/**
 * The intake handler. Spec: docs/05-backend-spec.md. Resource names, region,
 * table and SES state: AGENTS.md §7 — this file reads them from the environment
 * and does not restate them.
 *
 * ⚠️ THIS IS NOT DEPLOYED. Written at build step 8; nothing on this project
 * deploys before cutover (D11). AGENTS.md §7 records that a hand-built
 * `adr-intake-handler` already exists in the console, created before this repo,
 * and this file REPLACES it rather than describing it. docs/06's cutover
 * checklist carries the deployment steps and the CloudFront `/api/*` behaviour
 * the form depends on. Until both are done the form on /contact/ posts into
 * nothing, which is why that page also publishes the email address.
 *
 * ── THE SHAPE, AND WHY IT IS POST-REDIRECT-GET ─────────────────────────────
 *
 * The site ships ZERO JavaScript (AGENTS.md §7, and it is not "minimal" — none).
 * So the form is a plain HTML POST, and this handler answers with **303 See
 * Other** and a `Location` on the site. That gives, with no script anywhere:
 *
 *   - a working form with JavaScript disabled, which is the failure this whole
 *     project exists to fix;
 *   - no JSON response rendered as a raw page, which is what a plain POST to an
 *     API Gateway JSON endpoint shows the user;
 *   - no double submission on refresh, because the browser lands on a GET.
 *
 * docs/05's definition of done asks that the form "degrades to a mailto:
 * fallback with JavaScript disabled". It does not need to: there is nothing to
 * degrade FROM, because the form never used script. The email address is
 * published on /contact/ regardless.
 *
 * ── WHAT THIS DELIBERATELY DOES NOT IMPLEMENT ──────────────────────────────
 *
 * **THE 3-SECOND TIMESTAMP CHECK IS NOT IMPLEMENTED, AND THAT IS A DECISION.**
 * docs/05 asks to "reject submissions completed in under 3 seconds". It cannot
 * be done here and implementing it would produce a control that does nothing:
 * the check needs to know when the form was SERVED to that visitor, and
 * /contact/ is a static file cached at the CloudFront edge. A build-time
 * timestamp is the same value for every visitor and is hours or days old, so
 * `now - served` is always large — the check would pass for a bot exactly as it
 * passes for a human. A per-visitor token needs either a dynamic origin or
 * client-side script, and the site has neither by design.
 *
 * That is worse than omitting it: AGENTS.md Q22 and the Lighthouse row are both
 * records of what a control that exists on paper and not in fact costs here. So
 * it is omitted, said out loud, and the load is carried by the honeypot, the
 * Origin check, the aggregate API Gateway route throttle and the validation
 * below. (Aggregate, not per-IP — see above; the earlier wording here said
 * "rate limit" and let the reader supply the stronger meaning.)
 *
 * ── WHAT MUST BE CONFIGURED OUTSIDE THIS FILE ──────────────────────────────
 *
 *   - An AGGREGATE API Gateway route throttle. NOT per source IP: API Gateway
 *     throttling is per route and per stage across all callers, so docs/05's
 *     "5 requests / 5 minutes per source IP" is struck — per-IP needs AWS WAF.
 *     Never describe what ships as per-IP. docs/09 Part 6.3.
 *   - CloudFront behaviour: /api/* → the HTTP API origin §7 records.
 *   - CloudWatch alarms on Lambda `Errors` and on API Gateway 5xx for this
 *     route. NOT a dead-letter queue: `DeadLetterConfig` is used only for
 *     ASYNCHRONOUS invocations, API Gateway invokes synchronously, so a DLQ here
 *     would sit at depth 0 for ever and an alarm on it would be a permanently
 *     green light. docs/05 §Notification carries the replacement.
 *   - The `ses-alerts` SNS email subscription is CONFIRMED (§7) — R9 closed
 *     2026-09-01, so the bounce and complaint alarms reach someone.
 */
import { DynamoDBClient, PutItemCommand } from '@aws-sdk/client-dynamodb';
import { SESv2Client, SendEmailCommand } from '@aws-sdk/client-sesv2';
import { randomUUID } from 'node:crypto';
/* The field table and the honeypot name live in their own module so that
   `npm run check:intake` can import them without this file's module-scope
   `requireEnv()` calls running. See fields.mjs for why there are two tables. */
import { FIELDS, HONEYPOT } from './fields.mjs';

