// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
// See LICENSE.txt for license information.

package properties

import (
	"fmt"

	"github.com/mattermost/mattermost/server/public/model"
	"github.com/mattermost/mattermost/server/public/shared/request"
)

// MigrateBackfillCPADisplayName backfills the CPA display_name attribute on
// every CPA PropertyField that is missing one (absent key or empty string).
//
// This is the only public entry point that performs writes to CPA fields
// without going through the access-control layer. It does so deliberately:
// the backfill is a one-shot system migration and the access-control layer
// would otherwise reject writes against fields whose source plugin is not the
// caller (e.g. UAS-managed CPA fields with attrs["protected"]=true). Confining
// the bypass to this single, named, side-effect-bounded method avoids
// introducing a general "skip access control" surface that other code could
// reach for.
//
// The method is idempotent at the field level: fields that already have a
// non-empty display_name are skipped. The caller (app/migrations.go) is
// responsible for the System-key idempotency wrapper that prevents the whole
// migration from running twice.
//
// Returns the number of fields that were backfilled and the number that were
// skipped, so the caller can log a summary.
func (ps *PropertyService) MigrateBackfillCPADisplayName(rctx request.CTX) (backfilled int, skipped int, err error) {
	group, err := ps.Group(model.AccessControlPropertyGroupName)
	if err != nil {
		return 0, 0, fmt.Errorf("MigrateBackfillCPADisplayName: failed to get CPA property group: %w", err)
	}
	groupID := group.ID

	const cpaFieldLimit = 20
	var fieldsToUpdate []*model.PropertyField

	// Use the unexported searchPropertyFields to bypass access control.
	// AC would filter out (or strip options from) protected fields when
	// the caller is not the source plugin, which would corrupt the
	// fields we then try to write back. CPA creation is capped at 20
	// active fields, so a single page covers the full migration scope.
	fields, searchErr := ps.searchPropertyFields(groupID, model.PropertyFieldSearchOpts{
		PerPage: cpaFieldLimit,
	})
	if searchErr != nil {
		return 0, 0, fmt.Errorf("MigrateBackfillCPADisplayName: failed to search CPA fields: %w", searchErr)
	}

	for _, pf := range fields {
		cpaField, convErr := model.NewCPAFieldFromPropertyField(pf)
		if convErr != nil {
			return 0, 0, fmt.Errorf("MigrateBackfillCPADisplayName: failed to convert property field %q: %w", pf.ID, convErr)
		}

		// Backfill if display_name is absent OR empty-string. This covers
		// fields created before display_name existed, fields created after
		// without an explicit display_name (stored as ""), and fields
		// patched with display_name="".
		if cpaField.Attrs.DisplayName != "" {
			skipped++
			continue
		}

		cpaField.Attrs.DisplayName = cpaField.Name
		fieldsToUpdate = append(fieldsToUpdate, cpaField.ToPropertyField())
	}

	if len(fieldsToUpdate) > 0 {
		// Use the unexported updatePropertyFields for the same reason as
		// searchPropertyFields above: the AC layer rejects writes from the
		// system to fields owned by a source plugin.
		if _, _, _, updateErr := ps.updatePropertyFields(rctx, groupID, fieldsToUpdate); updateErr != nil {
			return 0, 0, fmt.Errorf("MigrateBackfillCPADisplayName: failed to update CPA fields: %w", updateErr)
		}
	}

	return len(fieldsToUpdate), skipped, nil
}