package benchmarks

import (
	"os"
	"path/filepath"
	"strings"
	"testing"

	"github.com/jfraeys/fetch_ml/internal/worker"
	"github.com/jfraeys/fetch_ml/internal/worker/integrity"
)

// BenchmarkDatasetSizeComparison finds the crossover point where native wins
// Run with: go test -tags native_libs -bench=BenchmarkDatasetSize ./tests/benchmarks/
func BenchmarkDatasetSizeComparison(b *testing.B) {
	sizes := []struct {
		name     string
		fileSize int
		numFiles int
		totalMB  int
	}{
		{"100MB", 10 * 1024 * 1024, 10, 100}, // 10 x 10MB = 100MB
		{"500MB", 50 * 1024 * 1024, 10, 500}, // 10 x 50MB = 500MB
		{"1GB", 100 * 1024 * 1024, 10, 1000}, // 10 x 100MB = 1GB
		{"2GB", 100 * 1024 * 1024, 20, 2000}, // 20 x 100MB = 2GB
		{"5GB", 100 * 1024 * 1024, 50, 5000}, // 50 x 100MB = 5GB
	}

	for _, tc := range sizes {
		tc := tc // capture range variable
		b.Run(tc.name+"/GoParallel", func(b *testing.B) {
			tmpDir := b.TempDir()
			createTestFiles(b, tmpDir, tc.numFiles, tc.fileSize)

			b.ResetTimer()
			b.ReportAllocs()
			for i := 0; i < b.N; i++ {
				_, err := integrity.DirOverallSHA256HexParallel(tmpDir)
				if err != nil {
					b.Fatal(err)
				}
			}
		})

		b.Run(tc.name+"/Native", func(b *testing.B) {
			tmpDir := b.TempDir()
			createTestFiles(b, tmpDir, tc.numFiles, tc.fileSize)

			b.ResetTimer()
			b.ReportAllocs()
			for i := 0; i < b.N; i++ {
				// Use DirOverallSHA256HexNative which calls native C++ implementation
				_, err := worker.DirOverallSHA256HexNative(tmpDir)
				if err != nil {
					if strings.Contains(err.Error(), "native hash requires") {
						b.Skip("Native hash not available: ", err)
					}
					b.Fatal(err)
				}
			}
		})
	}
}

func createTestFiles(b *testing.B, dir string, numFiles int, fileSize int) {
	data := make([]byte, fileSize)
	for i := range data {
		data[i] = byte(i % 256)
	}

	for i := range numFiles {
		path := filepath.Join(dir, "data", string(rune('a'+i%26)), "chunk.bin")
		if err := os.MkdirAll(filepath.Dir(path), 0750); err != nil {
			b.Fatal(err)
		}
		if err := os.WriteFile(path, data, 0640); err != nil {
			b.Fatal(err)
		}
	}
}