feat(exercises): switch catalog.yaml to directory-based catalog loader

internal/exercises/Catalog/Concepts/01_hello.yaml

@@ -0,0 +1,5 @@
+- slug: 01_hello
+  title: Hello, Go!
+  test_regex: ".*"
+  hints:
+    - Implement Hello() to return 'Hello, Go!'

internal/exercises/Catalog/Concepts/02_values.yaml

@@ -0,0 +1,5 @@
+- slug: 02_values
+  title: Values
+  test_regex: ".*"
+  hints:
+    - Use fmt.Sprintf to format values.

internal/exercises/Catalog/Concepts/03_variables.yaml

@@ -0,0 +1,5 @@
+- slug: 03_variables
+  title: Variables
+  test_regex: ".*"
+  hints:
+    - Use short declarations (:=) and return multiple values.

internal/exercises/Catalog/Concepts/04_constants.yaml

@@ -0,0 +1,5 @@
+- slug: 04_constants
+  title: Constants
+  test_regex: ".*"
+  hints:
+    - Use math.Pi and constant expressions.

internal/exercises/Catalog/Concepts/05_for.yaml

@@ -0,0 +1,5 @@
+- slug: 05_for
+  title: For
+  test_regex: ".*"
+  hints:
+    - Accumulate a sum with a for loop.

internal/exercises/Catalog/Concepts/06_if_else.yaml

@@ -0,0 +1,5 @@
+- slug: 06_if_else
+  title: If/Else
+  test_regex: ".*"
+  hints:
+    - Handle negative, zero, and positive cases.

internal/exercises/Catalog/Concepts/07_switch.yaml

@@ -0,0 +1,5 @@
+- slug: 07_switch
+  title: Switch
+  test_regex: ".*"
+  hints:
+    - Match multiple cases for weekend days.

internal/exercises/Catalog/Concepts/08_arrays.yaml

@@ -0,0 +1,5 @@
+- slug: 08_arrays
+  title: Arrays
+  test_regex: ".*"
+  hints:
+    - Iterate with range over a fixed-size array.

internal/exercises/Catalog/Concepts/09_slices.yaml

@@ -0,0 +1,5 @@
+- slug: 09_slices
+  title: Slices
+  test_regex: ".*"
+  hints:
+    - Append values then compute a sum.

internal/exercises/Catalog/Concepts/10_maps.yaml

@@ -0,0 +1,5 @@
+- slug: 10_maps
+  title: Maps
+  test_regex: ".*"
+  hints:
+    - Use strings.Fields and map[string]int for word counts.

internal/exercises/Catalog/Concepts/11_functions.yaml

@@ -0,0 +1,5 @@
+- slug: 11_functions
+  title: Functions
+  test_regex: ".*"
+  hints:
+    - Pass a function and call it.

internal/exercises/Catalog/Concepts/12_multi_return.yaml

@@ -0,0 +1,5 @@
+- slug: 12_multi_return
+  title: Multiple Return Values
+  test_regex: ".*"
+  hints:
+    - Return quotient, remainder, and an error for divide-by-zero.

internal/exercises/Catalog/Concepts/13_variadic.yaml

@@ -0,0 +1,5 @@
+- slug: 13_variadic
+  title: Variadic Functions
+  test_regex: ".*"
+  hints:
+    - Use '...' to accept any number of ints and sum them.

internal/exercises/Catalog/Concepts/14_closures.yaml

@@ -0,0 +1,5 @@
+- slug: 14_closures
+  title: Closures
+  test_regex: ".*"
+  hints:
+    - Implement a function that returns a closure, capturing an outer variable.

internal/exercises/Catalog/Concepts/15_recursion.yaml

@@ -0,0 +1,5 @@
+- slug: 15_recursion
+  title: Recursion
+  test_regex: ".*"
+  hints:
+    - Implement a recursive factorial function.

internal/exercises/Catalog/Concepts/16_range_built_in.yaml

@@ -0,0 +1,5 @@
+- slug: 16_range_built_in
+  title: Range over Built-in Types
+  test_regex: ".*"
+  hints:
+    - Use range to iterate over a slice and a map.

internal/exercises/Catalog/Concepts/17_pointers.yaml

@@ -0,0 +1,5 @@
+- slug: 17_pointers
+  title: Pointers
+  test_regex: ".*"
+  hints:
+    - Write a function that takes a pointer, modifies the value, and returns the pointer.

internal/exercises/Catalog/Concepts/18_strings_runes.yaml

@@ -0,0 +1,5 @@
+- slug: 18_strings_runes
+  title: Strings and Runes
+  test_regex: ".*"
+  hints:
+    - Iterate over a string with range to count runes, and demonstrate string manipulation.

