package main

import (
	"bytes"
	"errors"
	"fmt"
	"io/ioutil"
	"net/mail"
	"regexp"
	"strings"
)

type scraper interface {
	scrape(*mail.Message) ([]*Transaction, error)
}

type chaseScraper struct{}
type citiScraper struct{}

func Scrape(m *mail.Message) ([]*Transaction, error) {
	scraper, err := buildScraper(m)
	if err != nil {
		return nil, err
	}
	return scraper.scrape(m)
}

func buildScraper(m *mail.Message) (scraper, error) {
	subject := fmt.Sprint(m.Header["Subject"])
	if !containsAny(subject, "transaction", "report", "Transaction") {
		return nil, errors.New("cannot build scraper for subject " + subject)
	}
	from := fmt.Sprint(m.Header["From"])
	if strings.Contains(from, "Chase") {
		return newChaseScraper(), nil
	}
	if strings.Contains(from, "Citi") {
		return newCitiScraper(), nil
	}
	return nil, errors.New("unknown sender: " + from)
}

func newChaseScraper() scraper {
	return &chaseScraper{}
}

func newCitiScraper() scraper {
	return &citiScraper{}
}

func containsAny(a string, b ...string) bool {
	for i := range b {
		if strings.Contains(a, b[i]) {
			return true
		}
	}
	return false
}

func (c *chaseScraper) scrape(m *mail.Message) ([]*Transaction, error) {
	b, err := ioutil.ReadAll(m.Body)
	if err != nil {
		return nil, err
	}
	regexp := regexp.MustCompile(`A charge of \([^)]*\) (?P<amount>[\d\.]+) at (?P<account>.*) has been authorized`)
	matches := regexp.FindSubmatch(b)
	if len(matches) < 2 {
		return nil, fmt.Errorf("no full matches found")
	}
	results := make(map[string][]string)
	for i, name := range regexp.SubexpNames() {
		if i != 0 && name != "" {
			results[name] = append(results[name], string(matches[i]))
		}
	}
	if len(results) != 2 || len(results["amount"]) != len(results["account"]) {
		return nil, fmt.Errorf("unexpected matches found looking for transactions: %+v", results)
	}
	transactions := make([]*Transaction, len(results["amount"]))
	for i := range results["amount"] {
		transactions[i] = NewTransaction(results["amount"][i], results["account"][i], fmt.Sprint(m.Header["Date"]), Chase)
	}
	return transactions, nil
}

func (c *citiScraper) scrape(m *mail.Message) ([]*Transaction, error) {
	b, err := ioutil.ReadAll(m.Body)
	if err != nil {
		return nil, err
	}
	targetLineRegexp := regexp.MustCompile(`Account #: XXXX[0-9]{4} .*`)
	targetMatches := targetLineRegexp.FindAll(b, -1)
	if len(targetMatches) == 0 {
		return nil, errors.New("no lines with transactions found")
	}

	results := make(map[string][]string)
	for _, b := range targetMatches {
		// Account #: XXXX3837 $137.87 at AMZN Mktp US           Amzn.com/bill WA on 04/03/2020, 09:05 PM ET
		regexp := regexp.MustCompile(`Account #: XXXX[0-9]{4} \$(?P<amount>[0-9]+\.[0-9]*) at (?P<account>[^,]*)`)
		matches := regexp.FindSubmatch(b)
		if len(matches) < 2 {
			return nil, fmt.Errorf("no full matches found: %s", b)
		}
		for i, name := range regexp.SubexpNames() {
			if i != 0 && name != "" {
				if name == "account" {
					matches[i] = bytes.Split(matches[i], []byte(" on "))[0]
				}
				results[name] = append(results[name], string(matches[i]))
			}
		}
		if len(results) != 2 || len(results["amount"]) != len(results["account"]) {
			return nil, fmt.Errorf("unexpected matches found looking for transactions: %+v", results)
		}
	}

	transactions := make([]*Transaction, len(results["amount"]))
	for i := range results["amount"] {
		transactions[i] = NewTransaction(results["amount"][i], results["account"][i], fmt.Sprint(m.Header["Date"]), Citi)
	}

	return transactions, nil
}