// Command gen builds simple-icons.json.gz, the icon data the icons package
// embeds. It downloads the pinned simple-icons npm tarball, checks its
// sha256 and writes a gzipped JSON object {slug: svg path data}. The output
// is deterministic. It writes into the current directory; run it with
//
//	go generate ./internal/master/web/icons
package main

import (
	"archive/tar"
	"bytes"
	"compress/gzip"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"os"
	"path"
	"regexp"
	"strings"
)

const (
	tarballURL    = "https://registry.npmjs.org/simple-icons/-/simple-icons-16.35.0.tgz"
	tarballSHA256 = "20ebead4f6bc93464812a5e260d19fc4d84772e5eeff69a6fbea263ca2441c5f"
)

var pathData = regexp.MustCompile(`<path d="([^"]+)"`)

func main() {
	if err := run(); err != nil {
		fmt.Fprintln(os.Stderr, "gen:", err)
		os.Exit(1)
	}
}

func run() error {
	tgz, err := download(tarballURL)
	if err != nil {
		return err
	}
	if sum := sha256.Sum256(tgz); hex.EncodeToString(sum[:]) != tarballSHA256 {
		return fmt.Errorf("sha256 mismatch for %s: got %x, want %s", tarballURL, sum, tarballSHA256)
	}
	icons, license, err := extract(tgz)
	if err != nil {
		return err
	}
	var js bytes.Buffer
	enc := json.NewEncoder(&js)
	enc.SetEscapeHTML(false)
	if err := enc.Encode(icons); err != nil { // map keys are written sorted
		return err
	}
	var gz bytes.Buffer
	zw, err := gzip.NewWriterLevel(&gz, gzip.BestCompression)
	if err != nil {
		return err
	}
	if _, err := zw.Write(js.Bytes()); err != nil { // the header has no name and a zero mtime
		return err
	}
	if err := zw.Close(); err != nil {
		return err
	}
	if err := os.WriteFile("simple-icons.json.gz", gz.Bytes(), 0o644); err != nil {
		return err
	}
	if err := os.WriteFile("LICENSE-simple-icons.md", license, 0o644); err != nil {
		return err
	}
	fmt.Printf("wrote %d icons\n", len(icons))
	return nil
}

func download(url string) ([]byte, error) {
	resp, err := http.Get(url)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("GET %s: %s", url, resp.Status)
	}
	return io.ReadAll(resp.Body)
}

// extract returns the path data of every package/icons/*.svg by slug, and
// package/LICENSE.md.
func extract(tgz []byte) (icons map[string]string, license []byte, err error) {
	zr, err := gzip.NewReader(bytes.NewReader(tgz))
	if err != nil {
		return nil, nil, err
	}
	tr := tar.NewReader(zr)
	icons = map[string]string{}
	for {
		h, err := tr.Next()
		if err == io.EOF {
			break
		}
		if err != nil {
			return nil, nil, err
		}
		switch {
		case h.Name == "package/LICENSE.md":
			if license, err = io.ReadAll(tr); err != nil {
				return nil, nil, err
			}
		case path.Dir(h.Name) == "package/icons" && strings.HasSuffix(h.Name, ".svg"):
			svg, err := io.ReadAll(tr)
			if err != nil {
				return nil, nil, err
			}
			m := pathData.FindAllSubmatch(svg, -1)
			if len(m) != 1 {
				return nil, nil, fmt.Errorf("%s: want exactly one <path>, found %d", h.Name, len(m))
			}
			icons[strings.TrimSuffix(path.Base(h.Name), ".svg")] = string(m[0][1])
		}
	}
	if license == nil || len(icons) == 0 {
		return nil, nil, fmt.Errorf("tarball has no LICENSE.md or no icons")
	}
	return icons, license, nil
}