# Linear SDK Patterns - Implementation Guide

Detailed implementation examples and code patterns.

## Core Patterns

### Pattern 1: Client Singleton

```typescript
// lib/linear.ts
import { LinearClient } from "@linear/sdk";

let client: LinearClient | null = null;

export function getLinearClient(): LinearClient {
  if (!client) {
    if (!process.env.LINEAR_API_KEY) {
      throw new Error("LINEAR_API_KEY environment variable not set");
    }
    client = new LinearClient({
      apiKey: process.env.LINEAR_API_KEY,
    });
  }
  return client;
}
```

### Pattern 2: Pagination Handling

```typescript
import { LinearClient, Issue, IssueConnection } from "@linear/sdk";

async function* getAllIssues(
  client: LinearClient,
  filter?: Record<string, unknown>
): AsyncGenerator<Issue> {
  let hasNextPage = true;
  let endCursor: string | undefined;

  while (hasNextPage) {
    const connection: IssueConnection = await client.issues({
      filter,
      first: 50, // Max per page
      after: endCursor,
    });

    for (const issue of connection.nodes) {
      yield issue;
    }

    hasNextPage = connection.pageInfo.hasNextPage;
    endCursor = connection.pageInfo.endCursor;
  }
}

// Usage
for await (const issue of getAllIssues(client, { state: { name: { eq: "Todo" } } })) {
  console.log(issue.identifier, issue.title);
}
```

### Pattern 3: Error Handling Wrapper

```typescript
import { LinearClient, LinearError } from "@linear/sdk";

interface LinearResult<T> {
  success: boolean;
  data?: T;
  error?: {
    message: string;
    code?: string;
    retryable: boolean;
  };
}

async function linearOperation<T>(
  operation: () => Promise<T>
): Promise<LinearResult<T>> {
  try {
    const data = await operation();
    return { success: true, data };
  } catch (error) {
    if (error instanceof LinearError) {
      return {
        success: false,
        error: {
          message: error.message,
          code: error.type,
          retryable: error.type === "RateLimitedError",
        },
      };
    }
    return {
      success: false,
      error: {
        message: error instanceof Error ? error.message : "Unknown error",
        retryable: false,
      },
    };
  }
}

// Usage
const result = await linearOperation(() => client.createIssue({
  teamId: team.id,
  title: "New issue",
}));

if (result.success) {
  console.log("Issue created:", result.data);
} else if (result.error?.retryable) {
  // Implement retry logic
}
```

### Pattern 4: Batch Operations

```typescript
async function batchUpdateIssues(
  client: LinearClient,
  issueIds: string[],
  update: { stateId?: string; priority?: number }
): Promise<{ success: number; failed: number }> {
  const results = await Promise.allSettled(
    issueIds.map(id => client.updateIssue(id, update))
  );

  return {
    success: results.filter(r => r.status === "fulfilled").length,
    failed: results.filter(r => r.status === "rejected").length,
  };
}
```

### Pattern 5: Caching Layer

```typescript
interface CacheEntry<T> {
  data: T;
  expiresAt: number;
}

class LinearCache {
  private cache = new Map<string, CacheEntry<unknown>>();
  private ttl: number;

  constructor(ttlSeconds = 60) {
    this.ttl = ttlSeconds * 1000;
  }

  async get<T>(key: string, fetcher: () => Promise<T>): Promise<T> {
    const cached = this.cache.get(key) as CacheEntry<T> | undefined;

    if (cached && cached.expiresAt > Date.now()) {
      return cached.data;
    }

    const data = await fetcher();
    this.cache.set(key, { data, expiresAt: Date.now() + this.ttl });
    return data;
  }

  invalidate(key: string): void {
    this.cache.delete(key);
  }
}

// Usage
const cache = new LinearCache(300); // 5 minute TTL

const teams = await cache.get("teams", () => client.teams());
```

### Pattern 6: Type-Safe Filters

```typescript
import { IssueFilter } from "@linear/sdk";

function buildIssueFilter(options: {
  teamKeys?: string[];
  states?: string[];
  assigneeId?: string;
  priority?: number[];
}): IssueFilter {
  const filter: IssueFilter = {};

  if (options.teamKeys?.length) {
    filter.team = { key: { in: options.teamKeys } };
  }

  if (options.states?.length) {
    filter.state = { name: { in: options.states } };
  }

  if (options.assigneeId) {
    filter.assignee = { id: { eq: options.assigneeId } };
  }

  if (options.priority?.length) {
    filter.priority = { in: options.priority };
  }

  return filter;
}
```
