package parser

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

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

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

// tradeRepublicParser reads a Trade Republic account statement PDF.
//
// The layout varies between statements: a transaction may sit entirely on one
// line, or have its date, type and description stacked across several. Rather
// than guess, every token is assigned to whichever column heading its start
// position is closest to, which handles both shapes.
type tradeRepublicParser struct {
	digits int
}

var (
	trHeader = regexp.MustCompile(`^\s*DATE\b.*\bMONEY IN\b.*\bMONEY OUT\b.*\bBALANCE\b`)
	// The sign may be an ASCII hyphen or a typographic minus, depending on the
	// font the PDF was produced with.
	trAmount   = regexp.MustCompile(`[-\x{2212}]?€\s?[-\x{2212}]?[\d,]+\.\d{2}`)
	trToken    = regexp.MustCompile(`\S+`)
	trFullDate = regexp.MustCompile(`^\d{2} [A-Z][a-z]{2} \d{4}$`)
	trIBAN     = regexp.MustCompile(`\b[A-Z]{2}\d{2}[A-Z0-9]{11,30}\b`)
)

var (
	trTextColumns  = []string{"DATE", "TYPE", "DESCRIPTION"}
	trMoneyColumns = []string{"MONEY IN", "MONEY OUT", "BALANCE"}
)

// trAmountSlack lets an amount sit slightly left of the MONEY IN column
// without being mistaken for description text.
const trAmountSlack = 5

// trDateLayout is the date Trade Republic prints, e.g. "05 Jan 2026".
const trDateLayout = "02 Jan 2006"

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

// parseTradeRepublicText holds the whole parser, separated from PDF extraction
// so it can be tested against captured pdftotext output.
func parseTradeRepublicText(text string, digits int) ([]RawTxn, error) {
	var txns []RawTxn

	for _, page := range pages(text) {
		lines := strings.Split(page, "\n")
		header := -1
		for i, line := range lines {
			if trHeader.MatchString(line) {
				header = i
				break
			}
		}
		if header < 0 {
			continue // a cover page or disclaimer, with no transaction table
		}

		cols, err := trColumnStarts(lines[header])
		if err != nil {
			return nil, err
		}
		for _, block := range trBlocks(lines[header+1:]) {
			txn, ok, err := parseTradeRepublicBlock(block, cols, digits)
			if err != nil {
				return nil, err
			}
			if ok {
				txns = append(txns, txn)
			}
		}
	}
	return txns, nil
}

// trColumnStarts records where each heading begins on the header line; those
// positions are what every token is measured against.
func trColumnStarts(header string) (map[string]int, error) {
	cols := map[string]int{}
	for _, name := range append(append([]string{}, trTextColumns...), trMoneyColumns...) {
		i := strings.Index(header, name)
		if i < 0 {
			return nil, fmt.Errorf("statement header has no %q column: %q", name, strings.TrimSpace(header))
		}
		cols[name] = i
	}
	return cols, nil
}

// trBlocks groups the consecutive non-blank lines that make up one transaction.
func trBlocks(lines []string) [][]string {
	var (
		out   [][]string
		block []string
	)
	for _, line := range lines {
		if strings.TrimSpace(line) != "" {
			block = append(block, line)
			continue
		}
		if len(block) > 0 {
			out = append(out, block)
			block = nil
		}
	}
	if len(block) > 0 {
		out = append(out, block)
	}
	return out
}

// nearest returns the column whose start is closest to pos.
func nearest(pos int, cols map[string]int, names []string) string {
	best, bestDist := "", -1
	for _, name := range names {
		d := pos - cols[name]
		if d < 0 {
			d = -d
		}
		if bestDist < 0 || d < bestDist {
			best, bestDist = name, d
		}
	}
	return best
}

func parseTradeRepublicBlock(lines []string, cols map[string]int, digits int) (RawTxn, bool, error) {
	words := map[string][]string{}
	amounts := map[string]*int64{}
	var descChunks []string

	for _, line := range lines {
		// Amounts are found first: everything to their left is text, and the
		// cut keeps them from being read as description tokens.
		cut := len(line)
		for _, loc := range trAmount.FindAllStringIndex(line, -1) {
			if loc[0] < cols["MONEY IN"]-trAmountSlack {
				continue // a figure inside the description, not a money column
			}
			if loc[0] < cut {
				cut = loc[0]
			}
			v, err := parseTradeRepublicNumber(line[loc[0]:loc[1]], digits)
			if err != nil {
				return RawTxn{}, false, fmt.Errorf("amount %q: %w", line[loc[0]:loc[1]], err)
			}
			amounts[nearest(loc[0], cols, trMoneyColumns)] = &v
		}

		// A description fragment per line, so wrapped text can be rejoined.
		var lineDesc []string
		for _, loc := range trToken.FindAllStringIndex(line[:cut], -1) {
			column := nearest(loc[0], cols, trTextColumns)
			token := line[loc[0]:loc[1]]
			if column == "DESCRIPTION" {
				lineDesc = append(lineDesc, token)
				continue
			}
			words[column] = append(words[column], token)
		}
		if len(lineDesc) > 0 {
			descChunks = append(descChunks, strings.Join(lineDesc, " "))
		}
	}

	// A block without a full date and a balance is a heading or a footer.
	date := strings.Join(words["DATE"], " ")
	if !trFullDate.MatchString(date) || amounts["BALANCE"] == nil {
		return RawTxn{}, false, nil
	}
	d, err := time.Parse(trDateLayout, date)
	if err != nil {
		return RawTxn{}, false, fmt.Errorf("date %q: %w", date, err)
	}

	desc := trJoinWrapped(descChunks)
	amount := deref(amounts["MONEY IN"]) - deref(amounts["MONEY OUT"])

	return RawTxn{
		Date:         d.Format("2006-01-02"),
		Description:  desc,
		AmountMinor:  amount,
		Counterparty: trIBAN.FindString(desc),
		Type:         strings.Join(words["TYPE"], " "),
		BalanceMinor: amounts["BALANCE"],
	}, true, nil
}

// trJoinWrapped glues description fragments split across lines. A fragment
// ending in a hyphen was broken mid-word, so it joins without a space.
func trJoinWrapped(chunks []string) string {
	var out string
	for _, chunk := range chunks {
		switch {
		case out == "":
			out = chunk
		case len(out) > 1 && strings.HasSuffix(out, "-") && !strings.HasSuffix(out, " -"):
			out += chunk
		default:
			out += " " + chunk
		}
	}
	return out
}

// parseTradeRepublicNumber reads the €1,234.56 format.
func parseTradeRepublicNumber(s string, digits int) (int64, error) {
	return ParseAmount(strings.ReplaceAll(s, "€", ""), ".", ",", digits)
}

func deref(v *int64) int64 {
	if v == nil {
		return 0
	}
	return *v
}