interpres/encode_test.go

// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
// SPDX-License-Identifier: MIT

package interpres

import (
	"bytes"
	"context"
	"errors"
	"math"
	"reflect"
	"strings"
	"testing"
	"time"
)

func TestMarshalScalars(t *testing.T) {
	type Cfg struct {
		Title    string  `toml:"title"`
		Count    int     `toml:"count"`
		Unsigned uint64  `toml:"unsigned"`
		Ratio    float64 `toml:"ratio"`
		Enabled  bool    `toml:"enabled"`
		Disabled bool    `toml:"disabled"`
	}
	out, err := Marshal(Cfg{
		Title:    "demo",
		Count:    42,
		Unsigned: 99,
		Ratio:    3.14,
		Enabled:  true,
		Disabled: false,
	})
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want := "title = \"demo\"\ncount = 42\nunsigned = 99\nratio = 3.14\nenabled = true\ndisabled = false\n"
	if string(out) != want {
		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestMarshalFloatSpecials(t *testing.T) {
	type Cfg struct {
		PosInf float64 `toml:"pos_inf"`
		NegInf float64 `toml:"neg_inf"`
		NaN    float64 `toml:"nan"`
		Zero   float64 `toml:"zero"`
		IntVal float64 `toml:"int_val"`
		NegZ   float64 `toml:"neg_zero"`
	}
	out, err := Marshal(Cfg{
		PosInf: math.Inf(1),
		NegInf: math.Inf(-1),
		NaN:    math.NaN(),
		Zero:   0,
		IntVal: 7,
		NegZ:   math.Copysign(0, -1),
	})
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want := "pos_inf = inf\nneg_inf = -inf\nnan = nan\nzero = 0.0\nint_val = 7.0\nneg_zero = 0.0\n"
	if string(out) != want {
		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestMarshalFloatNormalizesNegativeZero(t *testing.T) {
	// The output contract normalises negative zero to "0.0".
	type Cfg struct {
		Z float64 `toml:"z"`
	}
	out, err := Marshal(Cfg{Z: math.Copysign(0, -1)})
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want := "z = 0.0\n"
	if string(out) != want {
		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestMarshalContextHonoursCancellation(t *testing.T) {
	ctx, cancel := context.WithCancel(context.Background())
	cancel()
	type C struct {
		A int `toml:"a"`
	}
	if _, err := MarshalContext(ctx, C{A: 1}); !errors.Is(err, context.Canceled) {
		t.Fatalf("MarshalContext returned %v, want context.Canceled", err)
	}
	if _, err := NewEncoder().MarshalContext(ctx, C{A: 1}); !errors.Is(err, context.Canceled) {
		t.Fatalf("Encoder.MarshalContext returned %v, want context.Canceled", err)
	}
}

