/**
 * Compares a journey summary (written by the measurement scripts) against the
 * committed baselines in tools/performance/journey-baselines.json.
 *
 * Rules, from docs/architecture/performance-journeys.md:
 * - A counter above `value + slack` fails. Counters are exact; `slack`
 *   (default 0, in the entry's unit) absorbs bundler noise and concurrent
 *   merges without letting growth accumulate past it.
 * - An entry with `toleranceRatio` (wall-clock) fails above
 *   `value * toleranceRatio`.
 * - A baseline without a measurement fails, so removing a measurement can
 *   never silently disable the ratchet.
 * - A measurement below its baseline prints a "can tighten" hint. Baselines
 *   are lowered by hand, with the measured output as evidence, never raised.
 * - Checking nothing is a failure: an empty baselines file, or `--only`
 *   naming an entry that does not exist, must not exit 0.
 * - An optional `note` (a string) says why an entry is enforced, such as a
 *   guard whose link to wall-clock is not validated (Principle 3). It is
 *   printed with a failure, so the author sees what the counter stands for.
 *
 * `--only <journey>/<counter>` (repeatable) restricts the check to the named
 * baselines, so a script that measures one counter can check that counter
 * without every other baseline failing as unmeasured.
 *
 * Usage:
 *   node tools/performance/check-journey-ratchet.mjs --summary <summary.json>
 *       [--baselines tools/performance/journey-baselines.json]
 *       [--only launch/renderer.initialBytes ...]
 */
import { readFile } from 'node:fs/promises';
import path from 'node:path';
import { fileURLToPath } from 'node:url';

export const DEFAULT_BASELINES_PATH =
    'tools/performance/journey-baselines.json';

/** The PR label that lets check-baseline-direction.mjs accept a weakening. */
export const BASELINE_INCREASE_LABEL = 'perf-baseline-increase';

// Three decimals: journey summaries round layout-shift scores to three.
function formatNumber(value) {
    return Number.isInteger(value)
        ? value.toLocaleString('en-US')
        : value.toLocaleString('en-US', { maximumFractionDigits: 3 });
}

function isPlainObject(value) {
    return typeof value === 'object' && value !== null && !Array.isArray(value);
}

export function validateBaselines(baselines) {
    if (!isPlainObject(baselines) || !isPlainObject(baselines.journeys)) {
        throw new Error(
            'Baselines file must be an object with a "journeys" map.'
        );
    }
    for (const [journey, entries] of Object.entries(baselines.journeys)) {
        if (!isPlainObject(entries)) {
            throw new Error(
                `Baseline journey "${journey}" must map counter names to entries.`
            );
        }
        for (const [name, entry] of Object.entries(entries)) {
            const label = `${journey}/${name}`;
            if (!isPlainObject(entry) || !Number.isFinite(entry.value)) {
                throw new Error(
                    `Baseline ${label} needs a finite numeric "value".`
                );
            }
            if (
                entry.toleranceRatio !== undefined &&
                !(
                    Number.isFinite(entry.toleranceRatio) &&
                    entry.toleranceRatio >= 1
                )
            ) {
                throw new Error(
                    `Baseline ${label} has an invalid "toleranceRatio" (must be >= 1).`
                );
            }
            if (
                entry.slack !== undefined &&
                !(Number.isInteger(entry.slack) && entry.slack >= 0)
            ) {
                throw new Error(
                    `Baseline ${label} has an invalid "slack" (must be an integer >= 0).`
                );
            }
            if (entry.note !== undefined && typeof entry.note !== 'string') {
                throw new Error(`Baseline ${label} has a non-string "note".`);
            }
            if (
                entry.slack !== undefined &&
                entry.toleranceRatio !== undefined
            ) {
                throw new Error(
                    `Baseline ${label} sets both "slack" and "toleranceRatio"; slack is for counters, toleranceRatio for wall-clock entries.`
                );
            }
        }
    }
    return baselines;
}

