// Package banksync implements the bank-sync and payment-inference operations.
package banksync

import (
	"context"
	"fmt"
	"fuj-management/go/internal/domain/synch"
	"fuj-management/go/internal/io/fio"
	"strings"
	"time"
)

// columnLabels is the canonical header for the payments sheet.
// Mirrors COLUMN_LABELS in scripts/sync_fio_to_sheets.py.
var columnLabels = []string{
	"Date", "Amount", "manual fix", "Person", "Purpose",
	"Inferred Amount", "Sender", "VS", "Message", "Bank ID", "Sync ID",
}

// sheetsWriter is the subset of *sheets.Client used by SyncToSheets.
type sheetsWriter interface {
	GetValues(ctx context.Context, spreadsheetID, a1Range string) ([][]any, error)
	AppendValues(ctx context.Context, spreadsheetID, a1Range string, rows [][]any) error
	WriteHeader(ctx context.Context, spreadsheetID string, labels []string) error
	SortByDateColumn(ctx context.Context, spreadsheetID string) error
}

// SyncOpts controls the date window and sort behaviour.
type SyncOpts struct {
	Days     int       // look-back window when From/To are zero
	From, To time.Time // explicit window (overrides Days)
	Sort     bool      // sort the sheet by Date after appending
}

// SyncToSheets fetches Fio transactions and appends new ones to the payments sheet.
// Returns the number of rows appended.
// Ports scripts/sync_fio_to_sheets.py sync_to_sheets.
func SyncToSheets(
	ctx context.Context,
	spreadsheetID string,
	fioClient fio.Client,
	sh sheetsWriter,
	opts SyncOpts,
) (int, error) {
	// 1. Read existing rows to collect known Sync IDs (column K, index 10).
	rows, err := sh.GetValues(ctx, spreadsheetID, "A1:K")
	if err != nil {
		return 0, fmt.Errorf("sync: read sheet: %w", err)
	}

	existingIDs := make(map[string]bool)
	if len(rows) > 0 {
		header := rows[0]
		if !headerMatches(header) {
			if err := sh.WriteHeader(ctx, spreadsheetID, columnLabels); err != nil {
				return 0, fmt.Errorf("sync: write header: %w", err)
			}
		} else {
			for _, row := range rows[1:] {
				if len(row) > 10 {
					if id, ok := row[10].(string); ok && id != "" {
						existingIDs[id] = true
					}
				}
			}
		}
	}

	// 2. Compute date window.
	from, to := opts.From, opts.To
	if from.IsZero() || to.IsZero() {
		to = time.Now()
		days := opts.Days
		if days <= 0 {
			days = 30
		}
		from = to.AddDate(0, 0, -days)
	}

	// 3. Fetch Fio transactions.
	txns, err := fioClient.FetchTransactions(ctx, from, to)
	if err != nil {
		return 0, fmt.Errorf("sync: fetch fio: %w", err)
	}

	// 4. Append new rows.
	var newRows [][]any
	for _, tx := range txns {
		currency := tx.Currency
		if currency == "" {
			currency = "CZK"
		}
		id := synch.GenerateSyncID(synch.Transaction{
			Date:     tx.Date,
			Amount:   tx.Amount,
			Currency: currency,
			Sender:   tx.Sender,
			VS:       tx.VS,
			Message:  tx.Message,
			BankID:   tx.BankID,
		})
		if existingIDs[id] {
			continue
		}
		newRows = append(newRows, []any{
			tx.Date, tx.Amount,
			"", "", "", "", // manual fix, Person, Purpose, Inferred Amount
			tx.Sender, tx.VS, tx.Message, tx.BankID, id,
		})
	}

	if len(newRows) == 0 {
		return 0, nil
	}

	if err := sh.AppendValues(ctx, spreadsheetID, "A2", newRows); err != nil {
		return 0, fmt.Errorf("sync: append: %w", err)
	}

	if opts.Sort {
		if err := sh.SortByDateColumn(ctx, spreadsheetID); err != nil {
			return 0, fmt.Errorf("sync: sort: %w", err)
		}
	}
	return len(newRows), nil
}

func headerMatches(row []any) bool {
	if len(row) < len(columnLabels) {
		return false
	}
	for i, label := range columnLabels {
		cell, _ := row[i].(string)
		if !strings.EqualFold(cell, label) {
			return false
		}
	}
	return true
}