package main

import "math"

func (operation *Operation) solution () (solution int64, err error) {
	var subSolution int64
	
	switch operation.opcode {
	case OpcodeAdd:
		for _, operand := range operation.operands {
			subSolution, err = operand.Solution()
			if err != nil { return }
			solution += subSolution
		}
		
	case OpcodeSubtract:
		if len(operation.operands) == 1 {
			solution, err = operation.operands[0].Solution()
			solution *= -1
			if err != nil { return }
			break
		}
	
		for index, operand := range operation.operands {
			subSolution, err = operand.Solution()
			if err != nil { return }
			if index == 0 {
				solution = subSolution
			} else {
				solution -= subSolution
			}
		}
		
	case OpcodeMultiply:
		solution = 1
		for _, operand := range operation.operands {
			subSolution, err = operand.Solution()
			if err != nil { return }
			solution *= subSolution
		}
		
	case OpcodeDivide:
		for index, operand := range operation.operands {
			subSolution, err = operand.Solution()
			if err != nil { return }
			if index == 0 {
				solution = subSolution
			} else if subSolution == 0 {
				err = ErrorDivideByZero
			} else {
				solution /= subSolution
			}
		}
		
	case OpcodePower:
		for index, operand := range operation.operands {
			subSolution, err = operand.Solution()
			if err != nil { return }
			if index == 0 {
				solution = subSolution
			} else {
				solution = integerPower(solution, subSolution)
			}
		}
		
	case OpcodeRoot:
		for index, operand := range operation.operands {
			subSolution, err = operand.Solution()
			if err != nil { return }
			if index == 0 {
				solution = subSolution
			} else {
				solution = integerRoot (
					solution, subSolution)
			}
		}
		
	case OpcodeModulo:
		for index, operand := range operation.operands {
			subSolution, err = operand.Solution()
			if err != nil { return }
			if index == 0 {
				solution = subSolution
			} else {
				if subSolution == 0 {
					err = ErrorDivideByZero
				} else {
					solution %= subSolution
				}
			}
		}
		
	case OpcodeOr:
		for _, operand := range operation.operands {
			subSolution, err = operand.Solution()
			if err != nil { return }
			solution |= subSolution
		}
		
	case OpcodeNot:
		if len(operation.operands) != 1 {
			err = ErrorWrongOperandCount
			return
		}

		subSolution, err = operation.operands[0].Solution()
		solution = ^subSolution
		
	case OpcodeAnd:
		for index, operand := range operation.operands {
			subSolution, err = operand.Solution()
			if err != nil { return }
			if index == 0 {
				solution = subSolution
			} else {
				solution &= subSolution
			}
		}
		
	case OpcodeXor:
		for index, operand := range operation.operands {
			subSolution, err = operand.Solution()
			if err != nil { return }
			if index == 0 {
				solution = subSolution
			} else {
				solution ^= subSolution
			}
		}
		
	case OpcodeLeftShift:
		if len(operation.operands) != 2 {
			err = ErrorWrongOperandCount
			return
		}

		var left, right int64
		left, err = operation.operands[0].Solution()
		if err != nil { return }
		right, err = operation.operands[1].Solution()
		if err != nil { return }

		if right < 0 {
			err = ErrorNegativeShiftAmount
			return
		}

		solution = left << right
		
	case OpcodeRightShift:
		if len(operation.operands) != 2 {
			err = ErrorWrongOperandCount
			return
		}

		var left, right int64
		left, err = operation.operands[0].Solution()
		if err != nil { return }
		right, err = operation.operands[1].Solution()
		if err != nil { return }

		if right < 0 {
			err = ErrorNegativeShiftAmount
			return
		}

		solution = left >> right
		
	case OpcodeMean:
		if len(operation.operands) == 0 { break }
		for _, operand := range operation.operands {
			subSolution, err = operand.Solution()
			if err != nil { break }
			solution += subSolution
		}
		solution /= int64(len(operation.operands))
		
	default:
		err = ErrorUnknownOpcode
	}
	return
}

func (operation *Operation) inexactSolution () (solution float64, err error) {
	var subSolution float64
	
	switch operation.opcode {
	case OpcodeAdd:
		for _, operand := range operation.operands {
			subSolution, err = operand.InexactSolution()
			if err != nil { return }
			solution += subSolution
		}
		
	case OpcodeSubtract:
		for index, operand := range operation.operands {
			subSolution, err = operand.InexactSolution()
			if err != nil { return }
			if index == 0 {
				solution = subSolution
			} else {
				solution -= subSolution
			}
		}
		
	case OpcodeMultiply:
		solution = 1
		for _, operand := range operation.operands {
			subSolution, err = operand.InexactSolution()
			if err != nil { return }
			solution *= subSolution
		}
		
	case OpcodeDivide:
		for index, operand := range operation.operands {
			subSolution, err = operand.InexactSolution()
			if err != nil { return }
			if index == 0 {
				solution = subSolution
			} else if subSolution == 0 {
				err = ErrorDivideByZero
			} else {
				solution /= subSolution
			}
		}
		
	case OpcodePower:
		for index, operand := range operation.operands {
			subSolution, err = operand.InexactSolution()
			if err != nil { return }
			if index == 0 {
				solution = subSolution
			} else {
				solution = math.Pow(solution, subSolution)
			}
		}
		
	case OpcodeRoot:
		for index, operand := range operation.operands {
			subSolution, err = operand.InexactSolution()
			if err != nil { return }
			if index == 0 {
				solution = subSolution
			} else {
				solution = math.Pow(solution, 1 / subSolution)
			}
		}
		
	case OpcodeModulo:
		for index, operand := range operation.operands {
			subSolution, err = operand.InexactSolution()
			if err != nil { return }
			if index == 0 {
				solution = subSolution
			} else {
				if subSolution == 0 {
					err = ErrorDivideByZero
				} else {
					solution = math.Mod (
						solution,
						subSolution)
				}
			}
		}
	
	case
		OpcodeOr, OpcodeNot, OpcodeAnd, OpcodeXor, OpcodeLeftShift,
		OpcodeRightShift:
		err = ErrorWrongType
		
	case OpcodeMean:
		if len(operation.operands) == 0 { break }
		for _, operand := range operation.operands {
			subSolution, err = operand.InexactSolution()
			if err != nil { break }
			solution += subSolution
		}
		solution /= float64(len(operation.operands))
		
	default:
		err = ErrorUnknownOpcode
	}
	return
}

func integerPower (x, y int64) (result int64) {
	if y == 0 {
		result = 1
		return
	}
	
	result = x
	for index := int64(2); index <= y; index ++ {
		result *= x
	}
	return
}

func integerRoot (x, y int64) (result int64) {
	// FIXME: find some algorithm for the nth root of an integer
	result = int64(math.Pow(float64(x), 1 / float64(y)))
	return
}