/**
 * A baseline entry is either a counter (exact) or a wall-clock entry (carries
 * `toleranceRatio`), and each is read only from its own summary section. A
 * value that moved to the other section is treated as missing, so a summary
 * schema regression fails the ratchet instead of slipping through it.
 */
function summarySection(entry) {
    return entry.toleranceRatio !== undefined ? 'wallClock' : 'counters';
}

/**
 * What the ratchet enforces: `value × toleranceRatio` for a wall-clock entry,
 * `value + slack` for a counter. check-baseline-direction.mjs compares this,
 * not the bare value, so a PR cannot lower a value while widening a tolerance.
 */
export function enforcedLimit(entry) {
    return entry.value * (entry.toleranceRatio ?? 1) + (entry.slack ?? 0);
}

function describeLimit(entry, unit) {
    if (entry.toleranceRatio !== undefined) {
        return `${formatNumber(enforcedLimit(entry))} (baseline ${formatNumber(entry.value)} × ${entry.toleranceRatio})`;
    }
    if (entry.slack) {
        return `${formatNumber(enforcedLimit(entry))} (baseline ${formatNumber(entry.value)} + slack ${formatNumber(entry.slack)}${unit})`;
    }
    return `baseline ${formatNumber(entry.value)}`;
}

function measuredValue(summaryJourney, name, entry) {
    if (!isPlainObject(summaryJourney)) return undefined;
    return summaryJourney[summarySection(entry)]?.[name];
}

/**
 * Pure comparison. Returns every outcome so the CLI and tests can render it;
 * `failures` non-empty means the ratchet is broken.
 */
export function compareToBaselines({ baselines, summary, only = [] }) {
    validateBaselines(baselines);
    const summaryJourneys = isPlainObject(summary?.journeys)
        ? summary.journeys
        : {};
    const result = {
        failures: [],
        tightenable: [],
        passed: [],
        unbaselined: [],
    };
    const selected = new Set(only);
    let evaluated = 0;

    for (const target of only) {
        const [journey, ...rest] = target.split('/');
        if (baselines.journeys[journey]?.[rest.join('/')] === undefined) {
            result.failures.push(
                `${target}: --only names a baseline that does not exist in the baselines file.`
            );
        }
    }

    for (const [journey, entries] of Object.entries(baselines.journeys)) {
        for (const [name, entry] of Object.entries(entries)) {
            const label = `${journey}/${name}`;
            if (selected.size > 0 && !selected.has(label)) continue;
            evaluated += 1;
            const unit = entry.unit ? ` ${entry.unit}` : '';
            const measured = measuredValue(
                summaryJourneys[journey],
                name,
                entry
            );

            if (measured === undefined) {
                result.failures.push(
                    `${label}: baseline ${formatNumber(entry.value)}${unit} has no measurement under journeys.${journey}.${summarySection(entry)} in the summary. The ratchet cannot be bypassed by dropping a measurement; restore it.`
                );
                continue;
            }
            if (typeof measured !== 'number' || !Number.isFinite(measured)) {
                result.failures.push(
                    `${label}: measured value ${JSON.stringify(measured)} is not a finite number.`
                );
                continue;
            }

            const limit = enforcedLimit(entry);
            const limitText = describeLimit(entry, unit);

            if (measured > limit) {
                const note = entry.note ? ` Note: ${entry.note}` : '';
                result.failures.push(
                    `${label}: ${formatNumber(measured)}${unit} exceeds ${limitText} by ${formatNumber(measured - limit)}${unit}. Bring the value back down; baselines only move down. If the growth is a deliberate trade-off, raise the baseline in ${DEFAULT_BASELINES_PATH}, make the case in the PR, and ask a maintainer to add the ${BASELINE_INCREASE_LABEL} label.${note}`
                );
            } else if (entry.slack && measured > entry.value) {
                result.passed.push(
                    `${label}: ${formatNumber(measured)}${unit} within ${limitText}; uses ${formatNumber(measured - entry.value)} of ${formatNumber(limit - entry.value)}${unit} slack.`
                );
            } else if (measured < entry.value) {
                result.tightenable.push(
                    `${label}: ${formatNumber(measured)}${unit} is below baseline ${formatNumber(entry.value)} by ${formatNumber(entry.value - measured)}${unit}. Lower the baseline in ${DEFAULT_BASELINES_PATH} with this run as evidence.`
                );
            } else {
                result.passed.push(
                    `${label}: ${formatNumber(measured)}${unit} within ${limitText}.`
                );
            }
        }
    }

