package parser

import (
	"bufio"
	"io"
	"math"
	"strconv"
	"strings"
	"time"

	"financeiro-carvalho/internal/model"
)

// ParseOFX parses OFX SGML files as exported by Brazilian banks.
// It is tolerant of the non-strict SGML format (no closing tags, BOM, etc.).
func ParseOFX(r io.Reader) ([]model.ImportRow, error) {
	scanner := bufio.NewScanner(r)
	scanner.Buffer(make([]byte, 1024*1024), 1024*1024)

	var rows []model.ImportRow
	var cur *model.ImportRow

	for scanner.Scan() {
		line := strings.TrimSpace(scanner.Text())
		line = strings.TrimPrefix(line, "\xef\xbb\xbf") // strip UTF-8 BOM if present

		if line == "" {
			continue
		}

		tag, value := splitOFXLine(line)

		switch tag {
		case "STMTTRN":
			if cur != nil {
				rows = append(rows, *cur)
			}
			cur = &model.ImportRow{}
		case "/STMTTRN":
			if cur != nil {
				rows = append(rows, *cur)
				cur = nil
			}
		case "DTPOSTED":
			if cur != nil {
				cur.Date = parseOFXDate(value)
			}
		case "TRNAMT":
			if cur != nil {
				amt, _ := strconv.ParseFloat(strings.ReplaceAll(value, ",", "."), 64)
				cur.Amount = math.Abs(amt)
				if amt < 0 {
					cur.Type = "expense"
				} else {
					cur.Type = "income"
				}
			}
		case "FITID":
			if cur != nil {
				cur.ExternalID = value
			}
		case "MEMO":
			if cur != nil && cur.Description == "" {
				cur.Description = cleanDescription(value)
			}
		case "NAME":
			if cur != nil {
				cur.Description = cleanDescription(value)
			}
		}
	}
	if cur != nil {
		rows = append(rows, *cur)
	}
	return rows, scanner.Err()
}

// splitOFXLine handles both "<TAG>value" and "TAG:value" formats.
func splitOFXLine(line string) (tag, value string) {
	if strings.HasPrefix(line, "<") {
		end := strings.Index(line, ">")
		if end < 0 {
			return "", ""
		}
		tag = strings.ToUpper(line[1:end])
		value = strings.TrimSpace(line[end+1:])
		return
	}
	// header lines like "OFXHEADER:100" — ignore
	return "", ""
}

// parseOFXDate handles formats: 20060102, 20060102120000, 20060102120000[-3:BRT]
func parseOFXDate(s string) string {
	s = strings.SplitN(s, "[", 2)[0] // strip timezone suffix
	s = strings.TrimSpace(s)
	formats := []string{"20060102150405", "20060102"}
	for _, f := range formats {
		if len(s) >= len(f) {
			t, err := time.Parse(f, s[:len(f)])
			if err == nil {
				return t.Format("2006-01-02")
			}
		}
	}
	return s
}

func cleanDescription(s string) string {
	s = strings.TrimSpace(s)
	// remove duplicate whitespace
	fields := strings.Fields(s)
	return strings.Join(fields, " ")
}