package store

import (
	"fmt"
	"sort"
	"sync"
	"time"

	"github.com/cosmic-clash/cosmic-clash/server/domain"
)

// CandidateCache is intentionally rebuildable. A real Redis implementation
// can satisfy this interface, but no cache operation is an ownership fence.
type CandidateCache struct {
	mu         sync.RWMutex
	candidates map[string]domain.Candidate
}

func NewCandidateCache() *CandidateCache {
	return &CandidateCache{candidates: make(map[string]domain.Candidate)}
}

// RebuildFromQueue is the safe restart/failover path for the cache. Queue
// expiry and state filtering happen at the authoritative source before the
// cache is atomically replaced; callers never have to reconstruct those
// rules from a stale Redis index.
func RebuildFromQueue(cache *CandidateCache, queue *domain.Queue, now time.Time) error {
	if cache == nil || queue == nil || now.IsZero() {
		return fmt.Errorf("invalid candidate rebuild arguments")
	}
	return cache.Rebuild(queue.Candidates(now))
}

func (c *CandidateCache) Upsert(candidate domain.Candidate) error {
	if candidate.TicketID == "" || candidate.PlayerID == "" || candidate.EnqueuedAt.IsZero() {
		return fmt.Errorf("invalid candidate")
	}
	c.mu.Lock()
	c.candidates[candidate.TicketID] = candidate
	c.mu.Unlock()
	return nil
}

func (c *CandidateCache) Remove(ticketID string) {
	c.mu.Lock()
	delete(c.candidates, ticketID)
	c.mu.Unlock()
}

func (c *CandidateCache) Snapshot(now time.Time) []domain.Candidate {
	c.mu.RLock()
	result := make([]domain.Candidate, 0, len(c.candidates))
	for _, candidate := range c.candidates {
		if !candidate.EnqueuedAt.After(now) {
			result = append(result, candidate)
		}
	}
	c.mu.RUnlock()
	sort.Slice(result, func(i, j int) bool {
		if !result[i].EnqueuedAt.Equal(result[j].EnqueuedAt) {
			return result[i].EnqueuedAt.Before(result[j].EnqueuedAt)
		}
		return result[i].TicketID < result[j].TicketID
	})
	return result
}

// Rebuild replaces the cache atomically with the authoritative queue view.
// Callers should invoke this after Redis restart, failover, or a cache miss;
// the supplied candidates must already have passed durable queue checks.
func (c *CandidateCache) Rebuild(candidates []domain.Candidate) error {
	rebuilt := make(map[string]domain.Candidate, len(candidates))
	for _, candidate := range candidates {
		if candidate.TicketID == "" || candidate.PlayerID == "" || candidate.EnqueuedAt.IsZero() {
			return fmt.Errorf("invalid candidate in rebuild")
		}
		if _, exists := rebuilt[candidate.TicketID]; exists {
			return fmt.Errorf("duplicate candidate in rebuild")
		}
		rebuilt[candidate.TicketID] = candidate
	}
	c.mu.Lock()
	c.candidates = rebuilt
	c.mu.Unlock()
	return nil
}