// SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Commercial
// SPDX-FileCopyrightText: 2025-2026 Christian Galo

package forms

import (
	"fmt"
	"net/http"
	"regexp"
	"strconv"
	"strings"
	"time"

	"github.com/google/uuid"
)

// Parsing (design D6; spec form-library "The handler parses through the
// declaration"). A handler reads a mutation's body through the
// declaration and never through r.FormValue, which merges the query string
// into the body and hides which one a value came from. Parse reads only
// declared names, so the declaration is also the write allowlist: the CSRF
// token, htmx's own parameters and anything else a body carries are
// ignored (Django's fields warning, Rails' permit! warning; lesson L§15).
//
// Parse never builds a domain object. It returns the values and the
// errors; the handler adds its own checks by field name or at the form
// level and builds the object only once the error set is empty (L§16).

// Values holds one form's values: the raw submitted string, whether the
// name was present at all, and the typed value where the field's rules
// passed. Go cannot tell an absent string from an empty one, so presence
// is recorded beside the value (lesson L§4).
type Values struct {
	raw     map[string]string
	present map[string]bool
	typed   map[string]any
}

// NewValues returns an empty value set, for binding a record to a form.
func NewValues() Values {
	return Values{
		raw:     map[string]string{},
		present: map[string]bool{},
		typed:   map[string]any{},
	}
}

func (v *Values) init() {
	if v.raw == nil {
		v.raw = map[string]string{}
		v.present = map[string]bool{}
		v.typed = map[string]any{}
	}
}

// Set records a field's raw value, marking it present. Binding a record to
// a form goes through here, so the record-bound render and the
// submission-bound render read the same way.
func (v *Values) Set(name, raw string) {
	v.init()
	v.raw[name] = raw
	v.present[name] = true
}

// SetBool records a checkbox's state. A ticked box carries the field's
// submitted value; an unticked one carries nothing, which is how the
// browser submits it. Either way, the typed bool is recorded too, so a
// bound checkbox answers Bool the same way a parsed one does (design D1).
func (v *Values) SetBool(f Field, on bool) {
	v.init()
	if on {
		v.Set(f.Name, f.CheckboxValue())
		v.setTyped(f.Name, true)
		return
	}
	v.raw[f.Name] = ""
	v.present[f.Name] = false
	v.setTyped(f.Name, false)
}

// Raw returns the submitted (or bound) string, trimmed as Parse trimmed it.
func (v Values) Raw(name string) string { return v.raw[name] }

// Present reports whether the name was submitted at all, which is not the
// same as carrying a value.
func (v Values) Present(name string) bool { return v.present[name] }

// String returns the value as text.
func (v Values) String(name string) string { return v.raw[name] }

// Int returns the value as a whole number, and false when the field is
// absent, empty, or was refused.
func (v Values) Int(name string) (int, bool) {
	n, ok := v.typed[name].(int)
	return n, ok
}

// Bool returns a checkbox's state. An absent checkbox is false, never an
// error (spec form-conventions "A checkbox is never required").
func (v Values) Bool(name string) bool {
	b, _ := v.typed[name].(bool)
	return b
}

// Time returns the value as an instant, and false when the field is
// absent, empty, or was refused.
func (v Values) Time(name string) (time.Time, bool) {
	t, ok := v.typed[name].(time.Time)
	return t, ok
}

// UUID returns the value as an identifier, and false when the field is
// absent, empty, or was refused.
func (v Values) UUID(name string) (uuid.UUID, bool) {
	id, ok := v.typed[name].(uuid.UUID)
	return id, ok
}

// setTyped records a field's typed value; an errored field never gets one,
// so a handler that reads a typed value is reading a value that passed.
func (v *Values) setTyped(name string, val any) {
	v.init()
	v.typed[name] = val
}

// Errors is one form's refusals: a message per field, plus the form-level
// message for a refusal that belongs to no field. The form-level slot is
// reached by the same call with an empty field name (lesson L§11).
type Errors struct {
	fields map[string]string
	form   string
}

