refactor: extract API handlers into internal packages

Move HTTP handler logic out of main into internal api and server packages,
slimming main to a thin entrypoint. Bundles bug fixes: login nil-panic,
empty-password validation, chirp sort ordering, duplicate-email 409, and
restricting the file server to the assets directory.

internal/server/server.go

@@ -0,0 +1,56 @@
+// Package server contains the HTTP handlers for the Chirpy API.
+package server
+
+import (
+	"net/http"
+	"sync/atomic"
+
+	"github.com/StevanFreeborn/chirpy/internal/database"
+)
+
+// Server holds the dependencies shared by all HTTP handlers.
+type Server struct {
+	fileServerHits atomic.Int32
+	db             *database.Queries
+	platform       string
+	jwtSecret      []byte
+	polkaKey       string
+	indexHTML      []byte
+}
+
+// New creates a Server with its dependencies wired in.
+func New(db *database.Queries, platform string, jwtSecret []byte, polkaKey string, indexHTML []byte) *Server {
+	return &Server{
+		db:        db,
+		platform:  platform,
+		jwtSecret: jwtSecret,
+		polkaKey:  polkaKey,
+		indexHTML: indexHTML,
+	}
+}
+
+// Handler returns the fully configured HTTP handler for the application.
+func (s *Server) Handler() http.Handler {
+	mux := http.NewServeMux()
+
+	mux.Handle("GET /app/assets/", s.handleFiles("/app/assets/"))
+	mux.HandleFunc("GET /app/{$}", s.HandleIndex)
+	mux.HandleFunc("GET /admin/metrics", s.HandleMetrics)
+	mux.HandleFunc("POST /admin/reset", s.HandleReset)
+
+	mux.HandleFunc("GET /api/healthz", s.HandleHealthChecks)
+
+	mux.HandleFunc("POST /api/login", s.HandleLogin)
+	mux.HandleFunc("POST /api/refresh", s.HandleRefresh)
+	mux.HandleFunc("POST /api/revoke", s.HandleRevoke)
+	mux.HandleFunc("POST /api/users", s.HandleCreateUser)
+	mux.HandleFunc("PUT /api/users", s.HandleUpdateUser)
+	mux.HandleFunc("POST /api/polka/webhooks", s.HandleWebhooks)
+
+	mux.HandleFunc("GET /api/chirps", s.HandleGetChirps)
+	mux.HandleFunc("GET /api/chirps/{id}", s.HandleGetChirp)
+	mux.HandleFunc("POST /api/chirps", s.HandleCreateChirp)
+	mux.HandleFunc("DELETE /api/chirps/{id}", s.HandleDeleteChirp)
+
+	return mux
+}