feat: start lang refactor

doc/cp.nvim.txt

@@ -25,18 +25,13 @@ COMMANDS                                                         *cp-commands*
         cp.nvim uses a single :CP command with intelligent argument parsing:
 
         Setup Commands ~
-            :CP {platform} {contest_id}
+            :CP {platform} {contest_id} [--lang {language}]
                                 Full setup: set platform and load contest metadata.
                                 Scrapes test cases and creates source file.
-                                Example: >
+                                --lang: Use specific language (default: platform default)
+                                Examples: >
                                     :CP codeforces 1933
-<
+                                    :CP codeforces 1933 --lang python
-            :CP {platform} {contest_id}
-                                Contest setup: set platform, load contest metadata,
-                                and scrape all test cases in the contest. 
-                                Opens the first problem after completion.
-                                Example: >
-                                    :CP atcoder abc324
 <
         View Commands ~
             :CP run [--debug] [n]
@@ -59,8 +54,14 @@ COMMANDS                                                         *cp-commands*
                                     :CP panel --debug 3  " Test 3, debug build
 <
 
-            :CP pick            Launch configured picker for interactive
+            :CP pick [--lang {language}]
+                                Launch configured picker for interactive
                                 platform/contest selection.
+                                --lang: Pre-select language for chosen contest.
+                                Example: >
+                                    :CP pick
+                                    :CP pick --lang python
+<
 
             :CP interact [script]
                                 Open an interactive terminal for the current problem.
@@ -70,15 +71,36 @@ COMMANDS                                                         *cp-commands*
                                 file. Only valid for interactive problems.
 
         Navigation Commands ~
-            :CP next            Navigate to next problem in current contest.
+            :CP next [--lang {language}]
+                                Navigate to next problem in current contest.
                                 Stops at last problem (no wrapping).
-
+                                --lang: Use specific language for next problem.
-
+                                By default, preserves current file's language if
-            :CP prev            Navigate to previous problem in current contest.
+                                enabled for the new problem, otherwise uses platform
+                                default.
+                                Examples: >
+                                    :CP next
+                                    :CP next --lang python
+<
+            :CP prev [--lang {language}]
+                                Navigate to previous problem in current contest.
                                 Stops at first problem (no wrapping).
-
+                                --lang: Use specific language for previous problem.
-            :CP {problem_id}    Jump to problem {problem_id} in a contest.
+                                By default, preserves current file's language if
+                                enabled for the new problem, otherwise uses platform
+                                default.
+                                Examples: >
+                                    :CP prev
+                                    :CP prev --lang cpp
+<
+            :CP {problem_id} [--lang {language}]
+                                Jump to problem {problem_id} in a contest.
                                 Requires that a contest has already been set up.
+                                --lang: Use specific language for this problem.
+                                Examples: >
+                                    :CP B
+                                    :CP C --lang python
+<
 
         State Restoration ~
             :CP                 Restore state from current file.
@@ -357,6 +379,49 @@ run CSES problems with Rust using the single schema:
         }
 <
 
+==============================================================================
+LANGUAGE SELECTION                                           *cp-lang-selection*
+
+cp.nvim supports multiple languages per problem. Each platform enables specific
+languages and has a default. You can override the language for any setup or
+navigation command using the --lang flag.
+
+Language Selection Behavior ~
+
+When setting up or navigating to a problem:
+
+1. Explicit --lang flag takes highest priority
+2. If no --lang flag, tries to preserve current file's language
+   (only if that language is enabled for the new problem)
+3. Falls back to platform's default language
+
+Multiple Solution Files ~
+
+Different languages create different solution files. For example:
+    1848a.cc        (C++ solution)
+    1848a.py        (Python solution)
+
+Both files can exist simultaneously with their own state. Switching between
+languages means switching between different files.
+
+Examples ~
+>
+    :CP codeforces 1848             " Use platform default (likely C++)
+    :CP codeforces 1848 --lang python   " Use Python explicitly
+
+    " In 1848a.cc (C++ file):
+    :CP next                        " Next problem tries to use C++
+    :CP next --lang python          " Next problem uses Python
+
+    " In 1848a.py (Python file):
+    :CP next                        " Next problem tries to use Python
+    :CP next --lang cpp             " Next problem switches to C++
+<
+Language Validation ~
+
+If you request a language that isn't enabled for a platform, cp.nvim will show
+a helpful error message listing available languages for that platform.
+
 ==============================================================================
 WORKFLOW                                                         *cp-workflow*
 
