package mmkv

import (
	"encoding/binary"
	"fmt"
	"hash/crc32"
	"io"

	"github.com/golang/protobuf/proto"
	"golang.org/x/exp/maps"
)

type vault map[string][]byte

func (v vault) Keys() []string {
	return maps.Keys(v)
}

func (v vault) Get(key string) ([]byte, bool) {
	val, ok := v[key]
	return val, ok
}

// metadata is optional. but if it exists, validate with it.
func loadVault(src io.Reader, m *metadata) (Vault, error) {
	fileSizeBuf := make([]byte, 4)
	_, err := io.ReadFull(src, fileSizeBuf)
	if err != nil {
		return nil, fmt.Errorf("failed to read file size: %w", err)
	}
	size := binary.LittleEndian.Uint32(fileSizeBuf)

	if m != nil && size != m.actualSize {
		return nil, fmt.Errorf("metadata and vault payload size mismatch")
	}

	buf := make([]byte, size)
	_, err = io.ReadFull(src, buf)
	if err != nil {
		return nil, fmt.Errorf("failed to read file: %w", err)
	}

	if m != nil && m.crc32 != crc32.ChecksumIEEE(buf) {
		return nil, fmt.Errorf("metadata and vault payload crc32 mismatch")
	}

	v := make(vault)

	// mmkv is not really protobuf compatible,
	// type of key & value (the first 4 bytes) is incorrect.
	// so skip the first 4 bytes & manually parse the rest.
	rd := proto.NewBuffer(buf[4:])

	for {
		if len(rd.Unread()) == 0 {
			break
		}

		key, err := rd.DecodeStringBytes()
		if err != nil {
			return nil, fmt.Errorf("failed to decode key: %w", err)
		}
		val, err := rd.DecodeRawBytes(false)
		if err != nil {
			return nil, fmt.Errorf("failed to decode value: %w", err)
		}
		v[key] = val

	}

	return v, nil
}