local config = require('pending.config')
local log = require('pending.log')

---@class pending.ForgeRef
---@field forge string
---@field owner string
---@field repo string
---@field type 'issue'|'pull_request'|'merge_request'
---@field number integer
---@field url string

---@class pending.ForgeCache
---@field title? string
---@field state 'open'|'closed'|'merged'
---@field labels? string[]
---@field fetched_at string

---@class pending.ForgeBackend
---@field name string
---@field shorthand string
---@field default_host string
---@field cli string
---@field auth_cmd string
---@field auth_status_args string[]
---@field default_icon string
---@field default_issue_format string
---@field _warned boolean
---@field parse_url fun(self: pending.ForgeBackend, url: string): pending.ForgeRef?
---@field api_args fun(self: pending.ForgeBackend, ref: pending.ForgeRef): string[]
---@field parse_state fun(self: pending.ForgeBackend, decoded: table): 'open'|'closed'|'merged'

---@class pending.forge
local M = {}

---@type pending.ForgeBackend[]
local _backends = {}

---@type table<string, pending.ForgeBackend>
local _by_name = {}

---@type table<string, pending.ForgeBackend>
local _by_shorthand = {}

---@type table<string, pending.ForgeBackend>
local _by_host = {}

---@type boolean
local _instances_resolved = false

---@param backend pending.ForgeBackend
---@return nil
function M.register(backend)
  backend._warned = false
  table.insert(_backends, backend)
  _by_name[backend.name] = backend
  _by_shorthand[backend.shorthand] = backend
  _by_host[backend.default_host] = backend
  _instances_resolved = false
end

---@return pending.ForgeBackend[]
function M.backends()
  return _backends
end

local function _ensure_instances()
  if _instances_resolved then
    return
  end
  _instances_resolved = true
  local cfg = config.get().forge or {}
  for _, backend in ipairs(_backends) do
    local forge_cfg = cfg[backend.name] or {}
    for _, inst in ipairs(forge_cfg.instances or {}) do
      _by_host[inst] = backend
    end
  end
end

---@param token string
---@return pending.ForgeRef?
function M._parse_shorthand(token)
  local prefix, rest = token:match('^(%l%l):(.+)$')
  if not prefix then
    return nil
  end
  local backend = _by_shorthand[prefix]
  if not backend then
    return nil
  end
  local owner, repo, number = rest:match('^([%w%.%-_]+)/([%w%.%-_]+)#(%d+)$')
  if not owner then
    return nil
  end
  local num = tonumber(number) --[[@as integer]]
  local url = 'https://' .. backend.default_host .. '/' .. owner .. '/' .. repo .. '/issues/' .. num
  return {
    forge = backend.name,
    owner = owner,
    repo = repo,
    type = 'issue',
    number = num,
    url = url,
  }
end

---@param url string
---@return pending.ForgeRef?
function M._parse_github_url(url)
  local backend = _by_name['github']
  if not backend then
    return nil
  end
  return backend:parse_url(url)
end

---@param url string
---@return pending.ForgeRef?
function M._parse_gitlab_url(url)
  local backend = _by_name['gitlab']
  if not backend then
    return nil
  end
  return backend:parse_url(url)
end

---@param url string
---@return pending.ForgeRef?
function M._parse_codeberg_url(url)
  local backend = _by_name['codeberg']
  if not backend then
    return nil
  end
  return backend:parse_url(url)
end

---@param token string
---@return pending.ForgeRef?
function M.parse_ref(token)
  local short = M._parse_shorthand(token)
  if short then
    return short
  end
  if not token:match('^https?://') then
    return nil
  end
  _ensure_instances()
  local host = token:match('^https?://([^/]+)')
  if not host then
    return nil
  end
  local backend = _by_host[host]
  if not backend then
    return nil
  end
  return backend:parse_url(token)
end

---@class pending.ForgeSpan
---@field ref pending.ForgeRef
---@field start_byte integer
---@field end_byte integer
---@field raw string

