refactor: improve error handling across modules

- Add custom error types for app_data, bridge, and database modules
- Enhance error reporting in reddit_to_telegram main function
- Replace generic error strings with structured error variants

Author: Massolari

src/app_data.gleam

@@ -12,7 +12,11 @@ pub type AppData {
   )
 }
 
-pub fn get() -> Result(AppData, String) {
+pub type Error {
+  MissingEnvVar(String)
+}
+
+pub fn get() -> Result(AppData, Error) {
   dotenv_gleam.config()
 
   use username <- result.try(get_env("REDDIT_USERNAME"))
@@ -30,8 +34,8 @@ pub fn get() -> Result(AppData, String) {
   )
 }
 
-fn get_env(key: String) -> Result(String, String) {
+fn get_env(key: String) -> Result(String, Error) {
   key
   |> envoy.get
-  |> result.map_error(fn(_) { "Missing " <> key <> " environment variable" })
+  |> result.map_error(fn(_) { MissingEnvVar(key) })
 }

src/bridge.gleam

@@ -1,7 +1,6 @@
 import gleam/dynamic/decode
 import gleam/json
 import gleam/result
-import gleam/string
 import reddit
 import simplifile
 
@@ -16,17 +15,22 @@ pub type Bridge {
   )
 }
 
-pub fn get() -> Result(List(Bridge), String) {
+pub type Error {
+  ReadFileError(simplifile.FileError)
+  DecodeError(json.DecodeError)
+}
+
+pub fn get() -> Result(List(Bridge), Error) {
   simplifile.read("./bridges.json")
-  |> result.map_error(fn(_) { "File bridges.json not found" })
+  |> result.map_error(fn(error) { ReadFileError(error) })
   |> result.try(bridges_decoder)
 }
 
-fn bridges_decoder(json_bridges: String) -> Result(List(Bridge), String) {
+fn bridges_decoder(json_bridges: String) -> Result(List(Bridge), Error) {
   bridge_decoder()
   |> decode.list
   |> json.parse(json_bridges, _)
-  |> result.map_error(fn(e) { "Couldn't decode bridges: " <> string.inspect(e) })
+  |> result.map_error(fn(e) { DecodeError(e) })
 }
 
 fn bridge_decoder() -> decode.Decoder(Bridge) {

src/database.gleam

@@ -5,10 +5,14 @@ import gleam/result
 import gleam/string
 import sqlight.{type Connection}
 
-pub fn connect() {
+pub type Error {
+  OpenError(sqlight.Error)
+}
+
+pub fn connect() -> Result(Connection, Error) {
   use connection <- result.map(
     sqlight.open("file:./db/data.sqlite3")
-    |> result.map_error(fn(error) { error.message }),
+    |> result.map_error(fn(error) { OpenError(error) }),
   )
 
   let _ = setup(connection)

src/reddit_to_telegram.gleam

@@ -7,18 +7,27 @@ import gleam/list
 import gleam/option.{type Option, None, Some}
 import gleam/pair
 import gleam/result
+import gleam/string
 import reddit
 import sqlight
 import telegram
 
+type Error {
+  AppDataError(app_data.Error)
+  BridgeError(bridge.Error)
+  DatabaseError(database.Error)
+}
+
 pub fn main() {
   let result = {
     io.println("Loading app data...")
-    use app_data <- result.try(app_data.get())
+    use app_data <- result.try(app_data.get() |> result.map_error(AppDataError))
     io.println("Loading bridges...")
-    use bridges <- result.try(bridge.get())
+    use bridges <- result.try(bridge.get() |> result.map_error(BridgeError))
     io.println("Connecting to database...")
-    use database <- result.map(database.connect())
+    use database <- result.map(
+      database.connect() |> result.map_error(DatabaseError),
+    )
 
     start(app_data, bridges, database)
   }
@@ -38,7 +47,10 @@ pub fn main() {
         }
       }
     }
-    Error(error) -> io.println("Error: " <> error)
+    Error(error) ->
+      error
+      |> string.inspect
+      |> io.println
   }
 }