package threadsapi

import (
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"strings"
	"time"

)

type PublishResult struct {
	MediaID   string `json:"media_id"`
	Permalink string `json:"permalink"`
}

type PublishTextInput struct {
	ThreadsUserID string
	AccessToken   string
	Text          string
	TopicTag      string
	ImageURL      string
	ImageURLs     []string
}

type PublishReplyInput struct {
	ThreadsUserID string
	AccessToken   string
	ReplyToID     string
	Text          string
	ImageURL      string
	ImageURLs     []string
}

func collectImageURLs(single string, list []string) []string {
	if len(list) > 0 {
		return normalizeImageURLs(list)
	}
	single = strings.TrimSpace(single)
	if single == "" {
		return nil
	}
	return []string{single}
}

// PublishText posts a new text or image thread via Graph API.
func PublishText(ctx context.Context, in PublishTextInput) (*PublishResult, error) {
	return publishMedia(ctx, publishMediaInput{
		ThreadsUserID: in.ThreadsUserID,
		AccessToken:   in.AccessToken,
		Text:          in.Text,
		TopicTag:      in.TopicTag,
		ImageURLs:     collectImageURLs(in.ImageURL, in.ImageURLs),
	})
}

// PublishReply posts a text or image reply via Graph API.
func PublishReply(ctx context.Context, in PublishReplyInput) (*PublishResult, error) {
	replyTo := strings.TrimSpace(in.ReplyToID)
	if replyTo == "" {
		return nil, fmt.Errorf("reply_to_id is required")
	}
	return publishMedia(ctx, publishMediaInput{
		ThreadsUserID: in.ThreadsUserID,
		AccessToken:   in.AccessToken,
		Text:          in.Text,
		ReplyToID:     replyTo,
		ImageURLs:     collectImageURLs(in.ImageURL, in.ImageURLs),
	})
}

func urlValues(token string) url.Values {
	params := url.Values{}
	params.Set("access_token", token)
	return params
}

func postThreadsContainer(ctx context.Context, userID string, params url.Values) (string, error) {
	endpoint := graphBaseURL + "/" + userID + "/threads?" + params.Encode()
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, endpoint, nil)
	if err != nil {
		return "", err
	}
	body, status, err := doRequest(req)
	if err != nil {
		return "", err
	}
	if status != http.StatusOK {
		return "", parseAPIError(body, status)
	}
	var payload struct {
		ID string `json:"id"`
	}
	if err := json.Unmarshal(body, &payload); err != nil {
		return "", err
	}
	if strings.TrimSpace(payload.ID) == "" {
		return "", fmt.Errorf("threads api did not return container id")
	}
	return payload.ID, nil
}

func createTextContainer(ctx context.Context, userID, token, text, topicTag string) (string, error) {
	params := urlValues(token)
	params.Set("media_type", "TEXT")
	params.Set("text", text)
	if tag := normalizeTopicTag(topicTag); tag != "" {
		params.Set("topic_tag", tag)
	}
	return postThreadsContainer(ctx, userID, params)
}

func normalizeTopicTag(value string) string {
	tag := strings.TrimSpace(value)
	tag = strings.TrimLeft(tag, "#")
	tag = strings.TrimSpace(tag)
	if len([]rune(tag)) > 40 {
		runes := []rune(tag)
		tag = string(runes[:40])
	}
	return tag
}

func createImageContainer(ctx context.Context, userID, token, text, imageURL, topicTag string) (string, error) {
	params := urlValues(token)
	params.Set("media_type", "IMAGE")
	params.Set("image_url", imageURL)
	if text != "" {
		params.Set("text", text)
	}
	if tag := normalizeTopicTag(topicTag); tag != "" {
		params.Set("topic_tag", tag)
	}
	return postThreadsContainer(ctx, userID, params)
}

func createImageReplyContainer(ctx context.Context, userID, token, replyTo, text, imageURL string) (string, error) {
	params := urlValues(token)
	params.Set("media_type", "IMAGE")
	params.Set("image_url", imageURL)
	if text != "" {
		params.Set("text", text)
	}
	params.Set("reply_to_id", replyTo)
	return postThreadsContainer(ctx, userID, params)
}

func createReplyContainer(ctx context.Context, userID, token, replyTo, text string) (string, error) {
	params := urlValues(token)
	params.Set("media_type", "TEXT")
	params.Set("text", text)
	params.Set("reply_to_id", replyTo)
	return postThreadsContainer(ctx, userID, params)
}

