# coding=utf-8
#
# Licensed to the Apache Software Foundation (ASF) under one
# or more contributor license agreements.  See the NOTICE file
# distributed with this work for additional information
# regarding copyright ownership.  The ASF licenses this file
# to you under the Apache License, Version 2.0 (the
# "License"); you may not use this file except in compliance
# with the License.  You may obtain a copy of the License at
#
#   http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing,
# software distributed under the License is distributed on an
# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
# KIND, either express or implied.  See the License for the
# specific language governing permissions and limitations
# under the License.

# Breadth-First Search

# Please refer to the bfs.sql_in file for the documentation

"""
@file bfs.py_in

@namespace graph
"""

import plpy
from graph_utils import validate_graph_coding
from graph_utils import get_graph_usage
from utilities.control import MinWarning
from utilities.utilities import _assert
from utilities.utilities import _check_groups
from utilities.utilities import get_table_qualified_col_str
from utilities.utilities import _grp_null_checks
from utilities.utilities import add_postfix
from utilities.utilities import extract_keyvalue_params
from utilities.utilities import unique_string, split_quoted_delimited_str
from utilities.validate_args import table_exists
from utilities.validate_args import columns_exist_in_table

m4_changequote(`<!', `!>')

def _validate_bfs(vertex_table, vertex_id, edge_table, edge_params,
    source_vertex, out_table, max_distance, directed, grouping_cols_list, **kwargs):

    validate_graph_coding(vertex_table, vertex_id, edge_table, edge_params,
        out_table,'BFS')

    _assert((max_distance >= 0) and isinstance(max_distance,int),
        """Graph BFS: Invalid max_distance type or value ({0}), must be integer,
        be greater than or equal to 0 and be less than max allowable integer
        (2147483647).""".
        format(max_distance))

    _assert(isinstance(directed,bool),
        """Graph BFS: Invalid value for directed ({0}), must be boolean.""".
        format(directed))

    _assert(isinstance(source_vertex,int),
        """Graph BFS: Source vertex {source_vertex} has to be an integer.""".
        format(**locals()))
    src_exists = plpy.execute("""
        SELECT * FROM {vertex_table} WHERE {vertex_id}={source_vertex}
        """.format(**locals()))
    if src_exists.nrows() == 0:
        plpy.error(
            """Graph BFS: Source vertex {source_vertex} is not present in the
            vertex table {vertex_table}.""".
            format(**locals()))

    vt_error = plpy.execute(
        """ SELECT {vertex_id}
            FROM {vertex_table}
            WHERE {vertex_id} IS NOT NULL
            GROUP BY {vertex_id}
            HAVING count(*) > 1 """.format(**locals()))
    if vt_error.nrows() != 0:
        plpy.error(
            """Graph BFS: Source vertex table {vertex_table} contains duplicate
            vertex id's.""".
            format(**locals()))

    summary_table = add_postfix(out_table, "_summary")
    _assert(not table_exists(summary_table),
        "Graph BFS: Output summary table already exists!")

    if grouping_cols_list is not None:
        _assert(columns_exist_in_table(edge_table, grouping_cols_list),
            """Graph BFS: Not all columns from {grouping_cols_list} are present
            in edge table ({edge_table}).""".
            format(**locals()))

    return None


def graph_bfs(schema_madlib, vertex_table, vertex_id, edge_table,
        edge_args, source_vertex, out_table, max_distance, directed, grouping_cols,
        **kwargs):

    """
    Breadth First Search algorithm for graphs [1].
    Args:
        @param vertex_table    Name of the table that contains the vertex data.
        @param vertex_id       Name of the column containing the vertex ids.
        @param edge_table      Name of the table that contains the edge data.
        @param edge_args       A comma-delimited string containing multiple
                               named arguments of the form "name=value".
        @param source_vertex   The source vertex id for the algorithm to start.
        @param out_table       Name of the table to store the result of BFS.
        @param max_distance    Maximum distance from the source_vertex to search for.
        @param directed        Graph will be treated as directed if this boolean flag
                               is set to TRUE. Graph is treated as undirected by default.
        @param grouping_cols   The list of grouping columns.