---@param text string
---@return pending.ForgeSpan[]
function M.find_refs(text)
  local results = {}
  local pos = 1
  while pos <= #text do
    local ws = text:find('%S', pos)
    if not ws then
      break
    end
    local token_end = text:find('%s', ws)
    local token = token_end and text:sub(ws, token_end - 1) or text:sub(ws)
    local ref = M.parse_ref(token)
    if ref then
      local eb = token_end and (token_end - 1) or #text
      table.insert(results, {
        ref = ref,
        start_byte = ws - 1,
        end_byte = eb,
        raw = token,
      })
    end
    pos = token_end and token_end or (#text + 1)
  end
  return results
end

---@param ref pending.ForgeRef
---@return string[]
function M._api_args(ref)
  local backend = _by_name[ref.forge]
  if not backend then
    return {}
  end
  return backend:api_args(ref)
end

---@param ref pending.ForgeRef
---@param cache? pending.ForgeCache
---@return string text
---@return string hl_group
function M.format_label(ref, cache)
  local cfg = config.get().forge or {}
  local forge_cfg = cfg[ref.forge] or {}
  local backend = _by_name[ref.forge]
  local default_icon = backend and backend.default_icon or ''
  local default_fmt = backend and backend.default_issue_format or '%i %o/%r#%n'
  local fmt = forge_cfg.issue_format or default_fmt
  local icon = forge_cfg.icon or default_icon
  local text = fmt
    :gsub('%%i', icon)
    :gsub('%%o', ref.owner)
    :gsub('%%r', ref.repo)
    :gsub('%%n', tostring(ref.number))
  local hl = 'PendingForge'
  if cache then
    if cache.state == 'closed' or cache.state == 'merged' then
      hl = 'PendingForgeClosed'
    end
  end
  return text, hl
end

---@param ref pending.ForgeRef
---@param callback fun(cache: pending.ForgeCache?)
function M.fetch_metadata(ref, callback)
  local args = M._api_args(ref)

  vim.system(args, { text = true }, function(result)
    if result.code ~= 0 or not result.stdout or result.stdout == '' then
      local forge_cfg = config.get().forge or {}
      local backend = _by_name[ref.forge]
      if
        backend
        and forge_cfg.warn_missing_cli ~= false
        and not backend._warned
      then
        backend._warned = true
        vim.system(backend.auth_status_args, { text = true }, function(auth_result)
          vim.schedule(function()
            if auth_result.code ~= 0 then
              log.warn(
                ('%s not authenticated — run `%s`'):format(backend.cli, backend.auth_cmd)
              )
            end
            callback(nil)
          end)
        end)
      else
        vim.schedule(function()
          callback(nil)
        end)
      end
      return
    end
    local ok, decoded = pcall(vim.json.decode, result.stdout)
    if not ok or not decoded then
      vim.schedule(function()
        callback(nil)
      end)
      return
    end
    local backend = _by_name[ref.forge]
    local state = backend and backend:parse_state(decoded) or 'open'
    local labels = {}
    if decoded.labels then
      for _, label in ipairs(decoded.labels) do
        if type(label) == 'string' then
          table.insert(labels, label)
        elseif type(label) == 'table' and label.name then
          table.insert(labels, label.name)
        end
      end
    end
    local cache = {
      title = decoded.title,
      state = state,
      labels = labels,
      fetched_at = os.date('!%Y-%m-%dT%H:%M:%SZ') --[[@as string]],
    }
    vim.schedule(function()
      callback(cache)
    end)
  end)
end

