Accidentally re-added caching_paged_reader

2025-06-07 03:13:33 -05:00
parent ea1b9f20cb
commit a829f0df9f
1 changed files with 0 additions and 72 deletions
@@ -1,72 +0,0 @@
 package squashfslow
 import (
 	"errors"
 	"math"
 )
 var errOutOfBounds = errors.New("out of bounds")
 var errUnexpectedOutOfBounds = errors.New("unexpected out of bounds")
 var errNilCollection = errors.New("nil collection")
 // readPagedItems calls readBLockOrPartial the correct number of times to cache
 // requestedItemIndex in currentItems, and then returns currentItems[requestedItemIndex].
 // Parameters:
 // - requestedItemIndex: The index of the item to be retrieved.
 // - blockSize: The number of items per block.
 // - currentItems: A slice of already-read items to manage in-memory storage. Must not be nil.
 // - readBlockOrPartial: A callback function that reads the next block. It takes the index of the block
 // to be read, and the number of items to read. It is normally passed block size, but if the last
 // block is incomplete, it will be passed the number of items in the last block.
 // Returns:
 //   - the T at requestedItemIndex
 //   - a non-nil error and the zero value of T if an error was encountered.
 func readPagedItems[T any](
 	requestedItemIndex int,
 	blockSize int,
 	currentItems *[]T,
 	totalItems int,
 	readBlockOrPartial func(idxBlock, numItems int) ([]T, error),
 ) (T, error) {
 	var zero T // Zero value for the item type, used for default return in error cases.
 	if currentItems == nil {
 		return zero, errNilCollection
 	}
 	if requestedItemIndex < 0 || requestedItemIndex >= totalItems {
 		return zero, errOutOfBounds
 	}
 	if len(*currentItems) > requestedItemIndex {
 		return (*currentItems)[requestedItemIndex], nil
 	}
 	// Calculate which block contains the requested item
 	blockNum := int(math.Ceil(float64(requestedItemIndex+1)/float64(blockSize))) - 1
 	// Calculate blocks to read
 	blocksRead := len(*currentItems) / blockSize
 	blocksToRead := blockNum - blocksRead + 1
 	// Read and append new blocks
 	for i := 0; i < blocksToRead; i++ {
 		startBlock := blocksRead + i
 		itemsLeft := totalItems - len(*currentItems)
 		itemsToRead := blockSize
 		if itemsToRead > itemsLeft {
 			itemsToRead = itemsLeft
 		}
 		items, err := readBlockOrPartial(startBlock, itemsToRead)
 		if err != nil {
 			return zero, err
 		}
 		*currentItems = append(*currentItems, items...)
 	}
 	// Ensure the slice contains the requested index after reading
 	if len(*currentItems) <= requestedItemIndex {
 		return zero, errUnexpectedOutOfBounds
 	}
 	return (*currentItems)[requestedItemIndex], nil
 }