import re
import sqlparse
from collections import namedtuple
from sqlparse.sql import Comparison, Identifier, Where
from .parseutils.utils import last_word, find_prev_keyword,\
    parse_partial_identifier
from .parseutils.tables import extract_tables
from .parseutils.ctes import isolate_query_ctes


Database = namedtuple("Database", [])
Schema = namedtuple("Schema", ["quoted"])
Schema.__new__.__defaults__ = (False,)
# FromClauseItem is a table/view/function used in the FROM clause
# `table_refs` contains the list of tables/... already in the statement,
# used to ensure that the alias we suggest is unique
FromClauseItem = namedtuple("FromClauseItem", "schema table_refs local_tables")
Table = namedtuple("Table", ["schema", "table_refs", "local_tables"])
TableFormat = namedtuple("TableFormat", [])
View = namedtuple("View", ["schema", "table_refs"])
# JoinConditions are suggested after ON, e.g. 'foo.barid = bar.barid'
JoinCondition = namedtuple("JoinCondition", ["table_refs", "parent"])
# Joins are suggested after JOIN, e.g. 'foo ON foo.barid = bar.barid'
Join = namedtuple("Join", ["table_refs", "schema"])

Function = namedtuple("Function", ["schema", "table_refs", "usage"])
# For convenience, don't require the `usage` argument in Function constructor
Function.__new__.__defaults__ = (None, tuple(), None)
Table.__new__.__defaults__ = (None, tuple(), tuple())
View.__new__.__defaults__ = (None, tuple())
FromClauseItem.__new__.__defaults__ = (None, tuple(), tuple())

Column = namedtuple(
    "Column",
    ["table_refs", "require_last_table", "local_tables", "qualifiable",
     "context"],
)
Column.__new__.__defaults__ = (None, None, tuple(), False, None)

Keyword = namedtuple("Keyword", ["last_token"])
Keyword.__new__.__defaults__ = (None,)
NamedQuery = namedtuple("NamedQuery", [])
Datatype = namedtuple("Datatype", ["schema"])
Alias = namedtuple("Alias", ["aliases"])

Path = namedtuple("Path", [])


class SqlStatement:
    def __init__(self, full_text, text_before_cursor):
        self.identifier = None
        self.word_before_cursor = word_before_cursor = last_word(
            text_before_cursor, include="many_punctuations"
        )
        full_text = _strip_named_query(full_text)
        text_before_cursor = _strip_named_query(text_before_cursor)

        full_text, text_before_cursor, self.local_tables = isolate_query_ctes(
            full_text, text_before_cursor
        )

        self.text_before_cursor_including_last_word = text_before_cursor

        # If we've partially typed a word then word_before_cursor won't be an
        # empty string. In that case we want to remove the partially typed
        # string before sending it to the sqlparser. Otherwise the last token
        # will always be the partially typed string which renders the smart
        # completion useless because it will always return the list of
        # keywords as completion.
        if self.word_before_cursor:
            if word_before_cursor[-1] == "(" or word_before_cursor[0] == "\\":
                parsed = sqlparse.parse(text_before_cursor)
            else:
                text_before_cursor = \
                    text_before_cursor[: -len(word_before_cursor)]
                parsed = sqlparse.parse(text_before_cursor)
                self.identifier = parse_partial_identifier(word_before_cursor)
        else:
            parsed = sqlparse.parse(text_before_cursor)

        full_text, text_before_cursor, parsed = _split_multiple_statements(
            full_text, text_before_cursor, parsed
        )

        self.full_text = full_text
        self.text_before_cursor = text_before_cursor
        self.parsed = parsed

        self.last_token = parsed and \
            parsed.token_prev(len(parsed.tokens))[1] or ""

    def is_insert(self):
        return self.parsed.token_first().value.lower() == "insert"

    def get_tables(self, scope="full"):
        """Gets the tables available in the statement.
        param `scope:` possible values: 'full', 'insert', 'before'
        If 'insert', only the first table is returned.
        If 'before', only tables before the cursor are returned.
        If not 'insert' and the stmt is an insert, the first table is skipped.
        """
        tables = extract_tables(
            self.full_text if scope == "full" else self.text_before_cursor
        )
        if scope == "insert":
            tables = tables[:1]
        elif self.is_insert():
            tables = tables[1:]
        return tables

    def get_previous_token(self, token):
        return self.parsed.token_prev(self.parsed.token_index(token))[1]

    def get_identifier_schema(self):
        schema = \
            (self.identifier and self.identifier.get_parent_name()) or None
        # If schema name is unquoted, lower-case it
        if schema and self.identifier.value[0] != '"':
            schema = schema.lower()

        return schema

    def reduce_to_prev_keyword(self, n_skip=0):
        prev_keyword, self.text_before_cursor = find_prev_keyword(
            self.text_before_cursor, n_skip=n_skip
        )
        return prev_keyword


def suggest_type(full_text, text_before_cursor):
    """Takes the full_text that is typed so far and also the text before the
    cursor to suggest completion type and scope.