---@param s pending.Store
function M.refresh(s)
  local forge_cfg = config.get().forge or {}
  if not forge_cfg.auto_close then
    return
  end
  local tasks = s:tasks()
  local pending_fetches = 0
  local any_changed = false
  local any_fetched = false
  for _, task in ipairs(tasks) do
    if task.status ~= 'deleted' and task._extra and task._extra._forge_ref then
      local ref = task._extra._forge_ref --[[@as pending.ForgeRef]]
      pending_fetches = pending_fetches + 1
      M.fetch_metadata(ref, function(cache)
        pending_fetches = pending_fetches - 1
        if cache then
          task._extra._forge_cache = cache
          any_fetched = true
          local forge_cfg = config.get().forge or {}
          if
            forge_cfg.auto_close
            and (cache.state == 'closed' or cache.state == 'merged')
            and (task.status == 'pending' or task.status == 'wip' or task.status == 'blocked')
          then
            task.status = 'done'
            task['end'] = os.date('!%Y-%m-%dT%H:%M:%SZ') --[[@as string]]
            task.modified = os.date('!%Y-%m-%dT%H:%M:%SZ') --[[@as string]]
            any_changed = true
          end
        else
          task._extra._forge_cache = {
            state = 'open',
            fetched_at = os.date('!%Y-%m-%dT%H:%M:%SZ') --[[@as string]],
          }
        end
        if pending_fetches == 0 then
          if any_changed then
            s:save()
          end
          local buffer = require('pending.buffer')
          if
            (any_changed or any_fetched)
            and buffer.bufnr()
            and vim.api.nvim_buf_is_valid(buffer.bufnr())
          then
            buffer.render()
          end
        end
      end)
    end
  end
  if pending_fetches == 0 then
    log.info('No linked tasks to refresh.')
  end
end

---@param opts {name: string, shorthand: string, default_host: string, cli?: string, auth_cmd?: string, auth_status_args?: string[], default_icon?: string, default_issue_format?: string}
---@return pending.ForgeBackend
function M.gitea_backend(opts)
  return {
    name = opts.name,
    shorthand = opts.shorthand,
    default_host = opts.default_host,
    cli = opts.cli or 'tea',
    auth_cmd = opts.auth_cmd or 'tea login add',
    auth_status_args = opts.auth_status_args or { opts.cli or 'tea', 'login', 'list' },
    default_icon = opts.default_icon or '',
    default_issue_format = opts.default_issue_format or '%i %o/%r#%n',
    _warned = false,
    parse_url = function(self, url)
      _ensure_instances()
      local host, owner, repo, kind, number =
        url:match('^https?://([^/]+)/([%w%.%-_]+)/([%w%.%-_]+)/(%a+)/(%d+)$')
      if not host then
        return nil
      end
      if kind ~= 'issues' and kind ~= 'pulls' then
        return nil
      end
      if _by_host[host] ~= self then
        return nil
      end
      local num = tonumber(number) --[[@as integer]]
      local ref_type = kind == 'pulls' and 'pull_request' or 'issue'
      return {
        forge = self.name,
        owner = owner,
        repo = repo,
        type = ref_type,
        number = num,
        url = url,
      }
    end,
    api_args = function(self, ref)
      local endpoint = ref.type == 'pull_request' and 'pulls' or 'issues'
      return {
        self.cli,
        'api',
        '/repos/' .. ref.owner .. '/' .. ref.repo .. '/' .. endpoint .. '/' .. ref.number,
      }
    end,
    parse_state = function(_, decoded)
      if decoded.state == 'closed' then
        return 'closed'
      end
      return 'open'
    end,
  }
end

