#!/usr/bin/env node
/**
 * API compatibility diff tool
 * Compares two OpenAPI 3.x specs (YAML or JSON) and reports additive vs breaking changes.
 *
 * Usage:
 *   node scripts/api-compat-diff.mjs <oldSpec> <newSpec> [--output json|text] [--fail-on-breaking]
 *
 * Output (text):
 *   - Added/removed operations
 *   - Added/removed responses
 *   - Parameter additions/removals/requiredness changes
 *   - Response content-type additions/removals
 *   - Request body additions/removals/requiredness and content-type changes
 *
 * Output (json):
 *   {
 *     additive: { operations, responses, parameters, responseContentTypes, requestBodies },
 *     breaking: { operations, responses, parameters, responseContentTypes, requestBodies }
 *   }
 *
 * Exit codes:
 *   0  => success
 *   1  => invalid/missing args or IO/parsing error
 *   2  => breaking changes detected with --fail-on-breaking
 */

import fs from 'fs';
import path from 'path';
import process from 'process';
import yaml from 'yaml';

function panic(message) {
  console.error(`[api-compat-diff] ${message}`);
  process.exit(1);
}

function parseArgs(argv) {
  const args = argv.slice(2);
  const opts = { output: 'text', failOnBreaking: false };

  if (args.length < 2) {
    panic('Usage: node scripts/api-compat-diff.mjs <oldSpec> <newSpec> [--output json|text] [--fail-on-breaking]');
  }

  [opts.oldSpec, opts.newSpec] = args.slice(0, 2);

  for (let i = 2; i < args.length; i += 1) {
    const arg = args[i];
    if (arg === '--output' && args[i + 1]) {
      opts.output = args[i + 1].toLowerCase();
      i += 1;
    } else if (arg === '--fail-on-breaking') {
      opts.failOnBreaking = true;
    }
  }

  if (!['text', 'json'].includes(opts.output)) {
    panic(`Unsupported output mode: ${opts.output}`);
  }

  return opts;
}

function loadSpec(specPath) {
  if (!fs.existsSync(specPath)) {
    panic(`Spec not found: ${specPath}`);
  }

  const raw = fs.readFileSync(specPath, 'utf8');
  const ext = path.extname(specPath).toLowerCase();

  try {
    if (ext === '.json') {
      return JSON.parse(raw);
    }
    return yaml.parse(raw);
  } catch (err) {
    panic(`Failed to parse ${specPath}: ${err.message}`);
  }
}

function normalizeParams(params) {
  const map = new Map();
  if (!Array.isArray(params)) return map;

  for (const param of params) {
    if (!param || typeof param !== 'object') continue;
    if (param.$ref) {
      map.set(`ref:${param.$ref}`, { required: param.required === true, isRef: true });
      continue;
    }
    const name = param.name;
    const loc = param.in;
    if (!name || !loc) continue;
    const key = `${name}:${loc}`;
    map.set(key, { required: param.required === true, isRef: false });
  }

  return map;
}

function describeParam(key, requiredFlag) {
  if (key.startsWith('ref:')) {
    return key.replace(/^ref:/, '');
  }
  const [name, loc] = key.split(':');
  const requiredLabel = requiredFlag ? ' (required)' : '';
  return `${name} in ${loc}${requiredLabel}`;
}

function enumerateOperations(spec) {
  const ops = new Map();
  if (!spec?.paths || typeof spec.paths !== 'object') {
    return ops;
  }

  for (const [pathKey, pathItem] of Object.entries(spec.paths)) {
    if (!pathItem || typeof pathItem !== 'object') {
      continue;
    }

    const pathParams = normalizeParams(pathItem.parameters ?? []);

    for (const method of Object.keys(pathItem)) {
      const lowerMethod = method.toLowerCase();
      if (!['get', 'put', 'post', 'delete', 'patch', 'head', 'options', 'trace'].includes(lowerMethod)) {
        continue;
      }

      const op = pathItem[method];
      if (!op || typeof op !== 'object') {
        continue;
      }

