// Package quota monitors Claude Code sessions for quota exhaustion and triggers
// account switches when thresholds are crossed.
package quota

import (
	"context"
	"log"
	"regexp"
	"strings"
	"time"

	"forge.secuaas.ovh/olivier/claude-failover/internal/config"
	"forge.secuaas.ovh/olivier/claude-failover/internal/state"
	"forge.secuaas.ovh/olivier/claude-failover/internal/tmux"
)

// SwitchRequest is emitted when quota exhaustion is detected, requesting
// the AccountSwitcher to activate a different account.
type SwitchRequest struct {
	From      string // current active account name
	To        string // desired account name (empty = auto-select)
	ResetTime string // human-readable reset time extracted from the pane
}

// quotaPatterns are substrings that indicate quota exhaustion in a pane.
// Must be specific enough to avoid matching Anthropic server errors (500/503)
// that happen to include generic words like "rate limit" in their payload.
var quotaPatterns = []string{
	"you've hit your limit",   // Claude Code TUI friendly message
	"rate_limit_error",        // Anthropic typed error (real HTTP 429)
	"quota exceeded",          // generic, but specific enough
	"usage limit reached",     // Claude Pro phrasing
	"claude pro usage",        // Claude Pro dashboard phrasing
	"too many requests",       // HTTP 429 status text
	"5-hour limit",            // Claude Code 5h window phrasing
}

// serverErrorPatterns indicate a transient upstream server error
// (Anthropic 500/503), NOT a quota hit. When any of these is present in
// the pane, we treat the "hit" as a false positive and do NOT swap.
var serverErrorPatterns = []string{
	"api_error",               // Anthropic typed error (HTTP 500)
	"overloaded_error",        // Anthropic typed error (HTTP 503)
	"internal server error",   // HTTP 500 status text
	"api error: 5",            // Claude TUI rendering of 5xx
}

// resetTimeRe extracts reset times like "resets 8pm", "resets at 11:30pm",
// "resets in 45 minutes".
var resetTimeRe = regexp.MustCompile(
	`(?i)resets?\s+(?:at\s+)?([0-9]+(?::[0-9]+)?\s*[ap]m|in\s+[0-9]+\s+(?:minute|hour)s?)`,
)

// Monitor polls tmux panes for quota exhaustion messages.
type Monitor struct {
	tmux     tmux.Client
	state    *state.State
	config   *config.Config
	switchCh chan SwitchRequest
	interval time.Duration
	logger   *log.Logger
	// suspectedHitAt tracks the first poll that detected a quota pattern
	// without a parseable reset time. A second consecutive hit is required
	// before emitting SwapRequested; a single-poll hit is ignored as likely
	// transient (e.g. Anthropic 500s containing "rate limit" in payload).
	// Mutated only from poll(), which runs on a single goroutine — no lock.
	suspectedHitAt time.Time
}

// New creates a Monitor with defaults from cfg.
func New(tc tmux.Client, s *state.State, cfg *config.Config) *Monitor {
	interval := cfg.Quota.PollInterval.Duration
	if interval == 0 {
		interval = 30 * time.Second
	}
	return &Monitor{
		tmux:     tc,
		state:    s,
		config:   cfg,
		switchCh: make(chan SwitchRequest, 1),
		interval: interval,
		logger:   log.Default(),
	}
}

// SwitchChan returns the channel on which SwitchRequests are sent.
func (m *Monitor) SwitchChan() <-chan SwitchRequest {
	return m.switchCh
}

// Run starts the quota monitor loop until ctx is cancelled.
func (m *Monitor) Run(ctx context.Context) {
	ticker := time.NewTicker(m.interval)
	defer ticker.Stop()
	for {
		select {
		case <-ctx.Done():
			return
		case <-ticker.C:
			m.poll()
		}
	}
}

// poll checks all sessions for quota exhaustion once.
func (m *Monitor) poll() {
	if m.state.ActiveAccount() != "" && m.isQuotaPaused() {
		return
	}

	// Cooldown guard: after a recent swap, refuse to trigger another one until
	// the cooldown elapses. Prevents ping-pong when the freshly-activated
	// account surfaces transient errors whose text happens to match
	// quotaPatterns (e.g. Anthropic 500s rendered as "rate limit" in the TUI).
	cooldown := m.config.Quota.ReactivateCooldown.Duration
	if cooldown == 0 {
		cooldown = 10 * time.Minute
	}
	if lastAt, _, lastTo := m.state.LastSwapInfo(); !lastAt.IsZero() {
		if since := time.Since(lastAt); since < cooldown {
			m.logger.Printf("[quota] swap cooldown active (since=%v < cooldown=%v, last_to=%q) — skipping detection",
				since.Round(time.Second), cooldown, lastTo)
			return
		}
	}

	blockedPool := 0
	blockedInteractive := 0
	var resetTime string
	var firstPattern, firstSession, firstSnippet string
	recordHit := func(session, tail string) {
		if firstPattern == "" {
			firstPattern = firstMatchingPattern(tail)
			firstSession = session
			firstSnippet = snippet(tail)
		}
	}

