// Package reconcile ports the three-phase payment reconciliation from scripts/match_payments.py.
package reconcile

import (
	"fuj-management/go/internal/domain/czech"
	"fuj-management/go/internal/domain/matching"
	"regexp"
	"strings"
)

// ExceptionKey identifies a fee override by normalized member name and period.
type ExceptionKey struct {
	Name   string // czech.Normalize(memberName)
	Period string // czech.Normalize("YYYY-MM")
}

// Exception is a manual fee override for one member in one period.
type Exception struct {
	Amount int
	Note   string
}

// FeeData holds the expected fee and attendance data for one member in one month.
type FeeData struct {
	Expected         int
	IsUnknown        bool // true when junior has exactly 1 session (manual review; Python sentinel "?")
	Attendance       int
	JuniorAttendance int // junior-tab sessions; used for the :NJ,MA breakdown in the juniors view
	AdultAttendance  int // adult-tab sessions for J-tier members; used for the :NJ,MA breakdown
}

// Member is one row from the attendance sheet.
type Member struct {
	Name string
	Tier string
	Fees map[string]FeeData // month ("YYYY-MM") → fee data
}

// Transaction is one payment row from the payments sheet.
// Date must already be a "YYYY-MM-DD" string (convert with matching.FormatDate before calling).
// InferredAmount, when non-nil, replaces Amount when person and purpose are pre-matched.
type Transaction struct {
	Date           string
	Amount         float64
	ManualFix      string   // "manual fix" column; non-empty disables re-inference
	Person         string   // comma-separated canonical names (empty → use inference)
	Purpose        string   // comma-separated "YYYY-MM" or "other:…" (empty → use inference)
	InferredAmount *float64 // nil → fall back to Amount
	Sender         string
	VS             string // Variabilní symbol (Czech variable payment symbol)
	Message        string
	BankID         string
	SyncID         string
	UserID         string
}

// TxEntry is the portion of a payment allocated to a single member+month.
type TxEntry struct {
	Amount     float64
	Date       string
	Sender     string
	Message    string
	Confidence string
}

// OtherEntry is a payment with purpose "other:…" allocated to a member.
type OtherEntry struct {
	Amount     float64
	Date       string
	Sender     string
	Message    string
	Purpose    string
	Confidence string
}

// MonthData is the ledger state for one member in one month.
type MonthData struct {
	Expected         int
	IsUnknown        bool // mirrors FeeData.IsUnknown; not overridden by exceptions
	OriginalExpected int
	AttendanceCount  int
	JuniorAttendance int // junior-tab sessions; for :NJ,MA breakdown in juniors view
	AdultAttendance  int // adult-tab sessions; for :NJ,MA breakdown
	Exception        *Exception
	Paid             float64
	Transactions     []TxEntry
}

// MemberResult is the reconciled ledger for one member.
type MemberResult struct {
	Tier              string
	Months            map[string]MonthData
	OtherTransactions []OtherEntry
	TotalBalance      int
}

// Result is the top-level output of Reconcile.
type Result struct {
	Members   map[string]MemberResult
	Unmatched []Transaction
	Credits   map[string]int // final balance for every member (may be negative)
}

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

// canonicalMemberKey returns a diacritic-, case-, and whitespace-insensitive key
// used to resolve Person-column values that drift from canonical attendance-sheet names.
// Ports scripts/match_payments.py canonical_member_key.
func canonicalMemberKey(name string) string {
	return strings.Join(strings.Fields(czech.Normalize(name)), " ")
}

type monthExpected struct {
	month    string
	expected int
}

// Reconcile matches transactions to members and months using three allocation phases:
//  1. Greedy: payment ≥ total expected → fill each month exactly; overflow → credit.
//  2. Proportional: payment < total → distribute by each month's share; last absorbs float remainder.
//  3. Even-split fallback: all expected fees are 0 (prepayment) → divide equally.
//
// defaultYear seeds czech.ParseMonthReferences in the inference fallback.
// Pass time.Now().Year() in production; pass a fixed year in tests.
//
// Ports scripts/match_payments.py reconcile.
func Reconcile(
	members []Member,
	sortedMonths []string,
	transactions []Transaction,
	exceptions map[ExceptionKey]Exception,
	defaultYear int,
) Result {
	memberNames := make([]string, len(members))
	memberTiers := make(map[string]string, len(members))
	memberFees := make(map[string]map[string]FeeData, len(members))

	for i, m := range members {
		memberNames[i] = m.Name
		memberTiers[m.Name] = m.Tier
		memberFees[m.Name] = m.Fees
	}

