// Package openai is a minimal client for the OpenAI Responses API (function calling) and the Embeddings API.
// Shapes follow https://developers.openai.com/api/docs/guides/function-calling and /guides/embeddings (checked 2026-10-08).
package openai

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"time"
)

type Client struct {
	BaseURL string // default https://api.openai.com/v1
	KeyFile string // read per call so a rotated key file is picked up without restart
	HTTP    *http.Client
	keyFn   func() (string, error)
}

func New(baseURL string, keyFn func() (string, error)) *Client {
	if baseURL == "" {
		baseURL = "https://api.openai.com/v1"
	}
	return &Client{BaseURL: baseURL, keyFn: keyFn, HTTP: &http.Client{Timeout: 120 * time.Second}}
}

// Tool is a function tool definition (strict mode: additionalProperties false and every property required).
type Tool struct {
	Type        string         `json:"type"`
	Name        string         `json:"name"`
	Description string         `json:"description"`
	Parameters  map[string]any `json:"parameters"`
	Strict      bool           `json:"strict"`
}

// Item is one input/output item of the Responses API. Only the fields this agent uses are modelled.
type Item struct {
	Type      string `json:"type"`                // message | function_call | function_call_output
	Role      string `json:"role,omitempty"`      // message: system | user | assistant
	Content   any    `json:"content,omitempty"`   // message: string (input) or []ContentPart (output)
	CallID    string `json:"call_id,omitempty"`   // function_call / function_call_output
	Name      string `json:"name,omitempty"`      // function_call
	Arguments string `json:"arguments,omitempty"` // function_call (JSON string)
	Output    string `json:"output,omitempty"`    // function_call_output
	ID        string `json:"id,omitempty"`
	Status    string `json:"status,omitempty"`
}

type ContentPart struct {
	Type string `json:"type"`
	Text string `json:"text"`
}

type Request struct {
	Model              string `json:"model"`
	Input              []Item `json:"input"`
	Tools              []Tool `json:"tools,omitempty"`
	ToolChoice         any    `json:"tool_choice,omitempty"` // "auto" | "required" | {"type":"function","name":...}
	PreviousResponseID string `json:"previous_response_id,omitempty"`
	MaxOutputTokens    int    `json:"max_output_tokens,omitempty"`
	ParallelToolCalls  *bool  `json:"parallel_tool_calls,omitempty"`
	Store              *bool  `json:"store,omitempty"`
}

type Response struct {
	ID     string `json:"id"`
	Status string `json:"status"`
	Model  string `json:"model"`
	Output []Item `json:"output"`
	Usage  struct {
		InputTokens  int `json:"input_tokens"`
		OutputTokens int `json:"output_tokens"`
		TotalTokens  int `json:"total_tokens"`
	} `json:"usage"`
	Error *struct {
		Message string `json:"message"`
		Type    string `json:"type"`
	} `json:"error"`
}

// FunctionCalls returns the function_call items of the output.
func (r *Response) FunctionCalls() []Item {
	var out []Item
	for _, it := range r.Output {
		if it.Type == "function_call" {
			out = append(out, it)
		}
	}
	return out
}

// Text concatenates assistant message text parts.
func (r *Response) Text() string {
	var b bytes.Buffer
	for _, it := range r.Output {
		if it.Type != "message" {
			continue
		}
		if parts, ok := it.Content.([]any); ok {
			for _, p := range parts {
				if m, ok := p.(map[string]any); ok {
					if t, ok := m["text"].(string); ok {
						b.WriteString(t)
					}
				}
			}
		}
	}
	return b.String()
}

func (c *Client) do(ctx context.Context, path string, body any, out any) error {
	key, err := c.keyFn()
	if err != nil {
		return fmt.Errorf("openai key: %w", err)
	}
	if key == "" {
		return fmt.Errorf("openai key is empty (secret not registered yet)")
	}
	b, _ := json.Marshal(body)
	req, err := http.NewRequestWithContext(ctx, "POST", c.BaseURL+path, bytes.NewReader(b))
	if err != nil {
		return err
	}
	req.Header.Set("Authorization", "Bearer "+key)
	req.Header.Set("Content-Type", "application/json")
	resp, err := c.HTTP.Do(req)
	if err != nil {
		return err
	}
	defer resp.Body.Close()
	rb, _ := io.ReadAll(io.LimitReader(resp.Body, 8<<20))
	if resp.StatusCode/100 != 2 {
		return fmt.Errorf("openai %s: status %d: %s", path, resp.StatusCode, truncate(string(rb), 600))
	}
	return json.Unmarshal(rb, out)
}

func (c *Client) CreateResponse(ctx context.Context, req Request) (*Response, error) {
	var r Response
	if err := c.do(ctx, "/responses", req, &r); err != nil {
		return nil, err
	}
	if r.Error != nil {
		return nil, fmt.Errorf("openai response error: %s", r.Error.Message)
	}
	return &r, nil
}

type embedRequest struct {
	Model string   `json:"model"`
	Input []string `json:"input"`
}

type embedResponse struct {
	Data []struct {
		Index     int       `json:"index"`
		Embedding []float32 `json:"embedding"`
	} `json:"data"`
}

// Embed returns one vector per input (text-embedding-3-small: 1536 dimensions by default).
func (c *Client) Embed(ctx context.Context, model string, inputs []string) ([][]float32, error) {
	var r embedResponse
	if err := c.do(ctx, "/embeddings", embedRequest{Model: model, Input: inputs}, &r); err != nil {
		return nil, err
	}
	out := make([][]float32, len(inputs))
	for _, d := range r.Data {
		if d.Index >= 0 && d.Index < len(out) {
			out[d.Index] = d.Embedding
		}
	}
	return out, nil
}

func truncate(s string, n int) string {
	if len(s) <= n {
		return s
	}
	return s[:n] + "..."
}