package renderer

import (
	"unicode"
	"unicode/utf8"

	"github.com/yuin/goldmark/ast"
	"github.com/yuin/goldmark/renderer"
	"github.com/yuin/goldmark/renderer/html"
	"github.com/yuin/goldmark/util"
)

// ConfluenceTextRenderer slightly alters the default goldmark behavior for
// inline text block. It allows for soft breaks
// (c.f. https://spec.commonmark.org/0.30/#softbreak)
// to be rendered into HTML as either '\n' (the goldmark default)
// or as ' '.
// This latter option is useful for Confluence,
// which inserts <br> tags into uploaded HTML where it sees '\n'.
// See also https://sembr.org/ for partial motivation.
type ConfluenceTextRenderer struct {
	html.Config
	softBreak rune
}

// NewConfluenceTextRenderer creates a new instance of the ConfluenceTextRenderer
func NewConfluenceTextRenderer(stripNL bool, opts ...html.Option) renderer.NodeRenderer {
	sb := '\n'
	if stripNL {
		sb = ' '
	}
	return &ConfluenceTextRenderer{
		Config:    html.NewConfig(),
		softBreak: sb,
	}
}

// RegisterFuncs implements NodeRenderer.RegisterFuncs .
func (r *ConfluenceTextRenderer) RegisterFuncs(reg renderer.NodeRendererFuncRegisterer) {
	reg.Register(ast.KindText, r.renderText)
}

// This is taken from https://github.com/yuin/goldmark/blob/v1.6.0/renderer/html/html.go#L719
// with the hardcoded '\n' for soft breaks swapped for the configurable r.softBreak
func (r *ConfluenceTextRenderer) renderText(w util.BufWriter, source []byte, node ast.Node, entering bool) (ast.WalkStatus, error) {
	if !entering {
		return ast.WalkContinue, nil
	}
	n := node.(*ast.Text)
	segment := n.Segment
	if n.IsRaw() {
		r.Writer.RawWrite(w, segment.Value(source))
	} else {
		value := segment.Value(source)
		r.Writer.Write(w, value)
		if n.HardLineBreak() || (n.SoftLineBreak() && r.HardWraps) {
			if r.XHTML {
				_, _ = w.WriteString("<br />\n")
			} else {
				_, _ = w.WriteString("<br>\n")
			}
		} else if n.SoftLineBreak() {
			if r.EastAsianLineBreaks != html.EastAsianLineBreaksNone && len(value) != 0 {
				sibling := node.NextSibling()
				if sibling != nil && sibling.Kind() == ast.KindText {
					if siblingText := sibling.(*ast.Text).Value(source); len(siblingText) != 0 {
						thisLastRune := util.ToRune(value, len(value)-1)
						siblingFirstRune, _ := utf8.DecodeRune(siblingText)
						// Inline the softLineBreak function as it's not public
						writeLineBreak := false
						switch r.EastAsianLineBreaks {
						case html.EastAsianLineBreaksNone:
							writeLineBreak = false
						case html.EastAsianLineBreaksSimple:
							writeLineBreak = !(util.IsEastAsianWideRune(thisLastRune) && util.IsEastAsianWideRune(siblingFirstRune))
						case html.EastAsianLineBreaksCSS3Draft:
							writeLineBreak = eastAsianLineBreaksCSS3DraftSoftLineBreak(thisLastRune, siblingFirstRune)
						}

						if writeLineBreak {
							_ = w.WriteByte(byte(r.softBreak))
						}
					}
				}
			} else {
				_ = w.WriteByte(byte(r.softBreak))
			}
		}
	}
	return ast.WalkContinue, nil
}

func eastAsianLineBreaksCSS3DraftSoftLineBreak(thisLastRune rune, siblingFirstRune rune) bool {
	// Implements CSS text level3 Segment Break Transformation Rules with some enhancements.
	// References:
	//   - https://www.w3.org/TR/2020/WD-css-text-3-20200429/#line-break-transform
	//   - https://github.com/w3c/csswg-drafts/issues/5086

	// Rule1:
	//   If the character immediately before or immediately after the segment break is
	//   the zero-width space character (U+200B), then the break is removed, leaving behind the zero-width space.
	if thisLastRune == '\u200B' || siblingFirstRune == '\u200B' {
		return false
	}

	// Rule2:
	//   Otherwise, if the East Asian Width property of both the character before and after the segment break is
	//   F, W, or H (not A), and neither side is Hangul, then the segment break is removed.
	thisLastRuneEastAsianWidth := util.EastAsianWidth(thisLastRune)
	siblingFirstRuneEastAsianWidth := util.EastAsianWidth(siblingFirstRune)
	if (thisLastRuneEastAsianWidth == "F" ||
		thisLastRuneEastAsianWidth == "W" ||
		thisLastRuneEastAsianWidth == "H") &&
		(siblingFirstRuneEastAsianWidth == "F" ||
			siblingFirstRuneEastAsianWidth == "W" ||
			siblingFirstRuneEastAsianWidth == "H") {
		return unicode.Is(unicode.Hangul, thisLastRune) || unicode.Is(unicode.Hangul, siblingFirstRune)
	}

	// Rule3:
	//   Otherwise, if either the character before or after the segment break belongs to
	//   the space-discarding character set and it is a Unicode Punctuation (P*) or U+3000,
	//   then the segment break is removed.
	if util.IsSpaceDiscardingUnicodeRune(thisLastRune) ||
		unicode.IsPunct(thisLastRune) ||
		thisLastRune == '\u3000' ||
		util.IsSpaceDiscardingUnicodeRune(siblingFirstRune) ||
		unicode.IsPunct(siblingFirstRune) ||
		siblingFirstRune == '\u3000' {
		return false
	}

	// Rule4:
	//   Otherwise, the segment break is converted to a space (U+0020).
	return true
}