package ctxmgr

import (
	"os"
	"strings"
	"sync"
)

const (
	EnvSemanticSummaryShadow = "SEMANTIC_SUMMARY_SHADOW"
	// REPLACE was sealed by Wave 5 X-2 (2026-09-18). Unsealed 2026-09-26 under an
	// explicit user authorization for the chat-semantic-replace closeout task:
	// wiring is fail-closed and gray-released via a session allowlist. Enabling
	// the master flag alone replaces nothing while the allowlist is empty.
	// See .doc/ops/short-term/2026-09-26-chat-semantic-replace.md and
	// .doc/ops/short-term/2026-09-18-wave5-deadcode-decisions.md#x-2 (history).
	EnvSemanticSummaryReplace = "SEMANTIC_SUMMARY_REPLACE"
	// EnvSemanticSummaryReplaceSessions is the fail-closed gray-release
	// allowlist: comma-separated chat session IDs eligible for narrative
	// replacement. Empty allowlist (default) replaces no session. "*" widens
	// eligibility to every session (present and future), mirroring
	// INTENT_PLAN_PROJECT_ALLOWLIST=*; the master flag still gates globally.
	EnvSemanticSummaryReplaceSessions = "SEMANTIC_SUMMARY_REPLACE_SESSIONS"
)

// SummaryFeatureFlags controls semantic summary rollout. REPLACE swaps the
// served chat Narrative only for allowlisted sessions (fail-closed gray).
type SummaryFeatureFlags struct {
	Shadow  bool
	Replace bool
	// ReplaceAllSessions is the "*" wildcard for ReplaceSessions: every
	// session (present and future) is eligible while the master Replace flag
	// stays on. An empty allowlist still replaces nothing.
	ReplaceAllSessions bool
	ReplaceSessions    map[string]struct{}
}

var (
	summaryFlagsMu     sync.RWMutex
	activeSummaryFlags = loadSummaryFlagsFromEnv()
)

func loadSummaryFlagsFromEnv() SummaryFeatureFlags {
	sessions, all := parseReplaceSessions(os.Getenv(EnvSemanticSummaryReplaceSessions))
	return SummaryFeatureFlags{
		Shadow:             envBoolDefault(EnvSemanticSummaryShadow, false),
		Replace:            envBoolDefault(EnvSemanticSummaryReplace, false),
		ReplaceAllSessions: all,
		ReplaceSessions:    sessions,
	}
}

// parseReplaceSessions splits the comma-separated allowlist. Any "*" token
// widens to all sessions; empty or ID-only values keep the explicit set.
func parseReplaceSessions(raw string) (map[string]struct{}, bool) {
	out := make(map[string]struct{})
	for _, part := range strings.Split(raw, ",") {
		id := strings.TrimSpace(part)
		if id == "*" {
			return nil, true
		}
		if id != "" {
			out[id] = struct{}{}
		}
	}
	return out, false
}

func envBoolDefault(key string, def bool) bool {
	v := strings.TrimSpace(os.Getenv(key))
	if v == "" {
		return def
	}
	return v == "1" || strings.EqualFold(v, "true") || strings.EqualFold(v, "yes")
}

// CurrentSummaryFlags returns the active summary feature flags.
func CurrentSummaryFlags() SummaryFeatureFlags {
	summaryFlagsMu.RLock()
	defer summaryFlagsMu.RUnlock()
	return activeSummaryFlags
}

// SemanticSummaryShadowEnabled reports whether shadow semantic summary is on.
func SemanticSummaryShadowEnabled() bool {
	return CurrentSummaryFlags().Shadow
}

// SemanticSummaryReplaceEnabled reports the REPLACE master env bit.
// Narrative replacement additionally requires the session allowlist
// (SemanticReplaceEnabledFor); the master bit alone replaces nothing.
func SemanticSummaryReplaceEnabled() bool {
	return CurrentSummaryFlags().Replace
}

// SemanticReplaceEnabledFor reports fail-closed gray eligibility: the master
// flag must be on AND the session must be in the allowlist (or the allowlist
// is the "*" wildcard). Empty allowlist replaces no session.
func SemanticReplaceEnabledFor(sessionID string) bool {
	f := CurrentSummaryFlags()
	if !f.Replace || sessionID == "" {
		return false
	}
	if f.ReplaceAllSessions {
		return true
	}
	_, ok := f.ReplaceSessions[sessionID]
	return ok
}

// SetSummaryFlagsForTest overrides flags in tests.
func SetSummaryFlagsForTest(f SummaryFeatureFlags) {
	summaryFlagsMu.Lock()
	activeSummaryFlags = f
	summaryFlagsMu.Unlock()
}

// ResetSummaryFlagsForTest restores flags from the process environment.
func ResetSummaryFlagsForTest() {
	summaryFlagsMu.Lock()
	activeSummaryFlags = loadSummaryFlagsFromEnv()
	summaryFlagsMu.Unlock()
}