created AGENTS.md

AGENTS.md

@@ -0,0 +1,118 @@
+# AGENTS.md
+
+Guidance for AI coding agents working in this repository.
+
+## Project
+
+Next.js frontend for a Paradox save file parser. It uploads a game save file to a
+backend service, polls until parsing finishes, and displays the result in a
+grid.
+
+- **Next.js 16** (App Router, Turbopack) with **React 19**
+- **TypeScript 6**, **ESLint 9** (flat config), **Prettier 3**
+- **ag-grid** for the data grid, **Bootstrap 5** for styling
+
+Source files live in `src/`:
+
+- `app/` for routes,
+- `components/` for shared UI
+- `services/` for backend calls
+- `lib/` for helpers
+- `config/` for app config
+- `types/` for .d.ts type declaration files
+
+## Terminal
+
+**On Windows, prefer `bash.exe`** — but only a real MSYS2, Cygwin, or
+MinGW/Git Bash installation, for example `D:\msys2\usr\bin\bash.exe`.
+
+**Never use `C:\Windows\System32\bash.exe`.** Despite its name it is not a
+POSIX bash; it is the launcher stub for WSL. Do not start WSL to run ordinary
+commands.
+
+If no MSYS/Cygwin/MinGW bash is installed, **use PowerShell** as the terminal.
+PowerShell is the fallback, never WSL.
+
+If bash reports `command not found` for `node` or `npm`, that is a `PATH`
+problem rather than a missing install: MSYS2 defaults `MSYS2_PATH_TYPE` to
+`minimal`, which discards the Windows `PATH`. Setting it to `inherit` fixes it.
+
+## Commands
+
+```sh
+npm run dev      # dev server
+npm run build    # production build
+npm run lint     # eslint
+npm run format   # prettier, rewrites files in src/
+npx tsc --noEmit # typecheck
+```
+
+### Checking your work
+
+**Always run `npm run lint` and `npm run build` after changing code.** They are
+the primary way to find errors in this project, and they catch different
+things:
+
+- `npm run lint` reports code errors and style violations. It must finish with
+  zero problems — no errors and no warnings.
+- `npm run build` catches type errors and build-time problems that lint cannot
+  see, such as Node APIs leaking into the edge runtime. It must exit cleanly
+  and print no warnings.
+
+`npx tsc --noEmit` is a faster way to check types alone while iterating, but it
+does not replace a full build.
+
+Do not report a change as finished until both commands pass.
+
+## Version control
+
+This project is managed with **git**.
+
+**Read-only git commands are fine to use without asking.**
+`git status`, `git log`, `git diff`, `git show`, `git blame` and similar inspection commands
+may be run freely.
+
+**Never run a git command that changes the repository without the user's
+explicit permission.**
+This is a strict ban, and it covers everything that writes to the history, the index,
+or the working tree including `add`, `commit`, `checkout`, `restore`, `reset`,
+`stash`, `branch`, `merge`, `rebase`, `push`, `rm`, etc.
+
+Ask first and wait for a clear yes before running such git command.
+
+## Conventions
+
+Prettier settings live in `.prettierrc` and are not negotiable: **4 spaces, no
+semicolons, single quotes, 80 column width**. Run `npm run format` after
+editing, or match the surrounding style exactly.
+
+Import from within `src/` using the `@/` alias, for example
+`import { getMsgFromError } from '@/lib/errors'`.
+
+Write doc comments as JSDoc (`/** ... */`), which editors show on hover.
+Plain `//` and `///` comments do not appear in tooltips.
+In `.ts` files put only prose in the JSDoc and let the signature carry the types;
+do not duplicate types in `{braces}`.
+
+Catch blocks should not annotate the error. Let it be `unknown` and convert it
+with the shared helper:
+
+```ts
+} catch (err) {
+    const errMsg = getMsgFromError(err)
+    ...
+}
+```
+
+Avoid `any`; `no-explicit-any` is enforced. Prefer `unknown` plus narrowing.
+
+## Things that will bite you
+
+**TypeScript is pinned to 6 on purpose.** Do not upgrade it to 7. The Next.js
+ESLint config depends on typescript-eslint, which refuses to run under
+TypeScript 7, and that would break `npm run lint` entirely.
+
+**`instrumentation.ts` is compiled for the edge runtime too and it can't be disabled.**
+Anything using `fs`, `path`, or other Node APIs must be imported behind the
+`process.env.NEXT_RUNTIME === 'nodejs'` guard, or the build warns and pulls
+Node-only code into the edge bundle.

