package rpm

import (
	"compress/gzip"
	"context"
	"encoding/xml"
	"fmt"
	"io"
	"net/http"
	"os"
	"path/filepath"
	"strings"
	"time"
)

type NewPackage struct {
	Name         string
	Version      string
	Arch         string
	Location     string
	Checksum     string
	ChecksumType string
	Size         int64
}

type Scanner struct {
	SourceURL  string
	LocalDir   string
	HTTPClient *http.Client
}

func NewScanner(sourceURL, localDir string) *Scanner {
	return &Scanner{
		SourceURL:  strings.TrimRight(sourceURL, "/"),
		LocalDir:   localDir,
		HTTPClient: &http.Client{Timeout: 5 * time.Minute},
	}
}

// Scan fetches the remote package list and returns packages not present on disk.
func (sc *Scanner) Scan(ctx context.Context) ([]NewPackage, error) {
	repomd, err := sc.fetchRepoMD(ctx)
	if err != nil {
		return nil, fmt.Errorf("fetch repomd.xml: %w", err)
	}

	var primaryEntry *RepoMDEntry
	for i := range repomd.Data {
		if repomd.Data[i].Type == "primary" {
			primaryEntry = &repomd.Data[i]
			break
		}
	}
	if primaryEntry == nil {
		return nil, fmt.Errorf("no primary entry in repomd.xml")
	}

	packages, err := sc.fetchPrimary(ctx, *primaryEntry)
	if err != nil {
		return nil, fmt.Errorf("fetch primary.xml: %w", err)
	}

	var missing []NewPackage
	for _, pkg := range packages {
		localPath := filepath.Join(sc.LocalDir, filepath.FromSlash(pkg.Location.Href))
		if _, err := os.Stat(localPath); os.IsNotExist(err) {
			ver := pkg.Version.Ver + "-" + pkg.Version.Rel
			if pkg.Version.Epoch != "0" && pkg.Version.Epoch != "" {
				ver = pkg.Version.Epoch + ":" + ver
			}
			missing = append(missing, NewPackage{
				Name:         pkg.Name,
				Version:      ver,
				Arch:         pkg.Arch,
				Location:     pkg.Location.Href,
				Checksum:     pkg.Checksum.Value,
				ChecksumType: pkg.Checksum.Type,
				Size:         pkg.Size.Package,
			})
		}
	}
	return missing, nil
}

func (sc *Scanner) fetchRepoMD(ctx context.Context) (*RepoMD, error) {
	data, err := sc.fetchBytes(ctx, sc.SourceURL+"/repodata/repomd.xml")
	if err != nil {
		return nil, err
	}
	var repomd RepoMD
	if err := xml.Unmarshal(data, &repomd); err != nil {
		return nil, fmt.Errorf("parse repomd.xml: %w", err)
	}
	return &repomd, nil
}

func (sc *Scanner) fetchPrimary(ctx context.Context, entry RepoMDEntry) ([]Package, error) {
	data, err := sc.fetchBytes(ctx, sc.SourceURL+"/"+entry.Location.Href)
	if err != nil {
		return nil, err
	}
	if entry.Checksum.Type == "sha256" {
		if err := verifyChecksum(data, entry.Checksum.Value); err != nil {
			return nil, fmt.Errorf("primary.xml.gz: %w", err)
		}
	}

	// Save upstream primary to disk so RegenerateMetadata can use it as source.
	dest := filepath.Join(sc.LocalDir, filepath.FromSlash(entry.Location.Href))
	if err := os.MkdirAll(filepath.Dir(dest), 0o755); err == nil {
		if err := writeFile(dest, data); err == nil {
			marker := filepath.Join(sc.LocalDir, "repodata", PrimarySourceFile)
			_ = os.WriteFile(marker, []byte(entry.Location.Href), 0o644)
		}
	}

	gz, err := gzip.NewReader(strings.NewReader(string(data)))
	if err != nil {
		return nil, fmt.Errorf("open gzip: %w", err)
	}
	defer gz.Close()
	var primary PrimaryMetadata
	if err := xml.NewDecoder(gz).Decode(&primary); err != nil {
		return nil, fmt.Errorf("parse primary.xml: %w", err)
	}
	return primary.Packages, nil
}

func (sc *Scanner) fetchBytes(ctx context.Context, url string) ([]byte, error) {
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
	if err != nil {
		return nil, err
	}
	resp, err := sc.HTTPClient.Do(req)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("HTTP %d for %s", resp.StatusCode, url)
	}
	return io.ReadAll(resp.Body)
}