	prefix := m.config.Pool.Autonomous.Prefix
	if prefix == "" {
		prefix = "ccl-auto-"
	}
	start := m.config.Pool.Autonomous.StartIndex
	for i := start; i < start+m.config.Pool.Autonomous.Max; i++ {
		name := sessionName(prefix, i)
		if !m.tmux.HasSession(name) {
			continue
		}
		// Only capture 3 lines — avoids false positives on stale history.
		tail, err := m.tmux.CapturePaneTail(name, 3)
		if err != nil {
			continue
		}
		if isQuotaExhausted(tail) {
			blockedPool++
			recordHit(name, tail)
			if rt := extractResetTime(tail); rt != "" {
				resetTime = rt
			}
		}
	}

	for _, ds := range m.config.Pool.Dedicated {
		if !m.tmux.HasSession(ds.Name) {
			continue
		}
		tail, err := m.tmux.CapturePaneTail(ds.Name, 3)
		if err != nil {
			continue
		}
		if isQuotaExhausted(tail) {
			blockedInteractive++
			recordHit(ds.Name, tail)
			if rt := extractResetTime(tail); rt != "" {
				resetTime = rt
			}
		}
	}

	if blockedPool < 2 && blockedInteractive < 1 {
		// No detection — clear any suspected-hit state so future transient
		// blips have to re-confirm from scratch.
		if !m.suspectedHitAt.IsZero() {
			m.logger.Printf("[quota] suspected hit cleared (no detection this poll)")
			m.suspectedHitAt = time.Time{}
		}
		return
	}

	// When no reset time can be parsed, the "hit" might be a transient
	// Anthropic 500 that happens to contain "rate limit" in its error
	// payload. Require two consecutive polls detecting a hit before
	// swapping, so a single-poll false positive is absorbed.
	if resetTime == "" {
		if m.suspectedHitAt.IsZero() {
			m.suspectedHitAt = time.Now()
			m.logger.Printf("[quota] suspected hit (no reset time): session=%q pattern=%q snippet=%q — awaiting confirmation next poll",
				firstSession, firstPattern, firstSnippet)
			return
		}
		// Second consecutive hit — proceed.
		m.logger.Printf("[quota] hit confirmed across %v — proceeding with swap",
			time.Since(m.suspectedHitAt).Round(time.Second))
	}
	m.suspectedHitAt = time.Time{}

	req := SwitchRequest{
		From:      m.state.ActiveAccount(),
		ResetTime: resetTime,
	}
	select {
	case m.switchCh <- req:
		m.logger.Printf("[quota] SwapRequested: from=%s pool=%d interactive=%d reset=%q trigger_session=%q pattern=%q snippet=%q",
			req.From, blockedPool, blockedInteractive, resetTime,
			firstSession, firstPattern, firstSnippet)
	default:
		// Swap already pending — do not queue another.
	}
}

// isQuotaPaused checks whether a swap is already in progress.
func (m *Monitor) isQuotaPaused() bool {
	// Lightweight proxy: if switch channel is full, a swap is pending.
	return len(m.switchCh) > 0
}

// isQuotaExhausted returns true if the pane content indicates quota exhaustion
// AND does not simultaneously show a transient server error (which would make
// the apparent quota match a false positive).
func isQuotaExhausted(paneContent string) bool {
	if firstMatchingPattern(paneContent) == "" {
		return false
	}
	return !hasServerError(paneContent)
}

// firstMatchingPattern returns the first quota pattern found in paneContent,
// or "" if none match. Exposed for diagnostic logging.
func firstMatchingPattern(paneContent string) string {
	lower := strings.ToLower(paneContent)
	for _, p := range quotaPatterns {
		if strings.Contains(lower, p) {
			return p
		}
	}
	return ""
}

// hasServerError reports whether the pane content shows an Anthropic 5xx /
// transient server error. Used to veto a quota match: a 500 is not a quota.
func hasServerError(paneContent string) bool {
	lower := strings.ToLower(paneContent)
	for _, p := range serverErrorPatterns {
		if strings.Contains(lower, p) {
			return true
		}
	}
	return false
}

// snippet returns a 120-char single-line excerpt of pane content for logging.
func snippet(s string) string {
	s = strings.ReplaceAll(s, "\n", " ")
	s = strings.ReplaceAll(s, "\r", "")
	s = strings.TrimSpace(s)
	if len(s) > 120 {
		s = s[:120]
	}
	return s
}

// extractResetTime parses a reset time string from pane content.
// Returns "" if none found.
func extractResetTime(content string) string {
	m := resetTimeRe.FindStringSubmatch(content)
	if len(m) >= 2 {
		return strings.TrimSpace(m[1])
	}
	return ""
}

func sessionName(prefix string, i int) string {
	return prefix + itoa(i)
}

func itoa(n int) string {
	if n == 0 {
		return "0"
	}
	b := make([]byte, 0, 10)
	for n > 0 {
		b = append([]byte{byte('0' + n%10)}, b...)
		n /= 10
	}
	return string(b)
}