package parser

import (
	"fmt"
	"regexp"
	"strings"
	"time"

	"git.petrovv.com/nikola/money/internal/config"
)

func init() {
	Register("nlb", func(acc *config.Account) (Parser, error) {
		return &nlbParser{digits: acc.Digits()}, nil
	})
}

// nlbParser reads an NLB izpisek PDF.
//
// A transaction starts on a line beginning with a dd.mm.yy date and ends with
// the signed amount and the running balance. Long descriptions and the other
// side's account number wrap onto indented continuation lines below.
type nlbParser struct {
	digits int
}

var (
	// A transaction line starts with a two-digit date.
	nlbStart = regexp.MustCompile(`^\d{2}\.\d{2}\.\d{2}\s`)
	// The whole line: date, free-form middle, signed amount, running balance.
	// Both the ASCII hyphen and the typographic minus U+2212 count as a sign;
	// which one a PDF carries depends on the font it was produced with.
	nlbLine = regexp.MustCompile(
		`^(?P<date>\d{2}\.\d{2}\.\d{2})\s+` +
			`(?P<middle>.*?)\s+` +
			`(?P<amount>[-+\x{2212}][\d.,]+)\s+` +
			`(?P<balance>[-\x{2212}]?[\d.,]+[-\x{2212}]?)\s*$`)
	// Columns inside a line are separated by four or more spaces.
	nlbFieldSplit = regexp.MustCompile(`\s{4,}`)
	// A Slovenian IBAN, which NLB prints in a column of its own. It is split
	// out only so that its wrapped fragments can be rejoined; the result goes
	// onto the end of the description, where every other parser keeps it.
	nlbAccount = regexp.MustCompile(`^SI\d{2}(?:\s?\d{4}){3}\s?\d{3}$`)
)

// nlbMinContinuationIndent is the shallowest indent a wrapped description line
// may have. The real threshold is the description column of the transaction
// the line belongs to, measured per line rather than hardcoded: pdftotext
// squeezes runs of spaces, so absolute columns shift with the font and page
// size of the PDF. This floor only rejects flush-left page furniture.
const nlbMinContinuationIndent = 2

// nlbDateLayout is the two-digit-year date NLB prints.
const nlbDateLayout = "02.01.06"

func (p *nlbParser) Parse(path string, acc *config.Account) ([]RawTxn, error) {
	text, err := pdfToText(path)
	if err != nil {
		return nil, err
	}
	return parseNLBText(text, p.digits)
}

// parseNLBText holds the whole parser, separated from PDF extraction so it can
// be tested against captured pdftotext output.
func parseNLBText(text string, digits int) ([]RawTxn, error) {
	var (
		txns []RawTxn
		// The account column per transaction, built up alongside because it
		// wraps in fragments of its own and has to be rejoined before it can
		// be appended to the description.
		trailing []string
		descAt   int // description column of the last transaction line
	)

	for _, page := range pages(text) {
		// Continuation lines may only attach to a transaction started on the
		// same page, so a wrapped line at the top of a page is page furniture.
		pageStart := len(txns)

		for i, line := range strings.Split(page, "\n") {
			if strings.TrimSpace(line) == "" {
				continue
			}

			if nlbStart.MatchString(line) {
				txn, account, col, err := parseNLBLine(line, digits)
				if err != nil {
					return nil, fmt.Errorf("line %d: %w", i+1, err)
				}
				txns = append(txns, txn)
				trailing = append(trailing, account)
				descAt = col
				continue
			}

			if len(txns) <= pageStart {
				continue // header, before any transaction on this page
			}
			// A wrapped description sits under the description column of the
			// transaction it continues; anything to the left of that is a
			// footer or a column heading.
			threshold := max(descAt, nlbMinContinuationIndent)
			if indent(line) < threshold {
				continue
			}

			parts := nlbFieldSplit.Split(strings.TrimSpace(line), -1)
			last := len(txns) - 1
			txns[last].Description += " " + parts[0]
			if len(parts) > 1 {
				trailing[last] = strings.TrimSpace(trailing[last] + " " + parts[1])
			}
		}
	}

	// The account column goes last rather than in the position it occupied on
	// the page, so that an IBAN wrapped over several lines stays contiguous
	// and a glob can match it.
	for i := range txns {
		txns[i].Description = strings.Join(strings.Fields(txns[i].Description+" "+trailing[i]), " ")
	}
	return txns, nil
}

// parseNLBLine parses one transaction line, returning the transaction, the
// account number found among its columns, and the column at which the
// description starts, which is where its wrapped lines will sit.
func parseNLBLine(line string, digits int) (RawTxn, string, int, error) {
	trimmed := strings.TrimRight(line, " \t\r")
	loc := nlbLine.FindStringSubmatchIndex(trimmed)
	if loc == nil {
		return RawTxn{}, "", 0, fmt.Errorf("line starts with a date but has no amount and balance: %q", strings.TrimSpace(line))
	}
	group := func(name string) string {
		i := nlbLine.SubexpIndex(name) * 2
		if loc[i] < 0 {
			return ""
		}
		return trimmed[loc[i]:loc[i+1]]
	}
	var (
		date    = group("date")
		middle  = group("middle")
		amount  = group("amount")
		balance = group("balance")
		descCol = loc[nlbLine.SubexpIndex("middle")*2]
	)

	d, err := time.Parse(nlbDateLayout, date)
	if err != nil {
		return RawTxn{}, "", 0, fmt.Errorf("date %q: %w", date, err)
	}

	amountMinor, err := parseNLBNumber(amount, digits)
	if err != nil {
		return RawTxn{}, "", 0, fmt.Errorf("amount %q: %w", amount, err)
	}
	balanceMinor, err := parseNLBNumber(balance, digits)
	if err != nil {
		return RawTxn{}, "", 0, fmt.Errorf("balance %q: %w", balance, err)
	}

	// The middle holds the description and, sometimes, the IBAN.
	var (
		account string
		desc    []string
	)
	for _, f := range nlbFieldSplit.Split(strings.TrimSpace(middle), -1) {
		if f == "" {
			continue
		}
		if nlbAccount.MatchString(f) {
			account = f
			continue
		}
		desc = append(desc, f)
	}

	return RawTxn{
		Date:         d.Format("2006-01-02"),
		Description:  strings.Join(desc, " "),
		AmountMinor:  amountMinor,
		BalanceMinor: &balanceMinor,
	}, account, descCol, nil
}

// parseNLBNumber reads the 1.234,56 format, where a trailing minus marks a
// negative balance.
func parseNLBNumber(s string, digits int) (int64, error) {
	return ParseAmount(s, ",", ".", digits)
}