package main

import (
	"html"
	"regexp"
	"strings"
	"unicode/utf8"
)

// The printer's admin pages are small, tolerant HTML (XHTML 1.0 with unclosed inputs). Only what the module
// reads is taken out of them: the title, the links, and the forms with their fields.

// Link is an anchor of a page.
type Link struct {
	Href string `json:"href"`
	Text string `json:"text"`
}

// Field is a named control of a form. A password field's value is never kept (ADR 0467 clause 4).
type Field struct {
	Name    string   `json:"name"`
	Type    string   `json:"type"`
	Value   string   `json:"value"`
	Checked *bool    `json:"checked,omitempty"`
	Label   string   `json:"label"`
	Options []Option `json:"options,omitempty"`
	id      string
	own     string // the label of this control alone: <label for>, a wrapping <label>, or a radio button's text after it
	row     string // what the control's table row (or <dt>) calls it
}

// Option is a choice of a select (Value and Text) or a button of a radio group (Value and Label).
type Option struct {
	Value string `json:"value"`
	Label string `json:"label,omitempty"`
	Text  string `json:"text,omitempty"`
}

// Form is a form of a page with its named fields.
type Form struct {
	Action string  `json:"action"`
	Method string  `json:"method"`
	Fields []Field `json:"fields"`
}

// Page is what a page of the admin site holds.
type Page struct {
	Title string `json:"title"`
	Links []Link `json:"links"`
	Forms []Form `json:"forms"`
}

var attrRE = regexp.MustCompile(`([A-Za-z_:][-A-Za-z0-9_:.]*)(?:\s*=\s*(?:"([^"]*)"|'([^']*)'|([^\s"'>]+)))?`)

// attrs reads a tag's attributes, names in lower case and values unescaped.
func attrs(s string) map[string]string {
	out := map[string]string{}
	for _, m := range attrRE.FindAllStringSubmatch(s, -1) {
		v := m[2] + m[3] + m[4]
		out[strings.ToLower(m[1])] = html.UnescapeString(v)
	}
	return out
}

func squash(s string) string { return strings.Join(strings.Fields(html.UnescapeString(s)), " ") }

// latin1 turns a body that is not UTF-8 into UTF-8, reading each byte as the character of the same number:
// the printer's pages say iso-8859-1.
func latin1(b []byte) string {
	if utf8.Valid(b) {
		return string(b)
	}
	r := make([]rune, len(b))
	for i, c := range b {
		r[i] = rune(c)
	}
	return string(r)
}

// tagEnd is the index of the '>' that closes the tag starting at s[0], skipping quoted values, or -1.
func tagEnd(s string) int {
	var q byte
	for i := 0; i < len(s); i++ {
		c := s[i]
		switch {
		case q != 0:
			if c == q {
				q = 0
			}
		case c == '"' || c == '\'':
			q = c
		case c == '>':
			return i
		}
	}
	return -1
}

