package vm

import (
	"bytes"
	"encoding/binary"
	"errors"
	"fmt"
	"math/big"

	"github.com/CityOfZion/neo-go/pkg/util"
)

// ScriptBuilder generates bytecode and will write all
// generated bytecode into its internal buffer.
type ScriptBuilder struct {
	buf *bytes.Buffer
}

func (sb *ScriptBuilder) emit(op OpCode, b []byte) error {
	if err := sb.buf.WriteByte(byte(op)); err != nil {
		return err
	}
	_, err := sb.buf.Write(b)
	return err
}

func (sb *ScriptBuilder) emitPush(op OpCode) error {
	return sb.buf.WriteByte(byte(op))
}

func (sb *ScriptBuilder) emitPushBool(b bool) error {
	if b {
		return sb.emitPush(OpPushT)
	}
	return sb.emitPush(OpPushF)
}

func (sb *ScriptBuilder) emitPushInt(i int64) error {
	if i == -1 {
		return sb.emitPush(OpPushM1)
	}
	if i == 0 {
		return sb.emitPush(OpPushF)
	}
	if i > 0 && i < 16 {
		val := OpCode((int(OpPush1) - 1 + int(i)))
		return sb.emitPush(val)
	}

	bInt := big.NewInt(i)
	val := util.ToArrayReverse(bInt.Bytes())
	return sb.emitPushArray(val)
}

func (sb *ScriptBuilder) emitPushArray(b []byte) error {
	var (
		err error
		n   = len(b)
	)

	if n == 0 {
		return errors.New("0 bytes given in pushArray")
	}
	if n <= int(OpPushBytes75) {
		return sb.emit(OpCode(n), b)
	} else if n < 0x100 {
		err = sb.emit(OpPushData1, []byte{byte(n)})
	} else if n < 0x10000 {
		buf := make([]byte, 2)
		binary.LittleEndian.PutUint16(buf, uint16(n))
		err = sb.emit(OpPushData2, buf)
	} else {
		buf := make([]byte, 4)
		binary.LittleEndian.PutUint32(buf, uint32(n))
		err = sb.emit(OpPushData4, buf)
	}
	if err != nil {
		return err
	}
	_, err = sb.buf.Write(b)
	return err
}

func (sb *ScriptBuilder) emitPushString(str string) error {
	return sb.emitPushArray([]byte(str))
}

func (sb *ScriptBuilder) emitSysCall(api string) error {
	lenAPI := len(api)
	if lenAPI == 0 {
		return errors.New("syscall argument cant be 0")
	}
	if lenAPI > 252 {
		return fmt.Errorf("invalid syscall argument: %s", api)
	}

	bapi := []byte(api)
	args := make([]byte, lenAPI+1)
	args[0] = byte(lenAPI)
	copy(args, bapi[1:])
	return sb.emit(OpSysCall, args)
}

func (sb *ScriptBuilder) emitPushCall(scriptHash []byte, tailCall bool) error {
	if len(scriptHash) != 20 {
		return errors.New("expected a 20 byte long scriptHash (uint160) for pushCall")
	}
	op := OpAppCall
	if tailCall {
		op = OpTailCall
	}
	return sb.emit(op, scriptHash)
}

func (sb *ScriptBuilder) emitJump(op OpCode, offset int16) error {
	if op != OpJMP && op != OpJMPIF && op != OpJMPIFNOT && op != OpCall {
		return fmt.Errorf("invalid jump opcode: %v", op)
	}
	return sb.emit(op, []byte{}) // convert to bits?
}

func (sb *ScriptBuilder) dumpOpcode() {
	buf := sb.buf.Bytes()
	for i := 0; i < len(buf); i++ {
		fmt.Printf("OPCODE AT INDEX \t %d \t 0x%2x \t %s \n", i, buf[i], OpCode(buf[i]))
	}
}