// NewErrors returns an empty error set.
func NewErrors() *Errors { return &Errors{fields: map[string]string{}} }

// Field records a refusal under one field. The last message wins: the
// convention is one concise message per field, not a list.
func (e *Errors) Field(name, msg string) {
	if e.fields == nil {
		e.fields = map[string]string{}
	}
	if name == "" {
		e.form = msg
		return
	}
	e.fields[name] = msg
}

// Form records a refusal that belongs to no field.
func (e *Errors) Form(msg string) { e.form = msg }

// Get returns one field's message, or the empty string.
func (e *Errors) Get(name string) string {
	if e == nil {
		return ""
	}
	return e.fields[name]
}

// FormError returns the form-level message, or the empty string.
func (e *Errors) FormError() string {
	if e == nil {
		return ""
	}
	return e.form
}

// Has reports whether one field was refused.
func (e *Errors) Has(name string) bool {
	if e == nil {
		return false
	}
	_, ok := e.fields[name]
	return ok
}

// Any reports whether anything was refused. This is the handler's branch
// point: build the domain object only when it is false.
func (e *Errors) Any() bool {
	if e == nil {
		return false
	}
	return len(e.fields) > 0 || e.form != ""
}

// Count returns how many fields were refused, the form level included.
func (e *Errors) Count() int {
	if e == nil {
		return 0
	}
	n := len(e.fields)
	if e.form != "" {
		n++
	}
	return n
}

// Parse reads r through the declaration and returns the values and the
// refusals. It reads r.PostForm for a mutation and r.URL.Query() for a
// search form, never r.FormValue, so the query string cannot shadow a
// body field. Repeated names on a scalar field take the first value, as
// Go's own form parsing does; a multi-valued control does not exist.
func (s FormSpec) Parse(r *http.Request) (Values, *Errors) {
	return s.ParseSide(r, BothSides, nil)
}

// ParseWith is Parse with the option sets of the fields whose options are
// loaded per request (a picker of the deployment's entitlement sets). A
// submitted value outside a field's options is a refusal, never a silent
// default (finding FA-8).
func (s FormSpec) ParseWith(r *http.Request, options map[string][]Option) (Values, *Errors) {
	return s.ParseSide(r, BothSides, options)
}

// ParseSide is ParseWith restricted to the fields that render on one side,
// so a create submission cannot carry an edit-only field and an edit
// submission cannot carry a create-only one. The side the form rendered is
// the side it is read as; BothSides reads every declared field, which is
// right for a form with one side.
func (s FormSpec) ParseSide(r *http.Request, side Side, options map[string][]Option) (Values, *Errors) {
	values := NewValues()
	errs := NewErrors()

	var source map[string][]string
	if s.Kind == KindSearch {
		source = r.URL.Query()
	} else {
		if err := r.ParseForm(); err != nil {
			errs.Form("The form could not be read. Please try again.")
			return values, errs
		}
		source = r.PostForm
	}

	fields := make([]Field, 0, len(s.Fields))
	for _, f := range s.Fields {
		if side != BothSides && !f.RendersOn(side) {
			continue
		}
		if f.Control == Static {
			// A static row states a fact where a control would be; it
			// carries no name, submits nothing, and is never parsed
			// (design D21). Reading one would invent a value the page
			// never offered.
			continue
		}
		fields = append(fields, f)
	}
	s.parseFields(source, fields, "", "", options, &values, errs)
	return values, errs
}

