frontend/src/pages/Analysis.tsx

@@ -1,10 +1,12 @@
 import { useState } from 'react';
+import { useNavigate } from 'react-router-dom';
 import { useMutation, useQuery } from '@tanstack/react-query';
 import { analysisApi, exportApi } from '../api/client';
-import { Search, CheckCircle, AlertCircle, Clock, FileText, Download, ChevronDown } from 'lucide-react';
+import { Search, CheckCircle, AlertCircle, Clock, FileText, Download, ChevronDown, History } from 'lucide-react';
 import type { CompanyAnalysis } from '../types';
 
 export function Analysis() {
+  const navigate = useNavigate();
   const [companyName, setCompanyName] = useState('');
   const [selectedModel, setSelectedModel] = useState('');
   const [result, setResult] = useState<CompanyAnalysis | null>(null);
@@ -157,6 +159,13 @@ export function Analysis() {
                     <FileText size={14} />
                     Export PDF
                   </button>
+                  <button
+                    onClick={() => navigate(`/history-diff?company=${encodeURIComponent(result.company_name)}`)}
+                    className="flex items-center gap-2 text-sm bg-secondary/20 hover:bg-secondary/30 text-secondary font-medium px-3 py-1.5 rounded-lg transition-colors"
+                  >
+                    <History size={14} />
+                    Compare with previous
+                  </button>
                 </div>
               </div>
               <div className="prose dark:prose-invert max-w-none">

frontend/src/pages/HistoryDiff.tsx

@@ -0,0 +1,249 @@
+import { useState } from 'react';
+import { useSearchParams } from 'react-router-dom';
+import { useQuery } from '@tanstack/react-query';
+import { analysisApi } from '../api/client';
+import type { AnalysisHistoryItem, AnalysisDiff } from '../api/client';
+import { History, ArrowRight, Plus, Minus, AlertCircle, Search } from 'lucide-react';
+
+export function HistoryDiff() {
+  const [searchParams, setSearchParams] = useSearchParams();
+  const [companyInput, setCompanyInput] = useState(searchParams.get('company') || '');
+
+  const company = searchParams.get('company') || '';
+  const fromId = searchParams.get('from');
+  const toId = searchParams.get('to');
+
+  // Fetch history when a company is selected
+  const historyQuery = useQuery({
+    queryKey: ['history', company],
+    queryFn: () => analysisApi.getCompanyHistory(company),
+    enabled: !!company,
+  });
+
+  // Fetch diff when both IDs are selected
+  const diffQuery = useQuery<AnalysisDiff>({
+    queryKey: ['diff', company, fromId, toId],
+    queryFn: () => analysisApi.diffAnalyses(company, Number(fromId), Number(toId)),
+    enabled: !!company && !!fromId && !!toId,
+  });
+
+  const handleSearch = (e: React.FormEvent) => {
+    e.preventDefault();
+    const name = companyInput.trim();
+    if (name) {
+      setSearchParams({ company: name });
+    }
+  };
+
+  const handleSelectRuns = (from: number, to: number) => {
+    setSearchParams({ company, from: String(from), to: String(to) });
+  };
+
+  const history: AnalysisHistoryItem[] = historyQuery.data || [];
+
+  return (
+    <div className="space-y-6">
+      {/* Header */}
+      <div>
+        <h2 className="text-xl font-semibold text-text-primary border-b-2 border-primary/30 pb-2 mb-2">
+          Historical Analysis Diff
+        </h2>
+        <p className="text-text-secondary">
+          Compare analysis runs for the same company to see what changed between them.
