import fs from 'fs';
import path from 'path';
import semver from 'semver';
import { UsageError } from 'clipanion';
import Enquirer from 'enquirer';

import * as miscUtils from './miscUtils';
import {SupportedPackageManagers, SupportedPackageManagerSet, Descriptor, Locator} from './types';

/**
 * Locates the active project's package manager specification.
 * 
 * If the specification exists but doesn't match the active package manager,
 * an error is thrown to prevent users from using the wrong package manager,
 * which would lead to inconsistent project layouts.
 * 
 * If the project doesn't include a specification file, we just assume that
 * whatever the user uses is exactly what they want to use. Since the version
 * isn't explicited, we fallback on known good versions.
 * 
 * Finally, if the project doesn't exist at all, we ask the user whether they
 * want to create one in the current project. If they do, we initialize a new
 * project using the default package managers, and configure it so that we
 * don't need to ask again in the future.
 */
export async function findProjectSpec(initialCwd: string, locator: Locator): Promise<Descriptor> {
    while (true) {
        const result = await loadSpec(initialCwd);

        switch (result.type) {
            case `NoProject`: {
                await initProjectAndSpec(result.target, locator);
            } break;

            case `NoSpec`: {
                // A locator is a valid descriptor (but not the other way around)
                return {name: locator.name, range: locator.reference};
            } break;

            case `Found`: {
                if (result.spec.name !== locator.name) {
                    throw new UsageError(`This project is configured to use ${result.spec.name}`);
                } else {
                    return result.spec;
                }
            } break;
        }
    }
}

type LoadSpecResult =
    | {type: `NoProject`, target: string}
    | {type: `NoSpec`, target: string}
    | {type: `Found`, spec: Descriptor};

async function loadSpec(initialCwd: string): Promise<LoadSpecResult> {
    let nextCwd = initialCwd;
    let currCwd = ``;

    let selection: any = null;

    while (nextCwd !== currCwd && selection === null) {
        currCwd = nextCwd;
        nextCwd = path.dirname(currCwd);

        const manifestPath = path.join(currCwd, `package.json`);
        if (!fs.existsSync(manifestPath))
            continue;

        const content = await fs.promises.readFile(manifestPath, `utf8`);

        let data;
        try {
            data = JSON.parse(content);
        } catch {}

        if (typeof data !== `object` || data === null)
            throw new UsageError(`Invalid package.json in ${path.relative(initialCwd, manifestPath)}`);

        selection = {data, manifestPath};
    }

    if (selection === null)
        return {type: `NoProject`, target: path.join(initialCwd, `package.json`)};

    const engines = selection.data.engines;
    if (typeof engines === `undefined`)
        return {type: `NoSpec`, target: selection.manifestPath};
    if (typeof engines !== `object` || engines === null)
        throw new UsageError(`Invalid 'engines' field in ${path.relative(initialCwd, selection.manifestPath)}; expected an object`);

    const pmSpec = engines.pm;
    if (typeof pmSpec === `undefined`)
        return {type: `NoSpec`, target: selection.manifestPath};
    if (typeof pmSpec !== `string`)
        throw new UsageError(`Invalid package manager specification in ${path.relative(initialCwd, selection.manifestPath)}; expected a semver range`);

    const match = pmSpec.match(/^(?!_)(.+)@(.+)$/);
    if (match === null || !semver.validRange(match[2]))
        throw new UsageError(`Invalid package manager specification in ${path.relative(initialCwd, selection.manifestPath)}; expected a semver range`);

    if (!SupportedPackageManagerSet.has(match[1]))
        throw new UsageError(`Unsupported package manager specification (${match})`);

    return {
        type: `Found`,
        spec: {
            name: match[1] as SupportedPackageManagers,
            range: match[2],
        },
    };
}

export async function persistPmSpec(updateTarget: string, locator: Locator, message: string) {
    const newSpec = `${locator.name}@^${locator.reference}`;

    let res: boolean;
    try {
        res = await Enquirer.prompt([{
            type: `confirm`,
            name: `confirm`,
            initial: true,
            message: message.replace(`{}`, newSpec),
        }]);
    } catch (err) {
        if (err === ``) {
            res = false;
        } else {
            throw err;
        }
    }

    if (!res)
        throw new miscUtils.Cancellation();

    const content = fs.existsSync(updateTarget)
        ? await fs.promises.readFile(updateTarget, `utf8`)
        : `{}`;

    const data = JSON.parse(content);

    data.engines = data.engines || {};
    data.engines.pm = newSpec;

    const serialized = JSON.stringify(data, null, 2);
    await fs.promises.writeFile(updateTarget, `${serialized}\n`);
}

export async function initProjectAndSpec(updateTarget: string, locator: Locator) {
    return await persistPmSpec(updateTarget, locator, `No configured project yet; set it to {}?`);
}

export async function initSpec(updateTarget: string, locator: Locator) {
    return await persistPmSpec(updateTarget, locator, `No configured local package manager yet; set it to {}?`);
}