local char = require('cmp.utils.char')

local matcher = {}

matcher.WORD_BOUNDALY_ORDER_FACTOR = 10

matcher.PREFIX_FACTOR = 8
matcher.NOT_FUZZY_FACTOR = 6

---@type function
matcher.debug = function(...)
  return ...
end

--- score
--
-- ### The score
--
--   The `score` is `matched char count` generally.
--
--   But cmp will fix the score with some of the below points so the actual score is not `matched char count`.
--
--   1. Word boundary order
--
--     cmp prefers the match that near by word-beggining.
--
--   2. Strict case
--
--     cmp prefers strict match than ignorecase match.
--
--
-- ### Matching specs.
--
--   1. Prefix matching per word boundary
--
--     `bora`         -> `border-radius` # imaginary score: 4
--      ^^~~              ^^     ~~
--
--   2. Try sequential match first
--
--     `woroff`       -> `word_offset`   # imaginary score: 6
--      ^^^~~~            ^^^  ~~~
--
--     * The `woroff`'s second `o` should not match `word_offset`'s first `o`
--
--   3. Prefer early word boundary
--
--     `call`         -> `call`          # imaginary score: 4.1
--      ^^^^              ^^^^
--     `call`         -> `condition_all` # imaginary score: 4
--      ^~~~              ^         ~~~
--
--   4. Prefer strict match
--
--     `Buffer`       -> `Buffer`        # imaginary score: 6.1
--      ^^^^^^            ^^^^^^
--     `buffer`       -> `Buffer`        # imaginary score: 6
--      ^^^^^^            ^^^^^^
--
--   5. Use remaining characters for substring match
--
--     `fmodify`        -> `fnamemodify`   # imaginary score: 1
--      ^~~~~~~             ^    ~~~~~~
--
--   6. Avoid unexpected match detection
--
--     `candlesingle` -> candle#accept#single
--      ^^^^^^~~~~~~     ^^^^^^        ~~~~~~
--
--      * The `accept`'s `a` should not match to `candle`'s `a`
--
---Match entry
---@param input string
---@param word string
---@param option { synonyms: string[], disallow_fuzzy_matching: boolean, disallow_partial_matching: boolean, disallow_prefix_unmatching: boolean }
---@return number
matcher.match = function(input, word, option)
  option = option or {}

  -- Empty input
  if #input == 0 then
    return matcher.PREFIX_FACTOR + matcher.NOT_FUZZY_FACTOR, {}
  end

  -- Ignore if input is long than word
  if #input > #word then
    return 0, {}
  end

  -- Check prefix matching.
  if option.disallow_prefix_unmatching then
    if not char.match(string.byte(input, 1), string.byte(word, 1)) then
      return 0, {}
    end
  end

  -- Gather matched regions
  local matches = {}
  local input_start_index = 1
  local input_end_index = 1
  local word_index = 1
  local word_bound_index = 1
  while input_end_index <= #input and word_index <= #word do
    local m = matcher.find_match_region(input, input_start_index, input_end_index, word, word_index)
    if m and input_end_index <= m.input_match_end then
      m.index = word_bound_index
      input_start_index = m.input_match_start + 1
      input_end_index = m.input_match_end + 1
      word_index = char.get_next_semantic_index(word, m.word_match_end)
      table.insert(matches, m)
    else
      word_index = char.get_next_semantic_index(word, word_index)
    end
    word_bound_index = word_bound_index + 1
  end

  -- Check partial matching.
  if option.disallow_partial_matching and #matches > 1 then
    return 0, {}
  end

  if #matches == 0 then
    return 0, {}
  end

  matcher.debug(word, matches)

  -- Add prefix bonus
  local prefix = false
  if matches[1].input_match_start == 1 and matches[1].word_match_start == 1 then
    prefix = true
  else
    for _, synonym in ipairs(option.synonyms or {}) do
      prefix = true
      local o = 1
      for i = matches[1].input_match_start, matches[1].input_match_end do
        if not char.match(string.byte(synonym, o), string.byte(input, i)) then
          prefix = false
          break
        end
        o = o + 1
      end
      if prefix then
        break
      end
    end
  end

