package windsurf

import (
	"crypto/sha256"
	"encoding/json"
	"fmt"
	"sync"
	"time"
)

const (
	poolTTL = 30 * time.Minute
	poolMax = 500
)

type ConversationEntry struct {
	CascadeID  string
	SessionID  string
	LSPort     int
	APIKey     string
	CreatedAt  time.Time
	LastAccess time.Time
}

type ConversationPool struct {
	mu    sync.Mutex
	pool  map[string]*ConversationEntry
	stats poolStats
}

type poolStats struct {
	Hits      int `json:"hits"`
	Misses    int `json:"misses"`
	Stores    int `json:"stores"`
	Evictions int `json:"evictions"`
	Expired   int `json:"expired"`
}

func NewConversationPool() *ConversationPool {
	cp := &ConversationPool{
		pool: make(map[string]*ConversationEntry),
	}
	go cp.pruneLoop()
	return cp
}

func (cp *ConversationPool) Checkout(fingerprint string) *ConversationEntry {
	if fingerprint == "" {
		cp.mu.Lock()
		cp.stats.Misses++
		cp.mu.Unlock()
		return nil
	}
	cp.mu.Lock()
	defer cp.mu.Unlock()
	entry, ok := cp.pool[fingerprint]
	if !ok {
		cp.stats.Misses++
		return nil
	}
	delete(cp.pool, fingerprint)
	if time.Since(entry.LastAccess) > poolTTL {
		cp.stats.Expired++
		cp.stats.Misses++
		return nil
	}
	cp.stats.Hits++
	return entry
}

func (cp *ConversationPool) Checkin(fingerprint string, entry *ConversationEntry) {
	if fingerprint == "" || entry == nil {
		return
	}
	now := time.Now()
	cp.mu.Lock()
	defer cp.mu.Unlock()
	if entry.CreatedAt.IsZero() {
		entry.CreatedAt = now
	}
	entry.LastAccess = now
	cp.pool[fingerprint] = entry
	cp.stats.Stores++
	cp.pruneLocked(now)
}

func (cp *ConversationPool) InvalidateFor(apiKey string, lsPort int) int {
	cp.mu.Lock()
	defer cp.mu.Unlock()
	dropped := 0
	for fp, e := range cp.pool {
		if (apiKey != "" && e.APIKey == apiKey) || (lsPort > 0 && e.LSPort == lsPort) {
			delete(cp.pool, fp)
			dropped++
		}
	}
	return dropped
}

func (cp *ConversationPool) pruneLocked(now time.Time) {
	for fp, e := range cp.pool {
		if now.Sub(e.LastAccess) > poolTTL {
			delete(cp.pool, fp)
			cp.stats.Expired++
		}
	}
	if len(cp.pool) <= poolMax {
		return
	}
	// LRU eviction: find oldest entries
	type fpTime struct {
		fp string
		t  time.Time
	}
	entries := make([]fpTime, 0, len(cp.pool))
	for fp, e := range cp.pool {
		entries = append(entries, fpTime{fp, e.LastAccess})
	}
	// Simple sort by time
	for i := 0; i < len(entries)-1; i++ {
		for j := i + 1; j < len(entries); j++ {
			if entries[j].t.Before(entries[i].t) {
				entries[i], entries[j] = entries[j], entries[i]
			}
		}
	}
	toDrop := len(entries) - poolMax
	for i := 0; i < toDrop; i++ {
		delete(cp.pool, entries[i].fp)
		cp.stats.Evictions++
	}
}

func (cp *ConversationPool) pruneLoop() {
	ticker := time.NewTicker(5 * time.Minute)
	defer ticker.Stop()
	for range ticker.C {
		cp.mu.Lock()
		cp.pruneLocked(time.Now())
		cp.mu.Unlock()
	}
}

// FingerprintBefore computes the fingerprint for resuming a conversation.
// Hash only user/tool turns (excluding the last one) for lookup.
// apiKey 参与 hash：cascade_id 绑定具体上游账号/LS，不同账号即使消息一致也不能复用，
// 否则 failover 切号后命中旧 cascade 会触发 "panel state not found"。
func FingerprintBefore(messages []ChatMessage, modelKey, apiKey string) string {
	turns := stableTurns(messages)
	if len(turns) < 2 {
		return ""
	}
	return hashFingerprint(modelKey, apiKey, turns[:len(turns)-1])
}

// FingerprintAfter computes the fingerprint after a successful turn.
func FingerprintAfter(messages []ChatMessage, modelKey, apiKey string) string {
	turns := stableTurns(messages)
	if len(turns) == 0 {
		return ""
	}
	return hashFingerprint(modelKey, apiKey, turns)
}

func stableTurns(messages []ChatMessage) []ChatMessage {
	var turns []ChatMessage
	for _, m := range messages {
		if m.Role == "user" || m.Role == "tool" {
			turns = append(turns, m)
		}
	}
	return turns
}

func hashFingerprint(modelKey, apiKey string, turns []ChatMessage) string {
	type canonicalImage struct {
		MimeType string `json:"mime_type"`
		SHA256   string `json:"sha256"`
		ByteLen  int    `json:"byte_len"`
		Caption  string `json:"caption,omitempty"`
	}
	type canonical struct {
		Role    string           `json:"role"`
		Content string           `json:"content"`
		Images  []canonicalImage `json:"images,omitempty"`
	}
	cans := make([]canonical, len(turns))
	for i, t := range turns {
		c := canonical{Role: t.Role, Content: t.Content}
		// 指纹只使用 ImageDigests，永不使用 base64。
		// 若 ImageDigests 为空则 canonical.Images 也省略（保持向后兼容：无图 hash 与旧版本一致）。
		if len(t.ImageDigests) > 0 {
			c.Images = make([]canonicalImage, len(t.ImageDigests))
			for j, d := range t.ImageDigests {
				c.Images[j] = canonicalImage{
					MimeType: d.MimeType,
					SHA256:   d.SHA256,
					ByteLen:  d.ByteLen,
					Caption:  d.Caption,
				}
			}
		}
		cans[i] = c
	}
	data, _ := json.Marshal(cans)
	h := sha256.Sum256([]byte(fmt.Sprintf("%s\x00\x00%s\x00\x00%s", modelKey, apiKey, data)))
	return fmt.Sprintf("%x", h)
}