := readLimited(r, size, maxBytes)
	if err != nil {
		return nil, Result{}, err
	}

	enabled := fp.VirusScanEnabled && fp.VirusTotalAPIKey != ""
	if !enabled {
		return data, Result{Status: "skipped"}, nil
	}

	vt := virustotal.NewScanner(fp.VirusTotalAPIKey, s.logger)
	scanResult, err := vt.ScanBytes(ctx, filename, data, virustotal.SHA256Hex(data))
	if err != nil {
		if errors.Is(err, virustotal.ErrMalicious) {
			return nil, Result{Status: "malicious"}, virustotal.ErrMalicious
		}
		return nil, Result{}, err
	}
	return data, Result{Status: scanResult.Status}, nil
}

// ScanBytes scans pre-loaded bytes when policy is already known.
func (s *Scanner) ScanBytes(ctx context.Context, filename string, data []byte) (Result, error) {
	enabled, apiKey, err := s.policies.ScanEnabled(ctx)
	if err != nil {
		return Result{}, err
	}
	if !enabled {
		return Result{Status: "skipped"}, nil
	}

	vt := virustotal.NewScanner(apiKey, s.logger)
	scanResult, err := vt.ScanBytes(ctx, filename, data, virustotal.SHA256Hex(data))
	if err != nil {
		if errors.Is(err, virustotal.ErrMalicious) {
			return Result{Status: "malicious"}, virustotal.ErrMalicious
		}
		return Result{}, err
	}
	return Result{Status: scanResult.Status}, nil
}

func readLimited(r io.Reader, size int64, maxBytes int64) ([]byte, error) {
	if size >= 0 && size <= memoryBufferLimit {
		limited := io.LimitReader(r, maxBytes+1)
		data, err := io.ReadAll(limited)
		if err != nil {
			return nil, err
		}
		if int64(len(data)) > maxBytes {
			return nil, errors.New("file exceeds max upload size")
		}
		return data, nil
	}

	tmp, err := os.CreateTemp("", "ulti-scan-*")
	if err != nil {
		return nil, err
	}
	tmpPath := tmp.Name()
	defer os.Remove(tmpPath)

	written, err := io.Copy(tmp, io.LimitReader(r, maxBytes+1))
	if err != nil {
		tmp.Close()
		return nil, err
	}
	if err := tmp.Close(); err != nil {
		return nil, err
	}
	if written > maxBytes {
		return nil, errors.New("file exceeds max upload size")
	}

	return os.ReadFile(filepath.Clean(tmpPath))
}

func virustotalMaxBytes() int64 {
	return 650 * 1024 * 1024
}

// ErrMalicious re-exports virustotal.ErrMalicious for handlers.
var ErrMalicious = virustotal.ErrMalicious

// NopReader helper for tests.
func NopReader(data []byte) io.Reader {
	return bytes.NewReader(data)
}