2 files changed, 366 insertions, 0 deletions
diff --git a/internal/mapping/mapping.go b/internal/mapping/mapping.go
new file mode 100644
index 0000000..77f9cab
--- /dev/null
+++ b/internal/mapping/mapping.go
@@ -0,0 +1,248 @@
+// Package mapping turns Multicase vouchers into Accounted journal entries:
+// it translates account numbers, posts customer and supplier subledger lines
+// to their control accounts and splits VAT out of gross amounts.
+package mapping
+
+import (
+	"bytes"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"math"
+	"os"
+	"sort"
+	"strings"
+
+	"simenandre.no/accounted-multicase-intgr/internal/accounted"
+	"simenandre.no/accounted-multicase-intgr/internal/multicase"
+)
+
+// VATCode describes one Multicase MVA code. Multicase posts revenue and cost
+// lines gross with the code attached and leaves the VAT split to the
+// receiving ledger, so a code with a rate needs an account to post VAT to.
+type VATCode struct {
+	Rate    float64 `json:"rate"`
+	Account string  `json:"account"`
+	TaxCode string  `json:"tax_code"`
+}
+
+type Config struct {
+	Accounts              map[string]string  `json:"accounts"`
+	CustomerLedgerAccount string             `json:"customer_ledger_account"`
+	SupplierLedgerAccount string             `json:"supplier_ledger_account"`
+	VATCodes              map[string]VATCode `json:"vat_codes"`
+	// RoundingAccount takes the öre left over when converted amounts no
+	// longer balance, up to MaxRoundingOre.
+	RoundingAccount string `json:"rounding_account"`
+	MaxRoundingOre  int64  `json:"max_rounding_ore"`
+	SourceType      string `json:"source_type"`
+	// VoucherSeries maps a Multicase BilagsArt to an Accounted series letter;
+	// "*" is the fallback. Empty means the company's default series.
+	VoucherSeries map[string]string `json:"voucher_series"`
+	// Dimensions maps "department" (AvdNr.) and "project" (Prosjekt) to SIE
+	// dimension numbers. Unset means the columns are not sent.
+	Dimensions map[string]string `json:"dimensions"`
+}
+
+func LoadConfig(path string) (*Config, error) {
+	b, err := os.ReadFile(path)
+	if err != nil {
+		return nil, err
+	}
+	var c Config
+	dec := json.NewDecoder(bytes.NewReader(b))
+	dec.DisallowUnknownFields()
+	if err := dec.Decode(&c); err != nil {
+		return nil, fmt.Errorf("%s: %w", path, err)
+	}
+	if c.SourceType == "" {
+		c.SourceType = "manual"
+	}
+	if c.MaxRoundingOre == 0 {
+		c.MaxRoundingOre = 100
+	}
+	for code, v := range c.VATCodes {
+		if v.Rate < 0 || v.Rate >= 100 {
+			return nil, fmt.Errorf("vat_codes.%s: rate must be a percentage between 0 and 100", code)
+		}
+		if v.Rate > 0 && v.Account == "" {
+			return nil, fmt.Errorf("vat_codes.%s: a code with a rate needs an account", code)
+		}
+	}
+	return &c, nil
+}
+
+// UnmappedError lists the Multicase accounts and VAT codes a voucher uses
+// that the config does not cover.
+type UnmappedError struct {
+	Accounts []string
+	VATCodes []string
+}
+
+func (e *UnmappedError) Error() string {
+	var parts []string
+	if len(e.Accounts) > 0 {
+		parts = append(parts, "unmapped accounts "+strings.Join(e.Accounts, ", "))
+	}
+	if len(e.VATCodes) > 0 {
+		parts = append(parts, "unknown VAT codes "+strings.Join(e.VATCodes, ", "))
+	}
+	return strings.Join(parts, "; ")
+}
+
+// ErrEmpty means every line of the voucher has a zero amount, as Multicase
+// writes for the customer line of a nullfaktura.
+var ErrEmpty = errors.New("voucher has no non-zero lines")
+
+// Build maps one voucher. The fiscal period is left for the caller to set.
