// WebUI image zettel are in the range 40000..49999
	ZidEmoji = ZettelID("00000000040001")

	// Other sxn code zettel are in the range 50000..59999
	ZidSxnPrelude = ZettelID("00000000059900")

	// Predefined Zettelmarkup zettel are in the range 60000..69999
	ZidRoleZettelZettel        = ZettelID("00000000060010")
	ZidRoleConfigurationZettel = ZettelID("00000000060020")
	ZidRoleRoleZettel          = ZettelID("00000000060030")
	ZidRoleTagZettel           = ZettelID("00000000060040")

	// Range 90000...99999 is reserved for zettel templates
	ZidTOCNewTemplate    = ZettelID("00000000090000")
	ZidTemplateNewZettel = ZettelID("00000000090001")
	ZidTemplateNewRole   = ZettelID("00000000090004")
	ZidTemplateNewTag    = ZettelID("00000000090003")
	ZidTemplateNewUser   = ZettelID("00000000090002")

	ZidDefaultHome = ZettelID("00010000000000")
)

// LengthZid factors the constant length of a zettel identifier

// Predefined Metadata values
const (
	ValueFalse             = "false"
	ValueTrue              = "true"
	ValueLangEN            = "en"
	ValueRoleConfiguration = "configuration"
	ValueRoleTag           = "tag"
	ValueRoleRole          = "role"
	ValueRoleZettel        = "zettel"
	ValueSyntaxCSS         = "css"
	ValueSyntaxDraw        = "draw"
	ValueSyntaxGif         = "gif"
	ValueSyntaxHTML        = "html"
	ValueSyntaxMarkdown    = "markdown"
	ValueSyntaxMD          = "md"

const (
	QueryKeyCommand   = "cmd"
	QueryKeyEncoding  = "enc"
	QueryKeyParseOnly = "parseonly"
	QueryKeyPart      = "part"
	QueryKeyPhrase    = "phrase"
	QueryKeyQuery     = "q"
	QueryKeyRole      = "role"
	QueryKeySeed      = "_seed"
	QueryKeyTag       = "tag"
)

// Supported encoding values.
const (
	EncodingHTML  = "html"

	return agg, nil
}

// TagZettel returns the tag zettel of a given tag.
//
// This method only works if c.AllowRedirect(true) was called.
func (c *Client) TagZettel(ctx context.Context, tag string) (api.ZettelID, error) {
	return c.fetchTagOrRoleZettel(ctx, api.QueryKeyTag, tag)
}

// RoleZettel returns the tag zettel of a given tag.
//
// This method only works if c.AllowRedirect(true) was called.
func (c *Client) RoleZettel(ctx context.Context, role string) (api.ZettelID, error) {
	return c.fetchTagOrRoleZettel(ctx, api.QueryKeyRole, role)
}

func (c *Client) fetchTagOrRoleZettel(ctx context.Context, key, val string) (api.ZettelID, error) {
	if c.client.CheckRedirect == nil {
		panic("client does not allow to track redirect")
	}
	ub := c.newURLBuilder('z').AppendKVQuery(key, val)
	resp, err := c.buildAndExecuteRequest(ctx, http.MethodGet, ub, nil, nil)
	if err != nil {
		return api.InvalidZID, err
	}
	defer resp.Body.Close()
	data, err := io.ReadAll(resp.Body)
	if err != nil {

module zettelstore.de/client.fossil

go 1.21

require zettelstore.de/sx.fossil v0.0.0-20231130150648-05ef116ba207

zettelstore.de/sx.fossil v0.0.0-20231130150648-05ef116ba207 h1:8ch54z0w53bps6a00NDofEqo3AJ1l7ITXyC3XyLmlY4=
zettelstore.de/sx.fossil v0.0.0-20231130150648-05ef116ba207/go.mod h1:Uw3OLM1ufOM4Xe0G51mvkTDUv2okd+HyDBMx+0ZG7ME=

	"strings"

	"zettelstore.de/client.fossil/api"
	"zettelstore.de/client.fossil/attrs"
	"zettelstore.de/client.fossil/sz"
	"zettelstore.de/client.fossil/text"
	"zettelstore.de/sx.fossil"


	"zettelstore.de/sx.fossil/sxhtml"
)

// Evaluator will transform a s-expression that encodes the zettel AST into an s-expression
// that represents HTML.
type Evaluator struct {
	sf            sx.SymbolFactory

	headingOffset int64
	unique        string

	noLinks       bool // true iff output must not include links

	symAttr     *sx.Symbol
	symList     *sx.Symbol
	symNoEscape *sx.Symbol
	symClass    *sx.Symbol
	symMeta     *sx.Symbol
	symP        *sx.Symbol
	symLI       *sx.Symbol
	symA        *sx.Symbol
	symHREF     *sx.Symbol
	symSpan     *sx.Symbol

	fns     map[string]EvalFn
	minArgs map[string]int



}

// NewEvaluator creates a new Evaluator object.
func NewEvaluator(headingOffset int, sf sx.SymbolFactory) *Evaluator {
	if sf == nil {
		sf = sx.MakeMappedFactory(128)
	}
	ev := &Evaluator{
		sf:            sf,

		headingOffset: int64(headingOffset),
		symAttr:       sf.MustMake(sxhtml.NameSymAttr),
		symList:       sf.MustMake(sxhtml.NameSymList),
		symNoEscape:   sf.MustMake(sxhtml.NameSymNoEscape),
		symClass:      sf.MustMake("class"),
		symMeta:       sf.MustMake("meta"),
		symP:          sf.MustMake("p"),
		symLI:         sf.MustMake("li"),
		symA:          sf.MustMake("a"),
		symHREF:       sf.MustMake("href"),
		symSpan:       sf.MustMake("span"),

		fns:     make(map[string]EvalFn, 128),
		minArgs: make(map[string]int, 128),
	}
	ev.bindCommon()
	ev.bindMetadata()
	ev.bindBlocks()
	ev.bindInlines()
	return ev
}



// SetUnique sets a prefix to make several HTML ids unique.
func (tr *Evaluator) SetUnique(s string) { tr.unique = s }

// SymbolFactory returns the symbol factory of this evaluator.
func (ev *Evaluator) SymbolFactory() sx.SymbolFactory { return ev.sf }

