feat: implement Postgres table analyzer with column type querying and metadata retrieval

internal/app/etl/table_analyzers/mssql.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"database/sql"
 	"fmt"
+	"strings"
 	"time"
 
 	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/config"
@@ -20,11 +21,154 @@ func NewMssqlTableAnalyzer(db *sql.DB) etl.TableAnalyzer {
 	return &MssqlTableAnalyzer{db: db}
 }
 
+const mssqlColumnMetadataQuery string = `
+SELECT 
+	c.name AS name,
+	t.name AS user_type,
+	CASE WHEN t.is_user_defined = 0 THEN t.name ELSE bt.name END AS system_type,
+	c.is_nullable AS nullable,
+	c.max_length AS max_length,
+	c.precision AS precision,
+	c.scale AS scale
+FROM sys.columns c
+JOIN sys.types t ON c.user_type_id = t.user_type_id
+LEFT JOIN sys.types bt ON t.is_user_defined = 1 AND bt.user_type_id = t.system_type_id
+JOIN sys.tables st ON c.object_id = st.object_id
+JOIN sys.schemas s ON st.schema_id = s.schema_id
+WHERE s.name = @schema AND st.name = @table
+ORDER BY c.column_id;`
+
+type rawColumnMssql struct {
+	name       string
+	userType   string
+	systemType string
+	nullable   bool
+	maxLength  int64
+	precision  int64
+	scale      int64
+}
+
+func (ta *MssqlTableAnalyzer) 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 *MssqlTableAnalyzer) rawColumnToColumnType(rawColumn rawColumnMssql) models.ColumnType {
+	const nullValue int64 = -1
+	stringTypes := map[string]bool{"varchar": true, "char": true, "nvarchar": true, "nchar": true, "text": true, "ntext": true}
+	decimalTypes := map[string]bool{"decimal": true, "numeric": true}
+
+	if stringTypes[rawColumn.systemType] {
+		if rawColumn.systemType == "nvarchar" || rawColumn.systemType == "nchar" {
+			if rawColumn.maxLength > 0 {
+				rawColumn.maxLength = rawColumn.maxLength / 2
+			}
+		}
+
+		rawColumn.precision, rawColumn.scale = nullValue, nullValue
+	} else if decimalTypes[rawColumn.systemType] {
+		rawColumn.maxLength = nullValue
+	} else {
+		rawColumn.maxLength, rawColumn.precision, rawColumn.scale = nullValue, nullValue, nullValue
+	}
+
+	columnType := 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,
+	)
+
+	return columnType
+}
+
 func (ta *MssqlTableAnalyzer) QueryColumnTypes(
 	ctx context.Context,
 	tableInfo config.TableInfo,
 ) ([]models.ColumnType, error) {
-	return []models.ColumnType{}, nil
+	localCtx, cancel := context.WithTimeout(ctx, 20*time.Second)
+	defer cancel()
+
+	rows, err := ta.db.QueryContext(localCtx, mssqlColumnMetadataQuery, sql.Named("schema", tableInfo.Schema), sql.Named("table", tableInfo.Table))
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	var columnTypes []models.ColumnType
+
+	for rows.Next() {
+		var rawColumn rawColumnMssql
+
+		if err := rows.Scan(
+			&rawColumn.name,
+			&rawColumn.userType,
+			&rawColumn.systemType,
+			&rawColumn.nullable,
+			&rawColumn.maxLength,
+			&rawColumn.precision,
+			&rawColumn.scale,
+		); err != nil {
+			return nil, err
+		}
+
+		columnTypes = append(columnTypes, ta.rawColumnToColumnType(rawColumn))
+	}
+
+	return columnTypes, nil
 }
 
 func (ta *MssqlTableAnalyzer) EstimateTotalRows(