package arch

import (
	"archive/tar"
	"bufio"
	"bytes"
	"compress/gzip"
	"context"
	"fmt"
	"io"
	"strings"
	"time"

	"tangled.org/odd.computer/isomorph/internal/fetch"
)

// pacman's repository databases (core.db, extra.db, multilib.db) list every binary package of a
// repository with its pkgbase, version and url in one small download, so they enumerate the
// distribution without touching GitLab. They carry no source URLs; those come from .SRCINFO.

// DefaultMirror serves the repository databases.
const DefaultMirror = "https://geo.mirror.pkgbuild.com"

// SyncRepos are the repositories of the released distribution.
var SyncRepos = []string{"core", "extra", "multilib"}

// SyncPackage is one binary package entry of a repository database.
type SyncPackage struct {
	Repo    string
	Name    string
	Base    string
	Version string
	URL     string
}

// SyncDB downloads and parses the x86_64 database of repo.
func (r *Resolver) SyncDB(ctx context.Context, repo string) ([]SyncPackage, error) {
	mirror := r.Mirror
	if mirror == "" {
		mirror = DefaultMirror
	}
	b, err := r.c.Get(ctx, mirror+"/"+repo+"/os/x86_64/"+repo+".db", fetch.WithTTL(6*time.Hour))
	if err != nil {
		return nil, fmt.Errorf("arch: %s.db: %w", repo, err)
	}
	return ParseSyncDB(b, repo)
}

// ParseSyncDB reads a gzip-compressed repository database.
func ParseSyncDB(b []byte, repo string) ([]SyncPackage, error) {
	zr, err := gzip.NewReader(bytes.NewReader(b))
	if err != nil {
		return nil, fmt.Errorf("arch: %s.db: %w", repo, err)
	}
	tr := tar.NewReader(zr)
	var out []SyncPackage
	for {
		h, err := tr.Next()
		if err == io.EOF {
			break
		}
		if err != nil {
			return nil, fmt.Errorf("arch: %s.db: %w", repo, err)
		}
		if h.Typeflag != tar.TypeReg || !strings.HasSuffix(h.Name, "/desc") {
			continue
		}
		fields := map[string]string{}
		sc := bufio.NewScanner(io.LimitReader(tr, 1<<20))
		sc.Buffer(make([]byte, 64<<10), 1<<20)
		key := ""
		for sc.Scan() {
			line := sc.Text()
			switch {
			case strings.HasPrefix(line, "%") && strings.HasSuffix(line, "%"):
				key = strings.Trim(line, "%")
			case line == "":
				key = ""
			case key != "" && fields[key] == "":
				fields[key] = line
			}
		}
		p := SyncPackage{Repo: repo, Name: fields["NAME"], Base: fields["BASE"], Version: fields["VERSION"], URL: fields["URL"]}
		if p.Base == "" {
			p.Base = p.Name
		}
		if p.Name != "" {
			out = append(out, p)
		}
	}
	return out, nil
}