package fetcher

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

// PageResult contains raw page data and the after token.
type PageResult struct {
	Posts   []JSONPost
	After   string
	Latency time.Duration
}

// buildSearchURL constructs the Reddit search.json URL.
func buildSearchURL(query string, after string, limit int) (string, error) {
	u, err := url.Parse("https://www.reddit.com/search.json")
	if err != nil {
		return "", err
	}
	q := u.Query()
	q.Set("q", query)
	q.Set("sort", "new")
	q.Set("type", "link")
	q.Set("limit", fmt.Sprintf("%d", limit))
	q.Set("restrict_sr", "false")
	if after != "" {
		q.Set("after", after)
	}
	u.RawQuery = q.Encode()
	return u.String(), nil
}

// FetchPage fetches a single search.json page and returns PageResult.
func (c *Client) FetchPage(ctx context.Context, query string, after string, limit int) (PageResult, error) {
	var res PageResult
	urlStr, err := buildSearchURL(query, after, limit)
	if err != nil {
		return res, err
	}
	// wait for rate limiter
	if c.limiter != nil {
		if err := c.limiter.Wait(ctx); err != nil {
			return res, err
		}
	}
	start := time.Now()
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, urlStr, nil)
	if err != nil {
		return res, err
	}
	req.Header.Set("User-Agent", c.userAgent)
	req.Header.Set("Accept", "application/json")

	resp, err := c.httpClient.Do(req)
	if err != nil {
		return res, err
	}
	defer resp.Body.Close()
	res.Latency = time.Since(start)

	if resp.StatusCode == http.StatusTooManyRequests {
		// honor Retry-After if given (seconds or HTTP-date)
		if ra := resp.Header.Get("Retry-After"); ra != "" {
			// Try seconds first
			if secs, perr := strconv.Atoi(ra); perr == nil {
				time.Sleep(time.Duration(secs) * time.Second)
			} else if d, derr := http.ParseTime(ra); derr == nil {
				// If HTTP-date, compute duration until then
				dur := time.Until(d)
				if dur > 0 {
					time.Sleep(dur)
				}
			}
		}
		return res, fmt.Errorf("rate limited: 429")
	}

	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		body, _ := io.ReadAll(resp.Body)
		return res, fmt.Errorf("http %d: %s", resp.StatusCode, string(body))
	}

	var api APIResponse
	dec := json.NewDecoder(resp.Body)
	if err := dec.Decode(&api); err != nil {
		return res, err
	}
	for _, child := range api.Data.Children {
		res.Posts = append(res.Posts, child.Data)
	}
	res.After = api.Data.After
	return res, nil
}