func publishContainer(ctx context.Context, userID, token, containerID string) (string, error) {
	params := url.Values{}
	params.Set("access_token", token)
	params.Set("creation_id", containerID)
	endpoint := graphBaseURL + "/" + userID + "/threads_publish?" + params.Encode()
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, endpoint, nil)
	if err != nil {
		return "", err
	}
	body, status, err := doRequest(req)
	if err != nil {
		return "", err
	}
	if status != http.StatusOK {
		return "", parseAPIError(body, status)
	}
	var payload struct {
		ID string `json:"id"`
	}
	if err := json.Unmarshal(body, &payload); err != nil {
		return "", err
	}
	if strings.TrimSpace(payload.ID) == "" {
		return "", fmt.Errorf("threads publish did not return media id")
	}
	return payload.ID, nil
}

func waitForContainerReady(ctx context.Context, containerID, token string, maxAttempts int) error {
	if maxAttempts <= 0 {
		maxAttempts = 12
	}
	for attempt := 0; attempt < maxAttempts; attempt++ {
		if attempt > 0 {
			select {
			case <-ctx.Done():
				return ctx.Err()
			case <-time.After(2 * time.Second):
			}
		}
		params := url.Values{}
		params.Set("access_token", token)
		params.Set("fields", "status,error_message")
		endpoint := graphBaseURL + "/" + containerID + "?" + params.Encode()
		req, err := http.NewRequestWithContext(ctx, http.MethodGet, endpoint, nil)
		if err != nil {
			return err
		}
		body, status, err := doRequest(req)
		if err != nil {
			return err
		}
		if status != http.StatusOK {
			return parseAPIError(body, status)
		}
		var payload struct {
			Status       string `json:"status"`
			ErrorMessage string `json:"error_message"`
		}
		if err := json.Unmarshal(body, &payload); err != nil {
			return err
		}
		switch strings.ToUpper(strings.TrimSpace(payload.Status)) {
		case "FINISHED":
			return nil
		case "ERROR", "EXPIRED":
			detail := strings.TrimSpace(payload.ErrorMessage)
			if detail != "" {
				return fmt.Errorf("threads container %s: %s", strings.ToLower(payload.Status), detail)
			}
			return fmt.Errorf("threads container status %s", payload.Status)
		}
	}
	return fmt.Errorf("threads container not ready in time")
}

func verifyReplyTarget(ctx context.Context, replyTo, token string) error {
	replyTo = strings.TrimSpace(replyTo)
	if replyTo == "" {
		return fmt.Errorf("reply_to_id is required")
	}
	if !IsNumericMediaID(replyTo) {
		return fmt.Errorf("reply_to_id 必須是 Threads 數字 media id，目前為 %q", replyTo)
	}
	params := url.Values{}
	params.Set("access_token", token)
	params.Set("fields", "id,is_reply,permalink")
	endpoint := graphBaseURL + "/" + url.PathEscape(replyTo) + "?" + params.Encode()
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, endpoint, nil)
	if err != nil {
		return err
	}
	body, status, err := doRequest(req)
	if err != nil {
		return err
	}
	if status != http.StatusOK {
		return fmt.Errorf("無法讀取回覆目標 %s：%w", replyTo, parseAPIError(body, status))
	}
	var payload struct {
		ID string `json:"id"`
	}
	if err := json.Unmarshal(body, &payload); err != nil {
		return fmt.Errorf("parse reply target: %w", err)
	}
	if strings.TrimSpace(payload.ID) == "" {
		return fmt.Errorf("回覆目標 %s 不存在或無權限讀取", replyTo)
	}
	return nil
}

func fetchPermalink(ctx context.Context, mediaID, token string) (string, error) {
	params := url.Values{}
	params.Set("access_token", token)
	params.Set("fields", "permalink")
	endpoint := graphBaseURL + "/" + mediaID + "?" + params.Encode()
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, endpoint, nil)
	if err != nil {
		return "", err
	}
	body, status, err := doRequest(req)
	if err != nil || status != http.StatusOK {
		return "", err
	}
	var payload struct {
		Permalink string `json:"permalink"`
	}
	if err := json.Unmarshal(body, &payload); err != nil {
		return "", err
	}
	return strings.TrimSpace(payload.Permalink), nil
}

func doRequest(req *http.Request) ([]byte, int, error) {
	client := &http.Client{Timeout: 25 * time.Second}
	res, err := client.Do(req)
	if err != nil {
		return nil, 0, err
	}
	defer res.Body.Close()
	body, err := io.ReadAll(io.LimitReader(res.Body, 1<<20))
	if err != nil {
		return nil, res.StatusCode, err
	}
	return body, res.StatusCode, nil
}