package gobridge

import (
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net"
	"reflect"
	"sync"
	"sync/atomic"
)

// poolConfig 是进程池内部配置，通过 Option 函数填充
type poolConfig struct {
	workers           int
	maxConnsPerWorker int
	pythonExe         string
	scriptArgs        []string
	workDir           string
	env               []string
	socketDir         string
	stdout            io.Writer
	stderr            io.Writer
	handler           any
}

// Option 是 NewPool 的函数选项
type Option func(*poolConfig)

// WithWorkers 设置 Python 进程数量（默认 2）
func WithWorkers(n int) Option {
	return func(c *poolConfig) { c.workers = n }
}

// WithMaxConns 设置每个进程的最大连接数（默认 4）
func WithMaxConns(n int) Option {
	return func(c *poolConfig) { c.maxConnsPerWorker = n }
}

// WithPythonExe 设置 Python 可执行文件（默认 "python3"）
// uv 模式：WithPythonExe("uv"), WithScriptArgs("run")
func WithPythonExe(exe string) Option {
	return func(c *poolConfig) { c.pythonExe = exe }
}

// WithScriptArgs 设置脚本路径之后的附加参数
func WithScriptArgs(args ...string) Option {
	return func(c *poolConfig) { c.scriptArgs = args }
}

// WithWorkDir 设置子进程工作目录（默认继承当前进程）
func WithWorkDir(workDir string) Option {
	return func(c *poolConfig) { c.workDir = workDir }
}

// WithEnv 设置附加环境变量，格式为 "KEY=VALUE"
func WithEnv(env ...string) Option {
	return func(c *poolConfig) { c.env = env }
}

// WithSocketDir 设置 UDS socket 文件目录（默认 /tmp）
func WithSocketDir(dir string) Option {
	return func(c *poolConfig) { c.socketDir = dir }
}

// WithStdout 设置子进程标准输出目标（默认 os.Stdout，传 io.Discard 可静默）
func WithStdout(w io.Writer) Option {
	return func(c *poolConfig) { c.stdout = w }
}

// WithStderr 设置子进程标准错误目标（默认 os.Stderr，传 io.Discard 可静默）
func WithStderr(w io.Writer) Option {
	return func(c *poolConfig) { c.stderr = w }
}

// WithHandlers 注册 Go handler struct，其所有公开方法自动暴露给 Python 通过 call_go() 调用。
//
//	type MyService struct{}
//	func (s *MyService) Multiply(ctx context.Context, a, b int) (int, error) { ... }
//
//	pool, err := gobridge.NewPool("worker.py", gobridge.WithHandlers(&MyService{}))
//	// Python: call_go("Multiply", 3, 4)
func WithHandlers(h any) Option {
	return func(c *poolConfig) { c.handler = h }
}

// ── Pool 接口 ────────────────────────────────────────────────────────────────

// Pool 是 Python worker 进程池的接口
type Pool interface {
	Close()
	acquire(ctx context.Context) (net.Conn, *worker, error)
	nextReqID() uint64
	callbackDispatch(ctx context.Context, msg Message) (any, string)
}

// ── goHandler ────────────────────────────────────────────────────────────────

type goHandler struct {
	fn      reflect.Value
	hasCtx  bool
	inTypes []reflect.Type
	outType reflect.Type
	hasErr  bool
}


// ── pool（内部实现）─────────────────────────────────────────────────────────

type pool struct {
	workers  []*worker
	idx      atomic.Uint64
	reqID    atomic.Uint64
	mu       sync.RWMutex
	handlers map[string]goHandler
}

// NewPool 创建并启动进程池。
//
//	pool, err := gobridge.NewPool("worker.py")
//	pool, err := gobridge.NewPool("worker.py", gobridge.WithWorkers(4))
//	pool, err := gobridge.NewPool("worker.py",
//	    gobridge.WithHandlers(&MyService{}),
//	    gobridge.WithWorkers(2),
//	)
func NewPool(script string, opts ...Option) (Pool, error) {
	cfg := &poolConfig{
		workers:           2,
		maxConnsPerWorker: 4,
		pythonExe:         "python3",
		socketDir:         "/tmp",
	}
	for _, o := range opts {
		o(cfg)
	}
	if script == "" {
		return nil, fmt.Errorf("gobridge: script must not be empty")
	}
	cfg.scriptArgs = append([]string{script}, cfg.scriptArgs...)

