package account

import (
	"context"
	"os"
	"sort"
	"strconv"
	"strings"
	"sync"

	"ds2api/internal/config"
)

type Pool struct {
	store                  *config.Store
	mu                     sync.Mutex
	queue                  []string
	inUse                  map[string]int
	waiters                []chan struct{}
	maxInflightPerAccount  int
	recommendedConcurrency int
	maxQueueSize           int
}

func NewPool(store *config.Store) *Pool {
	p := &Pool{
		store:                 store,
		inUse:                 map[string]int{},
		maxInflightPerAccount: maxInflightFromEnv(),
	}
	p.Reset()
	return p
}

func (p *Pool) Reset() {
	accounts := p.store.Accounts()
	sort.SliceStable(accounts, func(i, j int) bool {
		iHas := accounts[i].Token != ""
		jHas := accounts[j].Token != ""
		if iHas == jHas {
			return i < j
		}
		return iHas
	})
	ids := make([]string, 0, len(accounts))
	for _, a := range accounts {
		id := a.Identifier()
		if id != "" {
			ids = append(ids, id)
		}
	}
	recommended := defaultRecommendedConcurrency(len(ids), p.maxInflightPerAccount)
	queueLimit := maxQueueFromEnv(recommended)
	p.mu.Lock()
	defer p.mu.Unlock()
	p.drainWaitersLocked()
	p.queue = ids
	p.inUse = map[string]int{}
	p.recommendedConcurrency = recommended
	p.maxQueueSize = queueLimit
	config.Logger.Info(
		"[init_account_queue] initialized",
		"total", len(ids),
		"max_inflight_per_account", p.maxInflightPerAccount,
		"recommended_concurrency", p.recommendedConcurrency,
		"max_queue_size", p.maxQueueSize,
	)
}

func (p *Pool) Acquire(target string, exclude map[string]bool) (config.Account, bool) {
	p.mu.Lock()
	defer p.mu.Unlock()
	return p.acquireLocked(target, normalizeExclude(exclude))
}

func (p *Pool) AcquireWait(ctx context.Context, target string, exclude map[string]bool) (config.Account, bool) {
	if ctx == nil {
		ctx = context.Background()
	}
	exclude = normalizeExclude(exclude)
	for {
		if ctx.Err() != nil {
			return config.Account{}, false
		}

		p.mu.Lock()
		if acc, ok := p.acquireLocked(target, exclude); ok {
			p.mu.Unlock()
			return acc, true
		}
		if !p.canQueueLocked(target, exclude) {
			p.mu.Unlock()
			return config.Account{}, false
		}
		waiter := make(chan struct{})
		p.waiters = append(p.waiters, waiter)
		p.mu.Unlock()

		select {
		case <-ctx.Done():
			p.mu.Lock()
			p.removeWaiterLocked(waiter)
			p.mu.Unlock()
			return config.Account{}, false
		case <-waiter:
		}
	}
}

func (p *Pool) acquireLocked(target string, exclude map[string]bool) (config.Account, bool) {
	if target != "" {
		if exclude[target] || p.inUse[target] >= p.maxInflightPerAccount {
			return config.Account{}, false
		}
		acc, ok := p.store.FindAccount(target)
		if !ok {
			return config.Account{}, false
		}
		p.inUse[target]++
		p.bumpQueue(target)
		return acc, true
	}

	if acc, ok := p.tryAcquire(exclude, true); ok {
		return acc, true
	}
	if acc, ok := p.tryAcquire(exclude, false); ok {
		return acc, true
	}
	return config.Account{}, false
}

func (p *Pool) tryAcquire(exclude map[string]bool, requireToken bool) (config.Account, bool) {
	for i := 0; i < len(p.queue); i++ {
		id := p.queue[i]
		if exclude[id] || p.inUse[id] >= p.maxInflightPerAccount {
			continue
		}
		acc, ok := p.store.FindAccount(id)
		if !ok {
			continue
		}
		if requireToken && acc.Token == "" {
			continue
		}
		p.inUse[id]++
		p.bumpQueue(id)
		return acc, true
	}
	return config.Account{}, false
}