eslint.config.mjs

@@ -0,0 +1,9 @@
+import { defineConfig, globalIgnores } from 'eslint/config'
+import nextCoreWebVitals from 'eslint-config-next/core-web-vitals'
+import nextTypescript from 'eslint-config-next/typescript'
+
+export default defineConfig([
+    globalIgnores(['.next/**', 'node_modules/**', 'next-env.d.ts']),
+    nextCoreWebVitals,
+    nextTypescript,
+])

package.json

@@ -6,21 +6,26 @@
         "dev": "next dev --turbopack",
         "build": "next build",
         "start": "next start",
-        "lint": "next lint",
+        "lint": "eslint",
         "format": "npx prettier src --write"
     },
     "dependencies": {
-        "ag-grid-react": "^33",
+        "ag-grid-react": "^36",
         "bootstrap": "^5",
-        "next": "^15",
+        "next": "^16",
         "react": "^19",
         "react-dom": "^19"
     },
     "devDependencies": {
-        "@types/node": "^22",
+        "@types/node": "^26",
         "@types/react": "^19",
         "@types/react-dom": "^19",
+        "eslint": "^9",
+        "eslint-config-next": "^16",
         "prettier": "^3",
-        "typescript": "^5"
+        "typescript": "^6"
+    },
+    "allowScripts": {
+        "unrs-resolver": false
     }
 }

src/app/api/proxy/functions.ts

@@ -1,8 +1,10 @@
 import type { NextRequest } from 'next/server'
 import { NextResponse } from 'next/server'
 
-/// Resend request to backend.
-/// Body is being sent as stream.
+/**
+ * Resend request to backend.
+ * Body is being sent as stream.
+ */
 export async function redirectRequest(
     req: NextRequest,
     proxyUrl: string,
@@ -26,8 +28,7 @@ export async function redirectRequest(
         method: req.method,
         headers: req.headers,
         body: req.body,
-        // @ts-ignore
-        duplex: 'half', // some property required by nodejs but not defined in @types/node
+        duplex: 'half', // required by nodejs when the body is a stream, see src/types/fetch.d.ts
     })
 
     return new NextResponse(backendRes.body, {
@@ -41,9 +42,14 @@ export async function redirectRequest(
     })
 }
 
-/// Browsers send OPTIONS request sometimes to check webserver's allowed headers and methods.
-/// My C# backend doesn't support OPTIONS, so the proxy answer to OPTIONS request that all headers and methods are allowed.
-export async function responseToOPTIONS(
+/**
+ * Browsers send OPTIONS request sometimes to check webserver's allowed
+ * headers and methods.
+ * My C# backend doesn't support OPTIONS, so the proxy answer to OPTIONS
+ * request that all headers and methods are allowed.
+ */
+export async function respondToOPTIONS(
+    // eslint-disable-next-line @typescript-eslint/no-unused-vars -- required by the nextjs route handler signature
     req: NextRequest
 ): Promise<NextResponse> {
     // console.log('proxy responding to CORS OPTIONS', req.url)

src/app/api/proxy/saveParserBackend/[[...path]]/route.ts

@@ -1,9 +1,6 @@
 import type { NextRequest } from 'next/server'
 import { NextResponse } from 'next/server'
-import {
-    redirectRequest,
-    responseToOPTIONS as respondToOPTIONS,
-} from '@/app/api/proxy/functions'
+import { redirectRequest, respondToOPTIONS } from '@/app/api/proxy/functions'
 import { PROXY_PATHS } from '@/app/api/proxy/paths'
 import { appConfig } from '@/lib/configLoader'
 

src/app/browse/page.tsx

@@ -6,38 +6,47 @@ import {
     themeQuartz,
     colorSchemeDark,
 } from 'ag-grid-community'
-import { useState, useEffect } from 'react'
+import { useSyncExternalStore } from 'react'
+
+const DARK_SCHEME_QUERY = '(prefers-color-scheme: dark)'
+
+// add the vertical lines between cells
+const BASE_THEME = themeQuartz.withParams({
+    columnBorder: true,
+    headerColumnBorder: true,
+})
+// Built once, so the grid keeps seeing the same theme object between renders.
+const LIGHT_THEME = BASE_THEME
+const DARK_THEME = BASE_THEME.withPart(colorSchemeDark)
+
+// Notifies React whenever the browser's light/dark color scheme changes.
+function subscribeToColorScheme(onChange: () => void) {
+    const mediaQuery = window.matchMedia(DARK_SCHEME_QUERY)
+    mediaQuery.addEventListener('change', onChange)
+    return () => mediaQuery.removeEventListener('change', onChange)
+}
+
+function isDarkSchemePreferred() {
+    return window.matchMedia(DARK_SCHEME_QUERY).matches
+}
+
+// The server has no color scheme, so it always prerenders the light theme.
+function isDarkSchemePreferredOnServer() {
+    return false
+}
 
