// Package llm provides a thin OpenAI-compatible client used by the agent
// runtime. It hides the openai-go SDK types behind a small, provider-agnostic
// surface so that swapping the backend (a different SDK, a custom HTTP client,
// ...) only touches this package.
//
// The client speaks the standard Chat Completions protocol with tool calling,
// so any OpenAI-compatible endpoint (OpenAI, DeepSeek, Moonshot, vLLM, Ollama,
// ...) works by configuring base_url + api_key + model in the admin console.
package llm

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"

	"github.com/openai/openai-go"
	"github.com/openai/openai-go/option"
	"github.com/openai/openai-go/shared"
)

// Config describes one model endpoint. Built from a store.ModelConfig row at
// call time; api_key is decrypted by the caller.
type Config struct {
	BaseURL   string
	APIKey    string
	Model     string
	MaxTokens int // 0 = leave unset
}

// Role labels a message. Matches the OpenAI convention.
type Role string

const (
	RoleSystem    Role = "system"
	RoleUser      Role = "user"
	RoleAssistant Role = "assistant"
	RoleTool      Role = "tool"
)

// Message is a single chat message. For assistant messages with tool calls,
// ToolCalls is set and Content may be empty. For role=tool, ToolCallID links
// the result back to the call it answers.
type Message struct {
	Role       Role       `json:"role"`
	Content    string     `json:"content,omitempty"`
	ToolCalls  []ToolCall `json:"tool_calls,omitempty"`
	ToolCallID string     `json:"tool_call_id,omitempty"`
	// Name is the tool name for role=tool; some providers expect it.
	Name string `json:"name,omitempty"`
}

// ToolCall represents one tool invocation requested by the assistant.
type ToolCall struct {
	ID       string         `json:"id"`
	Name     string         `json:"name"`
	Arguments map[string]any `json:"arguments"`
}

// Function describes one tool the model may call, in JSON Schema form.
type Function struct {
	Name        string `json:"name"`
	Description string `json:"description"`
	// Parameters is a raw JSON Schema document for the arguments.
	Parameters []byte `json:"parameters"`
}

// Client is a stateless caller bound to one Config. Build one per request.
type Client struct {
	cfg Config
	oc  openai.Client
}

// New builds a client for the given config.
func New(cfg Config) *Client {
	opts := []option.RequestOption{
		option.WithAPIKey(cfg.APIKey),
	}
	if cfg.BaseURL != "" {
		opts = append(opts, option.WithBaseURL(cfg.BaseURL))
	}
	return &Client{cfg: cfg, oc: openai.NewClient(opts...)}
}

// StreamEvent is what RunStream yields. Exactly one field is non-zero per
// event. The caller routes them to the SSE layer (token / tool_calls / done).
type StreamEvent struct {
	// Delta is an incremental assistant text token (content streaming).
	Delta string
	// ToolCalls is set when the assistant requests tool calls in this chunk.
	// For a streaming response these accumulate until finish_reason == "tool_calls".
	ToolCalls []ToolCall
	// FinishReason is set on the terminal event ("stop", "tool_calls", ...).
	FinishReason string
	// Err carries a non-stream error (auth, network, parse).
	Err error
}

// RunStream issues a streaming chat completion and invokes onEvent for each
// chunk. It returns the fully-assembled assistant message (content + any tool
// calls) so the caller can append it to history. The context controls cancel.
func (c *Client) RunStream(ctx context.Context, messages []Message, tools []Function, onEvent func(StreamEvent)) (Message, error) {
	if onEvent == nil {
		onEvent = func(StreamEvent) {}
	}
	params := openai.ChatCompletionNewParams{
		Model:    openai.ChatModel(c.cfg.Model),
		Messages: toOpenAIMessages(messages),
		Tools:    toOpenAITools(tools),
	}
	if c.cfg.MaxTokens > 0 {
		params.MaxTokens = openai.Int(int64(c.cfg.MaxTokens))
	}

	stream := c.oc.Chat.Completions.NewStreaming(ctx, params)