@@ -374,6 +439,7 @@ https://atcoder.jp/contests/{contest_id}/tasks/{contest_id}_{problem_id}
 
 Usage examples: >
     :CP atcoder abc324            " Set up atcoder.jp/contests/abc324
+    :CP atcoder abc324 --lang python  " Set up with Python instead of default
 
 Codeforces ~
                                                                *cp-codeforces*
@@ -381,6 +447,7 @@ URL format: https://codeforces.com/contest/{contest_id}/problem/{problem_id}
 
 Usage examples: >
     :CP codeforces 1934           " Set up codeforces.com/contest/1934
+    :CP codeforces 1934 --lang cpp    " Set up with C++
 
 CSES ~
                                                                      *cp-cses*
@@ -404,7 +471,7 @@ Example: Setting up and solving AtCoder contest ABC324
 
 3. Code your solution, then test: >
     :CP run
-<   View test verdicts in I/O splits. For detailed analysis:
+<   View test verdicts in I/O splits. For detailed analysis: >
     :CP panel
 <   Navigate tests with <c-n>/<c-p>, exit with q
 
@@ -414,12 +481,16 @@ Example: Setting up and solving AtCoder contest ABC324
 
 5. Continue solving problems with :CP next/:CP prev navigation
 
-6. Switch to another file (e.g. previous contest): >
+6. Try a different language for a problem: >
+    :CP C --lang python
+<   Opens problem C with Python instead of C++
+
+7. Switch to another file (e.g. previous contest): >
     :e ~/contests/abc323/a.cpp
     :CP
 <   Automatically restores abc323 contest context
 
-7. Submit solutions on AtCoder website
+8. Submit solutions on AtCoder website
 
 ==============================================================================
 I/O VIEW                                                          *cp-io-view*

lua/cp/commands/init.lua

@@ -18,6 +18,7 @@ local actions = constants.ACTIONS
 ---@field interactor_cmd? string
 ---@field test_index? integer
 ---@field debug? boolean
+---@field language? string
 
 --- Turn raw args into normalized structure to later dispatch
 ---@param args string[] The raw command-line mode args
@@ -79,7 +80,16 @@ local function parse_command(args)
 
       return { type = 'action', action = first, test_index = test_index, debug = debug }
     else
-      return { type = 'action', action = first }
+      local language = nil
+      if #args >= 3 and args[2] == '--lang' then
+        language = args[3]
+      elseif #args >= 2 and args[2] ~= nil and args[2]:sub(1, 2) ~= '--' then
+        return {
+          type = 'error',
+          message = ("Unknown argument '%s' for action '%s'"):format(args[2], first),
+        }
+      end
+      return { type = 'action', action = first, language = language }
     end
   end
 
@@ -95,13 +105,18 @@ local function parse_command(args)
         platform = first,
         contest = args[2],
       }
-    elseif #args == 3 then
+    elseif #args == 4 and args[3] == '--lang' then
       return {
-        type = 'error',
+        type = 'contest_setup',
-        message = 'Setup contests with :CP <platform> <contest_id>.',
+        platform = first,
+        contest = args[2],
+        language = args[4],
       }
     else
-      return { type = 'error', message = 'Too many arguments' }
+      return {
+        type = 'error',
+        message = 'Invalid arguments. Usage: :CP <platform> <contest> [--lang <language>]',
+      }
     end
   end
 
@@ -110,6 +125,12 @@ local function parse_command(args)
       type = 'problem_jump',
       problem_id = first,
     }
+  elseif #args == 3 and args[2] == '--lang' then
+    return {
+      type = 'problem_jump',
+      problem_id = first,
+      language = args[3],
+    }
   end
 
