package web

import (
	"errors"

	"github.com/jackc/pgx/v5/pgconn"
)

// ConstraintMessages maps Postgres constraint names to the form field and
// message the operator should see when that constraint rejects a write.
// Handlers pass the constraints their form can plausibly hit; the names live
// next to the form they belong to (per docs/operator-ux-conventions.md §6)
// rather than in one global registry.
type ConstraintMessages map[string]FieldMessage

// FieldMessage is one field-level error: which form field to flag and what to say.
type FieldMessage struct {
	Field   string
	Message string
}

// FieldErrorsFromDB translates a failed database write into field-level form
// errors, so constraint violations render as 422 + FieldErrors (the §6
// validation contract) instead of leaking raw driver text ("SQLSTATE 23505")
// into the UI. It returns ok=false when err is not a recognizable constraint
// violation — the caller should then treat it as a server error (log + generic
// message), never render err.Error().
//
// Resolution order: an exact constraint-name match in msgs wins; otherwise a
// generic per-SQLSTATE-class message lands on the form-level "" field.
func FieldErrorsFromDB(err error, msgs ConstraintMessages) (FieldErrors, bool) {
	var pgErr *pgconn.PgError
	if !errors.As(err, &pgErr) {
		return nil, false
	}

	fe := New()
	if fm, hit := msgs[pgErr.ConstraintName]; hit {
		fe.Set(fm.Field, fm.Message)
		return fe, true
	}

	switch pgErr.Code {
	case "23505": // unique_violation
		fe.Set("", "A record with these values already exists.")
	case "23503": // foreign_key_violation
		fe.Set("", "A referenced record no longer exists or is still in use.")
	case "23514": // check_violation
		fe.Set("", "This combination of values is not allowed.")
	case "22001": // string_data_right_truncation
		fe.Set("", "One of the values is too long.")
	default:
		return nil, false
	}
	return fe, true
}