local M = {}

---@private
---@param version string
---@return string
local function create_err_msg(v)
  if type(v) == 'string' then
    return string.format('invalid version: "%s"', tostring(v))
  end
  return string.format('invalid version: %s (%s)', tostring(v), type(v))
end

---@private
--- Throws an error if `version` cannot be parsed.
---@param version string
local function assert_version(version, opt)
  local rv = M.parse(version, opt)
  if rv == nil then
    error(create_err_msg(version))
  end
  return rv
end

---@private
--- Compares the prerelease component of the two versions.
local function cmp_prerelease(v1, v2)
  if v1.prerelease and not v2.prerelease then
    return -1
  end
  if not v1.prerelease and v2.prerelease then
    return 1
  end
  if not v1.prerelease and not v2.prerelease then
    return 0
  end

  local v1_identifiers = vim.split(v1.prerelease, '.', { plain = true })
  local v2_identifiers = vim.split(v2.prerelease, '.', { plain = true })
  local i = 1
  local max = math.max(vim.tbl_count(v1_identifiers), vim.tbl_count(v2_identifiers))
  while i <= max do
    local v1_identifier = v1_identifiers[i]
    local v2_identifier = v2_identifiers[i]
    if v1_identifier ~= v2_identifier then
      local v1_num = tonumber(v1_identifier)
      local v2_num = tonumber(v2_identifier)
      local is_number = v1_num and v2_num
      if is_number then
        -- Number comparisons
        if not v1_num and v2_num then
          return -1
        end
        if v1_num and not v2_num then
          return 1
        end
        if v1_num == v2_num then
          return 0
        end
        if v1_num > v2_num then
          return 1
        end
        if v1_num < v2_num then
          return -1
        end
      else
        -- String comparisons
        if v1_identifier and not v2_identifier then
          return 1
        end
        if not v1_identifier and v2_identifier then
          return -1
        end
        if v1_identifier < v2_identifier then
          return -1
        end
        if v1_identifier > v2_identifier then
          return 1
        end
        if v1_identifier == v2_identifier then
          return 0
        end
      end
    end
    i = i + 1
  end

  return 0
end

---@private
local function cmp_version_core(v1, v2)
  if v1.major == v2.major and v1.minor == v2.minor and v1.patch == v2.patch then
    return 0
  end
  if
    v1.major > v2.major
    or (v1.major == v2.major and v1.minor > v2.minor)
    or (v1.major == v2.major and v1.minor == v2.minor and v1.patch > v2.patch)
  then
    return 1
  end
  return -1
end

--- Compares two strings (`v1` and `v2`) in semver format.
---@param v1 string Version.
---@param v2 string Version to compare with v1.
---@param opts table|nil Optional keyword arguments:
---                      - strict (boolean):  see `semver.parse` for details. Defaults to false.
---@return integer `-1` if `v1 < v2`, `0` if `v1 == v2`, `1` if `v1 > v2`.
function M.cmp(v1, v2, opts)
  opts = opts or { strict = false }
  local v1_parsed = assert_version(v1, opts)
  local v2_parsed = assert_version(v2, opts)

  local result = cmp_version_core(v1_parsed, v2_parsed)
  if result == 0 then
    result = cmp_prerelease(v1_parsed, v2_parsed)
  end
  return result
end

---@private
---@param labels string Prerelease and build component of semantic version string e.g. "-rc1+build.0".
---@return string|nil
local function parse_prerelease(labels)
  -- This pattern matches "-(alpha)+build.15".
  -- '^%-[%w%.]+$'
  local result = labels:match('^%-([%w%.]+)+.+$')
  if result then
    return result
  end
  -- This pattern matches "-(alpha)".
  result = labels:match('^%-([%w%.]+)')
  if result then
    return result
  end

  return nil
end

---@private
---@param labels string Prerelease and build component of semantic version string e.g. "-rc1+build.0".
---@return string|nil
local function parse_build(labels)
  -- Pattern matches "-alpha+(build.15)".
  local result = labels:match('^%-[%w%.]+%+([%w%.]+)$')
  if result then
    return result
  end