+        </p>
+      </div>
+
+      {/* Company Search */}
+      <form onSubmit={handleSearch} className="flex gap-4">
+        <div className="flex-1 relative">
+          <Search className="absolute left-4 top-1/2 -translate-y-1/2 text-text-secondary" size={18} />
+          <input
+            type="text"
+            value={companyInput}
+            onChange={(e) => setCompanyInput(e.target.value)}
+            placeholder="Enter company name (e.g., nvidia)"
+            className="w-full bg-bg-card/80 border border-primary/30 rounded-xl pl-12 pr-4 py-3 text-text-primary placeholder-text-secondary/50 focus:outline-none focus:border-primary focus:ring-2 focus:ring-primary/20 transition-all"
+          />
+        </div>
+        <button
+          type="submit"
+          disabled={!companyInput.trim()}
+          className="bg-gradient-to-r from-primary to-primary-dark text-white font-semibold py-3 px-6 rounded-xl hover:shadow-lg hover:shadow-primary/30 transition-all disabled:opacity-50 disabled:cursor-not-allowed flex items-center gap-2"
+        >
+          <History size={18} />
+          Load History
+        </button>
+      </form>
+
+      {/* History list */}
+      {company && historyQuery.isLoading && (
+        <div className="text-text-secondary animate-pulse">Loading analysis history...</div>
+      )}
+
+      {company && historyQuery.isError && (
+        <div className="flex items-center gap-2 bg-error/10 border border-error/20 text-error rounded-xl px-4 py-3">
+          <AlertCircle size={18} />
+          <span>Failed to load history. Check the company name and try again.</span>
+        </div>
+      )}
+
+      {company && history.length === 0 && !historyQuery.isLoading && (
+        <div className="text-text-secondary">No analysis history found for "{company}".</div>
+      )}
+
+      {history.length >= 2 && (
+        <div className="bg-bg-card/60 backdrop-blur-lg border border-primary/15 rounded-2xl p-6">
+          <h3 className="text-lg font-semibold text-text-primary border-b-2 border-primary/30 pb-2 mb-4">
+            Select Two Runs to Compare
+          </h3>
+          <div className="space-y-2">
+            {history.map((item, idx) => {
+              const next = history[idx + 1];
+              if (!next) return null;
+              const isSelected =
+                fromId === String(next.id) && toId === String(item.id);
+              return (
+                <button
+                  key={item.id}
+                  onClick={() => handleSelectRuns(next.id, item.id)}
+                  className={`w-full text-left flex items-center gap-3 px-4 py-3 rounded-xl border transition-all ${
+                    isSelected
+                      ? 'border-primary bg-primary/10'
+                      : 'border-primary/15 hover:border-primary/40 hover:bg-primary/5'
+                  }`}
+                >
+                  <span className="text-sm text-text-secondary font-mono">
+                    #{next.id}
+                  </span>
+                  <span className="text-xs text-text-secondary">
+                    {new Date(next.timestamp).toLocaleString()}
+                  </span>
+                  <ArrowRight size={14} className="text-primary" />
+                  <span className="text-sm text-text-secondary font-mono">
+                    #{item.id}
+                  </span>
+                  <span className="text-xs text-text-secondary">
+                    {new Date(item.timestamp).toLocaleString()}
+                  </span>
+                  {item.model && (
+                    <span className="ml-auto text-xs bg-primary/20 text-primary px-2 py-0.5 rounded">
+                      {item.model}
+                    </span>
+                  )}
+                </button>
+              );
+            })}
+          </div>
+        </div>
+      )}
+
+      {/* Diff Results */}
+      {diffQuery.isLoading && (
+        <div className="text-text-secondary animate-pulse">Computing diff...</div>
+      )}
+
+      {diffQuery.isError && (
+        <div className="flex items-center gap-2 bg-error/10 border border-error/20 text-error rounded-xl px-4 py-3">
+          <AlertCircle size={18} />
+          <span>Failed to compute diff. One or both analysis IDs may not exist.</span>
+        </div>
+      )}
+
