feat: add email filters with JMAP Sieve Scripts (RFC 9661)

Server-side email filtering with visual rule builder and raw Sieve editor.
Conditions (From/To/Subject/Size/Body), actions (Move/Forward/Star/Discard),
auto-save with rollback, drag-and-drop reorder, opaque script reset,
accessibility focus traps, toast validation, and 8-language i18n support.

lib/sieve/generator.ts

@@ -0,0 +1,169 @@
+import type { FilterRule, FilterCondition, FilterAction, FilterMetadata } from '@/lib/jmap/sieve-types';
+import { debug } from '@/lib/debug';
+
+const HEADER_MAP: Record<string, string> = {
+  from: 'From',
+  to: 'To',
+  cc: 'Cc',
+  subject: 'Subject',
+};
+
+function escapeString(value: string): string {
+  return value.replace(/\\/g, '\\\\').replace(/"/g, '\\"');
+}
+
+function generateCondition(condition: FilterCondition): string {
+  const { field, comparator, value } = condition;
+
+  if (field === 'size') {
+    const op = comparator === 'greater_than' ? ':over' : ':under';
+    return `size ${op} ${value}`;
+  }
+
+  if (field === 'body') {
+    const matchType = comparator === 'is' ? ':is' : ':contains';
+    return `body ${matchType} "${escapeString(value)}"`;
+  }
+
+  const headerName = field === 'header'
+    ? (condition.headerName || 'X-Unknown')
+    : HEADER_MAP[field];
+
+  const escaped = escapeString(value);
+
+  switch (comparator) {
+    case 'contains':
+      return `header :contains "${headerName}" "${escaped}"`;
+    case 'not_contains':
+      return `not header :contains "${headerName}" "${escaped}"`;
+    case 'is':
+      return `header :is "${headerName}" "${escaped}"`;
+    case 'not_is':
+      return `not header :is "${headerName}" "${escaped}"`;
+    case 'starts_with':
+      return `header :matches "${headerName}" "${escaped}*"`;
+    case 'ends_with':
+      return `header :matches "${headerName}" "*${escaped}"`;
+    case 'matches':
+      return `header :matches "${headerName}" "${escaped}"`;
+    default:
+      return `header :contains "${headerName}" "${escaped}"`;
+  }
+}
+
+function generateActions(actions: FilterAction[]): string[] {
+  return actions.map(action => {
+    switch (action.type) {
+      case 'move':
+        return `fileinto "${escapeString(action.value || '')}";`;
+      case 'copy':
+        return `fileinto :copy "${escapeString(action.value || '')}";`;
+      case 'forward':
+        return `redirect "${escapeString(action.value || '')}";`;
+      case 'mark_read':
+        return 'addflag "\\\\Seen";';
+      case 'star':
+        return 'addflag "\\\\Flagged";';
+      case 'add_label':
+        return `addflag "$${escapeString(action.value || '')}";`;
+      case 'discard':
+        return 'discard;';
+      case 'reject':
+        return `reject "${escapeString(action.value || '')}";`;
+      case 'keep':
+        return 'keep;';
+      case 'stop':
+        return 'stop;';
+    }
+  });
+}
+
+function computeRequires(rules: FilterRule[]): string[] {
+  const extensions = new Set<string>();
+  const enabledRules = rules.filter(r => r.enabled);
+
+  for (const rule of enabledRules) {
+    for (const condition of rule.conditions) {
+      if (condition.field === 'body') extensions.add('body');
+    }
+    for (const action of rule.actions) {
+      switch (action.type) {
+        case 'move':
+          extensions.add('fileinto');
+          break;
+        case 'copy':
+          extensions.add('fileinto');
+          extensions.add('copy');
+          break;
+        case 'mark_read':
+        case 'star':
+        case 'add_label':
+          extensions.add('imap4flags');
+          break;
+        case 'reject':
+          extensions.add('reject');
+          break;
+      }
+    }
+  }
+
+  return [...extensions].sort();
+}
+
+export function generateScript(rules: FilterRule[]): string {
+  const metadata: FilterMetadata = { version: 1, rules };
+  const metadataJson = JSON.stringify(metadata);
+  const lines: string[] = [];
+
+  lines.push('/* @metadata:begin');
+  lines.push(metadataJson);
+  lines.push('@metadata:end */');
+  lines.push('');
+
+  const requires = computeRequires(rules);
+  if (requires.length > 0) {
+    lines.push(`require [${requires.map(r => `"${r}"`).join(', ')}];`);
+  }
+
+  const enabledRules = rules.filter(r => r.enabled);
+
+  for (const rule of enabledRules) {
+    if (rule.conditions.length === 0 || rule.actions.length === 0) {
+      debug.warn(`Skipping rule "${rule.name}": empty conditions or actions`);
+      continue;
+    }
+
+    lines.push('');
+    lines.push(`# Rule: ${rule.name}`);
+
+    const conditions = rule.conditions.map(generateCondition);
+    let conditionStr: string;
+
+    if (conditions.length === 0) {
+      conditionStr = 'true';
+    } else if (conditions.length === 1) {
+      conditionStr = conditions[0];
+    } else {
+      const wrapper = rule.matchType === 'all' ? 'allof' : 'anyof';
+      conditionStr = `${wrapper}(${conditions.join(', ')})`;
+    }
+
+    const actionLines = generateActions(rule.actions);
+
+    if (rule.stopProcessing) {
+      const lastAction = rule.actions[rule.actions.length - 1];
+      if (!lastAction || !['stop', 'discard', 'reject'].includes(lastAction.type)) {
+        actionLines.push('stop;');
+      }
+    }
+
+    lines.push(`if ${conditionStr} {`);
+    for (const actionLine of actionLines) {
+      lines.push(`    ${actionLine}`);
+    }
+    lines.push('}');
+  }
+
+  lines.push('');
+  return lines.join('\n');
+}