  -- Pattern matches "+(build.15)".
  result = labels:match('^%+([%w%.]+)$')
  if result then
    return result
  end

  return nil
end

---@private
--- Extracts the major, minor, patch and preprelease and build components from
--- `version`.
---@param version string Version string
local function extract_components_strict(version)
  local major, minor, patch, prerelease_and_build = version:match('^v?(%d+)%.(%d+)%.(%d+)(.*)$')
  return tonumber(major), tonumber(minor), tonumber(patch), prerelease_and_build
end

---@private
--- Extracts the major, minor, patch and preprelease and build components from
--- `version`. When `minor` and `patch` components are not found (nil), coerce
--- them to 0.
---@param version string Version string
local function extract_components_loose(version)
  local major, minor, patch, prerelease_and_build = version:match('^v?(%d+)%.?(%d*)%.?(%d*)(.*)$')
  major = tonumber(major)
  minor = tonumber(minor) or 0
  patch = tonumber(patch) or 0
  return major, minor, patch, prerelease_and_build
end

---@private
--- Validates the prerelease and build string e.g. "-rc1+build.0". If the
--- prerelease, build or both are valid forms then it will return true, if it
--- is not of any valid form, it will return false.
---@param prerelease_and_build string
---@return boolean
local function is_prerelease_and_build_valid(prerelease_and_build)
  if prerelease_and_build == '' then
    return true
  end
  local has_build = parse_build(prerelease_and_build) ~= nil
  local has_prerelease = parse_prerelease(prerelease_and_build) ~= nil
  local has_prerelease_and_build = has_prerelease and has_build
  return has_build or has_prerelease or has_prerelease_and_build
end

--- Parses a semantic version string.
---
--- Ignores leading "v" and surrounding whitespace, e.g. " v1.0.1-rc1+build.2",
--- "1.0.1-rc1+build.2", "v1.0.1-rc1+build.2" and "v1.0.1-rc1+build.2 " are all parsed as:
--- <pre>
---   { major = 1, minor = 0, patch = 1, prerelease = "rc1", build = "build.2" }
--- </pre>
---
---@param version string Version string to be parsed.
---@param opts table|nil Optional keyword arguments:
---                      - strict (boolean):  Default false. If `true`, no coercion is attempted on
---                      input not strictly conforming to semver v2.0.0
---                      (https://semver.org/spec/v2.0.0.html). E.g. `parse("v1.2")` returns nil.
---@return table|nil parsed_version Parsed version table or `nil` if `version` is invalid.
function M.parse(version, opts)
  if type(version) ~= 'string' then
    error(create_err_msg(version))
  end

  opts = opts or { strict = false }

  version = vim.trim(version)

  local extract_components = opts.strict and extract_components_strict or extract_components_loose
  local major, minor, patch, prerelease_and_build = extract_components(version)

  -- If major is nil then that means that the version does not begin with a
  -- digit with or without a "v" prefix.
  if major == nil or not is_prerelease_and_build_valid(prerelease_and_build) then
    return nil
  end

  local prerelease = nil
  local build = nil
  if prerelease_and_build ~= nil then
    prerelease = parse_prerelease(prerelease_and_build)
    build = parse_build(prerelease_and_build)
  end

  return {
    major = major,
    minor = minor,
    patch = patch,
    prerelease = prerelease,
    build = build,
  }
end

---Returns `true` if `v1` are `v2` are equal versions.
---@param v1 string
---@param v2 string
---@return boolean
function M.eq(v1, v2)
  return M.cmp(v1, v2) == 0
end

---Returns `true` if `v1` is less than `v2`.
---@param v1 string
---@param v2 string
---@return boolean
function M.lt(v1, v2)
  return M.cmp(v1, v2) == -1
end

---Returns `true` if `v1` is greater than `v2`.
---@param v1 string
---@param v2 string
---@return boolean
function M.gt(v1, v2)
  return M.cmp(v1, v2) == 1
end

setmetatable(M, {
  __call = function()
    return vim.fn.api_info().version
  end,
})

return M