package fa

import (
	"context"
	"iter"
	"net/url"
	"strconv"

	"github.com/PuerkitoBio/goquery"

	"git.anthrove.art/public/go-fa-api/internal/urls"
)

// browsePerPage is FA's default page size for /browse/. We use it as the
// "this page is full → there's likely another one" threshold because the
// browse feed paginates via POST forms in the UI; detectNextPage's anchor-
// based heuristic doesn't fire on browse responses.
const browsePerPage = 72

// BrowseOptions configures /browse/ filters. Zero-value defaults match
// FA's web UI default: all ratings on, all categories, all art types,
// any species, 72 per page.
//
// The filter fields use FA's internal numeric IDs (1 = "All" / "Any" for
// category, atype, species). The exact list of valid values is huge and
// changes over time; for now we expose them as raw ints rather than
// pretending to enumerate them callers wanting a typed Category enum
// should grab the value off the browse form's <option> elements.
type BrowseOptions struct {
	// Ratings restricts results to these rating levels. nil/empty = all
	// three (general + mature + adult).
	Ratings []Rating

	// Category, ArtType, Species are FA's internal numeric IDs. Zero or 1
	// means "All / Any" (the default).
	Category int
	ArtType  int
	Species  int

	// PerPage is the page size. Valid values match the web UI: 24/36/48/60/72.
	// Zero defaults to 72.
	PerPage int

	// StartPage is the 1-based page to begin iteration on.
	StartPage int

	// MaxPages bounds the iterator. Zero = unbounded (be careful the feed
	// is effectively infinite).
	MaxPages int
}

// Browse iterates FA's global front-page feed (/browse/), newest first.
// Returns the same partially-populated *Submission shape as [Client.Gallery]:
// ID, Title, Author, ThumbURL, Rating. Call [Client.GetSubmission] with
// the ID to load the full record.
//
// The feed is effectively unbounded (millions of submissions across the
// site). Always set [BrowseOptions.MaxPages] in production code; without
// it the iterator will keep fetching until FA returns a partial page.
//
// Note: FA paginates browse via POST forms in the UI; this iterator
// instead uses GET with ?page=N, which is honoured for the rendered HTML.
// "Next page exists?" is inferred from item count: a full page
// (browsePerPage items) means we keep going; anything less is the tail.
func (c *Client) Browse(ctx context.Context, opts BrowseOptions, reqOpts ...Option) iter.Seq2[*Submission, error] {
	return func(yield func(*Submission, error) bool) {
		page := opts.StartPage
		if page < 1 {
			page = 1
		}
		pagesFetched := 0
		for {
			if opts.MaxPages > 0 && pagesFetched >= opts.MaxPages {
				return
			}
			pageURL := buildBrowseURL(page, opts)
			var items []*Submission
			err := c.fetch(ctx, pageURL, func(doc *goquery.Document) error {
				items, _ = parseGalleryPage(doc, c.cfg.jsonListings)
				return nil
			}, reqOpts...)
			if err != nil {
				yield(nil, err)
				return
			}
			pagesFetched++
			if len(items) == 0 {
				return
			}
			for _, s := range items {
				if !yield(s, nil) {
					return
				}
			}
			if len(items) < browsePerPage {
				return
			}
			page++
		}
	}
}

// buildBrowseURL constructs a /browse/ URL with the given page and any
// non-default filter fields. The form fields match what FA's UI POSTs on
// the front-page form; we send them as GET params instead.
func buildBrowseURL(page int, opts BrowseOptions) string {
	// Without any filters set, the simple path-form URL works.
	hasFilters := len(opts.Ratings) != 0 ||
		opts.Category > 1 || opts.ArtType > 1 || opts.Species > 1 ||
		opts.PerPage > 0
	if !hasFilters {
		return urls.Browse(page)
	}

	v := url.Values{}
	if page > 1 {
		v.Set("page", strconv.Itoa(page))
	}
	if opts.PerPage > 0 {
		v.Set("perpage", strconv.Itoa(opts.PerPage))
	}
	if opts.Category > 0 {
		v.Set("cat", strconv.Itoa(opts.Category))
	}
	if opts.ArtType > 0 {
		v.Set("atype", strconv.Itoa(opts.ArtType))
	}
	if opts.Species > 0 {
		v.Set("species", strconv.Itoa(opts.Species))
	}

	ratings := opts.Ratings
	if len(ratings) == 0 {
		ratings = []Rating{RatingGeneral, RatingMature, RatingAdult}
	}
	for _, r := range ratings {
		switch r {
		case RatingGeneral:
			v.Set("rating_general", "1")
		case RatingMature:
			v.Set("rating_mature", "1")
		case RatingAdult:
			v.Set("rating_adult", "1")
		}
	}

	return urls.Host + "/browse/?" + v.Encode()
}