	var (
		contentBuf  string
		toolBuf     []openai.ChatCompletionChunkChoiceDeltaToolCall
		finish      string
	)
	for stream.Next() {
		chunk := stream.Current()
		if len(chunk.Choices) == 0 {
			continue
		}
		ch := chunk.Choices[0]
		if ch.FinishReason != "" {
			finish = ch.FinishReason
		}
		delta := ch.Delta
		if delta.Content != "" {
			contentBuf += delta.Content
			onEvent(StreamEvent{Delta: delta.Content})
		}
		// Accumulate tool-call fragments by index. The SDK guarantees a stable
		// index across chunks for the same call; arguments stream in pieces.
		for _, tc := range delta.ToolCalls {
			for len(toolBuf) <= int(tc.Index) {
				toolBuf = append(toolBuf, openai.ChatCompletionChunkChoiceDeltaToolCall{})
			}
			slot := &toolBuf[tc.Index]
			slot.Index = tc.Index
			if tc.ID != "" {
				slot.ID = tc.ID
			}
			if tc.Function.Name != "" {
				slot.Function.Name = tc.Function.Name
			}
			slot.Function.Arguments += tc.Function.Arguments
		}
	}
	if err := stream.Err(); err != nil {
		// API errors arrive here as *openai.Error with a useful message.
		onEvent(StreamEvent{Err: err})
		return Message{}, fmt.Errorf("llm stream: %w", err)
	}
	if finish == "" {
		finish = "stop"
	}

	// Build the assembled tool calls (if any) and surface a single tool_calls
	// event so the caller can drive the execution loop.
	var calls []ToolCall
	for _, tc := range toolBuf {
		if tc.ID == "" && tc.Function.Name == "" {
			continue
		}
		args, _ := parseArguments(tc.Function.Arguments)
		calls = append(calls, ToolCall{
			ID:        tc.ID,
			Name:      tc.Function.Name,
			Arguments: args,
		})
	}
	if len(calls) > 0 {
		onEvent(StreamEvent{ToolCalls: calls, FinishReason: finish})
	} else {
		onEvent(StreamEvent{FinishReason: finish})
	}

	return Message{
		Role:      RoleAssistant,
		Content:   contentBuf,
		ToolCalls: calls,
	}, nil
}

// toOpenAIMessages converts our Message slice into the SDK's union type.
func toOpenAIMessages(ms []Message) []openai.ChatCompletionMessageParamUnion {
	out := make([]openai.ChatCompletionMessageParamUnion, 0, len(ms))
	for _, m := range ms {
		switch m.Role {
		case RoleSystem:
			out = append(out, openai.SystemMessage(m.Content))
		case RoleUser:
			out = append(out, openai.UserMessage(m.Content))
		case RoleAssistant:
			msg := &openai.ChatCompletionAssistantMessageParam{}
			msg.Content.OfString = openai.String(m.Content)
			for _, tc := range m.ToolCalls {
				args := marshalArguments(tc.Arguments)
				msg.ToolCalls = append(msg.ToolCalls, openai.ChatCompletionMessageToolCallParam{
					ID: tc.ID,
					Function: openai.ChatCompletionMessageToolCallFunctionParam{
						Name:      tc.Name,
						Arguments: args,
					},
				})
			}
			out = append(out, openai.ChatCompletionMessageParamUnion{
				OfAssistant: msg,
			})
		case RoleTool:
			out = append(out, openai.ToolMessage(m.Content, m.ToolCallID))
		}
	}
	return out
}

// toOpenAITools converts our Function list into SDK tool params. The
// parameters JSON Schema is decoded into the SDK's map form.
func toOpenAITools(fs []Function) []openai.ChatCompletionToolParam {
	if len(fs) == 0 {
		return nil
	}
	out := make([]openai.ChatCompletionToolParam, 0, len(fs))
	for _, f := range fs {
		params := f.Parameters
		if len(params) == 0 {
			params = []byte(`{"type":"object","properties":{}}`)
		}
		var schemaMap map[string]any
		// A malformed schema is non-fatal: fall back to an empty object so a
		// bad skill file never crashes a chat request.
		if err := json.Unmarshal(params, &schemaMap); err != nil || schemaMap == nil {
			schemaMap = map[string]any{"type": "object", "properties": map[string]any{}}
		}
		fd := shared.FunctionDefinitionParam{
			Name:       f.Name,
			Parameters: shared.FunctionParameters(schemaMap),
		}
		if f.Description != "" {
			fd.Description = openai.String(f.Description)
		}
		out = append(out, openai.ChatCompletionToolParam{Function: fd})
	}
	return out
}

// ErrNoResponse is returned when the stream produced no usable content and no
// tool calls (e.g. content filter). The caller can map this to a user-facing
// "无法生成回复" message.
var ErrNoResponse = errors.New("model returned no content")