// IsValidName returns true, if name is a valid symbol name.
func (tr *Evaluator) IsValidName(s string) bool { return tr.sf.IsValidName(s) }

// Make a new HTML symbol.
func (tr *Evaluator) Make(s string) *sx.Symbol { return tr.sf.MustMake(s) }







// EvaluateAttrbute transforms the given attributes into a HTML s-expression.
func (tr *Evaluator) EvaluateAttrbute(a attrs.Attributes) *sx.Pair {
	if len(a) == 0 {
		return nil
	}
	plist := sx.Nil()
	keys := a.Keys()
	for i := len(keys) - 1; i >= 0; i-- {
		key := keys[i]
		if key != attrs.DefaultAttribute && tr.IsValidName(key) {
			plist = plist.Cons(sx.Cons(tr.Make(key), sx.String(a[key])))
		}
	}
	if plist == nil {
		return nil
	}
	return plist.Cons(tr.symAttr)
}






// Evaluate a metadata s-expression into a list of HTML s-expressions.
func (ev *Evaluator) Evaluate(lst *sx.Pair, env *Environment) (*sx.Pair, error) {






















	result := ev.eval(lst, env)

	if err := env.err; err != nil {
		return nil, err
	}
	pair, isPair := sx.GetPair(result)
	if !isPair {
		return nil, fmt.Errorf("evaluation does not result in a pair, but %T/%v", result, result)
	}

	for i := 0; i < len(env.endnotes); i++ {
		// May extend tr.endnotes

		if env.endnotes[i].noteHx != nil {
			continue
		}

		objHx := ev.eval(env.endnotes[i].noteAST, env)
		if env.err != nil {
			break
		}
		noteHx, isHx := sx.GetPair(objHx)
		if !isHx {
			return nil, fmt.Errorf("endnote evaluation does not result in pair, but %T/%v", objHx, objHx)
		}
		env.endnotes[i].noteHx = noteHx
	}


	return pair, nil
}

// Endnotes returns a SHTML object with all collected endnotes.
func (ev *Evaluator) Endnotes(env *Environment) *sx.Pair {
	if env.err != nil || len(env.endnotes) == 0 {
		return nil
	}

	result := sx.Nil().Cons(ev.Make("ol"))
	symValue, symId, symRole := ev.Make("value"), ev.Make("id"), ev.Make("role")

	currResult := result.AppendBang(sx.Nil().Cons(sx.Cons(ev.symClass, sx.String("zs-endnotes"))).Cons(ev.symAttr))
	for i, fni := range env.endnotes {
		noteNum := strconv.Itoa(i + 1)


		attrs := fni.attrs.Cons(sx.Cons(ev.symClass, sx.String("zs-endnote"))).
			Cons(sx.Cons(symValue, sx.String(noteNum))).
			Cons(sx.Cons(symId, sx.String("fn:"+fni.noteID))).
			Cons(sx.Cons(symRole, sx.String("doc-endnote"))).
			Cons(ev.symAttr)

		backref := sx.Nil().Cons(sx.String("\u21a9\ufe0e")).
			Cons(sx.Nil().
				Cons(sx.Cons(ev.symClass, sx.String("zs-endnote-backref"))).
				Cons(sx.Cons(ev.symHREF, sx.String("#fnref:"+fni.noteID))).
				Cons(sx.Cons(symRole, sx.String("doc-backlink"))).
				Cons(ev.symAttr)).
			Cons(ev.symA)

		li := sx.Nil().Cons(ev.symLI)
		li.AppendBang(attrs).
			ExtendBang(fni.noteHx).
			AppendBang(sx.String(" ")).AppendBang(backref)
		currResult = currResult.AppendBang(li)
	}

	return result
}

// Environment where sz objects are evaluated to shtml objects



type Environment struct {
	err          error
	langStack    []string
	endnotes     []endnoteInfo
	quoteNesting uint
}
type endnoteInfo struct {
	noteID  string    // link id
	noteAST sx.Object // Endnote as AST
	attrs   *sx.Pair  // attrs a-list
	noteHx  *sx.Pair  // Endnote as SxHTML
}

// MakeEnvironment builds a new evaluation environment.
func MakeEnvironment(lang string) Environment {
	langStack := make([]string, 1, 16)
	langStack[0] = lang
	return Environment{
		err:          nil,
		langStack:    langStack,
		endnotes:     nil,
		quoteNesting: 0,
	}
}

// GetError returns the last error found.
func (env *Environment) GetError() error { return env.err }

// Reset the environment.
func (env *Environment) Reset() {

	env.langStack = env.langStack[0:1]
	env.endnotes = nil

	env.quoteNesting = 0
}

// PushAttribute adds the current attributes to the environment.
func (env *Environment) pushAttributes(a attrs.Attributes) {
	if value, ok := a.Get("lang"); ok {
		env.langStack = append(env.langStack, value)
	} else {
		env.langStack = append(env.langStack, env.getLanguage())
	}
}

// popAttributes removes the current attributes from the envrionment
func (env *Environment) popAttributes() {
	env.langStack = env.langStack[0 : len(env.langStack)-1]
}

// getLanguage returns the current language
func (env *Environment) getLanguage() string {
	return env.langStack[len(env.langStack)-1]
}

// EvalFn is a function to be called for evaluation.

type EvalFn func([]sx.Object, *Environment) sx.Object

func (ev *Evaluator) bind(name string, minArgs int, fn EvalFn) {
	ev.fns[name] = fn
	if minArgs > 0 {
		ev.minArgs[name] = minArgs
	}
}

// ResolveBinding returns the function bound to the given name.
func (ev *Evaluator) ResolveBinding(name string) EvalFn {
	if fn, found := ev.fns[name]; found {
		return fn
	}
	return nil
}


// Rebind overwrites a binding, but leaves the minimum number of arguments intact.
func (ev *Evaluator) Rebind(name string, fn EvalFn) {
	if _, found := ev.fns[name]; !found {
		panic(name)

