// Package llm provides an OpenAI-compatible client for LLM interactions.
// It handles chat completions with automatic tool call execution.
package llm

import (
	"context"
	"errors"
	"fmt"
	"io"
	"log/slog"
	"strings"
	"time"

	"code.chimeric.al/chimerical/odidere/internal/tool"

	openai "github.com/sashabaranov/go-openai"
)

// Config holds the configuration for an LLM client.
type Config struct {
	// Key is the API key for authentication.
	Key string `yaml:"key"`
	// Model is the model identifier.
	Model string `yaml:"model"`
	// SystemPrompt is prepended to all conversations.
	SystemPrompt string `yaml:"system_prompt"`
	// Timeout is the maximum duration for a query (e.g., "5m").
	// Defaults to 5 minutes if empty.
	Timeout string `yaml:"timeout"`
	// URL is the base URL of the OpenAI-compatible API endpoint.
	URL string `yaml:"url"`
}

// Validate checks that required configuration values are present and valid.
func (cfg Config) Validate() error {
	if cfg.Model == "" {
		return fmt.Errorf("missing model")
	}
	if cfg.Timeout != "" {
		if _, err := time.ParseDuration(cfg.Timeout); err != nil {
			return fmt.Errorf("invalid timeout: %w", err)
		}
	}
	if cfg.URL == "" {
		return fmt.Errorf("missing URL")
	}
	return nil
}

// Client wraps an OpenAI-compatible client with tool execution support.
type Client struct {
	client       *openai.Client
	log          *slog.Logger
	model        string
	registry     *tool.Registry
	systemPrompt string
	timeout      time.Duration
	tools        []openai.Tool
}

// NewClient creates a new LLM client with the provided configuration.
// The registry is optional; if nil, tool calling is disabled.
func NewClient(
	cfg Config,
	registry *tool.Registry,
	log *slog.Logger,
) (*Client, error) {
	if err := cfg.Validate(); err != nil {
		return nil, fmt.Errorf("invalid config: %w", err)
	}

	llm := &Client{
		log:          log,
		model:        cfg.Model,
		systemPrompt: cfg.SystemPrompt,
		registry:     registry,
	}

	if cfg.Timeout == "" {
		llm.timeout = 5 * time.Minute
	} else {
		d, err := time.ParseDuration(cfg.Timeout)
		if err != nil {
			return nil, fmt.Errorf("parse timeout: %v", err)
		}
		llm.timeout = d
	}

	// Setup client.
	clientConfig := openai.DefaultConfig(cfg.Key)
	clientConfig.BaseURL = cfg.URL
	llm.client = openai.NewClientWithConfig(clientConfig)

	// Parse tools.
	if llm.registry != nil {
		for _, name := range llm.registry.List() {
			t, _ := llm.registry.Get(name)
			llm.tools = append(llm.tools, t.OpenAI())
		}
	}

	return llm, nil
}

// ListModels returns available models from the LLM server.
func (c *Client) ListModels(ctx context.Context) ([]openai.Model, error) {
	ctx, cancel := context.WithTimeout(ctx, c.timeout)
	defer cancel()

	res, err := c.client.ListModels(ctx)
	if err != nil {
		return nil, fmt.Errorf("listing models: %w", err)
	}

	return res.Models, nil
}

// DefaultModel returns the configured default model.
func (c *Client) DefaultModel() string {
	return c.model
}

// Query sends messages to the LLM using the specified model.
// If model is empty, uses the default configured model.
// Returns all messages generated during the query, including tool calls
// and tool results. The final message is the last element in the slice.
func (c *Client) Query(
	ctx context.Context,
	messages []openai.ChatCompletionMessage,
	model string,
) ([]openai.ChatCompletionMessage, error) {
	ctx, cancel := context.WithTimeout(ctx, c.timeout)
	defer cancel()

	// Fallback to the default model.
	if model == "" {
		model = c.model
	}

	// Prepend system prompt, if configured and not already present.
	if c.systemPrompt != "" && (len(messages) == 0 ||
		messages[0].Role != openai.ChatMessageRoleSystem) {
		messages = append(
			[]openai.ChatCompletionMessage{{
				Role:    openai.ChatMessageRoleSystem,
				Content: c.systemPrompt,
			}},
			messages...,
		)
	}

	// Track messages generated during this query.
	var generated []openai.ChatCompletionMessage

	// Loop for tool calls.
	for {
		req := openai.ChatCompletionRequest{
			Model:    model,
			Messages: messages,
		}
		if len(c.tools) > 0 {
			req.Tools = c.tools
		}

		res, err := c.client.CreateChatCompletion(ctx, req)
		if err != nil {
			return nil, fmt.Errorf("chat completion: %w", err)
		}
		if len(res.Choices) == 0 {
			return nil, fmt.Errorf("no response choices returned")
		}

		choice := res.Choices[0]
		message := choice.Message

		// If no tool calls, we're done.
		if len(message.ToolCalls) == 0 {
			generated = append(generated, message)
			return generated, nil
		}

		// Add assistant message with tool calls to history.
		generated = append(generated, message)
		messages = append(messages, message)

		// Process each tool call.
		for _, tc := range message.ToolCalls {
			c.log.InfoContext(
				ctx,
				"calling tool",
				slog.String("name", tc.Function.Name),
				slog.String("args", tc.Function.Arguments),
			)

			result, err := c.registry.Execute(
				ctx, tc.Function.Name, tc.Function.Arguments,
			)
			if err != nil {
				c.log.Error(
					"failed to call tool",
					slog.Any("error", err),
					slog.String("name", tc.Function.Name),
				)
				result = fmt.Sprintf(
					`{"ok": false, "error": %q}`, err,
				)
			} else {
				c.log.Info(
					"called tool",
					slog.String("name", tc.Function.Name),
				)
			}

