package aptrepo

import (
	"crypto/sha256"
	"encoding/hex"
	"errors"
	"strconv"
	"strings"
	"time"
	"unicode"
	"unicode/utf8"

	"server-deploy/internal/installplan"
)

var metadataError = errors.New("invalid Docker repository metadata")

var pinnedPackageNames = [...]string{"docker-ce", "docker-ce-cli", "containerd.io", "docker-buildx-plugin", "docker-compose-plugin"}

// Resolve parses Release bytes already authenticated by the caller and binds
// explicitly pinned packages to that Release. It does not verify signatures.
func Resolve(release, index []byte, suite, arch string, versions map[string]string, now time.Time) (installplan.Lock, error) {
	if len(release) > 1<<20 || len(index) > 16<<20 || len(versions) != len(pinnedPackageNames) {
		return installplan.Lock{}, metadataError
	}
	for _, name := range pinnedPackageNames {
		if versions[name] == "" {
			return installplan.Lock{}, metadataError
		}
	}

	var fields map[string]string
	if err := parseControl(release, func(stanza map[string]string) error {
		if fields != nil {
			return metadataError
		}
		fields = stanza
		return nil
	}); err != nil {
		return installplan.Lock{}, metadataError
	}
	if fields["suite"] != suite || fields["origin"] != "Docker" || fields["label"] != "Docker CE" || !hasWord(fields["architectures"], arch) || !hasWord(fields["components"], "stable") {
		return installplan.Lock{}, metadataError
	}
	date, err := time.Parse(time.RFC1123Z, fields["date"])
	if err != nil || date.After(now.Add(10*time.Minute)) || date.Before(now.Add(-30*24*time.Hour)) {
		return installplan.Lock{}, metadataError
	}
	if value, ok := fields["valid-until"]; ok {
		expiry, err := time.Parse(time.RFC1123Z, value)
		if err != nil || !expiry.After(now) || expiry.Before(date) {
			return installplan.Lock{}, metadataError
		}
	}
	// Bind the exact uncompressed index bytes before interpreting any records.
	indexSum := sha256.Sum256(index)
	expectedPath := "stable/binary-" + arch + "/Packages"
	seenPaths := make(map[string]bool)
	matched := false
	for _, line := range strings.Split(fields["sha256"], "\n") {
		if strings.TrimSpace(line) == "" {
			continue
		}
		entry := strings.Fields(line)
		if len(entry) != 3 || !validSHA256(entry[0]) || seenPaths[entry[2]] {
			return installplan.Lock{}, metadataError
		}
		seenPaths[entry[2]] = true
		size, err := decimalSize(entry[1])
		if err != nil {
			return installplan.Lock{}, metadataError
		}
		if entry[2] == expectedPath {
			if size != uint64(len(index)) || entry[0] != hex.EncodeToString(indexSum[:]) {
				return installplan.Lock{}, metadataError
			}
			matched = true
		}
	}
	if !matched {
		return installplan.Lock{}, metadataError
	}

	selected := make(map[string]installplan.Package)
	seenRecords := make(map[[3]string]bool)
	if err := parseControl(index, func(record map[string]string) error {
		identity := [3]string{record["package"], record["version"], record["architecture"]}
		if identity[0] != "" && identity[1] != "" && identity[2] != "" {
			if seenRecords[identity] {
				return metadataError
			}
			seenRecords[identity] = true
		}
		version, target := versions[identity[0]]
		if !target {
			return nil
		}
		for _, field := range []string{"package", "version", "architecture", "filename", "size", "sha256"} {
			if record[field] == "" || strings.Contains(record[field], "\n") {
				return metadataError
			}
		}
		if identity[1] != version || identity[2] != arch {
			return nil
		}
		size, err := decimalSize(record["size"])
		if err != nil {
			return metadataError
		}
		selected[identity[0]] = installplan.Package{
			Name: identity[0], Version: version, Filename: record["filename"],
			Size: size, Digest: "sha256:" + record["sha256"],
		}
		return nil
	}); err != nil {
		return installplan.Lock{}, metadataError
	}

	releaseSum := sha256.Sum256(release)
	lock := installplan.Lock{
		ProtocolVersion: 1, Repository: "https://download.docker.com/linux/ubuntu",
		Suite: suite, Architecture: arch, ReleaseDigest: "sha256:" + hex.EncodeToString(releaseSum[:]),
	}
	for _, name := range pinnedPackageNames {
		p, ok := selected[name]
		if !ok {
			return installplan.Lock{}, metadataError
		}
		lock.Packages = append(lock.Packages, p)
	}
	if _, err := installplan.Validate(lock, suite, arch); err != nil {
		return installplan.Lock{}, metadataError
	}
	return lock, nil
}

// parseControl preserves continuation boundaries and rejects duplicate fields
// before invoking visit. Processing one stanza at a time bounds retained values.
func parseControl(raw []byte, visit func(map[string]string) error) error {
	if !utf8.Valid(raw) {
		return metadataError
	}
	text := strings.ReplaceAll(string(raw), "\r\n", "\n")
	for _, r := range text {
		if unicode.IsControl(r) && r != '\n' && r != '\t' {
			return metadataError
		}
	}
	fields := make(map[string]*strings.Builder)
	current := ""
	flush := func() error {
		if len(fields) == 0 {
			return nil
		}
		stanza := make(map[string]string, len(fields))
		for name, value := range fields {
			stanza[name] = value.String()
		}
		if err := visit(stanza); err != nil {
			return err
		}
		fields = make(map[string]*strings.Builder)
		current = ""
		return nil
	}
	for line := range strings.SplitSeq(text, "\n") {
		if line == "" {
			if err := flush(); err != nil {
				return err
			}
			continue
		}
		if line[0] == ' ' || line[0] == '\t' {
			if current == "" {
				return metadataError
			}
			fields[current].WriteByte('\n')
			fields[current].WriteString(strings.Trim(line, " \t"))
			continue
		}
		name, value, ok := strings.Cut(line, ":")
		if !ok || name == "" {
			return metadataError
		}
		for _, r := range name {
			if !(r >= 'a' && r <= 'z' || r >= 'A' && r <= 'Z' || r >= '0' && r <= '9' || r == '-') {
				return metadataError
			}
		}
		current = strings.ToLower(name)
		if _, exists := fields[current]; exists {
			return metadataError
		}
		fields[current] = &strings.Builder{}
		fields[current].WriteString(strings.Trim(value, " \t"))
	}
	return flush()
}

func hasWord(value, word string) bool {
	for _, item := range strings.Fields(value) {
		if item == word {
			return true
		}
	}
	return false
}

func decimalSize(value string) (uint64, error) {
	for _, r := range value {
		if r < '0' || r > '9' {
			return 0, metadataError
		}
	}
	size, err := strconv.ParseUint(value, 10, 64)
	if err != nil {
		return 0, metadataError
	}
	return size, nil
}

func validSHA256(value string) bool {
	if len(value) != 64 {
		return false
	}
	for _, r := range value {
		if !(r >= '0' && r <= '9' || r >= 'a' && r <= 'f') {
			return false
		}
	}
	return true
}