money/internal/config/config_test.go

package config

import (
	"os"
	"path/filepath"
	"strings"
	"testing"
)

// writeUserConfig points XDG_CONFIG_HOME at a temporary directory and puts a
// config file in it, so tests never touch the real one.
func writeUserConfig(t *testing.T, body string) string {
	t.Helper()
	dir := t.TempDir()
	t.Setenv("XDG_CONFIG_HOME", dir)
	if body == "" {
		return dir
	}
	cfgDir := filepath.Join(dir, "money")
	if err := os.MkdirAll(cfgDir, 0o755); err != nil {
		t.Fatal(err)
	}
	if err := os.WriteFile(filepath.Join(cfgDir, "config.toml"), []byte(body), 0o644); err != nil {
		t.Fatal(err)
	}
	return dir
}

func TestResolveRootPrecedence(t *testing.T) {
	home, err := os.UserHomeDir()
	if err != nil {
		t.Skip("no home directory in this environment")
	}

	t.Run("flag beats everything", func(t *testing.T) {
		writeUserConfig(t, "root = \"/from/config\"\n")
		t.Setenv("MONEY_ROOT", "/from/env")

		root, source, err := ResolveRoot("/from/flag")
		if err != nil {
			t.Fatal(err)
		}
		if root != "/from/flag" || source != RootFromFlag {
			t.Errorf("got %q from %q, want /from/flag from the flag", root, source)
		}
	})

	t.Run("env beats config", func(t *testing.T) {
		writeUserConfig(t, "root = \"/from/config\"\n")
		t.Setenv("MONEY_ROOT", "/from/env")

		root, source, err := ResolveRoot("")
		if err != nil {
			t.Fatal(err)
		}
		if root != "/from/env" || source != RootFromEnv {
			t.Errorf("got %q from %q, want /from/env from the environment", root, source)
		}
	})

	t.Run("config beats the default", func(t *testing.T) {
		writeUserConfig(t, "root = \"/from/config\"\n")
		t.Setenv("MONEY_ROOT", "")

		root, source, err := ResolveRoot("")
		if err != nil {
			t.Fatal(err)
		}
		if root != "/from/config" || source != RootFromConfig {
			t.Errorf("got %q from %q, want /from/config from the config file", root, source)
		}
	})

	t.Run("default when nothing is set", func(t *testing.T) {
		writeUserConfig(t, "") // XDG dir exists but holds no config file
		t.Setenv("MONEY_ROOT", "")

		root, source, err := ResolveRoot("")
		if err != nil {
			t.Fatal(err)
		}
		want := filepath.Join(home, "money")
		if root != want || source != RootFromDefault {
			t.Errorf("got %q from %q, want %q from the default", root, source, want)
		}
	})

	// A hand-written config file is likely to contain a tilde, which no shell
	// has expanded for us.
	t.Run("tilde in the config file is expanded", func(t *testing.T) {
		writeUserConfig(t, "root = \"~/finances\"\n")
		t.Setenv("MONEY_ROOT", "")

		root, _, err := ResolveRoot("")
		if err != nil {
			t.Fatal(err)
		}
		want := filepath.Join(home, "finances")
		if root != want {
			t.Errorf("root = %q, want %q", root, want)
		}
	})

	t.Run("relative paths become absolute", func(t *testing.T) {
		writeUserConfig(t, "")
		t.Setenv("MONEY_ROOT", "some/relative/dir")

		root, _, err := ResolveRoot("")
		if err != nil {
			t.Fatal(err)
		}
		if !filepath.IsAbs(root) {
			t.Errorf("root = %q, want an absolute path", root)
		}
	})
}

func TestAppendRule(t *testing.T) {
	root := t.TempDir()
	existing := "[[rule]]\ntag = \"salary\"\nmatch = \"*PAYROLL*\"\n"
	if err := os.WriteFile(filepath.Join(root, RulesFile), []byte(existing), 0o644); err != nil {
		t.Fatal(err)
	}

	if err := AppendRule(root, Rule{Match: "*LIDL*", Tag: "groceries", Account: "checking"}); err != nil {
		t.Fatal(err)
	}

	loaded, err := LoadRules(root)
	if err != nil {
		t.Fatalf("the file no longer parses after appending: %v", err)
	}
	if len(loaded.Rule) != 2 {
		t.Fatalf("got %d rules, want 2: %+v", len(loaded.Rule), loaded.Rule)
	}