    [1] https://en.wikipedia.org/wiki/Breadth-first_search
    """

    with MinWarning("warning"):

        INT_MAX = 2147483647

        params_types = {'src': str, 'dest': str}
        default_args = {'src': 'src', 'dest': 'dest'}
        edge_params = extract_keyvalue_params(edge_args,
                                            params_types,
                                            default_args)

        # Prepare the input for recording in the summary table
        if not vertex_id:
            v_st = ''
            vertex_id = "id"
        else:
            v_st = vertex_id

        if not edge_args:
            e_st = ''
        else:
            e_st = edge_args

        if not grouping_cols:
            g_st = ''
            glist = None
        else:
            g_st = grouping_cols
            glist = split_quoted_delimited_str(grouping_cols)

        if max_distance is None:
            d_st= "NULL"
            max_distance = INT_MAX
        else:
            d_st = max_distance

        if directed is None:
            dir_st= "NULL"
            directed = False
        else:
            dir_st = directed

        src = edge_params["src"]
        dest = edge_params["dest"]

        distribution = m4_ifdef(<!__POSTGRESQL__!>, <!''!>,
            <!"DISTRIBUTED BY ({0})".format(vertex_id)!>)
        local_distribution = m4_ifdef(<!__POSTGRESQL__!>, <!''!>,
            <!"DISTRIBUTED RANDOMLY"!>)

        _validate_bfs(vertex_table, vertex_id, edge_table,
            edge_params, source_vertex, out_table, max_distance, directed, glist)

        subq = unique_string(desp='subq')
        subq1 = unique_string(desp='subq1')
        sube = unique_string(desp='edge')
        sube1 = unique_string(desp='edge1')

        # Initialize grouping related variables
        insert_qry_undirected_init = ""
        grp_comma = ""
        and_grp_null_checks = ""
        grp_sube_comma = ""
        grp_sube1_comma = ""
        subq_grp_join = ''

        if grouping_cols and grouping_cols is not '':
            grp_comma = grouping_cols + ", "
            and_grp_null_checks = " AND " + _grp_null_checks(glist)
            grp_sube_comma = get_table_qualified_col_str(sube, glist) + " , "
            grp_sube1_comma = get_table_qualified_col_str(sube1, glist) + " , "

        # We keep a table of every vertex, the distance to that vertex from source
        # and the parent in the path to the vertex.
        # This table will be updated throughout the execution.
        dist_col = "dist"
        parent_col = "parent"
        curr_dist_val = 0

        # Creating the output table with the appropriate columns and data types
        plpy.execute("""
            CREATE TABLE {out_table} AS (
                SELECT
                    {grp_comma}
                    {src} AS {vertex_id},
                    {curr_dist_val}::INT AS {dist_col},
                    {src} AS {parent_col}
                FROM {edge_table}
                LIMIT 0
            ) {distribution}""".format(**locals()))

        # We keep a summary table to keep track of the parameters used for this
        # BFS run
        summary_table = add_postfix(out_table, "_summary")
        plpy.execute( """
            CREATE TABLE {summary_table}  (
                vertex_table            TEXT,
                vertex_id               TEXT,
                edge_table              TEXT,
                edge_args               TEXT,
                source_vertex           INTEGER,
                out_table               TEXT,
                max_distance            INTEGER,
                directed                BOOLEAN,
                grouping_cols           TEXT
            )
        """.format(**locals()))

        plpy.execute("""
            INSERT INTO {summary_table} VALUES
                ('{vertex_table}', '{v_st}', '{edge_table}', '{e_st}',
                {source_vertex}, '{out_table}', {d_st}, {dir_st}, '{g_st}')
        """.format(**locals()))

        # The queries for directed and undirected graphs share a common section.
        # There are additional clauses added to the undirected graph queries.
        # In the undirected case edges can be considered to go from {src} to
        # {dest} and {dest} to {src}

        if not directed:
            insert_qry_undirected_init = """ OR {dest} = {source_vertex}
                """.format(**locals())

