package syntax

import (
	"fmt"
	"strings"

	sitter "github.com/tree-sitter/go-tree-sitter"
	ts_go "github.com/tree-sitter/tree-sitter-go/bindings/go"
	ts_js "github.com/tree-sitter/tree-sitter-javascript/bindings/go"
)

type languagePack struct {
	// languagePack.id is the stable registry identifier (for example, "go").
	id string
	// languagePack.filetypes are normalized aliases resolved from buffer filetype.
	filetypes []string
	// languagePack.extensions are normalized filename extensions (for example, ".go").
	extensions []string

	// languagePack.newLanguage constructs the tree-sitter language handle.
	newLanguage func() *sitter.Language
	// languagePack.loadQuery returns highlights query source for this language.
	loadQuery func() ([]byte, error)
}

// resolvedLanguage stores compiled runtime assets for one language.
//
// Instances are cached in languageRegistry.compiledByLang and reused by all
// buffers that resolve to the same language id.
type resolvedLanguage struct {
	id       string
	language *sitter.Language
	query    *sitter.Query
}

// languageRegistry maps buffer metadata to language packs and lazily compiles
// tree-sitter language/query assets.
type languageRegistry struct {
	packs          []languagePack
	byFiletype     map[string]languagePack
	byExtension    map[string]languagePack
	compiledByLang map[string]*resolvedLanguage
}

// newLanguageRegistry constructs the default in-process language registry.
//
// It registers built-in packs and prepares lookup maps for filetype and
// extension resolution.
func newLanguageRegistry() *languageRegistry {
	r := &languageRegistry{
		packs:          []languagePack{},
		byFiletype:     map[string]languagePack{},
		byExtension:    map[string]languagePack{},
		compiledByLang: map[string]*resolvedLanguage{},
	}

	r.register(languagePack{
		id:          "go",
		filetypes:   []string{"go", "golang"},
		extensions:  []string{".go"},
		newLanguage: func() *sitter.Language { return sitter.NewLanguage(ts_go.Language()) },
		loadQuery:   loadGoHighlightsQuery,
	})

	r.register(languagePack{
		id:          "javascript",
		filetypes:   []string{"javascript", "js", "jsx"},
		extensions:  []string{".js", ".mjs", ".cjs", ".jsx"},
		newLanguage: func() *sitter.Language { return sitter.NewLanguage(ts_js.Language()) },
		loadQuery:   loadJavaScriptHighlightsQuery,
	})

	r.register(languagePack{
		id:          "gomod",
		filetypes:   []string{"gomod"},
		extensions:  []string{".mod"},
		newLanguage: func() *sitter.Language { return sitter.NewLanguage(ts_js.Language()) },
		loadQuery:   loadJavaScriptHighlightsQuery,
	})

	return r
}

// register adds a language pack and indexes it by normalized keys.
func (r *languageRegistry) register(pack languagePack) {
	r.packs = append(r.packs, pack)

	for _, ft := range pack.filetypes {
		n := normalizeKey(ft)
		if n != "" {
			r.byFiletype[n] = pack
		}
	}

	for _, ext := range pack.extensions {
		n := normalizeExtension(ext)
		if n != "" {
			r.byExtension[n] = pack
		}
	}
}

// resolve returns compiled language/query assets for a buffer identity.
//
// Resolution is filetype-first, extension-second. Results are compiled once
// per language id and cached in compiledByLang.
func (r *languageRegistry) resolve(filetype, filename string) (*resolvedLanguage, bool, error) {
	pack, ok := r.resolvePack(filetype, filename)
	if !ok {
		return nil, false, nil
	}

	if cached, ok := r.compiledByLang[pack.id]; ok {
		return cached, true, nil
	}

	lang := pack.newLanguage()
	if lang == nil {
		return nil, false, fmt.Errorf("language %q did not provide a language handle", pack.id)
	}

	qBytes, err := pack.loadQuery()
	if err != nil {
		return nil, false, fmt.Errorf("load query for %q: %w", pack.id, err)
	}

	q, qErr := sitter.NewQuery(lang, string(qBytes))
	if qErr != nil {
		return nil, false, fmt.Errorf("compile query for %q: %w", pack.id, qErr)
	}

	resolved := &resolvedLanguage{id: pack.id, language: lang, query: q}
	r.compiledByLang[pack.id] = resolved
	return resolved, true, nil
}

// resolvePack finds a registered language pack using normalized buffer
// metadata without compiling queries.
func (r *languageRegistry) resolvePack(filetype, filename string) (languagePack, bool) {
	if p, ok := r.byFiletype[normalizeKey(filetype)]; ok {
		return p, true
	}

	if p, ok := r.byExtension[extensionOf(filename)]; ok {
		return p, true
	}

	return languagePack{}, false
}

// normalizeKey canonicalizes filetype-like keys for registry lookups.
func normalizeKey(s string) string {
	s = strings.TrimSpace(strings.ToLower(s))
	s = strings.TrimPrefix(s, ".")
	return s
}

// normalizeExtension canonicalizes extension keys and guarantees a leading
// dot for non-empty values.
func normalizeExtension(ext string) string {
	ext = strings.TrimSpace(strings.ToLower(ext))
	if ext == "" {
		return ""
	}
	if !strings.HasPrefix(ext, ".") {
		ext = "." + ext
	}
	return ext
}

// extensionOf extracts a normalized extension from a filename.
// Returns empty string when no usable extension is present.
func extensionOf(filename string) string {
	name := strings.TrimSpace(strings.ToLower(filename))
	if name == "" {
		return ""
	}
	i := strings.LastIndex(name, ".")
	if i <= 0 || i == len(name)-1 {
		return ""
	}
	return name[i:]
}