package banksync

import (
	"context"
	"fmt"
	"fuj-management/go/internal/domain/matching"
	"fuj-management/go/internal/domain/reconcile"
	"fuj-management/go/internal/io/sheets"
	"strings"
	"time"
)

// InferOpts controls infer behaviour.
type InferOpts struct {
	DryRun bool // print planned updates without writing to the sheet
}

// AttendanceSource can load both adult and junior member lists.
type AttendanceSource interface {
	LoadAdults(ctx context.Context) ([]reconcile.Member, []string, error)
	LoadJuniors(ctx context.Context) ([]reconcile.Member, []string, error)
}

// sheetReadWriter is the subset of *sheets.Client used by InferPayments.
type sheetReadWriter interface {
	GetValues(ctx context.Context, spreadsheetID, a1Range string) ([][]any, error)
	BatchUpdateValues(ctx context.Context, spreadsheetID string, updates []sheets.ValueRange) error
}

// InferPayments fills empty Person/Purpose/Inferred Amount cells in the payments
// sheet using name and month matching against the member list.
// Returns the number of rows updated (or that would be updated on dry-run).
// Ports scripts/infer_payments.py infer_payments.
func InferPayments(
	ctx context.Context,
	spreadsheetID string,
	sh sheetReadWriter,
	attendance AttendanceSource,
	opts InferOpts,
) (int, error) {
	rows, err := sh.GetValues(ctx, spreadsheetID, "A1:Z")
	if err != nil {
		return 0, fmt.Errorf("infer: read sheet: %w", err)
	}
	if len(rows) == 0 {
		return 0, nil
	}

	header := rows[0]
	colIdx := func(label string) int {
		label = strings.ToLower(strings.TrimSpace(label))
		for i, h := range header {
			if strings.ToLower(strings.TrimSpace(fmt.Sprint(h))) == label {
				return i
			}
		}
		return -1
	}

	idxDate := colIdx("date")
	idxAmount := colIdx("amount")
	idxSender := colIdx("sender")
	idxMessage := colIdx("message")
	idxVS := colIdx("vs")
	idxManual := colIdx("manual fix")
	idxPerson := colIdx("person")
	idxPurpose := colIdx("purpose")
	idxInferred := colIdx("inferred amount")

	for _, req := range []string{"person", "purpose", "inferred amount"} {
		if colIdx(req) == -1 {
			return 0, fmt.Errorf("infer: required column %q not found in sheet", req)
		}
	}

	// Build union member list: adults + juniors, deduped by canonical key.
	adults, _, err := attendance.LoadAdults(ctx)
	if err != nil {
		return 0, fmt.Errorf("infer: load adults: %w", err)
	}
	juniors, _, err := attendance.LoadJuniors(ctx)
	if err != nil {
		return 0, fmt.Errorf("infer: load juniors: %w", err)
	}
	memberNames := dedupeMembers(append(adults, juniors...))

	defaultYear := time.Now().Year()

	var updates []sheets.ValueRange
	for i, row := range rows[1:] {
		rowNum := i + 2 // 1-based, skip header

		get := func(idx int) string {
			if idx < 0 || idx >= len(row) {
				return ""
			}
			return strings.TrimSpace(fmt.Sprint(row[idx]))
		}

		// Skip rule: any of manual fix / Person / Purpose non-empty → leave alone
		if get(idxManual) != "" || get(idxPerson) != "" || get(idxPurpose) != "" {
			continue
		}

		tx := matching.Transaction{
			Sender:  get(idxSender),
			Message: get(idxMessage),
			UserID:  get(idxVS),
		}
		if idxDate >= 0 && idxDate < len(row) {
			tx.Date = row[idxDate]
		}

		inferred := matching.InferTransactionDetails(tx, memberNames, defaultYear)
		if len(inferred.Members) == 0 && len(inferred.Months) == 0 {
			continue
		}

		var peeps []string
		for _, m := range inferred.Members {
			if m.Confidence == matching.ConfidenceReview {
				peeps = append(peeps, "[?] "+m.Name)
			} else {
				peeps = append(peeps, m.Name)
			}
		}
		personVal := strings.Join(peeps, ", ")
		purposeVal := strings.Join(inferred.Months, ", ")

		amountVal := ""
		if idxAmount >= 0 && idxAmount < len(row) {
			amountVal = fmt.Sprint(row[idxAmount])
		}

		if opts.DryRun {
			fmt.Printf("Row %d: would infer person=%q purpose=%q amount=%s\n",
				rowNum, personVal, purposeVal, amountVal)
		}

		// R1C1 range: "R{row}C{personCol+1}:R{row}C{inferredAmountCol+1}"
		r1c1 := fmt.Sprintf("R%dC%d:R%dC%d", rowNum, idxPerson+1, rowNum, idxInferred+1)
		updates = append(updates, sheets.ValueRange{
			Range:  r1c1,
			Values: [][]any{{personVal, purposeVal, amountVal}},
		})
	}

	if len(updates) == 0 || opts.DryRun {
		return len(updates), nil
	}

	if err := sh.BatchUpdateValues(ctx, spreadsheetID, updates); err != nil {
		return 0, fmt.Errorf("infer: batch update: %w", err)
	}
	return len(updates), nil
}

// dedupeMembers returns unique member names, deduped by canonical key.
func dedupeMembers(members []reconcile.Member) []string {
	seen := make(map[string]bool, len(members))
	var names []string
	for _, m := range members {
		key := strings.Join(strings.Fields(m.Name), " ")
		if !seen[key] {
			seen[key] = true
			names = append(names, m.Name)
		}
	}
	return names
}