	workers := make([]*worker, cfg.workers)
	for i := range workers {
		w, err := newWorker(cfg, i)
		if err != nil {
			for j := range i {
				workers[j].stop()
			}
			return nil, fmt.Errorf("create worker %d: %w", i, err)
		}
		workers[i] = w
	}

	p := &pool{workers: workers, handlers: make(map[string]goHandler)}

	if cfg.handler != nil {
		p.bindHandlers(cfg.handler)
	}

	return p, nil
}

func (p *pool) bindHandlers(h any) {
	rv := reflect.ValueOf(h)
	rt := rv.Type()
	for i := range rt.NumMethod() {
		m := rt.Method(i)
		if !m.IsExported() {
			continue
		}
		p.bindHandler(m.Name, rv.Method(i))
	}
}

func (p *pool) bindHandler(name string, fn reflect.Value) {
	errType := reflect.TypeFor[error]()
	ctxType := reflect.TypeFor[context.Context]()

	ft := fn.Type()
	h := goHandler{fn: fn}

	startIdx := 0
	if ft.NumIn() > 0 && ft.In(0).Implements(ctxType) {
		h.hasCtx = true
		startIdx = 1
	}
	for i := startIdx; i < ft.NumIn(); i++ {
		h.inTypes = append(h.inTypes, ft.In(i))
	}

	switch ft.NumOut() {
	case 0:
	case 1:
		if ft.Out(0).Implements(errType) {
			h.hasErr = true
		} else {
			h.outType = ft.Out(0)
		}
	case 2:
		if !ft.Out(1).Implements(errType) {
			panic(fmt.Sprintf("gobridge: handler %s: second return value must implement error", name))
		}
		h.outType = ft.Out(0)
		h.hasErr = true
	default:
		panic(fmt.Sprintf("gobridge: handler %s: must return at most (value, error)", name))
	}

	p.handlers[name] = h
}

func (p *pool) acquire(ctx context.Context) (net.Conn, *worker, error) {
	n := uint64(len(p.workers))
	if n == 0 {
		return nil, nil, fmt.Errorf("gobridge: pool has no workers")
	}

	var idx uint64
	if i := workerIndexFor(ctx, int(n)); i >= 0 {
		idx = uint64(i) % n // 防御：ctx 可能来自不同 pool
	} else {
		idx = p.idx.Add(1) % n
	}

	w := p.workers[idx]
	conn, err := w.acquire(ctx)
	return conn, w, err
}

func (p *pool) nextReqID() uint64 {
	return p.reqID.Add(1)
}

func (p *pool) callbackDispatch(ctx context.Context, msg Message) (any, string) {
	p.mu.RLock()
	h, ok := p.handlers[msg.Method]
	p.mu.RUnlock()
	if !ok {
		return nil, fmt.Sprintf("unknown go handler: %s", msg.Method)
	}

	var rawArgs []json.RawMessage
	if len(msg.Args) > 0 {
		if err := json.Unmarshal(msg.Args, &rawArgs); err != nil {
			return nil, fmt.Sprintf("unmarshal args: %v", err)
		}
	}

	if len(rawArgs) != len(h.inTypes) {
		return nil, fmt.Sprintf("arg count mismatch: want %d got %d", len(h.inTypes), len(rawArgs))
	}

	in := make([]reflect.Value, 0, len(h.inTypes)+1)
	if h.hasCtx {
		in = append(in, reflect.ValueOf(ctx))
	}
	for i, t := range h.inTypes {
		v := reflect.New(t)
		if err := json.Unmarshal(rawArgs[i], v.Interface()); err != nil {
			return nil, fmt.Sprintf("unmarshal arg %d: %v", i, err)
		}
		in = append(in, v.Elem())
	}

	out := h.fn.Call(in)

	if h.hasErr {
		errVal := out[len(out)-1]
		if !errVal.IsNil() {
			return nil, errVal.Interface().(error).Error()
		}
	}
	if h.outType == nil || len(out) == 0 {
		return nil, ""
	}
	return out[0].Interface(), ""
}

func (p *pool) Close() {
	for _, w := range p.workers {
		w.stop()
	}
}