	// Map canonical key → first attendance-sheet name with that key, so Person cells
	// that drift in diacritics/case/whitespace still resolve to the canonical name.
	canonicalByKey := make(map[string]string, len(memberNames))
	for _, name := range memberNames {
		key := canonicalMemberKey(name)
		if _, exists := canonicalByKey[key]; !exists {
			canonicalByKey[key] = name
		}
	}

	if exceptions == nil {
		exceptions = map[ExceptionKey]Exception{}
	}

	// Initialise ledger
	ledger := make(map[string]map[string]MonthData, len(memberNames))
	otherLedger := make(map[string][]OtherEntry, len(memberNames))

	for _, name := range memberNames {
		ledger[name] = make(map[string]MonthData, len(sortedMonths))
		otherLedger[name] = []OtherEntry{}
		for _, m := range sortedMonths {
			fd := memberFees[name][m]
			originalExpected := fd.Expected
			attendanceCount := fd.Attendance

			var expected int
			var exInfo *Exception
			exKey := ExceptionKey{
				Name:   czech.Normalize(name),
				Period: czech.Normalize(m),
			}
			if ex, ok := exceptions[exKey]; ok {
				expected = ex.Amount
				exCopy := ex
				exInfo = &exCopy
			} else {
				expected = originalExpected
			}

			ledger[name][m] = MonthData{
				Expected:         expected,
				IsUnknown:        fd.IsUnknown,
				OriginalExpected: originalExpected,
				AttendanceCount:  attendanceCount,
				JuniorAttendance: fd.JuniorAttendance,
				AdultAttendance:  fd.AdultAttendance,
				Exception:        exInfo,
				Paid:             0,
				Transactions:     []TxEntry{},
			}
		}
	}

	var unmatched []Transaction
	credits := make(map[string]int, len(memberNames))

	for _, tx := range transactions {
		personStr := strings.TrimSpace(tx.Person)
		purposeStr := strings.TrimSpace(tx.Purpose)
		personStr = questionMarkRe.ReplaceAllString(personStr, "")
		isOther := strings.HasPrefix(strings.ToLower(purposeStr), "other:")

		var matchedMembers []matching.Match
		var matchedMonths []string
		var amount float64

		if personStr != "" && purposeStr != "" {
			for p := range strings.SplitSeq(personStr, ",") {
				p = strings.TrimSpace(p)
				if p != "" {
					matchedMembers = append(matchedMembers, matching.Match{
						Name:       p,
						Confidence: matching.ConfidenceAuto,
					})
				}
			}
			if isOther {
				matchedMonths = []string{purposeStr}
			} else {
				for m := range strings.SplitSeq(purposeStr, ",") {
					m = strings.TrimSpace(m)
					if m != "" {
						matchedMonths = append(matchedMonths, m)
					}
				}
			}
			if tx.InferredAmount != nil {
				amount = *tx.InferredAmount
			} else {
				amount = tx.Amount
			}
		} else {
			// Inference fallback for rows not yet processed by infer_payments.py
			inferred := matching.InferTransactionDetails(
				matching.Transaction{
					Sender:  tx.Sender,
					Message: tx.Message,
					UserID:  tx.UserID,
					Date:    tx.Date,
				},
				memberNames,
				defaultYear,
			)
			matchedMembers = inferred.Members
			matchedMonths = inferred.Months
			amount = tx.Amount
		}

		if len(matchedMembers) == 0 || len(matchedMonths) == 0 {
			unmatched = append(unmatched, tx)
			continue
		}

