package completion

import (
	"context"
	"errors"
	"fmt"
	"sync"
)

var ErrInvalidRequest = errors.New("invalid completion request")

// Request 是统一的补全请求模型。
type Request struct {
	Language  string `json:"language,omitempty"`
	SessionID string `json:"sessionId,omitempty"`
	URI       string `json:"uri"`
	Text      string `json:"text"`
	Line      int    `json:"line"`
	Character int    `json:"character"`
}

// Item 对应一个补全候选项。
type Item struct {
	Label         string `json:"label"`
	Kind          int    `json:"kind,omitempty"`
	Detail        string `json:"detail,omitempty"`
	Documentation string `json:"documentation,omitempty"`
	InsertText    string `json:"insertText,omitempty"`
	SortText      string `json:"sortText,omitempty"`
	FilterText    string `json:"filterText,omitempty"`
}

// Response 是补全结果集合。
type Response struct {
	Items        []Item `json:"items"`
	IsIncomplete bool   `json:"isIncomplete"`
}

// Client 抽象 LSP 客户端所需的最小能力。
type Client interface {
	DidOpen(ctx context.Context, uri, text string, version int) error
	DidChange(ctx context.Context, uri, text string, version int) error
	Completion(ctx context.Context, uri string, line, character int) (Response, error)
}

type documentState struct {
	version int
}

// Service 负责文档生命周期同步（didOpen/didChange）与补全调用。
type Service struct {
	client Client

	mu        sync.Mutex
	documents map[string]*documentState
}

func NewService(client Client) *Service {
	return &Service{
		client:    client,
		documents: make(map[string]*documentState),
	}
}

// Complete 根据 URI 的历史状态决定发送 didOpen 或 didChange，再请求补全。
func (s *Service) Complete(ctx context.Context, req Request) (Response, error) {
	if err := validateRequest(req); err != nil {
		return Response{}, err
	}

	s.mu.Lock()
	defer s.mu.Unlock()

	state, opened := s.documents[req.URI]
	if !opened {
		if err := s.client.DidOpen(ctx, req.URI, req.Text, 1); err != nil {
			return Response{}, fmt.Errorf("didOpen failed: %w", err)
		}
		s.documents[req.URI] = &documentState{version: 1}
	} else {
		nextVersion := state.version + 1
		if err := s.client.DidChange(ctx, req.URI, req.Text, nextVersion); err != nil {
			return Response{}, fmt.Errorf("didChange failed: %w", err)
		}
		state.version = nextVersion
	}

	resp, err := s.client.Completion(ctx, req.URI, req.Line, req.Character)
	if err != nil {
		return Response{}, fmt.Errorf("completion failed: %w", err)
	}
	return resp, nil
}

// validateRequest 做基础参数校验，避免向 LSP 发送非法请求。
func validateRequest(req Request) error {
	if req.URI == "" {
		return ErrInvalidRequest
	}
	if req.Line < 0 || req.Character < 0 {
		return ErrInvalidRequest
	}
	return nil
}