// Unit tests for the pure distribution math extracted out of equalFlowControl.
// Decoupling target: the algorithm should be testable without a full MGC.

'use strict';

const test = require('node:test');
const assert = require('node:assert/strict');

const { computeEqualFlowDistribution } = require('../../src/control/strategies.js');

// Tiny helpers to make synthetic machines. The pure function still calls
// filterOutUnavailableMachines, which reads machine.state.getCurrentState()
// and machine.isValidActionForMode() — stub both so the algorithm sees the
// machine as available. groupFlow/groupCalcPower are injected.
function mkMachine(id, capability = { min: 0.01, max: 0.10, power: (flow) => flow * 1000 }, state = 'operational') {
    return {
        id,
        machine: {
            __testCapability: capability,
            state: { getCurrentState: () => state },
            isValidActionForMode: () => true,
        },
    };
}
const dummyLogger = { warn() {}, error() {}, debug() {}, info() {} };

// Default injected helpers: read from the synthetic machine's __testCapability.
const groupFlow = (m) => ({
    currentFxyYMin: m.__testCapability.min,
    currentFxyYMax: m.__testCapability.max,
});
const groupCalcPower = (m, flow) => m.__testCapability.power(flow);

function basicArgs(overrides = {}) {
    const m = { a: mkMachine('a').machine, b: mkMachine('b').machine, c: mkMachine('c').machine };
    return {
        machines: m, Qd: 0.06,
        dynamicTotals: { flow: { min: 0.01, max: 0.30 } },
        activeTotals:  { flow: { min: 0.03, max: 0.30 } },
        priorityList: ['a', 'b', 'c'],
        isMachineActive: () => true,
        groupFlow, groupCalcPower, logger: dummyLogger,
        ...overrides,
    };
}

test('default case: distributes Qd equally across active machines', () => {
    const r = computeEqualFlowDistribution(basicArgs({ Qd: 0.06 }));
    // 3 active pumps, demand 0.06 → 0.02 per pump.
    assert.equal(r.flowDistribution.length, 3);
    for (const entry of r.flowDistribution) {
        assert.ok(Math.abs(entry.flow - 0.02) < 1e-12, `entry.flow=${entry.flow}`);
    }
    assert.ok(Math.abs(r.totalFlow - 0.06) < 1e-12);
    // power(flow) = flow * 1000 in the test capability → 0.02 * 1000 = 20 W per pump.
    assert.ok(Math.abs(r.totalPower - 60) < 1e-9);
});

test('Qd above active capacity: starts additional priority machines until covered', () => {
    // Only one machine "active" to start with; demand exceeds its envelope.
    // Algorithm should bring more priority machines online via the high-demand branch.
    const active = new Set(['a']);
    const args = basicArgs({
        Qd: 0.18, // above any single pump's max (0.10)
        activeTotals: { flow: { min: 0.01, max: 0.10 } },
        isMachineActive: (id) => active.has(id),
    });
    const r = computeEqualFlowDistribution(args);
    // The algorithm reduces Qd iteratively (Qd /= i) until it fits per-pump max.
    // We don't assert exact splits — only that flowDistribution is non-empty
    // and totalFlow is finite, since the legacy algorithm is preserved as-is.
    assert.ok(r.flowDistribution.length >= 1);
    assert.ok(Number.isFinite(r.totalFlow));
    assert.ok(Number.isFinite(r.totalPower));
});

test('Qd below active min flow: routes excess machines to flow=0 and redistributes', () => {
    // demand below active min — algorithm shuts off lowest-priority machine(s)
    // and redistributes Qd across the remainder.
    const args = basicArgs({
        Qd: 0.015,
        dynamicTotals: { flow: { min: 0.01, max: 0.30 } },
        activeTotals:  { flow: { min: 0.03, max: 0.30 } }, // active min > Qd
    });
    const r = computeEqualFlowDistribution(args);
    const offCount = r.flowDistribution.filter(e => e.flow === 0).length;
    assert.ok(offCount >= 1, `expected ≥1 machine to be shut off, got distribution: ${JSON.stringify(r.flowDistribution)}`);
    const totalServed = r.flowDistribution.filter(e => e.flow > 0).reduce((s, e) => s + e.flow, 0);
    assert.ok(Math.abs(totalServed - 0.015) < 1e-12, `served flow ${totalServed} should equal Qd 0.015`);
});

test('totalCog is always 0 for equalFlow — preserves legacy contract', () => {
    // The historical algorithm sets totalCog = 0 in this strategy (BEP-Gravitation
    // is the only optimizer that produces a meaningful per-combination cog).
    // Pinned here so a future "improvement" doesn't silently introduce a fake value.
    const r = computeEqualFlowDistribution(basicArgs());
    assert.equal(r.totalCog, 0);
});

test('isMachineActive is consulted for COUNT but not for SELECTION (legacy quirk)', () => {
    // Pins pre-existing behaviour of the default branch: it counts how many
    // machines are active (countActive) to decide how to split Qd, but then
    // iterates the FIRST countActive machines in priority order — which may
    // include inactive ones. So 2 of 3 active + Qd within range → first 2 in
    // priorityList both get flow, regardless of which are actually active.
    //
    // This is a latent bug that pre-dates the strategies decoupling refactor.
    // Documenting it here so a future cleanup is a deliberate change with a
    // failing-then-passing test, not a silent semantic shift.
    const active = new Set(['a', 'c']);
    const r = computeEqualFlowDistribution(basicArgs({
        Qd: 0.06,
        isMachineActive: (id) => active.has(id),
    }));
    // Today: machinesInPriorityOrder[0]='a', [1]='b' → 'a' and 'b' both get 0.03.
    // 'c' (active but third in priority order) gets nothing.
    const aFlow = r.flowDistribution.find(e => e.machineId === 'a')?.flow;
    const bFlow = r.flowDistribution.find(e => e.machineId === 'b')?.flow;
    const cFlow = r.flowDistribution.find(e => e.machineId === 'c')?.flow;
    assert.equal(aFlow, 0.03, 'a (priority 0, active)');
    assert.equal(bFlow, 0.03, 'b (priority 1, INACTIVE — receives flow anyway, bug)');
    assert.equal(cFlow, undefined, 'c (priority 2, active — does NOT receive flow, bug)');
});

test('priorityList controls iteration order', () => {
    // The order in flowDistribution should match priorityList — i.e., machine 'c'
    // appears before machine 'a' when priorityList = ['c', 'b', 'a'].
    const r = computeEqualFlowDistribution(basicArgs({
        priorityList: ['c', 'b', 'a'],
    }));
    assert.equal(r.flowDistribution[0].machineId, 'c');
});