// Package steam implements a Steam free-games provider.
//
// Two sources, both without login (see AGENTS.md, free-games-notifier):
//   - Free to Keep: HTML scrape of the search page
//     https://store.steampowered.com/search/?maxprice=free&specials=1
//   - Free Weekend: JSON API https://store.steampowered.com/api/featuredcategories/
package steam

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

	"gogs.netdome.biz/paul/cheapo/internal/game"
	"golang.org/x/net/html"
)

const (
	searchURL     = "https://store.steampowered.com/search/?maxprice=free&specials=1"
	dealsURL      = "https://store.steampowered.com/search/?specials=1"
	featuredURL   = "https://store.steampowered.com/api/featuredcategories/"
	appDetailsURL = "https://store.steampowered.com/api/appdetails"
	userAgent     = "Mozilla/5.0 (X11; Linux x86_64; rv:127.0) Gecko/20100101 Firefox/127.0"
)

// Client queries the public Steam storefront.
type Client struct {
	HTTP *http.Client
}

// NewClient returns a Steam client.
func NewClient() *Client {
	return &Client{HTTP: &http.Client{Timeout: 30 * time.Second}}
}

// Name implements game.Provider.
func (c *Client) Name() string { return "steam" }

func (c *Client) get(ctx context.Context, u string) (*http.Response, error) {
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, u, nil)
	if err != nil {
		return nil, fmt.Errorf("steam: %w", err)
	}
	req.Header.Set("User-Agent", userAgent)
	resp, err := c.HTTP.Do(req)
	if err != nil {
		return nil, fmt.Errorf("steam: request failed: %w", err)
	}
	if resp.StatusCode != http.StatusOK {
		resp.Body.Close()
		return nil, fmt.Errorf("steam: unexpected status %s for %s", resp.Status, u)
	}
	return resp, nil
}

// GetFreeGames returns all current Steam free offers (free to keep + free weekend).
func (c *Client) GetFreeGames(ctx context.Context) ([]game.Game, error) {
	keep, err := c.getFreeToKeep(ctx)
	if err != nil {
		return nil, err
	}
	weekend, err := c.getFreeWeekend(ctx)
	if err != nil {
		// The weekend API is flaky/nonessential; don't fail the whole query.
		weekend = nil
	}
	games := append(keep, weekend...)
	return games, nil
}

// --- Free to Keep (HTML search page) ---

var (
	reAppID       = regexp.MustCompile(`/app/(\d+)`)
	rePriceStrip  = regexp.MustCompile(`\s+`)
	reDiscountPct = regexp.MustCompile(`-(\d+)%`)
)

func (c *Client) getFreeToKeep(ctx context.Context) ([]game.Game, error) {
	resp, err := c.get(ctx, searchURL)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()

	return c.parseSearchRows(resp.Body, parseResultRow)
}

// GetDeals returns currently discounted Steam games (specials search page,
// any discount), sorted by discount (deepest first).
func (c *Client) GetDeals(ctx context.Context) ([]game.Game, error) {
	resp, err := c.get(ctx, dealsURL)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()

	games, err := c.parseSearchRows(resp.Body, parseDealRow)
	if err != nil {
		return nil, err
	}
	sort.Slice(games, func(i, j int) bool {
		return games[i].DiscountPct > games[j].DiscountPct
	})
	return games, nil
}

// parseSearchRows walks a Steam search results page and applies parse per
// `a.search_result_row`, deduplicating by ID.
func (c *Client) parseSearchRows(r io.Reader, parse func(*html.Node) *game.Game) ([]game.Game, error) {
	doc, err := html.Parse(r)
	if err != nil {
		return nil, fmt.Errorf("steam: parse search page: %w", err)
	}

	var games []game.Game
	seen := map[string]bool{}

	var walk func(*html.Node)
	walk = func(n *html.Node) {
		if n.Type == html.ElementNode && n.Data == "a" {
			cls := classAttr(n)
			if strings.Contains(cls, "search_result_row") {
				if g := parse(n); g != nil && !seen[g.ID] {
					seen[g.ID] = true
					games = append(games, *g)
				}
			}
		}
		for ch := n.FirstChild; ch != nil; ch = ch.NextSibling {
			walk(ch)
		}
	}
	walk(doc)
	return games, nil
}

func classAttr(n *html.Node) string {
	for _, a := range n.Attr {
		if a.Key == "class" {
			return a.Val
		}
	}
	return ""
}