+func (c *Config) Build(v multicase.Voucher) (accounted.JournalEntry, error) {
+	unmapped := &UnmappedError{}
+	var lines []accounted.Line
+	add := func(account string, amount int64, desc, taxCode string, dims map[string]string) {
+		l := accounted.Line{Account: account, Description: desc, TaxCode: taxCode, Dimensions: dims}
+		if amount > 0 {
+			l.Debit = accounted.Money(amount)
+		} else {
+			l.Credit = accounted.Money(-amount)
+		}
+		lines = append(lines, l)
+	}
+
+	for _, l := range v.Lines {
+		if l.Amount == 0 {
+			continue
+		}
+		account, err := c.account(l)
+		if err != nil {
+			unmapped.Accounts = appendUnique(unmapped.Accounts, l.Account)
+			continue
+		}
+		desc := lineDescription(l)
+		dims := c.dimensions(l)
+		if l.VATCode == "" {
+			add(account, l.Amount, desc, "", dims)
+			continue
+		}
+		vat, ok := c.VATCodes[l.VATCode]
+		if !ok {
+			unmapped.VATCodes = appendUnique(unmapped.VATCodes, l.VATCode)
+			continue
+		}
+		if vat.Rate == 0 {
+			add(account, l.Amount, desc, vat.TaxCode, dims)
+			continue
+		}
+		net := SplitNet(l.Amount, vat.Rate)
+		add(account, net, desc, vat.TaxCode, dims)
+		if l.Amount-net != 0 {
+			add(vat.Account, l.Amount-net, desc, vat.TaxCode, nil)
+		}
+	}
+	if len(unmapped.Accounts) > 0 || len(unmapped.VATCodes) > 0 {
+		return accounted.JournalEntry{}, unmapped
+	}
+	if len(lines) == 0 {
+		return accounted.JournalEntry{}, ErrEmpty
+	}
+
+	var sum int64
+	for _, l := range lines {
+		sum += int64(l.Debit) - int64(l.Credit)
+	}
+	if sum != 0 {
+		if c.RoundingAccount == "" || abs(sum) > c.MaxRoundingOre {
+			return accounted.JournalEntry{}, fmt.Errorf("does not balance: off by %s", accounted.Money(sum))
+		}
+		add(c.RoundingAccount, -sum, "Öresavrundning", "", nil)
+	}
+
+	return accounted.JournalEntry{
+		EntryDate:     v.Date.Format("2006-01-02"),
+		Description:   truncate(strings.TrimSuffix(v.Label()+": "+v.Text, ": "), 200),
+		SourceType:    c.SourceType,
+		SourceID:      v.Key(),
+		VoucherSeries: c.series(v.Type),
+		Notes:         fmt.Sprintf("Multicase %s, BilagsArt %s, Bilagsnummer %s, BuntHodeID %s", v.Company, v.Type, v.Number, v.Batch),
+		Lines:         lines,
+	}, nil
+}
+
+func (c *Config) account(l multicase.Line) (string, error) {
+	switch {
+	case l.CustomerNo != "" && l.Account == l.CustomerNo && c.CustomerLedgerAccount != "":
+		return c.CustomerLedgerAccount, nil
+	case l.SupplierNo != "" && l.Account == l.SupplierNo && c.SupplierLedgerAccount != "":
+		return c.SupplierLedgerAccount, nil
+	}
+	if a, ok := c.Accounts[l.Account]; ok && a != "" {
+		return a, nil
+	}
+	return "", fmt.Errorf("unmapped account %s", l.Account)
+}
+
+func (c *Config) dimensions(l multicase.Line) map[string]string {
+	dims := map[string]string{}
+	if n := c.Dimensions["department"]; n != "" && l.Department != "" {
+		dims[n] = l.Department
+	}
+	if n := c.Dimensions["project"]; n != "" && l.Project != "" {
+		dims[n] = l.Project
+	}
+	if len(dims) == 0 {
+		return nil
+	}
+	return dims
+}
+
+func (c *Config) series(voucherType string) string {
+	if s, ok := c.VoucherSeries[voucherType]; ok {
+		return s
+	}
+	return c.VoucherSeries["*"]
+}
+
+// SplitNet returns the net part of a gross amount in öre at the given VAT
+// rate, rounded half away from zero. VAT is gross minus net, so the two
+// always add back up to the gross amount.
