defmodule Plausible.Stats.SQL.Expression do
  @moduledoc """
  This module is responsible for generating SQL/Ecto expressions
  for dimensions and metrics used in query SELECT statement.

  Each dimension and metric is tagged with with selected_as for easier
  usage down the line.
  """

  use Plausible
  use Plausible.Stats.SQL.Fragments

  import Ecto.Query

  alias Plausible.Stats.{Query, Filters, SQL, Time}

  @no_ref "Direct / None"
  @no_channel "Direct"
  @not_set "(not set)"

  defmacrop field_or_blank_value(q, key, expr, empty_value) do
    quote do
      select_merge_as(unquote(q), [t], %{
        unquote(key) =>
          fragment("if(empty(?), ?, ?)", unquote(expr), unquote(empty_value), unquote(expr))
      })
    end
  end

  defmacrop time_slots(query, period_in_seconds, first, last) do
    quote do
      fragment(
        """
        timeSlots(
          toTimeZone(greatest(?, ?), ?),
          toUInt32(timeDiff(greatest(?, ?), least(?, ?))),
          toUInt32(?)
        )
        """,
        s.start,
        ^unquote(first),
        ^unquote(query).timezone,
        s.start,
        ^unquote(first),
        s.timestamp,
        ^unquote(last),
        ^unquote(period_in_seconds)
      )
    end
  end

  def select_dimension(q, key, "time:month", :sessions, query) do
    {_first, last_datetime} = Time.utc_boundaries(query)

    select_merge_as(q, [t], %{
      key =>
        fragment(
          "toStartOfMonth(toTimeZone(least(?, ?), ?))",
          t.timestamp,
          ^last_datetime,
          ^query.timezone
        )
    })
  end

  def select_dimension(q, key, "time:month", _table, query) do
    select_merge_as(q, [t], %{
      key => fragment("toStartOfMonth(toTimeZone(?, ?))", t.timestamp, ^query.timezone)
    })
  end

  def select_dimension(q, key, "time:week", :sessions, query) do
    {_first, last_datetime} = Time.utc_boundaries(query)
    date_range = Query.date_range(query)

    select_merge_as(q, [t], %{
      key =>
        weekstart_not_before(
          to_timezone(fragment("least(?, ?)", t.timestamp, ^last_datetime), ^query.timezone),
          ^date_range.first
        )
    })
  end

  def select_dimension(q, key, "time:week", _table, query) do
    date_range = Query.date_range(query)

    select_merge_as(q, [t], %{
      key =>
        weekstart_not_before(
          to_timezone(t.timestamp, ^query.timezone),
          ^date_range.first
        )
    })
  end

  def select_dimension(q, key, "time:day", :sessions, query) do
    {_first, last_datetime} = Time.utc_boundaries(query)

    select_merge_as(q, [t], %{
      key =>
        fragment(
          "toDate(toTimeZone(least(?, ?), ?))",
          t.timestamp,
          ^last_datetime,
          ^query.timezone
        )
    })
  end

  def select_dimension(q, key, "time:day", _table, query) do
    select_merge_as(q, [t], %{
      key => fragment("toDate(toTimeZone(?, ?))", t.timestamp, ^query.timezone)
    })
  end

  def select_dimension(q, key, "time:hour", :sessions, query) when query.smear_session_metrics do
    # :TRICKY: ClickHouse timeSlots works off of unix epoch and is not
    #   timezone-aware. This means that for e.g. Asia/Katmandu (GMT+5:45)
    #   to work, we divide time into 15-minute buckets and later combine these
    #   via toStartOfHour
    {first, last} = Time.utc_boundaries(query)

    q
    |> join(:inner, [s], time_slot in time_slots(query, 15 * 60, first, last),
      as: :time_slot,
      hints: "ARRAY",
      on: true
    )
    |> select_merge_as([s, time_slot: time_slot], %{
      key => fragment("toStartOfHour(?)", time_slot)
    })
  end

  def select_dimension(q, key, "time:hour", _table, query) do
    select_merge_as(q, [t], %{
      key => fragment("toStartOfHour(toTimeZone(?, ?))", t.timestamp, ^query.timezone)
    })
  end