	// Appending, not prepending: the existing rule keeps precedence.
	if loaded.Rule[0].Tag != "salary" {
		t.Errorf("first rule = %+v, want the pre-existing salary rule", loaded.Rule[0])
	}
	added := loaded.Rule[1]
	if added.Match != "*LIDL*" || added.Tag != "groceries" || added.Account != "checking" {
		t.Errorf("appended rule = %+v", added)
	}
}

func TestAppendRuleCreatesFile(t *testing.T) {
	root := t.TempDir()
	if err := AppendRule(root, Rule{Match: "*LIDL*", Tag: "groceries"}); err != nil {
		t.Fatal(err)
	}
	loaded, err := LoadRules(root)
	if err != nil {
		t.Fatal(err)
	}
	if len(loaded.Rule) != 1 || loaded.Rule[0].Match != "*LIDL*" {
		t.Errorf("rules = %+v, want the one appended rule", loaded.Rule)
	}
	// An omitted account must not be written as an empty string.
	if loaded.Rule[0].Account != "" {
		t.Errorf("account = %q, want empty", loaded.Rule[0].Account)
	}
}

func TestAppendRuleRejectsIncomplete(t *testing.T) {
	root := t.TempDir()
	cases := map[string]Rule{
		"no pattern": {Tag: "groceries"},
		"no verdict": {Match: "*LIDL*"},
	}
	for name, r := range cases {
		if err := AppendRule(root, r); err == nil {
			t.Errorf("%s: expected an error", name)
		}
	}
	if _, err := os.Stat(filepath.Join(root, RulesFile)); !os.IsNotExist(err) {
		t.Error("a rejected rule must not create the file")
	}
}

// Globs and tags containing quotes must survive the round trip.
func TestAppendRuleQuotesValues(t *testing.T) {
	root := t.TempDir()
	if err := AppendRule(root, Rule{Match: `*"ODD" PAYEE*`, Tag: "misc"}); err != nil {
		t.Fatal(err)
	}
	loaded, err := LoadRules(root)
	if err != nil {
		t.Fatalf("quoted values broke the file: %v", err)
	}
	if loaded.Rule[0].Match != `*"ODD" PAYEE*` {
		t.Errorf("match = %q, want the quotes preserved", loaded.Rule[0].Match)
	}
}

// A note is documentation carried with the rule. It is a key rather than a
// comment precisely so it survives the round trip.
func TestAppendRuleWithNote(t *testing.T) {
	root := t.TempDir()
	note := `the "corner shop" — 4412 is the branch code`
	if err := AppendRule(root, Rule{Match: "*4412*", Tag: "groceries", Note: note}); err != nil {
		t.Fatal(err)
	}
	loaded, err := LoadRules(root)
	if err != nil {
		t.Fatalf("the note broke the file: %v", err)
	}
	if loaded.Rule[0].Note != note {
		t.Errorf("note = %q, want %q", loaded.Rule[0].Note, note)
	}
	// A note alone is not a rule; the usual validation still applies.
	if err := AppendRule(root, Rule{Note: "just a thought"}); err == nil {
		t.Error("expected a rule with only a note to be rejected")
	}
}

// Deleting a rule takes its note with it and leaves everyone else's alone.
func TestDeleteRuleTakesItsNote(t *testing.T) {
	root := t.TempDir()
	path := filepath.Join(root, RulesFile)
	original := `[[rule]]
match = "*LIDL*"
tag   = "groceries"
note  = "the weekly shop"

[[rule]]
match = "*ZARA*"
tag   = "clothes"
note  = "keep: for the January review"
`
	if err := os.WriteFile(path, []byte(original), 0o644); err != nil {
		t.Fatal(err)
	}
	if _, err := DeleteRules(root, []int{0}); err != nil {
		t.Fatal(err)
	}
	raw, err := os.ReadFile(path)
	if err != nil {
		t.Fatal(err)
	}
	if strings.Contains(string(raw), "weekly shop") {
		t.Errorf("rules.toml = %q, want the deleted rule's note gone with it", raw)
	}
	loaded, err := LoadRules(root)
	if err != nil {
		t.Fatal(err)
	}
	if len(loaded.Rule) != 1 || loaded.Rule[0].Note != "keep: for the January review" {
		t.Errorf("rules = %+v, want the surviving rule to keep its note", loaded.Rule)
	}
}

const rulesWithComments = `# Rules for my accounts.
# Order matters: the first match wins.