      const opId = `${lowerMethod} ${pathKey}`;

      const opParams = normalizeParams(op.parameters ?? []);
      const parameters = new Map(pathParams);
      for (const [key, val] of opParams.entries()) {
        parameters.set(key, val);
      }

      const responseContentTypes = new Map();
      const responses = new Set();
      const responseEntries = Object.entries(op.responses ?? {});
      for (const [code, resp] of responseEntries) {
        responses.add(code);
        const contentTypes = new Set(Object.keys(resp?.content ?? {}));
        responseContentTypes.set(code, contentTypes);
      }

      const requestBody = op.requestBody
        ? {
            present: true,
            required: op.requestBody.required === true,
            contentTypes: new Set(Object.keys(op.requestBody.content ?? {})),
          }
        : { present: false, required: false, contentTypes: new Set() };

      ops.set(opId, {
        method: lowerMethod,
        path: pathKey,
        responses,
        responseContentTypes,
        parameters,
        requestBody,
      });
    }
  }

  return ops;
}

function diffOperations(oldOps, newOps) {
  const additiveOps = [];
  const breakingOps = [];
  const additiveResponses = [];
  const breakingResponses = [];
  const additiveParams = [];
  const breakingParams = [];
  const additiveResponseContentTypes = [];
  const breakingResponseContentTypes = [];
  const additiveRequestBodies = [];
  const breakingRequestBodies = [];

  // Operations added or removed
  for (const [id] of newOps.entries()) {
    if (!oldOps.has(id)) {
      additiveOps.push(id);
    }
  }

  for (const [id] of oldOps.entries()) {
    if (!newOps.has(id)) {
      breakingOps.push(id);
    }
  }

  // Response- and parameter-level diffs for shared operations
  for (const [id, newOp] of newOps.entries()) {
    if (!oldOps.has(id)) continue;
    const oldOp = oldOps.get(id);

    for (const code of newOp.responses) {
      if (!oldOp.responses.has(code)) {
        additiveResponses.push(`${id} -> ${code}`);
      }
    }

    for (const code of oldOp.responses) {
      if (!newOp.responses.has(code)) {
        breakingResponses.push(`${id} -> ${code}`);
      }
    }

    for (const code of newOp.responses) {
      if (!oldOp.responses.has(code)) continue;
      const oldTypes = oldOp.responseContentTypes.get(code) ?? new Set();
      const newTypes = newOp.responseContentTypes.get(code) ?? new Set();

      for (const ct of newTypes) {
        if (!oldTypes.has(ct)) {
          additiveResponseContentTypes.push(`${id} -> ${code} (${ct})`);
        }
      }
      for (const ct of oldTypes) {
        if (!newTypes.has(ct)) {
          breakingResponseContentTypes.push(`${id} -> ${code} (${ct})`);
        }
      }
    }

    for (const [key, oldParam] of oldOp.parameters.entries()) {
      if (!newOp.parameters.has(key)) {
        breakingParams.push(`${id} -> - parameter ${describeParam(key, oldParam.required)}`);
      }
    }

    for (const [key, newParam] of newOp.parameters.entries()) {
      if (!oldOp.parameters.has(key)) {
        const target = newParam.required ? breakingParams : additiveParams;
        target.push(`${id} -> + parameter ${describeParam(key, newParam.required)}`);
        continue;
      }

      const oldParam = oldOp.parameters.get(key);
      if (oldParam.required !== newParam.required) {
        if (newParam.required) {
          breakingParams.push(`${id} -> parameter ${describeParam(key)} made required`);
        } else {
          additiveParams.push(`${id} -> parameter ${describeParam(key)} made optional`);
        }
      }
    }

    const { requestBody: oldBody } = oldOp;
    const { requestBody: newBody } = newOp;