/* Region comes from the Lambda runtime, which sets AWS_REGION to the function's
   own region — the one §7 records. Not hardcoded: a second copy of a fact §7
   owns is the copy that goes stale. */
const ddb = new DynamoDBClient({});
const ses = new SESv2Client({});

const TABLE = requireEnv('INTAKE_TABLE');
const SITE_ORIGIN = requireEnv('SITE_ORIGIN');
const NOTIFY_TO = requireEnv('NOTIFY_TO');
const MAIL_FROM = requireEnv('MAIL_FROM');

/** 24 months, docs/05 §Retention. It must match /legal/privacy/ exactly.
 *  ⚠️ Writing this attribute is NOT the mechanism — TTL must be enabled on the
 *  table, and AGENTS.md §7 records whether it is. */
const RETENTION_MONTHS = 24;

/** The public commitment, §4 and Q27. It must read identically here, on
 *  /contact/, and in any bio. Injected rather than typed so one edit moves all
 *  three; the deploy step sets it from `CONTACT.responseTime`. */
const RESPONSE_TIME = requireEnv('RESPONSE_TIME');

/**
 * ⚠️ INJECTED FOR EXACTLY THE REASON ABOVE, AND IT WAS HAND-TYPED UNTIL
 * 2026-08-31. The confirmation email spelled the no-retainer notice out in
 * prose, which made it a **fourth** hand-copy of `NO_RETAINER_NOTICE` — and the
 * copy **dropped the fourth clause the constant carries**, *"and does not itself
 * create a conflict check"*, which `docs/01` §`/contact/` requires. It also used
 * a hyphen where the constant uses an en dash.
 *
 * The reasoning three lines above applied to it identically and was not applied.
 * `npm run check:intake` compares field tables only, so a future softening of
 * the constant would never have reached this email and nothing would have
 * failed — the silent-drift shape §4 flags for the whole commitment class.
 * Found by `adversarial-reviewer`. The deploy step sets it from
 * `NO_RETAINER_NOTICE` in `src/data/site.ts`.
 *
 * ⚠️ AND THAT SENTENCE USED TO END "`docs/06` names it", WHICH IT DID NOT.
 * This variable became a `requireEnv` and reached no document — so the
 * deployment list said five variables while this file required six, and the
 * function would have thrown at cold start on every invocation. **The comment
 * asserting the documentation existed is what made it invisible.** `docs/06` and
 * `docs/05` now name all six. Found by `adversarial-reviewer` round 2.
 */
const NO_RETAINER_NOTICE = requireEnv('NO_RETAINER_NOTICE');

function requireEnv(name) {
  const value = process.env[name];
  if (!value) {
    // Fail at cold start, not per request: a function missing configuration
    // should not accept a submission it cannot store.
    throw new Error(`intake handler: ${name} is not set`);
  }
  return value;
}

/**
 * Strip HTML before storage and before anything enters an email body (docs/05).
 *
 * NOT AN HTML SANITISER, AND IT DOES NOT NEED TO BE — every field is stored and
 * rendered as PLAIN TEXT, never as markup, so the job is to make a value
 * incapable of becoming markup later, not to allow safe markup now.
 *
 * ⚠️ AND FOR THAT REASON IT STRIPS ANGLE BRACKETS RATHER THAN ENTITY-ENCODING
 * THEM. The first version of this function escaped `&` to `&`, which is
 * correct only when the sink is HTML: both sinks here are plain text, so the
 * reader of the confirmation email would have received the five literal
 * characters `&` wherever they had typed an ampersand. Encoding for the
 * wrong sink is a defect wearing the costume of a protection.
 */
function toPlainText(value) {
  return (
    value
      // Control characters, including the CR/LF that would let a value forge a
      // header line in an email, and the C1 range.
      //
      // `no-control-regex` is disabled ON PURPOSE and with the reason: that rule
      // exists to catch a control character that reached a pattern by ACCIDENT,
      // usually a mis-escaped literal. Here the control range IS the thing being
      // matched, and it is the one part of this function that stops a submitted
      // value from forging an email header. Rewriting it as a charCodeAt filter
      // to satisfy the linter would make the intent less legible, not more.
      // eslint-disable-next-line no-control-regex
      .replace(/[\u0000-\u001f\u007f-\u009f]/g, ' ')
      // Angle brackets removed rather than entity-encoded. The destination is
      // plain text — a DynamoDB string attribute and a text/plain email body —
      // so `&` would REACH THE READER as the five characters "&", which
      // is a defect rather than a protection. Encoding is right when the sink is
      // HTML; here the requirement is only that the value can never become
      // markup if it is later put into one, and no `<` satisfies that
      // permanently. Nothing else in the value is altered.
      .replace(/[<>]/g, '')
      .replace(/[ \t]{2,}/g, ' ')
      .trim()
  );
}

