package invoice

import (
	"bufio"
	"errors"
	"fmt"
	"io"
	"strings"
	"time"
)

func ParseMarkdown(r io.Reader) (Document, error) {
	var doc Document
	var section string
	var inAddress bool
	var tableHeader []string
	scanner := bufio.NewScanner(r)
	lineNo := 0
	for scanner.Scan() {
		lineNo++
		line := strings.TrimRight(scanner.Text(), "\r")
		trimmed := strings.TrimSpace(line)
		if strings.HasPrefix(trimmed, "#") && strings.HasPrefix(trimmed, "## ") {
			section = strings.TrimSpace(strings.TrimPrefix(trimmed, "## "))
			inAddress = false
			if strings.EqualFold(section, "Prestations") {
				tableHeader = nil
			}
			continue
		}
		if trimmed == "" {
			inAddress = false
			continue
		}

		switch strings.ToLower(section) {
		case "seller":
			if ok := parsePartyLine(&doc.Seller, line, &inAddress); ok {
				continue
			}
		case "buyer":
			if ok := parsePartyLine(&doc.Buyer, line, &inAddress); ok {
				continue
			}
		case "invoice":
			key, value, ok := splitKeyValue(line)
			if !ok {
				return doc, fmt.Errorf("line %d: expected key/value in Invoice section", lineNo)
			}
			switch normalizeKey(key) {
			case "number":
				doc.Invoice.Number = value
			case "subject":
				doc.Invoice.Subject = value
			case "location":
				doc.Invoice.Location = value
			case "date":
				parsed, err := time.Parse("2006-01-02", value)
				if err != nil {
					return doc, fmt.Errorf("line %d: invalid date %q", lineNo, value)
				}
				doc.Invoice.Date = parsed
			case "description":
				doc.Invoice.Description = value
			default:
				return doc, fmt.Errorf("line %d: unknown invoice field %q", lineNo, key)
			}
		case "items":
			if !strings.Contains(trimmed, "|") {
				return doc, fmt.Errorf("line %d: expected table row in Items section", lineNo)
			}
			cells := splitTableRow(line)
			if len(cells) == 0 {
				continue
			}
			if tableHeader == nil {
				tableHeader = cells
				continue
			}
			if isSeparatorRow(cells) {
				continue
			}
			item, err := parseItemRow(tableHeader, cells)
			if err != nil {
				return doc, fmt.Errorf("line %d: %w", lineNo, err)
			}
			doc.Items = append(doc.Items, item)
		case "payment":
			key, value, ok := splitKeyValue(line)
			if !ok {
				return doc, fmt.Errorf("line %d: expected key/value in Payment section", lineNo)
			}
			switch normalizeKey(key) {
			case "holder":
				doc.Payment.Holder = value
			case "iban":
				doc.Payment.IBAN = value
			default:
				return doc, fmt.Errorf("line %d: unknown payment field %q", lineNo, key)
			}
		default:
			continue
		}
	}
	if err := scanner.Err(); err != nil {
		return doc, err
	}
	return doc, nil
}

func parsePartyLine(party *Party, line string, inAddress *bool) bool {
	if *inAddress && (strings.HasPrefix(line, " ") || strings.HasPrefix(line, "\t")) {
		party.Address = append(party.Address, strings.TrimSpace(line))
		return true
	}
	key, value, ok := splitKeyValue(line)
	if !ok {
		return false
	}
	switch normalizeKey(key) {
	case "name":
		party.Name = value
		*inAddress = false
		return true
	case "address":
		*inAddress = true
		if value != "" {
			party.Address = append(party.Address, value)
		}
		return true
	case "siret":
		party.SIRET = value
		*inAddress = false
		return true
	case "email":
		party.Email = value
		*inAddress = false
		return true
	case "phone":
		party.Phone = value
		*inAddress = false
		return true
	default:
		return false
	}
}

func splitKeyValue(line string) (string, string, bool) {
	parts := strings.SplitN(line, ":", 2)
	if len(parts) != 2 {
		return "", "", false
	}
	key := strings.TrimSpace(parts[0])
	value := strings.TrimSpace(parts[1])
	return key, value, true
}

func normalizeKey(key string) string {
	k := strings.ToLower(strings.TrimSpace(key))
	replacer := strings.NewReplacer("é", "e", "è", "e", "ê", "e", "à", "a", "ç", "c")
	return replacer.Replace(k)
}

func splitTableRow(line string) []string {
	trimmed := strings.TrimSpace(line)
	if !strings.HasPrefix(trimmed, "|") {
		return nil
	}
	trimmed = strings.TrimPrefix(trimmed, "|")
	trimmed = strings.TrimSuffix(trimmed, "|")
	parts := strings.Split(trimmed, "|")
	var cells []string
	for _, part := range parts {
		cells = append(cells, strings.TrimSpace(part))
	}
	return cells
}

func isSeparatorRow(cells []string) bool {
	for _, cell := range cells {
		if cell == "" {
			continue
		}
		for _, r := range cell {
			if r != '-' {
				return false
			}
		}
	}
	return true
}

func parseItemRow(header, row []string) (Item, error) {
	if len(row) < len(header) {
		return Item{}, errors.New("row has fewer columns than header")
	}
	idxDesignation := -1
	idxPrice := -1
	idxQty := -1
	for i, col := range header {
		n := normalizeKey(col)
		switch {
		case strings.Contains(n, "designation"):
			idxDesignation = i
		case strings.Contains(n, "unitprice"), strings.Contains(n, "unit price"), strings.Contains(n, "price"), strings.Contains(n, "prix"):
			idxPrice = i
		case strings.Contains(n, "quantity"), strings.Contains(n, "quantite"), strings.Contains(n, "qty"):
			idxQty = i
		}
	}
	if idxDesignation == -1 || idxPrice == -1 || idxQty == -1 {
		return Item{}, errors.New("table header must include Designation, Unit price, Quantity")
	}
	item := Item{Designation: row[idxDesignation]}
	if item.Designation == "" {
		return Item{}, errors.New("empty designation")
	}
	price, err := ParseMoney(row[idxPrice])
	if err != nil {
		return Item{}, fmt.Errorf("invalid unit price: %w", err)
	}
	item.UnitPrice = price
	qty, err := ParseQuantity(row[idxQty])
	if err != nil {
		return Item{}, fmt.Errorf("invalid quantity: %w", err)
	}
	item.Quantity = qty
	return item, nil
}