// Package gobridge 提供 Go 与 Python 之间的双向通信桥接，
// 支持普通调用、流式输出、流式输入和双向流四种模式。
package gobridge

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

// Invoke 调用 Python 暴露的函数，支持四种模式：
//
//	普通调用：   Invoke[int](ctx, pool, "Add", 3, 4)
//	流式输出：   Invoke[chan int](ctx, pool, "RangeGen", 1, 10)     // Python yield → Go channel
//	流式输入：   Invoke[int](ctx, pool, "SumStream", inputChan)     // Go channel → Python Iterator
//	双向流：     Invoke[chan int](ctx, pool, "Transform", inputChan) // 两端均为流
//
// ctx 取消时会立即中断与 Python 的通信并返回 ctx.Err()。
// 对于流式输出/双向流，ctx 取消会关闭返回的 channel。
func Invoke[R any](ctx context.Context, pool Pool, method string, args ...any) (R, error) {
	rt := reflect.TypeFor[R]()

	// 查找 chan 类型的输入参数
	streamArgIdx := -1
	var streamCh reflect.Value
	for i, arg := range args {
		if arg != nil {
			rv := reflect.ValueOf(arg)
			if rv.Kind() == reflect.Chan {
				streamArgIdx = i
				streamCh = rv
				break
			}
		}
	}

	switch {
	case rt.Kind() == reflect.Chan && streamArgIdx >= 0:
		return invokeStreamBoth[R](ctx, pool, method, streamArgIdx, streamCh, rt, args...)
	case rt.Kind() == reflect.Chan:
		return invokeStreamOut[R](ctx, pool, method, rt, args...)
	case streamArgIdx >= 0:
		return invokeStreamIn[R](ctx, pool, method, streamArgIdx, streamCh, args...)
	default:
		return invokeRegular[R](ctx, pool, method, args...)
	}
}

// watchCtx 启动一个 goroutine 监听 ctx：
//   - ctx 取消时先发送 cancel 消息（Python 侧收到后注入 InterruptedError）
//   - 再关闭连接，解除阻塞中的读写操作
//
// 返回 stop 函数，必须在 conn 归还连接池前调用，可安全多次调用。
func watchCtx(ctx context.Context, conn net.Conn, id uint64) (stop func()) {
	done := make(chan struct{})
	var once sync.Once
	go func() {
		select {
		case <-ctx.Done():
			writeMsg(conn, Message{ID: id, Type: TypeCancel}) //nolint
			conn.Close()
		case <-done:
		}
	}()
	return func() { once.Do(func() { close(done) }) }
}

// chanRecv 从 ch 接收一个值，同时监听 ctx.Done()。
// 返回 (值, channel是否open, ctx是否已取消)。
func chanRecv(ctx context.Context, ch reflect.Value) (reflect.Value, bool, bool) {
	chosen, val, ok := reflect.Select([]reflect.SelectCase{
		{Dir: reflect.SelectRecv, Chan: ch},
		{Dir: reflect.SelectRecv, Chan: reflect.ValueOf(ctx.Done())},
	})
	if chosen == 1 {
		return reflect.Value{}, false, true
	}
	return val, ok, false
}

// contextErr 在 io 错误时优先返回 ctx 的错误原因
func contextErr(ctx context.Context, err error) error {
	if e := ctx.Err(); e != nil {
		return e
	}
	return err
}

func invokeRegular[R any](ctx context.Context, pool Pool, method string, args ...any) (R, error) {
	var zero R

	argsJSON, err := json.Marshal(args)
	if err != nil {
		return zero, fmt.Errorf("marshal args: %w", err)
	}

	conn, w, err := pool.acquire(ctx)
	if err != nil {
		return zero, err
	}

	id := pool.nextReqID()
	stop := watchCtx(ctx, conn, id)
	defer stop()

	if err := writeMsg(conn, Message{
		ID:     id,
		Type:   TypeCall,
		Method: method,
		Args:   argsJSON,
	}); err != nil {
		w.release(conn, false)
		return zero, contextErr(ctx, fmt.Errorf("write call: %w", err))
	}

	resp, err := readMsg(conn)
	if err != nil {
		w.release(conn, false)
		return zero, contextErr(ctx, fmt.Errorf("read response: %w", err))
	}

	stop()
	w.release(conn, true)

	if resp.Type == TypeError {
		return zero, fmt.Errorf("remote error: %s", resp.Error)
	}

	var result R
	if err := json.Unmarshal(resp.Data, &result); err != nil {
		return zero, fmt.Errorf("unmarshal result: %w", err)
	}
	return result, nil
}

func invokeStreamOut[R any](ctx context.Context, pool Pool, method string, rt reflect.Type, args ...any) (R, error) {
	var zero R

	argsJSON, err := json.Marshal(args)
	if err != nil {
		return zero, fmt.Errorf("marshal args: %w", err)
	}

	conn, w, err := pool.acquire(ctx)
	if err != nil {
		return zero, err
	}

	id := pool.nextReqID()
	if err := writeMsg(conn, Message{
		ID:     id,
		Type:   TypeCall,
		Method: method,
		Args:   argsJSON,
	}); err != nil {
		w.release(conn, false)
		return zero, contextErr(ctx, fmt.Errorf("write call: %w", err))
	}