/**
 * Email validation, server side. Deliberately structural rather than clever:
 * one @, something either side, a dot in the domain, no whitespace, no angle
 * brackets, within the RFC 5321 length. A regex that tries to implement RFC 5322
 * rejects real addresses, and the confirmation email in D18 is the real check —
 * if it does not arrive, the address was wrong whatever a regex said.
 */
function looksLikeEmail(value) {
  return (
    value.length <= 254 &&
    /^[^\s@<>]+@[^\s@<>.]+(\.[^\s@<>.]+)+$/.test(value) &&
    !value.includes('..')
  );
}

function parseBody(event) {
  const raw = event.isBase64Encoded
    ? Buffer.from(event.body ?? '', 'base64').toString('utf8')
    : (event.body ?? '');
  const type = headerOf(event, 'content-type') ?? '';
  if (type.includes('application/x-www-form-urlencoded')) {
    return Object.fromEntries(new URLSearchParams(raw));
  }
  // JSON is accepted so the endpoint stays testable with curl, and because a
  // future island could post JSON without changing this handler.
  if (type.includes('application/json')) {
    const parsed = JSON.parse(raw);
    if (
      parsed === null ||
      typeof parsed !== 'object' ||
      Array.isArray(parsed)
    ) {
      throw new Error('body is not an object');
    }
    return parsed;
  }
  throw new Error(`unsupported content-type: ${type}`);
}

/**
 * ⚠️ THE UNFORGEABLE VALUE, AND NOT THE USEFUL ONE. `requestContext.http
 * .sourceIp` is the TCP peer, which behind the CloudFront behaviour that routes
 * /api/* is a CloudFront EDGE — so this records AWS rather than the inquirer.
 *
 * IT READ `x-forwarded-for` FOR ONE REVISION AND THAT WAS WORSE. CloudFront
 * APPENDS the viewer address to a client-supplied XFF rather than replacing it,
 * so the leftmost entry is whatever the client sent: a submission with
 * `X-Forwarded-For: 8.8.8.8` stored `8.8.8.8`. That turns a field held for abuse
 * investigation into one that can be made to name an uninvolved third party, and
 * /legal/privacy/ promises the record holds "your IP address". A forgeable value
 * presented as an identification is worse than an honest useless one.
 *
 * The right value is CloudFront's own `CloudFront-Viewer-Address`, which
 * CloudFront generates and overwrites — but reaching it needs a CUSTOM origin
 * request policy on the /api/* behaviour (the managed
 * AllViewerAndCloudFrontHeaders forwards Host, which 403s every request at API
 * Gateway, which is why AllViewerExceptHostHeader was chosen). That is an
 * infrastructure change, and `docs/09` Part 7.2 measures what this field
 * actually contains at cutover rather than reasoning about the proxy chain —
 * with a decision table for each outcome. Do not "fix" this from the header
 * again without that measurement.
 */
function viewerIp(event) {
  return event.requestContext?.http?.sourceIp ?? 'unknown';
}

function headerOf(event, name) {
  const headers = event.headers ?? {};
  // API Gateway HTTP API lowercases header keys; a direct invoke or a test
  // harness may not, so this does not assume it.
  const hit = Object.keys(headers).find((k) => k.toLowerCase() === name);
  return hit ? headers[hit] : undefined;
}

