//! Deterministic, seedable workload generation. No external RNG crate: a small
//! SplitMix64 gives reproducible batches so a failing case can be replayed
//! exactly. `conflict` in [0,1] tunes how often a transaction touches the small
//! "hot" set (shared accounts / the shared counter / the shared AMM pool),
//! which is what drives the abort rate and destroys parallelism when high.

use crate::types::{Key, StateMap, TxKind, Txn, Value};

pub struct SplitMix64 {
    state: u64,
}

impl SplitMix64 {
    pub fn new(seed: u64) -> Self {
        SplitMix64 { state: seed }
    }
    pub fn next_u64(&mut self) -> u64 {
        self.state = self.state.wrapping_add(0x9E3779B97F4A7C15);
        let mut z = self.state;
        z = (z ^ (z >> 30)).wrapping_mul(0xBF58476D1CE4E5B9);
        z = (z ^ (z >> 27)).wrapping_mul(0x94D049BB133111EB);
        z ^ (z >> 31)
    }
    pub fn below(&mut self, n: u64) -> u64 {
        if n == 0 {
            0
        } else {
            self.next_u64() % n
        }
    }
    /// probability p in [0,1] scaled to 1e6.
    pub fn chance(&mut self, p_ppm: u64) -> bool {
        self.below(1_000_000) < p_ppm
    }
}

pub struct WorkloadConfig {
    pub num_txns: usize,
    pub num_accounts: u64,
    pub num_hot_accounts: u64,
    pub num_contracts: u64,
    pub num_hot_slots: u64,
    /// probability (0..1e6 ppm) that a given account/slot pick is from the hot set
    pub conflict_ppm: u64,
    /// simulated EVM execution cost per tx (keccak rounds). 0 = trivial tx.
    pub gas: u32,
    pub seed: u64,
}

/// Build the base state: every account funded, hot slots seeded, AMM pools seeded.
pub fn make_base_state(cfg: &WorkloadConfig) -> StateMap {
    let mut s = StateMap::new();
    for a in 0..cfg.num_accounts {
        s.insert(Key::Balance(a), 1_000_000u128);
    }
    for c in 0..cfg.num_contracts {
        // slot layout: 0..num_hot_slots = counters; then two AMM slots 1000,1001
        for slot in 0..cfg.num_hot_slots {
            s.insert(Key::Storage(c, slot), 0);
        }
        s.insert(Key::Storage(c, 1000), 1_000_000u128); // AMM reserve x
        s.insert(Key::Storage(c, 1001), 1_000_000u128); // AMM reserve y
    }
    s
}

impl WorkloadConfig {
    fn pick_account(&self, rng: &mut SplitMix64) -> u64 {
        if self.num_hot_accounts > 0 && rng.chance(self.conflict_ppm) {
            rng.below(self.num_hot_accounts)
        } else {
            self.num_hot_accounts + rng.below(self.num_accounts - self.num_hot_accounts)
        }
    }
}

/// Generate a batch. Mix: transfers, sweeps, increments, AMM swaps.
pub fn generate_batch(cfg: &WorkloadConfig) -> Vec<Txn> {
    let mut rng = SplitMix64::new(cfg.seed);
    let mut txns = Vec::with_capacity(cfg.num_txns);
    for _ in 0..cfg.num_txns {
        let roll = rng.below(100);
        let kind = if roll < 60 {
            // 60% transfers
            let from = cfg.pick_account(&mut rng);
            let mut to = cfg.pick_account(&mut rng);
            if to == from {
                to = (to + 1) % cfg.num_accounts;
            }
            let amount = 1 + rng.below(1000) as Value;
            TxKind::Transfer { from, to, amount }
        } else if roll < 75 {
            // 15% sweeps
            let from = cfg.pick_account(&mut rng);
            let mut to = cfg.pick_account(&mut rng);
            if to == from {
                to = (to + 1) % cfg.num_accounts;
            }
            TxKind::Sweep { from, to }
        } else if roll < 90 {
            // 15% shared-counter increments (the serializability stressor)
            let contract = rng.below(cfg.num_contracts.max(1));
            let slot = if cfg.num_hot_slots > 0 {
                rng.below(cfg.num_hot_slots)
            } else {
                0
            };
            TxKind::Increment { contract, slot }
        } else {
            // 10% AMM swaps against a shared pool
            let contract = rng.below(cfg.num_contracts.max(1));
            let dx = 1 + rng.below(10_000) as Value;
            TxKind::AmmSwap {
                contract,
                x_slot: 1000,
                y_slot: 1001,
                dx,
            }
        };
        txns.push(Txn { kind, gas: cfg.gas });
    }
    txns
}