-- Query syntax parser module
local M = {}

local utils = require('notex.utils')

-- Parse query string into structured object
function M.parse(query_string)
  local result = {
    filters = {},
    conditions = nil,
    order_by = nil,
    group_by = nil,
    limit = nil,
    raw_query = query_string,
    parse_errors = {}
  }

  if not query_string or query_string == "" then
    table.insert(result.parse_errors, "Empty query string")
    return result
  end

  -- Extract query block from markdown
  local query_content = M.extract_query_block(query_string)
  if not query_content then
    table.insert(result.parse_errors, "No valid query block found")
    return result
  end

  -- Parse query lines
  local lines = M.split_lines(query_content)
  local current_section = "filters" -- filters, where, order_by, group_by, limit

  for _, line in ipairs(lines) do
    line = line:trim()
    if line == "" or line:match("^%s*%-%-%-") then
      -- Skip empty lines and comments
      continue
    end

    -- Detect section changes
    local section = M.detect_section(line)
    if section then
      current_section = section
      continue
    end

    -- Parse based on current section
    if current_section == "filters" then
      M.parse_filter_line(line, result)
    elseif current_section == "where" then
      M.parse_condition_line(line, result)
    elseif current_section == "order_by" then
      M.parse_order_by_line(line, result)
    elseif current_section == "group_by" then
      M.parse_group_by_line(line, result)
    elseif current_section == "limit" then
      M.parse_limit_line(line, result)
    end
  end

  -- Validate parsed query
  M.validate_parsed_query(result)

  return result
end

-- Extract query block from markdown content
function M.extract_query_block(content)
  -- Match ```notex-query blocks
  local start_pos, end_pos, query_content = content:match("```notex%-query%s*\n(.*)\n```")
  if query_content then
    return query_content
  end

  -- Match inline query format
  local inline_query = content:match("```notex%-query%s*\n(.*)")
  if inline_query then
    return inline_query
  end

  return nil
end

-- Split content into lines
function M.split_lines(content)
  local lines = {}
  for line in content:gmatch("[^\r\n]+") do
    table.insert(lines, line)
  end
  return lines
end

-- Detect query section
function M.detect_section(line)
  local upper_line = line:upper()

  if upper_line:match("^FROM%s+") then
    return "filters"
  elseif upper_line:match("^WHERE%s+") then
    return "where"
  elseif upper_line:match("^ORDER%s+BY%s+") then
    return "order_by"
  elseif upper_line:match("^GROUP%s+BY%s+") then
    return "group_by"
  elseif upper_line:match("^LIMIT%s+") then
    return "limit"
  end

  return nil
end

-- Parse filter line (FROM clause or direct property filters)
function M.parse_filter_line(line, result)
  -- Handle FROM clause
  local from_match = line:match("^FROM%s+(.+)")
  if from_match then
    M.parse_property_filters(from_match, result)
    return
  end

  -- Handle direct property filters
  M.parse_property_filters(line, result)
end

-- Parse property filters
function M.parse_property_filters(filter_string, result)
  -- Parse YAML-style property filters
  local yaml_filters = M.parse_yaml_filters(filter_string)
  for key, value in pairs(yaml_filters) do
    result.filters[key] = value
  end
end

-- Parse YAML-style filters
function M.parse_yaml_filters(yaml_string)
  local filters = {}

  -- Handle key: value pairs
  for key, value in yaml_string:gmatch("(%w+)%s*:%s*(.+)") do
    -- Parse quoted values
    local quoted_value = value:match('^"(.*)"$')
    if quoted_value then
      filters[key] = quoted_value
    else
      -- Parse array values
      local array_match = value:match("^%[(.*)%]$")
      if array_match then
        local array_values = {}
        for item in array_match:gsub("%s", ""):gmatch("[^,]+") do
          table.insert(array_values, item:gsub("^['\"](.*)['\"]$", "%1"))
        end
        filters[key] = array_values
      else
        filters[key] = value:trim()
      end
    end
  end

  return filters
end

-- Parse WHERE condition line
function M.parse_condition_line(line, result)
  local condition_string = line:match("^WHERE%s+(.+)")
  if not condition_string then
    table.insert(result.parse_errors, "Invalid WHERE clause: " .. line)
    return
  end

  result.conditions = M.parse_conditions(condition_string)
end

-- Parse conditions with logical operators
function M.parse_conditions(condition_string)
  local conditions = {
    type = "AND",
    clauses = {}
  }

  -- Split by AND/OR operators
  local and_parts = M.split_logical_operators(condition_string, "AND")
  local or_parts = {}

  -- Check if this is an OR condition
  for _, part in ipairs(and_parts) do
    if part:match("OR") then
      local or_split = M.split_logical_operators(part, "OR")
      if #or_split > 1 then
        conditions.type = "OR"
        for _, or_part in ipairs(or_split) do
          table.insert(conditions.clauses, M.parse_single_condition(or_part))
        end
        return conditions
      end
    end
  end

  -- Parse AND conditions
  for _, and_part in ipairs(and_parts) do
    table.insert(conditions.clauses, M.parse_single_condition(and_part))
  end

  return conditions
end

-- Split by logical operator
function M.split_logical_operators(string, operator)
  local parts = {}
  local pattern = "%s+" .. operator .. "%s+"

  for part in string:gmatch("([^" .. pattern .. "]+)") do
    table.insert(parts, part:trim())
  end

  return parts
end

-- Parse single condition
function M.parse_single_condition(condition_string)
  condition_string = condition_string:trim()