func TestEncoderGroupByKindDefault(t *testing.T) {
	// NewEncoder must default to GroupByKind=true so legacy callers keep the
	// scalars-first ordering.
	type Cfg struct {
		Name string `toml:"name"`
		S    struct {
			Host string `toml:"host"`
		} `toml:"s"`
	}
	out, err := NewEncoder().Marshal(Cfg{Name: "x", S: struct {
		Host string `toml:"host"`
	}{Host: "h"}})
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want := "name = \"x\"\n\n[s]\nhost = \"h\"\n"
	if string(out) != want {
		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestEncoderGroupByKindFalsePreservesOrder(t *testing.T) {
	type Inner struct {
		Host string `toml:"host"`
	}
	type Cfg struct {
		Name   string `toml:"name"`
		Server Inner  `toml:"server"`
		Debug  bool   `toml:"debug"`
	}
	in := Cfg{
		Name:   "x",
		Server: Inner{Host: "h"},
		Debug:  true,
	}
	out, err := NewEncoder().GroupByKind(false).Marshal(in)
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	// With GroupByKind(false) the encoder walks entries in declaration order.
	// The output is still parseable, but a scalar that follows a header is
	// parsed as a sub-table key. That is the user's trade-off; see
	// docs/API.md.
	want := "name = \"x\"\n\n[server]\nhost = \"h\"\ndebug = true\n"
	if string(out) != want {
		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestEncoderGroupByKindTrueDefaultOrder(t *testing.T) {
	// The default (GroupByKind=true) must lift the trailing scalar ahead of
	// the [server] block so the document round-trips losslessly.
	type Inner struct {
		Host string `toml:"host"`
	}
	type Cfg struct {
		Name   string `toml:"name"`
		Server Inner  `toml:"server"`
		Debug  bool   `toml:"debug"`
	}
	in := Cfg{
		Name:   "x",
		Server: Inner{Host: "h"},
		Debug:  true,
	}
	out, err := NewEncoder().Marshal(in)
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want := "name = \"x\"\ndebug = true\n\n[server]\nhost = \"h\"\n"
	if string(out) != want {
		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestEncoderOmitEmptyArrays(t *testing.T) {
	type Cfg struct {
		Tags    []string `toml:"tags"`
		Secrets []string `toml:"secrets"`
	}
	out, err := NewEncoder().OmitEmptyArrays().Marshal(Cfg{
		Tags:    []string{"a", "b"},
		Secrets: []string{},
	})
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want := "tags = [\"a\", \"b\"]\n"
	if string(out) != want {
		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestEncoderDefaultEmitsEmptyArray(t *testing.T) {
	type Cfg struct {
		Tags []string `toml:"tags"`
	}
	out, err := NewEncoder().Marshal(Cfg{Tags: []string{}})
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want := "tags = []\n"
	if string(out) != want {
		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestEncoderOmitEmptyArrayOfTablesStillSkipped(t *testing.T) {
	type Item struct {
		Name string `toml:"name"`
	}
	type Cfg struct {
		Title string `toml:"title"`
		Items []Item `toml:"items"`
	}
	out, err := NewEncoder().OmitEmptyArrays().Marshal(Cfg{
		Title: "demo",
		Items: nil,
	})
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want := "title = \"demo\"\n"
	if string(out) != want {
		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestEncoderUseLiteralMultiline(t *testing.T) {
	type Cfg struct {
		Long string `toml:"long"`
	}
	long := strings.Repeat("a", 50) + "\nline two\nline three"
	out, err := NewEncoder().UseLiteralMultiline(20).Marshal(Cfg{Long: long})
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want := "long = '''\n" + long + "\n'''\n"
	if string(out) != want {
		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestEncoderUseLiteralMultilineBelowThreshold(t *testing.T) {
	// A multi-line value shorter than the threshold must remain escaped.
	type Cfg struct {
		Short string `toml:"short"`
	}
	out, err := NewEncoder().UseLiteralMultiline(1000).Marshal(Cfg{Short: "one\ntwo"})
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want := "short = \"one\\ntwo\"\n"
	if string(out) != want {
		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestEncoderUseLiteralMultilineThresholdZero(t *testing.T) {
	// UseLiteralMultiline(0) disables the literal form entirely.
	type Cfg struct {
		S string `toml:"s"`
	}
	out, err := NewEncoder().UseLiteralMultiline(0).Marshal(Cfg{S: "a\nb\nc\nd"})
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	if !bytes.HasPrefix(out, []byte("s = \"")) {
		t.Errorf("output mismatch, expected basic quoted form:\ngot: %q", out)
	}
}

func TestEncoderLiteralMultilineFallsBackWhenUnsafe(t *testing.T) {
	// The literal form carries the value verbatim, so content it cannot
	// represent must fall back to the escaped basic string instead of
	// producing output that does not re-parse.
	cases := []struct {
		name string
		in   string
	}{
		{"embedded delimiter", "before ''' after\nsecond line"},
		{"control character", "a\x01b\nsecond"},
		{"delete character", "a\x7fb\nsecond"},
		{"lone carriage return", "first\rsecond\nthird"},
	}
	for _, c := range cases {
		out, err := NewEncoder().UseLiteralMultiline(5).Marshal(map[string]any{"s": c.in})
		if err != nil {
			t.Fatalf("%s: marshal: %v", c.name, err)
		}
		if !bytes.HasPrefix(out, []byte("s = \"")) {
			t.Errorf("%s: expected the basic quoted form, got:\n%s", c.name, out)
		}
		re, err := Parse(out)
		if err != nil {
			t.Errorf("%s: re-parse: %v\ndoc:\n%s", c.name, err, out)
			continue
		}
		if re["s"] != c.in {
			t.Errorf("%s: round-trip changed the value: %q", c.name, re["s"])
		}
	}
}

// marshalerFunc adapts a plain function value to the Marshaler interface.
// Tests use it to express "this field produces this TOML value" without a
// dedicated struct definition.
type marshalerFunc func() (any, error)

func (f marshalerFunc) MarshalTOML() (any, error) { return f() }

// failingMarshalerFunc invokes MarshalTOML to a fixed error; it lets us check
// that a MarshalTOML failure propagates back to Marshal.
type failingMarshalerFunc struct{}

func (failingMarshalerFunc) MarshalTOML() (any, error) {
	return nil, errors.New("oops")
}