        # This step inserts into the output table the source vertex for each
        # group in which it is present. Grouping behavior is not predictable
        # when there are NULLs in any grouping column. Therefore those rows
        # are explicitly removed from analysis
        insert_qry_init = """
            INSERT INTO {out_table}
            SELECT {grp_comma}
                {source_vertex} AS {vertex_id},
                {curr_dist_val} AS {dist_col},
                NULL AS {parent_col}
            FROM {edge_table}
            WHERE ({src} = {source_vertex} {insert_qry_undirected_init})
                {and_grp_null_checks}
            GROUP BY {grp_comma} {vertex_id}, {dist_col}
        """.format(**locals())
        plpy.execute(insert_qry_init.format(**locals()))

        # Create a table that will hold the new vertices to be explored next.
        message = unique_string(desp='message')
        plpy.execute("""
            CREATE TEMP TABLE {message} AS
            SELECT {grp_comma} {vertex_id}, {parent_col}
            FROM {out_table}
        """.format(**locals()))

        # After initialization of the output table, number of nodes connected
        # by edges to the source vertex in each group is counted. This is also used
        # below in the BFS iteration while-loop
        edge_grp_join = ""
        subq1_grp_join = ""
        if grouping_cols:
            subq_grp_join = ' AND ' + _check_groups(subq, sube, glist)
            subq1_grp_join = ' AND ' + _check_groups(subq1, sube1, glist)
            edge_grp_join = ' AND ' + _check_groups(edge_table, out_table, glist)

        count_qry = """ SELECT count(*) AS count FROM {message}
            """.format(**locals())
        vct = plpy.execute(count_qry.format(**locals()))[0]['count']

        # This insert statement is executed within the BFS iteration while-loop
        # below. It is used to discover and store all nodes (not already found)
        # connected to those found in the immediate previous iteration, which
        # are stored in the {message} table.
        toupdate = unique_string(desp='toupdate')
        insert_toupdate_table = """
            CREATE TEMP TABLE {toupdate} AS
            SELECT {grp_sube_comma} {sube}.{dest} AS {vertex_id}, {sube}.{src} AS {parent_col}
            FROM (
                SELECT {grp_comma} {src}, {dest}
                FROM {edge_table}
                WHERE NOT EXISTS (
                    SELECT 1
                    FROM {out_table}
                    WHERE {out_table}.{vertex_id} = {edge_table}.{dest}
                            {edge_grp_join}
                )
            ) AS {sube}
            INNER JOIN {message} AS {subq}
            ON ({sube}.{src}={subq}.{vertex_id} {subq_grp_join})
        """
        if not directed:
            insert_toupdate_table += """
                UNION ALL
                SELECT {grp_sube1_comma} {sube1}.{src} AS {vertex_id},
                        {sube1}.{dest} AS {parent_col}
                FROM (
                    SELECT {grp_comma} {src}, {dest}
                    FROM {edge_table}
                    WHERE NOT EXISTS (
                        SELECT 1
                        FROM {out_table}
                        WHERE {out_table}.{vertex_id} = {edge_table}.{src}
                            {edge_grp_join}
                    )
                ) AS {sube1}
                INNER JOIN {message} AS {subq1}
                ON ({sube1}.{dest}={subq1}.{vertex_id} {subq1_grp_join})
            """.format(**locals())

        insert_message_loop = """
            CREATE TEMP TABLE {message} AS
            SELECT {grp_comma} {vertex_id}, {{curr_dist_val}}+1 AS {dist_col},
                    MIN({parent_col})
            FROM {toupdate}
            GROUP BY {grp_comma} {vertex_id}
        """.format(**locals())

        insert_qry_loop = """
            INSERT INTO {out_table}
            SELECT * FROM {message}
        """.format(**locals())

        # Main loop for traversing the graph
        while vct > 0 and curr_dist_val < max_distance:
            # The loop consists of two steps:
            # 1) Disover and store all nodes that are linked to nodes found in
            #    the immediate previous iteration of the loop that have not already
            #    been found in all previous iterations
            # 2) Check for any nodes linked to those discovered in Step 1 above
            #    that have not yet been discovered
            #
            # If a node has multiple possible parents then the parent with the
            # smallest ID is chosen for output