// ParsePage reads a page. Unknown markup is skipped, and what is not closed is closed at the end.
func ParsePage(body []byte) Page {
	s := latin1(body)
	var p Page
	var (
		inTitle  bool
		title    strings.Builder
		link     *Link
		formOpen bool
		form     Form
		labelFor string
		inLabel  bool
		label    strings.Builder
		labelIDs = map[string]string{}
		wrapped  []int // fields inside a label that names none, by index in form.Fields
		selIdx   = -1
		inOption bool
		optValue string
		optHasV  bool
		optSel   bool
		optText  strings.Builder
		inTextA  bool
		textA    strings.Builder
		textAIdx = -1
		// Where a control stands in its row: Brother pages lay a setting out as <tr><th>name</th><td>control</td></tr>
		// or <dt>name</dt><dd>control</dd>; the first cell names the row.
		cellN    int
		cellOpen bool
		cellText strings.Builder
		rowFirst string
		lastText string
		tailIdx  = -1
	)
	finishOption := func() {
		if !inOption || selIdx < 0 {
			inOption = false
			return
		}
		v := optValue
		if !optHasV {
			v = squash(optText.String())
		}
		f := &form.Fields[selIdx]
		if len(f.Options) == 0 {
			f.Value = v // a browser shows the first option when none is selected
		}
		f.Options = append(f.Options, Option{Value: v, Text: squash(optText.String())})
		if optSel {
			f.Value = v
		}
		inOption = false
	}
	closeForm := func() {
		finishOption()
		selIdx = -1
		if formOpen {
			p.Forms = append(p.Forms, form)
		}
		formOpen = false
		form = Form{}
	}
	addField := func(f Field) {
		f.row = rowFirst
		if (cellOpen && cellN == 1) || f.row == "" {
			f.row = lastText
		}
		lastText = "" // text before a control names that control alone
		form.Fields = append(form.Fields, f)
		if inLabel && labelFor == "" {
			wrapped = append(wrapped, len(form.Fields)-1)
		}
	}
	text := func(t string) {
		switch {
		case inTitle:
			title.WriteString(t)
		case inOption:
			optText.WriteString(t)
		case inTextA:
			textA.WriteString(t)
		}
		if !inTitle && !inOption && !inTextA && link == nil {
			if q := squash(t); q != "" {
				switch {
				case tailIdx >= 0:
					// the text right after a radio button is that button's, not the next field's
					if form.Fields[tailIdx].own == "" {
						form.Fields[tailIdx].own = q
					}
				case !inLabel:
					lastText = q
				}
			}
			if cellOpen && cellN == 1 {
				cellText.WriteString(t)
			}
		}
		if link != nil {
			link.Text += t
		}
		if inLabel {
			label.WriteString(t)
		}
	}
	i := 0
	for i < len(s) {
		lt := strings.IndexByte(s[i:], '<')
		if lt < 0 {
			text(s[i:])
			break
		}
		text(s[i : i+lt])
		i += lt
		switch {
		case strings.HasPrefix(s[i:], "<!--"):
			end := strings.Index(s[i:], "-->")
			if end < 0 {
				i = len(s)
			} else {
				i += end + 3
			}
			continue
		case strings.HasPrefix(s[i:], "<!") || strings.HasPrefix(s[i:], "<?"):
			end := strings.IndexByte(s[i:], '>')
			if end < 0 {
				i = len(s)
			} else {
				i += end + 1
			}
			continue
		}
		end := tagEnd(s[i:])
		if end < 0 {
			break
		}
		tailIdx = -1
		raw := s[i+1 : i+end]
		i += end + 1
		closing := strings.HasPrefix(raw, "/")
		raw = strings.TrimSuffix(strings.TrimPrefix(raw, "/"), "/")
		name := raw
		rest := ""
		if sp := strings.IndexAny(raw, " \t\r\n"); sp >= 0 {
			name, rest = raw[:sp], raw[sp:]
		}
		name = strings.ToLower(name)
		if !closing && (name == "script" || name == "style") {
			if e := strings.Index(strings.ToLower(s[i:]), "</"+name); e >= 0 {
				i += e
			} else {
				i = len(s)
			}
			continue
		}
		a := map[string]string{}
		if !closing {
			a = attrs(rest)
		}
		switch name {
		case "title":
			inTitle = !closing
		case "tr":
			cellN, cellOpen, rowFirst, lastText = 0, false, "", ""
			cellText.Reset()
		case "td", "th", "dt", "dd":
			if cellOpen && cellN == 1 {
				rowFirst = squash(cellText.String())
			}
			cellOpen = false
			if name == "dt" && !closing {
				cellN, rowFirst, lastText = 0, "", ""
			}
			if !closing {
				cellN++
				if name == "dd" && cellN < 2 {
					cellN = 2
				}
				cellOpen = true
				cellText.Reset()
			}
		case "a":
			if closing {
				if link != nil {
					link.Text = squash(link.Text)
					p.Links = append(p.Links, *link)
				}
				link = nil
			} else if href, ok := a["href"]; ok {
				link = &Link{Href: href}
			}
		case "form":
			closeForm()
			lastText = ""
			if !closing {
				formOpen = true
				form = Form{Action: a["action"], Method: strings.ToLower(a["method"])}
				if form.Method == "" {
					form.Method = "get"
				}
			}
		case "label":
			if closing {
				t := squash(label.String())
				if labelFor != "" {
					labelIDs[labelFor] = t
				}
				for _, k := range wrapped {
					form.Fields[k].own = t
				}
				inLabel, labelFor, wrapped = false, "", nil
				label.Reset()
			} else {
				inLabel, labelFor = true, a["for"]
				label.Reset()
			}
		case "input":
			if closing || a["name"] == "" {
				break
			}
			typ := strings.ToLower(a["type"])
			if typ == "" {
				typ = "text"
			}
			if typ == "submit" || typ == "button" || typ == "image" || typ == "reset" {
				break
			}
			f := Field{Name: a["name"], Type: typ, Value: a["value"], id: a["id"]}
			if typ == "password" {
				f.Value = ""
			}
			if typ == "checkbox" || typ == "radio" {
				_, on := a["checked"]
				f.Checked = &on
			}
			addField(f)
			if typ == "radio" {
				tailIdx = len(form.Fields) - 1
			}
		case "select":
			finishOption()
			selIdx = -1
			if !closing && a["name"] != "" {
				addField(Field{Name: a["name"], Type: "select", id: a["id"]})
				selIdx = len(form.Fields) - 1
			}
		case "option":
			finishOption()
			if !closing && selIdx >= 0 {
				inOption = true
				optValue, optHasV = a["value"], false
				if _, ok := a["value"]; ok {
					optHasV = true
				}
				_, optSel = a["selected"]
				optText.Reset()
			}
		case "textarea":
			if closing {
				if inTextA && textAIdx >= 0 {
					form.Fields[textAIdx].Value = html.UnescapeString(textA.String())
				}
				inTextA = false
			} else if a["name"] != "" {
				addField(Field{Name: a["name"], Type: "textarea", id: a["id"]})
				inTextA, textAIdx = true, len(form.Fields)-1
				textA.Reset()
			}
		}
	}
	closeForm()
	p.Title = squash(title.String())
	for fi := range p.Forms {
		var fields []Field
		groups := map[string]int{}
		for k := range p.Forms[fi].Fields {
			f := p.Forms[fi].Fields[k]
			if f.own == "" && f.id != "" {
				f.own = labelIDs[f.id]
			}
			if f.Type != "radio" {
				f.Label = f.own
				if f.Label == "" && f.Type != "hidden" {
					f.Label = f.row
				}
				fields = append(fields, f)
				continue
			}
			g, ok := groups[f.Name]
			if !ok {
				g = len(fields)
				groups[f.Name] = g
				fields = append(fields, Field{Name: f.Name, Type: "radio", Label: f.row})
			}
			fields[g].Options = append(fields[g].Options, Option{Value: f.Value, Label: f.own})
			if f.Checked != nil && *f.Checked {
				fields[g].Value = f.Value
			}
		}
		p.Forms[fi].Fields = fields
	}
	return p
}