M.register({
  name = 'github',
  shorthand = 'gh',
  default_host = 'github.com',
  cli = 'gh',
  auth_cmd = 'gh auth login',
  auth_status_args = { 'gh', 'auth', 'status' },
  default_icon = '',
  default_issue_format = '%i %o/%r#%n',
  _warned = false,
  parse_url = function(self, url)
    _ensure_instances()
    local host, owner, repo, kind, number =
      url:match('^https?://([^/]+)/([%w%.%-_]+)/([%w%.%-_]+)/(%a+)/(%d+)$')
    if not host then
      return nil
    end
    if kind ~= 'issues' and kind ~= 'pull' then
      return nil
    end
    if _by_host[host] ~= self then
      return nil
    end
    local num = tonumber(number) --[[@as integer]]
    local ref_type = kind == 'pull' and 'pull_request' or 'issue'
    return {
      forge = 'github',
      owner = owner,
      repo = repo,
      type = ref_type,
      number = num,
      url = url,
    }
  end,
  api_args = function(_, ref)
    return {
      'gh',
      'api',
      '/repos/' .. ref.owner .. '/' .. ref.repo .. '/issues/' .. ref.number,
    }
  end,
  parse_state = function(_, decoded)
    if decoded.pull_request and decoded.pull_request.merged_at then
      return 'merged'
    elseif decoded.state == 'closed' then
      return 'closed'
    end
    return 'open'
  end,
})

M.register({
  name = 'gitlab',
  shorthand = 'gl',
  default_host = 'gitlab.com',
  cli = 'glab',
  auth_cmd = 'glab auth login',
  auth_status_args = { 'glab', 'auth', 'status' },
  default_icon = '',
  default_issue_format = '%i %o/%r#%n',
  _warned = false,
  parse_url = function(self, url)
    _ensure_instances()
    local host, path, kind, number = url:match('^https?://([^/]+)/(.+)/%-/([%w_]+)/(%d+)$')
    if not host then
      return nil
    end
    if kind ~= 'issues' and kind ~= 'merge_requests' then
      return nil
    end
    if _by_host[host] ~= self then
      return nil
    end
    local owner, repo = path:match('^(.+)/([^/]+)$')
    if not owner then
      return nil
    end
    local num = tonumber(number) --[[@as integer]]
    local ref_type = kind == 'merge_requests' and 'merge_request' or 'issue'
    return {
      forge = 'gitlab',
      owner = owner,
      repo = repo,
      type = ref_type,
      number = num,
      url = url,
    }
  end,
  api_args = function(_, ref)
    local encoded = (ref.owner .. '/' .. ref.repo):gsub('/', '%%2F')
    local endpoint = ref.type == 'merge_request' and 'merge_requests' or 'issues'
    return {
      'glab',
      'api',
      '/projects/' .. encoded .. '/' .. endpoint .. '/' .. ref.number,
    }
  end,
  parse_state = function(_, decoded)
    if decoded.state == 'merged' then
      return 'merged'
    elseif decoded.state == 'closed' then
      return 'closed'
    end
    return 'open'
  end,
})

M.register({
  name = 'codeberg',
  shorthand = 'cb',
  default_host = 'codeberg.org',
  cli = 'tea',
  auth_cmd = 'tea login add',
  auth_status_args = { 'tea', 'login', 'list' },
  default_icon = '',
  default_issue_format = '%i %o/%r#%n',
  _warned = false,
  parse_url = function(self, url)
    _ensure_instances()
    local host, owner, repo, kind, number =
      url:match('^https?://([^/]+)/([%w%.%-_]+)/([%w%.%-_]+)/(%a+)/(%d+)$')
    if not host then
      return nil
    end
    if kind ~= 'issues' and kind ~= 'pulls' then
      return nil
    end
    if _by_host[host] ~= self then
      return nil
    end
    local num = tonumber(number) --[[@as integer]]
    local ref_type = kind == 'pulls' and 'pull_request' or 'issue'
    return {
      forge = 'codeberg',
      owner = owner,
      repo = repo,
      type = ref_type,
      number = num,
      url = url,
    }
  end,
  api_args = function(_, ref)
    local endpoint = ref.type == 'pull_request' and 'pulls' or 'issues'
    return {
      'tea',
      'api',
      '/repos/' .. ref.owner .. '/' .. ref.repo .. '/' .. endpoint .. '/' .. ref.number,
    }
  end,
  parse_state = function(_, decoded)
    if decoded.state == 'closed' then
      return 'closed'
    end
    return 'open'
  end,
})

return M