func TestMarshalerReturningTime(t *testing.T) {
	// A Marshaler may return a date-time scalar; the encoder must emit it
	// using its canonical form.
	when := time.Date(2026, 6, 26, 10, 0, 0, 0, time.UTC)
	type Cfg struct {
		M marshalerFunc `toml:"m"`
	}
	out, err := Marshal(Cfg{M: marshalerFunc(func() (any, error) { return when, nil })})
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want := "m = 2026-06-26T10:00:00Z\n"
	if string(out) != want {
		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestMarshalerReturningDifferentStruct(t *testing.T) {
	// A Marshaler returning a struct (not a scalar) is treated as a sub-table
	// by the encoder.
	type Inner struct {
		V string `toml:"v"`
	}
	type Cfg struct {
		P marshalerFunc `toml:"p"`
	}
	out, err := Marshal(Cfg{P: marshalerFunc(func() (any, error) {
		return Inner{V: "x"}, nil
	})})
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want := "[p]\nv = \"x\"\n"
	if string(out) != want {
		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestMarshalerReturningSliceOfMaps(t *testing.T) {
	// A Marshaler returning []map[string]any becomes an array of tables.
	type Cfg struct {
		Items marshalerFunc `toml:"items"`
	}
	out, err := Marshal(Cfg{Items: marshalerFunc(func() (any, error) {
		return []map[string]any{
			{"k": "a"},
			{"k": "b"},
		}, nil
	})})
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want := "[[items]]\nk = \"a\"\n\n[[items]]\nk = \"b\"\n"
	if string(out) != want {
		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestMarshalerErrorPropagates(t *testing.T) {
	type Cfg struct {
		F failingMarshalerFunc `toml:"f"`
	}
	if _, err := Marshal(Cfg{F: failingMarshalerFunc{}}); err == nil {
		t.Fatal("expected an error from MarshalTOML")
	} else if !strings.Contains(err.Error(), "oops") {
		t.Errorf("err = %v, want substring \"oops\"", err)
	}
}

func TestMarshalEmbeddedScalarStruct(t *testing.T) {
	// A field declared directly as a scalar-struct type (here LocalDateTime)
	// must be encoded as a TOML scalar at the parent level, not rendered as
	// a sub-table.
	ldt := LocalDateTime{Time: time.Date(2026, 6, 26, 0, 0, 0, 0, time.UTC)}
	type Cfg struct {
		Name string        `toml:"name"`
		S    LocalDateTime `toml:"s"`
	}
	out, err := Marshal(Cfg{Name: "x", S: ldt})
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want := "name = \"x\"\ns = 2026-06-26T00:00:00\n"
	if string(out) != want {
		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestEncoderChainedOptions(t *testing.T) {
	// All chainable options combined; verify they compose without errors.
	type Inner struct {
		V string `toml:"v"`
	}
	type Cfg struct {
		S string `toml:"s"`
		I Inner  `toml:"i"`
	}
	long := strings.Repeat("x", 200)
	out, err := NewEncoder().
		GroupByKind(false).
		OmitEmptyArrays().
		UseLiteralMultiline(50).
		Marshal(Cfg{S: "short", I: Inner{V: long}})
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	_ = out // success path is enough; per-option correctness is exercised above.
}

func TestMarshalStringEscapes(t *testing.T) {
	cases := []struct {
		name string
		in   string
		want string // the TOML scalar value (without "s = " prefix)
	}{
		{"plain", "hello", `"hello"`},
		{"quote", `say "hi"`, `"say \"hi\""`},
		{"backslash", `a\b`, `"a\\b"`},
		{"newline", "line1\nline2", `"line1\nline2"`},
		{"tab", "col1\tcol2", `"col1\tcol2"`},
		{"cr", "line\rmore", `"line\rmore"`},
		{"control", "a\x01b", `"a\u0001b"`},
		{"unicode", "\u201csmart\u201d", `"“smart”"`}, // printable unicode; not escaped
		{"empty", "", `""`},
		{"slash_only", "a/b", `"a/b"`},
	}
	for _, c := range cases {
		out, err := Marshal(struct {
			S string `toml:"s"`
		}{S: c.in})
		if err != nil {
			t.Fatalf("%s: marshal: %v", c.name, err)
		}
		got := strings.TrimSuffix(string(out), "\n")
		want := "s = " + c.want
		if got != want {
			t.Errorf("%s:\ngot:  %s\nwant: %s", c.name, got, want)
		}
	}
}