  -- Compute prefix match score
  local score = prefix and matcher.PREFIX_FACTOR or 0
  local offset = prefix and matches[1].index - 1 or 0
  local idx = 1
  for _, m in ipairs(matches) do
    local s = 0
    for i = math.max(idx, m.input_match_start), m.input_match_end do
      s = s + 1
      idx = i
    end
    idx = idx + 1
    if s > 0 then
      s = s * (1 + m.strict_ratio)
      s = s * (1 + math.max(0, matcher.WORD_BOUNDALY_ORDER_FACTOR - (m.index - offset)) / matcher.WORD_BOUNDALY_ORDER_FACTOR)
      score = score + s
    end
  end

  -- Check remaining input as fuzzy
  if matches[#matches].input_match_end < #input then
    if not option.disallow_fuzzy_matching then
      if prefix and matcher.fuzzy(input, word, matches) then
        return score, matches
      end
    end
    return 0, {}
  end

  return score + matcher.NOT_FUZZY_FACTOR, matches
end

--- fuzzy
matcher.fuzzy = function(input, word, matches)
  local last_match = matches[#matches]

  -- Lately specified middle of text.
  local input_index = last_match.input_match_end + 1
  for i = 1, #matches - 1 do
    local curr_match = matches[i]
    local next_match = matches[i + 1]
    local word_offset = 0
    local word_index = char.get_next_semantic_index(word, curr_match.word_match_end)
    while word_offset + word_index < next_match.word_match_start and input_index <= #input do
      if char.match(string.byte(word, word_index + word_offset), string.byte(input, input_index)) then
        input_index = input_index + 1
        word_offset = word_offset + 1
      else
        word_index = char.get_next_semantic_index(word, word_index + word_offset)
        word_offset = 0
      end
    end
  end

  -- Remaining text fuzzy match.
  local last_input_index = input_index
  local matched = false
  local word_offset = 0
  local word_index = last_match.word_match_end + 1
  local input_match_start = -1
  local input_match_end = -1
  local word_match_start = -1
  local strict_count = 0
  local match_count = 0
  while word_offset + word_index <= #word and input_index <= #input do
    local c1, c2 = string.byte(word, word_index + word_offset), string.byte(input, input_index)
    if char.match(c1, c2) then
      if not matched then
        input_match_start = input_index
        word_match_start = word_index + word_offset
      end
      matched = true
      input_index = input_index + 1
      strict_count = strict_count + (c1 == c2 and 1 or 0)
      match_count = match_count + 1
    elseif matched then
      input_index = last_input_index
      input_match_end = input_index - 1
    end
    word_offset = word_offset + 1
  end
  if input_index > #input then
    table.insert(matches, {
      input_match_start = input_match_start,
      input_match_end = input_match_end,
      word_match_start = word_match_start,
      word_match_end = word_index + word_offset - 1,
      strict_ratio = strict_count / match_count,
      fuzzy = true,
    })
    return true
  end
  return false
end

--- find_match_region
matcher.find_match_region = function(input, input_start_index, input_end_index, word, word_index)
  -- determine input position ( woroff -> word_offset )
  while input_start_index < input_end_index do
    if char.match(string.byte(input, input_end_index), string.byte(word, word_index)) then
      break
    end
    input_end_index = input_end_index - 1
  end

  -- Can't determine input position
  if input_end_index < input_start_index then
    return nil
  end

  local input_match_start = -1
  local input_index = input_end_index
  local word_offset = 0
  local strict_count = 0
  local match_count = 0
  while input_index <= #input and word_index + word_offset <= #word do
    local c1 = string.byte(input, input_index)
    local c2 = string.byte(word, word_index + word_offset)
    if char.match(c1, c2) then
      -- Match start.
      if input_match_start == -1 then
        input_match_start = input_index
      end

      strict_count = strict_count + (c1 == c2 and 1 or 0)
      match_count = match_count + 1
      word_offset = word_offset + 1
    else
      -- Match end (partial region)
      if input_match_start ~= -1 then
        return {
          input_match_start = input_match_start,
          input_match_end = input_index - 1,
          word_match_start = word_index,
          word_match_end = word_index + word_offset - 1,
          strict_ratio = strict_count / match_count,
          fuzzy = false,
        }
      else
        return nil
      end
    end
    input_index = input_index + 1
  end

  -- Match end (whole region)
  if input_match_start ~= -1 then
    return {
      input_match_start = input_match_start,
      input_match_end = input_index - 1,
      word_match_start = word_index,
      word_match_end = word_index + word_offset - 1,
      strict_ratio = strict_count / match_count,
      fuzzy = false,
    }
  end

  return nil
end

return matcher