	}
	ev.fns[name] = fn
}

func (ev *Evaluator) bindCommon() {
	ev.bind(sx.ListName, 0, ev.evalList)
	ev.bind("quote", 1, func(args []sx.Object, _ *Environment) sx.Object { return args[0] })
}

func (ev *Evaluator) bindMetadata() {
	ev.bind(sz.NameSymMeta, 0, ev.evalList)
	evalMetaString := func(args []sx.Object, env *Environment) sx.Object {
		a := make(attrs.Attributes, 2).
			Set("name", ev.getSymbol(ev.eval(args[0], env), env).Name()).
			Set("content", getString(args[1], env).String())
		return ev.EvaluateMeta(a)
	}
	ev.bind(sz.NameSymTypeCredential, 2, evalMetaString)
	ev.bind(sz.NameSymTypeEmpty, 2, evalMetaString)
	ev.bind(sz.NameSymTypeID, 2, evalMetaString)
	ev.bind(sz.NameSymTypeNumber, 2, evalMetaString)
	ev.bind(sz.NameSymTypeString, 2, evalMetaString)
	ev.bind(sz.NameSymTypeTimestamp, 2, evalMetaString)
	ev.bind(sz.NameSymTypeURL, 2, evalMetaString)
	ev.bind(sz.NameSymTypeWord, 2, evalMetaString)

	evalMetaSet := func(args []sx.Object, env *Environment) sx.Object {
		var sb strings.Builder
		lst := ev.eval(args[1], env)
		for elem := getList(lst, env); elem != nil; elem = elem.Tail() {
			sb.WriteByte(' ')
			sb.WriteString(getString(elem.Car(), env).String())
		}
		s := sb.String()
		if len(s) > 0 {
			s = s[1:]
		}
		a := make(attrs.Attributes, 2).
			Set("name", ev.getSymbol(ev.eval(args[0], env), env).Name()).
			Set("content", s)
		return ev.EvaluateMeta(a)
	}
	ev.bind(sz.NameSymTypeIDSet, 2, evalMetaSet)
	ev.bind(sz.NameSymTypeTagSet, 2, evalMetaSet)
	ev.bind(sz.NameSymTypeWordSet, 2, evalMetaSet)
	ev.bind(sz.NameSymTypeZettelmarkup, 2, func(args []sx.Object, env *Environment) sx.Object {
		a := make(attrs.Attributes, 2).
			Set("name", ev.getSymbol(ev.eval(args[0], env), env).String()).
			Set("content", text.EvaluateInlineString(getList(args[1], env)))
		return ev.EvaluateMeta(a)
	})
}

// EvaluateMeta returns HTML meta object for an attribute.
func (ev *Evaluator) EvaluateMeta(a attrs.Attributes) *sx.Pair {
	return sx.Nil().Cons(ev.EvaluateAttrbute(a)).Cons(ev.symMeta)
}

func (ev *Evaluator) bindBlocks() {
	ev.bind(sz.NameSymBlock, 0, ev.evalList)
	ev.bind(sz.NameSymPara, 0, func(args []sx.Object, env *Environment) sx.Object {






		return ev.evalSlice(args, env).Cons(ev.symP)
	})
	ev.bind(sz.NameSymHeading, 5, func(args []sx.Object, env *Environment) sx.Object {
		nLevel := getInt64(args[0], env)
		if nLevel <= 0 {
			env.err = fmt.Errorf("%v is a negative level", nLevel)
			return sx.Nil()
		}
		level := strconv.FormatInt(nLevel+ev.headingOffset, 10)

		a := ev.getAttributes(args[1], env)
		env.pushAttributes(a)
		defer env.popAttributes()
		if fragment := getString(args[3], env).String(); fragment != "" {
			a = a.Set("id", ev.unique+fragment)
		}

		if result, isPair := sx.GetPair(ev.eval(args[4], env)); isPair && result != nil {
			if len(a) > 0 {
				result = result.Cons(ev.EvaluateAttrbute(a))
			}
			return result.Cons(ev.Make("h" + level))
		}
		return sx.MakeList(ev.Make("h"+level), sx.String("<MISSING TEXT>"))
	})
	ev.bind(sz.NameSymThematic, 0, func(args []sx.Object, env *Environment) sx.Object {
		result := sx.Nil()
		if len(args) > 0 {
			if attrList := getList(ev.eval(args[0], env), env); attrList != nil {
				result = result.Cons(ev.EvaluateAttrbute(sz.GetAttributes(attrList)))
			}
		}
		return result.Cons(ev.Make("hr"))
	})

	ev.bind(sz.NameSymListOrdered, 0, ev.makeListFn("ol"))
	ev.bind(sz.NameSymListUnordered, 0, ev.makeListFn("ul"))
	ev.bind(sz.NameSymDescription, 0, func(args []sx.Object, env *Environment) sx.Object {
		if len(args) == 0 {
			return sx.Nil()
		}
		items := sx.Nil().Cons(ev.Make("dl"))
		curItem := items
		for pos := 0; pos < len(args); pos++ {
			term := getList(ev.eval(args[pos], env), env)
			curItem = curItem.AppendBang(term.Cons(ev.Make("dt")))
			pos++
			if pos >= len(args) {
				break
			}
			ddBlock := getList(ev.eval(args[pos], env), env)
			if ddBlock == nil {
				continue
			}
			for ddlst := ddBlock; ddlst != nil; ddlst = ddlst.Tail() {
				dditem := getList(ddlst.Car(), env)
				curItem = curItem.AppendBang(dditem.Cons(ev.Make("dd")))
			}
		}
		return items
	})

	ev.bind(sz.NameSymListQuote, 0, func(args []sx.Object, env *Environment) sx.Object {
		if args == nil {
			return sx.Nil()
		}
		result := sx.Nil().Cons(ev.Make("blockquote"))
		currResult := result
		for _, elem := range args {
			if quote, isPair := sx.GetPair(ev.eval(elem, env)); isPair {
				currResult = currResult.AppendBang(quote.Cons(ev.symP))
			}
		}
		return result
	})

	ev.bind(sz.NameSymTable, 1, func(args []sx.Object, env *Environment) sx.Object {
		thead := sx.Nil()
		if header := getList(ev.eval(args[0], env), env); !sx.IsNil(header) {
			thead = sx.Nil().Cons(ev.evalTableRow(header)).Cons(ev.Make("thead"))
		}

