package storage

import (
	"fmt"
	"strconv"

	"github.com/metazla/meta-core/internal/kv"
)

// SchemaVersion is the key-layout version this build of meta-core expects.
// Distinct from the snapshot manifest version (which is on-disk format);
// this number describes the record layout — primarily, "are roots UUIDs or
// content-hash tokens, and do reverse-index keys cid:* exist?"
//
// The Redis → SQLite move did not change the record layout (file:<rid>/<field>,
// cid:<cid>), so it did not bump this: the one-time migration copied records
// verbatim.
//
// Bump only when a layout change can't be detected from the data itself or
// healed by the write path. Each bump is a flag day in alpha: operators wipe
// and restart.
const SchemaVersion = 2

// SchemaVersionKey is the sentinel under which we record SchemaVersion.
// Checked on every meta-core boot.
const SchemaVersionKey = "meta-core:schema-version"

// EnsureSchemaVersion verifies the store matches the expected schema version.
// Called once at startup, before any other reads/writes.
//
// Behavior:
//   - sentinel present and matches expected → OK
//   - sentinel missing AND no roots → fresh store, stamp sentinel
//   - sentinel missing AND roots exist → legacy data, refuse
//   - sentinel present but mismatched → refuse, point operator at clean:all
//
// Refusal is hard-fail; the caller is expected to log.Fatalf and exit.
// The error message names the wipe remediation because in alpha there
// is no automated migration — operators bring up a clean store.
func (c *Client) EnsureSchemaVersion(expected int) error {
	return c.update(func(tx *kv.Tx) error {
		ctx := tx.Context()
		have, ok, err := tx.Get(ctx, SchemaVersionKey)
		if err != nil {
			return fmt.Errorf("get schema version: %w", err)
		}
		if !ok {
			n, err := tx.Count(ctx, rootsNS)
			if err != nil {
				return fmt.Errorf("count roots: %w", err)
			}
			if n > 0 {
				return fmt.Errorf(
					"the store has %d indexed roots but no %q sentinel — this is alpha "+
						"data from before the UUID-rooted schema landed. Delete the "+
						"database file to wipe and restart, or downgrade meta-core to a compatible build",
					n, SchemaVersionKey)
			}
			return tx.Put(SchemaVersionKey, strconv.Itoa(expected))
		}
		if have == strconv.Itoa(expected) {
			return nil
		}
		return fmt.Errorf(
			"store schema version is %q, this build of meta-core expects %d. "+
				"Delete the database file to wipe and restart, or use a meta-core "+
				"build that matches the existing data",
			have, expected)
	})
}