// Name lifecycle: phases, prices and the payment split.
//
// WHAT THIS IS FOR
// These are the rules the covenant will encode. Until the covenant exists they
// are still needed, by three callers that must all agree:
//
//   · the storefront, to quote a renewal or a takeover
//   · the wallet UI, to show "ACTIVE until block X" and warn before expiry
//   · the covenant tests, as the reference the contract is checked against
//
// So they live here as pure functions of block height, deliberately written the
// way a covenant computes: integer arithmetic on satoshis and heights, no
// floating point, no clock, no oracle. When the CashScript contract is written it
// must produce identical numbers, and these functions are the fixture.
//
// SEE Decentralized.DNS/DESIGN-covenant-registry.md for the reasoning behind
// every constant here. The short version of the two least obvious ones:
//
//   Decay, not a step. The takeover price glides from the IDLE premium down to
//   the OPEN floor. A step would put a starting pistol on one block and hand the
//   name to whoever paid the biggest miner fee — which is the outcome the pricing
//   is trying to prevent. A glide is also demand discovery without an oracle: a
//   name people want gets bought on the way down at what someone will actually
//   pay, and never reaches the floor.
//
//   No miner share by default. Paying miners is only possible as transaction fee,
//   and a fee attached to a takeover is a discount for the one party who also
//   controls block ordering and can read the demand signal out of the mempool.
//   Commit–reveal neutralises that, but then the design's safety depends on
//   commit–reveal being right. Folding the share into the fund removes the
//   problem structurally. Flip `SPLIT.minerPercent` to 15 to restore it.

// ---------- time ----------

/** ~10-minute blocks. Whole-year registrations only, so this is exact enough. */
export const BLOCKS_PER_YEAR = 52_560;
export const BLOCKS_PER_MONTH = 4_380;

/** Grace window after expiry during which the owner may still reclaim. */
export const GRACE_MONTHS = 6;
export const GRACE_BLOCKS = GRACE_MONTHS * BLOCKS_PER_MONTH;

export const MIN_REGISTRATION_YEARS = 1;

// ---------- phases ----------

export const PHASE = {
  active: "active", // owner holds it, renewal not yet due
  idle: "idle",     // expired; owner may reclaim cheaply, others may take over dearly
  open: "open",     // grace elapsed; anyone may buy at the floor
};

/**
 * Which phase a name is in at a given block height.
 * `expiryHeight` and `idleEndHeight` are covenant parameters.
 */
export function phaseAt({ height, expiryHeight, idleEndHeight }) {
  if (height < expiryHeight) return PHASE.active;
  if (height < idleEndHeight) return PHASE.idle;
  return PHASE.open;
}

export const idleEndFor = (expiryHeight) => expiryHeight + GRACE_BLOCKS;
export const expiryFor = (startHeight, years) => startHeight + BLOCKS_PER_YEAR * years;

// ---------- tiers ----------

// Length-based, because it is the one metric a covenant can be given as a
// parameter and a buyer can predict without consulting us. Dictionary words and
// reserved terms are handled at registration time by assigning a higher tier —
// the contract only ever sees the tier number.
//
// Satoshi figures are chipnet placeholders carrying USD *intent* (see the table
// in the design note). Mainnet needs repricing against a real BCH price, and
// once a name is minted its tier is fixed for that covenant's lifetime — the
// migrate path is the only way to reprice. That is a deliberate trade for having
// no oracle.
export const TIERS = [
  { tier: 1, maxLength: 2, renewalSats: 2_000_000n },  // ~$200/yr intent
  { tier: 2, maxLength: 4, renewalSats: 500_000n },    // ~$50/yr
  { tier: 3, maxLength: 7, renewalSats: 200_000n },    // ~$20/yr
  { tier: 4, maxLength: Infinity, renewalSats: 100_000n }, // ~$10/yr
];

/** Multipliers on the annual renewal price. */
export const IDLE_PREMIUM_MULTIPLE = 50n; // tier 3: $20 -> $1000
export const OPEN_FLOOR_MULTIPLE = 5n;    // tier 3: $20 -> $100

/** Tier for a name, by label length. `name` may be "alice" or "alice.nav". */
export function tierForName(name) {
  const label = String(name).split(".")[0];
  if (!label.length) throw new Error("empty name has no tier");
  return TIERS.find((t) => label.length <= t.maxLength).tier;
}

export function tierConfig(tier) {
  const t = TIERS.find((x) => x.tier === tier);
  if (!t) throw new Error(`unknown tier ${tier}`);
  return t;
}

export const renewalPriceSats = (tier, years = 1) =>
  tierConfig(tier).renewalSats * BigInt(years);

export const idlePremiumSats = (tier) => tierConfig(tier).renewalSats * IDLE_PREMIUM_MULTIPLE;
export const openFloorSats = (tier) => tierConfig(tier).renewalSats * OPEN_FLOOR_MULTIPLE;

