package keyvalue

import (
	"sync"
	"sync/atomic"
	"time"

	"github.com/hack-pad/hackpadfs"
	"github.com/hack-pad/hackpadfs/keyvalue/blob"
)

// FileRecord represents a file inside a Store.
// A FileRecord's receivers may only be called once and their return values cached by the wrapping FS. Therefore, each receiver must return consistent values unless otherwise specified.
//
// NOTE: Does not require retrieving the file's name. The name can be stored separately to simplify your store.
type FileRecord interface {
	// Data returns the Blob representing a copy of this file's contents. Returns an error if file is a directory.
	Data() (blob.Blob, error)
	// ReadDir returns this file's directory entries. Returns an error if not a directory or failed during retrieval.
	ReadDirNames() ([]string, error)
	// Size returns the number of bytes in this file's contents.
	// May return the size at initial fetch time, rather than at call time.
	Size() int64
	// Mode returns this file's FileMode.
	Mode() hackpadfs.FileMode
	// ModTime returns this file's last modified time.
	ModTime() time.Time
	// Sys returns the underlying data source (can return nil)
	Sys() interface{}
}

var (
	_ FileRecord = &BaseFileRecord{}
)

// BaseFileRecord is a FileRecord with a convenient constructor for easier Store implementations.
type BaseFileRecord struct {
	modTime     time.Time
	sys         interface{}
	getData     func() (blob.Blob, error)
	getDirNames func() ([]string, error)
	initialSize int64
	mode        hackpadfs.FileMode
}

// NewBaseFileRecord returns a new BaseFileRecord for the given file's metadata and getters.
// getData and getDirNames may be set to nil if not applicable to this file's type.
//
// Initial size is the currently known byte size of the record. This value is used for optimized Stat() calls.
// Sys may be set to nil, it's returned as the result of FileInfo.Sys().
// 'getData' must return the contents of the file or an error if retrieval fails, but may be nil if this is a directory.
// 'getDirNames' must return this directory's child names, but may be nil if this is a regular file.
func NewBaseFileRecord(
	initialSize int64,
	modTime time.Time,
	mode hackpadfs.FileMode,
	sys interface{},
	getData func() (blob.Blob, error),
	getDirNames func() ([]string, error),
) *BaseFileRecord {
	return &BaseFileRecord{
		getData:     getData,
		getDirNames: getDirNames,

		initialSize: initialSize,
		modTime:     modTime,
		mode:        mode,
		sys:         sys,
	}
}

// Data implements keyvalue.FileRecord
func (b *BaseFileRecord) Data() (blob.Blob, error) {
	if b.getData == nil {
		if b.mode.IsDir() {
			return nil, hackpadfs.ErrIsDir
		}
		return nil, hackpadfs.ErrNotImplemented
	}
	return b.getData()
}

// ReadDirNames implements keyvalue.FileRecord
func (b *BaseFileRecord) ReadDirNames() ([]string, error) {
	if b.getDirNames == nil {
		if !b.mode.IsDir() {
			return nil, hackpadfs.ErrNotDir
		}
		return nil, hackpadfs.ErrNotImplemented
	}
	return b.getDirNames()
}

// Size implements keyvalue.FileRecord
func (b *BaseFileRecord) Size() int64 {
	return b.initialSize
}

// Mode implements keyvalue.FileRecord
func (b *BaseFileRecord) Mode() hackpadfs.FileMode {
	return b.mode
}

// ModTime implements keyvalue.FileRecord
func (b *BaseFileRecord) ModTime() time.Time {
	return b.modTime
}

// Sys implements keyvalue.FileRecord
func (b *BaseFileRecord) Sys() interface{} {
	return b.sys
}

type runOnceFileRecord struct {
	modTime      time.Time
	record       FileRecord
	data         blob.Blob
	sys          interface{}
	dataErr      error
	dirNamesErr  error
	dirNames     []string
	size         int64
	dataDone     atomic.Bool
	dataOnce     sync.Once
	dirNamesOnce sync.Once
	modeOnce     sync.Once
	modTimeOnce  sync.Once
	sizeOnce     sync.Once
	sysOnce      sync.Once
	mode         hackpadfs.FileMode
}

func (r *runOnceFileRecord) Data() (blob.Blob, error) {
	r.dataOnce.Do(func() {
		r.data, r.dataErr = r.record.Data()
		r.dataDone.Store(true)
	})
	return r.data, r.dataErr
}

func (r *runOnceFileRecord) ReadDirNames() ([]string, error) {
	r.dirNamesOnce.Do(func() {
		r.dirNames, r.dirNamesErr = r.record.ReadDirNames()
	})
	return r.dirNames, r.dirNamesErr
}

func (r *runOnceFileRecord) Size() int64 {
	r.sizeOnce.Do(func() {
		r.size = r.record.Size()
	})
	if r.dataDone.Load() {
		return int64(r.data.Len())
	}
	return r.size
}

func (r *runOnceFileRecord) Mode() hackpadfs.FileMode {
	r.modeOnce.Do(func() {
		r.mode = r.record.Mode()
	})
	return r.mode
}

func (r *runOnceFileRecord) ModTime() time.Time {
	r.modTimeOnce.Do(func() {
		r.modTime = r.record.ModTime()
	})
	return r.modTime
}

func (r *runOnceFileRecord) Sys() interface{} {
	r.sysOnce.Do(func() {
		r.sys = r.record.Sys()
	})
	return r.sys
}