feat: added functionality for insert and select

internals/vm/vm.go

@@ -1,6 +1,7 @@
 package vm
 
 import (
+	"encoding/binary"
 	"fmt"
 	"os"
 	"strings"
@@ -30,6 +31,29 @@ const (
 	StatementInsert
 )
 
+const (
+	idSize       = 8
+	usernameSize = 32
+	emailSize    = 255
+
+	idOffset       = 0
+	usernameOffset = idOffset + idSize
+	emailOffset    = usernameOffset + usernameSize
+
+	pageSize    = 4096
+	maxPages    = 100
+	rowSize     = idSize + usernameSize + emailSize
+	rowsPerPage = pageSize / rowSize
+	maxRows     = rowsPerPage * maxPages
+)
+
+type ExecuteResult int
+
+const (
+	ExecuteSuccess ExecuteResult = iota
+	ExecuteTableFull
+)
+
 type row struct {
 	id       uint
 	username string
@@ -41,11 +65,6 @@ type Statement struct {
 	row   row
 }
 
-const (
-	_pageSize = 4096
-	maxPages  = 100
-)
-
 type Table struct {
 	numOfRows uint
 	pages     [maxPages]any
@@ -63,6 +82,61 @@ func NewTable() *Table {
 	return &newTable
 }
 
+func rowToUse(table *Table, rowNo uint) []byte {
+	pageNo := rowNo / rowsPerPage
+	var page []byte
+	if table.pages[pageNo] == nil {
+		page = make([]byte, pageSize)
+		table.pages[pageNo] = page
+	} else {
+		i := table.pages[pageNo]
+		if t, ok := i.([]byte); !ok {
+			page = []byte(t)
+		} else {
+			page = t
+		}
+	}
+	rowOffset := rowNo % rowsPerPage
+	byteOffset := rowOffset * rowSize
+	return page[byteOffset : byteOffset+rowSize]
+}
+
+func (row *row) seralizeRow(page []byte) {
+	binary.NativeEndian.PutUint64(page[idOffset:], uint64(row.id))
+
+	usernameBuff := page[usernameOffset : usernameOffset+usernameSize]
+	clear(usernameBuff)
+	copy(usernameBuff, row.username)
+
+	emailBuff := page[emailOffset : emailOffset+emailSize]
+	clear(emailBuff)
+	copy(emailBuff, row.email)
+}
+
+func (row *row) deSeralizeRow(page []byte) {
+	row.id = uint(binary.NativeEndian.Uint64(page[idOffset:idSize]))
+	row.username = string(page[usernameOffset : usernameOffset+usernameSize])
+	row.email = string(page[emailOffset : emailOffset+emailSize])
+}
+
+func (statement *Statement) execInsert(table *Table) ExecuteResult {
+	if table.numOfRows >= maxRows {
+		return ExecuteTableFull
+	}
+	statement.row.seralizeRow(rowToUse(table, table.numOfRows))
+	table.numOfRows += 1
+	return ExecuteSuccess
+}
+
+func (statement *Statement) execSelect(table *Table) ExecuteResult {
+	var row row
+	for i := range table.numOfRows {
+		row.deSeralizeRow(rowToUse(table, i))
+		fmt.Printf("%v\n", row)
+	}
+	return ExecuteSuccess
+}
+
 func DoMetaCommands(inputBuffer *InputBuffer) MetaCommandResults {
 	metacommand := MetaCommandUnrecognised
 	if inputBuffer.Buffer == ".exit" {
@@ -94,11 +168,13 @@ func (statement *Statement) PrepareStatements(inputBuffer *InputBuffer) PrepareR
 	return PrepareUnrecognised
 }
 
-func (statement *Statement) ExecuteStatement(table *Table) {
+func (statement *Statement) ExecuteStatement(table *Table) ExecuteResult {
+	var result ExecuteResult
 	switch statement.stype {
 	case StatementInsert:
-		fmt.Println("This is where the logic of insert statement should go")
+		result = statement.execInsert(table)
 	case StatementSelect:
-		fmt.Println("This is where the logic of select statement should go")
+		result = statement.execSelect(table)
 	}
+	return result
 }