    if (oldBody.present && !newBody.present) {
      breakingRequestBodies.push(`${id} -> - requestBody`);
    } else if (!oldBody.present && newBody.present) {
      const target = newBody.required ? breakingRequestBodies : additiveRequestBodies;
      const label = newBody.required ? 'required' : 'optional';
      target.push(`${id} -> + requestBody (${label})`);
    } else if (oldBody.present && newBody.present) {
      if (oldBody.required !== newBody.required) {
        if (newBody.required) {
          breakingRequestBodies.push(`${id} -> requestBody made required`);
        } else {
          additiveRequestBodies.push(`${id} -> requestBody made optional`);
        }
      }

      for (const ct of newBody.contentTypes) {
        if (!oldBody.contentTypes.has(ct)) {
          additiveRequestBodies.push(`${id} -> requestBody content-type added: ${ct}`);
        }
      }
      for (const ct of oldBody.contentTypes) {
        if (!newBody.contentTypes.has(ct)) {
          breakingRequestBodies.push(`${id} -> requestBody content-type removed: ${ct}`);
        }
      }
    }
  }

  return {
    additive: {
      operations: additiveOps.sort(),
      responses: additiveResponses.sort(),
      parameters: additiveParams.sort(),
      responseContentTypes: additiveResponseContentTypes.sort(),
      requestBodies: additiveRequestBodies.sort(),
    },
    breaking: {
      operations: breakingOps.sort(),
      responses: breakingResponses.sort(),
      parameters: breakingParams.sort(),
      responseContentTypes: breakingResponseContentTypes.sort(),
      requestBodies: breakingRequestBodies.sort(),
    },
  };
}

function renderText(diff) {
  const lines = [];
  lines.push('Additive:');
  lines.push(`  Operations: ${diff.additive.operations.length}`);
  diff.additive.operations.forEach((op) => lines.push(`    + ${op}`));
  lines.push(`  Responses: ${diff.additive.responses.length}`);
  diff.additive.responses.forEach((resp) => lines.push(`    + ${resp}`));
  lines.push(`  Parameters: ${diff.additive.parameters.length}`);
  diff.additive.parameters.forEach((param) => lines.push(`    + ${param}`));
  lines.push(`  Response content-types: ${diff.additive.responseContentTypes.length}`);
  diff.additive.responseContentTypes.forEach((ct) => lines.push(`    + ${ct}`));
  lines.push(`  Request bodies: ${diff.additive.requestBodies.length}`);
  diff.additive.requestBodies.forEach((rb) => lines.push(`    + ${rb}`));
  lines.push('Breaking:');
  lines.push(`  Operations: ${diff.breaking.operations.length}`);
  diff.breaking.operations.forEach((op) => lines.push(`    - ${op}`));
  lines.push(`  Responses: ${diff.breaking.responses.length}`);
  diff.breaking.responses.forEach((resp) => lines.push(`    - ${resp}`));
  lines.push(`  Parameters: ${diff.breaking.parameters.length}`);
  diff.breaking.parameters.forEach((param) => lines.push(`    - ${param}`));
  lines.push(`  Response content-types: ${diff.breaking.responseContentTypes.length}`);
  diff.breaking.responseContentTypes.forEach((ct) => lines.push(`    - ${ct}`));
  lines.push(`  Request bodies: ${diff.breaking.requestBodies.length}`);
  diff.breaking.requestBodies.forEach((rb) => lines.push(`    - ${rb}`));
  return lines.join('\n');
}

function main() {
  const opts = parseArgs(process.argv);
  const oldSpec = loadSpec(opts.oldSpec);
  const newSpec = loadSpec(opts.newSpec);

  const diff = diffOperations(enumerateOperations(oldSpec), enumerateOperations(newSpec));

  if (opts.output === 'json') {
    console.log(JSON.stringify(diff, null, 2));
  } else {
    console.log(renderText(diff));
  }

  if (opts.failOnBreaking && (
    diff.breaking.operations.length > 0
    || diff.breaking.responses.length > 0
    || diff.breaking.parameters.length > 0
    || diff.breaking.responseContentTypes.length > 0
    || diff.breaking.requestBodies.length > 0
  )) {
    process.exit(2);
  }
}

if (import.meta.url === `file://${process.argv[1]}`) {
  main();
}