   return { type = 'error', message = 'Unknown command or no contest context.' }
@@ -139,12 +160,12 @@ function M.handle_command(opts)
     elseif cmd.action == 'panel' then
       ui.toggle_panel({ debug = cmd.debug, test_index = cmd.test_index })
     elseif cmd.action == 'next' then
-      setup.navigate_problem(1)
+      setup.navigate_problem(1, cmd.language)
     elseif cmd.action == 'prev' then
-      setup.navigate_problem(-1)
+      setup.navigate_problem(-1, cmd.language)
     elseif cmd.action == 'pick' then
       local picker = require('cp.commands.picker')
-      picker.handle_pick_action()
+      picker.handle_pick_action(cmd.language)
     end
   elseif cmd.type == 'problem_jump' then
     local platform = state.get_platform()
@@ -173,13 +194,13 @@ function M.handle_command(opts)
     end
 
     local setup = require('cp.setup')
-    setup.setup_contest(platform, contest_id, problem_id)
+    setup.setup_contest(platform, contest_id, problem_id, cmd.language)
   elseif cmd.type == 'cache' then
     local cache_commands = require('cp.commands.cache')
     cache_commands.handle_cache_command(cmd)
   elseif cmd.type == 'contest_setup' then
     local setup = require('cp.setup')
-    setup.setup_contest(cmd.platform, cmd.contest, nil)
+    setup.setup_contest(cmd.platform, cmd.contest, nil, cmd.language)
     return
   end
 end

lua/cp/commands/picker.lua

@@ -4,8 +4,9 @@ local config_module = require('cp.config')
 local logger = require('cp.log')
 
 --- Dispatch `:CP pick` to appropriate picker
+---@param language? string
 ---@return nil
-function M.handle_pick_action()
+function M.handle_pick_action(language)
   local config = config_module.get_config()
 
   if not (config.ui and config.ui.picker) then
@@ -53,7 +54,7 @@ function M.handle_pick_action()
     picker = fzf_picker
   end
 
-  picker.pick()
+  picker.pick(language)
 end
 
 return M

lua/cp/config.lua

@@ -351,6 +351,50 @@ function M.get_config()
   return current_config or M.defaults
 end
 
+---Validate and get effective language config for a platform
+---@param platform_id string
+---@param language_id string
+---@return { valid: boolean, effective?: CpLanguage, extension?: string, error?: string }
+function M.get_language_for_platform(platform_id, language_id)
+  local cfg = M.get_config()
+
+  if not cfg.platforms[platform_id] then
+    return { valid = false, error = string.format("Unknown platform '%s'", platform_id) }
+  end
+
+  if not cfg.languages[language_id] then
+    return { valid = false, error = string.format("Unknown language '%s'", language_id) }
+  end
+
+  local platform = cfg.platforms[platform_id]
+  if not vim.tbl_contains(platform.enabled_languages, language_id) then
+    local available = table.concat(platform.enabled_languages, ', ')
+    return {
+      valid = false,
+      error = string.format(
+        "Language '%s' not enabled for %s. Available: %s",
+        language_id,
+        platform_id,
+        available
+      ),
+    }
+  end
+
+  local effective = cfg.runtime.effective[platform_id][language_id]
+  if not effective then
+    return {
+      valid = false,
+      error = string.format('No effective config for %s/%s', platform_id, language_id),
+    }
+  end
+
+  return {
+    valid = true,
+    effective = effective,
+    extension = effective.extension,
+  }
+end
+
 ---@param contest_id string
 ---@param problem_id? string
 ---@return string

lua/cp/pickers/fzf_lua.lua

@@ -2,7 +2,7 @@ local picker_utils = require('cp.pickers')
 
 local M = {}
 
-local function contest_picker(platform, refresh)
+local function contest_picker(platform, refresh, language)
   local constants = require('cp.constants')
   local platform_display_name = constants.PLATFORM_DISPLAY_NAMES[platform]
   local fzf = require('fzf-lua')
@@ -42,19 +42,24 @@ local function contest_picker(platform, refresh)
 
         if contest then
           local cp = require('cp')
-          cp.handle_command({ fargs = { platform, contest.id } })
+          local fargs = { platform, contest.id }
+          if language then
+            table.insert(fargs, '--lang')
+            table.insert(fargs, language)
+          end
+          cp.handle_command({ fargs = fargs })
         end
       end,
       ['ctrl-r'] = function()
         local cache = require('cp.cache')
         cache.clear_contest_list(platform)
-        contest_picker(platform, true)
+        contest_picker(platform, true, language)
       end,
     },
   })
 end
 