		tbody := sx.Nil()
		if len(args) > 1 {
			tbody = sx.Nil().Cons(ev.Make("tbody"))
			curBody := tbody
			for _, row := range args[1:] {
				curBody = curBody.AppendBang(ev.evalTableRow(getList(ev.eval(row, env), env)))
			}
		}

		table := sx.Nil()
		if tbody != nil {
			table = table.Cons(tbody)
		}
		if thead != nil {
			table = table.Cons(thead)
		}
		if table == nil {
			return sx.Nil()
		}
		return table.Cons(ev.Make("table"))
	})
	ev.bind(sz.NameSymCell, 0, ev.makeCellFn(""))
	ev.bind(sz.NameSymCellCenter, 0, ev.makeCellFn("center"))
	ev.bind(sz.NameSymCellLeft, 0, ev.makeCellFn("left"))
	ev.bind(sz.NameSymCellRight, 0, ev.makeCellFn("right"))

	symDiv := ev.Make("div")
	ev.bind(sz.NameSymRegionBlock, 2, ev.makeRegionFn(symDiv, true))
	ev.bind(sz.NameSymRegionQuote, 2, ev.makeRegionFn(ev.Make("blockquote"), false))
	ev.bind(sz.NameSymRegionVerse, 2, ev.makeRegionFn(symDiv, false))

	ev.bind(sz.NameSymVerbatimComment, 1, func(args []sx.Object, env *Environment) sx.Object {
		if ev.getAttributes(args[0], env).HasDefault() {
			if len(args) > 1 {
				if s := getString(args[1], env); s != "" {
					t := sx.String(s.String())
					return sx.Nil().Cons(t).Cons(ev.Make(sxhtml.NameSymBlockComment))
				}
			}
		}
		return nil
	})

	ev.bind(sz.NameSymVerbatimEval, 2, func(args []sx.Object, env *Environment) sx.Object {
		return ev.evalVerbatim(ev.getAttributes(args[0], env).AddClass("zs-eval"), getString(args[1], env))
	})
	ev.bind(sz.NameSymVerbatimHTML, 2, ev.evalHTML)
	ev.bind(sz.NameSymVerbatimMath, 2, func(args []sx.Object, env *Environment) sx.Object {
		return ev.evalVerbatim(ev.getAttributes(args[0], env).AddClass("zs-math"), getString(args[1], env))
	})
	ev.bind(sz.NameSymVerbatimProg, 2, func(args []sx.Object, env *Environment) sx.Object {
		a := ev.getAttributes(args[0], env)
		content := getString(args[1], env)
		if a.HasDefault() {
			content = sx.String(visibleReplacer.Replace(content.String()))
		}
		return ev.evalVerbatim(a, content)
	})
	ev.bind(sz.NameSymVerbatimZettel, 0, nilFn)

	ev.bind(sz.NameSymBLOB, 3, func(args []sx.Object, env *Environment) sx.Object {
		return ev.evalBLOB(getList(args[0], env), getString(args[1], env), getString(args[2], env))
	})

	ev.bind(sz.NameSymTransclude, 2, func(args []sx.Object, env *Environment) sx.Object {
		ref, isPair := sx.GetPair(ev.eval(args[1], env))
		if !isPair {
			return sx.Nil()
		}
		refKind := ref.Car()
		if sx.IsNil(refKind) {
			return sx.Nil()
		}
		if refValue := getString(ref.Tail().Car(), env); refValue != "" {
			if refSym, isRefSym := sx.GetSymbol(refKind); isRefSym && refSym.Name() == sz.NameSymRefStateExternal {
				a := ev.getAttributes(args[0], env).Set("src", refValue.String()).AddClass("external")
				return sx.Nil().Cons(sx.Nil().Cons(ev.EvaluateAttrbute(a)).Cons(ev.Make("img"))).Cons(ev.symP)
			}
			return sx.MakeList(
				ev.Make(sxhtml.NameSymInlineComment),
				sx.String("transclude"),
				refKind,
				sx.String("->"),
				refValue,
			)
		}
		return ev.evalSlice(args, env)
	})
}

func (ev *Evaluator) makeListFn(tag string) EvalFn {
	sym := ev.Make(tag)
	return func(args []sx.Object, env *Environment) sx.Object {
		result := sx.Nil().Cons(sym)
		last := result
		for _, elem := range args {
			item := sx.Nil().Cons(ev.symLI)
			if res, isPair := sx.GetPair(ev.eval(elem, env)); isPair {
				item.ExtendBang(res)
			}
			last = last.AppendBang(item)
		}
		return result
	}
}

func (ev *Evaluator) evalTableRow(pairs *sx.Pair) *sx.Pair {
	row := sx.Nil().Cons(ev.Make("tr"))
	if pairs == nil {
		return nil
	}
	curRow := row
	for pair := pairs; pair != nil; pair = pair.Tail() {
		curRow = curRow.AppendBang(pair.Car())
	}
	return row
}

func (ev *Evaluator) makeCellFn(align string) EvalFn {
	return func(args []sx.Object, env *Environment) sx.Object {
		tdata := ev.evalSlice(args, env)
		if align != "" {
			tdata = tdata.Cons(ev.EvaluateAttrbute(attrs.Attributes{"class": align}))
		}
		return tdata.Cons(ev.Make("td"))
	}
}

func (ev *Evaluator) makeRegionFn(sym *sx.Symbol, genericToClass bool) EvalFn {
	return func(args []sx.Object, env *Environment) sx.Object {
		a := ev.getAttributes(args[0], env)
		env.pushAttributes(a)
		defer env.popAttributes()
		if genericToClass {
			if val, found := a.Get(""); found {
				a = a.Remove("").AddClass(val)
			}
		}
		result := sx.Nil()
		if len(a) > 0 {
			result = result.Cons(ev.EvaluateAttrbute(a))
		}
		result = result.Cons(sym)
		currResult := result.LastPair()
		if region, isPair := sx.GetPair(ev.eval(args[1], env)); isPair {
			currResult = currResult.ExtendBang(region)
		}
		if len(args) > 2 {
			if cite, isPair := sx.GetPair(ev.eval(args[2], env)); isPair && cite != nil {
				currResult.AppendBang(cite.Cons(ev.Make("cite")))
			}
		}
		return result
	}
}