  -- Handle NOT operator
  local negated = false
  if condition_string:match("^NOT%s+") then
    negated = true
    condition_string = condition_string:sub(4):trim()
  end

  -- Parse comparison operators
  local operators = {
    { pattern = ">=%s*", type = ">=" },
    { pattern = "<=%s*", type = "<=" },
    { pattern = "!=%s*", type = "!=" },
    { pattern = ">%s*", type = ">" },
    { pattern = "<%s*", type = "<" },
    { pattern = "=%s*", type = "=" },
    { pattern = "%s+CONTAINS%s+", type = "CONTAINS" },
    { pattern = "%s+STARTS_WITH%s+", type = "STARTS_WITH" },
    { pattern = "%s+ENDS_WITH%s+", type = "ENDS_WITH" },
    { pattern = "%s+INCLUDES%s+", type = "INCLUDES" },
    { pattern = "%s+BEFORE%s+", type = "BEFORE" },
    { pattern = "%s+AFTER%s+", type = "AFTER" },
    { pattern = "%s+WITHIN%s+", type = "WITHIN" }
  }

  for _, op in ipairs(operators) do
    local field, value = condition_string:match("^(.-)" .. op.pattern .. "(.+)$")
    if field and value then
      return {
        type = "comparison",
        field = field:trim(),
        operator = op.type,
        value = M.parse_value(value:trim()),
        negated = negated
      }
    end
  end

  -- If no operator found, treat as existence check
  return {
    type = "existence",
    field = condition_string,
    negated = negated
  }
end

-- Parse value (handle quotes, numbers, booleans)
function M.parse_value(value_string)
  -- Handle quoted strings
  local quoted = value_string:match('^"(.*)"$')
  if quoted then
    return quoted
  end

  -- Handle single quoted strings
  quoted = value_string:match("^'(.*)'$")
  if quoted then
    return quoted
  end

  -- Handle numbers
  local number = tonumber(value_string)
  if number then
    return number
  end

  -- Handle booleans
  local lower = value_string:lower()
  if lower == "true" then
    return true
  elseif lower == "false" then
    return false
  end

  -- Handle date/time relative values (e.g., "7d" for 7 days)
  local time_match = value_string:match("^(%d+)([hdwmy])$")
  if time_match then
    local amount = tonumber(time_match[1])
    local unit = time_match[2]
    return { type = "relative_time", amount = amount, unit = unit }
  end

  -- Default to string
  return value_string
end

-- Parse ORDER BY line
function M.parse_order_by_line(line, result)
  local order_string = line:match("^ORDER%s+BY%s+(.+)")
  if not order_string then
    table.insert(result.parse_errors, "Invalid ORDER BY clause: " .. line)
    return
  end

  local field, direction = order_string:match("^(%w+)%s*(ASC|DESC)?$")
  if not field then
    table.insert(result.parse_errors, "Invalid ORDER BY format: " .. order_string)
    return
  end

  result.order_by = {
    field = field,
    direction = direction and direction:upper() or "ASC"
  }
end

-- Parse GROUP BY line
function M.parse_group_by_line(line, result)
  local group_string = line:match("^GROUP%s+BY%s+(.+)")
  if not group_string then
    table.insert(result.parse_errors, "Invalid GROUP BY clause: " .. line)
    return
  end

  result.group_by = group_string:trim()
end

-- Parse LIMIT line
function M.parse_limit_line(line, result)
  local limit_string = line:match("^LIMIT%s+(.+)")
  if not limit_string then
    table.insert(result.parse_errors, "Invalid LIMIT clause: " .. line)
    return
  end

  local limit = tonumber(limit_string)
  if not limit or limit <= 0 then
    table.insert(result.parse_errors, "Invalid LIMIT value: " .. limit_string)
    return
  end

  result.limit = limit
end

-- Validate parsed query
function M.validate_parsed_query(query)
  -- Check if we have any filters or conditions
  if next(query.filters) == nil and not query.conditions then
    table.insert(query.parse_errors, "Query must have at least one filter or condition")
  end

  -- Validate field names (basic check)
  local valid_fields = {} -- Could be populated from schema
  for field, _ in pairs(query.filters) do
    if not M.is_valid_field_name(field) then
      table.insert(query.parse_errors, "Invalid field name: " .. field)
    end
  end

  -- Validate conditions
  if query.conditions then
    M.validate_conditions(query.conditions, query.parse_errors)
  end
end

-- Check if field name is valid
function M.is_valid_field_name(field)
  return field:match("^[%w_%-%.]+$") ~= nil
end

-- Validate conditions recursively
function M.validate_conditions(conditions, errors)
  if conditions.type == "comparison" then
    if not M.is_valid_field_name(conditions.field) then
      table.insert(errors, "Invalid field name in condition: " .. conditions.field)
    end
  elseif conditions.type == "existence" then
    if not M.is_valid_field_name(conditions.field) then
      table.insert(errors, "Invalid field name in existence check: " .. conditions.field)
    end
  elseif conditions.clauses then
    for _, clause in ipairs(conditions.clauses) do
      M.validate_conditions(clause, errors)
    end
  end
end

-- Generate query hash for caching
function M.generate_query_hash(query)
  local hash_input = vim.json.encode({
    filters = query.filters,
    conditions = query.conditions,
    order_by = query.order_by,
    group_by = query.group_by,
    limit = query.limit
  })

  return utils.sha256(hash_input)
end

return M