Source File
	parquet.go

Belonging Package
	github.com/polarsignals/iceberg-go

package iceberg

import (
	"encoding/binary"
	"fmt"
	"io"

	"github.com/parquet-go/parquet-go"
)

func ManifestEntryV1FromParquet(path string, size int64, schema *Schema, r io.ReaderAt) (ManifestEntry, *Schema, error) {
	df, schema, err := DataFileFromParquet(path, size, schema, r)
	if err != nil {
		return nil, nil, err
	}

	return NewManifestEntryV1(EntryStatusADDED, size, df), schema, nil
}

func DataFileFromParquet(path string, size int64, schema *Schema, r io.ReaderAt) (DataFile, *Schema, error) {
	f, err := parquet.OpenFile(r, size)
	if err != nil {
		return nil, nil, err
	}
	latestSchema, err := schema.Merge(parquetSchemaToIcebergSchema(-1, f.Schema()))
	if err != nil {
		return nil, nil, err
	}

	bldr := NewDataFileV1Builder(
		path,
		ParquetFile,
		map[string]any{}, // TODO: At present Parquet writes are assumed to be unpartitioned.
		f.NumRows(),
		size,
	)

	// Create the upper and lower bounds for each column.
	numColumns := latestSchema.NumFields()
	upper, lower := make(map[int][]byte, numColumns), make(map[int][]byte, numColumns)
	for i := 0; i < numColumns; i++ {
		// Check if this columns exists in the parquet file. If it does add the upper and lower bounds.
		// If it doesn't exist, then the bounds will be nil.
		col, ok := f.Schema().Lookup(latestSchema.Fields()[i].Name)
		if ok {
			upper[i] = maxColValue(col.ColumnIndex, f)
			lower[i] = minColValue(col.ColumnIndex, f)
		}
	}

	bldr.WithLowerBounds(lower)
	bldr.WithUpperBounds(upper)
	bldr.WithColumnSizes(colSizes(f))

	// Create the schema.
	return bldr.Build(), latestSchema, nil
}

func colSizes(f *parquet.File) map[int]int64 {
	sizes := make(map[int]int64, len(f.Metadata().RowGroups[0].Columns))
	for _, rg := range f.Metadata().RowGroups {
		for i, chunk := range rg.Columns {
			sizes[i] += chunk.MetaData.TotalUncompressedSize
		}
	}
	return sizes
}

// maxColValue returns the maximum value of a column in a parquet file.
func maxColValue(col int, r *parquet.File) []byte {
	var maxval parquet.Value
	for _, rg := range r.RowGroups() {
		index, err := rg.ColumnChunks()[col].ColumnIndex()
		if err != nil {
			return nil
		}

		for j := 0; j < index.NumPages(); j++ {
			v := index.MaxValue(j)
			if maxval.IsNull() {
				maxval = v
				continue
			}

			if compare(maxval, v) == -1 {
				maxval = v
			}
		}
	}

	// Create the byte representation of the max value.
	return binarySingleValueSerialize(maxval)
}

// https://iceberg.apache.org/spec/#appendix-d-single-value-serialization
func binarySingleValueSerialize(v parquet.Value) []byte {
	if v.IsNull() {
		return nil
	}

	switch v.Kind() {
	case parquet.ByteArray:
		return v.Bytes()
	case parquet.FixedLenByteArray:
		return v.Bytes()
	case parquet.Double:
		b := make([]byte, 8)
		binary.LittleEndian.PutUint64(b, uint64(v.Double()))
		return b
	case parquet.Int64:
		b := make([]byte, 8)
		binary.LittleEndian.PutUint64(b, uint64(v.Int64()))
		return b
	case parquet.Int32:
		b := make([]byte, 4)
		binary.LittleEndian.PutUint32(b, uint32(v.Int32()))
		return b
	case parquet.Float:
		b := make([]byte, 4)
		binary.LittleEndian.PutUint32(b, uint32(v.Float()))
		return b
	case parquet.Boolean:
		switch v.Boolean() {
		case true:
			return []byte{1}
		default:
			return []byte{0}
		}
	default:
		panic(fmt.Sprintf("unsupported value comparison: %v", v.Kind()))
	}
}

// minColValue returns the minimum value of a column in a parquet file.
func minColValue(col int, r *parquet.File) []byte {
	var minval parquet.Value
	for _, rg := range r.RowGroups() {
		index, err := rg.ColumnChunks()[col].ColumnIndex()
		if err != nil {
			return nil
		}

		for j := 0; j < index.NumPages(); j++ {
			v := index.MinValue(j)
			if minval.IsNull() {
				minval = v
				continue
			}

			if compare(minval, v) == 1 {
				minval = v
			}
		}
	}

	// Create the byte representation of the min value.
	return binarySingleValueSerialize(minval)
}

// compares two parquet values. 0 if they are equal, -1 if v1 < v2, 1 if v1 > v2.
func compare(v1, v2 parquet.Value) int {
	switch v1.Kind() {
	case parquet.Int32:
		return parquet.Int32Type.Compare(v1, v2)
	case parquet.Int64:
		return parquet.Int64Type.Compare(v1, v2)
	case parquet.Float:
		return parquet.FloatType.Compare(v1, v2)
	case parquet.Double:
		return parquet.DoubleType.Compare(v1, v2)
	case parquet.ByteArray, parquet.FixedLenByteArray:
		return parquet.ByteArrayType.Compare(v1, v2)
	case parquet.Boolean:
		return parquet.BooleanType.Compare(v1, v2)
	default:
		panic(fmt.Sprintf("unsupported value comparison: %v", v1.Kind()))
	}
}

func parquetSchemaToIcebergSchema(id int, schema *parquet.Schema) *Schema {
	fields := make([]NestedField, 0, len(schema.Fields()))
	for i, f := range schema.Fields() {
		fields = append(fields, NestedField{
			Type:     parquetTypeToIcebergType(f.Type()),
			ID:       i,
			Name:     f.Name(),
			Required: f.Required(),
		})
	}
	return NewSchema(id, fields...)
}

func parquetTypeToIcebergType(t parquet.Type) Type {
	switch t.Kind() {
	case parquet.Boolean:
		return BooleanType{}
	case parquet.Int32:
		return Int32Type{}
	case parquet.Int64:
		return Int64Type{}
	case parquet.Float:
		return Float32Type{}
	case parquet.Double:
		return Float64Type{}
	case parquet.ByteArray:
		return BinaryType{}
	default:
		panic(fmt.Sprintf("unsupported parquet type: %v", t.Kind()))
	}
}

The pages are generated with Golds v0.8.2. (GOOS=linux GOARCH=amd64)
Golds is a Go 101 project developed by Tapir Liu.
PR and bug reports are welcome and can be submitted to the issue list.
Please follow @zigo_101 (reachable from the left QR code) to get the latest news of Golds.