const redirect = (path) => ({
  statusCode: 303,
  headers: {
    Location: `${SITE_ORIGIN}${path}`,
    // A redirect that a CDN or a browser caches would send the next visitor
    // straight to the confirmation page without submitting anything.
    'Cache-Control': 'no-store',
  },
  body: '',
});

const SUCCESS = '/contact/received/';
const FAILURE = '/contact/could-not-send/';

export async function handler(event) {
  /**
   * ORIGIN CHECK, AND IT IS THE CONTROL CORS IS USUALLY MISTAKEN FOR. A form
   * POST is a top-level navigation: it is exempt from CORS preflight, so an
   * `Access-Control-Allow-Origin` setting on the endpoint does not stop another
   * site from posting a form here. Checking the header does.
   *
   * Firefox omits `Origin` on some same-origin form navigations, so `Referer` is
   * accepted as a fallback — both must MATCH the site origin when present, and
   * a request with neither is refused.
   */
  const origin = headerOf(event, 'origin');
  const referer = headerOf(event, 'referer');
  const originOk = origin
    ? origin === SITE_ORIGIN
    : referer
      ? referer.startsWith(`${SITE_ORIGIN}/`)
      : false;
  if (!originOk) {
    return {
      statusCode: 403,
      headers: { 'Cache-Control': 'no-store' },
      body: '',
    };
  }

  let body;
  try {
    body = parseBody(event);
  } catch {
    return redirect(FAILURE);
  }

  /**
   * THE HONEYPOT GETS THE SUCCESS PAGE, NOT AN ERROR. Telling a bot it was
   * detected is how the next version of the bot stops filling the field. A
   * human cannot reach this field — it is `display: none`, `tabindex="-1"` and
   * `aria-hidden` — so a non-empty value is not a mistake anyone made.
   */
  if (typeof body[HONEYPOT] === 'string' && body[HONEYPOT].trim() !== '') {
    return redirect(SUCCESS);
  }

  const clean = {};
  const errors = [];
  for (const field of FIELDS) {
    const rawValue = body[field.name];
    const value = typeof rawValue === 'string' ? rawValue.trim() : '';
    if (value === '') {
      if (field.required) errors.push(`${field.name} is required`);
      continue;
    }
    // REJECT over the cap rather than truncating (docs/05). A silently
    // truncated matter summary is a file read wrongly.
    if (field.max && value.length > field.max) {
      errors.push(`${field.name} exceeds ${field.max} characters`);
      continue;
    }
    if (field.options && !field.options.includes(value)) {
      errors.push(`${field.name} is not one of the offered values`);
      continue;
    }
    if (field.name === 'email' && !looksLikeEmail(value)) {
      errors.push('email is not a well-formed address');
      continue;
    }
    clean[field.name] = toPlainText(value);
  }

  // Explicit, unchecked by default, and required (docs/05). An unchecked box
  // sends no value at all, so absence is the failure case.
  if (body.consent !== 'on' && body.consent !== 'true') {
    errors.push('consent was not given');
  }

  if (errors.length > 0) {
    // Logged for the operator, never returned to the caller: an error list is a
    // description of the validation rules, which is a gift to whoever is
    // probing them.
    console.warn('intake rejected', { errors });
    return redirect(FAILURE);
  }

  const now = new Date();
  const id = randomUUID();
  /* NO `|| 0` FALLBACK (removed 2026-08-31): DynamoDB will not expire an item
     whose TTL is more than five years past, so `ttl: 0` means RETAINED FOREVER
     while /legal/privacy/ promises deletion. Let a bad value fail the write. */
  const ttl = Math.floor(
    Date.UTC(
      now.getUTCFullYear(),
      now.getUTCMonth() + RETENTION_MONTHS,
      now.getUTCDate(),
      now.getUTCHours(),
      now.getUTCMinutes(),
      now.getUTCSeconds(),
    ) / 1000,
  );

