import { mkdir, readFile, writeFile } from "node:fs/promises";
import path from "node:path";
import { fileURLToPath } from "node:url";

const scriptDirectory = path.dirname(fileURLToPath(import.meta.url));
const repoRoot = path.resolve(scriptDirectory, "..");
const openApiPath = path.join(repoRoot, "openapi", "RpgRoller.json");
const outputPath = path.join(repoRoot, "RpgRoller", "wwwroot", "generated", "api-client.js");

function escapePathSegment(segment) {
    return segment.replaceAll("\\", "\\\\").replaceAll("\"", "\\\"");
}

function collectOperations(document) {
    const operations = [];
    for (const [pathKey, pathItem] of Object.entries(document.paths ?? {})) {
        for (const [method, operation] of Object.entries(pathItem ?? {})) {
            if (operation === null || typeof operation !== "object") {
                continue;
            }

            if (typeof operation.operationId !== "string" || operation.operationId.length === 0) {
                throw new Error(`Missing operationId for ${method.toUpperCase()} ${pathKey}`);
            }

            operations.push({
                operationId: operation.operationId,
                method: method.toUpperCase(),
                path: pathKey
            });
        }
    }

    if (operations.length === 0) {
        throw new Error("OpenAPI document does not define any operations.");
    }

    return operations.sort((left, right) => left.operationId.localeCompare(right.operationId));
}

function buildClientSource(operations) {
    const operationEntries = operations
        .map((operation) => `    ${operation.operationId}: { method: "${operation.method}", path: "${escapePathSegment(operation.path)}" }`)
        .join(",\n");

    const helper = `const apiOperations = {\n${operationEntries}\n};\n`;

    const sendFunction = `
async function send(operation, pathParams = {}) {
    let resolvedPath = operation.path;
    for (const [key, value] of Object.entries(pathParams)) {
        resolvedPath = resolvedPath.replace(\`{\${key}}\`, encodeURIComponent(String(value)));
    }

    const response = await fetch(resolvedPath, {
        method: operation.method,
        headers: {
            "Accept": "application/json"
        }
    });

    if (!response.ok) {
        const errorPayload = await response.json().catch(() => ({ error: "Unknown API error." }));
        throw new Error(errorPayload.error ?? \`Request failed with status \${response.status}\`);
    }

    return response.json();
}
`.trim();

    const exports = operations
        .map((operation) => {
            const params = [...operation.path.matchAll(/\{([^}]+)\}/g)].map((match) => match[1]);
            const signature = params.length === 0 ? "" : params.join(", ");
            const pathParams = params.length === 0
                ? "{}"
                : `{ ${params.map((name) => `${name}: ${name}`).join(", ")} }`;

            return `export async function ${operation.operationId}(${signature}) {\n    return send(apiOperations.${operation.operationId}, ${pathParams});\n}`;
        })
        .join("\n\n");

    return `/* This file is generated by scripts/generate-api-client.mjs. */\n\nexport { apiOperations };\n\n${helper}\n${sendFunction}\n\n${exports}\n`;
}

const openApiText = await readFile(openApiPath, "utf8");
const document = JSON.parse(openApiText);
const operations = collectOperations(document);
const clientSource = buildClientSource(operations);

await mkdir(path.dirname(outputPath), { recursive: true });
await writeFile(outputPath, clientSource, "utf8");
console.log(`Generated API client: ${path.relative(repoRoot, outputPath)}`);