go-migrate-db/internal/app/etl/table_analyzers/postgres.go

package table_analyzers

import (
	"context"
	"strings"
	"time"

	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/config"
	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/etl"
	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/models"
	"github.com/jackc/pgx/v5/pgxpool"
)

type PostgresTableAnalyzer struct {
	db *pgxpool.Pool
}

func NewPostgresTableAnalyzer(db *pgxpool.Pool) etl.TableAnalyzer {
	return &PostgresTableAnalyzer{db: db}
}

const postgresColumnMetadataQuery string = `
SELECT 
  c.column_name AS name,
  c.data_type AS user_type,
  c.udt_name AS system_type,
  (CASE WHEN c.is_nullable = 'YES' THEN TRUE ELSE FALSE END) AS nullable,
  COALESCE(c.character_maximum_length, -1) AS max_length,
  COALESCE(c.numeric_precision, -1) AS precision,
  COALESCE(c.numeric_scale, -1) AS scale
FROM information_schema.columns c
WHERE c.table_schema = $1 AND c.table_name = $2
ORDER BY c.ordinal_position;`

type rawColumnPostgres struct {
	name       string
	userType   string
	systemType string
	nullable   bool
	maxLength  int64
	precision  int64
	scale      int64
}

func (ta *PostgresTableAnalyzer) systemTypeToUnifiedType(systemType string) string {
	systemType = strings.ToLower(systemType)

	if systemType == "varchar" || systemType == "char" || systemType == "nvarchar" || systemType == "nchar" || systemType == "text" || systemType == "ntext" {
		return "STRING"
	}

	if systemType == "int" || systemType == "int4" || systemType == "integer" || systemType == "smallint" || systemType == "int2" || systemType == "bigint" || systemType == "int8" || systemType == "tinyint" {
		return "INTEGER"
	}

	if systemType == "decimal" || systemType == "numeric" {
		return "DECIMAL"
	}

	if systemType == "float" || systemType == "real" || systemType == "double precision" {
		return "FLOAT"
	}

	if systemType == "bit" || systemType == "boolean" {
		return "BOOLEAN"
	}

	if systemType == "date" {
		return "DATE"
	}
	if systemType == "time" || systemType == "time without time zone" {
		return "TIME"
	}
	if systemType == "datetime" || systemType == "datetime2" || systemType == "timestamp" || systemType == "timestamptz" || systemType == "timestamp with time zone" {
		return "TIMESTAMP"
	}

	if systemType == "binary" || systemType == "varbinary" || systemType == "image" || systemType == "bytea" {
		return "BINARY"
	}

	if systemType == "uniqueidentifier" || systemType == "uuid" {
		return "UUID"
	}

	if systemType == "json" {
		return "JSON"
	}

	if systemType == "geometry" || systemType == "geography" {
		return "GEOMETRY"
	}

	return strings.ToUpper(systemType)
}

func (ta *PostgresTableAnalyzer) rawColumnToColumnType(rawColumn rawColumnPostgres) models.ColumnType {
	const nullValue int64 = -1
	stringTypes := map[string]bool{"varchar": true, "char": true, "text": true}
	decimalTypes := map[string]bool{"decimal": true, "numeric": true}

	if stringTypes[rawColumn.systemType] {
		rawColumn.precision, rawColumn.scale = nullValue, nullValue
	} else if decimalTypes[rawColumn.systemType] {
		rawColumn.maxLength = nullValue
	} else {
		rawColumn.maxLength, rawColumn.precision, rawColumn.scale = nullValue, nullValue, nullValue
	}

	return models.NewColumnType(
		rawColumn.name,
		rawColumn.maxLength != nullValue,
		rawColumn.precision != nullValue || rawColumn.scale != nullValue,
		rawColumn.userType,
		rawColumn.systemType,
		ta.systemTypeToUnifiedType(rawColumn.systemType),
		rawColumn.nullable,
		rawColumn.maxLength,
		rawColumn.precision,
		rawColumn.scale,
	)
}

func (ta *PostgresTableAnalyzer) QueryColumnTypes(
	ctx context.Context,
	tableInfo config.TableInfo,
) ([]models.ColumnType, error) {
	localCtx, cancel := context.WithTimeout(ctx, 20*time.Second)
	defer cancel()

	rows, err := ta.db.Query(localCtx, postgresColumnMetadataQuery, tableInfo.Schema, tableInfo.Table)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var colTypes []models.ColumnType

	for rows.Next() {
		var column rawColumnPostgres

		if err := rows.Scan(
			&column.name,
			&column.userType,
			&column.systemType,
			&column.nullable,
			&column.maxLength,
			&column.precision,
			&column.scale,
		); err != nil {
			return nil, err
		}

		colTypes = append(colTypes, ta.rawColumnToColumnType(column))
	}

	return colTypes, nil
}

func (ta *PostgresTableAnalyzer) EstimateTotalRows(
	ctx context.Context,
	tableInfo config.TableInfo,
) (int64, error) {
	return 0, nil
}

func (ta *PostgresTableAnalyzer) CalculatePartitionRanges(
	ctx context.Context,
	tableInfo config.TableInfo,
	partitionColumn string,
	maxPartitions int64,
) ([]models.Partition, error) {
	return []models.Partition{}, nil
}