// Package ledger — the open-ledger stream primitive: append-only,
// hash-chained public JSON entries in the deployment bucket, keyed by
// (account, app) exactly as the fleet page groups routes. The chain
// hashes STORED entry bytes verbatim: the writer marshals once and the
// hash commits to exactly those bytes, so verification needs no
// canonicalization pass in any language.
// Spec: docs/superpowers/specs/2026-08-03-open-ledgers-design.md §2.
package ledger

import (
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"regexp"
	"strings"

	"github.com/carlosframework/platform/internal/release"
)

const (
	Schema     = 1
	MaxPayload = 64 << 10
	MaxBlob    = 4 << 20
)

type Entry struct {
	Schema     int             `json:"schema"`
	Ledger     string          `json:"ledger"`
	Writer     string          `json:"writer"`
	TS         string          `json:"ts"`
	Payload    json.RawMessage `json:"payload"`
	PrevKey    string          `json:"prev_key"`
	PrevSHA256 string          `json:"prev_sha256"`
}

type Head struct {
	Schema     int    `json:"schema"`
	UpdatedAt  string `json:"updated_at"`
	HeadKey    string `json:"head_key"`
	HeadSHA256 string `json:"head_sha256"`
	Count      int    `json:"count"`
}

type Manifest struct {
	Schema  int      `json:"schema"`
	Public  bool     `json:"public"`
	Ledgers []string `json:"ledgers"`
	Title   string   `json:"title"`
}

var nameRe = regexp.MustCompile(`^[a-z0-9][a-z0-9-]{0,63}$`)

func ValidName(s string) bool {
	return nameRe.MatchString(s)
}

func Prefix(sqid, app, name string) string {
	return release.LedgerAppPrefix(sqid, app) + name + "/"
}

func HeadKey(sqid, app, name string) string {
	return Prefix(sqid, app, name) + "HEAD.json"
}

func ManifestKey(sqid, app string) string {
	return release.LedgerAppPrefix(sqid, app) + "ledgers.json"
}

func BlobKey(sqid, app, name, sha string) string {
	return Prefix(sqid, app, name) + "blobs/" + sha
}

// tsCompact strips the separators RFC3339 puts in a UTC timestamp so entry
// keys sort chronologically as plain strings.
func tsCompact(ts string) string {
	return strings.NewReplacer("-", "", ":", "").Replace(ts)
}

func EntryKey(sqid, app, name, ts, sha string) string {
	return Prefix(sqid, app, name) + "entries/" + tsCompact(ts) + "-" + sha[:12] + ".json"
}

func SHA256Hex(b []byte) string {
	sum := sha256.Sum256(b)
	return hex.EncodeToString(sum[:])
}