  # :NOTE: This is not exposed in Query APIv2
  def select_dimension(q, key, "time:minute", :sessions, query)
      when query.smear_session_metrics do
    {first, last} = Time.utc_boundaries(query)

    q
    |> join(:inner, [s], time_slot in time_slots(query, 60, first, last),
      as: :time_slot,
      hints: "ARRAY",
      on: true
    )
    |> select_merge_as([s, time_slot: time_slot], %{
      key => fragment("?", time_slot)
    })
  end

  # :NOTE: This is not exposed in Query APIv2
  def select_dimension(q, key, "time:minute", _table, query) do
    select_merge_as(q, [t], %{
      key => fragment("toStartOfMinute(toTimeZone(?, ?))", t.timestamp, ^query.timezone)
    })
  end

  def select_dimension(q, key, "event:name", _table, _query),
    do: select_merge_as(q, [t], %{key => t.name})

  def select_dimension(q, key, "event:page", _table, _query),
    do: select_merge_as(q, [t], %{key => t.pathname})

  def select_dimension(q, key, "event:hostname", _table, _query),
    do: select_merge_as(q, [t], %{key => t.hostname})

  def select_dimension(q, key, "event:props:" <> property_name, _table, _query) do
    select_merge_as(q, [t], %{
      key =>
        fragment(
          "if(not empty(?), ?, '(none)')",
          get_by_key(t, :meta, ^property_name),
          get_by_key(t, :meta, ^property_name)
        )
    })
  end

  def select_dimension(q, key, "visit:entry_page", _table, _query),
    do: select_merge_as(q, [t], %{key => t.entry_page})

  def select_dimension(q, key, "visit:entry_page_hostname", _table, _query),
    do: select_merge_as(q, [t], %{key => t.hostname})

  def select_dimension(q, key, "visit:exit_page", _table, _query),
    do: select_merge_as(q, [t], %{key => t.exit_page})

  def select_dimension(q, key, "visit:exit_page_hostname", _table, _query),
    do: select_merge_as(q, [t], %{key => t.exit_page_hostname})

  def select_dimension(q, key, "visit:utm_medium", _table, _query),
    do: field_or_blank_value(q, key, t.utm_medium, @not_set)

  def select_dimension(q, key, "visit:utm_source", _table, _query),
    do: field_or_blank_value(q, key, t.utm_source, @not_set)

  def select_dimension(q, key, "visit:utm_campaign", _table, _query),
    do: field_or_blank_value(q, key, t.utm_campaign, @not_set)

  def select_dimension(q, key, "visit:utm_content", _table, _query),
    do: field_or_blank_value(q, key, t.utm_content, @not_set)

  def select_dimension(q, key, "visit:utm_term", _table, _query),
    do: field_or_blank_value(q, key, t.utm_term, @not_set)

  def select_dimension(q, key, "visit:source", _table, _query),
    do: field_or_blank_value(q, key, t.source, @no_ref)

  def select_dimension(q, key, "visit:channel", _table, _query),
    do: field_or_blank_value(q, key, t.acquisition_channel, @no_channel)

  def select_dimension(q, key, "visit:referrer", _table, _query),
    do: field_or_blank_value(q, key, t.referrer, @no_ref)

  def select_dimension(q, key, "visit:device", _table, _query),
    do: field_or_blank_value(q, key, t.device, @not_set)

  def select_dimension(q, key, "visit:os", _table, _query),
    do: field_or_blank_value(q, key, t.os, @not_set)

  def select_dimension(q, key, "visit:os_version", _table, _query),
    do: field_or_blank_value(q, key, t.os_version, @not_set)

