package interest

import (
	"context"

	"github.com/bluesky-social/indigo/atproto/syntax"

	"atmoquest/internal/profile"
)

// Match describes an attendee who shares interests with the viewer.
type Match struct {
	DID             syntax.DID
	DisplayName     string
	AvatarURL       string
	SharedInterests []string
	Connected       bool
}

// FindMatches returns attendees who share at least one interest with the
// viewer, sorted by number of shared interests (descending). It fetches
// each attendee's quest profile from their PDS to read interests.
func FindMatches(
	ctx context.Context,
	viewerInterests []string,
	attendeeDIDs []string,
	viewerDID syntax.DID,
	connSet map[string]bool,
	pdsLookup func(syntax.DID) string,
	avatarFn func(pds string, did syntax.DID) (string, string), // returns (displayName, avatarURL)
) []Match {
	if len(viewerInterests) == 0 {
		return nil
	}

	viewerSet := make(map[string]bool, len(viewerInterests))
	for _, i := range viewerInterests {
		viewerSet[i] = true
	}

	var matches []Match
	for _, didStr := range attendeeDIDs {
		if didStr == viewerDID.String() {
			continue
		}

		did, err := syntax.ParseDID(didStr)
		if err != nil {
			continue
		}

		pds := pdsLookup(did)
		quest, err := profile.FetchQuest(ctx, pds, did)
		if err != nil || quest == nil || len(quest.Interests) == 0 {
			continue
		}

		var shared []string
		for _, interest := range quest.Interests {
			if viewerSet[interest] {
				shared = append(shared, interest)
			}
		}
		if len(shared) == 0 {
			continue
		}

		displayName, avatarURL := avatarFn(pds, did)

		matches = append(matches, Match{
			DID:             did,
			DisplayName:     displayName,
			AvatarURL:       avatarURL,
			SharedInterests: shared,
			Connected:       connSet[didStr],
		})
	}

	// Sort by number of shared interests descending (bubble sort — small N).
	for i := 0; i < len(matches); i++ {
		for j := i + 1; j < len(matches); j++ {
			if len(matches[j].SharedInterests) > len(matches[i].SharedInterests) {
				matches[i], matches[j] = matches[j], matches[i]
			}
		}
	}

	// Cap at 20 results.
	if len(matches) > 20 {
		matches = matches[:20]
	}

	return matches
}