package hatmill

//go:generate go run internal/codegen/codegen.go -input defs.json -elemfile element/generated.go -elempkg element -attribfile attribute/generated.go -attribpkg attribute
import (
	"bytes"
	"fmt"
	"html"
	"io"
)

// Term represents a fragment of HTML markup, and is one of VoidElement, ParentElement, Terms, or Text.
type Term interface {
	io.WriterTo

	// isHtml is a no-op method to prevent external Term implementations, because
	// Go doesn't have sum types.
	isHtml()
}

// writeStringsTo attempts to write the strings in ss to w, incrementing n by the
// number of bytes written.
func writeStringsTo(w io.Writer, n *int64, ss ...string) error {
	for _, s := range ss {
		nCurr, err := io.WriteString(w, s)
		*n += int64(nCurr)
		if err != nil {
			return err
		}
	}
	return nil
}

// Attrib represents an HTML attribute.
type Attrib struct {
	Key   string
	Value fmt.Stringer
}

// WriteTo writes a to w as an HTML attribute in the form key="value",  or
// simply key if value is empty. Special characters in value are replaced with
// HTML entities. It returns the number of bytes written and any
// error encountered.
func (a Attrib) WriteTo(w io.Writer) (n int64, err error) {
	err = writeStringsTo(w, &n, a.Key)
	if err != nil {
		return
	}
	var value string
	if a.Value != nil {
		value = html.EscapeString(a.Value.String())
	}
	if value != "" {
		err = writeStringsTo(w, &n, "='", value, "'")
	}
	return
}

// VoidElement represents a void HTML element, that is one that cannot have
// children.
type VoidElement struct {
	TagName string
	Attribs []Attrib
}

func (VoidElement) isHtml() {}

// WriteTo writes the HTML markup represented by e to w, returning the number
// of bytes written and any error encountered.
func (e VoidElement) WriteTo(w io.Writer) (n int64, err error) {
	err = writeStringsTo(w, &n, "<", e.TagName)
	if err != nil {
		return
	}

	for _, attrib := range e.Attribs {
		err = writeStringsTo(w, &n, " ")
		if err != nil {
			return
		}

		var nCurr int64
		nCurr, err = attrib.WriteTo(w)
		n += int64(nCurr)
		if err != nil {
			return
		}
	}

	err = writeStringsTo(w, &n, ">")
	return
}

// ParentElement represents an HTML element that can have children.
type ParentElement struct {
	VoidElement
	Children Terms
}

func (e ParentElement) isHtml() {}

// WriteTo writes the HTML markup represented by e to w, returning the number
// of bytes written and any error encountered.
func (e ParentElement) WriteTo(w io.Writer) (n int64, err error) {
	n, err = e.VoidElement.WriteTo(w)
	if err != nil {
		return
	}

	var nChildren int64
	nChildren, err = e.Children.WriteTo(w)
	n += nChildren
	if err != nil {
		return
	}

	err = writeStringsTo(w, &n, "</", e.TagName, ">")
	return
}

// Text represents an HTML text node.
type Text string

func (Text) isHtml() {}

var entities = map[byte][]byte{
	'&':  []byte("&amp;"),
	'<':  []byte("&lt;"),
	'>':  []byte("&gt;"),
	'\'': []byte("&#39;"),
	'"':  []byte("&#34;"),
}

type escapedWriter struct {
	io.Writer
}

func (w escapedWriter) Write(p []byte) (n int, err error) {
	const specialChars = `&<>'"`
	for len(p) > 0 {
		var nCurr int
		idx := bytes.IndexAny(p, specialChars)
		if idx == -1 {
			nCurr, err = w.Writer.Write(p)
			n += nCurr
			return
		}

		nCurr, err = w.Writer.Write(p[:idx])
		n += nCurr
		if err != nil {
			return n, err
		}

		entity := entities[p[idx]]
		nCurr, err = w.Writer.Write(entity)
		n += nCurr
		if err != nil {
			return n, err
		}
		p = p[idx+1:]
	}
	return n, nil
}

// WriteTo writes the contents of t to w, returning the number of bytes written
// and any error encountered. It replaces special characters with HTML entities.
func (t Text) WriteTo(w io.Writer) (n int64, err error) {
	err = writeStringsTo(escapedWriter{Writer: w}, &n, string(t))
	return
}

// RawText represents an HTML text node. Unlike Text, its contents are not
// escaped when written, so it should be used with care. It is intended mainly
// for use in <style> and <script> elements.
type RawText string

func (RawText) isHtml() {}

// WriteTo writes the contents of t to w, returning the number of bytes written
// and any error encountered. It does not escape special characters.
func (t RawText) WriteTo(w io.Writer) (n int64, err error) {
	err = writeStringsTo(w, &n, string(t))
	return
}

// WriteDocument writes an HTML5 DOCTYPE declaration, followed by root.
// root should probably be an <html> element.
func WriteDocument(w io.Writer, root ParentElement) (n int64, err error) {
	err = writeStringsTo(w, &n, "<!DOCTYPE html>")
	if err != nil {
		return
	}

	var nroot int64
	nroot, err = root.WriteTo(w)
	n += nroot
	return
}

// Terms is a list of HTML nodes.
type Terms []Term

func (Terms) isHtml() {}

func (ts Terms) WriteTo(w io.Writer) (n int64, err error) {
	for _, t := range ts {
		var nCurr int64
		nCurr, err = t.WriteTo(w)
		n += int64(nCurr)
		if err != nil {
			return
		}
	}
	return
}