// render.go — source to HTML: tree-sitter highlighting, coverage classes and
// note anchors baked into one <ol> per chunk.
package main

import (
	"bytes"
	"html/template"
	"sort"
	"strconv"
	"strings"

	sitter "github.com/tree-sitter/go-tree-sitter"
	tsrust "github.com/tree-sitter/tree-sitter-rust/bindings/go"
)

// Lines per content-visibility chunk: the browser skips layout and paint of
// offscreen chunks wholesale, instead of managing one containment context
// per line.
const chunkLines = 800

// approximate rendered line height, for contain-intrinsic-size placeholders
const lineHeightPx = 19

// render builds the code HTML: <ol> chunks of chunkLines lines, each line an
// <li> with syntax spans, coverage classes and note anchors. One pre-sized
// builder, no fmt, minimal escaping — large files are browser-bound, so the
// output is kept as small and flat as possible.
func (f *File) render(src []byte, hl *highlighter) {
	classes := hl.classify(f.Path, src)
	f.Total = bytes.Count(src, []byte{'\n'})
	if len(src) > 0 && src[len(src)-1] != '\n' {
		f.Total++
	}
	f.Covered = 0
	for i := 1; i < len(f.Cov) && i <= f.Total; i++ {
		if f.Cov[i] != 0 {
			f.Covered++
		}
	}
	if f.Total > 0 {
		f.Pct = f.Covered * 100 / f.Total
	}
	sort.Slice(f.Notes, func(i, j int) bool { return f.Notes[i].Start < f.Notes[j].Start })
	for ni, n := range f.Notes {
		for l := n.Start; l <= n.End && l > 0; l++ {
			if _, taken := f.NoteAt[l]; !taken {
				f.NoteAt[l] = ni
			}
		}
	}

	var b strings.Builder
	b.Grow(len(src) + len(src)/2 + f.Total*48)
	var num []byte
	writeInt := func(n int) { num = strconv.AppendInt(num[:0], int64(n), 10); b.Write(num) }
	start := 0
	for ln := 1; ln <= f.Total; ln++ {
		end := start
		for end < len(src) && src[end] != '\n' {
			end++
		}
		if (ln-1)%chunkLines == 0 {
			if ln > 1 {
				b.WriteString("</ol>")
			}
			rem := f.Total - (ln - 1)
			if rem > chunkLines {
				rem = chunkLines
			}
			b.WriteString(`<ol class="code" style="counter-reset: ln `)
			writeInt(ln - 1)
			b.WriteString(`; --h: `)
			writeInt(rem * lineHeightPx)
			b.WriteString(`px">`)
		}
		b.WriteString(`<li id="L`)
		writeInt(ln)
		b.WriteByte('"')
		mask := uint8(0)
		if ln < len(f.Cov) {
			mask = f.Cov[ln]
		}
		ni, noted := f.NoteAt[ln]
		if mask != 0 || noted {
			b.WriteString(` class="`)
			if mask != 0 {
				b.WriteString("cov am")
				writeInt(int(mask))
				if noted {
					b.WriteString(" noted")
				}
			} else {
				b.WriteString("noted")
			}
			b.WriteByte('"')
		}
		if noted {
			b.WriteString(` data-note="note-`)
			writeInt(f.Notes[ni].ID)
			b.WriteByte('"')
		}
		b.WriteByte('>')
		emitLine(&b, src[start:end], classes[start:end], hl.classNames)
		b.WriteString("</li>")
		start = end + 1
	}
	if f.Total > 0 {
		b.WriteString("</ol>")
	}
	f.Body = template.HTML(b.String())
}

// emitLine writes one line's spans, merging runs of the same class across
// whitespace-only gaps ("pub fn" is one span, not two) to keep the DOM flat.
func emitLine(b *strings.Builder, line []byte, cls []int16, names []string) {
	open := int16(0)
	i := 0
	for i < len(line) {
		j := i
		c := cls[i]
		for j < len(line) && cls[j] == c {
			j++
		}
		if c == 0 {
			allSpace := true
			for k := i; k < j; k++ {
				if line[k] != ' ' && line[k] != '\t' {
					allSpace = false
					break
				}
			}
			if !(allSpace && open != 0 && j < len(line) && cls[j] == open) {
				if open != 0 {
					b.WriteString("</span>")
					open = 0
				}
			}
			escapeTo(b, line[i:j])
		} else {
			if open != c {
				if open != 0 {
					b.WriteString("</span>")
				}
				b.WriteString(`<span class="s-`)
				b.WriteString(names[c])
				b.WriteString(`">`)
				open = c
			}
			escapeTo(b, line[i:j])
		}
		i = j
	}
	if open != 0 {
		b.WriteString("</span>")
	}
}

