feat: auto-track fields on context for zero-arg ValidateAll/ResetFields

Fields created via Context.Field are now tracked on the page context,
so ValidateAll() and ResetFields() with no arguments operate on all
fields by default. Explicit field args still work for selective use.

Also switches MinLen/MaxLen to utf8.RuneCountInString for correct
unicode handling and replaces fmt.Errorf with errors.New where
format strings are unnecessary.

context.go

@@ -32,6 +32,7 @@ type Context struct {
 	mu                sync.RWMutex
 	ctxDisposedChan   chan struct{}
 	reqCtx            context.Context
+	fields            []*Field
 	subscriptions     []Subscription
 	subsMu            sync.Mutex
 	disposeOnce       sync.Once
@@ -480,6 +481,50 @@ func (c *Context) unsubscribeAll() {
 	}
 }
 
+// Field creates a signal with validation rules attached.
+// The initial value seeds both the signal and the reset target.
+// The field is tracked on the context so ValidateAll/ResetFields
+// can operate on all fields by default.
+func (c *Context) Field(initial any, rules ...Rule) *Field {
+	f := &Field{
+		signal:     c.Signal(initial),
+		rules:      rules,
+		initialVal: initial,
+	}
+	target := c
+	if c.isComponent() {
+		target = c.parentPageCtx
+	}
+	target.fields = append(target.fields, f)
+	return f
+}
+
+// ValidateAll runs Validate on each field, returning true only if all pass.
+// With no arguments it validates every field tracked on this context.
+func (c *Context) ValidateAll(fields ...*Field) bool {
+	if len(fields) == 0 {
+		fields = c.fields
+	}
+	ok := true
+	for _, f := range fields {
+		if !f.Validate() {
+			ok = false
+		}
+	}
+	return ok
+}
+
+// ResetFields resets each field to its initial value and clears errors.
+// With no arguments it resets every field tracked on this context.
+func (c *Context) ResetFields(fields ...*Field) {
+	if len(fields) == 0 {
+		fields = c.fields
+	}
+	for _, f := range fields {
+		f.Reset()
+	}
+}
+
 func newContext(id string, route string, v *V) *Context {
 	if v == nil {
 		panic("create context failed: app pointer is nil")

field.go

@@ -0,0 +1,58 @@
+package via
+
+// Field is a signal with built-in validation rules and error state.
+// It embeds *signal, so all signal methods (Bind, String, Int, Bool, SetValue, Text, ID)
+// work transparently.
+type Field struct {
+	*signal
+	rules      []Rule
+	errors     []string
+	initialVal any
+}
+
+// Validate runs all rules against the current value.
+// Clears previous errors, populates new ones, returns true if all rules pass.
+func (f *Field) Validate() bool {
+	f.errors = nil
+	val := f.String()
+	for _, r := range f.rules {
+		if err := r.validate(val); err != nil {
+			f.errors = append(f.errors, err.Error())
+		}
+	}
+	return len(f.errors) == 0
+}
+
+// HasError returns true if this field has any validation errors.
+func (f *Field) HasError() bool {
+	return len(f.errors) > 0
+}
+
+// FirstError returns the first validation error message, or "" if valid.
+func (f *Field) FirstError() string {
+	if len(f.errors) > 0 {
+		return f.errors[0]
+	}
+	return ""
+}
+
+// Errors returns all current validation error messages.
+func (f *Field) Errors() []string {
+	return f.errors
+}
+
+// AddError manually adds an error message (useful for server-side or cross-field validation).
+func (f *Field) AddError(msg string) {
+	f.errors = append(f.errors, msg)
+}
+
+// ClearErrors removes all validation errors from this field.
+func (f *Field) ClearErrors() {
+	f.errors = nil
+}
+
+// Reset restores the field value to its initial value and clears all errors.
+func (f *Field) Reset() {
+	f.SetValue(f.initialVal)
+	f.errors = nil
+}

