package code

import (
	"bytes"
	"encoding/binary"
	"fmt"
)

type Instructions []byte

type Opcode byte

func (o Opcode) String() string {
	def, err := Lookup(byte(o))
	if err != nil {
		return ""
	}
	return def.Name
}

const (
	OpConstant Opcode = iota
	OpAdd
	OpPop
	OpSub
	OpMul
	OpDiv
	OpTrue
	OpFalse
	OpEqual
	OpNotEqual
	OpGreaterThan
	OpGreaterThanEqual
	OpMinus
	OpBang
	OpJumpNotTruthy
	OpJump
	OpNull
	OpAssignGlobal
	OpAssignLocal
	OpGetGlobal
	OpSetGlobal
	OpArray
	OpHash
	OpGetItem
	OpSetItem
	OpCall
	OpReturn
	OpGetLocal
	OpSetLocal
	OpGetBuiltin
	OpClosure
	OpGetFree
	OpCurrentClosure
	OpNoop
)

type Definition struct {
	Name          string
	OperandWidths []int
}

var definitions = map[Opcode]*Definition{
	OpConstant:         {"OpConstant", []int{2}},
	OpAssignGlobal:     {"OpAssignGlobal", []int{2}},
	OpAssignLocal:      {"OpAssignLocal", []int{1}},
	OpAdd:              {"OpAdd", []int{}},
	OpPop:              {"OpPop", []int{}},
	OpSub:              {"OpSub", []int{}},
	OpMul:              {"OpMul", []int{}},
	OpDiv:              {"OpDiv", []int{}},
	OpTrue:             {"OpTrue", []int{}},
	OpFalse:            {"OpFalse", []int{}},
	OpEqual:            {"OpEqual", []int{}},
	OpNotEqual:         {"OpNotEqual", []int{}},
	OpGreaterThan:      {"OpGreaterThan", []int{}},
	OpGreaterThanEqual: {"OpGreaterThanEqual", []int{}},
	OpMinus:            {"OpMinus", []int{}},
	OpBang:             {"OpBang", []int{}},
	OpJumpNotTruthy:    {"OpJumpNotTruthy", []int{2}},
	OpJump:             {"OpJump", []int{2}},
	OpNull:             {"OpNull", []int{}},
	OpGetGlobal:        {"OpGetGlobal", []int{2}},
	OpSetGlobal:        {"OpSetGlobal", []int{2}},
	OpArray:            {"OpArray", []int{2}},
	OpHash:             {"OpHash", []int{2}},
	OpGetItem:          {"OpGetItem", []int{}},
	OpSetItem:          {"OpSetItem", []int{}},
	OpCall:             {"OpCall", []int{1}},
	OpReturn:           {"OpReturn", []int{}},
	OpGetLocal:         {"OpGetLocal", []int{1}},
	OpSetLocal:         {"OpSetLocal", []int{1}},
	OpGetBuiltin:       {"OpGetBuiltin", []int{1}},
	OpClosure:          {"OpClosure", []int{2, 1}},
	OpGetFree:          {"OpGetFree", []int{1}},
	OpCurrentClosure:   {"OpCurrentClosure", []int{}},
	OpNoop:             {"OpNoop", []int{}},
}

func Lookup(op byte) (*Definition, error) {
	def, ok := definitions[Opcode(op)]
	if !ok {
		return nil, fmt.Errorf("opcode %d undefined", op)
	}

	return def, nil
}

func Make(op Opcode, operands ...int) []byte {
	def, ok := definitions[op]
	if !ok {
		return []byte{}
	}

	instructions := 1
	for _, w := range def.OperandWidths {
		instructions += w
	}

	instruction := make([]byte, instructions)
	instruction[0] = byte(op)

	offset := 1
	for i, o := range operands {
		width := def.OperandWidths[i]
		switch width {
		case 2:
			binary.BigEndian.PutUint16(instruction[offset:], uint16(o))
		case 1:
			instruction[offset] = byte(o)
		}
		offset += width
	}

	return instruction
}

func (ins Instructions) String() string {
	var out bytes.Buffer

	i := 0
	for i < len(ins) {
		def, err := Lookup(ins[i])
		if err != nil {
			fmt.Fprintf(&out, "ERROR: %s\n", err)
			continue
		}

		operands, read := ReadOperands(def, ins[i+1:])

		fmt.Fprintf(&out, "%04d %s\n", i, ins.fmtInstruction(def, operands))

		i += 1 + read
	}

	return out.String()
}

func (ins Instructions) fmtInstruction(def *Definition, operands []int) string {
	operandCount := len(def.OperandWidths)

	if len(operands) != operandCount {
		return fmt.Sprintf("ERROR: operand len %d does not match defined %d\n", len(operands), operandCount)
	}

	switch operandCount {
	case 0:
		return def.Name
	case 1:
		return fmt.Sprintf("%s %d", def.Name, operands[0])
	case 2:
		return fmt.Sprintf("%s %d %d", def.Name, operands[0], operands[1])

	}

	return fmt.Sprintf("ERROR: unhandled operandCount for %s\n", def.Name)
}

func ReadOperands(def *Definition, ins Instructions) ([]int, int) {
	operands := make([]int, len(def.OperandWidths))
	offset := 0

	for i, width := range def.OperandWidths {
		switch width {
		case 2:
			operands[i] = int(ReadUint16(ins[offset:]))
		case 1:
			operands[i] = int(ReadUint8(ins[offset:]))

		}

		offset += width
	}

	return operands, offset
}

func ReadUint16(ins Instructions) uint16 {
	return binary.BigEndian.Uint16(ins)
}

func ReadUint8(ins Instructions) uint8 {
	return ins[0]
}