/**
 * Computes the statistics of `data/example/example.gpx` with the engine, and writes them to
 * `data/example/example-data.ts`, where the pages that show an example (the home page, the
 * documentation) take them from. Run it when the example, or the way the engine computes the
 * statistics, changes:
 *
 *     npm run generate:example
 *
 * The engine has to be built (`wasm-pack build --target bundler`, in
 * `wasm`).
 */
import fs from 'fs';
import path from 'path';
import { fileURLToPath, pathToFileURL } from 'url';
import prettier from 'prettier';

const here = path.dirname(fileURLToPath(import.meta.url));
const example = path.resolve(here, '../data/example');
const packageDirectory = path.resolve(here, '../../../../wasm/pkg');

export const exampleGPX = path.join(example, 'example.gpx');
export const exampleData = path.join(example, 'example-data.ts');

/** Whether the engine is built. */
export function engineIsBuilt() {
    return fs.existsSync(path.join(packageDirectory, 'gpx_wasm_bg.wasm'));
}

/** Loads the engine in Node: the package is made for bundlers, which import the wasm file. */
async function loadEngine() {
    const glue = await import(pathToFileURL(path.join(packageDirectory, 'gpx_wasm_bg.js')).href);
    const { instance } = await WebAssembly.instantiate(
        fs.readFileSync(path.join(packageDirectory, 'gpx_wasm_bg.wasm')),
        { './gpx_wasm_bg.js': glue }
    );
    glue.__wbg_set_wasm(instance.exports);
    (instance.exports.__wbindgen_start as () => void)();
    return glue as typeof import('gpx-wasm');
}

type Values = Float64Array | BigInt64Array | undefined;

/** The arrays that the engine has for the example, which are all the pages need. */
export async function computeExampleData() {
    const engine = await loadEngine();
    engine.start();
    const data = fs.readFileSync(exampleGPX);
    engine.load_files(new Uint8Array(data), Uint32Array.from([data.length]), ['example']);

    // numbers are enough for the times, which are milliseconds
    const numbers = (values: Values | Uint32Array) =>
        values && Array.from(values as ArrayLike<number | bigint>, (value) => Number(value));
    const length = engine.total_distance().length;
    const points = Array.from({ length }, (_, index) => engine.selection_point(index)!);
    const slopeSegmentStarts = Array.from(engine.slope_segment_starts());
    return {
        global: engine.selection_statistics(),
        totalDistance: numbers(engine.total_distance()),
        movingDistance: numbers(engine.moving_distance()),
        totalTime: numbers(engine.total_time()),
        movingTime: numbers(engine.moving_time()),
        elevationGain: numbers(engine.elevation_gain()),
        elevationLoss: numbers(engine.elevation_loss()),
        slope: points.map((point) => point.slope!),
        slopeSegmentStarts,
        slopeSegmentSlopes: numbers(engine.slope_segment_slopes()),
        // the length of each segment, which is the one of its trackpoints
        slopeSegmentDistances: slopeSegmentStarts.map(
            (start) => points[start].slopeSegmentDistance!
        ),
        lng: numbers(engine.lng()),
        lat: numbers(engine.lat()),
        ele: numbers(engine.ele()),
        timestamps: points.map((point) => point.time!),
        speed: numbers(engine.speed()),
        atemp: numbers(engine.atemp()),
    };
}

async function generate() {
    const data = await computeExampleData();
    const source = `// Generated by src/lib/scripts/example-statistics.ts from example.gpx: do not edit.
export const exampleData = ${JSON.stringify(data)};
`;
    const options = (await prettier.resolveConfig(exampleData)) ?? {};
    fs.writeFileSync(
        exampleData,
        await prettier.format(source, { ...options, parser: 'typescript' })
    );
    console.log(`Wrote ${path.relative(process.cwd(), exampleData)}`);
}

if (process.argv[1] && pathToFileURL(process.argv[1]).href === import.meta.url) {
    generate();
}