package stylemap

import (
	"fmt"
	"io"
	"log"
	"os"
	"prose/watcher"
	"strings"
	"sync"

	"github.com/bep/godartsass/v2"
)

type styleMap struct {
	mu          sync.RWMutex
	stylesheets map[string]string
	transpiler  *godartsass.Transpiler
}

// New returns a new styleMap.
func New() (watcher.AutoMap[string, string], error) {
	folder, err := os.ReadDir("styles/")
	if err != nil {
		return nil, fmt.Errorf("could not load styles directory: %w", err)
	}

	sassTranspiler, err := godartsass.Start(godartsass.Options{})
	if err != nil {
		return nil, fmt.Errorf("could not start sass transpiler: %w", err)
	}

	sm := &styleMap{
		stylesheets: make(map[string]string),
		transpiler:  sassTranspiler,
	}

	for _, s := range folder {
		err := sm.fetchLocked(s.Name())
		if err != nil {
			return nil, fmt.Errorf("could not generate styles for %s: %w", s.Name(), err)
		}
		log.Printf("loaded stylesheet %q", s.Name())
	}

	go watcher.Watch("styles/", sm)

	return sm, nil
}

func (sm *styleMap) Get(filename string) (string, bool) {
	sm.mu.RLock()
	defer sm.mu.RUnlock()
	contents, ok := sm.stylesheets[filename]
	return contents, ok
}

func (sm *styleMap) Delete(filename string) error {
	sm.mu.Lock()
	defer sm.mu.Unlock()
	if s, ok := strings.CutSuffix(filename, ".scss"); ok {
		filename = s + ".css"
	}
	delete(sm.stylesheets, filename)
	return nil
}

func (sm *styleMap) Fetch(filename string) (err error) {
	sm.mu.Lock()
	defer sm.mu.Unlock()
	return sm.fetchLocked(filename)
}

func (sm *styleMap) fetchLocked(filename string) (err error) {
	var outfile, contents string
	if strings.HasSuffix(filename, ".scss") {
		outfile, contents, err = sm.loadSCSS(filename)
	} else {
		outfile, contents, err = sm.loadCSS(filename)
	}
	if err != nil {
		return
	}
	sm.stylesheets[outfile] = contents
	return
}

func (sm *styleMap) loadSCSS(filename string) (string, string, error) {
	in, err := os.Open("styles/" + filename)
	if err != nil {
		return "", "", fmt.Errorf("could not open stylesheet %s: %w", filename, err)
	}
	stylesheet, err := io.ReadAll(in)
	if err != nil {
		return "", "", fmt.Errorf("could not read stylesheet %s: %w", filename, err)
	}
	res, err := sm.transpiler.Execute(godartsass.Args{
		Source: string(stylesheet),
	})
	if err != nil {
		return "", "", fmt.Errorf("could not generate stylesheet %s: %w", filename, err)
	}
	return strings.TrimSuffix(filename, ".scss") + ".css", res.CSS, nil
}

func (sm *styleMap) loadCSS(filename string) (string, string, error) {
	in, err := os.Open("styles/" + filename)
	if err != nil {
		return "", "", fmt.Errorf("could not open style infile %s: %w", filename, err)
	}
	var buf strings.Builder
	_, err = io.Copy(&buf, in)
	if err != nil {
		return "", "", fmt.Errorf("could not copy stylesheet %s: %w", filename, err)
	}
	return filename, buf.String(), nil
}