From a35d6b836a3b2b4f6c4ddd34bed2a05942157b05 Mon Sep 17 00:00:00 2001
From: zutto <zutto@localdomain.localtld>
Date: Sat, 16 Apr 2022 23:10:49 +0300
Subject: [PATCH] init headers

---
 pkg/headers/headers.go      | 69 +++++++++++++++++++++++++++++++++++++
 pkg/headers/headers_test.go | 33 ++++++++++++++++++
 pkg/headers/helper.go       | 35 +++++++++++++++++++
 3 files changed, 137 insertions(+)
 create mode 100644 pkg/headers/headers.go
 create mode 100644 pkg/headers/headers_test.go
 create mode 100644 pkg/headers/helper.go

diff --git a/pkg/headers/headers.go b/pkg/headers/headers.go
new file mode 100644
index 0000000..b25ecbe
--- /dev/null
+++ b/pkg/headers/headers.go
@@ -0,0 +1,69 @@
+// Package headers provides headers for the db binary files
+package headers
+
+import (
+	"encoding/binary"
+	"errors"
+)
+
+type Headers struct {
+	HeaderString []byte // Header string
+	PageSize     uint64 // Page size for chunks
+	DBVersion    uint16 // Version of the db
+
+	// Reserved for future use.
+	WAL    bool   // Enable write-ahead-logging
+	Commit []byte // SHA256 sum of the current DB - Could be switched to ULID/UUID in future.
+}
+
+// constant HeaderString
+const HeaderString = "zutto/db/"
+
+//Commit data length - mapped to be 32 bytes for now, to match SHA256SUM
+const CommitDataLength = 32
+
+// Static lengths of the headers HeaderString length(uint16, 2 bytes)- Pagesize (uint64, 8 bytes) + DBVersion (int16, 2 bytes) + WAL (int8//bool, 1 byte) + Commit (SHA256 32 bytes)
+const StaticHeadersLength = 13 + CommitDataLength
+
+// Generate generates []byte output from the headers
+func (h *Headers) Generate() *[]byte {
+	var HeaderStringLength int = len(h.HeaderString)
+
+	//Output array
+	var data []byte = make([]byte, HeaderStringLength+StaticHeadersLength)
+
+	//Headerstring
+	binary.LittleEndian.PutUint16(data[0:2], uint16(HeaderStringLength))
+	copy(data[2:2+HeaderStringLength], h.HeaderString[:])
+
+	//add the simpler metadata
+	binary.LittleEndian.PutUint64(data[2+HeaderStringLength:10+HeaderStringLength], h.PageSize)
+	binary.LittleEndian.PutUint16(data[10+HeaderStringLength:12+HeaderStringLength], h.DBVersion)
+
+	//Convert bool-value to byte with a helper function true = byte(1), false = byte(0)
+	data[12+HeaderStringLength] = ToSingleByte(h.WAL)
+
+	//commit data, extr
+	copy(data[13+HeaderStringLength:13+CommitDataLength+HeaderStringLength], h.Commit[0:CommitDataLength])
+
+	return &data
+}
+
+// Parse parses the headers
+// Accepts 2 parameters, Input *[]byte's and Padding
+// Returns error in case of errors.
+func (h *Headers) Parse(Input *[]byte, Padding int) error {
+	if Padding+len((*Input)) < StaticHeadersLength {
+		return errors.New("Input was not correct length")
+	}
+
+	var HeaderStringLength int = int(binary.LittleEndian.Uint16((*Input)[Padding : Padding+2]))
+	h.HeaderString = (*Input)[2+Padding : Padding+2+HeaderStringLength]
+	h.PageSize = binary.LittleEndian.Uint64((*Input)[2+HeaderStringLength+Padding : Padding+10+HeaderStringLength])
+	h.DBVersion = binary.LittleEndian.Uint16((*Input)[10+HeaderStringLength+Padding : Padding+12+HeaderStringLength])
+
+	h.WAL = ByteToBool((*Input)[12+HeaderStringLength])
+	h.Commit = ((*Input)[13+HeaderStringLength+Padding : Padding+13+CommitDataLength+HeaderStringLength])
+
+	return nil
+}
diff --git a/pkg/headers/headers_test.go b/pkg/headers/headers_test.go
new file mode 100644
index 0000000..097b2b1
--- /dev/null
+++ b/pkg/headers/headers_test.go
@@ -0,0 +1,33 @@
+package headers
+
+import (
+	"crypto/rand"
+	"reflect"
+	"testing"
+)
+
+func TestHeaders_Generate(t *testing.T) {
+
+	h := Headers{
+		HeaderString: []byte(HeaderString),
+		PageSize:     uint64(256 ^ 2),
+		DBVersion:    uint16(1),
+
+		WAL:    true,
+		Commit: make([]byte, CommitDataLength),
+	}
+
+	_, err := rand.Read(h.Commit[:CommitDataLength])
+	if err != nil {
+		t.Error("Failed to generate random string")
+	}
+
+	output := h.Generate()
+
+	h2 := Headers{}
+	h2.Parse(output, 0)
+
+	if !reflect.DeepEqual(h, h2) {
+		t.Error("deepequal failed")
+	}
+}
diff --git a/pkg/headers/helper.go b/pkg/headers/helper.go
new file mode 100644
index 0000000..e378650
--- /dev/null
+++ b/pkg/headers/helper.go
@@ -0,0 +1,35 @@
+package headers
+
+// ByteHelper provides helping functions to less-fun-types
+type SingleByteType interface {
+	bool | ~uint8
+}
+type BoolType interface {
+	bool
+}
+
+func ByteToBool(Input byte) bool {
+	if byte(1) == Input {
+		return true
+	}
+
+	return false
+}
+
+// ToSingleByte converts single-byte types, such as int8 and bool to single bytes.
+func ToSingleByte[T SingleByteType](input T) byte {
+	switch input := any(input).(type) {
+	case uint8:
+		return byte(input)
+	case int8:
+		return byte(input)
+	case bool:
+		if input {
+			return byte(1)
+		} else {
+			return byte(0)
+		}
+	default:
+		return byte(-0)
+	}
+}