feat: add FastAPI REST backend

Expose all address generation functions as HTTP endpoints:
- POST /api/hd/generate, /api/hd/encrypt, /api/hd/decrypt
- POST /api/p2pk, /api/p2pkh, /api/p2sh, /api/p2wpkh, /api/p2tr
- Add fastapi and uvicorn to requirements.txt

requirements.txt

@@ -5,3 +5,5 @@ six==1.17.0
 pytest
 bip-utils
 pycryptodome
+fastapi
+uvicorn

src/api.py

@@ -0,0 +1,160 @@
+"""
+FastAPI backend for the Bitcoin Address Generator.
+Exposes all address generation functions as HTTP endpoints.
+"""
+
+from fastapi import FastAPI, HTTPException
+from fastapi.middleware.cors import CORSMiddleware
+from pydantic import BaseModel
+from typing import Any, Dict, Optional
+
+try:
+    from src.hd_wallet import generate_hd_wallet, encrypt_wallet, decrypt_wallet
+    from src.p2pk import generate_p2pk
+    from src.p2pkh import generate_legacy_address
+    from src.p2sh import generate_p2sh_multisig
+    from src.p2wpkh import generate_segwit_address
+    from src.p2tr import generate_p2tr_address
+except ImportError:
+    from hd_wallet import generate_hd_wallet, encrypt_wallet, decrypt_wallet
+    from p2pk import generate_p2pk
+    from p2pkh import generate_legacy_address
+    from p2sh import generate_p2sh_multisig
+    from p2wpkh import generate_segwit_address
+    from p2tr import generate_p2tr_address
+
+app = FastAPI(title="Bitcoin Address Generator API")
+
+app.add_middleware(
+    CORSMiddleware,
+    allow_origins=["http://localhost:5173", "http://localhost:4173", "file://", "*"],
+    allow_methods=["*"],
+    allow_headers=["*"],
+)
+
+
+# ── HD Wallet ──────────────────────────────────────────────────────────────────
+
+class HDGenerateRequest(BaseModel):
+    network: str = "mainnet"
+    bip_type: str = "bip84"
+    mnemonic: Optional[str] = None
+    passphrase: str = ""
+    account: int = 0
+    num_addresses: int = 5
+
+
+class HDEncryptRequest(BaseModel):
+    wallet: Dict[str, Any]
+    password: str
+
+
+class HDDecryptRequest(BaseModel):
+    wallet: Dict[str, Any]
+    password: str
+
+
+@app.post("/api/hd/generate")
+def hd_generate(req: HDGenerateRequest):
+    try:
+        return generate_hd_wallet(
+            network=req.network,
+            bip_type=req.bip_type,
+            mnemonic=req.mnemonic or None,
+            passphrase=req.passphrase,
+            account=req.account,
+            num_addresses=req.num_addresses,
+        )
+    except ValueError as e:
+        raise HTTPException(status_code=400, detail=str(e))
+
+
+@app.post("/api/hd/encrypt")
+def hd_encrypt(req: HDEncryptRequest):
+    try:
+        return encrypt_wallet(req.wallet, req.password)
+    except Exception as e:
+        raise HTTPException(status_code=400, detail=str(e))
+
+
+@app.post("/api/hd/decrypt")
+def hd_decrypt(req: HDDecryptRequest):
+    try:
+        return decrypt_wallet(req.wallet, req.password)
+    except ValueError as e:
+        raise HTTPException(status_code=400, detail=str(e))
+
+
+# ── Single address types ───────────────────────────────────────────────────────
+
+class P2PKRequest(BaseModel):
+    network: str = "mainnet"
+    compressed: bool = False
+
+
+class P2PKHRequest(BaseModel):
+    network: str = "mainnet"
+    compressed: bool = True
+
+
+class P2SHRequest(BaseModel):
+    network: str = "mainnet"
+    m: int = 2
+    n: int = 3
+    compressed: bool = True
+
+
+class P2WPKHRequest(BaseModel):
+    network: str = "mainnet"
+    compressed: bool = True
+
+
+class P2TRRequest(BaseModel):
+    network: str = "mainnet"
+
+
+@app.post("/api/p2pk")
+def p2pk(req: P2PKRequest):
+    try:
+        return generate_p2pk(network=req.network, compressed=req.compressed)
+    except ValueError as e:
+        raise HTTPException(status_code=400, detail=str(e))
+
+
+@app.post("/api/p2pkh")
+def p2pkh(req: P2PKHRequest):
+    try:
+        return generate_legacy_address(network=req.network, compressed=req.compressed)
+    except ValueError as e:
+        raise HTTPException(status_code=400, detail=str(e))
+
+
+@app.post("/api/p2sh")
+def p2sh(req: P2SHRequest):
+    try:
+        return generate_p2sh_multisig(
+            network=req.network, m=req.m, n=req.n, compressed=req.compressed
+        )
+    except ValueError as e:
+        raise HTTPException(status_code=400, detail=str(e))
+
+
+@app.post("/api/p2wpkh")
+def p2wpkh(req: P2WPKHRequest):
+    try:
+        return generate_segwit_address(network=req.network, compressed=req.compressed)
+    except ValueError as e:
+        raise HTTPException(status_code=400, detail=str(e))
+
+
+@app.post("/api/p2tr")
+def p2tr(req: P2TRRequest):
+    try:
+        return generate_p2tr_address(network=req.network)
+    except ValueError as e:
+        raise HTTPException(status_code=400, detail=str(e))
+
+
+@app.get("/api/health")
+def health():
+    return {"status": "ok"}