// parseFields reads one group of fields out of source and applies the
// declaration's rules to each. namePrefix is what the submitted names carry
// ahead of the field name and errPrefix what the error keys do: both empty
// for an ordinary form, "rows.<instance>." or "staged.<i>." for one group
// of a batch, so one set of rules reads a form, a row and a delta alike and
// none of them can drift from the others.
func (s FormSpec) parseFields(source map[string][]string, fields []Field, namePrefix, errPrefix string, options map[string][]Option, out *Values, errs *Errors) {
	values := out
	for _, f := range fields {
		key := errPrefix + f.Name
		submitted := namePrefix + f.Name
		if !f.Shown(*values) {
			// A field the operator never saw (its ShowIf condition on an
			// earlier field's value did not match) is neither validated
			// nor carried into Values: the control was not on the page,
			// so nothing was there to type (design D2, ShowIf's doc on
			// the trust model). ShowIf.Field must therefore be declared
			// earlier in Fields, so its value is already in Values here.
			continue
		}
		vals, present := source[submitted]
		raw := ""
		if present && len(vals) > 0 {
			raw = vals[0]
		}
		raw = strings.TrimSpace(raw)

		if f.Control == Checkbox {
			// A checkbox's absence is false and never an error; a ticked
			// box submits the declared value (lessons L§21, L§34).
			on := present && raw == f.CheckboxValue()
			values.raw[f.Name] = raw
			values.present[f.Name] = present
			values.setTyped(f.Name, on)
			continue
		}

		values.raw[f.Name] = raw
		values.present[f.Name] = present

		opts := f.Options
		if runtime, ok := options[f.Name]; ok {
			opts = runtime
		}

		if f.Control == Select || f.Control == Radio {
			if !optionExists(opts, raw) {
				if raw == "" {
					// A Radio group has no "choose nothing" member the way a
					// Select's enabled empty option does (render.go's
					// fieldAttrs mirrors this): an Optional radio group left
					// untouched is a legitimate empty submission, not a
					// missing choice.
					if f.Control == Radio && f.Optional {
						continue
					}
					errs.Field(key, chooseMessage(f))
				} else {
					errs.Field(key, "Choose "+article(f.Label)+" from the list.")
				}
				continue
			}
			if raw == "" {
				// A deliberate empty option (the edit side's "None") is a
				// legitimate submission that clears the column.
				continue
			}
			s.assignTyped(values, f, key, raw, errs)
			continue
		}

		if raw == "" {
			if !f.Optional {
				errs.Field(key, enterMessage(f))
			}
			continue
		}
		if f.MaxLen > 0 && len([]rune(raw)) > f.MaxLen {
			errs.Field(key, fmt.Sprintf("%s must be %d characters or fewer.", f.Label, f.MaxLen))
			continue
		}
		if f.Pattern != "" {
			re, err := regexp.Compile(f.Pattern)
			if err != nil || !re.MatchString(raw) {
				msg := f.PatternHint
				if msg == "" {
					msg = f.Label + " is not in the expected format."
				}
				errs.Field(key, msg)
				continue
			}
		}
		s.assignTyped(values, f, key, raw, errs)
	}
}

// assignTyped converts one passing raw value and applies the range rules
// the control has. A field that fails here keeps its raw text for the
// re-render and gets no typed value (lesson L§11, finding FA-23).
func (s FormSpec) assignTyped(values *Values, f Field, key, raw string, errs *Errors) {
	switch f.Control {
	case Number:
		n, err := strconv.Atoi(raw)
		if err != nil {
			errs.Field(key, f.Label+" must be a whole number.")
			return
		}
		if f.Min != "" {
			if min, err := strconv.Atoi(f.Min); err == nil && n < min {
				errs.Field(key, fmt.Sprintf("%s must be %d or more.", f.Label, min))
				return
			}
		}
		if f.Max != "" {
			if max, err := strconv.Atoi(f.Max); err == nil && n > max {
				errs.Field(key, fmt.Sprintf("%s must be %d or fewer.", f.Label, max))
				return
			}
		}
		values.setTyped(f.Name, n)
	case Date, DateTime:
		layout := "2006-01-02"
		if f.Control == DateTime {
			layout = "2006-01-02T15:04"
		}
		t, err := time.Parse(layout, raw)
		if err != nil {
			errs.Field(key, f.Label+" is not a valid date.")
			return
		}
		if f.Min != "" {
			if min, err := time.Parse(layout, f.Min); err == nil && t.Before(min) {
				errs.Field(key, f.Label+" is earlier than this form allows.")
				return
			}
		}
		if f.Max != "" {
			if max, err := time.Parse(layout, f.Max); err == nil && t.After(max) {
				errs.Field(key, f.Label+" is later than this form allows.")
				return
			}
		}
		values.setTyped(f.Name, t)
	case Select, Radio, Hidden:
		// A picker's values are usually identifiers, read back with
		// Values.UUID. Parsing here keeps the handler from parsing a
		// second time and disagreeing about what a bad value means; a
		// value that is not an identifier simply has no typed form, which
		// is correct for the pickers whose values are enum strings.
		if id, err := uuid.Parse(raw); err == nil {
			values.setTyped(f.Name, id)
		}
	}
}

