package ledger

import (
	"bufio"
	"bytes"
	"fmt"
	"io"
	"os"
	"regexp"
	"strconv"
	"unicode"
)

type transaction struct {
	date        string
	description string
	payee       string
	recipients  []transactionRecipient
}

func (t transaction) empty() bool {
	return fmt.Sprint(t) == fmt.Sprint(transaction{})
}

type transactionRecipient struct {
	name     string
	value    float64
	currency string
}

func (t transactionRecipient) empty() bool {
	return t == (transactionRecipient{})
}

func (file File) transactions() ([]transaction, error) {
	f, err := os.Open(string(file))
	if err != nil {
		return nil, err
	}
	defer f.Close()

	r := bufio.NewReaderSize(f, 2048)

	result := make([]transaction, 0)
	for {
		one, err := readTransaction(r)
		if !one.empty() {
			result = append(result, one)
		}
		if err == io.EOF {
			return result, nil
		}
		if err != nil {
			return result, err
		}
	}
}

func readTransaction(r *bufio.Reader) (transaction, error) {
	result, err := _readTransaction(r)
	if err != nil {
		return result, err
	}
	if result.empty() {
		return result, nil
	}
	if result.payee == "" && len(result.recipients) < 2 {
		return result, fmt.Errorf("found a transaction with no payee and less than 2 recipeints: %+v", result)
	}
	if result.payee != "" && len(result.recipients) < 1 {
		return result, fmt.Errorf("found a transaction with payee but no recipeints: %+v", result)
	}
	return result, nil
}

func _readTransaction(r *bufio.Reader) (transaction, error) {
	readTransactionLeadingWhitespace(r)

	firstLine, err := readTransactionLine(r)
	if len(bytes.TrimSpace(firstLine)) == 0 {
		return transaction{}, err
	}

	dateDescriptionPattern := regexp.MustCompile(`^([0-9]+-[0-9]+-[0-9]+)\s+(.*)$`)
	dateDescriptionMatches := dateDescriptionPattern.FindAllSubmatch(firstLine, 4)
	if len(dateDescriptionMatches) != 1 {
		return transaction{}, fmt.Errorf("bad first line: %v matches: %q", len(dateDescriptionMatches), firstLine)
	} else if len(dateDescriptionMatches[0]) != 3 {
		return transaction{}, fmt.Errorf("bad first line: %v submatches: %q", len(dateDescriptionMatches[0]), firstLine)
	}
	result := transaction{
		date:        string(dateDescriptionMatches[0][1]),
		description: string(dateDescriptionMatches[0][2]),
	}

	for {
		name, value, currency, err := readTransactionAccount(r)
		if name != "" {
			if currency == "" {
				result.payee = name
			} else {
				result.recipients = append(result.recipients, transactionRecipient{
					name:     name,
					value:    value,
					currency: currency,
				})
			}
		}
		if name == "" || err != nil {
			return result, err
		}
	}
}

func readTransactionLeadingWhitespace(r *bufio.Reader) {
	b, err := r.Peek(2048)
	if err != nil && err != io.EOF {
		return
	}

	i := 0
	for i < len(b) {
		if len(bytes.TrimSpace(b[:i])) != 0 {
			break
		}
		i++
	}

	if i > 0 {
		r.Read(make([]byte, i-1))
	}
}

func readTransactionLine(r *bufio.Reader) ([]byte, error) {
	for {
		b, err := _readTransactionLine(r)
		if err != nil || (len(bytes.TrimSpace(b)) > 0 && bytes.TrimSpace(b)[0] != '#') {
			return b, err
		}
	}
}

func _readTransactionLine(r *bufio.Reader) ([]byte, error) {
	b, err := r.Peek(2048)
	if len(b) == 0 {
		return nil, err
	}

	endOfLine := len(b)
	if idx := bytes.Index(b, []byte{'\n'}); idx > -1 {
		endOfLine = idx
	}

	b2 := make([]byte, endOfLine)
	n, err := r.Read(b2)
	if err == io.EOF {
		err = nil
	}

	if check, _ := r.Peek(1); len(check) == 1 && check[0] == '\n' {
		r.Read(make([]byte, 1))
	}

	return b2[:n], err
}

func readTransactionAccount(r *bufio.Reader) (string, float64, string, error) {
	line, err := readTransactionLine(r)
	if err != nil {
		return "", 0, "", err
	}

	if len(line) > 0 && !unicode.IsSpace(rune(line[0])) {
		r2 := *r
		*r = *bufio.NewReader(io.MultiReader(bytes.NewReader(append(line, '\n')), &r2))
		return "", 0, "", nil
	}

	fields := bytes.Fields(line)
	switch len(fields) {
	case 1: // payee
		return string(fields[0]), 0, "", nil
	case 2: // $00.00
		b := bytes.TrimLeft(fields[1], "$")
		value, err := strconv.ParseFloat(string(b), 64)
		if err != nil {
			return "", 0, "", err
		}
		return string(fields[0]), value, string(USD), nil
	case 3: // 00.00 XYZ
		value, err := strconv.ParseFloat(string(fields[2]), 64)
		if err != nil {
			return "", 0, "", err
		}
		return string(fields[0]), value, string(fields[3]), nil
	default:
		return "", 0, "", fmt.Errorf("cannot interpret %q", line)
	}
}