// vfs/gc/gc.go
package gc

import (
	"fmt"
	"io"
	"s1d3sw1ped/SteamCache2/vfs"
	"s1d3sw1ped/SteamCache2/vfs/vfserror"
)

// Ensure GCFS implements VFS.
var _ vfs.VFS = (*GCFS)(nil)

// GCFS is a virtual file system that calls a GC handler when the disk is full. The GC handler is responsible for freeing up space on the disk. The GCFS is a wrapper around another VFS.
type GCFS struct {
	vfs.VFS
	multiplier int

	// protected by mu
	gcHanderFunc GCHandlerFunc
}

// GCHandlerFunc is a function that is called when the disk is full and the GCFS needs to free up space. It is passed the VFS and the size of the file that needs to be written. Its up to the implementation to free up space. How much space is freed is also up to the implementation.
type GCHandlerFunc func(vfs vfs.VFS, size uint)

func New(vfs vfs.VFS, multiplier int, gcHandlerFunc GCHandlerFunc) *GCFS {
	if multiplier <= 0 {
		multiplier = 1 // if the multiplier is less than or equal to 0 set it to 1 will be slow but the user can set it to a higher value if they want
	}
	return &GCFS{
		VFS:          vfs,
		multiplier:   multiplier,
		gcHanderFunc: gcHandlerFunc,
	}
}

// Create overrides the Create method of the VFS interface. It tries to create the key, if it fails due to disk full error, it calls the GC handler and tries again. If it still fails it returns the error.
func (g *GCFS) Create(key string, size int64) (io.WriteCloser, error) {
	w, err := g.VFS.Create(key, size) // try to create the key

	// if it fails due to disk full error, call the GC handler and try again in a loop that will continue until it succeeds or the error is not disk full
	for err == vfserror.ErrDiskFull && g.gcHanderFunc != nil { // if the error is disk full and there is a GC handler
		g.gcHanderFunc(g.VFS, uint(size*int64(g.multiplier))) // call the GC handler
		w, err = g.VFS.Create(key, size)
	}

	return w, err
}

func (g *GCFS) Name() string {
	return fmt.Sprintf("GCFS(%s)", g.VFS.Name()) // wrap the name of the VFS with GCFS so we can see that its a GCFS
}