// optionExists reports whether value is one the control offered as a
// choice. A disabled option is not one: it is the "Choose a ..."
// placeholder, which a browser will not submit and the server must not
// accept, so a select that needs a choice refuses the empty value while an
// optional select, whose first option is an enabled "None", accepts it.
func optionExists(options []Option, value string) bool {
	for _, o := range options {
		if o.Disabled {
			continue
		}
		if o.Value == value {
			return true
		}
	}
	return false
}

// enterMessage is the refusal for a required text-shaped field.
func enterMessage(f Field) string {
	return "Enter " + article(f.Label) + "."
}

// chooseMessage is the refusal for a select or a radio group.
func chooseMessage(f Field) string {
	return "Choose " + article(f.Label) + "."
}

// article lowercases a label and prefixes the indefinite article, so
// "Entitlement set" becomes "an entitlement set" and the two refusal
// messages read as sentences rather than as field names.
func article(label string) string {
	if label == "" {
		return "a value"
	}
	lower := strings.ToLower(label)
	switch lower[0] {
	case 'a', 'e', 'i', 'o', 'u':
		return "an " + lower
	}
	return "a " + lower
}

// Batch is one request through a batch form's declaration (design D1's
// "Rows family contract"; spec form-library "A batch form renders the
// caller's rows and one tray"). Every posting control of a Rows form sends
// the whole form, so one request carries what was pressed, every open
// editor's typed values, the whole staged batch and the tray's own fields;
// ParseBatch reads all four through the declaration and nothing else.
//
// ParseBatch validates shape, not domain: the handler decides what Act
// means, re-reads the records the batch names, and refuses a delta whose
// record has moved under it (design D3).
type Batch struct {
	// Act is what was pressed and Key the record it was pressed on, from
	// the row action's own hx-vals. Both are the library's names, not
	// declared fields: a declaration names controls, and these name the
	// press.
	Act string
	Key string
	// Open are the record keys whose editors were open, in the order the
	// hidden inputs carried them.
	Open []string
	// Rows are those editors' values, keyed by record key, each read
	// through the row fields' own rules.
	Rows map[string]Values
	// Staged is the batch as submitted, in index order, each delta's values
	// read through the row and delta fields' rules. Line and Error are the
	// render's, never the request's, so both are empty here.
	Staged []StagedDelta
	// Tray holds the tray's own fields.
	Tray Values
	// Errors are the refusals, keyed "rows.<instance>.<field>",
	// "staged.<i>.<field>", the tray field's own name, and the form level.
	Errors *Errors
}

// Row returns one open editor as the render wants it: its values, and its
// refusals under the declaration's bare field names, so the handler hands
// back what it parsed without re-keying anything by hand.
func (b Batch) Row(instance string) RowBinding {
	rb := RowBinding{Values: b.Rows[instance], Errors: NewErrors()}
	prefix := "rows." + instance + "."
	for key, msg := range b.Errors.fields {
		if strings.HasPrefix(key, prefix) {
			rb.Errors.Field(strings.TrimPrefix(key, prefix), msg)
		}
	}
	return rb
}