 // TODO: create tabs with general info, tables, plots
 
 // Page that shows a save file's parsed data in a grid.
 export default function BrowseSaveDataPage() {
-    const [agTheme, setAgTheme] = useState(themeQuartz)
-
-    // Keep the grid theme in sync with the browser's light/dark color scheme.
-    useEffect(() => {
-        const prefersDark = window.matchMedia(
-            '(prefers-color-scheme: dark)'
-        ).matches
-        setAgTheme(
-            prefersDark ? themeQuartz.withPart(colorSchemeDark) : themeQuartz
-        )
-
-        const listener = (e: MediaQueryListEvent) => {
-            setAgTheme(
-                e.matches ? themeQuartz.withPart(colorSchemeDark) : themeQuartz
-            )
-        }
-
-        window
-            .matchMedia('(prefers-color-scheme: dark)')
-            .addEventListener('change', listener)
-        return () => {
-            window
-                .matchMedia('(prefers-color-scheme: dark)')
-                .removeEventListener('change', listener)
-        }
-    }, [])
+    // Read the color scheme straight from the browser instead of mirroring it
+    // into state, which would need an extra render to catch up.
+    const prefersDark = useSyncExternalStore(
+        subscribeToColorScheme,
+        isDarkSchemePreferred,
+        isDarkSchemePreferredOnServer
+    )
+    const agTheme = prefersDark ? DARK_THEME : LIGHT_THEME
 
     return (
         <div style={{ height: '500px' }}>

src/app/login/page.tsx

@@ -3,6 +3,7 @@
 import { useState } from 'react'
 import { authService } from '@/services/AuthService'
 import FormError from '@/components/FormError'
+import { getMsgFromError } from '@/lib/errors'
 
 // Page with the login form.
 export default function LoginPage() {
@@ -35,9 +36,10 @@ export default function LoginPage() {
                 formData.password
             )
             console.log('Logged in:', result)
-        } catch (err: any) {
-            console.error(err.message)
-            setError(err.message)
+        } catch (err) {
+            const errMsg = getMsgFromError(err)
+            console.error(errMsg)
+            setError(errMsg)
         }
     }
 

src/app/register/page.tsx

@@ -4,6 +4,7 @@ import { useState } from 'react'
 import { useRouter } from 'next/navigation'
 import { authService } from '@/services/AuthService'
 import FormError from '@/components/FormError'
+import { getMsgFromError } from '@/lib/errors'
 
 // Page with the registration form.
 export default function RegisterPage() {
@@ -43,9 +44,10 @@ export default function RegisterPage() {
             )
             console.log('Registered:', result)
             router.push('/login') // Redirect after success
-        } catch (err: any) {
-            console.error(err.message)
-            setError(err.message)
+        } catch (err) {
+            const errMsg = getMsgFromError(err)
+            console.error(errMsg)
+            setError(errMsg)
         }
     }
 

src/components/SaveFileUploadingDialog.tsx

@@ -7,6 +7,7 @@ import {
 } from '@/services/SaveParserBackendService'
 import { useState } from 'react'
 import FormError from './FormError'
+import { getMsgFromError } from '@/lib/errors'
 
 export enum GameEnum {
     EU4 = 'eu4',
@@ -71,16 +72,18 @@ export default function SaveFileUploadingDialog() {
                         clearInterval(intervalId)
                         setUploadDisabled(false)
                     }
-                } catch (err: any) {
-                    console.error('Error while polling status:', err)
+                } catch (err) {
+                    const errMsg = getMsgFromError(err)
+                    console.error('Error while polling status:', errMsg)
                     clearInterval(intervalId)
-                    setError(err.message)
+                    setError(errMsg)
                     setUploadDisabled(false)
                 }
             }, pollInterval)
-        } catch (err: any) {
-            console.error(err.message)
-            setError(err.message)
+        } catch (err) {
+            const errMsg = getMsgFromError(err)
+            console.error(errMsg)
+            setError(errMsg)
             setUploadDisabled(false)
         }
     }
@@ -145,7 +148,7 @@ export default function SaveFileUploadingDialog() {
                     </div>
                 )}
 
