From d4ff726a2721bd49e3f5c2c4726ebd995c7c6d79 Mon Sep 17 00:00:00 2001
From: David Florness <david@florness.com>
Date: Sun, 13 Mar 2022 21:05:49 -0400
Subject: [PATCH] Print helpful error message when the map schema is
 incompatible

---
 cmd/tallyard/main.go | 25 +++++++++++++++++++++++--
 election/map.go      | 10 ++++++----
 2 files changed, 29 insertions(+), 6 deletions(-)

diff --git a/cmd/tallyard/main.go b/cmd/tallyard/main.go
index a94895d..d33bc94 100644
--- a/cmd/tallyard/main.go
+++ b/cmd/tallyard/main.go
@@ -2,6 +2,7 @@ package main
 
 import (
 	"encoding/json"
+	"errors"
 	"flag"
 	"fmt"
 	"io/ioutil"
@@ -63,7 +64,27 @@ func main() {
 
 	// setup the elections store
 	electionsMap, err := getElections(authInfo.UserID)
-	if err != nil {
+	if errors.Is(err, election.SchemaVersionError) {
+		log.Error(err)
+		fmt.Println("We couldn't load this device's stored elections because the current")
+		fmt.Println("schema version is incompatible with your current tallyard's schema.")
+		fmt.Println()
+		fmt.Println("The only currently-supported ways to solve this are to either")
+		fmt.Println()
+		fmt.Println("1. delete your saved elections file to start from scratch.  Node that this")
+		fmt.Println("   will remove your personal records of any of your concluded/in-progress")
+		fmt.Println("   elections!!")
+		fmt.Println()
+		fmt.Printf ("    rm %s/tallyard/elections.json\n", xdg.DataHome())
+		fmt.Println("    tallyard")
+		fmt.Println()
+		fmt.Println("2. downgrade tallyard to a previous version that supports your election")
+		fmt.Println("   schema.  This is usually the version right before your current")
+		fmt.Printf ("   version (%s) if you just upgraded and things were working beforehand.\n", tallyard.Version)
+		fmt.Println("   Please feel free to join the #tallyard:hnitbjorg.xyz matrix for help")
+		fmt.Println("   with this.")
+		os.Exit(1)
+	} else if err != nil {
 		log.Panic(err)
 	}
 	client.Store = matrix.NewTallyardStore(electionsMap)
@@ -235,7 +256,7 @@ func getElections(userID id.UserID) (*election.ElectionsMap, error) {
 	log.Info("unmarshalling elections file...")
 	em, err := election.UnmarshalElectionsMapFrom(jsonBytes, userID, saveElections)
 	if err != nil {
-		return nil, fmt.Errorf("couldn't read elections map: %s", err)
+		return nil, fmt.Errorf("couldn't read elections map: %w", err)
 	}
 
 	return em, nil
diff --git a/election/map.go b/election/map.go
index 3613135..5153820 100644
--- a/election/map.go
+++ b/election/map.go
@@ -2,6 +2,7 @@ package election
 
 import (
 	"encoding/json"
+	"errors"
 	"fmt"
 	"sync"
 
@@ -41,16 +42,17 @@ func NewElectionsMap(userID id.UserID, save func(*ElectionsMap)) *ElectionsMap {
 	}
 }
 
+var SchemaVersionError error = errors.New("the stored elections schema version is incompitable with the latest schema version")
+
 func UnmarshalElectionsMapFrom(jsonBytes []byte, userID id.UserID, save func(*ElectionsMap)) (*ElectionsMap, error) {
 	em := &ElectionsMap{}
 	err := json.Unmarshal(jsonBytes, em)
+	if em.Version != electionsMapVersion {
+		return nil, SchemaVersionError
+	}
 	if err != nil {
 		return nil, fmt.Errorf("error unmarshalling elections: %s", err)
 	}
-	if em.Version != electionsMapVersion {
-		return nil, fmt.Errorf("Your stored elections schema version (%d) is incompitable with the latest schema version (%d).",
-			em.Version, electionsMapVersion)
-	}
 	if userID != em.UserID {
 		// TODO support multiple users?
 		return nil, fmt.Errorf("user IDs don't match")
-- 
2.38.4