# Weekly shop.
[[rule]]
match = "*LIDL*"
tag   = "groceries"

[[rule]]
match = "*PAYROLL*"
tag   = "salary"

# Moving money to myself.
[[rule]]
match = "*TO SAVINGS*"
tag   = "transfer"
`

// Deleting must edit the file textually: a user's comments and layout are not
// recoverable from the parsed rules.
func TestDeleteRulesKeepsCommentsAndOrder(t *testing.T) {
	root := t.TempDir()
	path := filepath.Join(root, RulesFile)
	if err := os.WriteFile(path, []byte(rulesWithComments), 0o644); err != nil {
		t.Fatal(err)
	}

	n, err := DeleteRules(root, []int{1}) // the payroll rule, which has no comment
	if err != nil {
		t.Fatal(err)
	}
	if n != 1 {
		t.Errorf("deleted %d rules, want 1", n)
	}

	loaded, err := LoadRules(root)
	if err != nil {
		t.Fatal(err)
	}
	if len(loaded.Rule) != 2 {
		t.Fatalf("got %d rules, want 2: %+v", len(loaded.Rule), loaded.Rule)
	}
	if loaded.Rule[0].Match != "*LIDL*" || loaded.Rule[1].Match != "*TO SAVINGS*" {
		t.Errorf("surviving rules = %+v, want the order preserved", loaded.Rule)
	}

	body, err := os.ReadFile(path)
	if err != nil {
		t.Fatal(err)
	}
	text := string(body)
	for _, want := range []string{
		"# Rules for my accounts.",
		"# Order matters: the first match wins.",
		"# Weekly shop.",
		"# Moving money to myself.",
	} {
		if !strings.Contains(text, want) {
			t.Errorf("comment %q was lost:\n%s", want, text)
		}
	}
	if strings.Contains(text, "PAYROLL") {
		t.Errorf("the deleted rule is still there:\n%s", text)
	}
}

// A comment directly above a rule documents it and goes with it; a heading
// separated by a blank line does not.
func TestDeleteRulesTakesAttachedComment(t *testing.T) {
	root := t.TempDir()
	if err := os.WriteFile(filepath.Join(root, RulesFile), []byte(rulesWithComments), 0o644); err != nil {
		t.Fatal(err)
	}

	if _, err := DeleteRules(root, []int{0}); err != nil { // the commented LIDL rule
		t.Fatal(err)
	}
	body, _ := os.ReadFile(filepath.Join(root, RulesFile))
	text := string(body)

	if strings.Contains(text, "# Weekly shop.") {
		t.Errorf("the rule's own comment should have gone with it:\n%s", text)
	}
	if !strings.Contains(text, "# Rules for my accounts.") {
		t.Errorf("the file heading must survive:\n%s", text)
	}
}

func TestDeleteRulesMultiple(t *testing.T) {
	root := t.TempDir()
	if err := os.WriteFile(filepath.Join(root, RulesFile), []byte(rulesWithComments), 0o644); err != nil {
		t.Fatal(err)
	}

	n, err := DeleteRules(root, []int{0, 2})
	if err != nil {
		t.Fatal(err)
	}
	if n != 2 {
		t.Errorf("deleted %d, want 2", n)
	}
	loaded, err := LoadRules(root)
	if err != nil {
		t.Fatal(err)
	}
	if len(loaded.Rule) != 1 || loaded.Rule[0].Match != "*PAYROLL*" {
		t.Errorf("remaining = %+v, want only the payroll rule", loaded.Rule)
	}
}

func TestDeleteRulesAll(t *testing.T) {
	root := t.TempDir()
	if err := os.WriteFile(filepath.Join(root, RulesFile), []byte(rulesWithComments), 0o644); err != nil {
		t.Fatal(err)
	}
	if _, err := DeleteRules(root, []int{0, 1, 2}); err != nil {
		t.Fatal(err)
	}
	loaded, err := LoadRules(root)
	if err != nil {
		t.Fatalf("emptying the file must leave it loadable: %v", err)
	}
	if len(loaded.Rule) != 0 {
		t.Errorf("got %+v, want no rules", loaded.Rule)
	}
}

func TestDeleteRulesOutOfRange(t *testing.T) {
	root := t.TempDir()
	if err := os.WriteFile(filepath.Join(root, RulesFile), []byte(rulesWithComments), 0o644); err != nil {
		t.Fatal(err)
	}
	if _, err := DeleteRules(root, []int{7}); err == nil {
		t.Error("expected an error for an out-of-range position")
	}
	loaded, _ := LoadRules(root)
	if len(loaded.Rule) != 3 {
		t.Error("a rejected delete must leave the file untouched")
	}
}