func (ev *Evaluator) evalVerbatim(a attrs.Attributes, s sx.String) sx.Object {
	a = setProgLang(a)
	code := sx.Nil().Cons(s)
	if al := ev.EvaluateAttrbute(a); al != nil {
		code = code.Cons(al)
	}
	code = code.Cons(ev.Make("code"))
	return sx.Nil().Cons(code).Cons(ev.Make("pre"))
}

func (ev *Evaluator) bindInlines() {
	ev.bind(sz.NameSymInline, 0, ev.evalList)
	ev.bind(sz.NameSymText, 1, func(args []sx.Object, env *Environment) sx.Object { return getString(args[0], env) })
	ev.bind(sz.NameSymSpace, 0, func(args []sx.Object, env *Environment) sx.Object {
		if len(args) == 0 {
			return sx.String(" ")
		}
		return getString(args[0], env)
	})
	ev.bind(sz.NameSymSoft, 0, func([]sx.Object, *Environment) sx.Object { return sx.String(" ") })
	symBR := ev.Make("br")
	ev.bind(sz.NameSymHard, 0, func([]sx.Object, *Environment) sx.Object { return sx.Nil().Cons(symBR) })

	ev.bind(sz.NameSymLinkInvalid, 2, func(args []sx.Object, env *Environment) sx.Object {
		a := ev.getAttributes(args[0], env)
		env.pushAttributes(a)
		defer env.popAttributes()
		var inline *sx.Pair
		if len(args) > 2 {
			inline = ev.evalSlice(args[2:], env)
		}
		if inline == nil {
			inline = sx.Nil().Cons(ev.eval(args[1], env))
		}
		return inline.Cons(ev.symSpan)
	})
	evalHREF := func(args []sx.Object, env *Environment) sx.Object {
		a := ev.getAttributes(args[0], env)
		env.pushAttributes(a)
		defer env.popAttributes()
		refValue := getString(args[1], env)
		return ev.evalLink(a.Set("href", refValue.String()), refValue, args[2:], env)
	}
	ev.bind(sz.NameSymLinkZettel, 2, evalHREF)
	ev.bind(sz.NameSymLinkSelf, 2, evalHREF)
	ev.bind(sz.NameSymLinkFound, 2, evalHREF)
	ev.bind(sz.NameSymLinkBroken, 2, func(args []sx.Object, env *Environment) sx.Object {
		a := ev.getAttributes(args[0], env)
		env.pushAttributes(a)
		defer env.popAttributes()
		refValue := getString(args[1], env)
		return ev.evalLink(a.AddClass("broken"), refValue, args[2:], env)
	})
	ev.bind(sz.NameSymLinkHosted, 2, evalHREF)
	ev.bind(sz.NameSymLinkBased, 2, evalHREF)
	ev.bind(sz.NameSymLinkQuery, 2, func(args []sx.Object, env *Environment) sx.Object {
		a := ev.getAttributes(args[0], env)
		env.pushAttributes(a)
		defer env.popAttributes()
		refValue := getString(args[1], env)
		query := "?" + api.QueryKeyQuery + "=" + url.QueryEscape(refValue.String())
		return ev.evalLink(a.Set("href", query), refValue, args[2:], env)
	})
	ev.bind(sz.NameSymLinkExternal, 2, func(args []sx.Object, env *Environment) sx.Object {
		a := ev.getAttributes(args[0], env)
		env.pushAttributes(a)
		defer env.popAttributes()
		refValue := getString(args[1], env)
		return ev.evalLink(a.Set("href", refValue.String()).AddClass("external"), refValue, args[2:], env)
	})

	ev.bind(sz.NameSymEmbed, 3, func(args []sx.Object, env *Environment) sx.Object {
		ref := getList(ev.eval(args[1], env), env)
		syntax := getString(args[2], env)
		if syntax == api.ValueSyntaxSVG {
			embedAttr := sx.MakeList(
				ev.symAttr,
				sx.Cons(ev.Make("type"), sx.String("image/svg+xml")),
				sx.Cons(ev.Make("src"), sx.String("/"+getString(ref.Tail(), env).String()+".svg")),
			)
			return sx.MakeList(
				ev.Make("figure"),
				sx.MakeList(
					ev.Make("embed"),
					embedAttr,
				),
			)
		}
		a := ev.getAttributes(args[0], env)
		a = a.Set("src", getString(ref.Tail().Car(), env).String())
		if len(args) > 3 {
			var sb strings.Builder
			flattenText(&sb, sx.MakeList(args[3:]...))
			if d := sb.String(); d != "" {
				a = a.Set("alt", d)
			}
		}
		return sx.MakeList(ev.Make("img"), ev.EvaluateAttrbute(a))
	})
	ev.bind(sz.NameSymEmbedBLOB, 3, func(args []sx.Object, env *Environment) sx.Object {
		a, syntax, data := ev.getAttributes(args[0], env), getString(args[1], env), getString(args[2], env)
		summary, hasSummary := a.Get(api.KeySummary)
		if !hasSummary {
			summary = ""
		}
		return ev.evalBLOB(
			sx.MakeList(ev.Make(sx.ListName), sx.String(summary)),
			syntax,
			data,
		)
	})

	ev.bind(sz.NameSymCite, 2, func(args []sx.Object, env *Environment) sx.Object {
		a := ev.getAttributes(args[0], env)
		env.pushAttributes(a)
		defer env.popAttributes()
		result := sx.Nil()
		if key := getString(args[1], env); key != "" {
			if len(args) > 2 {
				result = ev.evalSlice(args[2:], env).Cons(sx.String(", "))
			}
			result = result.Cons(key)
		}
		if len(a) > 0 {
			result = result.Cons(ev.EvaluateAttrbute(a))
		}
		if result == nil {
			return nil
		}
		return result.Cons(ev.symSpan)
	})

	ev.bind(sz.NameSymMark, 3, func(args []sx.Object, env *Environment) sx.Object {
		result := ev.evalSlice(args[3:], env)
		if !ev.noLinks {
			if fragment := getString(args[2], env); fragment != "" {
				a := attrs.Attributes{"id": fragment.String() + ev.unique}
				return result.Cons(ev.EvaluateAttrbute(a)).Cons(ev.symA)
			}
		}
		return result.Cons(ev.symSpan)
	})