    for (const [journey, summaryJourney] of Object.entries(summaryJourneys)) {
        const measuredNames = [
            ...Object.keys(summaryJourney?.counters ?? {}),
            ...Object.keys(summaryJourney?.wallClock ?? {}),
        ];
        for (const name of measuredNames) {
            if (baselines.journeys[journey]?.[name] === undefined) {
                result.unbaselined.push(
                    `${journey}/${name}: measured but has no baseline yet. Add one to ${DEFAULT_BASELINES_PATH} once the counter is validated.`
                );
            }
        }
    }

    if (evaluated === 0) {
        result.failures.push(
            `No baselines were checked. ${DEFAULT_BASELINES_PATH} must keep at least one entry; a ratchet that guards nothing must not pass.`
        );
    }

    return result;
}

export function formatResult(result) {
    const lines = [];
    for (const line of result.passed) lines.push(`ok       ${line}`);
    for (const line of result.tightenable) lines.push(`tighten  ${line}`);
    for (const line of result.unbaselined) lines.push(`note     ${line}`);
    for (const line of result.failures) lines.push(`FAIL     ${line}`);
    const checked =
        result.passed.length +
        result.tightenable.length +
        result.failures.length;
    lines.push(
        result.failures.length > 0
            ? `Journey ratchet failed: ${result.failures.length} of ${checked} baselines exceeded.`
            : `Journey ratchet OK: ${checked} baselines checked, ${result.tightenable.length} can be tightened.`
    );
    return lines.join('\n');
}

export function parseArgs(argv) {
    const options = {
        summary: null,
        baselines: DEFAULT_BASELINES_PATH,
        only: [],
    };
    for (let index = 0; index < argv.length; index += 1) {
        const argument = argv[index];
        if (argument === '--') continue;
        if (argument === '--summary') {
            options.summary = argv[++index];
        } else if (argument.startsWith('--summary=')) {
            options.summary = argument.slice('--summary='.length);
        } else if (argument === '--baselines') {
            options.baselines = argv[++index];
        } else if (argument.startsWith('--baselines=')) {
            options.baselines = argument.slice('--baselines='.length);
        } else if (argument === '--only') {
            options.only.push(argv[++index]);
        } else if (argument.startsWith('--only=')) {
            options.only.push(argument.slice('--only='.length));
        } else {
            throw new Error(`Unknown argument: ${argument}`);
        }
        if (
            options.summary === undefined ||
            options.baselines === undefined ||
            options.only.includes(undefined)
        ) {
            throw new Error(`Missing value for ${argument}`);
        }
    }
    for (const target of options.only) {
        if (!/^[^/]+\/.+$/.test(target)) {
            throw new Error(
                `--only expects <journey>/<counter>, received "${target}".`
            );
        }
    }
    if (!options.summary) {
        throw new Error('--summary <journey-summary.json> is required.');
    }
    return options;
}

async function readJson(filePath, description) {
    try {
        return JSON.parse(await readFile(filePath, 'utf8'));
    } catch (error) {
        throw new Error(
            `Cannot read ${description} at ${filePath}: ${error.message}`
        );
    }
}

const isMain =
    process.argv[1] &&
    path.resolve(process.argv[1]) ===
        path.resolve(fileURLToPath(import.meta.url));

if (isMain) {
    try {
        const options = parseArgs(process.argv.slice(2));
        const baselines = await readJson(
            path.resolve(options.baselines),
            'baselines'
        );
        const summary = await readJson(
            path.resolve(options.summary),
            'journey summary'
        );
        const result = compareToBaselines({
            baselines,
            summary,
            only: options.only,
        });
        const output = formatResult(result);
        if (result.failures.length > 0) {
            console.error(output);
            process.exitCode = 1;
        } else {
            console.log(output);
        }
    } catch (error) {
        console.error(`check-journey-ratchet: ${error.message}`);
        process.exitCode = 1;
    }
}