field_test.go

@@ -0,0 +1,206 @@
+package via
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/ryanhamamura/via/h"
+	"github.com/stretchr/testify/assert"
+)
+
+func newTestField(initial any, rules ...Rule) *Field {
+	v := New()
+	var f *Field
+	v.Page("/", func(c *Context) {
+		f = c.Field(initial, rules...)
+		c.View(func() h.H { return h.Div() })
+	})
+	return f
+}
+
+func TestFieldCreation(t *testing.T) {
+	f := newTestField("hello", Required())
+	assert.Equal(t, "hello", f.String())
+	assert.NotEmpty(t, f.ID())
+}
+
+func TestFieldSignalDelegation(t *testing.T) {
+	f := newTestField(42)
+	assert.Equal(t, "42", f.String())
+	assert.Equal(t, 42, f.Int())
+
+	f.SetValue("new")
+	assert.Equal(t, "new", f.String())
+
+	// Bind returns an h.H element
+	assert.NotNil(t, f.Bind())
+}
+
+func TestFieldValidateSingleRule(t *testing.T) {
+	f := newTestField("", Required())
+	assert.False(t, f.Validate())
+	assert.True(t, f.HasError())
+	assert.Equal(t, "This field is required", f.FirstError())
+
+	f.SetValue("ok")
+	assert.True(t, f.Validate())
+	assert.False(t, f.HasError())
+	assert.Equal(t, "", f.FirstError())
+}
+
+func TestFieldValidateMultipleRules(t *testing.T) {
+	f := newTestField("ab", Required(), MinLen(3))
+	assert.False(t, f.Validate())
+	errs := f.Errors()
+	assert.Len(t, errs, 1)
+	assert.Equal(t, "Must be at least 3 characters", errs[0])
+
+	f.SetValue("")
+	assert.False(t, f.Validate())
+	errs = f.Errors()
+	assert.Len(t, errs, 2)
+}
+
+func TestFieldErrors(t *testing.T) {
+	f := newTestField("")
+	assert.Nil(t, f.Errors())
+	assert.False(t, f.HasError())
+	assert.Equal(t, "", f.FirstError())
+}
+
+func TestFieldAddError(t *testing.T) {
+	f := newTestField("ok")
+	f.AddError("username taken")
+	assert.True(t, f.HasError())
+	assert.Equal(t, "username taken", f.FirstError())
+	assert.Len(t, f.Errors(), 1)
+}
+
+func TestFieldClearErrors(t *testing.T) {
+	f := newTestField("", Required())
+	f.Validate()
+	assert.True(t, f.HasError())
+	f.ClearErrors()
+	assert.False(t, f.HasError())
+}
+
+func TestFieldReset(t *testing.T) {
+	f := newTestField("initial", Required(), MinLen(3))
+	f.SetValue("changed")
+	f.AddError("some error")
+
+	f.Reset()
+	assert.Equal(t, "initial", f.String())
+	assert.False(t, f.HasError())
+}
+
+func TestValidateAll(t *testing.T) {
+	v := New()
+	v.Page("/", func(c *Context) {
+		c.Field("", Required(), MinLen(3))
+		c.Field("", Required(), Email())
+		c.View(func() h.H { return h.Div() })
+
+		// both empty → both fail
+		assert.False(t, c.ValidateAll())
+	})
+
+	v2 := New()
+	v2.Page("/", func(c *Context) {
+		c.Field("joe", Required(), MinLen(3))
+		c.Field("joe@x.com", Required(), Email())
+		c.View(func() h.H { return h.Div() })
+
+		assert.True(t, c.ValidateAll())
+	})
+}
+
+func TestValidateAllPartialFailure(t *testing.T) {
+	v := New()
+	v.Page("/", func(c *Context) {
+		good := c.Field("valid", Required())
+		bad := c.Field("", Required())
+		c.View(func() h.H { return h.Div() })
+
+		ok := c.ValidateAll()
+		assert.False(t, ok)
+		assert.False(t, good.HasError())
+		assert.True(t, bad.HasError())
+	})
+}
+
+func TestValidateAllSelectiveArgs(t *testing.T) {
+	v := New()
+	v.Page("/", func(c *Context) {
+		a := c.Field("", Required())
+		b := c.Field("ok", Required())
+		cField := c.Field("", Required())
+		c.View(func() h.H { return h.Div() })
+
+		// only validate a and b — cField should be untouched
+		ok := c.ValidateAll(a, b)
+		assert.False(t, ok)
+		assert.True(t, a.HasError())
+		assert.False(t, b.HasError())
+		assert.False(t, cField.HasError(), "unselected field should not be validated")
+	})
+}
+
+func TestResetFields(t *testing.T) {
+	v := New()
+	v.Page("/", func(c *Context) {
+		a := c.Field("a", Required())
+		b := c.Field("b", Required())
+		c.View(func() h.H { return h.Div() })
+
+		a.SetValue("changed-a")
+		b.SetValue("changed-b")
+		a.AddError("err")
+
+		c.ResetFields()
+		assert.Equal(t, "a", a.String())
+		assert.Equal(t, "b", b.String())
+		assert.False(t, a.HasError())
+	})
+}
+
+func TestResetFieldsSelectiveArgs(t *testing.T) {
+	v := New()
+	v.Page("/", func(c *Context) {
+		a := c.Field("a")
+		b := c.Field("b")
+		c.View(func() h.H { return h.Div() })
+
+		a.SetValue("changed-a")
+		b.SetValue("changed-b")
+
+		// only reset a
+		c.ResetFields(a)
+		assert.Equal(t, "a", a.String())
+		assert.Equal(t, "changed-b", b.String(), "unselected field should not be reset")
+	})
+}
+
+func TestFieldValidateClearsPreviousErrors(t *testing.T) {
+	f := newTestField("", Required())
+	f.Validate()
+	assert.True(t, f.HasError())
+
+	f.SetValue("ok")
+	f.Validate()
+	assert.False(t, f.HasError())
+}
+
+func TestFieldCustomValidator(t *testing.T) {
+	f := newTestField("bad", Custom(func(val string) error {
+		if val == "bad" {
+			return fmt.Errorf("no bad words")
+		}
+		return nil
+	}))
+	assert.False(t, f.Validate())
+	assert.Equal(t, "no bad words", f.FirstError())
+
+	f.SetValue("good")
+	assert.True(t, f.Validate())
+}

