package chunker

import (
	"bytes"
	"crypto/rand"
	"testing"
)

func TestChunker(t *testing.T) {
	t.Run("small file produces single chunk", func(t *testing.T) {
		chunker := NewChunker(1024 * 1024)         // 1MB average
		data := bytes.Repeat([]byte("hello"), 100) // 500 bytes

		chunks, err := chunker.ChunkReader(bytes.NewReader(data))
		if err != nil {
			t.Fatalf("chunking failed: %v", err)
		}

		if len(chunks) != 1 {
			t.Errorf("expected 1 chunk, got %d", len(chunks))
		}

		if chunks[0].Size != int64(len(data)) {
			t.Errorf("expected chunk size %d, got %d", len(data), chunks[0].Size)
		}
	})

	t.Run("large file produces multiple chunks", func(t *testing.T) {
		chunker := NewChunker(256 * 1024) // 256KB average chunk size

		// Generate 2MB of random data
		data := make([]byte, 2*1024*1024)
		if _, err := rand.Read(data); err != nil {
			t.Fatalf("failed to generate random data: %v", err)
		}

		chunks, err := chunker.ChunkReader(bytes.NewReader(data))
		if err != nil {
			t.Fatalf("chunking failed: %v", err)
		}

		// Should produce multiple chunks - with FastCDC we expect around 8 chunks for 2MB with 256KB average
		if len(chunks) < 4 || len(chunks) > 16 {
			t.Errorf("expected 4-16 chunks, got %d", len(chunks))
		}

		// Verify chunks reconstruct original data
		var reconstructed []byte
		for _, chunk := range chunks {
			reconstructed = append(reconstructed, chunk.Data...)
		}

		if !bytes.Equal(data, reconstructed) {
			t.Error("reconstructed data doesn't match original")
		}

		// Verify offsets
		var expectedOffset int64
		for i, chunk := range chunks {
			if chunk.Offset != expectedOffset {
				t.Errorf("chunk %d: expected offset %d, got %d", i, expectedOffset, chunk.Offset)
			}
			expectedOffset += chunk.Size
		}
	})

	t.Run("deterministic chunking", func(t *testing.T) {
		chunker1 := NewChunker(256 * 1024)
		chunker2 := NewChunker(256 * 1024)

		// Use deterministic data
		data := bytes.Repeat([]byte("abcdefghijklmnopqrstuvwxyz"), 20000) // ~520KB

		chunks1, err := chunker1.ChunkReader(bytes.NewReader(data))
		if err != nil {
			t.Fatalf("chunking failed: %v", err)
		}

		chunks2, err := chunker2.ChunkReader(bytes.NewReader(data))
		if err != nil {
			t.Fatalf("chunking failed: %v", err)
		}

		// Should produce same chunks
		if len(chunks1) != len(chunks2) {
			t.Fatalf("different number of chunks: %d vs %d", len(chunks1), len(chunks2))
		}

		for i := range chunks1 {
			if chunks1[i].Hash != chunks2[i].Hash {
				t.Errorf("chunk %d: different hashes", i)
			}
			if chunks1[i].Size != chunks2[i].Size {
				t.Errorf("chunk %d: different sizes", i)
			}
		}
	})
}

func TestChunkBoundaries(t *testing.T) {
	chunker := NewChunker(256 * 1024) // 256KB average

	// FastCDC uses avg/4 for min and avg*4 for max
	avgSize := int64(256 * 1024)
	minSize := avgSize / 4
	maxSize := avgSize * 4

	// Test that minimum chunk size is respected
	data := make([]byte, minSize+1024)
	if _, err := rand.Read(data); err != nil {
		t.Fatalf("failed to generate random data: %v", err)
	}

	chunks, err := chunker.ChunkReader(bytes.NewReader(data))
	if err != nil {
		t.Fatalf("chunking failed: %v", err)
	}

	for i, chunk := range chunks {
		// Last chunk can be smaller than minimum
		if i < len(chunks)-1 && chunk.Size < minSize {
			t.Errorf("chunk %d size %d is below minimum %d", i, chunk.Size, minSize)
		}
		if chunk.Size > maxSize {
			t.Errorf("chunk %d size %d exceeds maximum %d", i, chunk.Size, maxSize)
		}
	}
}