/**
 * ADR-121 Phase 18 — Witness ledger (chain) tests.
 *
 * Covers:
 *  - Empty ledger verifies as valid (zero entries, zero failures)
 *  - Single-entry chain (genesis with prevContentHash=null)
 *  - Multi-entry chain — sequence + prev-hash linkage
 *  - Tamper detection at every position (genesis, middle, tail)
 *  - Sequence mismatch detection
 *  - Wrong version rejected
 *  - Verification result reports the FIRST failure position
 *  - Same signer key carries across appends
 */

import { describe, it, expect } from 'vitest';
import {
  appendToLedger,
  verifyEntry,
  verifyLedger,
  generateLedgerKeypair,
  type BenchmarkLedger,
} from '../witness-ledger.js';

function input(name: string, ts: string, results: unknown) {
  return {
    benchmark: name,
    timestamp: ts,
    commit: `commit-${name}`,
    model: 'test-model',
    corpus: { id: 'fp-corpus', size: 10 },
    queries: { id: 'fp-queries', count: 3 },
    results,
  };
}

describe('appendToLedger — chain construction', () => {
  it('initializes a fresh ledger with a single genesis entry', () => {
    const { ledger, entry } = appendToLedger(undefined, input('b1', '2026-01-01T00:00:00Z', { recall: 0.5 }));
    expect(ledger.version).toBe(1);
    expect(ledger.entries.length).toBe(1);
    expect(entry.sequence).toBe(1);
    expect(entry.prevContentHash).toBeNull();
  });

  it('chains a second entry to the genesis', () => {
    const kp = generateLedgerKeypair();
    const { ledger: l1, entry: e1 } = appendToLedger(undefined, input('b1', '2026-01-01T00:00:00Z', { recall: 0.5 }), kp);
    const { ledger: l2, entry: e2 } = appendToLedger(l1, input('b2', '2026-01-02T00:00:00Z', { recall: 0.7 }), kp);

    expect(l2.entries.length).toBe(2);
    expect(e2.sequence).toBe(2);
    expect(e2.prevContentHash).toBe(e1.contentHash);
  });

  it('three-entry chain has correct sequence + links', () => {
    const kp = generateLedgerKeypair();
    let ledger: BenchmarkLedger | undefined;
    const hashes: string[] = [];
    for (let i = 0; i < 3; i++) {
      const result = appendToLedger(ledger, input(`b${i}`, `2026-01-0${i + 1}T00:00:00Z`, { i }), kp);
      ledger = result.ledger;
      hashes.push(result.entry.contentHash);
    }
    expect(ledger!.entries.length).toBe(3);
    expect(ledger!.entries[0]!.prevContentHash).toBeNull();
    expect(ledger!.entries[1]!.prevContentHash).toBe(hashes[0]);
    expect(ledger!.entries[2]!.prevContentHash).toBe(hashes[1]);
    expect(ledger!.entries.map(e => e.sequence)).toEqual([1, 2, 3]);
  });

  it('same keypair → same publicKey on every entry', () => {
    const kp = generateLedgerKeypair();
    let ledger: BenchmarkLedger | undefined;
    const pubs: string[] = [];
    for (let i = 0; i < 3; i++) {
      const r = appendToLedger(ledger, input(`b${i}`, `2026-01-0${i + 1}T00:00:00Z`, { i }), kp);
      ledger = r.ledger;
      pubs.push(r.entry.publicKey);
    }
    expect(new Set(pubs).size).toBe(1);
  });

  it('no keypair → fresh ephemeral key per entry (different publicKeys)', () => {
    let ledger: BenchmarkLedger | undefined;
    const pubs: string[] = [];
    for (let i = 0; i < 3; i++) {
      const r = appendToLedger(ledger, input(`b${i}`, `2026-01-0${i + 1}T00:00:00Z`, { i }));
      ledger = r.ledger;
      pubs.push(r.entry.publicKey);
    }
    expect(new Set(pubs).size).toBe(3);
  });
});

describe('verifyLedger — happy path', () => {
  it('empty ledger is valid', () => {
    const result = verifyLedger({ version: 1, entries: [] });
    expect(result.valid).toBe(true);
    expect(result.entryCount).toBe(0);
    expect(result.firstFailureAt).toBe(-1);
  });

  it('single-entry chain verifies', () => {
    const { ledger } = appendToLedger(undefined, input('b1', '2026-01-01T00:00:00Z', { r: 1 }));
    const result = verifyLedger(ledger);
    expect(result.valid).toBe(true);
    expect(result.entryCount).toBe(1);
  });