-function M.pick()
+function M.pick(language)
   local fzf = require('fzf-lua')
   local platforms = picker_utils.get_platforms()
   local entries = vim.tbl_map(function(platform)
@@ -79,7 +84,7 @@ function M.pick()
         end
 
         if platform then
-          contest_picker(platform.id)
+          contest_picker(platform.id, false, language)
         end
       end,
     },

lua/cp/pickers/telescope.lua

@@ -8,7 +8,7 @@ local picker_utils = require('cp.pickers')
 
 local M = {}
 
-local function contest_picker(opts, platform, refresh)
+local function contest_picker(opts, platform, refresh, language)
   local constants = require('cp.constants')
   local platform_display_name = constants.PLATFORM_DISPLAY_NAMES[platform]
   local contests = picker_utils.get_platform_contests(platform, refresh)
@@ -43,13 +43,18 @@ local function contest_picker(opts, platform, refresh)
 
           if selection then
             local cp = require('cp')
-            cp.handle_command({ fargs = { platform, selection.value.id } })
+            local fargs = { platform, selection.value.id }
+            if language then
+              table.insert(fargs, '--lang')
+              table.insert(fargs, language)
+            end
+            cp.handle_command({ fargs = fargs })
           end
         end)
 
         map('i', '<c-r>', function()
           actions.close(prompt_bufnr)
-          contest_picker(opts, platform, true)
+          contest_picker(opts, platform, true, language)
         end)
 
         return true
@@ -58,9 +63,8 @@ local function contest_picker(opts, platform, refresh)
     :find()
 end
 
-function M.pick(opts)
+function M.pick(language)
-  opts = opts or {}
+  local opts = {}
-
   local platforms = picker_utils.get_platforms()
 
   pickers
@@ -83,7 +87,7 @@ function M.pick(opts)
           actions.close(prompt_bufnr)
 
           if selection then
-            contest_picker(opts, selection.value.id)
+            contest_picker(opts, selection.value.id, false, language)
           end
         end)
         return true

lua/cp/setup.lua

@@ -8,6 +8,18 @@ local logger = require('cp.log')
 local scraper = require('cp.scraper')
 local state = require('cp.state')
 
+---Get the language of the current file from cache
+---@return string|nil
+local function get_current_file_language()
+  local current_file = vim.fn.expand('%:p')
+  if current_file == '' then
+    return nil
+  end
+  cache.load()
+  local file_state = cache.get_file_state(current_file)
+  return file_state and file_state.language or nil
+end
+
 ---@class TestCaseLite
 ---@field input string
 ---@field expected string
@@ -86,6 +98,14 @@ function M.setup_contest(platform, contest_id, problem_id, language)
   state.set_platform(platform)
   state.set_contest_id(contest_id)
 
+  if language then
+    local lang_result = config_module.get_language_for_platform(platform, language)
+    if not lang_result.valid then
+      logger.log(lang_result.error, vim.log.levels.ERROR)
+      return
+    end
+  end
+
   local is_new_contest = old_platform ~= platform and old_contest_id ~= contest_id
 
   cache.load()
@@ -173,6 +193,15 @@ function M.setup_problem(problem_id, language)
   local config = config_module.get_config()
   local lang = language
     or (config.platforms[platform] and config.platforms[platform].default_language)
+
+  if language then
+    local lang_result = config_module.get_language_for_platform(platform, language)
+    if not lang_result.valid then
+      logger.log(lang_result.error, vim.log.levels.ERROR)
+      return
+    end
+  end
+
   local source_file = state.get_source_file(lang)
   if not source_file then
     return
@@ -235,7 +264,8 @@ function M.setup_problem(problem_id, language)
 end
 
 ---@param direction integer
-function M.navigate_problem(direction)
+---@param language? string
+function M.navigate_problem(direction, language)
   if direction == 0 then
     return
   end
@@ -274,7 +304,15 @@ function M.navigate_problem(direction)
     require('cp.ui.views').disable()
   end
 
-  M.setup_contest(platform, contest_id, problems[new_index].id)
+  local lang = language or get_current_file_language()
+  if lang then
+    local lang_result = config_module.get_language_for_platform(platform, lang)
+    if not lang_result.valid then
+      lang = nil
+    end
+  end
+
+  M.setup_contest(platform, contest_id, problems[new_index].id, lang)
 end
 
 return M