func TestMarshalDateTime(t *testing.T) {
	type Cfg struct {
		Offset time.Time     `toml:"offset"`
		Local  LocalDateTime `toml:"local"`
		Day    LocalDate     `toml:"day"`
		Clock  LocalTime     `toml:"clock"`
	}
	out, err := Marshal(Cfg{
		Offset: time.Date(2026, 6, 26, 10, 0, 0, 0, time.UTC),
		Local:  LocalDateTime{Time: time.Date(2026, 6, 26, 7, 32, 0, 0, time.UTC)},
		Day:    LocalDate{Time: time.Date(2026, 6, 26, 0, 0, 0, 0, time.UTC)},
		Clock:  LocalTime{Time: time.Date(0, 1, 1, 7, 32, 0, 0, time.UTC)},
	})
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want := "offset = 2026-06-26T10:00:00Z\nlocal = 2026-06-26T07:32:00\nday = 2026-06-26\nclock = 07:32:00\n"
	if string(out) != want {
		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestMarshalDateTimeFractional(t *testing.T) {
	out, err := Marshal(struct {
		LDT LocalDateTime `toml:"ldt"`
		LT  LocalTime     `toml:"lt"`
	}{
		LDT: LocalDateTime{Time: time.Date(2026, 6, 26, 7, 32, 0, 123456789, time.UTC)},
		LT:  LocalTime{Time: time.Date(0, 1, 1, 7, 32, 0, 123, time.UTC)},
	})
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want := "ldt = 2026-06-26T07:32:00.123456789\nlt = 07:32:00.000000123\n"
	if string(out) != want {
		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestMarshalArraysOfScalars(t *testing.T) {
	type Cfg struct {
		Tags   []string `toml:"tags"`
		Ports  []int    `toml:"ports"`
		Mixed  []any    `toml:"mixed"`
		Empty  []int    `toml:"empty"`
		EmptyS []string `toml:"empty_s"`
	}
	out, err := Marshal(Cfg{
		Tags:   []string{"a", "b"},
		Ports:  []int{80, 443},
		Mixed:  []any{int64(1), "x", true},
		Empty:  nil,
		EmptyS: []string{},
	})
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want := "tags = [\"a\", \"b\"]\nports = [80, 443]\nmixed = [1, \"x\", true]\nempty_s = []\n"
	if string(out) != want {
		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestMarshalNestedArrays(t *testing.T) {
	type Cfg struct {
		Matrix [][]int    `toml:"matrix"`
		Words  [][]string `toml:"words"`
	}
	out, err := Marshal(Cfg{
		Matrix: [][]int{{1, 2}, {3, 4}},
		Words:  [][]string{{"a", "b"}, {"c"}},
	})
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want := "matrix = [[1, 2], [3, 4]]\nwords = [[\"a\", \"b\"], [\"c\"]]\n"
	if string(out) != want {
		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestMarshalMixedArrayWithInlineTable(t *testing.T) {
	// Parse accepts a mixed array (TOML allows any value kinds in one array),
	// so Marshal of the parsed tree must re-emit it. The table element has no
	// header form inside a value array and renders inline.
	tree, err := Parse([]byte("arr = [1, {a = 2}, \"x\"]\n"))
	if err != nil {
		t.Fatalf("parse: %v", err)
	}
	out, err := Marshal(tree)
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want := "arr = [1, {a = 2}, \"x\"]\n"
	if string(out) != want {
		t.Fatalf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
	re, err := Parse(out)
	if err != nil {
		t.Fatalf("re-parse: %v", err)
	}
	if !reflect.DeepEqual(tree, re) {
		t.Fatalf("round-trip changed the tree:\nwas: %#v\nnow: %#v", tree, re)
	}
}

func TestMarshalNestedInlineTables(t *testing.T) {
	tree := map[string]any{
		"mix": []any{
			int64(1),
			map[string]any{"deep": map[string]any{"n": int64(0)}, "list": []any{"a", true}},
			map[string]any{},
		},
	}
	out, err := Marshal(tree)
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want := "mix = [1, {deep = {n = 0}, list = [\"a\", true]}, {}]\n"
	if string(out) != want {
		t.Fatalf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestMarshalInlineTableWithDatetime(t *testing.T) {
	when := time.Date(1979, 5, 27, 7, 32, 0, 0, time.UTC)
	tree := map[string]any{
		"mix": []any{when, map[string]any{"t": LocalDateTime{when}}},
	}
	out, err := Marshal(tree)
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want := "mix = [1979-05-27T07:32:00Z, {t = 1979-05-27T07:32:00}]\n"
	if string(out) != want {
		t.Fatalf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestMarshalArrayOfTablesStaysHeaderForm(t *testing.T) {
	tree, err := Parse([]byte("[[items]]\nname = \"a\"\n\n[[items]]\nname = \"b\"\n"))
	if err != nil {
		t.Fatalf("parse: %v", err)
	}
	out, err := Marshal(tree)
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want := "[[items]]\nname = \"a\"\n\n[[items]]\nname = \"b\"\n"
	if string(out) != want {
		t.Fatalf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestMarshalFloatExponentNoLeadingZero(t *testing.T) {
	// strconv.FormatFloat with 'g' would produce "1e+06" (leading zero in
	// exponent). The encoder must strip it so the output is "1e+6".
	type Cfg struct {
		Large float64 `toml:"large"`
		Small float64 `toml:"small"`
	}
	out, err := Marshal(Cfg{Large: 1e6, Small: 1e-5})
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	// Parse to check the output is valid TOML (for a strict parser that
	// rejects leading zeros in exponents).
	if _, err := Parse(out); err != nil {
		t.Fatalf("marshalled output is not valid TOML:\n%s\nerror: %v", out, err)
	}
	if string(out) != "large = 1e+6\nsmall = 1e-5\n" {
		t.Errorf("output mismatch:\ngot: %q", out)
	}
}