// maxStagedDeltas caps how many deltas one request may carry. The render
// writes one group per staged change and a set holds tens of rules, so the
// cap is out of reach in use; it exists because the groups arrive as
// numbered names a forged body could number as high as it likes.
const maxStagedDeltas = 200

// ParseBatch reads a batch form's request through its declaration.
func (s FormSpec) ParseBatch(r *http.Request) Batch {
	return s.ParseBatchWith(r, nil)
}

// ParseBatchWith is ParseBatch with the option sets of the fields whose
// options are loaded per request, exactly as ParseWith is to Parse: a
// submitted value outside a field's options is a refusal. A batch form
// whose select offers a per-record option (a stored value the console
// offers back rather than writes) passes every value it ever renders here,
// because one request carries every row and every delta at once.
func (s FormSpec) ParseBatchWith(r *http.Request, options map[string][]Option) Batch {
	if s.Family != Rows {
		panic(fmt.Sprintf("forms: %s is a %s form; ParseBatch reads a batch form", s.Name, s.Family))
	}
	batch := Batch{Rows: map[string]Values{}, Tray: NewValues(), Errors: NewErrors()}
	if err := r.ParseForm(); err != nil {
		batch.Errors.Form("The form could not be read. Please try again.")
		return batch
	}
	source := r.PostForm

	batch.Act = strings.TrimSpace(firstValue(source, "act"))
	batch.Key = strings.TrimSpace(firstValue(source, "key"))

	seen := map[string]bool{}
	for _, raw := range source["open"] {
		instance := strings.TrimSpace(raw)
		if instance == "" || seen[instance] {
			continue
		}
		seen[instance] = true
		batch.Open = append(batch.Open, instance)
	}

	rowFields := s.placed(PlaceRow)
	deltaFields := s.placed(PlaceRow, PlaceDelta)
	trayFields := s.placed(PlaceTray)

	// A row that is not open submits nothing and is not read: its record is
	// on the page as text, and requiredness applies to what someone typed.
	for _, instance := range batch.Open {
		prefix := "rows." + instance + "."
		values := NewValues()
		s.parseFields(source, rowFields, prefix, prefix, options, &values, batch.Errors)
		batch.Rows[instance] = values
	}

	for i := 0; ; i++ {
		prefix := stagedPrefix(i) + "."
		_, hasVerb := source[prefix+"verb"]
		_, hasKey := source[prefix+"key"]
		if !hasVerb && !hasKey {
			break
		}
		if i >= maxStagedDeltas {
			batch.Errors.Form(fmt.Sprintf("A batch holds at most %d changes.", maxStagedDeltas))
			break
		}
		values := NewValues()
		s.parseFields(source, deltaFields, prefix, prefix, options, &values, batch.Errors)
		batch.Staged = append(batch.Staged, StagedDelta{
			Verb:   strings.TrimSpace(firstValue(source, prefix+"verb")),
			Key:    strings.TrimSpace(firstValue(source, prefix+"key")),
			Values: values,
		})
	}

	s.parseFields(source, trayFields, "", "", options, &batch.Tray, batch.Errors)
	return batch
}

// placed returns the declared fields with one of these placements, in
// declaration order, with the static rows dropped for the same reason Parse
// drops them: a row that states a fact submits nothing.
func (s FormSpec) placed(placements ...Placement) []Field {
	want := map[Placement]bool{}
	for _, p := range placements {
		want[p] = true
	}
	out := make([]Field, 0, len(s.Fields))
	for _, f := range s.Fields {
		if f.Control == Static || !want[f.Placement] {
			continue
		}
		out = append(out, f)
	}
	return out
}

// firstValue returns the first submitted value under a name, as Go's own
// form parsing does for a scalar field.
func firstValue(source map[string][]string, name string) string {
	if vals, ok := source[name]; ok && len(vals) > 0 {
		return vals[0]
	}
	return ""
}