Refactor: reduce code duplication with shared abstractions

- Add BaseClient HTTP abstraction (internal/api/http.go) to eliminate
  duplicated HTTP boilerplate across Todoist, Trello, and PlanToEat clients
- Add response helpers (internal/handlers/response.go) for JSON/HTML responses
- Add generic cache wrapper (internal/handlers/cache.go) using Go generics
- Consolidate HandleCompleteAtom/HandleUncompleteAtom into handleAtomToggle
- Merge TabsHandler into Handler, delete tabs.go
- Extract sortTasksByUrgency and filterAndSortTrelloTasks helpers
- Update tests to work with new BaseClient structure

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

1 files changed, 143 insertions, 0 deletions

diff --git a/internal/api/http.go b/internal/api/http.go
new file mode 100644
index 0000000..8854625
--- /dev/null
+++ b/internal/api/http.go
@@ -0,0 +1,143 @@
+package api
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"time"
+)
+
+// BaseClient provides common HTTP functionality for API clients
+type BaseClient struct {
+	HTTPClient *http.Client
+	BaseURL    string
+}
+
+// NewBaseClient creates a new BaseClient with default settings
+func NewBaseClient(baseURL string) BaseClient {
+	return BaseClient{
+		HTTPClient: &http.Client{Timeout: 15 * time.Second},
+		BaseURL:    baseURL,
+	}
+}
+
+// Get performs a GET request and decodes the JSON response
+func (c *BaseClient) Get(ctx context.Context, path string, headers map[string]string, result interface{}) error {
+	req, err := http.NewRequestWithContext(ctx, "GET", c.BaseURL+path, nil)
+	if err != nil {
+		return fmt.Errorf("failed to create request: %w", err)
+	}
+
+	for k, v := range headers {
+		req.Header.Set(k, v)
+	}
+
+	return c.doJSON(req, result)
+}
+
+// Post performs a POST request with JSON body and decodes the response
+func (c *BaseClient) Post(ctx context.Context, path string, headers map[string]string, body interface{}, result interface{}) error {
+	var bodyReader io.Reader
+	if body != nil {
+		jsonData, err := json.Marshal(body)
+		if err != nil {
+			return fmt.Errorf("failed to marshal request body: %w", err)
+		}
+		bodyReader = bytes.NewBuffer(jsonData)
+	}
+
+	req, err := http.NewRequestWithContext(ctx, "POST", c.BaseURL+path, bodyReader)
+	if err != nil {
+		return fmt.Errorf("failed to create request: %w", err)
+	}
+
+	if body != nil {
+		req.Header.Set("Content-Type", "application/json")
+	}
+
+	for k, v := range headers {
+		req.Header.Set(k, v)
+	}
+
+	return c.doJSON(req, result)
+}
+
+// PostForm performs a POST request with form-encoded body
+func (c *BaseClient) PostForm(ctx context.Context, path string, headers map[string]string, formData string, result interface{}) error {
+	req, err := http.NewRequestWithContext(ctx, "POST", c.BaseURL+path, bytes.NewBufferString(formData))
+	if err != nil {
+		return fmt.Errorf("failed to create request: %w", err)
+	}
+
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+	for k, v := range headers {
+		req.Header.Set(k, v)
+	}
+
+	return c.doJSON(req, result)
+}
+
+// PostEmpty performs a POST request with no body and expects no response body
+func (c *BaseClient) PostEmpty(ctx context.Context, path string, headers map[string]string) error {
+	req, err := http.NewRequestWithContext(ctx, "POST", c.BaseURL+path, nil)
+	if err != nil {
+		return fmt.Errorf("failed to create request: %w", err)
+	}
+
+	for k, v := range headers {
+		req.Header.Set(k, v)
+	}
+
+	resp, err := c.HTTPClient.Do(req)
+	if err != nil {
+		return fmt.Errorf("request failed: %w", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
+		body, _ := io.ReadAll(resp.Body)
+		return fmt.Errorf("API error (status %d): %s", resp.StatusCode, string(body))
+	}
+
+	return nil
+}
+
+// Put performs a PUT request with form-encoded body
+func (c *BaseClient) Put(ctx context.Context, path string, headers map[string]string, formData string, result interface{}) error {
+	req, err := http.NewRequestWithContext(ctx, "PUT", c.BaseURL+path, bytes.NewBufferString(formData))
+	if err != nil {
+		return fmt.Errorf("failed to create request: %w", err)
+	}
+
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+	for k, v := range headers {
+		req.Header.Set(k, v)
+	}
+
+	return c.doJSON(req, result)
+}
+
+// doJSON executes the request and decodes JSON response
+func (c *BaseClient) doJSON(req *http.Request, result interface{}) error {
+	resp, err := c.HTTPClient.Do(req)
+	if err != nil {
+		return fmt.Errorf("request failed: %w", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
+		body, _ := io.ReadAll(resp.Body)
+		return fmt.Errorf("API error (status %d): %s", resp.StatusCode, string(body))
+	}
+
+	if result != nil {
+		if err := json.NewDecoder(resp.Body).Decode(result); err != nil {
+			return fmt.Errorf("failed to decode response: %w", err)
+		}
+	}
+
+	return nil
+}