const PRIORITY_STEP = 10;

function numericPriority(source) {
    return Number.isInteger(source.epgPriority) && source.epgPriority >= 0
        ? source.epgPriority
        : Number.MAX_SAFE_INTEGER;
}

function sortEpgSources(list, { enabledOnly = false } = {}) {
    return list
        .filter(source => source.type === 'epg' && (!enabledOnly || source.enabled))
        .slice()
        .sort((left, right) => numericPriority(left) - numericPriority(right) || left.id - right.id);
}

function migrateEpgPriorities(database) {
    const epgSources = database.sources.filter(source => source.type === 'epg');
    let next = epgSources.reduce((maximum, source) => Number.isInteger(source.epgPriority)
        ? Math.max(maximum, source.epgPriority + PRIORITY_STEP)
        : maximum, 0);
    for (const source of epgSources) {
        if (!Number.isInteger(source.epgPriority) || source.epgPriority < 0) {
            source.epgPriority = next;
            next += PRIORITY_STEP;
        }
    }
    return database;
}

function nextEpgPriority(sources) {
    return sortEpgSources(sources).reduce((maximum, source) => Math.max(maximum, numericPriority(source) + PRIORITY_STEP), 0);
}

function validateCompleteOrder(allSources, orderedIds) {
    if (!Array.isArray(orderedIds)) return { code: 'INVALID_ORDER', message: 'orderedIds must be an array' };
    if (orderedIds.some(id => !Number.isInteger(id) || id <= 0)) return { code: 'INVALID_ORDER_ID', message: 'orderedIds must contain positive integer IDs' };
    if (new Set(orderedIds).size !== orderedIds.length) return { code: 'DUPLICATE_SOURCE_ID', message: 'orderedIds contains duplicate IDs' };
    const byId = new Map(allSources.map(source => [source.id, source]));
    const unknown = orderedIds.find(id => !byId.has(id));
    if (unknown !== undefined) return { code: 'UNKNOWN_SOURCE_ID', message: `Unknown source ID: ${unknown}` };
    const nonEpg = orderedIds.find(id => byId.get(id).type !== 'epg');
    if (nonEpg !== undefined) return { code: 'SOURCE_NOT_EPG', message: `Source ${nonEpg} is not an EPG source` };
    const expected = allSources.filter(source => source.type === 'epg').map(source => source.id);
    if (orderedIds.length !== expected.length || expected.some(id => !orderedIds.includes(id))) {
        return { code: 'INCOMPLETE_EPG_ORDER', message: 'orderedIds must contain every EPG source' };
    }
    return null;
}

function applyEpgOrder(allSources, orderedIds, updatedAt = new Date().toISOString()) {
    const error = validateCompleteOrder(allSources, orderedIds);
    if (error) throw Object.assign(new Error(error.message), error);
    orderedIds.forEach((id, index) => {
        const source = allSources.find(item => item.id === id);
        source.epgPriority = index * PRIORITY_STEP;
        source.updated_at = updatedAt;
    });
    return sortEpgSources(allSources);
}

module.exports = { applyEpgOrder, migrateEpgPriorities, nextEpgPriority, numericPriority, PRIORITY_STEP, sortEpgSources, validateCompleteOrder };