	ev.bind(sz.NameSymEndnote, 1, func(args []sx.Object, env *Environment) sx.Object {
		a := ev.getAttributes(args[0], env)
		env.pushAttributes(a)
		defer env.popAttributes()
		attrPlist := sx.Nil()
		if len(a) > 0 {
			if attrs := ev.EvaluateAttrbute(a); attrs != nil {
				attrPlist = attrs.Tail()
			}
		}

		text, isPair := sx.GetPair(args[1])
		if !isPair {
			return sx.Nil()
		}

		noteNum := strconv.Itoa(len(env.endnotes) + 1)
		noteID := ev.unique + noteNum
		env.endnotes = append(env.endnotes, endnoteInfo{
			noteID: noteID, noteAST: ev.eval(text, env), noteHx: nil, attrs: attrPlist})
		hrefAttr := sx.Nil().Cons(sx.Cons(ev.Make("role"), sx.String("doc-noteref"))).
			Cons(sx.Cons(ev.symHREF, sx.String("#fn:"+noteID))).
			Cons(sx.Cons(ev.symClass, sx.String("zs-noteref"))).
			Cons(ev.symAttr)
		href := sx.Nil().Cons(sx.String(noteNum)).Cons(hrefAttr).Cons(ev.symA)
		supAttr := sx.Nil().Cons(sx.Cons(ev.Make("id"), sx.String("fnref:"+noteID))).Cons(ev.symAttr)
		return sx.Nil().Cons(href).Cons(supAttr).Cons(ev.Make("sup"))
	})

	ev.bind(sz.NameSymFormatDelete, 1, ev.makeFormatFn("del"))
	ev.bind(sz.NameSymFormatEmph, 1, ev.makeFormatFn("em"))
	ev.bind(sz.NameSymFormatInsert, 1, ev.makeFormatFn("ins"))
	ev.bind(sz.NameSymFormatMark, 1, ev.makeFormatFn("mark"))
	ev.bind(sz.NameSymFormatQuote, 1, ev.evalQuote)
	ev.bind(sz.NameSymFormatSpan, 1, ev.makeFormatFn("span"))
	ev.bind(sz.NameSymFormatStrong, 1, ev.makeFormatFn("strong"))
	ev.bind(sz.NameSymFormatSub, 1, ev.makeFormatFn("sub"))
	ev.bind(sz.NameSymFormatSuper, 1, ev.makeFormatFn("sup"))

	ev.bind(sz.NameSymLiteralComment, 1, func(args []sx.Object, env *Environment) sx.Object {
		if ev.getAttributes(args[0], env).HasDefault() {
			if len(args) > 1 {
				if s := getString(ev.eval(args[1], env), env); s != "" {
					return sx.Nil().Cons(s).Cons(ev.Make(sxhtml.NameSymInlineComment))
				}
			}
		}
		return sx.Nil()
	})
	ev.bind(sz.NameSymLiteralHTML, 2, ev.evalHTML)
	kbdSym := ev.Make("kbd")
	ev.bind(sz.NameSymLiteralInput, 2, func(args []sx.Object, env *Environment) sx.Object {
		return ev.evalLiteral(args, nil, kbdSym, env)
	})
	codeSym := ev.Make("code")
	ev.bind(sz.NameSymLiteralMath, 2, func(args []sx.Object, env *Environment) sx.Object {
		a := ev.getAttributes(args[0], env).AddClass("zs-math")
		return ev.evalLiteral(args, a, codeSym, env)
	})
	sampSym := ev.Make("samp")
	ev.bind(sz.NameSymLiteralOutput, 2, func(args []sx.Object, env *Environment) sx.Object {
		return ev.evalLiteral(args, nil, sampSym, env)
	})
	ev.bind(sz.NameSymLiteralProg, 2, func(args []sx.Object, env *Environment) sx.Object {
		return ev.evalLiteral(args, nil, codeSym, env)
	})

	ev.bind(sz.NameSymLiteralZettel, 0, nilFn)
}

func (ev *Evaluator) makeFormatFn(tag string) EvalFn {
	sym := ev.Make(tag)
	return func(args []sx.Object, env *Environment) sx.Object {
		a := ev.getAttributes(args[0], env)
		env.pushAttributes(a)
		defer env.popAttributes()
		if val, hasClass := a.Get(""); hasClass {
			a = a.Remove("").AddClass(val)
		}
		res := ev.evalSlice(args[1:], env)
		if len(a) > 0 {
			res = res.Cons(ev.EvaluateAttrbute(a))
		}
		return res.Cons(sym)
	}
}

type quoteData struct {
	primLeft, primRight string
	secLeft, secRight   string
	nbsp                bool
}

var langQuotes = map[string]quoteData{
	"":              {"&quot;", "&quot;", "&quot;", "&quot;", false},
	api.ValueLangEN: {"&ldquo;", "&rdquo;", "&lsquo;", "&rsquo;", false},
	"de":            {"&bdquo;", "&ldquo;", "&sbquo;", "&lsquo;", false},
	"fr":            {"&laquo;", "&raquo;", "&lsaquo;", "&rsaquo;", true},
}

func getQuoteData(lang string) quoteData {
	langFields := strings.FieldsFunc(lang, func(r rune) bool { return r == '-' || r == '_' })
	for len(langFields) > 0 {
		langSup := strings.Join(langFields, "-")
		quotes, ok := langQuotes[langSup]
		if ok {
			return quotes
		}
		langFields = langFields[0 : len(langFields)-1]
	}
	return langQuotes[""]
}

func getQuotes(data *quoteData, env *Environment) (string, string) {
	if env.quoteNesting%2 == 0 {
		return data.primLeft, data.primRight
	}
	return data.secLeft, data.secRight
}

func (ev *Evaluator) evalQuote(args []sx.Object, env *Environment) sx.Object {
	a := ev.getAttributes(args[0], env)
	env.pushAttributes(a)
	defer env.popAttributes()

	if val, hasClass := a.Get(""); hasClass {
		a = a.Remove("").AddClass(val)
	}
	quotes := getQuoteData(env.getLanguage())
	leftQ, rightQ := getQuotes(&quotes, env)