+func SplitNet(gross int64, rate float64) int64 {
+	bp := int64(math.Round(rate * 100))
+	num, den := gross*10000, 10000+bp
+	if num >= 0 {
+		return (2*num + den) / (2 * den)
+	}
+	return (2*num - den) / (2 * den)
+}
+
+func lineDescription(l multicase.Line) string {
+	desc := l.Reference
+	if l.Currency != "" && l.CurrencyAmt != "" && l.CurrencyAmt != "0" {
+		desc = strings.TrimSpace(fmt.Sprintf("%s (%s %s)", desc, l.Currency, l.CurrencyAmt))
+	}
+	return truncate(desc, 200)
+}
+
+func appendUnique(list []string, s string) []string {
+	for _, x := range list {
+		if x == s {
+			return list
+		}
+	}
+	list = append(list, s)
+	sort.Strings(list)
+	return list
+}
+
+func truncate(s string, n int) string {
+	r := []rune(s)
+	if len(r) <= n {
+		return s
+	}
+	return string(r[:n])
+}
+
+func abs(n int64) int64 {
+	if n < 0 {
+		return -n
+	}
+	return n
+}
diff --git a/internal/mapping/mapping_test.go b/internal/mapping/mapping_test.go
new file mode 100644
index 0000000..d9190cd
--- /dev/null
+++ b/internal/mapping/mapping_test.go
@@ -0,0 +1,118 @@
+package mapping
+
+import (
+	"errors"
+	"testing"
+	"time"
+
+	"simenandre.no/accounted-multicase-intgr/internal/accounted"
+	"simenandre.no/accounted-multicase-intgr/internal/multicase"
+)
+
+func config() *Config {
+	return &Config{
+		Accounts:              map[string]string{"3000": "3001", "1460": "1460", "4301": "4000"},
+		CustomerLedgerAccount: "1510",
+		VATCodes: map[string]VATCode{
+			"3": {Rate: 25, Account: "2611"},
+			"6": {Rate: 0},
+		},
+		RoundingAccount: "3740",
+		MaxRoundingOre:  100,
+		SourceType:      "manual",
+	}
+}
+
+func voucher(lines ...multicase.Line) multicase.Voucher {
+	return multicase.Voucher{
+		Type: "11", TypeText: "Faktura", Number: "100", Text: "Demo kunde",
+		Date: time.Date(2026, 10, 1, 0, 0, 0, 0, time.UTC), Lines: lines,
+	}
+}
+
+func TestSplitNet(t *testing.T) {
+	tests := []struct {
+		gross, want int64
+		rate        float64
+	}{
+		{270019, 216015, 25},
+		{-270019, -216015, 25},
+		{12500, 10000, 25},
+		{1, 1, 25},
+		{11200, 10000, 12},
+		{5000, 5000, 0},
+	}
+	for _, tt := range tests {
+		if got := SplitNet(tt.gross, tt.rate); got != tt.want {
+			t.Errorf("SplitNet(%d, %v) = %d, want %d", tt.gross, tt.rate, got, tt.want)
+		}
+	}
+}
+
+func TestBuildSplitsVATAndMapsCustomerLedger(t *testing.T) {
+	e, err := config().Build(voucher(
+		multicase.Line{Account: "3000", Amount: -270019, VATCode: "3", CustomerNo: "20001"},
+		multicase.Line{Account: "20001", Amount: 270019, CustomerNo: "20001"},
+	))
+	if err != nil {
+		t.Fatal(err)
+	}
+	want := []accounted.Line{
+		{Account: "3001", Credit: 216015},
+		{Account: "2611", Credit: 54004},
+		{Account: "1510", Debit: 270019},
+	}
+	if len(e.Lines) != len(want) {
+		t.Fatalf("lines = %+v", e.Lines)
+	}
+	for i, w := range want {
+		g := e.Lines[i]
+		if g.Account != w.Account || g.Debit != w.Debit || g.Credit != w.Credit {
+			t.Errorf("line %d = %+v, want %+v", i, g, w)
+		}
+	}
+	if e.SourceID != "multicase:11:100" || e.EntryDate != "2026-10-01" || e.Description != "Faktura 100: Demo kunde" {
+		t.Errorf("header = %+v", e)
+	}
+}
+
+func TestBuildReportsUnmapped(t *testing.T) {
+	_, err := config().Build(voucher(
+		multicase.Line{Account: "9999", Amount: -100},
+		multicase.Line{Account: "1460", Amount: 100, VATCode: "42"},
+	))
+	var u *UnmappedError
+	if !errors.As(err, &u) || len(u.Accounts) != 1 || u.Accounts[0] != "9999" || len(u.VATCodes) != 1 || u.VATCodes[0] != "42" {
+		t.Fatalf("err = %v", err)
+	}
+}
+
+func TestBuildRounding(t *testing.T) {
+	e, err := config().Build(voucher(
+		multicase.Line{Account: "1460", Amount: 1978734},
+		multicase.Line{Account: "4301", Amount: -1832162},
+		multicase.Line{Account: "4301", Amount: -146573},
+	))
+	if err != nil {
+		t.Fatal(err)
+	}
+	last := e.Lines[len(e.Lines)-1]
+	if last.Account != "3740" || last.Debit != 1 {
+		t.Errorf("rounding line = %+v", last)
+	}
+
+	_, err = config().Build(voucher(
+		multicase.Line{Account: "1460", Amount: 1000},
+		multicase.Line{Account: "4301", Amount: -500},
+	))
+	if err == nil {
+		t.Error("expected an error for a voucher off by more than max_rounding_ore")
+	}
+}
+
+func TestBuildSkipsZeroLines(t *testing.T) {
+	_, err := config().Build(voucher(multicase.Line{Account: "20001", Amount: 0, CustomerNo: "20001"}))
+	if !errors.Is(err, ErrEmpty) {
+		t.Fatalf("err = %v, want ErrEmpty", err)
+	}
+}