package api

import (
	"context"
	"net/http"

	"git.golem15.com/golem15/summercms/modules/wire"
	"git.golem15.com/jakub/sm-bm-plugin/models"
	"gorm.io/gorm"
)

// A write of a material's content may carry the revision the writer last
// read (D-01, D-04). When it does and the stored revision differs, the write
// is refused with 409 and nothing is written; when it does not, the write
// overwrites as before, so callers that never send a revision keep working.
// The compare and the write run on the row locked FOR UPDATE, so two writers
// holding the same revision cannot both succeed.

// conflictMessage is the message of a 409 answer to a stale revision.
const conflictMessage = "The material was changed since the revision you sent."

// staleRevision reports whether a write that sent revision sent must be
// refused: true when it sent one and it is not the stored one.
func staleRevision(sent *uint, stored uint) bool {
	return sent != nil && *sent != stored
}

// revise bumps the revision of material id inside tx when its content
// differs from before (models.ReviseMaterial). Every content writer of the
// API calls it after its write.
func (h *Handlers) revise(ctx context.Context, tx *gorm.DB, id uint, before string) error {
	_, _, err := models.ReviseMaterial(tx.WithContext(ctx), id, before)
	return err
}

// writeConflict answers 409 to a write that sent a stale revision, with the
// current revision, its updated_at and the material as the management API
// shows it, so the writer can diff or pull. Under MCP the body is left out,
// as in every other MCP answer.
func writeConflict(w http.ResponseWriter, r *http.Request, db *gorm.DB, id uint) {
	var cur models.Material
	if err := preloadMaterial(db).First(&cur, id).Error; err != nil {
		writeOpaque500(w)
		return
	}
	people, err := loadMaterialPeople(db, cur)
	if err != nil {
		writeOpaque500(w)
		return
	}
	wire.WriteJSON(w, http.StatusConflict, map[string]any{
		"error":      true,
		"message":    conflictMessage,
		"revision":   cur.Revision,
		"updated_at": models.FormatDateTime(cur.UpdatedAt),
		"data":       managedMaterialView(newManagedMaterialJSON(cur, people), viaMCP(r), false),
	})
}