/**
 * API client boundary for same-origin backend communication.
 * Strictly uses relative URLs (/api/v1/...) with no mock toggles or hardcoded origins.
 */

const MAX_PROMPT_BYTES = 16 * 1024 * 1024; // 16 MiB
const MAX_FIELD_BYTES = 8 * 1024; // 8 KiB for Confluence URL / PAT

/**
 * Returns the UTF-8 byte length of a string.
 * @param {string} str
 * @returns {number}
 */
export function getUtf8ByteLength(str) {
  if (typeof str !== 'string') return 0;
  return new TextEncoder().encode(str).length;
}

/**
 * Validates Confluence URL and PAT strings according to contract limits.
 * @param {{ url: string, pat: string }} credentials
 * @throws {Error} If credentials fail validation
 */
export function validateCredentials({ url, pat }) {
  if (!url || typeof url !== 'string' || !url.trim()) {
    const err = new Error('Confluence URL is required.');
    err.code = 'invalid_input';
    throw err;
  }
  if (!pat || typeof pat !== 'string' || !pat.trim()) {
    const err = new Error('Personal Access Token (PAT) is required.');
    err.code = 'invalid_input';
    throw err;
  }

  const urlBytes = getUtf8ByteLength(url);
  if (urlBytes > MAX_FIELD_BYTES) {
    const err = new Error('Confluence URL exceeds the 8 KiB limit.');
    err.code = 'invalid_input';
    throw err;
  }

  const patBytes = getUtf8ByteLength(pat);
  if (patBytes > MAX_FIELD_BYTES) {
    const err = new Error('Personal Access Token exceeds the 8 KiB limit.');
    err.code = 'invalid_input';
    throw err;
  }

  try {
    const parsed = new URL(url);
    if (!['http:', 'https:'].includes(parsed.protocol)) {
      throw new Error();
    }
  } catch {
    const err = new Error('Confluence URL must be a valid HTTP or HTTPS URL.');
    err.code = 'invalid_input';
    throw err;
  }
}

/**
 * Parses and normalizes API error responses.
 * @param {Response} response
 * @returns {Promise<Error>}
 */
async function parseApiError(response) {
  let code = 'execution_failed';
  let message = `Request failed with status ${response.status}`;

  let rawText = '';
  try {
    rawText = await response.text();
    if (rawText) {
      const data = JSON.parse(rawText);
      if (data && data.error) {
        if (typeof data.error.code === 'string') {
          code = data.error.code;
        }
        if (typeof data.error.message === 'string') {
          message = data.error.message;
        }
        const err = new Error(message);
        err.code = code;
        err.status = response.status;
        return err;
      }
    }
  } catch {
    // Non-JSON body fallback
  }

  // Non-JSON or empty error body fallback based on HTTP status
  if (response.status === 400) {
    code = 'invalid_input';
  } else if (response.status === 403) {
    // Differentiate origin / destination denials from PAT failures per CONTRACTS §2
    const lower = (rawText || response.statusText || '').toLowerCase();
    if (lower.includes('origin')) {
      code = 'origin_denied';
      message = 'Request forbidden: origin denied.';
    } else if (lower.includes('destination') || lower.includes('host')) {
      code = 'destination_denied';
      message = 'Request forbidden: destination URL not permitted.';
    } else if (lower.includes('auth') || lower.includes('pat') || lower.includes('token') || lower.includes('credential')) {
      code = 'confluence_auth_failed';
      message = 'Confluence authentication failed.';
    } else {
      // Ingress / reverse proxy 403 rejection
      code = 'origin_denied';
      message = 'Request forbidden by server policy.';
    }
  } else if (response.status === 404) {
    code = 'artifact_not_found';
  } else if (response.status === 409) {
    code = 'busy';
  } else if (response.status === 413) {
    code = 'request_too_large';
  } else if (response.status === 502) {
    code = 'upstream_failed';
  } else if (response.status === 504) {
    code = 'query_timeout';
  }

  const err = new Error(message);
  err.code = code;
  err.status = response.status;
  return err;
}

/**
 * Verifies credentials against the backend.
 * @param {{ url: string, pat: string }} credentials
 * @param {{ signal?: AbortSignal }} [options]
 * @returns {Promise<{ valid: boolean }>}
 */
export async function verifyCredentials(credentials, { signal } = {}) {
  validateCredentials(credentials);

  const response = await fetch('/api/v1/auth/verify', {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json'
    },
    body: JSON.stringify({
      url: credentials.url.trim(),
      pat: credentials.pat.trim()
    }),
    signal
  });

  if (!response.ok) {
    throw await parseApiError(response);
  }

  return await response.json();
}

/**
 * Submits a research prompt with credentials.
 * @param {{ prompt: string, credentials: { url: string, pat: string } }} params
 * @param {{ signal?: AbortSignal }} [options]
 * @returns {Promise<object>} Query result object
 */
export async function submitQuery({ prompt, credentials }, { signal } = {}) {
  if (!prompt || typeof prompt !== 'string' || !prompt.trim()) {
    const err = new Error('Prompt cannot be empty.');
    err.code = 'invalid_input';
    throw err;
  }

  const promptBytes = getUtf8ByteLength(prompt);
  if (promptBytes > MAX_PROMPT_BYTES) {
    const err = new Error(`Prompt exceeds the 16 MiB UTF-8 limit (${promptBytes} bytes).`);
    err.code = 'invalid_input';
    throw err;
  }

  validateCredentials(credentials);

  const response = await fetch('/api/v1/query', {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json'
    },
    body: JSON.stringify({
      prompt: prompt, // Preserve original untrimmed text inside payload while verifying trimmed was non-empty
      credentials: {
        url: credentials.url.trim(),
        pat: credentials.pat.trim()
      }
    }),
    signal
  });

  if (!response.ok) {
    throw await parseApiError(response);
  }

  return await response.json();
}

/**
 * Downloads an artifact by its backend-issued ID.
 * @param {string} artifactId
 * @param {{ signal?: AbortSignal }} [options]
 * @returns {Promise<{ blob: Blob, filename: string }>}
 */
export async function downloadArtifact(artifactId, { signal } = {}) {
  if (!artifactId || typeof artifactId !== 'string') {
    const err = new Error('Invalid artifact ID.');
    err.code = 'invalid_input';
    throw err;
  }

  const response = await fetch(`/api/v1/artifacts/${encodeURIComponent(artifactId)}`, {
    method: 'GET',
    signal
  });

  if (!response.ok) {
    throw await parseApiError(response);
  }

  // Extract filename from Content-Disposition if present
  let filename = 'download';
  const disposition = response.headers.get('Content-Disposition');
  if (disposition) {
    const match = disposition.match(/filename=["']?([^"';]+)["']?/i);
    if (match && match[1]) {
      filename = match[1].trim();
    }
  }

  const blob = await response.blob();
  return { blob, filename };
}