internal/exercises/Catalog/Concepts/19_structs.yaml

@@ -0,0 +1,5 @@
+- slug: 19_structs
+  title: Structs
+  test_regex: ".*"
+  hints:
+    - Define a struct with fields for name and age, then create an instance.

internal/exercises/Catalog/Concepts/20_methods.yaml

@@ -0,0 +1,5 @@
+- slug: 20_methods
+  title: Methods
+  test_regex: ".*"
+  hints:
+    - Add a method to a struct that calculates something based on its fields.

internal/exercises/Catalog/Concepts/21_interfaces.yaml

@@ -0,0 +1,5 @@
+- slug: 21_interfaces
+  title: Interfaces
+  test_regex: ".*"
+  hints:
+    - Define an interface and implement it for a struct.

internal/exercises/Catalog/Concepts/22_enums.yaml

@@ -0,0 +1,5 @@
+- slug: 22_enums
+  title: Enums
+  test_regex: ".*"
+  hints:
+    - Use iota to create a set of related constants as an enumeration.

internal/exercises/Catalog/Concepts/23_struct_embedding.yaml

@@ -0,0 +1,5 @@
+- slug: 23_struct_embedding
+  title: Struct Embedding
+  test_regex: ".*"
+  hints:
+    - Embed one struct within another and access the inner struct's fields directly.

internal/exercises/Catalog/Concepts/24_generics.yaml

@@ -0,0 +1,5 @@
+- slug: 24_generics
+  title: Generics
+  test_regex: ".*"
+  hints:
+    - Write a generic function that works with different types.

internal/exercises/Catalog/Concepts/25_range_iterators.yaml

@@ -0,0 +1,5 @@
+- slug: 25_range_iterators
+  title: Range over Iterators
+  test_regex: ".*"
+  hints:
+    - Implement a custom iterator and use range over it.

internal/exercises/Catalog/Concepts/26_errors.yaml

@@ -0,0 +1,5 @@
+- slug: 26_errors
+  title: Errors
+  test_regex: ".*"
+  hints:
+    - Write a function that returns an error and handle it.

internal/exercises/Catalog/Concepts/27_custom_errors.yaml

@@ -0,0 +1,5 @@
+- slug: 27_custom_errors
+  title: Custom Errors
+  test_regex: ".*"
+  hints:
+    - Define a custom error type and return it from a function.

internal/exercises/Catalog/Concepts/28_defer.yaml

@@ -0,0 +1,5 @@
+- slug: 28_defer
+  title: Defer
+  test_regex: ".*"
+  hints:
+    - Use `f.Close()` with `defer` keyword.

internal/exercises/Catalog/Concepts/29_go_routines.yaml

@@ -0,0 +1,5 @@
+- slug: 29_go_routines
+  title: Go Routines
+  test_regex: ".*"
+  hints:
+    - Use `go` keyword to execute functions concurrently using go routines.

internal/exercises/Catalog/Concepts/30_channels.yaml

@@ -0,0 +1,5 @@
+- slug: 30_channels
+  title: Channels
+  test_regex: ".*"
+  hints:
+    - Use `make(chan T)` to create a channel and `<-` to send and receive on it.

internal/exercises/Catalog/Concepts/31_mutexes.yaml

@@ -0,0 +1,5 @@
+- slug: 31_mutexes
+  title: Mutexes
+  test_regex: ".*"
+  hints:
+    - Use `sync.Mutex` to synchronize access to a shared resource.

internal/exercises/Catalog/Concepts/32_sorting.yaml

@@ -0,0 +1,5 @@
+- slug: 32_sorting
+  title: Sorting
+  test_regex: ".*"
+  hints:
+    - Use `slice.Sort` for sorting slices.

internal/exercises/Catalog/Concepts/33_string_formatting.yaml

@@ -0,0 +1,5 @@
+- slug: 33_string_formatting
+  title: String Formatting
+  test_regex: ".*"
+  hints:
+    - Use `fmt.Sprintf` and `%s`, `%d`, `%f` formatting directives to format strings, integers, and floats.

internal/exercises/Catalog/Concepts/34_channel_buffering.yaml

@@ -0,0 +1,5 @@
+- slug: 34_channel_buffering
+  title: Channel Buffering
+  test_regex: ".*"
+  hints:
+    - Use `make(chan T, N)` to create a buffered channel and `<-` to send and receive on it.

internal/exercises/Catalog/Concepts/35_channel_sync.yaml

@@ -0,0 +1,5 @@
+- slug: 35_channel_sync
+  title: Channel Synchronization
+  test_regex: ".*"
+  hints:
+    - Use a buffered boolean channel and wait till go routine completes.

