package vaultik

import (
	"errors"
	"fmt"

	"sneak.berlin/go/vaultik/internal/database"
	"sneak.berlin/go/vaultik/internal/log"
)

// errStorageBindingMismatch is returned when the local index database is
// bound to a different destination than the configured one.
var errStorageBindingMismatch = errors.New(
	"local index is bound to a different backup destination")

// EnsureStorageBinding guarantees that the local index database is
// bound to the currently-configured storage destination. Every mutating
// command must call this before touching either the local index or the
// destination store, because the two live in lockstep: the local index
// records which chunks/blobs already exist at the destination, and
// mismatched destination + local index produces silent corruption (the
// scanner sees "known" chunks and skips uploads, then writes snapshots
// whose manifests reference blobs that aren't on the new destination).
//
// Behaviour:
//   - On first use (empty stored value), record the configured
//     destination (storage_url, or the s3.* endpoint, bucket and
//     prefix) and log the binding.
//   - When the stored value matches the configured destination, do
//     nothing and return nil.
//   - When the two differ, refuse with an error that tells the user
//     how to recover (revert the config, or run `vaultik database
//     purge` to discard the local index and rebuild against the new
//     destination on the next backup).
//
// Read-only inspection commands (remote info, snapshot list, etc.)
// deliberately don't call this: they can be run against a bare
// destination store without any binding state.
func (v *Vaultik) EnsureStorageBinding() error {
	if v.Repositories == nil || v.Config == nil {
		// NewForTesting builds a Vaultik with no DB or config;
		// there's nothing to bind and no binding to check. Callers
		// exercising the bind path use a real DB and populate Config
		// explicitly (see storage_bind_test.go).
		return nil
	}

	configured := v.Config.StorageURL
	if configured == "" {
		// The s3.* form: bind on its endpoint, bucket and prefix,
		// written the way storage_url would name the same destination.
		s3 := v.Config.S3
		configured = "s3://" + s3.Bucket + "/" + s3.Prefix + "?endpoint=" + s3.Endpoint
	}

	stored, err := v.Repositories.LocalMeta.Get(v.ctx, database.LocalMetaKeyStorageURL)
	if err != nil {
		return fmt.Errorf("reading local storage binding: %w", err)
	}

	if stored == "" {
		err = v.Repositories.LocalMeta.Set(
			v.ctx, database.LocalMetaKeyStorageURL, configured)
		if err != nil {
			return fmt.Errorf("recording local storage binding: %w", err)
		}

		log.Info("Bound local index to storage destination", "storage_url", configured)

		return nil
	}

	if stored == configured {
		return nil
	}

	return fmt.Errorf("%w\n%s",
		errStorageBindingMismatch, buildBindingMismatchMessage(stored, configured))
}

// buildBindingMismatchMessage assembles the multi-line explanation
// shown when the local index is bound to a different destination than
// the currently-configured one (the first line lives in the
// errStorageBindingMismatch sentinel). Kept as a separate function so
// the multi-line text is expressed as a plain string literal rather
// than a fmt.Errorf argument (staticcheck ST1005 disallows trailing
// punctuation on error format strings).
func buildBindingMismatchMessage(stored, configured string) string {
	return "  local index bound to: " + stored + "\n" +
		"  currently configured: " + configured + "\n" +
		"\n" +
		"The local index database tracks which chunks and blobs already exist at the\n" +
		"destination store. Using it against a different destination would silently\n" +
		"skip uploads (the scanner would treat every chunk as already present), leaving\n" +
		"future snapshots referencing blobs that don't exist at the new destination.\n" +
		"\n" +
		"To proceed, either:\n" +
		"  - revert storage_url (or the s3.* endpoint, bucket and prefix) in your\n" +
		"    config to the bound destination, or\n" +
		"  - run 'vaultik database delete' to discard the local index and rebuild it\n" +
		"    from a fresh full backup against the new destination"
}