  it('multi-entry chain verifies', () => {
    const kp = generateLedgerKeypair();
    let ledger: BenchmarkLedger | undefined;
    for (let i = 0; i < 5; i++) {
      ledger = appendToLedger(ledger, input(`b${i}`, `2026-01-0${i + 1}T00:00:00Z`, { i }), kp).ledger;
    }
    const result = verifyLedger(ledger!);
    expect(result.valid).toBe(true);
    expect(result.entryCount).toBe(5);
  });

  it('unknown version rejected', () => {
    const result = verifyLedger({ version: 99 } as unknown as BenchmarkLedger);
    expect(result.valid).toBe(false);
    expect(result.reason).toMatch(/version/);
  });
});

describe('verifyLedger — tamper detection', () => {
  function buildChain(n: number): BenchmarkLedger {
    const kp = generateLedgerKeypair();
    let ledger: BenchmarkLedger | undefined;
    for (let i = 0; i < n; i++) {
      ledger = appendToLedger(ledger, input(`b${i}`, `2026-01-0${i + 1}T00:00:00Z`, { i }), kp).ledger;
    }
    return ledger!;
  }

  it('detects tampering at the genesis entry', () => {
    const ledger = buildChain(3);
    const tampered: BenchmarkLedger = {
      ...ledger,
      entries: [
        { ...ledger.entries[0]!, results: { i: 999 } }, // tamper genesis
        ledger.entries[1]!,
        ledger.entries[2]!,
      ],
    };
    const result = verifyLedger(tampered);
    expect(result.valid).toBe(false);
    expect(result.firstFailureAt).toBe(0);
  });

  it('detects tampering at a middle entry', () => {
    const ledger = buildChain(3);
    const tampered: BenchmarkLedger = {
      ...ledger,
      entries: [
        ledger.entries[0]!,
        { ...ledger.entries[1]!, results: { i: 999 } },
        ledger.entries[2]!,
      ],
    };
    const result = verifyLedger(tampered);
    expect(result.valid).toBe(false);
    expect(result.firstFailureAt).toBe(1);
  });

  it('detects tampering at the tail entry', () => {
    const ledger = buildChain(3);
    const tampered: BenchmarkLedger = {
      ...ledger,
      entries: [
        ledger.entries[0]!,
        ledger.entries[1]!,
        { ...ledger.entries[2]!, results: { i: 999 } },
      ],
    };
    const result = verifyLedger(tampered);
    expect(result.valid).toBe(false);
    expect(result.firstFailureAt).toBe(2);
  });

  it('detects removed entry (sequence mismatch)', () => {
    const ledger = buildChain(3);
    const tampered: BenchmarkLedger = {
      ...ledger,
      entries: [ledger.entries[0]!, ledger.entries[2]!], // skip middle
    };
    const result = verifyLedger(tampered);
    expect(result.valid).toBe(false);
    // The first wrong entry is at index 1 (sequence expected 2, got 3 OR bad prevHash)
    expect(result.firstFailureAt).toBe(1);
  });

  it('detects swapped entries', () => {
    const ledger = buildChain(3);
    const tampered: BenchmarkLedger = {
      ...ledger,
      entries: [ledger.entries[1]!, ledger.entries[0]!, ledger.entries[2]!],
    };
    const result = verifyLedger(tampered);
    expect(result.valid).toBe(false);
  });

  it('detects forged prevContentHash with otherwise valid signature', () => {
    const ledger = buildChain(3);
    const tampered: BenchmarkLedger = {
      ...ledger,
      entries: [
        ledger.entries[0]!,
        { ...ledger.entries[1]!, prevContentHash: 'ff'.repeat(32) },
        ledger.entries[2]!,
      ],
    };
    const result = verifyLedger(tampered);
    expect(result.valid).toBe(false);
    expect(result.firstFailureAt).toBe(1);
  });
});

describe('verifyEntry — single-entry signature check', () => {
  it('valid entry verifies', () => {
    const { entry } = appendToLedger(undefined, input('b1', '2026-01-01T00:00:00Z', { r: 1 }));
    expect(verifyEntry(entry)).toBe(true);
  });

  it('tampered entry fails', () => {
    const { entry } = appendToLedger(undefined, input('b1', '2026-01-01T00:00:00Z', { r: 1 }));
    const tampered = { ...entry, results: { r: 999 } };
    expect(verifyEntry(tampered)).toBe(false);
  });
});