// Deleting nothing is a no-op, not a rewrite.
func TestDeleteRulesEmptySelection(t *testing.T) {
	root := t.TempDir()
	path := filepath.Join(root, RulesFile)
	if err := os.WriteFile(path, []byte(rulesWithComments), 0o644); err != nil {
		t.Fatal(err)
	}
	if n, err := DeleteRules(root, nil); err != nil || n != 0 {
		t.Fatalf("n=%d err=%v, want 0 and no error", n, err)
	}
	body, _ := os.ReadFile(path)
	if string(body) != rulesWithComments {
		t.Error("the file was rewritten despite deleting nothing")
	}
}

func TestUserConfigPathFollowsXDG(t *testing.T) {
	t.Setenv("XDG_CONFIG_HOME", "/custom/config")
	path, err := UserConfigPath()
	if err != nil {
		t.Fatal(err)
	}
	if want := "/custom/config/money/config.toml"; path != want {
		t.Errorf("path = %q, want %q", path, want)
	}

	// Unset, it falls back to ~/.config.
	t.Setenv("XDG_CONFIG_HOME", "")
	home, err := os.UserHomeDir()
	if err != nil {
		t.Skip("no home directory in this environment")
	}
	path, err = UserConfigPath()
	if err != nil {
		t.Fatal(err)
	}
	if want := filepath.Join(home, ".config", "money", "config.toml"); path != want {
		t.Errorf("path = %q, want %q", path, want)
	}
}

// A missing config file is normal, not an error.
func TestLoadUserConfigMissingFile(t *testing.T) {
	writeUserConfig(t, "")
	c, path, err := LoadUserConfig()
	if err != nil {
		t.Fatalf("a missing config file should not be an error: %v", err)
	}
	if c.Root != "" {
		t.Errorf("root = %q, want empty", c.Root)
	}
	if path == "" {
		t.Error("expected the path to be reported even when the file is absent")
	}
}

// A malformed config file is an error, so a typo does not silently send the
// tool to the wrong directory.
func TestLoadUserConfigMalformed(t *testing.T) {
	writeUserConfig(t, "root = this is not valid toml\n")
	if _, _, err := LoadUserConfig(); err == nil {
		t.Error("expected an error for a malformed config file")
	}
}

func TestAppendTransfer(t *testing.T) {
	root := t.TempDir()
	existing := "[[rule]]\nmatch = \"*LIDL*\"\ntag = \"groceries\"\n"
	if err := os.WriteFile(filepath.Join(root, RulesFile), []byte(existing), 0o644); err != nil {
		t.Fatal(err)
	}

	tr := Transfer{
		FromAccount: "nlb", FromDesc: "*TO REVOLUT*",
		ToAccount: "revolut", ToDesc: "*FROM NLB*",
		Note: `the monthly "top-up"`,
	}
	if err := AppendTransfer(root, tr); err != nil {
		t.Fatal(err)
	}

	loaded, err := LoadRules(root)
	if err != nil {
		t.Fatalf("the file no longer parses after appending: %v", err)
	}
	if len(loaded.Rule) != 1 {
		t.Errorf("got %d rules, want the existing one untouched", len(loaded.Rule))
	}
	if len(loaded.Transfer) != 1 || loaded.Transfer[0] != tr {
		t.Errorf("transfers = %+v, want %+v", loaded.Transfer, tr)
	}
}

