package main

import (
	"bufio"
	"bytes"
	"fmt"
	"io"
	"strconv"
	"strings"
)

type Transaction struct {
	Date        string
	Description string
	Payer       string
	Payee       string
	Amount      float32
}

func readTransaction(r io.Reader) (Transaction, error) {
	lines := make([][]byte, 3)
	for i := range lines {
		line, err := nextLine(r)
		if err != nil {
			return Transaction{}, err
		}
		lines[i] = line
	}
	for i := range lines {
		if len(lines[i]) == 0 {
			return Transaction{}, fmt.Errorf("stub transaction: line %d empty: %q, %q, %q", i, lines[0], lines[1], lines[2])
		}
	}
	var transaction Transaction
	for _, foo := range []func([][]byte) error{
		transaction.readDate,
		transaction.readDescription,
		transaction.readAmount,
		transaction.readPayerPayee,
	} {
		if err := foo(lines); err != nil {
			return Transaction{}, err
		}
	}
	return transaction, nil
}

func nextLine(r io.Reader) ([]byte, error) {
	line, err := readLine(r)
	for err == nil && len(bytes.TrimSpace(line)) == 0 {
		line, err = readLine(r)
	}
	return line, err
}

func readLine(r io.Reader) ([]byte, error) {
	w := bytes.NewBuffer(make([]byte, 0, 128))
	buff := make([]byte, 1)
	n, err := r.Read(buff)
	for err == nil && n > 0 && buff[0] != '\n' {
		w.Write(buff)
		n, err = r.Read(buff)
	}
	return w.Bytes(), err
}

func words(b []byte) [][]byte {
	scanner := bufio.NewScanner(bytes.NewReader(b))
	scanner.Split(bufio.ScanWords)
	words := make([][]byte, 0)
	for scanner.Scan() {
		words = append(words, []byte(scanner.Text()))
	}
	return words
}

func (transaction *Transaction) readDate(lines [][]byte) error {
	transaction.Date = string(words(lines[0])[0])
	return nil
}

func (transaction *Transaction) readDescription(lines [][]byte) error {
	transaction.Description = string(bytes.Join(words(lines[0])[1:], []byte(" ")))
	return nil
}

func (transaction *Transaction) readAmount(lines [][]byte) error {
	amount := string(words(lines[1])[1])
	f, err := strconv.ParseFloat(strings.Trim(amount, "$"), 32)
	transaction.Amount = float32(f)
	return err
}

func (transaction *Transaction) readPayerPayee(lines [][]byte) error {
	payer := string(words(lines[1])[0])
	payee := string(words(lines[2])[0])
	if transaction.Amount >= 0 {
		tmp := payer
		payer = payee
		payee = tmp
	} else {
		transaction.Amount *= -1
	}
	transaction.Payer = payer
	transaction.Payee = payee
	return nil
}

func (transaction Transaction) Marshal() string {
	return fmt.Sprintf(
		"%-25s%s\n%25s%-50s$%.2f\n%25s%s",
		transaction.Date,
		transaction.Description,
		"",
		transaction.Payee,
		transaction.Amount,
		"",
		transaction.Payer,
	)
}