+      {diffQuery.data && <DiffView diff={diffQuery.data} />}
+    </div>
+  );
+}
+
+function DiffView({ diff }: { diff: AnalysisDiff }) {
+  return (
+    <div className="bg-bg-card/60 backdrop-blur-lg border border-primary/15 rounded-2xl p-6 space-y-6">
+      <h3 className="text-lg font-semibold text-text-primary border-b-2 border-primary/30 pb-2">
+        Diff: #{diff.from_id} &rarr; #{diff.to_id}
+      </h3>
+
+      {/* Summary */}
+      <div className="bg-primary/5 border border-primary/20 rounded-xl p-4">
+        <div className="text-sm font-medium text-text-primary">{diff.summary}</div>
+        <div className="flex items-center gap-4 mt-2 text-xs text-text-secondary">
+          <span>{new Date(diff.from_timestamp).toLocaleString()}</span>
+          <ArrowRight size={12} />
+          <span>{new Date(diff.to_timestamp).toLocaleString()}</span>
+        </div>
+      </div>
+
+      {/* Patent count delta */}
+      <div className="flex items-center gap-3">
+        <span className="text-sm text-text-secondary">Patent mention delta:</span>
+        <span
+          className={`text-lg font-bold ${
+            diff.patent_count_delta > 0
+              ? 'text-success'
+              : diff.patent_count_delta < 0
+              ? 'text-error'
+              : 'text-text-secondary'
+          }`}
+        >
+          {diff.patent_count_delta > 0 ? '+' : ''}
+          {diff.patent_count_delta}
+        </span>
+      </div>
+
+      {/* Added patents */}
+      {diff.added_patents.length > 0 && (
+        <div>
+          <h4 className="text-sm font-semibold text-success flex items-center gap-1 mb-2">
+            <Plus size={14} />
+            New Patents ({diff.added_patents.length})
+          </h4>
+          <div className="flex flex-wrap gap-2">
+            {diff.added_patents.map((p) => (
+              <span
+                key={p}
+                className="text-xs bg-success/10 border border-success/20 text-success px-2 py-1 rounded font-mono"
+              >
+                {p}
+              </span>
+            ))}
+          </div>
+        </div>
+      )}
+
+      {/* Removed patents */}
+      {diff.removed_patents.length > 0 && (
+        <div>
+          <h4 className="text-sm font-semibold text-error flex items-center gap-1 mb-2">
+            <Minus size={14} />
+            Removed Patents ({diff.removed_patents.length})
+          </h4>
+          <div className="flex flex-wrap gap-2">
+            {diff.removed_patents.map((p) => (
+              <span
+                key={p}
+                className="text-xs bg-error/10 border border-error/20 text-error px-2 py-1 rounded font-mono"
+              >
+                {p}
+              </span>
+            ))}
+          </div>
+        </div>
+      )}
+
+      {/* Changed fields */}
+      {Object.keys(diff.changed_fields).length > 0 && (
+        <div>
+          <h4 className="text-sm font-semibold text-text-primary mb-2">Changed Fields</h4>
+          <div className="space-y-1">
+            {Object.entries(diff.changed_fields).map(([field, vals]) => (
+              <div key={field} className="flex items-center gap-2 text-sm">
+                <span className="text-text-secondary font-mono">{field}:</span>
+                <span className="text-error line-through">{vals.from || 'null'}</span>
+                <ArrowRight size={12} className="text-text-secondary" />
+                <span className="text-success">{vals.to || 'null'}</span>
+              </div>
+            ))}
+          </div>
+        </div>
+      )}
+    </div>
+  );
+}

tests/test_analysis_diff.py

@@ -0,0 +1,244 @@
+"""Tests for historical analysis diff endpoint."""
+
+from datetime import datetime
+from unittest.mock import MagicMock, patch
+
+import pytest
+from fastapi.testclient import TestClient
+
+from SPARC.api import AnalysisDiffResponse, _compute_analysis_diff, _extract_patent_ids, app
+from SPARC.auth import UserResponse, get_current_user
+
+
+# ---------- helpers ----------
+
+def _mock_user():
+    """Return a fake authenticated user for dependency override."""
+    return UserResponse(
+        id=1,
+        email="test@example.com",
+        role="user",
+        created_at=datetime(2025, 1, 1),
+    )
+
+
+@pytest.fixture
+def auth_client():
+    """TestClient with auth dependency overridden."""