            # In the directed graph case only nodes in the {dest} column of
            # the edge table are searched to find new nodes reachable from
            # previously discovered nodes

            # In the undirected graph case edges are treated as non-directional
            # (or bidirectional). Nodes in both the {src} and {dest} columns of
            # the edge table are searched to find new nodes reachable from
            # previously discovered nodes.
            #
            # This approach does NOT require the user to provide a forward edge
            # and a reverse edge between the same two nodes to indicate the
            # graph's undirected nature. However, it will work in that scenario
            # as well.

            # Discover and store all nodes (not already found) connected to
            # those found in the immediate previous iteration
            plpy.execute("DROP TABLE IF EXISTS {0}".format(toupdate))
            plpy.execute(insert_toupdate_table.format(**locals()))

            plpy.execute("DROP TABLE IF EXISTS {0}".format(message))
            plpy.execute(insert_message_loop.format(**locals()))

            plpy.execute(insert_qry_loop.format(**locals()))

            # Update distance value for next iteration
            curr_dist_val = curr_dist_val + 1

            # Count / find any nodes that are connected to those discovered and
            # stored in this iteration. This is used to check if the iterations
            # need to continue.
            vct = plpy.execute(count_qry.format(**locals()))[0]['count']

        # Filter out the infinite paths (disconnected pairs)
        plpy.execute(""" UPDATE {out_table} SET parent = {source_vertex}
                         WHERE {vertex_id} = {source_vertex}
                    """.format(**locals()))

        plpy.execute(""" DELETE FROM {0} WHERE parent IS NULL
            """.format(out_table))
        # Drop temp tables
        plpy.execute("DROP TABLE IF EXISTS {0},{1}".format(toupdate, message))

    return None

def graph_bfs_help(schema_madlib, message, **kwargs):
    """
    Help function for graph_bfs

    Args:
        @param schema_madlib
        @param message: string, Help message string
        @param kwargs

    Returns:
        String. Help/usage information
    """
    if not message:
        help_string = """
-----------------------------------------------------------------------
                            SUMMARY
-----------------------------------------------------------------------

Given a graph and a source vertex, the Breadth-first Search (BFS) algorithm
finds all nodes reachable from the source vertex.

For more details on function usage:
    SELECT {schema_madlib}.graph_bfs('usage')
            """
    elif message.lower() in ['usage', 'help', '?']:
        help_string = """
Given a graph and a source vertex, the Breadth-first Search (BFS) algorithm
finds all nodes reachable from the source vertex.

{graph_usage}

----------------------------------------------------------------------------
                            OUTPUT
----------------------------------------------------------------------------
The output of BFS ('out_table' above) contains a row for every vertex of that is
reachable from the source_vertex. In the presence of grouping columns, only those
edges are used for which there are no NULL values in any grouping column.
The output table will have the following columns (in addition to the
grouping columns):
  - vertex_id : The id for any node reachable from source_vertex in addition to
                the source_vertex. Will use the input parameter 'vertex_id' for
                column naming.
  - dist      : The distance in number of edges (or hops) from the source_vertex
                to where this vertex is located.
  - parent    : The parent of this vertex in BFS traversal of the graph from
                source_vertex. Will use 'parent' for column naming. For the
                case where vertex_id = source_vertex, the value for parent is NULL.
"""
    else:
        help_string = "No such option. Use {schema_madlib}.graph_bfs()"

    return help_string.format(schema_madlib=schema_madlib,
        graph_usage=get_graph_usage(schema_madlib, 'graph_bfs',
    """source_vertex INT,  -- The source vertex id for the algorithm to start.
    out_table     TEXT, -- Name of the table to store the result of BFS.
    max_distance  INT,  -- Maximum distance from source_vertex to search through in the graph.
    directed      INT,  -- If TRUE the graph will be treated as directed.
    grouping_cols TEXT  -- A comma-separated list of grouping columns."""))
# ---------------------------------------------------------------------