// Both sides are required: a one-sided definition can never pair anything, so
// it is refused rather than written and silently ignored.
func TestTransferNeedsBothSides(t *testing.T) {
	full := Transfer{FromAccount: "a", FromDesc: "*OUT*", ToAccount: "b", ToDesc: "*IN*"}
	cases := map[string]func(*Transfer){
		"no from_account": func(t *Transfer) { t.FromAccount = "" },
		"no from_desc":    func(t *Transfer) { t.FromDesc = "" },
		"no to_account":   func(t *Transfer) { t.ToAccount = "" },
		"no to_desc":      func(t *Transfer) { t.ToDesc = "" },
	}
	for name, break_ := range cases {
		root := t.TempDir()
		tr := full
		break_(&tr)
		if err := AppendTransfer(root, tr); err == nil {
			t.Errorf("%s: expected an error", name)
		}
		if _, err := os.Stat(filepath.Join(root, RulesFile)); !os.IsNotExist(err) {
			t.Errorf("%s: a rejected transfer must not create the file", name)
		}
	}

	// The same check applies to a file written by hand.
	root := t.TempDir()
	body := "[[transfer]]\nfrom_account = \"nlb\"\nfrom_desc = \"*OUT*\"\nto_account = \"revolut\"\n"
	if err := os.WriteFile(filepath.Join(root, RulesFile), []byte(body), 0o644); err != nil {
		t.Fatal(err)
	}
	if _, err := LoadRules(root); err == nil {
		t.Error("expected a half-written transfer to be refused on load")
	}
}

// Rules and transfers share a file, so deleting one kind must not take a
// neighbouring block of the other kind with it.
func TestDeleteLeavesTheOtherKindAlone(t *testing.T) {
	root := t.TempDir()
	path := filepath.Join(root, RulesFile)
	original := `[[rule]]
match = "*LIDL*"
tag   = "groceries"

# Moving money to the broker.
[[transfer]]
from_account = "nlb"
from_desc    = "*TO TRADEREPUBLIC*"
to_account   = "traderepublic"
to_desc      = "*FROM NLB*"

[[rule]]
match = "*ZARA*"
tag   = "clothes"
`
	if err := os.WriteFile(path, []byte(original), 0o644); err != nil {
		t.Fatal(err)
	}

	// Deleting the first rule must stop at the transfer that follows it.
	if _, err := DeleteRules(root, []int{0}); err != nil {
		t.Fatal(err)
	}
	loaded, err := LoadRules(root)
	if err != nil {
		t.Fatal(err)
	}
	if len(loaded.Rule) != 1 || loaded.Rule[0].Tag != "clothes" {
		t.Errorf("rules = %+v, want only the clothes rule left", loaded.Rule)
	}
	if len(loaded.Transfer) != 1 {
		t.Fatalf("transfers = %+v, want the transfer untouched", loaded.Transfer)
	}
	raw, err := os.ReadFile(path)
	if err != nil {
		t.Fatal(err)
	}
	if !strings.Contains(string(raw), "# Moving money to the broker.") {
		t.Errorf("rules.toml = %q, want the transfer's own comment kept", raw)
	}

	// And deleting the transfer leaves the remaining rule alone.
	if _, err := DeleteTransfers(root, []int{0}); err != nil {
		t.Fatal(err)
	}
	loaded, err = LoadRules(root)
	if err != nil {
		t.Fatal(err)
	}
	if len(loaded.Transfer) != 0 || len(loaded.Rule) != 1 {
		t.Errorf("after deleting the transfer: %d rules, %d transfers; want 1 and 0",
			len(loaded.Rule), len(loaded.Transfer))
	}
	if raw, err = os.ReadFile(path); err != nil {
		t.Fatal(err)
	}
	if strings.Contains(string(raw), "Moving money to the broker") {
		t.Errorf("rules.toml = %q, want the deleted transfer's comment gone with it", raw)
	}
}

func TestDeleteTransfersOutOfRange(t *testing.T) {
	root := t.TempDir()
	if err := AppendTransfer(root, Transfer{
		FromAccount: "a", FromDesc: "*OUT*", ToAccount: "b", ToDesc: "*IN*",
	}); err != nil {
		t.Fatal(err)
	}
	if _, err := DeleteTransfers(root, []int{3}); err == nil {
		t.Error("expected an out-of-range position to be refused")
	}
}