// escapeTo escapes the three characters that matter in text content.
func escapeTo(b *strings.Builder, s []byte) {
	last := 0
	for i, c := range s {
		var rep string
		switch c {
		case '&':
			rep = "&amp;"
		case '<':
			rep = "&lt;"
		case '>':
			rep = "&gt;"
		default:
			continue
		}
		b.Write(s[last:i])
		b.WriteString(rep)
		last = i + 1
	}
	b.Write(s[last:])
}

// ── highlighting ──────────────────────────────────────────────────────────

type highlighter struct {
	lang       *sitter.Language
	query      *sitter.Query
	captureCls []int16 // capture index -> class id
	classNames []string
}

// resolveKey finds the theme syntax key for a capture name by stripping dot
// segments; "" when the theme has no entry at all.
func resolveKey(t *Theme, name string) string {
	for key := name; key != ""; {
		if s, ok := t.Syntax[key]; ok && s.Color != "" {
			return key
		}
		if i := strings.LastIndex(key, "."); i >= 0 {
			key = key[:i]
		} else {
			break
		}
	}
	return ""
}

// nearFg reports whether a capture would render indistinguishably from plain
// foreground text in the theme. Spans for such captures are pure DOM weight.
func nearFg(t *Theme, name string) bool {
	key := resolveKey(t, name)
	if key == "" {
		return true // no color -> falls through to fg anyway
	}
	return colorDist(hex6(t.Syntax[key].Color), hex6(t.Fg)) < 2000
}

func newHighlighter(dark, light *Theme) *highlighter {
	h := &highlighter{classNames: []string{""}}
	h.lang = sitter.NewLanguage(tsrust.Language())
	scm, _ := tfs.ReadFile("assets/rust.scm")
	q, qerr := sitter.NewQuery(h.lang, string(scm))
	if qerr != nil {
		fatal("rust query: %v", qerr)
	}
	h.query = q
	for _, name := range q.CaptureNames() {
		// skip captures that both themes paint (nearly) as foreground —
		// punctuation and friends are the bulk of all spans
		if nearFg(dark, name) && nearFg(light, name) {
			h.captureCls = append(h.captureCls, 0)
			continue
		}
		key := resolveKey(dark, name)
		if key == "" {
			key = resolveKey(light, name)
		}
		cls := strings.ReplaceAll(key, ".", "-")
		id := int16(0)
		for i, n := range h.classNames {
			if n == cls {
				id = int16(i)
			}
		}
		if id == 0 {
			h.classNames = append(h.classNames, cls)
			id = int16(len(h.classNames) - 1)
		}
		h.captureCls = append(h.captureCls, id)
	}
	return h
}

type paint struct {
	start, end uint
	pattern    uint
	cls        int16
}

// classify is safe for concurrent use: the shared query is immutable, and
// parser and cursor are per-call.
func (h *highlighter) classify(path string, src []byte) []int16 {
	classes := make([]int16, len(src))
	if !strings.HasSuffix(path, ".rs") {
		return classes
	}
	parser := sitter.NewParser()
	defer parser.Close()
	parser.SetLanguage(h.lang)
	tree := parser.Parse(src, nil)
	defer tree.Close()

	qc := sitter.NewQueryCursor()
	defer qc.Close()
	matches := qc.Matches(h.query, tree.RootNode(), src)
	var paints []paint
	for m := matches.Next(); m != nil; m = matches.Next() {
		for _, c := range m.Captures {
			if cls := h.captureCls[c.Index]; cls != 0 {
				paints = append(paints, paint{c.Node.StartByte(), c.Node.EndByte(), m.PatternIndex, cls})
			}
		}
	}
	// later patterns in the query paint over earlier ones
	sort.Slice(paints, func(i, j int) bool { return paints[i].pattern < paints[j].pattern })
	for _, p := range paints {
		for i := p.start; i < p.end && int(i) < len(classes); i++ {
			classes[i] = p.cls
		}
	}
	return classes
}