internal/exercises/Catalog/Concepts/36_json.yaml

@@ -0,0 +1,9 @@
+- slug: 36_json
+  title: JSON
+  test_regex: ".*"
+  hints:
+    - Use the encoding/json package to work with JSON data.
+    - Implement MarshalPerson to convert a struct into JSON using json.Marshal.
+    - Implement UnmarshalPerson to convert a JSON string into a struct using json.Unmarshal.
+    - Handle and return errors properly in both functions.
+

internal/exercises/Catalog/Concepts/37_sorting_by_functions.yaml

@@ -0,0 +1,10 @@
+- slug: 37_sorting_by_functions
+  title: "Sorting by Functions"
+  difficulty: beginner
+  topics: ["slices", "sorting", "functions"]
+  hints:
+      - "Implement sort.Interface with Len(), Less(), and Swap() methods"
+      - "Create custom slice types like ByName and ByAge (e.g., type ByName []Person)"
+      - "Use sort.Sort() to sort slices with your custom comparison logic"
+      - "Remember to make copies of slices to avoid modifying the original"
+

internal/exercises/Catalog/Concepts/37_xml.yaml

@@ -0,0 +1,8 @@
+- slug: 37_xml
+  title: XML Encoding and Decoding
+  test_regex: ".*"
+  hints:
+    - Use encoding/xml package for marshaling and unmarshaling XML data.
+    - Add XML struct tags using `xml:"fieldname"` to map struct fields to XML elements.
+    - Use xml.Marshal to convert structs to XML bytes.
+    - Use xml.Unmarshal to parse XML bytes into structs.

internal/exercises/Catalog/Concepts/38_time_formatting.yaml

@@ -0,0 +1,10 @@
+- slug: 38_time_formatting
+  title: "Time Formatting"
+  difficulty: beginner
+  topics: ["time", "formatting", "parsing"]
+  hints:
+      - "Use time.Now().Format() to format current time with a specific layout"
+      - "Use time.Parse() to parse time strings with known layouts"
+      - "Use time.LoadLocation() to work with different timezones"
+      - "Extract time components using .Date() and .Clock() methods"
+

internal/exercises/Catalog/Concepts/39_channel_directions.yaml

@@ -0,0 +1,9 @@
+- slug: 39_channel_directions
+  title: Channel Directions
+  test_regex: ".*"
+  hints:
+    - Create two channels, one for sending jobs and one for receiving results.
+    - Start 5 workers using go routines.
+    - Send 50 jobs to the worker pool.
+    - Receive results from the worker pool and store them in a `rs` slice.
+    - Enforce type safety by specifying the channel directions in worker function.

internal/exercises/Catalog/Concepts/39_panic.yaml

@@ -0,0 +1,9 @@
+- slug: 39_panic
+  title: Panic and Recover
+  test_regex: ".*"
+  hints:
+    - "Use `panic()` to simulate runtime errors when appropriate."
+    - "Use `defer` with `recover()` to catch and handle panics."
+    - "Recovering from panics allows graceful handling of unexpected situations."
+    - "Remember: `recover()` only works inside a deferred function."
+

internal/exercises/Catalog/Concepts/40_channel_select.yaml

@@ -0,0 +1,6 @@
+- slug: 40_channel_select
+  title: Channel Select
+  test_regex: ".*"
+  hints:
+    - Use `select` to handle multiple channel operations concurrently.
+    - Use `time.After` to simulate a 5 microsecond timeout.

internal/exercises/Catalog/Concepts/41_time_delay.yaml

@@ -0,0 +1,10 @@
+- slug: 41_time_delay
+  title: "Delays and Timers in Go"
+  difficulty: beginner
+  topics: ["time", "sleep", "channels", "timer"]
+  test_regex: ".*"
+  hints:
+    - "Use time.Sleep() to pause execution for a duration."
+    - "Convert milliseconds to time.Duration using time.Millisecond."
+    - "Use a buffered channel to send a signal after waiting."
+    - "Use time.After or time.Sleep to trigger events after delays."

internal/exercises/Catalog/Concepts/42_wait_group.yaml

@@ -0,0 +1,12 @@
+- slug: 42_wait_group
+  title: WaitGroups
+  test_regex: ".*"
+  difficulty: beginner
+  topics: ["concurrency", "sync", "goroutines"]
+  hints:
+    - "Use sync.WaitGroup to wait for all launched goroutines."
+    - "Call wg.Add(1) before starting a goroutine and wg.Done() when it finishes."
+    - "Close result channels after wg.Wait() so collectors can range over them."
+    - "Capture loop variables correctly inside goroutines (e.g., `n := n`)."
+    - "Return results as a slice — order does not need to match input order"
+

internal/exercises/Catalog/Concepts/43_worker_pools.yaml

@@ -0,0 +1,10 @@
+- slug: 43_worker_pools
+  title: Worker Pools
+  test_regex: ".*"
+  hints:
+    - Create separate channels for jobs (send work) and results (receive processed data).
+    - Launch multiple worker goroutines that read from jobs channel and write to results channel.
+    - Use channel directions (<-chan for receive-only, chan<- for send-only) in worker function signature.
+    - Close the jobs channel after sending all work to signal workers to finish.
+    - Use strings.TrimSpace() to clean message strings by removing leading/trailing whitespace.
+    - Collect exactly len(logs) results to ensure all work is processed.