+    app.dependency_overrides[get_current_user] = _mock_user
+    client = TestClient(app, raise_server_exceptions=False)
+    yield client
+    app.dependency_overrides.clear()
+
+
+# ---------- unit tests for helpers ----------
+
+class TestExtractPatentIds:
+    """Test _extract_patent_ids utility."""
+
+    def test_extracts_standard_ids(self):
+        text = "Patent US-12345678-B2 covers the device. Also see US-9876543-A1."
+        ids = _extract_patent_ids(text)
+        assert "US-12345678-B2" in ids
+        assert "US-9876543-A1" in ids
+
+    def test_empty_text(self):
+        assert _extract_patent_ids("") == set()
+        assert _extract_patent_ids(None) == set()  # type: ignore[arg-type]
+
+
+class TestComputeAnalysisDiff:
+    """Test _compute_analysis_diff logic."""
+
+    def test_identical_analyses(self):
+        rec = {
+            "id": 1,
+            "company_name": "nvidia",
+            "analysis_type": "portfolio",
+            "model": "openai/gpt-4o",
+            "response": "Patent US-12345678-B2 is notable.",
+            "timestamp": datetime(2025, 5, 1),
+        }
+        diff = _compute_analysis_diff(rec, dict(rec, id=2, timestamp=datetime(2025, 5, 2)))
+        assert diff.patent_count_delta == 0
+        assert diff.added_patents == []
+        assert diff.removed_patents == []
+
+    def test_added_and_removed_patents(self):
+        from_rec = {
+            "id": 1,
+            "company_name": "nvidia",
+            "analysis_type": "portfolio",
+            "model": "openai/gpt-4o",
+            "response": "Patent US-12345678-B2 and US-11111111-A1.",
+            "timestamp": datetime(2025, 5, 1),
+        }
+        to_rec = {
+            "id": 2,
+            "company_name": "nvidia",
+            "analysis_type": "portfolio",
+            "model": "openai/gpt-4o",
+            "response": "Patent US-12345678-B2 and US-99999999-B1.",
+            "timestamp": datetime(2025, 5, 2),
+        }
+        diff = _compute_analysis_diff(from_rec, to_rec)
+        assert "US-99999999-B1" in diff.added_patents
+        assert "US-11111111-A1" in diff.removed_patents
+        assert diff.patent_count_delta == 0  # one added, one removed
+
+    def test_model_change_detected(self):
+        from_rec = {
+            "id": 1,
+            "company_name": "nvidia",
+            "analysis_type": "portfolio",
+            "model": "openai/gpt-4o",
+            "response": "",
+            "timestamp": datetime(2025, 5, 1),
+        }
+        to_rec = {
+            "id": 2,
+            "company_name": "nvidia",
+            "analysis_type": "portfolio",
+            "model": "anthropic/claude-3.5-sonnet",
+            "response": "",
+            "timestamp": datetime(2025, 5, 2),
+        }
+        diff = _compute_analysis_diff(from_rec, to_rec)
+        assert "model" in diff.changed_fields
+        assert diff.changed_fields["model"]["from"] == "openai/gpt-4o"
+        assert diff.changed_fields["model"]["to"] == "anthropic/claude-3.5-sonnet"
+
+
+# ---------- API endpoint tests ----------
+
+class TestDiffEndpoint:
+    """Test GET /analyze/{company_name}/diff."""
+
+    @patch("SPARC.api._get_job_db")
+    def test_happy_path(self, mock_get_db, auth_client):
+        """Diff returns structured response when both IDs exist."""
