package main

import (
	"context"
	"time"

	"github.com/jackc/pgx/v5"
	"github.com/jackc/pgx/v5/pgxpool"
)

type HostRow struct {
	ID               int64
	Hostname         string
	Protocol         string
	HtmlTitle        string
	IframeAllowed    bool
	BestIconHash     string
	IconDownloadedAt *time.Time
}

// fetchHostsPage gets a page of hosts with titles, ordered by icon_downloaded_at for disk locality.
// Icons written to disk at similar times are physically adjacent on the EBS volume —
// reading in write order maximizes OS readahead cache hits.
func fetchHostsPage(ctx context.Context, pool *pgxpool.Pool, lastTime *time.Time, lastID int64, limit int) ([]HostRow, error) {
	// Two-phase: first hosts with icons (ordered by download time), then hosts without
	var rows pgx.Rows
	var err error
	if lastTime != nil {
		rows, err = pool.Query(ctx, `
			SELECT id, hostname, protocol, html_title, COALESCE(iframe_allowed, true), COALESCE(best_icon_hash, ''), icon_downloaded_at
			FROM hosts
			WHERE html_title IS NOT NULL AND icon_downloaded_at > $1
			ORDER BY icon_downloaded_at
			LIMIT $2
		`, lastTime, limit)
	} else if lastID > 0 {
		// No more timestamped hosts — fetch remaining (no icon) by id
		rows, err = pool.Query(ctx, `
			SELECT id, hostname, protocol, html_title, COALESCE(iframe_allowed, true), '', NULL::timestamptz
			FROM hosts
			WHERE html_title IS NOT NULL AND icon_downloaded_at IS NULL AND id > $1
			ORDER BY id
			LIMIT $2
		`, lastID, limit)
	} else {
		// Start: fetch timestamped hosts first
		rows, err = pool.Query(ctx, `
			SELECT id, hostname, protocol, html_title, COALESCE(iframe_allowed, true), COALESCE(best_icon_hash, ''), icon_downloaded_at
			FROM hosts
			WHERE html_title IS NOT NULL AND icon_downloaded_at IS NOT NULL
			ORDER BY icon_downloaded_at
			LIMIT $1
		`, limit)
	}
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var hosts []HostRow
	for rows.Next() {
		var h HostRow
		if err := rows.Scan(&h.ID, &h.Hostname, &h.Protocol, &h.HtmlTitle, &h.IframeAllowed, &h.BestIconHash, &h.IconDownloadedAt); err != nil {
			return nil, err
		}
		hosts = append(hosts, h)
	}
	return hosts, rows.Err()
}