		if isOther {
			nAlloc := len(matchedMembers)
			perAlloc := 0.0
			if nAlloc > 0 {
				perAlloc = amount / float64(nAlloc)
			}
			for _, m := range matchedMembers {
				memberName := canonicalByKey[canonicalMemberKey(m.Name)]
				if memberName != "" {
					otherLedger[memberName] = append(otherLedger[memberName], OtherEntry{
						Amount:     perAlloc,
						Date:       tx.Date,
						Sender:     tx.Sender,
						Message:    tx.Message,
						Purpose:    purposeStr,
						Confidence: string(m.Confidence),
					})
				}
			}
			continue
		}

		memberShare := 0.0
		if len(matchedMembers) > 0 {
			memberShare = amount / float64(len(matchedMembers))
		}

		for _, m := range matchedMembers {
			memberName := canonicalByKey[canonicalMemberKey(m.Name)]
			if memberName == "" {
				unmatched = append(unmatched, tx)
				continue
			}

			var inWindow []monthExpected
			outCount := 0
			for _, month := range matchedMonths {
				if md, ok := ledger[memberName][month]; ok {
					inWindow = append(inWindow, monthExpected{month: month, expected: md.Expected})
				} else {
					outCount++
				}
			}

			nTotal := len(matchedMonths)
			outCredit := 0.0
			if outCount > 0 && nTotal > 0 {
				outCredit = memberShare / float64(nTotal) * float64(outCount)
				credits[memberName] += int(outCredit)
			}

			inWindowShare := memberShare - outCredit

			if len(inWindow) == 0 {
				continue
			}

			totalExpected := 0
			for _, mw := range inWindow {
				totalExpected += mw.expected
			}

			if totalExpected > 0 && inWindowShare >= float64(totalExpected) {
				// Greedy: payment covers all expected fees; overflow → credit
				credits[memberName] += int(inWindowShare - float64(totalExpected))
				for _, mw := range inWindow {
					alloc := float64(mw.expected)
					md := ledger[memberName][mw.month]
					md.Paid += alloc
					md.Transactions = append(md.Transactions, TxEntry{
						Amount:     alloc,
						Date:       tx.Date,
						Sender:     tx.Sender,
						Message:    tx.Message,
						Confidence: string(m.Confidence),
					})
					ledger[memberName][mw.month] = md
				}
			} else if totalExpected > 0 {
				// Proportional: distribute by each month's share; last month absorbs float remainder
				remaining := inWindowShare
				for i, mw := range inWindow {
					var alloc float64
					if i == len(inWindow)-1 {
						alloc = remaining
					} else {
						alloc = inWindowShare * float64(mw.expected) / float64(totalExpected)
					}
					remaining -= alloc
					md := ledger[memberName][mw.month]
					md.Paid += alloc
					md.Transactions = append(md.Transactions, TxEntry{
						Amount:     alloc,
						Date:       tx.Date,
						Sender:     tx.Sender,
						Message:    tx.Message,
						Confidence: string(m.Confidence),
					})
					ledger[memberName][mw.month] = md
				}
			} else {
				// Even-split fallback: prepayment before attendance recorded
				perMonth := inWindowShare / float64(len(inWindow))
				for _, mw := range inWindow {
					md := ledger[memberName][mw.month]
					md.Paid += perMonth
					md.Transactions = append(md.Transactions, TxEntry{
						Amount:     perMonth,
						Date:       tx.Date,
						Sender:     tx.Sender,
						Message:    tx.Message,
						Confidence: string(m.Confidence),
					})
					ledger[memberName][mw.month] = md
				}
			}
		}
	}

	// Final total balances: window balance + out-of-window credits accumulated above
	finalBalances := make(map[string]int, len(memberNames))
	for _, name := range memberNames {
		windowBalance := 0
		for _, mdata := range ledger[name] {
			windowBalance += int(mdata.Paid) - mdata.Expected
		}
		finalBalances[name] = windowBalance + credits[name]
	}

	membersResult := make(map[string]MemberResult, len(memberNames))
	for _, name := range memberNames {
		membersResult[name] = MemberResult{
			Tier:              memberTiers[name],
			Months:            ledger[name],
			OtherTransactions: otherLedger[name],
			TotalBalance:      finalBalances[name],
		}
	}

	if unmatched == nil {
		unmatched = []Transaction{}
	}

	return Result{
		Members:   membersResult,
		Unmatched: unmatched,
		Credits:   finalBalances,
	}
}