  def select_dimension(q, key, "visit:browser", _table, _query),
    do: field_or_blank_value(q, key, t.browser, @not_set)

  def select_dimension(q, key, "visit:browser_version", _table, _query),
    do: field_or_blank_value(q, key, t.browser_version, @not_set)

  def select_dimension(q, key, "visit:country", _table, _query),
    do: select_merge_as(q, [t], %{key => t.country})

  def select_dimension(q, key, "visit:region", _table, _query),
    do: select_merge_as(q, [t], %{key => t.region})

  def select_dimension(q, key, "visit:city", _table, _query),
    do: select_merge_as(q, [t], %{key => t.city})

  def select_dimension(q, key, "visit:country_name", _table, _query),
    do: select_merge_as(q, [t], %{key => t.country_name})

  def select_dimension(q, key, "visit:region_name", _table, _query),
    do: select_merge_as(q, [t], %{key => t.region_name})

  def select_dimension(q, key, "visit:city_name", _table, _query),
    do: select_merge_as(q, [t], %{key => t.city_name})

  def select_dimension_internal(q, "visit:entry_page") do
    select_merge_as(q, [t], %{
      entry_page: fragment("any(?)", field(t, :entry_page))
    })
  end

  def select_dimension_internal(q, "visit:entry_page_hostname") do
    select_merge_as(q, [t], %{
      entry_page_hostname: fragment("any(?)", field(t, :entry_page_hostname))
    })
  end

  def select_dimension_internal(q, "visit:exit_page") do
    # As exit page changes with every pageview event over the lifetime
    # of a session, only the most recent value must be considered.
    select_merge_as(q, [t], %{
      exit_page: fragment("argMax(?, ?)", field(t, :exit_page), field(t, :events))
    })
  end

  def select_dimension_internal(q, "visit:exit_page_hostname") do
    select_merge_as(q, [t], %{
      exit_page_hostname:
        fragment("argMax(?, ?)", field(t, :exit_page_hostname), field(t, :events))
    })
  end

  def select_dimension_internal(q, _dimension), do: q

  def select_dimension_from_join(q, key, "visit:entry_page"),
    do: select_merge_as(q, [..., t], %{key => t.entry_page})

  def select_dimension_from_join(q, key, "visit:entry_page_hostname"),
    do: select_merge_as(q, [..., t], %{key => t.entry_page_hostaname})

  def select_dimension_from_join(q, key, "visit:exit_page"),
    do: select_merge_as(q, [..., t], %{key => t.exit_page})

  def select_dimension_from_join(q, key, "visit:exit_page_hostname"),
    do: select_merge_as(q, [..., t], %{key => t.exit_page_hostname})

  def select_dimension_from_join(q, _key, _dimension), do: q

  def event_metric(:pageviews, _query) do
    wrap_alias([e], %{
      pageviews: scale_sample(fragment("countIf(? = 'pageview')", e.name))
    })
  end

  def event_metric(:events, _query) do
    wrap_alias([e], %{
      events: scale_sample(fragment("countIf(? != 'engagement')", e.name))
    })
  end

  def event_metric(:visitors, _query) do
    wrap_alias([e], %{
      visitors: scale_sample(fragment("uniq(?)", e.user_id))
    })
  end

  def event_metric(:visits, _query) do
    wrap_alias([e], %{
      visits: scale_sample(fragment("uniq(?)", e.session_id))
    })
  end

  on_ee do
    def event_metric(:total_revenue, _query) do
      wrap_alias(
        [e],
        %{
          total_revenue:
            fragment("toDecimal64(sum(?) * any(_sample_factor), 3)", e.revenue_reporting_amount)
        }
      )
    end

    def event_metric(:average_revenue, _query) do
      wrap_alias(
        [e],
        %{
          average_revenue: fragment("toDecimal64(avg(?), 3)", e.revenue_reporting_amount)
        }
      )
    end
  end

