feat(server): implement basic backend API

- Added basic Express server setup in `src/server/main.ts`.
- Configured `dotenv` to load environment variables.
- Implemented in-memory storage for session state (pending, success, failed).
- Created `/api/digiid/start` endpoint:
    - Generates session ID and nonce.
    - Constructs callback URL from `PUBLIC_URL`.
    - Determines `unsecure` flag based on URL scheme.
    - Stores initial session state.
    - Generates QR code data URL.
    - Returns `sessionId` and `qrCodeDataUrl`.
    - Includes placeholder for `digiidTs.generateDigiIDUri`.
- Created `/api/digiid/callback` endpoint:
    - Receives address, uri, signature from DigiID app.
    - Parses nonce from received URI.
    - Looks up session by nonce.
    - Reconstructs expected callback URL.
    - Updates session state based on placeholder verification.
    - Includes placeholder for `digiidTs.verifyDigiIDCallback`.
    - Responds 200 OK as per DigiID protocol.
- Created `/api/digiid/status/:sessionId` endpoint:
    - Retrieves and returns session status, address, and error.
- Added address type helper `getDigiByteAddressType` in `src/server/utils.ts` (with placeholder logic for DGA).
- Added `dev:backend` script to `package.json` using `nodemon` and `ts-node/esm`.
- Added `"type": "module"` to `package.json`.
- Installed `@types/dotenv`.
- (Note: Outstanding TypeScript linter errors related to async Express handlers require further investigation).

1 files changed, 20 insertions, 0 deletions

diff --git a/src/server/utils.ts b/src/server/utils.ts
new file mode 100644
index 0000000..0b1333f
--- /dev/null
+++ b/src/server/utils.ts
@@ -0,0 +1,20 @@
+// Simple utility to determine DigiByte address type based on prefix
+
+export type DigiByteAddressType = 'DigiByte (DGB)' | 'DigiAsset (DGA)' | 'Unknown';
+
+export function getDigiByteAddressType(address: string): DigiByteAddressType {
+  if (address.startsWith('dgb1')) {
+    return 'DigiByte (DGB)';
+  }
+  // Add other prefixes if DigiAssets use a distinct one, e.g., 'dga1'
+  // For now, assume non-DGB is DigiAsset, but this might need refinement
+  // depending on actual DigiAsset address formats.
+  // If the digiid-ts library provides a helper for this, use that instead.
+  else if (address) { // Basic check to differentiate from empty/null
+    // Assuming DigiAssets might start differently or be the fallback
+    // This is a placeholder assumption.
+    // A more robust check based on DigiAsset address specification is needed.
+    return 'DigiAsset (DGA)'; // Placeholder - ADJUST BASED ON ACTUAL DGA PREFIX
+  }
+  return 'Unknown';
+} 
\ No newline at end of file