// parseResultRow extracts one game from a `a.search_result_row` element.
func parseResultRow(a *html.Node) *game.Game {
	href := ""
	for _, at := range a.Attr {
		if at.Key == "href" {
			href = at.Val
		}
	}
	m := reAppID.FindStringSubmatch(href)
	if m == nil {
		return nil
	}
	appID := m[1]

	var title, price, discount string
	var find func(*html.Node)
	find = func(n *html.Node) {
		if n.Type == html.ElementNode {
			cls := classAttr(n)
			switch {
			case strings.Contains(cls, "title") && title == "":
				title = textOf(n)
			case strings.Contains(cls, "discount_final_price") && price == "":
				price = textOf(n)
			case strings.Contains(cls, "discount_pct") && discount == "":
				discount = textOf(n)
			}
		}
		for ch := n.FirstChild; ch != nil; ch = ch.NextSibling {
			find(ch)
		}
	}
	find(a)

	// Free filter: price text "Free" (localized variants start with "Free" or
	// are "0"), or a 100 % discount badge.
	price = rePriceStrip.ReplaceAllString(price, " ")
	free := strings.HasPrefix(price, "Free") || price == "0" ||
		strings.Contains(discount, "-100%") || strings.Contains(discount, "100%")
	if !free {
		return nil
	}

	return &game.Game{
		Title:    strings.TrimSpace(title),
		ID:       "steam-" + appID,
		Slug:     appID,
		URL:      "https://store.steampowered.com/app/" + appID + "/",
		Store:    "steam",
		Kind:     "free-to-keep",
		PriceFmt: strings.TrimSpace(strings.TrimPrefix(price, "Statt ")),
	}
}

// parseDealRow extracts one discounted game from a `a.search_result_row` on
// the specials page (any discount, with original/final price and percent).
func parseDealRow(a *html.Node) *game.Game {
	href := ""
	for _, at := range a.Attr {
		if at.Key == "href" {
			href = at.Val
		}
	}
	m := reAppID.FindStringSubmatch(href)
	if m == nil {
		return nil
	}
	appID := m[1]

	var title, orig, final, discount string
	var find func(*html.Node)
	find = func(n *html.Node) {
		if n.Type == html.ElementNode {
			cls := classAttr(n)
			switch {
			case strings.Contains(cls, "title") && title == "":
				title = textOf(n)
			case strings.Contains(cls, "discount_original_price") && orig == "":
				orig = textOf(n)
			case strings.Contains(cls, "discount_final_price") && final == "":
				final = textOf(n)
			case strings.Contains(cls, "discount_pct") && discount == "":
				discount = textOf(n)
			}
		}
		for ch := n.FirstChild; ch != nil; ch = ch.NextSibling {
			find(ch)
		}
	}
	find(a)

	if strings.TrimSpace(final) == "" {
		return nil
	}
	pct := 0
	if dm := reDiscountPct.FindStringSubmatch(discount); dm != nil {
		pct, _ = strconv.Atoi(dm[1])
	}
	if pct <= 0 {
		return nil
	}

	return &game.Game{
		Title:         strings.TrimSpace(title),
		ID:            "steam-" + appID,
		Slug:          appID,
		URL:           "https://store.steampowered.com/app/" + appID + "/",
		Store:         "steam",
		Kind:          "deal",
		PriceFmt:      strings.TrimSpace(orig),
		FinalPriceFmt: strings.TrimSpace(final),
		DiscountPct:   pct,
	}
}

func textOf(n *html.Node) string {
	var b strings.Builder
	var visit func(*html.Node)
	visit = func(x *html.Node) {
		if x.Type == html.TextNode {
			b.WriteString(x.Data)
		}
		for ch := x.FirstChild; ch != nil; ch = ch.NextSibling {
			visit(ch)
		}
	}
	visit(n)
	return b.String()
}

