Add implementation plan for env-var-controlled sign-up

docs/plans/2026-08-19-allow-signup-env.md

@@ -0,0 +1,179 @@
+# Env-Var-Controlled Sign-Up Implementation Plan
+
+**Goal:** Gate sign-up and the sign-in "Sign Up" link on the `PODSTALK_ALLOW_SIGNUP` environment variable instead of the number of existing users.
+
+**Architecture:** Add an `AllowSignup bool` field to the `AuthHandler`. `main.go` reads `PODSTALK_ALLOW_SIGNUP` and sets it on the handler. The signup handler and the sign-in page link both consult this boolean. `store.UserCount()` stays as a general utility but is no longer used by authentication.
+
+**Tech Stack:** Go (net/http), `strconv.ParseBool` for env parsing.
+
+---
+
+## File Structure
+
+- Modify: `main.go` — read env var, set `AllowSignup` on the `AuthHandler`.
+- Modify: `handler/auth.go` — replace count-based gating with the `AllowSignup` flag.
+- No changes to `store/store.go` (`UserCount` is left in place).
+- No changes to templates (the `HasUser` key drives the nav link already).
+
+---
+
+### Task 1: Add `AllowSignup` field and switch signup gating
+
+**Files:**
+- Modify: `handler/auth.go`
+
+- [ ] **Step 1: Add the `AllowSignup` field to `AuthHandler` and replace the count-based redirect**
+
+Replace:
+
+```go
+type AuthHandler struct {
+	Store    *store.Store
+	Sessions *SessionStore
+	Tpl      *Templates
+}
+
+func (h *AuthHandler) ServeSignup(w http.ResponseWriter, r *http.Request) {
+	count, err := h.Store.UserCount()
+	if err == nil && count > 0 {
+		http.Redirect(w, r, "/signin", http.StatusSeeOther)
+		return
+	}
+```
+
+with:
+
+```go
+type AuthHandler struct {
+	Store       *store.Store
+	Sessions    *SessionStore
+	Tpl         *Templates
+	AllowSignup bool
+}
+
+func (h *AuthHandler) ServeSignup(w http.ResponseWriter, r *http.Request) {
+	if !h.AllowSignup {
+		http.Redirect(w, r, "/signin", http.StatusSeeOther)
+		return
+	}
+```
+
+- [ ] **Step 2: Replace the `hasUsers()` helper with an `allowSignup()` helper**
+
+Replace:
+
+```go
+func (h *AuthHandler) hasUsers() bool {
+	count, err := h.Store.UserCount()
+	return err == nil && count > 0
+}
+```
+
+with:
+
+```go
+func (h *AuthHandler) allowSignup() bool {
+	return h.AllowSignup
+}
+```
+
+- [ ] **Step 3: Update the three `HasUser` template renders to use `allowSignup()`**
+
+Replace every occurrence of `"HasUser": h.hasUsers()` with `"HasUser": h.allowSignup()`. There are three (the initial GET render and the two error paths in the POST handler).
+
+- [ ] **Step 4: Commit**
+
+```bash
+git add handler/auth.go
+git commit -m "Gate sign-up on AllowSignup field instead of user count"
+```
+
+---
+
+### Task 2: Read the env var in `main.go` and wire it up
+
+**Files:**
+- Modify: `main.go`
+
+- [ ] **Step 1: Add `strconv` to imports**
+
+In `main.go`, add `"strconv"` to the import block (after `"os"`).
+
+- [ ] **Step 2: Parse `PODSTALK_ALLOW_SIGNUP` and set it on the handler**
+
+After the existing `baseURL` block, add:
+
+```go
+	allowSignup := false
+	if v := os.Getenv("PODSTALK_ALLOW_SIGNUP"); v != "" {
+		allowSignup = envBool(v)
+	}
+```
+
+Change the `authH` literal to include the flag:
+
+```go
+	authH := &handler.AuthHandler{Store: st, Sessions: sessions, Tpl: tpl, AllowSignup: allowSignup}
+```
+
+At the bottom (near `envOrDefault`), add the `envBool` helper:
+
+```go
+// envBool interprets a string as a truthy boolean.
+func envBool(v string) bool {
+	if b, err := strconv.ParseBool(v); err == nil {
+		return b
+	}
+	switch strings.ToLower(strings.TrimSpace(v)) {
+	case "yes", "on":
+		return true
+	}
+	return false
+}
+```
+
+Add `"strings"` to the imports if not already present (it is not present in `main.go`; add it).
+
+- [ ] **Step 3: Commit**
+
+```bash
+git add main.go
+git commit -m "Read PODSTALK_ALLOW_SIGNUP env var to control sign-up"
+```
+
+---
+
+### Task 3: Verify
+
+- [ ] **Step 1: Run the build script per AGENTS.md**
+
+Run: `./scripts/build`
+Expected: PASS (gofmt, go vet, go build, docker build all succeed).
+
+- [ ] **Step 2: Manual sanity check (sandbox permitting)**
+
+Run: `PODSTALK_ALLOW_SIGNUP=true go run . &` then `curl -s -o /dev/null -w "%{http_code}\n" -X GET localhost:8080/signup` → expect a 200 render.
+Run: `PODSTALK_ALLOW_SIGNUP=false go run . &` then `curl -s -o /dev/null -w "%{http_code}\n" -X GET localhost:8080/signup` → expect 303 redirect to `/signin`.
+
+- [ ] **Step 3: Final commit (if the build produced no fixes) and push**
+
+```bash
+git status
+git push
+```
+
+---
+
+## Self-Review
+
+**1. Spec coverage:**
+- Env var `PODSTALK_ALLOW_SIGNUP` parsed in `main.go` → Task 2 Step 2. ✓
+- Default (unset) = disabled → Task 2 Step 2 (`allowSignup := false`, only overridden when set non-empty). ✓
+- Truthy values (`true`, `1`, `yes`, `on`) enabled → `ParseBool` covers `1`/`true`, the switch covers `yes`/`on`. ✓
+- Signup handler redirects when disabled → Task 1 Step 1. ✓
+- Sign-in "Sign Up" link driven by same flag → Task 1 Steps 2–3 (`HasUser`). ✓
+- `store.UserCount()` unchanged → noted in File Structure. ✓
+
+**2. Placeholder scan:** No TBD/TODO; every task has concrete code. ✓
+
+**3. Type consistency:** `AllowSignup` field, `allowSignup()` method, and `envBool` helper are named consistently throughout. ✓