func TestMarshalStructAsTable(t *testing.T) {
	type Server struct {
		Host string `toml:"host"`
		Port int    `toml:"port"`
	}
	type Cfg struct {
		Title  string `toml:"title"`
		Server Server `toml:"server"`
	}
	out, err := Marshal(Cfg{
		Title:  "demo",
		Server: Server{Host: "127.0.0.1", Port: 9090},
	})
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want := "title = \"demo\"\n\n[server]\nhost = \"127.0.0.1\"\nport = 9090\n"
	if string(out) != want {
		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestMarshalArrayOfTables(t *testing.T) {
	type Item struct {
		Name string `toml:"name"`
		Qty  int    `toml:"qty"`
	}
	type Cfg struct {
		Items []Item `toml:"items"`
	}
	out, err := Marshal(Cfg{
		Items: []Item{
			{Name: "a", Qty: 1},
			{Name: "b", Qty: 2},
		},
	})
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want := "[[items]]\nname = \"a\"\nqty = 1\n\n[[items]]\nname = \"b\"\nqty = 2\n"
	if string(out) != want {
		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestMarshalEmptyArrayOfTablesIsSkipped(t *testing.T) {
	type Item struct {
		Name string `toml:"name"`
	}
	type Cfg struct {
		Title string `toml:"title"`
		Items []Item `toml:"items"`
	}
	out, err := Marshal(Cfg{
		Title: "demo",
		Items: nil,
	})
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want := "title = \"demo\"\n"
	if string(out) != want {
		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestMarshalNestedTablesAndArrays(t *testing.T) {
	type SMTP struct {
		Host string `toml:"host"`
		Port int    `toml:"port"`
	}
	type Form struct {
		Name string `toml:"name"`
		SMTP SMTP   `toml:"smtp"`
	}
	type Cfg struct {
		Port  int    `toml:"port"`
		Forms []Form `toml:"forms"`
	}
	out, err := Marshal(Cfg{
		Port: 8080,
		Forms: []Form{
			{Name: "contact", SMTP: SMTP{Host: "h1", Port: 587}},
			{Name: "feedback", SMTP: SMTP{Host: "h2", Port: 25}},
		},
	})
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want := "port = 8080\n\n[[forms]]\nname = \"contact\"\n\n[forms.smtp]\nhost = \"h1\"\nport = 587\n\n[[forms]]\nname = \"feedback\"\n\n[forms.smtp]\nhost = \"h2\"\nport = 25\n"
	if string(out) != want {
		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestMarshalStructTags(t *testing.T) {
	type Cfg struct {
		Keep     string `toml:"keep"`
		Rename   string `toml:"renamed"`
		Skip     string `toml:"-"`
		Untagged string
	}
	out, err := Marshal(Cfg{
		Keep: "k", Rename: "r", Skip: "s", Untagged: "u",
	})
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want := "keep = \"k\"\nrenamed = \"r\"\nuntagged = \"u\"\n"
	if string(out) != want {
		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestMarshalEmbeddedStructPromoted(t *testing.T) {
	type Base struct {
		ID int `toml:"id"`
	}
	type Derived struct {
		Base
		Name string `toml:"name"`
	}
	out, err := Marshal(Derived{ID: 1, Name: "x"})
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want := "id = 1\nname = \"x\"\n"
	if string(out) != want {
		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestMarshalEmbeddedStructAsTable(t *testing.T) {
	type Inner struct {
		Host string `toml:"host"`
	}
	type Cfg struct {
		Inner Inner  `toml:"inner"`
		Name  string `toml:"name"`
	}
	out, err := Marshal(Cfg{Inner: Inner{Host: "h"}, Name: "n"})
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want := "name = \"n\"\n\n[inner]\nhost = \"h\"\n"
	if string(out) != want {
		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestMarshalTagOptionOmitZero(t *testing.T) {
	type Server struct {
		Host string `toml:"host"`
	}
	type Cfg struct {
		Name   string    `toml:"name,omitzero"`
		Count  int       `toml:"count,omitzero"`
		Ratio  float64   `toml:"ratio,omitzero"`
		When   time.Time `toml:"when,omitzero"`
		Server Server    `toml:"server,omitzero"`
		Always string    `toml:"always"`
	}
	out, err := Marshal(Cfg{Always: "kept"})
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	// Every omitzero field sits at its zero value, so only always is emitted.
	want := "always = \"kept\"\n"
	if string(out) != want {
		t.Fatalf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}