internal/exercises/Catalog/Concepts/44_atomic_counters.yaml

@@ -0,0 +1,7 @@
+- slug: 44_atomic_counters
+  title: Atomic Counters
+  test_regex: ".*"
+  hints:
+    - Use `sync/atomic` package to create and increment atomic counter.
+    - Launch 10,000 anonymous go routines that simultaneously increment the counter.
+    - Use WaitGroups to wait for all go routines to finish. 

internal/exercises/Catalog/Concepts/45_range_over_channels.yaml

@@ -0,0 +1,5 @@
+- slug: 45_range_over_channels
+  title: Range over channels
+  test_regex: ".*"
+  hints:
+    - Use `for i := range ch {...}` syntax to range over a channels. 

internal/exercises/Catalog/Concepts/46_non_blocking_channel_operations.yaml

@@ -0,0 +1,7 @@
+- slug: 46_non_blocking_channel_operations
+  title: Non-blocking channel operations
+  test_regex: ".*"
+  hints:
+    - Use `default` case in select to handle non-blocking channel operations.
+    - Safely increment `dropped` using mutex `Lock()` and `Unlock()`.
+

internal/exercises/Catalog/Concepts/64_timers.yaml

@@ -0,0 +1,15 @@
+- slug: 64_timers
+  title: "Timers"
+  difficulty: medium
+  topics: ["time", "goroutines", "concurrency", "synchronization"]
+  test_regex: ".*"
+  hints:
+    - "Use a map[string]*time.Timer to track active timers by key."
+    - "Use a mutex to safely access the timers map concurrently."
+    - "Start a timer with time.AfterFunc(d, fn) to run a callback after duration d."
+    - "If Start is called again for an existing key, stop and replace the old timer."
+    - "Stop should remove the timer from the map and prevent the callback from firing."
+    - "Reset can call timer.Reset(d) to reschedule the same callback."
+    - "Remember to remove timers from the map after they fire to avoid memory leaks."
+    - "Write tests to verify Start, Stop, and Reset behavior, including concurrency scenarios."
+

internal/exercises/Catalog/Concepts/68_rate_limiting.yaml

@@ -0,0 +1,13 @@
+- slug: 68_rate_limiting
+  title: Rate Limiting
+  test_regex: ".*"
+  difficulty: medium
+  topics: ["time", "concurrency", "maps"]
+  hints:
+    - "Implement a RateLimiter struct that tracks request timestamps per key using a map[string][]time.Time."
+    - "Use a mutex to safely handle concurrent access to the map."
+    - "In the Allow method, remove timestamps older than the interval and check if the number of recent requests exceeds the limit."
+    - "Reset should clear the request history for a key; if the key does not exist, do nothing."
+    - "Consider edge cases: multiple keys, concurrent access, and requests exactly at the interval boundary."
+    - "In tests, use time.Sleep with a small buffer above the interval to avoid flakiness."
+    - "Initialize the timestamps map in NewRateLimiter to prevent nil pointer errors."

internal/exercises/Catalog/Projects/01_text_analyzer.yaml

@@ -0,0 +1,5 @@
+- slug: 01_text_analyzer
+  title: Text Analyzer (Easy)
+  test_regex: ".*"
+  hints:
+    - Implement functions to count characters, words, and unique words in a given text.

internal/exercises/Catalog/Projects/02_shape_calculator.yaml

@@ -0,0 +1,5 @@
+- slug: 02_shape_calculator
+  title: Shape Area Calculator (Medium)
+  test_regex: ".*"
+  hints:
+    - Define structs for different shapes, implement methods to calculate their areas, and use an interface for common shape behavior.

internal/exercises/Catalog/Projects/03_task_scheduler.yaml

@@ -0,0 +1,5 @@
+- slug: 03_task_scheduler
+  title: Task Scheduler (Hard)
+  test_regex: ".*"
+  hints:
+    - Create a task scheduler with features like adding/removing tasks, a custom iterator, closures for task execution, and custom error handling.

internal/exercises/Catalog/Projects/04_http_server.yaml

@@ -0,0 +1,5 @@
+- slug: 04_http_server
+  title: HTTP Server (Easy)
+  test_regex: ".*"
+  hints:
+    - Implement a basic HTTP server that responds to GET requests.

internal/exercises/Catalog/Projects/05_cli_todo_list.yaml

@@ -0,0 +1,5 @@
+- slug: 05_cli_todo_list
+  title: CLI Todo List (Medium)
+  test_regex: ".*"
+  hints:
+    - Build a command-line tool to manage a todo list, including adding, listing, and completing tasks.