package api

import (
	"fuj-management/go/internal/domain/czech"
	"regexp"
	"sort"
	"strings"
	"time"

	domreconcile "fuj-management/go/internal/domain/reconcile"
)

// getMonthLabels builds display labels for sortedMonths, merging month names
// (e.g. "Dec+Jan 2026") when mergedMonths maps a source month into this target.
// Mirrors scripts/views.py:get_month_labels.
func getMonthLabels(sortedMonths []string, mergedMonths map[string]string) map[string]string {
	labels := make(map[string]string, len(sortedMonths))
	for _, m := range sortedMonths {
		dt, err := time.Parse("2006-01", m)
		if err != nil {
			labels[m] = m
			continue
		}
		var mergedIn []string
		for src, dst := range mergedMonths {
			if dst == m {
				mergedIn = append(mergedIn, src)
			}
		}
		sort.Strings(mergedIn)
		if len(mergedIn) == 0 {
			labels[m] = dt.Format("Jan 2006")
			continue
		}
		allMonths := append(mergedIn, m) //nolint:gocritic // intentional: mergedIn already owned
		sort.Strings(allMonths)
		years := map[int]bool{}
		for _, x := range allMonths {
			if d, err2 := time.Parse("2006-01", x); err2 == nil {
				years[d.Year()] = true
			}
		}
		parts := make([]string, 0, len(allMonths))
		if len(years) > 1 {
			for _, x := range allMonths {
				if d, err2 := time.Parse("2006-01", x); err2 == nil {
					parts = append(parts, d.Format("Jan 2006"))
				}
			}
			labels[m] = strings.Join(parts, "+")
		} else {
			for _, x := range allMonths {
				if d, err2 := time.Parse("2006-01", x); err2 == nil {
					parts = append(parts, d.Format("Jan"))
				}
			}
			labels[m] = strings.Join(parts, "+") + " " + dt.Format("2006")
		}
	}
	return labels
}

// labelsForMonths returns the display labels for sortedMonths in slice order.
func labelsForMonths(sortedMonths []string, labels map[string]string) []string {
	out := make([]string, len(sortedMonths))
	for i, m := range sortedMonths {
		out[i] = labels[m]
	}
	return out
}

var questionMarkRe = regexp.MustCompile(`\[\?\]\s*`)

// canonicalKey returns a normalized form of a person name used for deduplication.
// Mirrors scripts/match_payments.py:canonical_member_key.
func canonicalKey(name string) string {
	return strings.Join(strings.Fields(czech.Normalize(name)), " ")
}

// groupRawPaymentsByPerson groups transactions by the "person" column,
// canonicalizing names against memberNames where possible.
// Mirrors scripts/views.py:group_payments_by_person (without the
// "Unmatched / Unknown" bucket that is payments-view-specific).
func groupRawPaymentsByPerson(txns []domreconcile.Transaction, memberNames []string) map[string][]RawTransaction {
	canonicalByKey := make(map[string]string, len(memberNames))
	for _, n := range memberNames {
		k := canonicalKey(n)
		if _, exists := canonicalByKey[k]; !exists {
			canonicalByKey[k] = n
		}
	}
	grouped := make(map[string][]RawTransaction)
	for _, tx := range txns {
		person := strings.TrimSpace(tx.Person)
		if person == "" {
			continue
		}
		for _, p := range strings.Split(person, ",") {
			p = questionMarkRe.ReplaceAllString(p, "")
			p = strings.TrimSpace(p)
			if p == "" {
				continue
			}
			key := p
			if canonical, ok := canonicalByKey[canonicalKey(p)]; ok {
				key = canonical
			}
			grouped[key] = append(grouped[key], rawTxFromDomain(tx))
		}
	}
	for k := range grouped {
		sort.Slice(grouped[k], func(i, j int) bool {
			return grouped[k][i].Date > grouped[k][j].Date
		})
	}
	return grouped
}

// rawTxFromDomain converts a domain Transaction to the wire RawTransaction.
func rawTxFromDomain(tx domreconcile.Transaction) RawTransaction {
	inferredAmount := 0.0
	if tx.InferredAmount != nil {
		inferredAmount = *tx.InferredAmount
	}
	return RawTransaction{
		Date:           tx.Date,
		Amount:         tx.Amount,
		ManualFix:      tx.ManualFix,
		Person:         tx.Person,
		Purpose:        tx.Purpose,
		InferredAmount: inferredAmount,
		Sender:         tx.Sender,
		VS:             tx.VS,
		Message:        tx.Message,
		BankID:         tx.BankID,
		SyncID:         tx.SyncID,
	}
}

// memberTxFromDomain converts a domain TxEntry to a wire MemberTxEntry.
func memberTxFromDomain(te domreconcile.TxEntry) MemberTxEntry {
	return MemberTxEntry{
		Amount:     te.Amount,
		Date:       te.Date,
		Sender:     te.Sender,
		Message:    te.Message,
		Confidence: te.Confidence,
	}
}

// memberOtherFromDomain converts a domain OtherEntry to a wire MemberOtherEntry.
func memberOtherFromDomain(oe domreconcile.OtherEntry) MemberOtherEntry {
	return MemberOtherEntry{
		Amount:     oe.Amount,
		Date:       oe.Date,
		Sender:     oe.Sender,
		Message:    oe.Message,
		Purpose:    oe.Purpose,
		Confidence: oe.Confidence,
	}
}

// settledBalance computes the settled balance: sum of (paid − expected) for months
// strictly before currentMonth. Months with IsUnknown=true are excluded to match
// Python's isinstance(exp, int) guard (skips "?" months).
func settledBalance(mr domreconcile.MemberResult, currentMonth string) int {
	total := 0
	for m, md := range mr.Months {
		if m >= currentMonth || md.IsUnknown {
			continue
		}
		total += int(md.Paid) - md.Expected
	}
	return total
}

// ensureSlice returns s unchanged when non-nil, or an empty (non-nil) slice so
// json.Marshal emits [] instead of null.
func ensureSlice[T any](s []T) []T {
	if s == nil {
		return []T{}
	}
	return s
}