// Package models provides the models for the KermaGo application
package models

import (
	"crypto/sha256"
	"encoding/binary"
	"encoding/hex"
	"errors"
	"math"
	"time"

	"github.com/docker/go/canonical/json"
	"golang.org/x/exp/slices"
	"golang.org/x/exp/utf8string"
)

/*
A Block is a struct that represents a block as per the Kerma specification
*/
type Block struct {
	Type    string            `json:"type" binding:"required"`
	Txids   []string          `json:"txids" binding:"required"`
	Nonce   string            `json:"nonce" binding:"required"`
	Previd  *string           `json:"previd"`
	Created int64             `json:"created" binding:"required"`
	Target  string            `json:"T" binding:"required"`
	Miner   string            `json:"miner,omitempty"`
	Note    string            `json:"note,omitempty"`
	Height  uint64            `json:"-"`
	UTXOSet map[string]uint64 `json:"-"`
}

/*
Hash returns the sha256 hash of the canonical JSON of the block
*/
func (b *Block) Hash() (string, error) {
	block, err := b.MarshalJson()
	if err != nil {
		return "", errors.New("could not parse block as json")
	}
	hashSum := sha256.Sum256(block)

	return hex.EncodeToString(hashSum[:]), nil
}

/*
GetID returns the block id
*/
func (b *Block) GetID() string {
	id, err := b.Hash()
	if err != nil {
		return ""
	}

	return id
}

/*
GetType returns the type of the block
*/
func (b *Block) GetType() string {
	return b.Type
}

/*
GetEntity returns the block
*/
func (b *Block) GetEntity() interface{} {
	return b
}

/*
Validate is responsible for validating the block; returns an error if unsuccessful
*/
func (b *Block) Validate() error {
	if b.Type != "block" {
		return errors.New("object not a block")
	}

	if b.IsGenesisBlock() {
		return nil
	}

	if b.Previd == nil && !b.IsGenesisBlock() {
		return errors.New("illegal genesis block detected")
	}

	if b.Target != GetGenesisBlock().Target {
		return errors.New("incorrect target supplied")
	}

	if b.Created < GetGenesisBlock().Created {
		return errors.New("timestamp before genesis block")
	}

	// TODO: check if this should be millis
	if b.Created > time.Now().UnixMilli() {
		return errors.New("block created in the future")
	}

	if b.Miner != "" {
		if !utf8string.NewString(b.Miner).IsASCII() {
			return errors.New("miner is not an ascii printable string")
		}

		if len(b.Miner) > 128 {
			return errors.New("miner length incorrect")
		}
	}

	if b.Note != "" {
		if !utf8string.NewString(b.Note).IsASCII() {
			return errors.New("note is not an ascii printable string")
		}

		if len(b.Note) > 128 {
			return errors.New("note length incorrect")
		}
	}

	_, err := hex.DecodeString(b.Nonce)
	if err != nil {
		return err
	}

	_, err = hex.DecodeString(*b.Previd)
	if err != nil {
		return err
	}

	bid, err := b.Hash()
	if err != nil {
		return err
	}

	bidBytes, _ := hex.DecodeString(bid)
	bint := binary.BigEndian.Uint64(bidBytes)
	if err != nil {
		return err
	}

	tidBytes, _ := hex.DecodeString(b.Target)
	tid := binary.BigEndian.Uint64(tidBytes)
	if err != nil {
		return err
	}

	if bint >= tid {
		return errors.New("proof-of-work equation not satisfied")
	}

	return nil
}

/*
String returns the canonical JSON of the block as a string
*/
func (b *Block) String() string {
	res, _ := b.MarshalJson()
	return string(res)
}

/*
ContainsTransaction checks if the block contains the specified transaction
*/
func (b *Block) ContainsTransaction(txid string) bool {
	return slices.Contains(b.Txids, txid)
}

/*
MarshalJson returns the canonical JSON of the block
*/
func (b *Block) MarshalJson() ([]byte, error) {
	return json.MarshalCanonical(b)
}

/*
UnmarshalJSON creates a block from the input JSON byte array
*/
func (b *Block) UnmarshalJSON(data []byte) error {
	if len(data) == 0 {
		return nil
	}

	type tmp Block
	err := json.Unmarshal(data, (*tmp)(b))
	if err != nil {
		return err
	}

	err = b.Validate()
	if err != nil {
		return err
	}

	return nil
}

/*
IsGenesisBlock checks if the block is the genesis block
*/
func (b *Block) IsGenesisBlock() bool {
	return b.String() == GetGenesisBlock().String()
}

/*
GetGenesisBlock returns the genesis block
*/
func GetGenesisBlock() *Block {
	genesis := Block{
		Type:    "block",
		Target:  "00000002af000000000000000000000000000000000000000000000000000000",
		Created: 1624219079,
		Miner:   "dionyziz",
		Nonce:   "0000000000000000000000000000000000000000000000000000002634878840",
		Note:    "The Economist 2021-06-20: Crypto-miners are probably to blame for the graphics-chip shortage",
		Previd:  nil,
		Txids:   []string{},
		Height:  0,
		UTXOSet: map[string]uint64{},
	}
	return &genesis
}

/*
GetBlockReward returns the block reward
*/
func GetBlockReward() uint64 {
	// 5 * (10^13)
	return 5 * uint64(math.Pow(10, 13))
}