			// Content cannot be empty.
			if strings.TrimSpace(result) == "" {
				result = `{"ok": true, "result": null}`
			}

			// Add tool result to messages.
			toolResult := openai.ChatCompletionMessage{
				Role:       openai.ChatMessageRoleTool,
				Content:    result,
				Name:       tc.Function.Name,
				ToolCallID: tc.ID,
			}
			generated = append(generated, toolResult)
			messages = append(messages, toolResult)
		}
		// Loop to get LLM's response after tool execution.
	}
}

// StreamEvent wraps a ChatCompletionMessage produced during streaming.
type StreamEvent struct {
	Message openai.ChatCompletionMessage
}

// QueryStream sends messages to the LLM using the specified model and
// streams results. Each complete message (assistant reply, tool call,
// tool result) is sent to the events channel as it becomes available.
// The channel is closed before returning.
// Returns all messages generated during the query.
func (c *Client) QueryStream(
	ctx context.Context,
	messages []openai.ChatCompletionMessage,
	model string,
	events chan<- StreamEvent,
) error {
	defer close(events)

	ctx, cancel := context.WithTimeout(ctx, c.timeout)
	defer cancel()

	// Fallback to the default model.
	if model == "" {
		model = c.model
	}

	// Prepend system prompt, if configured and not already present.
	if c.systemPrompt != "" && (len(messages) == 0 ||
		messages[0].Role != openai.ChatMessageRoleSystem) {
		messages = append(
			[]openai.ChatCompletionMessage{{
				Role:    openai.ChatMessageRoleSystem,
				Content: c.systemPrompt,
			}},
			messages...,
		)
	}

	// Loop for tool calls.
	for {
		req := openai.ChatCompletionRequest{
			Model:    model,
			Messages: messages,
		}
		if len(c.tools) > 0 {
			req.Tools = c.tools
		}

		stream, err := c.client.CreateChatCompletionStream(ctx, req)
		if err != nil {
			return fmt.Errorf("chat completion stream: %w", err)
		}

		// Accumulate the streamed response.
		var (
			content   strings.Builder
			reasoning strings.Builder
			toolCalls []openai.ToolCall
			role      string
		)
		for {
			chunk, err := stream.Recv()
			if errors.Is(err, io.EOF) {
				break
			}
			if err != nil {
				stream.Close()
				return fmt.Errorf("stream recv: %w", err)
			}
			if len(chunk.Choices) == 0 {
				continue
			}

			// Check the first Choice. Only one is expected, since
			// our request does not set N > 1.
			delta := chunk.Choices[0].Delta
			if delta.Role != "" {
				role = delta.Role
			}
			if delta.Content != "" {
				content.WriteString(delta.Content)
			}
			if delta.ReasoningContent != "" {
				reasoning.WriteString(delta.ReasoningContent)
			}

			// Accumulate tool call deltas by index.
			for _, tc := range delta.ToolCalls {
				i := 0
				if tc.Index != nil {
					i = *tc.Index
				}
				// Grow the slice as needed.
				for len(toolCalls) <= i {
					toolCalls = append(
						toolCalls,
						openai.ToolCall{
							Type: openai.ToolTypeFunction,
						},
					)
				}
				if tc.ID != "" {
					toolCalls[i].ID = tc.ID
				}
				if tc.Function.Name != "" {
					toolCalls[i].Function.Name +=
						tc.Function.Name
				}
				if tc.Function.Arguments != "" {
					toolCalls[i].Function.Arguments +=
						tc.Function.Arguments
				}
			}
		}
		stream.Close()

		// Build the complete message from accumulated buffers.
		message := openai.ChatCompletionMessage{
			Role:             role,
			Content:          content.String(),
			ReasoningContent: reasoning.String(),
			ToolCalls:        toolCalls,
		}
		events <- StreamEvent{Message: message}

		// If no tool calls, we're done.
		if len(toolCalls) == 0 {
			return nil
		}

		// Add assistant message with tool calls to history.
		messages = append(messages, message)

		// Process each tool call.
		for _, tc := range message.ToolCalls {
			c.log.InfoContext(
				ctx,
				"calling tool",
				slog.String("name", tc.Function.Name),
				slog.String("args", tc.Function.Arguments),
			)

			result, err := c.registry.Execute(
				ctx, tc.Function.Name, tc.Function.Arguments,
			)
			if err != nil {
				c.log.Error(
					"failed to call tool",
					slog.Any("error", err),
					slog.String("name", tc.Function.Name),
				)
				result = fmt.Sprintf(
					`{"ok": false, "error": %q}`, err,
				)
			} else {
				c.log.Info(
					"called tool",
					slog.String("name", tc.Function.Name),
				)
			}
			// Content cannot be empty.
			if strings.TrimSpace(result) == "" {
				result = `{"ok": true, "result": null}`
			}

			// Add tool result to messages.
			toolResult := openai.ChatCompletionMessage{
				Content:    result,
				Name:       tc.Function.Name,
				Role:       openai.ChatMessageRoleTool,
				ToolCallID: tc.ID,
			}
			messages = append(messages, toolResult)
			events <- StreamEvent{Message: toolResult}
		}
		// Loop to get LLM's response after tool execution.
	}
}