func (p *Pool) bumpQueue(accountID string) {
	for i, id := range p.queue {
		if id != accountID {
			continue
		}
		p.queue = append(p.queue[:i], p.queue[i+1:]...)
		p.queue = append(p.queue, accountID)
		return
	}
}

func (p *Pool) Release(accountID string) {
	if accountID == "" {
		return
	}
	p.mu.Lock()
	defer p.mu.Unlock()
	count := p.inUse[accountID]
	if count <= 0 {
		return
	}
	if count == 1 {
		delete(p.inUse, accountID)
		p.notifyWaiterLocked()
		return
	}
	p.inUse[accountID] = count - 1
	p.notifyWaiterLocked()
}

func (p *Pool) Status() map[string]any {
	p.mu.Lock()
	defer p.mu.Unlock()
	available := make([]string, 0, len(p.queue))
	inUseAccounts := make([]string, 0, len(p.inUse))
	inUseSlots := 0
	for _, id := range p.queue {
		if p.inUse[id] < p.maxInflightPerAccount {
			available = append(available, id)
		}
	}
	for id, count := range p.inUse {
		if count > 0 {
			inUseAccounts = append(inUseAccounts, id)
			inUseSlots += count
		}
	}
	sort.Strings(inUseAccounts)
	return map[string]any{
		"available":                len(available),
		"in_use":                   inUseSlots,
		"total":                    len(p.store.Accounts()),
		"available_accounts":       available,
		"in_use_accounts":          inUseAccounts,
		"max_inflight_per_account": p.maxInflightPerAccount,
		"recommended_concurrency":  p.recommendedConcurrency,
		"waiting":                  len(p.waiters),
		"max_queue_size":           p.maxQueueSize,
	}
}

func maxInflightFromEnv() int {
	for _, key := range []string{"DS2API_ACCOUNT_MAX_INFLIGHT", "DS2API_ACCOUNT_CONCURRENCY"} {
		raw := strings.TrimSpace(os.Getenv(key))
		if raw == "" {
			continue
		}
		n, err := strconv.Atoi(raw)
		if err == nil && n > 0 {
			return n
		}
	}
	return 2
}

func defaultRecommendedConcurrency(accountCount, maxInflightPerAccount int) int {
	if accountCount <= 0 {
		return 0
	}
	if maxInflightPerAccount <= 0 {
		maxInflightPerAccount = 2
	}
	return accountCount * maxInflightPerAccount
}

func normalizeExclude(exclude map[string]bool) map[string]bool {
	if exclude == nil {
		return map[string]bool{}
	}
	return exclude
}

func (p *Pool) canQueueLocked(target string, exclude map[string]bool) bool {
	if target != "" {
		if exclude[target] {
			return false
		}
		if _, ok := p.store.FindAccount(target); !ok {
			return false
		}
	}
	if p.maxQueueSize <= 0 {
		return false
	}
	return len(p.waiters) < p.maxQueueSize
}

func (p *Pool) notifyWaiterLocked() {
	if len(p.waiters) == 0 {
		return
	}
	waiter := p.waiters[0]
	p.waiters = p.waiters[1:]
	close(waiter)
}

func (p *Pool) removeWaiterLocked(waiter chan struct{}) bool {
	for i, w := range p.waiters {
		if w != waiter {
			continue
		}
		p.waiters = append(p.waiters[:i], p.waiters[i+1:]...)
		return true
	}
	return false
}

func (p *Pool) drainWaitersLocked() {
	for _, waiter := range p.waiters {
		close(waiter)
	}
	p.waiters = nil
}

func maxQueueFromEnv(defaultSize int) int {
	for _, key := range []string{"DS2API_ACCOUNT_MAX_QUEUE", "DS2API_ACCOUNT_QUEUE_SIZE"} {
		raw := strings.TrimSpace(os.Getenv(key))
		if raw == "" {
			continue
		}
		n, err := strconv.Atoi(raw)
		if err == nil && n >= 0 {
			return n
		}
	}
	if defaultSize < 0 {
		return 0
	}
	return defaultSize
}