	env.quoteNesting++
	res := ev.evalSlice(args[1:], env)
	env.quoteNesting--

	lastPair := res.LastPair()
	if lastPair.IsNil() {
		res = sx.Cons(sx.MakeList(ev.symNoEscape, sx.String(leftQ), sx.String(rightQ)), sx.Nil())
	} else {
		if quotes.nbsp {
			lastPair.AppendBang(sx.MakeList(ev.symNoEscape, sx.String("&nbsp;"), sx.String(rightQ)))
			res = res.Cons(sx.MakeList(ev.symNoEscape, sx.String(leftQ), sx.String("&nbsp;")))
		} else {
			lastPair.AppendBang(sx.MakeList(ev.symNoEscape, sx.String(rightQ)))
			res = res.Cons(sx.MakeList(ev.symNoEscape, sx.String(leftQ)))
		}
	}
	if len(a) > 0 {
		res = res.Cons(ev.EvaluateAttrbute(a))
		return res.Cons(ev.symSpan)
	}




	return res.Cons(ev.symList)
}

var visibleReplacer = strings.NewReplacer(" ", "\u2423")

func (ev *Evaluator) evalLiteral(args []sx.Object, a attrs.Attributes, sym *sx.Symbol, env *Environment) sx.Object {
	if a == nil {
		a = ev.getAttributes(args[0], env)
	}
	a = setProgLang(a)
	literal := getString(args[1], env).String()
	if a.HasDefault() {
		a = a.RemoveDefault()
		literal = visibleReplacer.Replace(literal)
	}
	res := sx.Nil().Cons(sx.String(literal))
	if len(a) > 0 {
		res = res.Cons(ev.EvaluateAttrbute(a))
	}
	return res.Cons(sym)
}

func setProgLang(a attrs.Attributes) attrs.Attributes {
	if val, found := a.Get(""); found {
		a = a.AddClass("language-" + val).Remove("")
	}
	return a
}

func (ev *Evaluator) evalHTML(args []sx.Object, env *Environment) sx.Object {
	if s := getString(ev.eval(args[1], env), env); s != "" && IsSafe(s.String()) {
		return sx.Nil().Cons(s).Cons(ev.symNoEscape)
	}
	return nil
}

func (ev *Evaluator) evalBLOB(description *sx.Pair, syntax, data sx.String) sx.Object {
	if data == "" {
		return sx.Nil()
	}
	switch syntax {
	case "":
		return sx.Nil()
	case api.ValueSyntaxSVG:
		return sx.Nil().Cons(sx.Nil().Cons(data).Cons(ev.symNoEscape)).Cons(ev.symP)
	default:
		imgAttr := sx.Nil().Cons(sx.Cons(ev.Make("src"), sx.String("data:image/"+syntax.String()+";base64,"+data.String())))
		var sb strings.Builder
		flattenText(&sb, description)
		if d := sb.String(); d != "" {
			imgAttr = imgAttr.Cons(sx.Cons(ev.Make("alt"), sx.String(d)))
		}
		return sx.Nil().Cons(sx.Nil().Cons(imgAttr.Cons(ev.symAttr)).Cons(ev.Make("img"))).Cons(ev.symP)
	}
}

func flattenText(sb *strings.Builder, lst *sx.Pair) {
	for elem := lst; elem != nil; elem = elem.Tail() {
		switch obj := elem.Car().(type) {
		case sx.String:
			sb.WriteString(obj.String())
		case *sx.Symbol:
			if obj.Name() == sz.NameSymSpace {
				sb.WriteByte(' ')
				break
			}
		case *sx.Pair:
			flattenText(sb, obj)
		}
	}
}

func (ev *Evaluator) evalList(args []sx.Object, env *Environment) sx.Object {
	return ev.evalSlice(args, env)
}
func nilFn([]sx.Object, *Environment) sx.Object { return sx.Nil() }


func (ev *Evaluator) eval(obj sx.Object, env *Environment) sx.Object {
	if env.err != nil {


		return sx.Nil()
	}
	if sx.IsNil(obj) {
		return obj

	}
	lst, isLst := sx.GetPair(obj)
	if !isLst {
		return obj


	}
	sym, found := sx.GetSymbol(lst.Car())
	if !found {
		env.err = fmt.Errorf("symbol expected, but got %T/%v", lst.Car(), lst.Car())
		return sx.Nil()
	}
	name := sym.Name()
	fn, found := ev.fns[name]
	if !found {
		env.err = fmt.Errorf("symbol %q not bound", name)
		return sx.Nil()
	}
	var args []sx.Object
	for cdr := lst.Cdr(); !sx.IsNil(cdr); {
		pair, isPair := sx.GetPair(cdr)
		if !isPair {
			break
		}
		args = append(args, pair.Car())
		cdr = pair.Cdr()
	}
	if minArgs, hasMinArgs := ev.minArgs[name]; hasMinArgs {
		if minArgs > len(args) {
			env.err = fmt.Errorf("%v needs at least %d arguments, but got only %d", name, minArgs, len(args))
			return sx.Nil()
		}

	}
	result := fn(args, env)

	if env.err != nil {

		return sx.Nil()
	}

	return result

}


func (ev *Evaluator) evalSlice(args []sx.Object, env *Environment) *sx.Pair {
	result := sx.Cons(sx.Nil(), sx.Nil())
	curr := result
	for _, arg := range args {
		elem := ev.eval(arg, env)
		if env.err != nil {
			return nil
		}
		curr = curr.AppendBang(elem)
	}
	return result.Tail()


}

func (ev *Evaluator) evalLink(a attrs.Attributes, refValue sx.String, inline []sx.Object, env *Environment) sx.Object {
	result := ev.evalSlice(inline, env)
	if len(inline) == 0 {
		result = sx.Nil().Cons(refValue)
	}
	if ev.noLinks {
		return result.Cons(ev.symSpan)
	}
	return result.Cons(ev.EvaluateAttrbute(a)).Cons(ev.symA)
}

func (ev *Evaluator) getSymbol(val sx.Object, env *Environment) *sx.Symbol {
	if env.err == nil {
		if sym, ok := sx.GetSymbol(val); ok {
			return sym
		}
		env.err = fmt.Errorf("%v/%T is not a symbol", val, val)
	}
	return ev.Make("???")
}
func getString(val sx.Object, env *Environment) sx.String {
	if env.err != nil {
		return ""
	}
	if s, ok := sx.GetString(val); ok {
		return s
	}
	env.err = fmt.Errorf("%v/%T is not a string", val, val)
	return ""
}
func getList(val sx.Object, env *Environment) *sx.Pair {
	if env.err == nil {
		if res, isPair := sx.GetPair(val); isPair {
			return res
		}
		env.err = fmt.Errorf("%v/%T is not a list", val, val)
	}
	return nil
}
func getInt64(val sx.Object, env *Environment) int64 {
	if env.err != nil {
		return -1017
	}
	if num, ok := sx.GetNumber(val); ok {
		return int64(num.(sx.Int64))
	}
	env.err = fmt.Errorf("%v/%T is not a number", val, val)
	return -1017
}









func (ev *Evaluator) getAttributes(arg sx.Object, env *Environment) attrs.Attributes {
	return sz.GetAttributes(getList(ev.eval(arg, env), env))



















