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splotch.go
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splotch.go
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package inkdb
import (
"encoding/gob"
"errors"
"fmt"
"io"
"os"
)
// this is kept as a variable instead of a constant for the sake of testing. Benchmarks scale each splotch larger than I might otherwise want.
var MaxRowsPerSplotch int = 65535 //2^16-1
// all of the item at the top of the file.
type fileHeadings struct {
LargestKey SplotchKey
LinesStored int
}
// this is per folder. Holds all of the stored items, as well as their values. Can be generated from a file.
type inkSplotch struct {
fileLocation string //what file is this stored in
storedItems []*storedItem
smallestKey SplotchKey //the smallest key added to this
headings fileHeadings
unsavedItems []*storedItem
hasFullyLoaded bool
}
func NewInkSplotch(fileLocation string) (*inkSplotch, error) {
splotch := &inkSplotch{
fileLocation: fileLocation,
}
//check that the file already exists.
if _, err := os.Stat(fileLocation); errors.Is(err, os.ErrNotExist) {
// it doesn't exist.
return splotch, splotch.SaveToFile()
} else if err == nil {
//file already exists. So we will try to load from it
return splotch, splotch.PartialLoad()
} else {
//some unknown error occurred
return nil, err
}
}
// checks if it still has space for more items to be added.
func (splotch *inkSplotch) IsFull() bool {
return splotch.headings.LinesStored >= MaxRowsPerSplotch
}
// get the smallest and largest end currently stored
func (splotch *inkSplotch) GetEnds() (smallest, largest SplotchKey) {
return splotch.smallestKey, splotch.headings.LargestKey
}
// take data, automatically create a key for it, and stores the data.
func (splotch *inkSplotch) AutoAppend(value []byte) error {
if splotch.headings.LinesStored == MaxRowsPerSplotch {
return ErrSplotchFull
}
newKey := splotch.headings.LargestKey.NextKey()
splotch.headings.LargestKey = newKey
fullData := storedItem{
Key: newKey,
Value: value,
}
splotch.unsavedItems = append(splotch.unsavedItems, &fullData)
splotch.storedItems = append(splotch.storedItems, &fullData)
splotch.headings.LinesStored++
if splotch.headings.LinesStored == 1 {
splotch.smallestKey = newKey
}
return nil
}
// takes a data key pair, and attempts to store it by that key. More prone to errors than AutoAppend
func (splotch *inkSplotch) Append(fullData storedItem) error {
if splotch.IsFull() {
return ErrSplotchFull
}
if splotch.headings.LargestKey.GreaterOrEqual(fullData.Key) {
return ErrSplotchRangeExceeded
}
splotch.headings.LargestKey = fullData.Key
splotch.unsavedItems = append(splotch.unsavedItems, &fullData)
splotch.storedItems = append(splotch.storedItems, &fullData)
splotch.headings.LinesStored++
if splotch.headings.LinesStored == 1 {
splotch.smallestKey = fullData.Key
}
return nil
}
// get a vale based on the key. Returns nil if none are found.
func (splotch *inkSplotch) Get(by SplotchKey) ([]byte, error) {
found, err := splotch.GetStoredItem(by)
return found.Value, err
}
// gets the stored item (key and value) from the storage.
func (splotch *inkSplotch) GetStoredItem(by SplotchKey) (storedItem, error) {
if by.GreaterThan(splotch.headings.LargestKey) || by.LessThan(splotch.smallestKey) {
return storedItem{}, ErrSplotchRangeExceeded
}
if !splotch.hasFullyLoaded {
if err := splotch.FullyLoad(); err != nil {
return storedItem{}, err
}
}
//it should be in here. So lets write a bit of a binary search function
found, err := splotch.SearchFor(func(a storedItem) bool {
return by.LessThan(a.Key)
}, func(a storedItem) bool {
return by.Equal(a.Key)
})
return found, err
}
// search for the given data based on the functions LessThan, and Equal.
func (splotch *inkSplotch) SearchFor(lessThan func(storedItem) bool, equal func(storedItem) bool) (storedItem, error) {
if splotch.headings.LinesStored == 0 {
//checks if it is empty. If it is, it cannot have anything.
return storedItem{}, ErrSplotchRangeExceeded
}
zeroVal := *splotch.storedItems[0]
lastVal := *splotch.storedItems[len(splotch.storedItems)-1]
//the edges can cause errors, so we check them right away
if equal(zeroVal) {
return zeroVal, nil
}
if equal(lastVal) {
return lastVal, nil
}
if lessThan(zeroVal) ||
!lessThan(lastVal) {
//its outside of our range. because its not the first or last one, and it's larger than the last(largest) one, and smaller than the first(smallest) one.
return storedItem{}, ErrSplotchRangeExceeded
}
//it should be within here.
