// Topics: create (POST /posts.json — Discourse creates topics by posting
// the first post with a title), list per category (GET /c/<...>.json) and
// latest (GET /latest.json), fetch one (GET /t/<id>.json).
package discourse

import (
	"context"
	"fmt"
	"strings"
)

// TopicSummary is one row of a topic list.
type TopicSummary struct {
	ID         int    `json:"id"`
	Title      string `json:"title"`
	Slug       string `json:"slug"`
	CategoryID int    `json:"category_id"`
	PostsCount int    `json:"posts_count"`
	CreatedAt  string `json:"created_at"`
	UpdatedAt  string `json:"updated_at"`
	Closed     bool   `json:"closed"`
	Archived   bool   `json:"archived"`
}

// Topic is the full topic payload (GET /t/<id>.json); posts live under
// PostStream.Posts.
type Topic struct {
	ID         int    `json:"id"`
	Title      string `json:"title"`
	Slug       string `json:"slug"`
	CategoryID int    `json:"category_id"`
	CreatedAt  string `json:"created_at"`
	Closed     bool   `json:"closed"`
	Archived   bool   `json:"archived"`
	PostStream struct {
		Posts []Post `json:"posts"`
	} `json:"post_stream"`
}

// CreateTopicRequest creates a topic: title + markdown body + category.
type CreateTopicRequest struct {
	Title    string   `json:"title"`
	Raw      string   `json:"raw"`
	Category int      `json:"category"`
	Tags     []string `json:"tags,omitempty"`
}

// CreateTopicResult is the POST /posts.json response for a topic
// creation: the first post's id plus the new topic's id and slug.
type CreateTopicResult struct {
	PostID    int    `json:"id"`
	TopicID   int    `json:"topic_id"`
	TopicSlug string `json:"topic_slug"`
}

// URL renders the topic's canonical URL on this instance.
func (r CreateTopicResult) URL(baseURL string) string {
	if r.TopicID == 0 {
		return ""
	}
	slug := r.TopicSlug
	if slug == "" {
		slug = "topic"
	}
	return strings.TrimSuffix(baseURL, "/") + "/t/" + slug + "/" + fmt.Sprint(r.TopicID)
}

// CreateTopic posts a new topic into the category and returns its ids.
func (c *Client) CreateTopic(ctx context.Context, req CreateTopicRequest) (*CreateTopicResult, error) {
	if strings.TrimSpace(req.Title) == "" {
		return nil, fmt.Errorf("%w: topic title is required", ErrInvalidRequest)
	}
	if req.Category == 0 {
		return nil, fmt.Errorf("%w: topic category id is required", ErrInvalidRequest)
	}
	var out CreateTopicResult
	if err := c.Post(ctx, "/posts.json", req, &out); err != nil {
		return nil, err
	}
	if out.TopicID == 0 {
		return nil, fmt.Errorf("%w: topic created but response carries no topic_id", ErrMalformedResponse)
	}
	return &out, nil
}

// ListTopics returns the topic list of a category, addressed by id
// (GET /c/<id>.json) or slug (GET /c/<slug>.json). Pass slug="" with id>0
// or id=0 with a slug.
func (c *Client) ListTopics(ctx context.Context, id int, slug string) ([]TopicSummary, error) {
	if id == 0 && slug == "" {
		return nil, fmt.Errorf("%w: category id or slug is required", ErrInvalidRequest)
	}
	var path string
	if id > 0 {
		if slug != "" {
			path = "/c/" + quotePathSegment(slug) + "/" + fmt.Sprint(id) + ".json"
		} else {
			path = "/c/" + fmt.Sprint(id) + ".json"
		}
	} else {
		path = "/c/" + quotePathSegment(slug) + ".json"
	}
	var payload struct {
		TopicList struct {
			Topics []TopicSummary `json:"topics"`
		} `json:"topic_list"`
	}
	if err := c.Get(ctx, path, &payload); err != nil {
		return nil, err
	}
	return payload.TopicList.Topics, nil
}

// LatestTopics returns the instance's latest topic list (GET /latest.json).
func (c *Client) LatestTopics(ctx context.Context) ([]TopicSummary, error) {
	var payload struct {
		TopicList struct {
			Topics []TopicSummary `json:"topics"`
		} `json:"topic_list"`
	}
	if err := c.Get(ctx, "/latest.json", &payload); err != nil {
		return nil, err
	}
	return payload.TopicList.Topics, nil
}

// GetTopic fetches one topic by id, posts included.
func (c *Client) GetTopic(ctx context.Context, id int) (*Topic, error) {
	if id <= 0 {
		return nil, fmt.Errorf("%w: topic id must be > 0", ErrInvalidRequest)
	}
	var topic Topic
	if err := c.Get(ctx, "/t/"+fmt.Sprint(id)+".json", &topic); err != nil {
		return nil, err
	}
	return &topic, nil
}