// ---------- takeover price ----------

/**
 * What a stranger must pay to take the name at this height.
 *
 * ACTIVE  — not for sale at any price; the owner holds it.
 * IDLE    — glides linearly from the premium down to the floor.
 * OPEN    — the floor, indefinitely.
 *
 * Integer arithmetic throughout, in the order a covenant would do it: multiply
 * before dividing so the remainder is not lost, and never touch floating point.
 */
export function takeoverPriceSats({ height, expiryHeight, idleEndHeight, tier }) {
  const phase = phaseAt({ height, expiryHeight, idleEndHeight });
  if (phase === PHASE.active) return null; // not purchasable

  const floor = openFloorSats(tier);
  if (phase === PHASE.open) return floor;

  const premium = idlePremiumSats(tier);
  const span = BigInt(idleEndHeight - expiryHeight);
  const remaining = BigInt(idleEndHeight - height); // 1..span within IDLE
  return floor + ((premium - floor) * remaining) / span;
}

/** What the owner pays to reclaim or renew — never affected by phase or demand. */
export function reclaimPriceSats({ tier, years = 1 }) {
  return renewalPriceSats(tier, years);
}

// ---------- the split ----------

/**
 * Recommended: 30 / 0 / 70 in IDLE, 0 / 0 / 100 in OPEN.
 *
 * The owner's 30% is a buy-out while they are still entitled to reclaim. Once
 * OPEN, that entitlement has lapsed and so does the justification, so the share
 * goes to zero rather than paying an absent party in perpetuity.
 *
 * `minerPercent` is 0 by design — see the header. Set it to 15 to restore the
 * miner share; the remainder is taken out of the fund, and the amount is left
 * unspent so it becomes transaction fee (the only way to pay miners at all).
 */
export const SPLIT = {
  ownerPercentIdle: 30n,
  ownerPercentOpen: 0n,
  minerPercent: 0n, // 15n restores the miner share
};

/**
 * Split a takeover payment into the outputs a covenant must require.
 *
 * `minerFeeSats` is NOT an output — it is the amount left unspent, which the
 * miner collects as fee. Callers building the transaction must under-spend by
 * exactly this much.
 */
export function splitTakeover({ amountSats, phase }) {
  const amount = BigInt(amountSats);
  if (amount <= 0n) throw new Error("takeover amount must be positive");
  if (phase === PHASE.active) throw new Error("an ACTIVE name is not for sale");

  const ownerPercent = phase === PHASE.idle ? SPLIT.ownerPercentIdle : SPLIT.ownerPercentOpen;
  const ownerSats = (amount * ownerPercent) / 100n;
  const minerFeeSats = (amount * SPLIT.minerPercent) / 100n;
  // The fund takes the remainder, so integer division can never lose or
  // conjure a satoshi — the three parts always sum to the amount exactly.
  const fundSats = amount - ownerSats - minerFeeSats;
  return { ownerSats, minerFeeSats, fundSats, totalSats: amount };
}

// ---------- commit–reveal ----------

// Applies to first registrations AND takeovers. One confirmation is enough to
// make ordering unforgeable: an attacker seeing a reveal cannot produce a commit
// older than one already in a block. The upper bound stops speculative
// pre-commits from being hoarded indefinitely.
export const COMMIT = {
  minConfirmations: 1,
  maxConfirmations: 1008, // ~1 week
  saltBytes: 16,
};

export const commitIsMature = (commitHeight, atHeight) => {
  const age = atHeight - commitHeight;
  return age >= COMMIT.minConfirmations && age <= COMMIT.maxConfirmations;
};

// ---------- fund ----------

export const FUND = {
  // 2-of-3 multisig, published, with visible spending from day one. Baked into
  // the covenant at mint and therefore permanent: if this key is lost every
  // future takeover pays into a hole, and if it is compromised the attacker
  // collects the fund share forever. The migrate path (design note §4.6) is the
  // only escape, which is why it must exist from the first version.
  address: null, // set before any mainnet covenant is deployed
  multisig: "2-of-3",
  purpose: "Bitcoin Cash development and infrastructure",
  // Voluntary and opt-in — it touches only names in this registry, not the
  // chain and not miners' rewards. That distinction is the answer to the
  // inevitable comparison with the 2020 IFP, and it only holds if the fund is
  // transparent from the start rather than after the first accusation.
  voluntary: true,
};

/** Everything a UI needs to describe a name's standing at a glance. */
export function describeLifecycle({ height, expiryHeight, idleEndHeight, tier }) {
  const phase = phaseAt({ height, expiryHeight, idleEndHeight });
  return {
    phase,
    tier,
    blocksUntilExpiry: Math.max(0, expiryHeight - height),
    blocksUntilOpen: Math.max(0, idleEndHeight - height),
    reclaimPriceSats: reclaimPriceSats({ tier }),
    takeoverPriceSats: takeoverPriceSats({ height, expiryHeight, idleEndHeight, tier }),
    ownerCanReclaim: phase !== PHASE.open,
    // The number that actually protects a present owner: their option is tens of
    // times cheaper than a stranger's, so renewing always beats being bought out.
    ownerAdvantage:
      phase === PHASE.idle
        ? Number(idlePremiumSats(tier) / reclaimPriceSats({ tier }))
        : null,
  };
}