-                {/* add link to <ConditionalView cond={done}> /browse?id=${saveStatus.id} */}
+                {/* TODO: add link to <ConditionalView cond={done}> /browse?id=${saveStatus.id} */}
             </div>
         </div>
     )

src/instrumentation.ts

@@ -4,5 +4,10 @@
 export async function register() {
     console.log('hello from instrumentation.ts!')
     await import('@/lib/customConsoleLog') // replaces console.log
-    await import('@/lib/configLoader') // forces loadConfig() to run at server startup
+
+    // Importing configLoader outside of this block will produce warning.
+    // Next.js compiles this file for some "edge runtime", where no fs and path modules exist.
+    if (process.env.NEXT_RUNTIME === 'nodejs') {
+        await import('@/lib/configLoader') // forces loadConfig() to run at server startup
+    }
 }

src/lib/customConsoleLog.ts

@@ -2,7 +2,7 @@
 function injectConsoleLog() {
     const originalLog = console.log
 
-    function customLog(message?: any, ...optionalParams: any[]) {
+    function customLog(message?: unknown, ...optionalParams: unknown[]) {
         const now = new Date()
         const timestamp = now.toTimeString().split(' ')[0] // hh:mm:ss
         originalLog(`[${timestamp}] ${message}`, ...optionalParams)

src/lib/errors.ts

@@ -0,0 +1,7 @@
+/**
+ * Extracts a readable message from an unknown thrown value, since anything
+ * (not just an Error) can be thrown and caught.
+ */
+export function getMsgFromError(err: unknown): string {
+    return err instanceof Error ? err.message : String(err)
+}

src/services/SaveParserBackendService.ts

@@ -61,7 +61,7 @@ export class SaveParserBackendService {
     }
 
     // Fetches the fully parsed data for a save once its parsing is done.
-    async getParsedSave(id: string): Promise<Record<string, any>> {
+    async getParsedSave(id: string): Promise<Record<string, unknown>> {
         const url = `${this.API_BASE}/getParsedSave?id=${encodeURIComponent(id)}`
         const response = await fetch(url)
 

src/types/fetch.d.ts

@@ -0,0 +1,6 @@
+// Node's fetch needs `duplex: 'half'` for stream bodies,
+// but lib.dom's RequestInit doesn't declare it.
+// This interface is automatically merged with RequestInit from lib.dom.d.ts
+interface RequestInit {
+    duplex?: 'half'
+}

tsconfig.json

@@ -1,27 +1,33 @@
 {
-  "compilerOptions": {
-    "target": "ES2017",
-    "lib": ["dom", "dom.iterable", "esnext"],
-    "allowJs": true,
-    "skipLibCheck": true,
-    "strict": true,
-    "noEmit": true,
-    "esModuleInterop": true,
-    "module": "esnext",
-    "moduleResolution": "bundler",
-    "resolveJsonModule": true,
-    "isolatedModules": true,
-    "jsx": "preserve",
-    "incremental": true,
-    "plugins": [
-      {
-        "name": "next"
-      }
+    "compilerOptions": {
+        "target": "ES2017",
+        "lib": ["dom", "dom.iterable", "esnext"],
+        "allowJs": true,
+        "skipLibCheck": true,
+        "strict": true,
+        "noEmit": true,
+        "esModuleInterop": true,
+        "module": "esnext",
+        "moduleResolution": "bundler",
+        "resolveJsonModule": true,
+        "isolatedModules": true,
+        "jsx": "react-jsx",
+        "incremental": true,
+        "plugins": [
+            {
+                "name": "next"
+            }
+        ],
+        "paths": {
+            "@/*": ["./src/*"]
+        }
+    },
+    "include": [
+        "next-env.d.ts",
+        "**/*.ts",
+        "**/*.tsx",
+        ".next/types/**/*.ts",
+        ".next/dev/types/**/*.ts"
     ],
-    "paths": {
-      "@/*": ["./src/*"]
-    }
-  },
-  "include": ["next-env.d.ts", "**/*.ts", "**/*.tsx", ".next/types/**/*.ts"],
-  "exclude": ["node_modules"]
+    "exclude": ["node_modules"]
 }