	when := time.Date(2026, 9, 17, 12, 0, 0, 0, time.UTC)
	out, err = Marshal(Cfg{Name: "x", Count: 1, Ratio: 0.5, When: when, Server: Server{Host: "h"}, Always: "kept"})
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want = "name = \"x\"\ncount = 1\nratio = 0.5\nwhen = 2026-09-17T12:00:00Z\nalways = \"kept\"\n\n[server]\nhost = \"h\"\n"
	if string(out) != want {
		t.Fatalf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestMarshalTagOptionOmitEmpty(t *testing.T) {
	type Cfg struct {
		Tags   []string       `toml:"tags,omitempty"`
		Ports  []int          `toml:"ports,omitempty"`
		Matrix [][]int        `toml:"matrix,omitempty"`
		Extra  map[string]any `toml:"extra,omitempty"`
		Name   string         `toml:"name,omitempty"`
		Keep   []string       `toml:"keep"`
	}
	out, err := Marshal(Cfg{
		Ports:  []int{},
		Matrix: [][]int{{1}},
		Extra:  map[string]any{},
		Name:   "set",
		Keep:   []string{},
	})
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	// tags is nil (omitted anyway), ports and extra are empty collections
	// dropped by omitempty, matrix is populated, name is a string the option
	// does not cover, keep is empty but carries no option so it emits [].
	want := "matrix = [[1]]\nname = \"set\"\nkeep = []\n"
	if string(out) != want {
		t.Fatalf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestMarshalTagOptionOnTaggedEmbeddedStruct(t *testing.T) {
	type Inner struct {
		N int `toml:"n"`
	}
	type Cfg struct {
		Inner Inner  `toml:"inner,omitzero"`
		Name  string `toml:"name"`
	}
	out, err := Marshal(Cfg{Name: "x"})
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want := "name = \"x\"\n"
	if string(out) != want {
		t.Fatalf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestMarshalMapKeysSorted(t *testing.T) {
	m := map[string]any{
		"zeta":  1,
		"alpha": 2,
		"mu":    3,
	}
	out, err := Marshal(m)
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want := "alpha = 2\nmu = 3\nzeta = 1\n"
	if string(out) != want {
		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestMarshalMapWithSubMap(t *testing.T) {
	m := map[string]any{
		"meta": map[string]any{"x": 1, "y": 2},
		"a":    "z",
	}
	out, err := Marshal(m)
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want := "a = \"z\"\n\n[meta]\nx = 1\ny = 2\n"
	if string(out) != want {
		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestMarshalMarshaler(t *testing.T) {
	type Port int
	type Cfg struct {
		P Port `toml:"p"`
	}
	out, err := Marshal(Cfg{P: 8080})
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want := "p = 8080\n"
	if string(out) != want {
		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestMarshalMarshalerReturningScalar(t *testing.T) {
	type Wrapped struct {
		Value string `toml:"value"`
	}
	type Alias struct{}
	out, err := Marshal(struct {
		W Wrapped `toml:"w"`
	}{W: Wrapped{Value: "hello"}})
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want := "[w]\nvalue = \"hello\"\n"
	if string(out) != want {
		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
	_ = Alias{}
}

func TestMarshalMarshalerReturningDifferentShape(t *testing.T) {
	out, err := Marshal(struct {
		C Custom `toml:"c"`
	}{C: Custom{tag: "x"}})
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	// Custom returns a string from MarshalTOML.
	want := "c = \"x\"\n"
	if string(out) != want {
		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestMarshalNilPointerFieldSkipped(t *testing.T) {
	type Cfg struct {
		Name   string  `toml:"name"`
		Hidden *string `toml:"hidden"`
	}
	out, err := Marshal(Cfg{Name: "x"})
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want := "name = \"x\"\n"
	if string(out) != want {
		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestMarshalNonNilPointerFollowed(t *testing.T) {
	v := "v"
	type Cfg struct {
		Name   string  `toml:"name"`
		Hidden *string `toml:"hidden"`
	}
	out, err := Marshal(Cfg{Name: "n", Hidden: &v})
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want := "name = \"n\"\nhidden = \"v\"\n"
	if string(out) != want {
		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestMarshalTopLevelMustBeStructOrMap(t *testing.T) {
	if _, err := Marshal(42); err == nil {
		t.Errorf("expected error marshalling int at top level")
	}
	if _, err := Marshal("hello"); err == nil {
		t.Errorf("expected error marshalling string at top level")
	}
	if _, err := Marshal(nil); err == nil {
		t.Errorf("expected error marshalling nil")
	}
}

