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package syntax

// Cache holds the spans of one source text and re-scans it only when the text
// has actually changed.
//
// Scanning a file is cheap but not free, and the editor redraws far more often
// than the text changes — every cursor move, every scroll. The revision number
// the buffer hands out is what tells the two apart.
//
//	cache.Update(buf.Text(), buf.Revision())
//	for line := top; line < bottom; line++ {
//		draw(line, cache.Line(line))
//	}
type Cache struct {
	language Language
	scanned  bool
	revision int
	lines    [][]Span
}

// NewCache returns a cache that colours one language, or one that colours
// nothing for LanguageNone — which is what a file this package does not
// understand gets.
//
//	cache := syntax.NewCache(syntax.LanguageOf(path))
func NewCache(language Language) *Cache {
	return &Cache{language: language}
}

// Language returns the language this cache colours.
func (c *Cache) Language() Language { return c.language }

// Enabled reports whether this cache colours anything.
func (c *Cache) Enabled() bool { return c.language != LanguageNone }

// SetLanguage changes what is coloured, discarding what was scanned. Call it
// when the window's file changes, as Save As does.
func (c *Cache) SetLanguage(language Language) {
	c.language = language
	c.scanned = false
	c.lines = nil
}

// Update re-scans src when revision differs from the one already scanned.
func (c *Cache) Update(src string, revision int) {
	if !c.Enabled() {
		return
	}
	if c.scanned && c.revision == revision {
		return
	}

	c.lines = Highlight(c.language, src)
	c.revision = revision
	c.scanned = true
}

// Line returns the spans of line i from the last scan, or nil when there are
// none — an empty line, a line past the end, or colouring turned off.
func (c *Cache) Line(i int) []Span {
	if i < 0 || i >= len(c.lines) {
		return nil
	}
	return c.lines[i]
}

// LineCount returns how many lines the last scan covered.
func (c *Cache) LineCount() int { return len(c.lines) }