internal/examples/signup/main.go

@@ -0,0 +1,87 @@
+package main
+
+import (
+	"github.com/ryanhamamura/via"
+	"github.com/ryanhamamura/via/h"
+)
+
+func main() {
+	v := via.New()
+	v.Config(via.Options{
+		DocumentTitle: "Signup",
+		ServerAddress: ":8080",
+	})
+
+	v.AppendToHead(h.StyleEl(h.Raw(`
+		body { font-family: system-ui, sans-serif; max-width: 420px; margin: 2rem auto; padding: 0 1rem; }
+		label { display: block; font-weight: 600; margin-top: 1rem; }
+		input { display: block; width: 100%; padding: 0.4rem; margin-top: 0.25rem; box-sizing: border-box; }
+		.error { color: #c00; font-size: 0.85rem; margin-top: 0.2rem; }
+		.success { color: #080; margin-top: 1rem; }
+		.actions { margin-top: 1.5rem; display: flex; gap: 0.5rem; }
+	`)))
+
+	v.Page("/", func(c *via.Context) {
+		username := c.Field("", via.Required(), via.MinLen(3), via.MaxLen(20))
+		email := c.Field("", via.Required(), via.Email())
+		age := c.Field("", via.Required(), via.Min(13), via.Max(120))
+		// Optional field — only validated when non-empty
+		website := c.Field("", via.Pattern(`^$|^https?://\S+$`, "Must be a valid URL"))
+
+		var success string
+
+		signup := c.Action(func() {
+			success = ""
+			if !c.ValidateAll() {
+				c.Sync()
+				return
+			}
+			// Server-side check
+			if username.String() == "admin" {
+				username.AddError("Username is already taken")
+				c.Sync()
+				return
+			}
+			success = "Account created for " + username.String() + "!"
+			c.ResetFields()
+			c.Sync()
+		})
+
+		reset := c.Action(func() {
+			success = ""
+			c.ResetFields()
+			c.Sync()
+		})
+
+		c.View(func() h.H {
+			return h.Div(
+				h.H1(h.Text("Sign Up")),
+
+				h.Label(h.Text("Username")),
+				h.Input(h.Type("text"), h.Placeholder("pick a username"), username.Bind()),
+				h.If(username.HasError(), h.Div(h.Class("error"), h.Text(username.FirstError()))),
+
+				h.Label(h.Text("Email")),
+				h.Input(h.Type("email"), h.Placeholder("you@example.com"), email.Bind()),
+				h.If(email.HasError(), h.Div(h.Class("error"), h.Text(email.FirstError()))),
+
+				h.Label(h.Text("Age")),
+				h.Input(h.Type("number"), h.Placeholder("your age"), age.Bind()),
+				h.If(age.HasError(), h.Div(h.Class("error"), h.Text(age.FirstError()))),
+
+				h.Label(h.Text("Website (optional)")),
+				h.Input(h.Type("url"), h.Placeholder("https://example.com"), website.Bind()),
+				h.If(website.HasError(), h.Div(h.Class("error"), h.Text(website.FirstError()))),
+
+				h.Div(h.Class("actions"),
+					h.Button(h.Text("Sign Up"), signup.OnClick()),
+					h.Button(h.Text("Reset"), reset.OnClick()),
+				),
+
+				h.If(success != "", h.P(h.Class("success"), h.Text(success))),
+			)
+		})
+	})
+
+	v.Start()
+}

