package appconfig

import "strings"

// Agent-owned vars (parent spec §7.3): CARLOS_PURGE is set by the platform
// when the box has a cache and REMOVED when it does not — the removal half
// is load-bearing, since the env layers are tenant-supplied and a tenant
// advertising a purge channel that does not exist would have apps skip
// their own invalidation and serve stale content indefinitely.
// CARLOS_CONTROL_SOCKET is stripped for the stronger reason: a
// tenant-chosen socket path is a name the agent never vouched for. This
// mirrors the exec backend's withoutVars (internal/activator/backend_exec.go);
// the two lists must not drift.
//
// The sync appends CARLOS_PURGE=header UNCONDITIONALLY because cache
// construction is unconditional in carlos agent (internal/host/agent.go,
// edge.NewCache at startup) — every box this sync runs on serves through
// that cache. The day the cache grows an off switch, this must learn to
// read it.
func agentOwned(name string) bool {
	return name == "CARLOS_PURGE" || name == "CARLOS_CONTROL_SOCKET"
}

// applyAgentVars rewrites one rendered env file: tenant-supplied
// agent-owned vars are dropped and the agent's own CARLOS_PURGE=header is
// appended last (last assignment wins under systemd EnvironmentFile, so
// even a hand-staged earlier line could not override it — but we strip
// those anyway). Deterministic and idempotent, so syncHost's bytes.Equal
// convergence check still short-circuits the steady state.
//
// RenderEnv (materialize.go) emits exactly one `KEY=value\n` line per var,
// keys sorted, and nothing else — no comments, no blank lines — so dropping
// blank lines here is a no-op against its actual output; it's kept because a
// transformation over line-oriented KEY=value content should not depend on
// its input never containing one.
func applyAgentVars(rendered []byte) []byte {
	var out strings.Builder
	for _, line := range strings.Split(string(rendered), "\n") {
		s := strings.TrimSpace(line)
		if s == "" {
			continue
		}
		if name, _, ok := strings.Cut(s, "="); ok && agentOwned(strings.TrimSpace(name)) {
			continue
		}
		out.WriteString(line)
		out.WriteByte('\n')
	}
	out.WriteString("CARLOS_PURGE=header\n")
	return []byte(out.String())
}