  def event_metric(:sample_percent, _query) do
    wrap_alias([], %{
      sample_percent:
        fragment("if(any(_sample_factor) > 1, round(100 / any(_sample_factor)), 100)")
    })
  end

  def event_metric(:percentage, _query), do: %{}
  def event_metric(:conversion_rate, _query), do: %{}
  def event_metric(:scroll_depth, _query), do: %{}
  def event_metric(:group_conversion_rate, _query), do: %{}
  def event_metric(:total_visitors, _query), do: %{}

  def event_metric(:time_on_page, query) do
    selected =
      case query.time_on_page_data do
        %{include_new_metric: false} ->
          wrap_alias(
            [e],
            %{
              # :KLUDGE: We would like to but can't use constant 0 here as it leads to cyclic aliases if there's no other
              # metrics selected other than time_on_page.
              __internal_total_time_on_page: fragment("sumArray([0])"),
              __internal_total_time_on_page_visits: fragment("sumArray([0])")
            }
          )

        %{include_new_metric: true, cutoff: nil} ->
          wrap_alias(
            [e],
            %{
              __internal_total_time_on_page: fragment("sum(?) / 1000", e.engagement_time),
              __internal_total_time_on_page_visits:
                fragment("uniqIf(?, ? = 'engagement')", e.session_id, e.name)
            }
          )

        %{include_new_metric: true, cutoff: cutoff} ->
          wrap_alias(
            [e],
            %{
              __internal_total_time_on_page:
                fragment(
                  "sumIf(?, ? >= ?) / 1000",
                  e.engagement_time,
                  e.timestamp,
                  ^cutoff
                ),
              __internal_total_time_on_page_visits:
                fragment(
                  "uniqIf(?, ? = 'engagement' and ? >= ?)",
                  e.session_id,
                  e.name,
                  e.timestamp,
                  ^cutoff
                )
            }
          )
      end

    if query.time_on_page_data.include_legacy_metric do
      selected
    else
      Map.merge(
        selected,
        wrap_alias([e], %{
          time_on_page:
            time_on_page(
              selected_as(:__internal_total_time_on_page),
              selected_as(:__internal_total_time_on_page_visits)
            )
        })
      )
    end
  end

  def event_metric(unknown, _query), do: raise("Unknown metric: #{unknown}")

  def session_metric(:bounce_rate, query) do
    # :TRICKY: If page is passed to query, we only count bounce rate where users _entered_ at page.
    event_page_filter = Filters.get_toplevel_filter(query, "event:page")
    condition = SQL.WhereBuilder.build_condition(:entry_page, event_page_filter)

    wrap_alias([], %{
      bounce_rate:
        fragment(
          # :TRICKY: Before PR #4493, we could have sessions where `sum(is_bounce * sign)`
          # is negative, leading to an underflow and >100% bounce rate. This works around
          # that issue.
          "toUInt32(greatest(ifNotFinite(round(sumIf(is_bounce * sign, ?) / sumIf(sign, ?) * 100), 0), 0))",
          ^condition,
          ^condition
        ),
      __internal_visits: fragment("toUInt32(greatest(sum(sign), 0))")
    })
  end

  def session_metric(:exit_rate, _query) do
    wrap_alias([s], %{
      __internal_visits: fragment("toUInt32(greatest(sum(sign), 0))")
    })
  end

  def session_metric(:visits, query) when query.smear_session_metrics do
    wrap_alias([s], %{
      visits: scale_sample(fragment("uniq(?)", s.session_id))
    })
  end

  def session_metric(:visits, _query) do
    wrap_alias([s], %{
      visits: scale_sample(fragment("greatest(sum(?), 0)", s.sign))
    })
  end

  def session_metric(:pageviews, _query) do
    wrap_alias([s], %{
      pageviews: scale_sample(fragment("greatest(sum(? * ?), 0)", s.sign, s.pageviews))
    })
  end

  def session_metric(:events, _query) do
    wrap_alias([s], %{
      events: scale_sample(fragment("greatest(sum(? * ?), 0)", s.sign, s.events))
    })
  end

