feat(llm): cohere support (#167)

should be good set of defaults now, one in US, one in canada, and
microsoft :/

Signed-off-by: Aaron Pham <contact@aarnphm.xyz>

lua/avante/providers/cohere.lua

@@ -0,0 +1,121 @@
+local Utils = require("avante.utils")
+local P = require("avante.providers")
+
+---@alias CohereFinishReason "COMPLETE" | "LENGTH" | "ERROR"
+---
+---@class CohereChatStreamResponse
+---@field event_type "stream-start" | "text-generation" | "stream-end"
+---@field is_finished boolean
+---
+---@class CohereTextGenerationResponse: CohereChatStreamResponse
+---@field text string
+---
+---@class CohereStreamEndResponse: CohereChatStreamResponse
+---@field response CohereChatResponse
+---@field finish_reason CohereFinishReason
+---
+---@class CohereChatResponse
+---@field text string
+---@field generation_id string
+---@field chat_history CohereMessage[]
+---@field finish_reason CohereFinishReason
+---@field meta {api_version: {version: integer}, billed_units: {input_tokens: integer, output_tokens: integer}, tokens: {input_tokens: integer, output_tokens: integer}}
+---
+---@class CohereMessage
+---@field role? "USER" | "SYSTEM" | "CHATBOT"
+---@field message string
+---
+---@class AvanteProviderFunctor
+local M = {}
+
+M.api_key_name = "CO_API_KEY"
+
+M.has = function()
+  return os.getenv(M.api_key_name) and true or false
+end
+
+M.parse_message = function(opts)
+  local user_prompt = opts.base_prompt
+    .. "\n\nCODE:\n"
+    .. "```"
+    .. opts.code_lang
+    .. "\n"
+    .. opts.code_content
+    .. "\n```"
+    .. "\n\nQUESTION:\n"
+    .. opts.question
+
+  if opts.selected_code_content ~= nil then
+    user_prompt = opts.base_prompt
+      .. "\n\nCODE CONTEXT:\n"
+      .. "```"
+      .. opts.code_lang
+      .. "\n"
+      .. opts.code_content
+      .. "\n```"
+      .. "\n\nCODE:\n"
+      .. "```"
+      .. opts.code_lang
+      .. "\n"
+      .. opts.selected_code_content
+      .. "\n```"
+      .. "\n\nQUESTION:\n"
+      .. opts.question
+  end
+
+  return {
+    preamble = opts.system_prompt,
+    message = user_prompt,
+  }
+end
+
+M.parse_stream_data = function(data, opts)
+  ---@type CohereChatStreamResponse
+  local json = vim.json.decode(data)
+  if json.is_finished then
+    opts.on_complete(nil)
+    return
+  end
+  if json.event_type ~= nil then
+    ---@cast json CohereStreamEndResponse
+    if json.event_type == "stream-end" and json.finish_reason == "COMPLETE" then
+      opts.on_complete(nil)
+      return
+    end
+    ---@cast json CohereTextGenerationResponse
+    if json.event_type == "text-generation" then
+      opts.on_chunk(json.text)
+    end
+  end
+end
+
+M.parse_curl_args = function(provider, code_opts)
+  local base, body_opts = P.parse_config(provider)
+
+  local headers = {
+    ["Accept"] = "application/json",
+    ["Content-Type"] = "application/json",
+    ["X-Client-Name"] = "avante.nvim/Neovim/"
+      .. vim.version().major
+      .. "."
+      .. vim.version().minor
+      .. "."
+      .. vim.version().patch,
+  }
+  if not P.env.is_local("openai") then
+    headers["Authorization"] = "Bearer " .. os.getenv(base.api_key_name or M.api_key_name)
+  end
+
+  return {
+    url = Utils.trim(base.endpoint, { suffix = "/" }) .. "/v1/chat",
+    proxy = base.proxy,
+    insecure = base.allow_insecure,
+    headers = headers,
+    body = vim.tbl_deep_extend("force", {
+      model = base.model,
+      stream = true,
+    }, M.parse_message(code_opts), body_opts),
+  }
+end
+
+return M