/**
 * Property-Based Test: Property 41 - Lazy Loading Implementation
 * Validates: Requirements 15.5
 *
 * Tests that the parsed model cache correctly implements lazy loading:
 * - Models are only parsed once (cache hit avoids re-parsing)
 * - Cache evicts oldest entries when at capacity
 * - Uploaded files (no path key) are not cached
 */

import { describe, it, expect, beforeEach } from 'vitest';
import fc from 'fast-check';

// ─── Extracted cache logic (mirrors app.js implementation) ───────────────────

/**
 * Creates a parsed model cache with LRU-style eviction.
 * @param {number} maxSize
 */
function createModelCache(maxSize) {
    const cache = new Map();

    return {
        get(key) {
            return cache.get(key);
        },
        set(key, value) {
            if (cache.size >= maxSize) {
                // Evict oldest (first inserted) entry
                const firstKey = cache.keys().next().value;
                cache.delete(firstKey);
            }
            cache.set(key, value);
        },
        has(key) {
            return cache.has(key);
        },
        size() {
            return cache.size;
        },
        clear() {
            cache.clear();
        },
        keys() {
            return Array.from(cache.keys());
        }
    };
}

/**
 * Simulates the model selection flow with caching.
 * Returns { parsedModel, cacheHit } where cacheHit indicates if cache was used.
 */
async function selectModelWithCache(cache, modelPath, parseModel) {
    const cached = cache.get(modelPath);
    if (cached) {
        return { parsedModel: cached, cacheHit: true };
    }
    const parsed = await parseModel(modelPath);
    cache.set(modelPath, parsed);
    return { parsedModel: parsed, cacheHit: false };
}

// ─── Tests ────────────────────────────────────────────────────────────────────

describe('Property 41: Lazy Loading Implementation', () => {
    /**
     * **Validates: Requirements 15.5**
     *
     * Property: For any model path, selecting the same model twice should
     * result in a cache hit on the second selection (parse is called only once).
     */
    it('should cache parsed models and avoid re-parsing on repeated selection', async () => {
        await fc.assert(
            fc.asyncProperty(
                fc.string({ minLength: 1, maxLength: 50 }).filter(s => s.trim().length > 0),
                async (modelPath) => {
                    const cache = createModelCache(10);
                    let parseCallCount = 0;

                    const mockParse = async (path) => {
                        parseCallCount++;
                        return { metadata: { fileName: path }, graph: { nodes: [] } };
                    };

                    // First selection: should parse
                    const first = await selectModelWithCache(cache, modelPath, mockParse);
                    expect(first.cacheHit).toBe(false);
                    expect(parseCallCount).toBe(1);

                    // Second selection: should use cache
                    const second = await selectModelWithCache(cache, modelPath, mockParse);
                    expect(second.cacheHit).toBe(true);
                    expect(parseCallCount).toBe(1); // No additional parse call

                    // Both results should be the same object
                    expect(second.parsedModel).toBe(first.parsedModel);
                }
            ),
            { numRuns: 100 }
        );
    });

    /**
     * **Validates: Requirements 15.5**
     *
     * Property: For any set of distinct model paths up to cache capacity,
     * all models should be cached after selection.
     */
    it('should cache all models within capacity', async () => {
        await fc.assert(
            fc.asyncProperty(
                fc.array(
                    fc.string({ minLength: 1, maxLength: 30 }).filter(s => s.trim().length > 0),
                    { minLength: 1, maxLength: 8 }
                ).map(arr => [...new Set(arr)]), // unique paths
                async (modelPaths) => {
                    const cacheSize = 10;
                    const cache = createModelCache(cacheSize);
                    const mockParse = async (path) => ({ metadata: { fileName: path } });

                    for (const path of modelPaths) {
                        await selectModelWithCache(cache, path, mockParse);
                    }

                    // All unique paths (up to cache size) should be cached
                    const expectedCached = modelPaths.slice(-cacheSize);
                    for (const path of expectedCached) {
                        expect(cache.has(path)).toBe(true);
                    }
                }
            ),
            { numRuns: 100 }
        );
    });

    /**
     * **Validates: Requirements 15.5**
     *
     * Property: When cache is at capacity and a new model is added,
     * the oldest entry is evicted and cache size stays at maxSize.
     */
    it('should evict oldest entry when cache is full', async () => {
        await fc.assert(
            fc.asyncProperty(
                fc.integer({ min: 1, max: 8 }),
                async (maxSize) => {
                    const cache = createModelCache(maxSize);
                    const mockParse = async (path) => ({ metadata: { fileName: path } });

                    // Fill cache to capacity with unique paths
                    const paths = Array.from({ length: maxSize }, (_, i) => `model_${i}.onnx`);
                    for (const path of paths) {
                        await selectModelWithCache(cache, path, mockParse);
                    }

                    expect(cache.size()).toBe(maxSize);

                    // Add one more model (should evict oldest)
                    const newPath = 'model_new.onnx';
                    await selectModelWithCache(cache, newPath, mockParse);

                    // Cache size should not exceed maxSize
                    expect(cache.size()).toBe(maxSize);

                    // New model should be in cache
                    expect(cache.has(newPath)).toBe(true);

                    // Oldest model (first inserted) should be evicted
                    expect(cache.has(paths[0])).toBe(false);
                }
            ),
            { numRuns: 50 }
        );
    });

    /**
     * **Validates: Requirements 15.5**
     *
     * Property: For any sequence of model selections with repeated paths,
     * the total number of parse calls should equal the number of unique paths
     * (not the total number of selections).
     */
    it('should parse each unique model path exactly once', async () => {
        await fc.assert(
            fc.asyncProperty(
                fc.array(
                    fc.integer({ min: 0, max: 4 }).map(i => `model_${i}.onnx`),
                    { minLength: 2, maxLength: 20 }
                ),
                async (selectionSequence) => {
                    const cacheSize = 10; // Large enough to hold all 5 possible models
                    const cache = createModelCache(cacheSize);
                    const parseCallCounts = new Map();

                    const mockParse = async (path) => {
                        parseCallCounts.set(path, (parseCallCounts.get(path) || 0) + 1);
                        return { metadata: { fileName: path } };
                    };

                    for (const path of selectionSequence) {
                        await selectModelWithCache(cache, path, mockParse);
                    }

                    // Each unique path should have been parsed exactly once
                    for (const [, count] of parseCallCounts) {
                        expect(count).toBe(1);
                    }
                }
            ),
            { numRuns: 100 }
        );
    });
});