index := BinarySearch(splotch.storedItems,
func(item *storedItem) bool {
return lessThan(*item)
},
func(item *storedItem) bool {
return equal(*item)
},
)
if index == -1 {
return storedItem{}, fmt.Errorf("within range, but item not found")
}
//then we've found it.
return *splotch.storedItems[index], nil
}
// loads only the required elements for basic operations.
func (splotch *inkSplotch) PartialLoad() error {
if _, err := os.Stat(splotch.fileLocation); err != nil {
//the file does not exist
return err
}
//if the file already exists, if it does, load this data. if not, create a new blank file for it.
f, err := os.OpenFile(splotch.fileLocation, os.O_RDONLY, 0666)
if err != nil {
return err
}
dec := gob.NewDecoder(f)
if err := dec.Decode(&splotch.headings); err != nil {
return err
}
var smallest storedItem
err = dec.Decode(&smallest)
if err == io.EOF {
//then there is no smallest yet, and we can return
return nil
}
if err != nil {
//a catch case for any other errors
return err
}
splotch.smallestKey = smallest.Key
splotch.storedItems = []*storedItem{&smallest}
//the file should consist of the largest key. Then line by line each item.
//then that data should be put into splotch
return nil
}
// loads all of the data from disc into memory.
func (splotch *inkSplotch) FullyLoad() error {
if _, err := os.Stat(splotch.fileLocation); err != nil {
//the file does not exist
return err
}
//if the file already exists, if it does, load this data. if not, create a new blank file for it.
f, err := os.OpenFile(splotch.fileLocation, os.O_RDONLY, 0666) //TODO: fix the permissions to be closer to what we need...
if err != nil {
return err
}
dec := gob.NewDecoder(f)
if err := dec.Decode(&splotch.headings); err != nil {
return err
}
splotch.storedItems = []*storedItem{}
for {
var nextValue storedItem
err := dec.Decode(&nextValue)
if err == io.EOF {
//we've read every item from the file.
break
}
if err != nil {
//we've hit an unexpected error
return err
}
splotch.storedItems = append(splotch.storedItems, &nextValue)
}
//we now need to re-append all of the added values we already had (if any), and update the largest value in the header again.
splotch.storedItems = append(splotch.storedItems, splotch.unsavedItems...)
if len(splotch.unsavedItems) != 0 {
splotch.headings.LargestKey = splotch.storedItems[len(splotch.storedItems)-1].Key
}
splotch.hasFullyLoaded = true
return nil
}
// saves any changes from memory to the disc.
func (splotch *inkSplotch) SaveToFile() error {
//first, we write the largest value we've found so far.
f, err := os.OpenFile(splotch.fileLocation, os.O_CREATE|os.O_WRONLY, 0644)
if err != nil {
return err
}
enc := gob.NewEncoder(f)
if err := enc.Encode(&splotch.headings); err != nil {
return err
}
_, err = f.Seek(0, 2) //go to the end of the file
if err != nil {
return err
}
for _, item := range splotch.unsavedItems {
if err := enc.Encode(&item); err != nil {
return err
}
}
splotch.unsavedItems = []*storedItem{}
return f.Close()
}
// get all of the storedItems from <from>, to <to>
func (splotch *inkSplotch) GetAll(from, to SplotchKey) ([]storedItem, error) {
if from.GreaterThan(splotch.headings.LargestKey) || to.LessThan(splotch.smallestKey) {
//outside our range, no need to care.
return nil, ErrSplotchRangeExceeded
}
if !splotch.hasFullyLoaded {
if err := splotch.FullyLoad(); err != nil {
return nil, err
}
}
//this can be sped up by checking first if the range would fully contain this, start within but go on, start outside but finish within, or if it is fully contained, and handle it from there.
//if this is fully contained, then just return all items.
//if it just starts/stops here, find that point, and take the rest.
//if it's contained within this, find the start and end, and return that portion.
startIndex := 0
if from.GreaterThan(splotch.smallestKey) {
//it starts somewhere within us.
startIndex = BinarySearch(splotch.storedItems, func(item *storedItem) bool {
return item.Key.GreaterThan(from)
},
func(item *storedItem) bool {
return item.Key.Equal(from)
},
)
}
endIndex := len(splotch.storedItems) - 1
if to.LessThan(splotch.headings.LargestKey) {
//it ends within us.
endIndex = BinarySearch(splotch.storedItems, func(item *storedItem) bool {
return item.Key.GreaterThan(to)
},
func(item *storedItem) bool {
return item.Key.Equal(to)
},
)
}
foundItems := make([]storedItem, 0, endIndex-startIndex)
for i := startIndex; i <= endIndex; i++ {
//just do the iteration so we can convert the type
foundItems = append(foundItems, *splotch.storedItems[i])
}
return foundItems, nil
}