  /**
   * DYNAMODB FIRST, THEN MAIL — docs/05: "SES failure must never lose the
   * submission." The order is the whole guarantee. If SES fails after this
   * write, the record exists and a resend has something to resend; if the write
   * fails, nothing was accepted and the inquirer is told so. (This said "the DLQ
   * replay" — there is no DLQ and there cannot usefully be one on a
   * synchronously invoked function; see the note at the top of this file.)
   */
  try {
    await ddb.send(
      new PutItemCommand({
        TableName: TABLE,
        Item: {
          /* ⚠️ `submissionId` IS THE TABLE'S PARTITION KEY AND THERE IS NO SORT
             KEY. A DynamoDB key schema cannot be altered after creation, so this
             attribute name is fixed by the table `AGENTS.md` §7 names, not
             chosen here — and an item missing it fails the whole write with
             `ValidationException`, which this function converts into the failure
             page. Verify against `describe-table` before changing either name;
             `submittedAt` is an ordinary attribute and is free.               */
          submissionId: { S: id },
          submittedAt: { S: now.toISOString() },
          ttl: { N: String(ttl) },
          // Abuse investigation only (docs/05). Named so a later reader does not
          // repurpose them: they are not analytics and not part of the reply.
          /* Behind CloudFront this is the EDGE address, not the inquirer's.
             See `viewerIp()` — and read it before changing this. */
          sourceIp: { S: viewerIp(event) },
          userAgent: {
            S: (headerOf(event, 'user-agent') ?? 'unknown').slice(0, 400),
          },
          consentAt: { S: now.toISOString() },
          ...Object.fromEntries(
            Object.entries(clean).map(([k, v]) => [k, { S: v }]),
          ),
        },
      }),
    );
  } catch (error) {
    console.error('intake: DynamoDB write failed', error);
    return redirect(FAILURE);
  }

  // `f.label`, not `f.name` — see the note on `label` in fields.mjs. The
  // notification to the operator gets the same rendering: one shape, so the two
  // messages cannot describe the same submission differently.
  const summaryLines = FIELDS.filter((f) => clean[f.name] !== undefined)
    .map((f) => `${f.label}: ${clean[f.name]}`)
    .join('\n');

  /**
   * TWO EMAILS — D18, and the second one is why the form beats a mailto: link.
   * `Promise.allSettled`, not `Promise.all`: the record is already stored, so a
   * failure on either message must be logged rather than lost, and one failing
   * must not prevent the other from being attempted.
   */
  const results = await Promise.allSettled([
    ses.send(
      new SendEmailCommand({
        FromEmailAddress: MAIL_FROM,
        Destination: { ToAddresses: [NOTIFY_TO] },
        // Replyable to the inquirer (docs/05), which is what makes the
        // notification usable without copying an address out of it.
        ReplyToAddresses: [clean.email],
        Content: {
          Simple: {
            Subject: { Data: `Intake — ${clean.name} (${clean.practiceArea})` },
            Body: {
              Text: {
                // The bare id, because it is the partition key: this line is
                // what gets pasted into the console to find the record, so it
                // must be the key and not a rendering of it.
                Data: `Received ${now.toISOString()}\nsubmissionId ${id}\n\n${summaryLines}\n`,
              },
            },
          },
        },
      }),
    ),
    ses.send(
      new SendEmailCommand({
        FromEmailAddress: MAIL_FROM,
        Destination: { ToAddresses: [clean.email] },
        Content: {
          Simple: {
            Subject: { Data: 'Your inquiry has been received' },
            Body: {
              Text: {
                Data: [
                  `Thank you — your inquiry has been received.`,
                  ``,
                  RESPONSE_TIME,
                  ``,
                  NO_RETAINER_NOTICE,
                  ``,
                  `What you sent:`,
                  ``,
                  summaryLines,
                  ``,
                  `How this information is handled, and how to ask for it to be`,
                  `deleted: ${SITE_ORIGIN}/legal/privacy/`,
                  ``,
                ].join('\n'),
              },
            },
          },
        },
      }),
    ),
  ]);

  results.forEach((result, i) => {
    if (result.status === 'rejected') {
      console.error(
        `intake: SES send ${i === 0 ? 'notification' : 'confirmation'} failed`,
        { id, reason: result.reason },
      );
    }
  });

  // The submission is stored. Mail failures are an operator problem, not the
  // inquirer's, and telling them it failed would invite a second submission of
  // a record that already exists.
  return redirect(SUCCESS);
}