// A tolerance survives the round trip through the file, and a definition
// without one keeps meaning what it always meant: exact amounts.
func TestAppendTransferWithTolerance(t *testing.T) {
	root := t.TempDir()
	tr := Transfer{
		FromAccount: "nlb", FromDesc: "*TO REVOLUT*",
		ToAccount: "revolut", ToDesc: "*FROM NLB*",
		TolerancePct: 1.5,
		Note:         "NLB takes a wire fee",
	}
	if err := AppendTransfer(root, tr); err != nil {
		t.Fatal(err)
	}

	body, err := os.ReadFile(filepath.Join(root, RulesFile))
	if err != nil {
		t.Fatal(err)
	}
	if !strings.Contains(string(body), "tolerance_pct = 1.5") {
		t.Errorf("file = %q, want the tolerance written unquoted", body)
	}

	loaded, err := LoadRules(root)
	if err != nil {
		t.Fatal(err)
	}
	if len(loaded.Transfer) != 1 || loaded.Transfer[0] != tr {
		t.Errorf("transfers = %+v, want %+v", loaded.Transfer, tr)
	}
}

// The default is exact, so an unset tolerance must not be written out as a key
// suggesting the definition decided something.
func TestAppendTransferOmitsAZeroTolerance(t *testing.T) {
	root := t.TempDir()
	tr := Transfer{
		FromAccount: "nlb", FromDesc: "*TO REVOLUT*",
		ToAccount: "revolut", ToDesc: "*FROM NLB*",
	}
	if err := AppendTransfer(root, tr); err != nil {
		t.Fatal(err)
	}
	body, err := os.ReadFile(filepath.Join(root, RulesFile))
	if err != nil {
		t.Fatal(err)
	}
	if strings.Contains(string(body), "tolerance_pct") {
		t.Errorf("file = %q, want no tolerance key", body)
	}
}

// A negative tolerance is a typo, and one at 100% or beyond would let any
// amount pair with any other, leaving the dates to decide alone.
func TestTransferToleranceIsBounded(t *testing.T) {
	full := Transfer{FromAccount: "a", FromDesc: "*OUT*", ToAccount: "b", ToDesc: "*IN*"}
	for _, pct := range []float64{-1, 100, 250} {
		root := t.TempDir()
		tr := full
		tr.TolerancePct = pct
		if err := AppendTransfer(root, tr); err == nil {
			t.Errorf("tolerance_pct %g: expected an error", pct)
		}
		if _, err := os.Stat(filepath.Join(root, RulesFile)); !os.IsNotExist(err) {
			t.Errorf("tolerance_pct %g: a rejected transfer must not create the file", pct)
		}
	}

	// The same check applies to a file written by hand.
	root := t.TempDir()
	body := "[[transfer]]\nfrom_account = \"a\"\nfrom_desc = \"*OUT*\"\n" +
		"to_account = \"b\"\nto_desc = \"*IN*\"\ntolerance_pct = 150\n"
	if err := os.WriteFile(filepath.Join(root, RulesFile), []byte(body), 0o644); err != nil {
		t.Fatal(err)
	}
	if _, err := LoadRules(root); err == nil {
		t.Error("expected an out-of-range tolerance to be refused on load")
	}
}

// Editing rewrites the rule where it sits: the position is what still breaks
// ties between equally specific rules, so a rule that moved could start beating
// one it never used to.
func TestReplaceRuleKeepsPositionAndComments(t *testing.T) {
	root := t.TempDir()
	path := filepath.Join(root, RulesFile)
	if err := os.WriteFile(path, []byte(rulesWithComments), 0o644); err != nil {
		t.Fatal(err)
	}

	edited := Rule{Match: "*LIDL SOFIA*", Tag: "groceries", Account: "checking", Note: "just the branch"}
	if err := ReplaceRule(root, 0, edited); err != nil {
		t.Fatal(err)
	}

	loaded, err := LoadRules(root)
	if err != nil {
		t.Fatalf("the file no longer parses after editing: %v", err)
	}
	if len(loaded.Rule) != 3 {
		t.Fatalf("got %d rules, want the same 3: %+v", len(loaded.Rule), loaded.Rule)
	}
	if loaded.Rule[0] != edited {
		t.Errorf("rule 1 = %+v, want %+v", loaded.Rule[0], edited)
	}
	if loaded.Rule[1].Match != "*PAYROLL*" || loaded.Rule[2].Match != "*TO SAVINGS*" {
		t.Errorf("the rest = %+v, want them where they were", loaded.Rule[1:])
	}