+        db = MagicMock()
+        mock_get_db.return_value = db
+
+        from_rec = {
+            "id": 10,
+            "company_name": "nvidia",
+            "analysis_type": "portfolio",
+            "model": "openai/gpt-4o",
+            "response": "Patent US-12345678-B2 found.",
+            "timestamp": datetime(2025, 5, 1),
+        }
+        to_rec = {
+            "id": 20,
+            "company_name": "nvidia",
+            "analysis_type": "portfolio",
+            "model": "openai/gpt-4o",
+            "response": "Patent US-12345678-B2 and US-99999999-A1 found.",
+            "timestamp": datetime(2025, 5, 10),
+        }
+        db.get_analysis_by_id.side_effect = lambda aid: from_rec if aid == 10 else to_rec
+
+        response = auth_client.get("/analyze/nvidia/diff?from=10&to=20")
+        assert response.status_code == 200
+        data = response.json()
+        assert data["company_name"] == "nvidia"
+        assert data["from_id"] == 10
+        assert data["to_id"] == 20
+        assert "US-99999999-A1" in data["added_patents"]
+        assert data["patent_count_delta"] == 1
+
+    @patch("SPARC.api._get_job_db")
+    def test_from_id_not_found(self, mock_get_db, auth_client):
+        """Returns 404 when 'from' analysis ID doesn't exist."""
+        db = MagicMock()
+        mock_get_db.return_value = db
+        db.get_analysis_by_id.return_value = None
+
+        response = auth_client.get("/analyze/nvidia/diff?from=999&to=1000")
+        assert response.status_code == 404
+        assert "999" in response.json()["detail"]
+
+    @patch("SPARC.api._get_job_db")
+    def test_to_id_not_found(self, mock_get_db, auth_client):
+        """Returns 404 when 'to' analysis ID doesn't exist."""
+        db = MagicMock()
+        mock_get_db.return_value = db
+
+        from_rec = {
+            "id": 10,
+            "company_name": "nvidia",
+            "analysis_type": "portfolio",
+            "model": "openai/gpt-4o",
+            "response": "",
+            "timestamp": datetime(2025, 5, 1),
+        }
+        db.get_analysis_by_id.side_effect = lambda aid: from_rec if aid == 10 else None
+
+        response = auth_client.get("/analyze/nvidia/diff?from=10&to=999")
+        assert response.status_code == 404
+        assert "999" in response.json()["detail"]
+
+    @patch("SPARC.api._get_job_db")
+    def test_company_mismatch(self, mock_get_db, auth_client):
+        """Returns 404 when analysis belongs to a different company."""
+        db = MagicMock()
+        mock_get_db.return_value = db
+
+        rec = {
+            "id": 10,
+            "company_name": "intel",
+            "analysis_type": "portfolio",
+            "model": "openai/gpt-4o",
+            "response": "",
+            "timestamp": datetime(2025, 5, 1),
+        }
+        db.get_analysis_by_id.return_value = rec
+
+        response = auth_client.get("/analyze/nvidia/diff?from=10&to=20")
+        assert response.status_code == 404
+
+
+class TestHistoryEndpoint:
+    """Test GET /analyze/{company_name}/history."""
+
+    @patch("SPARC.api._get_job_db")
+    def test_returns_history_list(self, mock_get_db, auth_client):
+        """History endpoint returns list of past analysis runs."""
+        db = MagicMock()
+        mock_get_db.return_value = db
+        db.list_company_analyses.return_value = [
+            {
+                "id": 20,
+                "company_name": "nvidia",
+                "analysis_type": "portfolio",
+                "model": "openai/gpt-4o",
+                "response": "...",
+                "timestamp": datetime(2025, 5, 10),
+            },
+            {
+                "id": 10,
+                "company_name": "nvidia",
+                "analysis_type": "portfolio",
+                "model": "openai/gpt-4o",
+                "response": "...",
+                "timestamp": datetime(2025, 5, 1),
+            },
+        ]
+
+        response = auth_client.get("/analyze/nvidia/history")
+        assert response.status_code == 200
+        data = response.json()
+        assert len(data) == 2
+        assert data[0]["id"] == 20
+        assert data[1]["id"] == 10
+
+    @patch("SPARC.api._get_job_db")
+    def test_empty_history(self, mock_get_db, auth_client):
+        """History endpoint returns empty list when no analyses exist."""
+        db = MagicMock()
+        mock_get_db.return_value = db
+        db.list_company_analyses.return_value = []
+
+        response = auth_client.get("/analyze/nvidia/history")
+        assert response.status_code == 200
+        assert response.json() == []