package ratelimit

import (
	"context"
	"net/http"
	"strconv"
	"sync"
	"time"

	"github.com/rs/zerolog/log"
)

// Window holds per-window usage state.
type Window struct {
	Utilization float64   // 0-100 from API
	ResetsAt    time.Time // when window resets
}

// Snapshot is a read-only copy of a Window's state.
type Snapshot struct {
	Utilization float64
	ResetsAt    time.Time
}

// Tracker polls /api/oauth/usage and tracks per-window token usage.
type Tracker struct {
	tokenFn  func() string // returns current OAuth access token
	mu       sync.RWMutex
	fiveHour Window
	sevenDay Window
	sonnet   Window
	extra    ExtraUsage
}

// NewTracker creates a tracker. tokenFn should return the current access token.
func NewTracker(tokenFn func() string) *Tracker {
	return &Tracker{tokenFn: tokenFn}
}

// Start begins the background poll loop.
func (t *Tracker) Start(ctx context.Context) {
	go func() {
		// Poll immediately on start
		t.poll(ctx)
		for {
			select {
			case <-ctx.Done():
				return
			case <-time.After(5 * time.Minute):
				t.poll(ctx)
			}
		}
	}()
}

// UpdateFromHeaders extracts rate limit data from /v1/messages response headers.
// This provides real-time utilization updates without polling the usage API.
func (t *Tracker) UpdateFromHeaders(h http.Header) {
	t.mu.Lock()
	defer t.mu.Unlock()

	if v := h.Get("Anthropic-Ratelimit-Unified-5h-Utilization"); v != "" {
		if f, err := strconv.ParseFloat(v, 64); err == nil {
			t.fiveHour.Utilization = f * 100 // header is 0-1, we store 0-100
		}
	}
	if v := h.Get("Anthropic-Ratelimit-Unified-5h-Reset"); v != "" {
		if ts, err := strconv.ParseInt(v, 10, 64); err == nil {
			t.fiveHour.ResetsAt = time.Unix(ts, 0).UTC().Truncate(time.Minute)
		}
	}
	if v := h.Get("Anthropic-Ratelimit-Unified-7d-Utilization"); v != "" {
		if f, err := strconv.ParseFloat(v, 64); err == nil {
			t.sevenDay.Utilization = f * 100
		}
	}
	if v := h.Get("Anthropic-Ratelimit-Unified-7d-Reset"); v != "" {
		if ts, err := strconv.ParseInt(v, 10, 64); err == nil {
			t.sevenDay.ResetsAt = time.Unix(ts, 0).UTC().Truncate(time.Minute)
		}
	}
}

// FiveHour returns a snapshot of the 5-hour window.
func (t *Tracker) FiveHour() Snapshot {
	t.mu.RLock()
	defer t.mu.RUnlock()
	return Snapshot{
		Utilization: t.fiveHour.Utilization,
		ResetsAt:    t.fiveHour.ResetsAt,
	}
}

// SevenDay returns a snapshot of the 7-day window.
func (t *Tracker) SevenDay() Snapshot {
	t.mu.RLock()
	defer t.mu.RUnlock()
	return Snapshot{
		Utilization: t.sevenDay.Utilization,
		ResetsAt:    t.sevenDay.ResetsAt,
	}
}

// Sonnet returns a snapshot of the 7-day sonnet window.
func (t *Tracker) Sonnet() Snapshot {
	t.mu.RLock()
	defer t.mu.RUnlock()
	return Snapshot{
		Utilization: t.sonnet.Utilization,
		ResetsAt:    t.sonnet.ResetsAt,
	}
}

// Extra returns the current extra usage state.
func (t *Tracker) Extra() ExtraUsage {
	t.mu.RLock()
	defer t.mu.RUnlock()
	return t.extra
}

func (t *Tracker) poll(ctx context.Context) {
	token := t.tokenFn()
	if token == "" {
		return
	}

	usage, err := fetchUsage(ctx, token)
	if err != nil {
		log.Warn().Err(err).Msg("usage poll failed")
		return
	}

	t.mu.Lock()
	defer t.mu.Unlock()

	if usage.FiveHour != nil {
		t.updateWindow(&t.fiveHour, usage.FiveHour)
	}
	if usage.SevenDay != nil {
		t.updateWindow(&t.sevenDay, usage.SevenDay)
	}
	if usage.SevenDaySonnet != nil {
		t.updateWindow(&t.sonnet, usage.SevenDaySonnet)
	}
	if usage.ExtraUsage != nil {
		t.extra = *usage.ExtraUsage
	}

	log.Debug().
		Float64("5h_util", t.fiveHour.Utilization).
		Time("5h_resets", t.fiveHour.ResetsAt).
		Float64("7d_util", t.sevenDay.Utilization).
		Time("7d_resets", t.sevenDay.ResetsAt).
		Msg("usage poll")

	// Warn on high utilization
	if t.fiveHour.Utilization > 80 {
		log.Warn().Float64("utilization", t.fiveHour.Utilization).Time("resets_at", t.fiveHour.ResetsAt).Msg("5h window utilization high")
	}
	if t.sevenDay.Utilization > 80 {
		log.Warn().Float64("utilization", t.sevenDay.Utilization).Time("resets_at", t.sevenDay.ResetsAt).Msg("7d window utilization high")
	}
}

func (t *Tracker) updateWindow(w *Window, rl *RateLimit) {
	if rl.Utilization != nil {
		w.Utilization = *rl.Utilization
	}
	if rl.ResetsAt != nil {
		parsed, err := time.Parse(time.RFC3339Nano, *rl.ResetsAt)
		if err != nil {
			parsed, err = time.Parse(time.RFC3339, *rl.ResetsAt)
		}
		if err == nil {
			w.ResetsAt = parsed.UTC().Truncate(time.Minute)
		}
	}
}