}

var unsafeSnippets = []string{
	"<script", "</script",
	"<iframe", "</iframe",
}

	NameSymDescription     = "DESCRIPTION"
	NameSymEmbed           = "EMBED"
	NameSymEmbedBLOB       = "EMBED-BLOB"
	NameSymEndnote         = "ENDNOTE"
	NameSymFormatEmph      = "FORMAT-EMPH"
	NameSymFormatDelete    = "FORMAT-DELETE"
	NameSymFormatInsert    = "FORMAT-INSERT"
	NameSymFormatMark      = "FORMAT-MARK"
	NameSymFormatQuote     = "FORMAT-QUOTE"
	NameSymFormatSpan      = "FORMAT-SPAN"
	NameSymFormatSub       = "FORMAT-SUB"
	NameSymFormatSuper     = "FORMAT-SUPER"
	NameSymFormatStrong    = "FORMAT-STRONG"
	NameSymHard            = "HARD"
	NameSymHeading         = "HEADING"

	SymDescription     *sx.Symbol
	SymEmbed           *sx.Symbol
	SymEmbedBLOB       *sx.Symbol
	SymEndnote         *sx.Symbol
	SymFormatEmph      *sx.Symbol
	SymFormatDelete    *sx.Symbol
	SymFormatInsert    *sx.Symbol
	SymFormatMark      *sx.Symbol
	SymFormatQuote     *sx.Symbol
	SymFormatSpan      *sx.Symbol
	SymFormatSub       *sx.Symbol
	SymFormatSuper     *sx.Symbol
	SymFormatStrong    *sx.Symbol
	SymHard            *sx.Symbol
	SymHeading         *sx.Symbol

	zs.SymDescription = sf.MustMake(NameSymDescription)
	zs.SymEmbed = sf.MustMake(NameSymEmbed)
	zs.SymEmbedBLOB = sf.MustMake(NameSymEmbedBLOB)
	zs.SymEndnote = sf.MustMake(NameSymEndnote)
	zs.SymFormatEmph = sf.MustMake(NameSymFormatEmph)
	zs.SymFormatDelete = sf.MustMake(NameSymFormatDelete)
	zs.SymFormatInsert = sf.MustMake(NameSymFormatInsert)
	zs.SymFormatMark = sf.MustMake(NameSymFormatMark)
	zs.SymFormatQuote = sf.MustMake(NameSymFormatQuote)
	zs.SymFormatSpan = sf.MustMake(NameSymFormatSpan)
	zs.SymFormatSub = sf.MustMake(NameSymFormatSub)
	zs.SymFormatSuper = sf.MustMake(NameSymFormatSuper)
	zs.SymFormatStrong = sf.MustMake(NameSymFormatStrong)
	zs.SymHard = sf.MustMake(NameSymHard)
	zs.SymHeading = sf.MustMake(NameSymHeading)

<title>Change Log</title>

<a name="0_17"></a>
<h2>Changes for Version 0.17.0 (pending)</h2>

<a name="0_16"></a>
<h2>Changes for Version 0.16.0 (2023-11-30)</h2>
  *  Refactor shtml transformator to support evaluating the language tree of a
     zettel AST. Its API has been changes, since evaluation is now top-down,
     where previous transformation was bottom.up.
  *  Add API call to retrieve role zettel.
  *  Added constants for role zettel and to mark text within zettelmarkup.

<a name="0_15"></a>
<h2>Changes for Version 0.15.0 (2023-10-26)</h2>
  *  Tag zettel: API, constant values
  *  Refactorings b/c Sx

<a name="0_14"></a>
<h2>Changes for Version 0.14.0 (2023-09-23)</h2>
  *  Remove support for JSON encoding

<a name="0_13"></a>
<h2>Changes for Version 0.13.0 (2023-08-07)</h2>
  *  API uses plain data or sx data, but no JSON encoded data.
  *  Dependency sx is now hosted on Fossil repository, same for this library.

<a name="0_12"></a>

<title>Home</title>

This repository contains Go client software to
access [https://zettelstore.de|Zettelstore] via its API.

<h3>Latest Release: 0.16.0 (2023-11-30)</h3>
  *  [./changes.wiki#0_16|Change summary]
  *  [/timeline?p=v0.16.0&bt=v0.15.0&y=ci|Check-ins for version 0.16.0],
     [/vdiff?to=v0.16.0&from=v0.15.0|content diff]
  *  [/timeline?df=v0.16.0&y=ci|Check-ins derived from the 0.16.0 release],
     [/vdiff?from=v0.16.0&to=trunk|content diff]
  *  [/timeline?t=release|Timeline of all past releases]

<h3>Use instructions</h3>

If you want to import this library into your own [https://go.dev/|Go] software,
you must execute a <code>go get</code> command. Since Go treats non-standard
software and non-standard platforms quite badly, you must use some non-standard
commands.

First, you must install the version control system
[https://fossil-scm.org|Fossil], which is a superior solution compared to Git,
in too many use cases. It is just a single executable, nothing more. Make sure,
it is in your search path for commands.

How you can execute the following Go command to retrieve a given version of
this library:

<code>GOVCS=zettelstore.de:fossil go get -x
zettelstore.de/client.fossil@HASH</code>

where <code>HASH</code> is the hash value of the commit you want to use.

Go currently seems not to support software versions when the software is
managed by Fossil. This explains the need for the hash value. However, this
methods works and you can use the client software to access a Zettelstore.