rule.go

@@ -0,0 +1,130 @@
+package via
+
+import (
+	"errors"
+	"fmt"
+	"regexp"
+	"strconv"
+	"strings"
+	"unicode/utf8"
+)
+
+// Rule defines a single validation check for a Field.
+type Rule struct {
+	validate func(val string) error
+}
+
+// Required rejects empty or whitespace-only values.
+func Required(msg ...string) Rule {
+	m := "This field is required"
+	if len(msg) > 0 {
+		m = msg[0]
+	}
+	return Rule{func(val string) error {
+		if strings.TrimSpace(val) == "" {
+			return errors.New(m)
+		}
+		return nil
+	}}
+}
+
+// MinLen rejects values shorter than n characters.
+func MinLen(n int, msg ...string) Rule {
+	m := fmt.Sprintf("Must be at least %d characters", n)
+	if len(msg) > 0 {
+		m = msg[0]
+	}
+	return Rule{func(val string) error {
+		if utf8.RuneCountInString(val) < n {
+			return errors.New(m)
+		}
+		return nil
+	}}
+}
+
+// MaxLen rejects values longer than n characters.
+func MaxLen(n int, msg ...string) Rule {
+	m := fmt.Sprintf("Must be at most %d characters", n)
+	if len(msg) > 0 {
+		m = msg[0]
+	}
+	return Rule{func(val string) error {
+		if utf8.RuneCountInString(val) > n {
+			return errors.New(m)
+		}
+		return nil
+	}}
+}
+
+// Min parses the value as an integer and rejects values less than n.
+func Min(n int, msg ...string) Rule {
+	m := fmt.Sprintf("Must be at least %d", n)
+	if len(msg) > 0 {
+		m = msg[0]
+	}
+	return Rule{func(val string) error {
+		v, err := strconv.Atoi(val)
+		if err != nil {
+			return errors.New("Must be a valid number")
+		}
+		if v < n {
+			return errors.New(m)
+		}
+		return nil
+	}}
+}
+
+// Max parses the value as an integer and rejects values greater than n.
+func Max(n int, msg ...string) Rule {
+	m := fmt.Sprintf("Must be at most %d", n)
+	if len(msg) > 0 {
+		m = msg[0]
+	}
+	return Rule{func(val string) error {
+		v, err := strconv.Atoi(val)
+		if err != nil {
+			return errors.New("Must be a valid number")
+		}
+		if v > n {
+			return errors.New(m)
+		}
+		return nil
+	}}
+}
+
+// Pattern rejects values that don't match the regular expression re.
+func Pattern(re string, msg ...string) Rule {
+	m := "Invalid format"
+	if len(msg) > 0 {
+		m = msg[0]
+	}
+	compiled := regexp.MustCompile(re)
+	return Rule{func(val string) error {
+		if !compiled.MatchString(val) {
+			return errors.New(m)
+		}
+		return nil
+	}}
+}
+
+var emailRegexp = regexp.MustCompile(`^[a-zA-Z0-9._%+\-]+@[a-zA-Z0-9.\-]+\.[a-zA-Z]{2,}$`)
+
+// Email rejects values that don't look like an email address.
+func Email(msg ...string) Rule {
+	m := "Invalid email address"
+	if len(msg) > 0 {
+		m = msg[0]
+	}
+	return Rule{func(val string) error {
+		if !emailRegexp.MatchString(val) {
+			return errors.New(m)
+		}
+		return nil
+	}}
+}
+
+// Custom creates a rule from a user-provided validation function.
+// The function should return nil for valid input and an error for invalid input.
+func Custom(fn func(string) error) Rule {
+	return Rule{validate: fn}
+}

