package api

import (
	"log/slog"
	"net/http"
	"strings"
)

// Router builds the HTTP surface. Kept out of main.go so it can be exercised in
// tests with a fake KeyStore, which is where the auth wiring actually gets
// verified.
type Router struct {
	Auth    *Authenticator
	Logger  *slog.Logger
	Version string

	// Ready reports whether dependencies are healthy. Nil means always ready.
	Ready func() error
}

func (rt *Router) Handler() http.Handler {
	mux := http.NewServeMux()

	// Unauthenticated. Liveness must not touch the database: a health check
	// that fails when Postgres blips will get the process killed by whatever
	// supervises it, which turns a database wobble into an outage.
	mux.Handle("GET /healthz", rt.healthz())

	// Readiness DOES check dependencies. That is the difference.
	mux.Handle("GET /readyz", rt.readyz())

	// Everything below needs a key.
	authed := func(scope string, h http.Handler) http.Handler {
		return rt.Auth.Authenticate(RequireScope(scope, h))
	}

	mux.Handle("GET /v1/whoami", rt.Auth.Authenticate(Whoami()))
	mux.Handle("GET /v1/reference/ping", authed(ScopeReference, rt.stub("reference")))

	// Deliberately NO catch-all mux.Handle("/", ...) here.
	//
	// A "/" pattern matches every path, so it would also swallow method
	// mismatches: POST /healthz would match "/" and return 404 instead of the
	// 405 that Go's ServeMux produces on its own. jsonifyErrors below rewrites
	// ServeMux's plain-text 404 and 405 bodies into the standard envelope,
	// which keeps both correct status codes and uniform JSON errors.
	return Chain(mux,
		WithRequestID,
		WithRecovery(rt.Logger),
		WithLogging(rt.Logger),
		jsonifyErrors,
	)
}

func (rt *Router) healthz() http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		WriteJSON(w, http.StatusOK, map[string]string{
			"status":  "ok",
			"version": rt.Version,
		})
	})
}

func (rt *Router) readyz() http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if rt.Ready != nil {
			if err := rt.Ready(); err != nil {
				rt.Logger.Warn("readiness check failed", "err", err)
				WriteError(w, http.StatusServiceUnavailable, "not_ready", "Dependencies are unavailable.")

				return
			}
		}

		WriteJSON(w, http.StatusOK, map[string]string{"status": "ready"})
	})
}

// jsonifyErrors converts net/http's built-in plain-text 404 and 405 responses
// into the same JSON envelope every other error uses, so a client never has to
// branch on Content-Type to read an error.
func jsonifyErrors(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		rw := &errorRewriter{ResponseWriter: w}

		next.ServeHTTP(rw, r)

		rw.finish()
	})
}

type errorRewriter struct {
	http.ResponseWriter
	intercepted bool
	wroteHeader bool
	status      int
}

func (e *errorRewriter) WriteHeader(code int) {
	if e.wroteHeader {
		return
	}

	e.wroteHeader = true
	e.status = code

	// Only touch responses net/http generated itself.
	//
	// Checking for an EMPTY Content-Type does not work: http.NotFound sets
	// "text/plain; charset=utf-8" before calling WriteHeader, so by the time we
	// see it the header is already populated. Test for "not already JSON"
	// instead - every handler in this package writes JSON, so anything else at
	// a 404 or 405 came from net/http.
	if code == http.StatusNotFound || code == http.StatusMethodNotAllowed {
		if !strings.HasPrefix(e.Header().Get("Content-Type"), "application/json") {
			e.intercepted = true
			e.Header().Set("Content-Type", "application/json; charset=utf-8")
		}
	}

	e.ResponseWriter.WriteHeader(code)
}

func (e *errorRewriter) Write(b []byte) (int, error) {
	if !e.wroteHeader {
		e.WriteHeader(http.StatusOK)
	}

	// Swallow the plain-text body; finish writes the JSON one.
	if e.intercepted {
		return len(b), nil
	}

	return e.ResponseWriter.Write(b)
}

func (e *errorRewriter) finish() {
	if !e.intercepted {
		return
	}

	code, msg := "not_found", "No such endpoint."
	if e.status == http.StatusMethodNotAllowed {
		code, msg = "method_not_allowed", "That method is not allowed on this endpoint."
	}

	_ = writeErrorBody(e.ResponseWriter, code, msg)
}

func (rt *Router) stub(name string) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		WriteJSON(w, http.StatusOK, map[string]string{"endpoint": name, "status": "not implemented yet"})
	})
}