feat: Add data models and PostgreSQL storage layer

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

backend/internal/storage/db.go

@@ -0,0 +1,109 @@
+package storage
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+	"os"
+
+	_ "github.com/lib/pq"
+)
+
+type DB struct {
+	*sql.DB
+}
+
+func NewDB(ctx context.Context) (*DB, error) {
+	host := getEnv("DB_HOST", "localhost")
+	port := getEnv("DB_PORT", "5432")
+	user := getEnv("DB_USER", "postgres")
+	password := getEnv("DB_PASSWORD", "postgres")
+	dbname := getEnv("DB_NAME", "training_tracker")
+
+	connStr := fmt.Sprintf(
+		"host=%s port=%s user=%s password=%s dbname=%s sslmode=disable",
+		host, port, user, password, dbname,
+	)
+
+	db, err := openDB(connStr)
+	if err != nil {
+		return nil, err
+	}
+
+	if err := db.PingContext(ctx); err != nil {
+		return nil, fmt.Errorf("failed to ping database: %w", err)
+	}
+
+	return &DB{db}, nil
+}
+
+func openDB(connStr string) (*sql.DB, error) {
+	db, err := sql.Open("postgres", connStr)
+	if err != nil {
+		return nil, fmt.Errorf("failed to open database: %w", err)
+	}
+	return db, nil
+}
+
+func (db *DB) Migrate(ctx context.Context) error {
+	migrations := []string{
+		`CREATE TABLE IF NOT EXISTS exercises (
+			id SERIAL PRIMARY KEY,
+			name VARCHAR(255) NOT NULL,
+			type VARCHAR(50) NOT NULL,
+			muscle_group VARCHAR(100),
+			description TEXT,
+			created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+		)`,
+		`CREATE TABLE IF NOT EXISTS training_plans (
+			id SERIAL PRIMARY KEY,
+			name VARCHAR(255) NOT NULL,
+			description TEXT,
+			created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+		)`,
+		`CREATE TABLE IF NOT EXISTS plan_exercises (
+			id SERIAL PRIMARY KEY,
+			plan_id INTEGER REFERENCES training_plans(id) ON DELETE CASCADE,
+			exercise_id INTEGER REFERENCES exercises(id) ON DELETE CASCADE,
+			sets INTEGER,
+			reps INTEGER,
+			duration INTEGER,
+			sort_order INTEGER DEFAULT 0
+		)`,
+		`CREATE TABLE IF NOT EXISTS sessions (
+			id SERIAL PRIMARY KEY,
+			plan_id INTEGER REFERENCES training_plans(id) ON DELETE SET NULL,
+			date TIMESTAMP NOT NULL,
+			notes TEXT,
+			created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+		)`,
+		`CREATE TABLE IF NOT EXISTS session_entries (
+			id SERIAL PRIMARY KEY,
+			session_id INTEGER REFERENCES sessions(id) ON DELETE CASCADE,
+			exercise_id INTEGER REFERENCES exercises(id) ON DELETE CASCADE,
+			weight DECIMAL(10, 2),
+			reps INTEGER,
+			sets_completed INTEGER,
+			duration INTEGER,
+			distance DECIMAL(10, 2),
+			heart_rate INTEGER,
+			notes TEXT,
+			created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+		)`,
+	}
+
+	for _, migration := range migrations {
+		if _, err := db.ExecContext(ctx, migration); err != nil {
+			return fmt.Errorf("migration failed: %w", err)
+		}
+	}
+
+	return nil
+}
+
+func getEnv(key, defaultValue string) string {
+	if value := os.Getenv(key); value != "" {
+		return value
+	}
+	return defaultValue
+}