rule_test.go

@@ -0,0 +1,116 @@
+package via
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestRequired(t *testing.T) {
+	r := Required()
+	assert.NoError(t, r.validate("hello"))
+	assert.Error(t, r.validate(""))
+	assert.Error(t, r.validate("   "))
+}
+
+func TestRequiredCustomMessage(t *testing.T) {
+	r := Required("name needed")
+	err := r.validate("")
+	assert.EqualError(t, err, "name needed")
+}
+
+func TestMinLen(t *testing.T) {
+	r := MinLen(3)
+	assert.NoError(t, r.validate("abc"))
+	assert.NoError(t, r.validate("abcd"))
+	assert.Error(t, r.validate("ab"))
+	assert.Error(t, r.validate(""))
+}
+
+func TestMinLenCustomMessage(t *testing.T) {
+	r := MinLen(5, "too short")
+	err := r.validate("ab")
+	assert.EqualError(t, err, "too short")
+}
+
+func TestMaxLen(t *testing.T) {
+	r := MaxLen(5)
+	assert.NoError(t, r.validate("abc"))
+	assert.NoError(t, r.validate("abcde"))
+	assert.Error(t, r.validate("abcdef"))
+}
+
+func TestMaxLenCustomMessage(t *testing.T) {
+	r := MaxLen(2, "too long")
+	err := r.validate("abc")
+	assert.EqualError(t, err, "too long")
+}
+
+func TestMin(t *testing.T) {
+	r := Min(5)
+	assert.NoError(t, r.validate("5"))
+	assert.NoError(t, r.validate("10"))
+	assert.Error(t, r.validate("4"))
+	assert.Error(t, r.validate("abc"))
+}
+
+func TestMinCustomMessage(t *testing.T) {
+	r := Min(10, "need 10+")
+	err := r.validate("3")
+	assert.EqualError(t, err, "need 10+")
+}
+
+func TestMax(t *testing.T) {
+	r := Max(10)
+	assert.NoError(t, r.validate("10"))
+	assert.NoError(t, r.validate("5"))
+	assert.Error(t, r.validate("11"))
+	assert.Error(t, r.validate("abc"))
+}
+
+func TestMaxCustomMessage(t *testing.T) {
+	r := Max(5, "too big")
+	err := r.validate("6")
+	assert.EqualError(t, err, "too big")
+}
+
+func TestPattern(t *testing.T) {
+	r := Pattern(`^\d{3}$`)
+	assert.NoError(t, r.validate("123"))
+	assert.Error(t, r.validate("12"))
+	assert.Error(t, r.validate("abcd"))
+}
+
+func TestPatternCustomMessage(t *testing.T) {
+	r := Pattern(`^\d+$`, "digits only")
+	err := r.validate("abc")
+	assert.EqualError(t, err, "digits only")
+}
+
+func TestEmail(t *testing.T) {
+	r := Email()
+	assert.NoError(t, r.validate("user@example.com"))
+	assert.NoError(t, r.validate("a.b+c@foo.co"))
+	assert.Error(t, r.validate("notanemail"))
+	assert.Error(t, r.validate("@example.com"))
+	assert.Error(t, r.validate("user@"))
+	assert.Error(t, r.validate(""))
+}
+
+func TestEmailCustomMessage(t *testing.T) {
+	r := Email("bad email")
+	err := r.validate("nope")
+	assert.EqualError(t, err, "bad email")
+}
+
+func TestCustom(t *testing.T) {
+	r := Custom(func(val string) error {
+		if val != "magic" {
+			return fmt.Errorf("must be magic")
+		}
+		return nil
+	})
+	assert.NoError(t, r.validate("magic"))
+	assert.EqualError(t, r.validate("other"), "must be magic")
+}