// --- Free Weekend (featured categories JSON API) ---

type featuredItem struct {
	Name        string `json:"name"`
	HeaderImage string `json:"header_image"`
	URL         string `json:"url"`
	Body        string `json:"body"`
}

type featuredSection struct {
	ID    interface{}    `json:"id"`
	Name  string         `json:"name"`
	Items []featuredItem `json:"items"`
}

func (c *Client) getFreeWeekend(ctx context.Context) ([]game.Game, error) {
	resp, err := c.get(ctx, featuredURL)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()
	body, err := io.ReadAll(resp.Body)
	if err != nil {
		return nil, fmt.Errorf("steam: read featured response: %w", err)
	}

	var sections map[string]featuredSection
	if err := json.Unmarshal(body, &sections); err != nil {
		return nil, fmt.Errorf("steam: decode featured response: %w", err)
	}

	var games []game.Game
	seen := map[string]bool{}
	for _, sec := range sections {
		for _, it := range sec.Items {
			name := strings.ToLower(it.Name)
			bod := strings.ToLower(it.Body)
			if !strings.Contains(name, "free weekend") &&
				!strings.Contains(bod, "free weekend") &&
				!strings.Contains(bod, "play for free") {
				continue
			}
			title, appID := itemTitleAndAppID(ctx, c, it)
			if seen[appID+title] {
				continue
			}
			seen[appID+title] = true
			g := game.Game{
				Title:    title,
				Store:    "steam",
				Kind:     "free-weekend",
				URL:      it.URL,
				Seller:   "",
				PriceFmt: strings.TrimSpace(it.Body),
			}
			if appID != "" {
				g.ID = "steam-" + appID
				g.Slug = appID
			} else {
				g.ID = "steam-weekend-" + title
			}
			games = append(games, g)
		}
	}
	return games, nil
}

var reWeekendTitle = regexp.MustCompile(`(?i)play\s+(.+?)\s+for\s+free`)

// itemTitleAndAppID resolves a meaningful title and the appid for a weekend item.
func itemTitleAndAppID(ctx context.Context, c *Client, it featuredItem) (string, string) {
	appID := ""
	if m := reAppID.FindStringSubmatch(it.URL); m != nil {
		appID = m[1]
	}

	// Prefer a specific name over generic "Free Weekend" labels.
	generic := map[string]bool{"free weekend": true, "free to play": true, "": true}
	if !generic[strings.ToLower(it.Name)] {
		return it.Name, appID
	}
	if m := reWeekendTitle.FindStringSubmatch(it.Body); m != nil {
		return strings.TrimSpace(m[1]), appID
	}
	if appID != "" {
		if name := fetchAppName(ctx, c, appID); name != "" {
			return name, appID
		}
	}
	if it.Name != "" {
		return it.Name, appID
	}
	return "Unknown Free Weekend Game", appID
}

func fetchAppName(ctx context.Context, c *Client, appID string) string {
	u := fmt.Sprintf("%s?appids=%s&l=en", appDetailsURL, url.QueryEscape(appID))
	resp, err := c.get(ctx, u)
	if err != nil {
		return ""
	}
	defer resp.Body.Close()
	var data map[string]struct {
		Data struct {
			Name string `json:"name"`
		} `json:"data"`
	}
	if json.NewDecoder(resp.Body).Decode(&data) != nil {
		return ""
	}
	if d, ok := data[appID]; ok {
		return d.Data.Name
	}
	return ""
}