package businessapi

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"mime/multipart"
	"net/http"
	"net/url"
)

// graphAPIGet performs an authenticated GET to the Graph API and unmarshals the response.
func (c *Client) graphAPIGet(ctx context.Context, path string, params url.Values, result any) error {
	u := fmt.Sprintf("https://graph.facebook.com/%s/%s", c.config.APIVersion, path)
	if len(params) > 0 {
		u += "?" + params.Encode()
	}

	req, err := http.NewRequestWithContext(ctx, "GET", u, nil)
	if err != nil {
		return fmt.Errorf("failed to create request: %w", err)
	}
	req.Header.Set("Authorization", "Bearer "+c.config.AccessToken)

	return c.executeRequest(req, result)
}

// graphAPIPost performs an authenticated POST with a JSON body.
// body may be nil for action-only endpoints (e.g. publish a flow).
func (c *Client) graphAPIPost(ctx context.Context, path string, body any, result any) error {
	u := fmt.Sprintf("https://graph.facebook.com/%s/%s", c.config.APIVersion, path)

	var reqBody io.Reader
	if body != nil {
		jsonData, err := json.Marshal(body)
		if err != nil {
			return fmt.Errorf("failed to marshal request body: %w", err)
		}
		reqBody = bytes.NewBuffer(jsonData)
	}

	req, err := http.NewRequestWithContext(ctx, "POST", u, reqBody)
	if err != nil {
		return fmt.Errorf("failed to create request: %w", err)
	}
	req.Header.Set("Authorization", "Bearer "+c.config.AccessToken)
	if body != nil {
		req.Header.Set("Content-Type", "application/json")
	}

	return c.executeRequest(req, result)
}

// graphAPIPostForm performs an authenticated POST with multipart form fields.
func (c *Client) graphAPIPostForm(ctx context.Context, path string, fields map[string]string, result any) error {
	u := fmt.Sprintf("https://graph.facebook.com/%s/%s", c.config.APIVersion, path)

	var buf bytes.Buffer
	writer := multipart.NewWriter(&buf)
	for k, v := range fields {
		if err := writer.WriteField(k, v); err != nil {
			return fmt.Errorf("failed to write form field %s: %w", k, err)
		}
	}
	if err := writer.Close(); err != nil {
		return fmt.Errorf("failed to close multipart writer: %w", err)
	}

	req, err := http.NewRequestWithContext(ctx, "POST", u, &buf)
	if err != nil {
		return fmt.Errorf("failed to create request: %w", err)
	}
	req.Header.Set("Authorization", "Bearer "+c.config.AccessToken)
	req.Header.Set("Content-Type", writer.FormDataContentType())

	return c.executeRequest(req, result)
}

// graphAPIDelete performs an authenticated DELETE request.
func (c *Client) graphAPIDelete(ctx context.Context, path string, params url.Values) error {
	u := fmt.Sprintf("https://graph.facebook.com/%s/%s", c.config.APIVersion, path)
	if len(params) > 0 {
		u += "?" + params.Encode()
	}

	req, err := http.NewRequestWithContext(ctx, "DELETE", u, nil)
	if err != nil {
		return fmt.Errorf("failed to create request: %w", err)
	}
	req.Header.Set("Authorization", "Bearer "+c.config.AccessToken)

	return c.executeRequest(req, nil)
}

// executeRequest runs an HTTP request, handles error responses, and optionally unmarshals the body.
func (c *Client) executeRequest(req *http.Request, result any) error {
	resp, err := c.httpClient.Do(req)
	if err != nil {
		return fmt.Errorf("request failed: %w", err)
	}
	defer resp.Body.Close()

	body, err := io.ReadAll(resp.Body)
	if err != nil {
		return fmt.Errorf("failed to read response: %w", err)
	}

	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		var errResp ErrorResponse
		if err := json.Unmarshal(body, &errResp); err == nil && errResp.Error.Message != "" {
			return fmt.Errorf("API error: %s (code: %d)", errResp.Error.Message, errResp.Error.Code)
		}
		return fmt.Errorf("API returned status %d: %s", resp.StatusCode, string(body))
	}

	if result != nil && len(body) > 0 {
		if err := json.Unmarshal(body, result); err != nil {
			return fmt.Errorf("failed to parse response: %w", err)
		}
	}
	return nil
}

// postToMessagesEndpoint POSTs an arbitrary body to the phone number's /messages endpoint.
// Used by sendMessage (typed) and by reaction/read-receipt (different top-level shape).
func (c *Client) postToMessagesEndpoint(ctx context.Context, body any) (string, error) {
	path := c.config.PhoneNumberID + "/messages"

	jsonData, err := json.Marshal(body)
	if err != nil {
		return "", fmt.Errorf("failed to marshal message: %w", err)
	}

	u := fmt.Sprintf("https://graph.facebook.com/%s/%s", c.config.APIVersion, path)
	req, err := http.NewRequestWithContext(ctx, "POST", u, bytes.NewBuffer(jsonData))
	if err != nil {
		return "", fmt.Errorf("failed to create request: %w", err)
	}
	req.Header.Set("Authorization", "Bearer "+c.config.AccessToken)
	req.Header.Set("Content-Type", "application/json")

	resp, err := c.httpClient.Do(req)
	if err != nil {
		return "", fmt.Errorf("failed to send request: %w", err)
	}
	defer resp.Body.Close()

	respBody, err := io.ReadAll(resp.Body)
	if err != nil {
		return "", fmt.Errorf("failed to read response: %w", err)
	}

	if resp.StatusCode != http.StatusOK {
		var errResp ErrorResponse
		if err := json.Unmarshal(respBody, &errResp); err == nil {
			return "", fmt.Errorf("API error: %s (code: %d)", errResp.Error.Message, errResp.Error.Code)
		}
		return "", fmt.Errorf("API returned status %d: %s", resp.StatusCode, string(respBody))
	}

	var sendResp SendMessageResponse
	if err := json.Unmarshal(respBody, &sendResp); err != nil {
		return "", nil // some endpoints (read receipt) return non-message JSON
	}
	if len(sendResp.Messages) == 0 {
		return "", nil
	}
	return sendResp.Messages[0].ID, nil
}