func TestMarshalMapKeyMustBeString(t *testing.T) {
	m := map[int]any{1: "x"}
	if _, err := Marshal(m); err == nil {
		t.Errorf("expected error for non-string map key")
	}
}

func TestMarshalUnexportedFieldSkipped(t *testing.T) {
	type Cfg struct {
		Pub  string `toml:"pub"`
		priv string
	}
	out, err := Marshal(Cfg{Pub: "p", priv: "s"})
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want := "pub = \"p\"\n"
	if string(out) != want {
		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestMarshalBareAndQuotedKeys(t *testing.T) {
	type Cfg struct {
		Bare string `toml:"bare_key"`
		Dash string `toml:"with-dash"`
		Num  string `toml:"num123"`
		Q    string `toml:"needs space"`
		Dot  string `toml:"needs.dot"`
	}
	out, err := Marshal(Cfg{
		Bare: "a", Dash: "b", Num: "c", Q: "d", Dot: "e",
	})
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	want := "bare_key = \"a\"\nwith-dash = \"b\"\nnum123 = \"c\"\n\"needs space\" = \"d\"\n\"needs.dot\" = \"e\"\n"
	if string(out) != want {
		t.Errorf("output mismatch:\ngot:  %q\nwant: %q", out, want)
	}
}

func TestMarshalThenParseRoundTrip(t *testing.T) {
	type Server struct {
		Host    string   `toml:"host"`
		Port    int      `toml:"port"`
		Enabled bool     `toml:"enabled"`
		Tags    []string `toml:"tags"`
	}
	type Form struct {
		Name    string   `toml:"name"`
		Allowed []string `toml:"allowed"`
	}
	type Cfg struct {
		Title  string    `toml:"title"`
		Count  int       `toml:"count"`
		Ratio  float64   `toml:"ratio"`
		Server Server    `toml:"server"`
		Forms  []Form    `toml:"forms"`
		Due    time.Time `toml:"due"`
		Day    LocalDate `toml:"day"`
	}
	in := Cfg{
		Title: "demo",
		Count: 42,
		Ratio: 3.14,
		Server: Server{
			Host: "127.0.0.1", Port: 9090, Enabled: true,
			Tags: []string{"a", "b"},
		},
		Forms: []Form{
			{Name: "contact", Allowed: []string{"x"}},
			{Name: "feedback", Allowed: nil},
		},
		Due: time.Date(2026, 6, 26, 10, 0, 0, 0, time.UTC),
		Day: LocalDate{Time: time.Date(2026, 6, 26, 0, 0, 0, 0, time.UTC)},
	}
	out, err := Marshal(in)
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	tree1, err := Parse(out)
	if err != nil {
		t.Fatalf("parse of marshalled: %v\noutput:\n%s", err, out)
	}
	// Decode back into the struct.
	var out2 Cfg
	if err := Unmarshal(out, &out2); err != nil {
		t.Fatalf("unmarshal of marshalled: %v", err)
	}
	if !reflect.DeepEqual(in, out2) {
		t.Errorf("round-trip mismatch:\nin:  %#v\nout: %#v", in, out2)
	}
	_ = tree1
}

func TestMarshalRoundTripFromUntypedTree(t *testing.T) {
	src := []byte(`title = "demo"
count = 42
ratio = 3.14
enabled = true

[server]
host = "127.0.0.1"
port = 9090

[[items]]
name = "a"
qty = 1

[[items]]
name = "b"
qty = 2

[meta]
created = 2026-06-26T10:00:00Z
`)
	tree1, err := Parse(src)
	if err != nil {
		t.Fatalf("parse src: %v", err)
	}
	out, err := Marshal(tree1)
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	tree2, err := Parse(out)
	if err != nil {
		t.Fatalf("re-parse marshalled: %v\noutput:\n%s", err, out)
	}
	if !reflect.DeepEqual(tree1, tree2) {
		t.Errorf("round-trip mismatch:\nbefore: %#v\nafter:  %#v", tree1, tree2)
	}
}

func TestMarshalUintOverflow(t *testing.T) {
	type Cfg struct {
		Big uint64 `toml:"big"`
	}
	if _, err := Marshal(Cfg{Big: 1<<63 + 1}); err == nil {
		t.Errorf("expected overflow error")
	}
}

func TestMarshalKeyRequiresUTF8(t *testing.T) {
	m := map[string]any{"\xff": "x"}
	if _, err := Marshal(m); err == nil {
		t.Errorf("expected error for invalid UTF-8 key")
	}
}

func TestMarshalStringRequiresUTF8(t *testing.T) {
	type Cfg struct {
		S string `toml:"s"`
	}
	if _, err := Marshal(Cfg{S: "abc\xff"}); err == nil {
		t.Errorf("expected error for invalid UTF-8 string")
	}
}