	// The comment above a rule says why it is there, which editing its glob
	// does not change.
	text, err := os.ReadFile(path)
	if err != nil {
		t.Fatal(err)
	}
	for _, want := range []string{"# Rules for my accounts.", "# Weekly shop.", "# Moving money to myself."} {
		if !strings.Contains(string(text), want) {
			t.Errorf("comment %q was lost:\n%s", want, text)
		}
	}
	if strings.Contains(string(text), `"*LIDL*"`) {
		t.Errorf("the old pattern is still there:\n%s", text)
	}
}

// A rule and the transfer below it share the file, so a replacement has to end
// where the next block of any kind begins.
func TestReplaceRuleLeavesTheOtherKindAlone(t *testing.T) {
	root := t.TempDir()
	path := filepath.Join(root, RulesFile)
	original := `[[rule]]
match = "*LIDL*"
tag   = "groceries"

# Moving money to the broker.
[[transfer]]
from_account = "nlb"
from_desc    = "*TO TRADEREPUBLIC*"
to_account   = "traderepublic"
to_desc      = "*FROM NLB*"

[[rule]]
match = "*ZARA*"
tag   = "clothes"
`
	if err := os.WriteFile(path, []byte(original), 0o644); err != nil {
		t.Fatal(err)
	}

	if err := ReplaceRule(root, 0, Rule{Match: "*KAUFLAND*", Tag: "groceries"}); err != nil {
		t.Fatal(err)
	}
	loaded, err := LoadRules(root)
	if err != nil {
		t.Fatal(err)
	}
	if len(loaded.Transfer) != 1 || loaded.Transfer[0].FromDesc != "*TO TRADEREPUBLIC*" {
		t.Errorf("transfers = %+v, want the definition untouched", loaded.Transfer)
	}
	if len(loaded.Rule) != 2 || loaded.Rule[0].Match != "*KAUFLAND*" || loaded.Rule[1].Match != "*ZARA*" {
		t.Errorf("rules = %+v, want only the first one rewritten", loaded.Rule)
	}
	raw, _ := os.ReadFile(path)
	if !strings.Contains(string(raw), "# Moving money to the broker.") {
		t.Errorf("the transfer's comment was lost:\n%s", raw)
	}
}

// Editing a rule that sets a type keeps it: the caller decides what the rule
// becomes, and a pattern left out of the replacement is a pattern removed.
func TestReplaceRuleWritesEveryPattern(t *testing.T) {
	root := t.TempDir()
	body := "[[rule]]\nmatch = \"*SPOTIFY*\"\ntype  = \"CARD_PAYMENT\"\ntag   = \"music\"\n"
	if err := os.WriteFile(filepath.Join(root, RulesFile), []byte(body), 0o644); err != nil {
		t.Fatal(err)
	}

	kept := Rule{Match: "*SPOTIFY*", Type: "CARD_PAYMENT", Tag: "subscriptions"}
	if err := ReplaceRule(root, 0, kept); err != nil {
		t.Fatal(err)
	}
	loaded, err := LoadRules(root)
	if err != nil {
		t.Fatal(err)
	}
	if loaded.Rule[0] != kept {
		t.Errorf("rule = %+v, want %+v", loaded.Rule[0], kept)
	}

	// A type-only rule is a rule; a rule with neither pattern is not.
	if err := ReplaceRule(root, 0, Rule{Type: "CARD_PAYMENT", Tag: "cards"}); err != nil {
		t.Errorf("a type-only rule was refused: %v", err)
	}
	if err := ReplaceRule(root, 0, Rule{Tag: "nothing"}); err == nil {
		t.Error("expected a rule with no pattern to be rejected")
	}
	if err := ReplaceRule(root, 0, Rule{Match: "*X*"}); err == nil {
		t.Error("expected a rule with no tag to be rejected")
	}
}

func TestReplaceRuleOutOfRange(t *testing.T) {
	root := t.TempDir()
	if err := AppendRule(root, Rule{Match: "*LIDL*", Tag: "groceries"}); err != nil {
		t.Fatal(err)
	}
	for _, pos := range []int{-1, 1, 7} {
		if err := ReplaceRule(root, pos, Rule{Match: "*X*", Tag: "x"}); err == nil {
			t.Errorf("position %d: expected an error", pos)
		}
	}
	loaded, _ := LoadRules(root)
	if len(loaded.Rule) != 1 || loaded.Rule[0].Match != "*LIDL*" {
		t.Errorf("rules = %+v, want the file untouched", loaded.Rule)
	}
}