	ch := reflect.MakeChan(rt, 64)

	go func() {
		stop := watchCtx(ctx, conn, id)
		defer func() {
			stop()
			ch.Close()
			w.release(conn, ctx.Err() == nil)
		}()
		for {
			msg, err := readMsg(conn)
			if err != nil || msg.Type == TypeEnd || msg.Type == TypeError {
				return
			}
			if msg.Type == TypeChunk {
				val := reflect.New(rt.Elem())
				if err := json.Unmarshal(msg.Data, val.Interface()); err != nil {
					return
				}
				ch.Send(val.Elem())
			}
		}
	}()

	return ch.Interface().(R), nil
}

func invokeStreamIn[R any](ctx context.Context, pool Pool, method string, streamArgIdx int, streamCh reflect.Value, args ...any) (R, error) {
	var zero R

	jsonArgs := make([]any, len(args))
	copy(jsonArgs, args)
	jsonArgs[streamArgIdx] = nil

	argsJSON, err := json.Marshal(jsonArgs)
	if err != nil {
		return zero, fmt.Errorf("marshal args: %w", err)
	}

	conn, w, err := pool.acquire(ctx)
	if err != nil {
		return zero, err
	}

	id := pool.nextReqID()
	stop := watchCtx(ctx, conn, id)
	defer stop()

	if err := writeMsg(conn, Message{
		ID:           id,
		Type:         TypeCall,
		Method:       method,
		Args:         argsJSON,
		StreamInput:  true,
		StreamArgIdx: streamArgIdx,
	}); err != nil {
		w.release(conn, false)
		return zero, contextErr(ctx, fmt.Errorf("write call: %w", err))
	}

	for {
		val, ok, cancelled := chanRecv(ctx, streamCh)
		if cancelled {
			w.release(conn, false)
			return zero, ctx.Err()
		}
		if !ok {
			break
		}
		chunkData, err := json.Marshal(val.Interface())
		if err != nil {
			w.release(conn, false)
			return zero, fmt.Errorf("marshal chunk: %w", err)
		}
		if err := writeMsg(conn, Message{ID: id, Type: TypeChunk, Data: chunkData}); err != nil {
			w.release(conn, false)
			return zero, contextErr(ctx, fmt.Errorf("write chunk: %w", err))
		}
	}

	if err := writeMsg(conn, Message{ID: id, Type: TypeEnd}); err != nil {
		w.release(conn, false)
		return zero, contextErr(ctx, fmt.Errorf("write end: %w", err))
	}

	resp, err := readMsg(conn)
	if err != nil {
		w.release(conn, false)
		return zero, contextErr(ctx, fmt.Errorf("read response: %w", err))
	}

	stop()
	w.release(conn, true)

	if resp.Type == TypeError {
		return zero, fmt.Errorf("remote error: %s", resp.Error)
	}

	var result R
	if err := json.Unmarshal(resp.Data, &result); err != nil {
		return zero, fmt.Errorf("unmarshal result: %w", err)
	}
	return result, nil
}

func invokeStreamBoth[R any](ctx context.Context, pool Pool, method string, streamArgIdx int, streamCh reflect.Value, rt reflect.Type, args ...any) (R, error) {
	var zero R

	jsonArgs := make([]any, len(args))
	copy(jsonArgs, args)
	jsonArgs[streamArgIdx] = nil

	argsJSON, err := json.Marshal(jsonArgs)
	if err != nil {
		return zero, fmt.Errorf("marshal args: %w", err)
	}

	conn, w, err := pool.acquire(ctx)
	if err != nil {
		return zero, err
	}

	id := pool.nextReqID()
	if err := writeMsg(conn, Message{
		ID:           id,
		Type:         TypeCall,
		Method:       method,
		Args:         argsJSON,
		StreamInput:  true,
		StreamArgIdx: streamArgIdx,
	}); err != nil {
		w.release(conn, false)
		return zero, contextErr(ctx, fmt.Errorf("write call: %w", err))
	}

	outCh := reflect.MakeChan(rt, 64)

	// 写入 goroutine：输入 channel → Python chunks
	go func() {
		for {
			val, ok, cancelled := chanRecv(ctx, streamCh)
			if cancelled || !ok {
				break
			}
			data, err := json.Marshal(val.Interface())
			if err != nil {
				break
			}
			if err := writeMsg(conn, Message{ID: id, Type: TypeChunk, Data: data}); err != nil {
				break
			}
		}
		writeMsg(conn, Message{ID: id, Type: TypeEnd}) //nolint
	}()

	// 读取 goroutine：Python chunks → 输出 channel
	go func() {
		stop := watchCtx(ctx, conn, id)
		defer func() {
			stop()
			outCh.Close()
			w.release(conn, ctx.Err() == nil)
		}()
		for {
			msg, err := readMsg(conn)
			if err != nil || msg.Type == TypeEnd || msg.Type == TypeError {
				return
			}
			if msg.Type == TypeChunk {
				val := reflect.New(rt.Elem())
				if err := json.Unmarshal(msg.Data, val.Interface()); err != nil {
					return
				}
				outCh.Send(val.Elem())
			}
		}
	}()

	return outCh.Interface().(R), nil
}