  def session_metric(:visitors, _query) do
    wrap_alias([s], %{
      visitors: scale_sample(fragment("uniq(?)", s.user_id))
    })
  end

  def session_metric(:visit_duration, _query) do
    wrap_alias([], %{
      visit_duration:
        fragment("toUInt32(greatest(ifNotFinite(round(sum(duration * sign) / sum(sign)), 0), 0))"),
      __internal_visits: fragment("toUInt32(greatest(sum(sign), 0))")
    })
  end

  def session_metric(:views_per_visit, _query) do
    wrap_alias([s], %{
      views_per_visit:
        fragment(
          "greatest(ifNotFinite(round(sum(? * ?) / sum(?), 2), 0), 0)",
          s.sign,
          s.pageviews,
          s.sign
        ),
      __internal_visits: fragment("toUInt32(greatest(sum(sign), 0))")
    })
  end

  def session_metric(:sample_percent, _query) do
    wrap_alias([], %{
      sample_percent:
        fragment("if(any(_sample_factor) > 1, round(100 / any(_sample_factor)), 100)")
    })
  end

  def session_metric(:percentage, _query), do: %{}
  def session_metric(:conversion_rate, _query), do: %{}
  def session_metric(:group_conversion_rate, _query), do: %{}

  @doc """
  The fragment matches events to goals by:
  1. Checking if the pathname matches the goal's page regex pattern
  2. Verifying the event name matches the expected name for the goal type
  3. Validating scroll depth is within threshold (for scroll goals)
  4. Ensuring all custom properties match (if any are defined on the goal)

  Returns an array of goal indices that the event matches.
  """
  defmacro event_goal_join(goal_join_data) do
    quote do
      fragment(
        """
        arrayIntersect(
          multiMatchAllIndices(?, ?),
          arrayMap(
            (expected_name, threshold, index, custom_props_keys, custom_props_values) -> if(
              expected_name = ? and ? between threshold and 100 and
              (empty(custom_props_keys) OR arrayAll((k, v) -> ?[indexOf(?, k)] = v, custom_props_keys, custom_props_values)),
              index, -1
            ),
            ?,
            ?,
            ?,
            ?,
            ?
          )
        )
        """,
        e.pathname,
        type(^unquote(goal_join_data).page_regexes, {:array, :string}),
        e.name,
        e.scroll_depth,
        field(e, :"meta.value"),
        field(e, :"meta.key"),
        type(^unquote(goal_join_data).event_names_by_type, {:array, :string}),
        type(^unquote(goal_join_data).scroll_thresholds, {:array, :integer}),
        type(^unquote(goal_join_data).indices, {:array, :integer}),
        type(^unquote(goal_join_data).custom_props_keys, {:array, {:array, :string}}),
        type(^unquote(goal_join_data).custom_props_values, {:array, {:array, :string}})
      )
    end
  end

  @doc """
  Optimized variant of `event_goal_join/1` for use when no goals have custom
  property filters. Omits all references to `meta.key` and `meta.value`,
  preventing ClickHouse from reading those expensive Array(String) columns at
  scan time.
  """
  defmacro event_goal_join_no_props(goal_join_data) do
    quote do
      fragment(
        """
        arrayIntersect(
          multiMatchAllIndices(?, ?),
          arrayMap(
            (expected_name, threshold, index) -> if(
              expected_name = ? and ? between threshold and 100,
              index, -1
            ),
            ?,
            ?,
            ?
          )
        )
        """,
        e.pathname,
        type(^unquote(goal_join_data).page_regexes, {:array, :string}),
        e.name,
        e.scroll_depth,
        type(^unquote(goal_join_data).event_names_by_type, {:array, :string}),
        type(^unquote(goal_join_data).scroll_thresholds, {:array, :integer}),
        type(^unquote(goal_join_data).indices, {:array, :integer})
      )
    end
  end
end