func TestLocalDateString(t *testing.T) {
	ld := LocalDate{Time: time.Date(1979, 5, 27, 0, 0, 0, 0, time.UTC)}
	if got := ld.String(); got != "1979-05-27" {
		t.Errorf("LocalDate.String() = %q, want 1979-05-27", got)
	}
}

func TestLocalDateTimeString(t *testing.T) {
	ldt := LocalDateTime{Time: time.Date(1979, 5, 27, 7, 32, 0, 0, time.UTC)}
	if got := ldt.String(); got != "1979-05-27T07:32:00" {
		t.Errorf("LocalDateTime.String() = %q, want 1979-05-27T07:32:00", got)
	}
	ldt2 := LocalDateTime{Time: time.Date(1979, 5, 27, 7, 32, 0, 5, time.UTC)}
	if got := ldt2.String(); got != "1979-05-27T07:32:00.000000005" {
		t.Errorf("LocalDateTime.String() = %q, want 1979-05-27T07:32:00.000000005", got)
	}
	ldt3 := LocalDateTime{Time: time.Date(1979, 5, 27, 7, 32, 0, 500, time.UTC)}
	if got := ldt3.String(); got != "1979-05-27T07:32:00.000000500" {
		t.Errorf("LocalDateTime.String() = %q, want 1979-05-27T07:32:00.000000500", got)
	}
}

func TestLocalTimeString(t *testing.T) {
	lt := LocalTime{Time: time.Date(0, 1, 1, 7, 32, 0, 0, time.UTC)}
	if got := lt.String(); got != "07:32:00" {
		t.Errorf("LocalTime.String() = %q, want 07:32:00", got)
	}
}

func TestEncoderEquivalenceToMarshal(t *testing.T) {
	type Cfg struct {
		Title string `toml:"title"`
		Count int    `toml:"count"`
	}
	in := Cfg{Title: "x", Count: 7}
	a, err := Marshal(in)
	if err != nil {
		t.Fatalf("marshal: %v", err)
	}
	b, err := NewEncoder().Marshal(in)
	if err != nil {
		t.Fatalf("encoder marshal: %v", err)
	}
	if !reflect.DeepEqual(a, b) {
		t.Errorf("Marshal and Encoder disagree:\n%s\n%s", a, b)
	}
}

type Custom struct {
	tag string
}

func (c Custom) MarshalTOML() (any, error) { return c.tag, nil }

// encodeErrBad is a Marshaler whose MarshalTOML always fails.
type encodeErrBad struct {
	msg string
}

func (encodeErrBad) MarshalTOML() (any, error) { return nil, errors.New("bad timestamp") }

func TestEncodeErrorCarriesPath(t *testing.T) {
	type Inner struct {
		Port encodeErrBad `toml:"port"`
	}
	type Cfg struct {
		Server Inner `toml:"server"`
	}
	_, err := Marshal(Cfg{Server: Inner{Port: encodeErrBad{}}})
	if err == nil {
		t.Fatal("expected a marshal error")
	}
	ee, ok := errors.AsType[*EncodeError](err)
	if !ok {
		t.Fatalf("expected an *EncodeError, got %T: %v", err, err)
	}
	if ee.Path != "server.port" {
		t.Fatalf("Path = %q, want %q", ee.Path, "server.port")
	}
	if ee.Err == nil || ee.Err.Error() != "bad timestamp" {
		t.Fatalf("Err = %v", ee.Err)
	}
	if err.Error() != "interpres: server.port: bad timestamp" {
		t.Fatalf("message = %q", err.Error())
	}
}

func TestEncodeErrorTopLevelPathHasNoLeadingDot(t *testing.T) {
	type Cfg struct {
		Port encodeErrBad `toml:"port"`
	}
	_, err := Marshal(Cfg{})
	ee, ok := errors.AsType[*EncodeError](err)
	if !ok {
		t.Fatalf("expected an *EncodeError, got %T: %v", err, err)
	}
	if ee.Path != "port" {
		t.Fatalf("Path = %q, want %q", ee.Path, "port")
	}
	if err.Error() != "interpres: port: bad timestamp" {
		t.Fatalf("message = %q", err.Error())
	}
}

func TestEncodeErrorHeterogeneousArrayPath(t *testing.T) {
	type Item struct {
		N int `toml:"n"`
	}
	cfg := map[string]any{
		"items": []any{Item{}, 3},
	}
	_, err := Marshal(cfg)
	if err == nil {
		t.Fatal("expected a heterogeneous array error")
	}
	ee, ok := errors.AsType[*EncodeError](err)
	if !ok {
		t.Fatalf("expected an *EncodeError, got %T: %v", err, err)
	}
	if ee.Path != "items[0]" {
		t.Fatalf("Path = %q, want %q", ee.Path, "items[0]")
	}
}