    Returns a tuple with a type of entity ('table', 'column' etc) and a scope.
    A scope for a column category will be a list of tables.
    """

    if full_text.startswith("\\i "):
        return (Path(),)

    # This is a temporary hack; the exception handling
    # here should be removed once sqlparse has been fixed
    try:
        stmt = SqlStatement(full_text, text_before_cursor)
    except (TypeError, AttributeError):
        return []

    return suggest_based_on_last_token(stmt.last_token, stmt)


named_query_regex = re.compile(r"^\s*\\ns\s+[A-z0-9\-]+\s+")


def _strip_named_query(txt):
    """
    This will strip "save named query" command in the beginning of the line:
    '\ns zzz SELECT * FROM abc'   -> 'SELECT * FROM abc'
    '  \ns zzz SELECT * FROM abc' -> 'SELECT * FROM abc'
    """

    if named_query_regex.match(txt):
        txt = named_query_regex.sub("", txt)
    return txt


function_body_pattern = re.compile(r"(\$[^$]*\$)([\s\S]*?)\1", re.M)


def _find_function_body(text):
    split = function_body_pattern.search(text)
    return (split.start(2), split.end(2)) if split else (None, None)


def _statement_from_function(full_text, text_before_cursor, statement):
    current_pos = len(text_before_cursor)
    body_start, body_end = _find_function_body(full_text)
    if body_start is None:
        return full_text, text_before_cursor, statement
    if not body_start <= current_pos < body_end:
        return full_text, text_before_cursor, statement
    full_text = full_text[body_start:body_end]
    text_before_cursor = text_before_cursor[body_start:]
    parsed = sqlparse.parse(text_before_cursor)
    return _split_multiple_statements(full_text, text_before_cursor, parsed)


def _split_multiple_statements(full_text, text_before_cursor, parsed):
    if len(parsed) > 1:
        # Multiple statements being edited -- isolate the current one by
        # cumulatively summing statement lengths to find the one that bounds
        # the current position
        current_pos = len(text_before_cursor)
        stmt_start, stmt_end = 0, 0

        for statement in parsed:
            stmt_len = len(str(statement))
            stmt_start, stmt_end = stmt_end, stmt_end + stmt_len

            if stmt_end >= current_pos:
                text_before_cursor = full_text[stmt_start:current_pos]
                full_text = full_text[stmt_start:]
                break

    elif parsed:
        # A single statement
        statement = parsed[0]
    else:
        # The empty string
        return full_text, text_before_cursor, None

    token2 = None
    if statement.get_type() in ("CREATE", "CREATE OR REPLACE"):
        token1 = statement.token_first()
        if token1:
            token1_idx = statement.token_index(token1)
            token2 = statement.token_next(token1_idx)[1]
    if token2 and token2.value.upper() == "FUNCTION":
        full_text, text_before_cursor, statement = _statement_from_function(
            full_text, text_before_cursor, statement
        )
    return full_text, text_before_cursor, statement


def suggest_based_on_last_token(token, stmt):

    if isinstance(token, str):
        token_v = token.lower()
    elif isinstance(token, Comparison):
        # If 'token' is a Comparison type such as
        # 'select * FROM abc a JOIN def d ON a.id = d.'. Then calling
        # token.value on the comparison type will only return the lhs of the
        # comparison. In this case a.id. So we need to do token.tokens to get
        # both sides of the comparison and pick the last token out of that
        # list.
        token_v = token.tokens[-1].value.lower()
    elif isinstance(token, Where):
        # sqlparse groups all tokens from the where clause into a single token
        # list. This means that token.value may be something like
        # 'where foo > 5 and '. We need to look "inside" token.tokens to handle
        # suggestions in complicated where clauses correctly
        prev_keyword = stmt.reduce_to_prev_keyword()
        return suggest_based_on_last_token(prev_keyword, stmt)
    elif isinstance(token, Identifier):
        # If the previous token is an identifier, we can suggest datatypes if
        # we're in a parenthesized column/field list, e.g.:
        #       CREATE TABLE foo (Identifier <CURSOR>
        #       CREATE FUNCTION foo (Identifier <CURSOR>
        # If we're not in a parenthesized list, the most likely scenario is the
        # user is about to specify an alias, e.g.:
        #       SELECT Identifier <CURSOR>
        #       SELECT foo FROM Identifier <CURSOR>
        prev_keyword, _ = find_prev_keyword(stmt.text_before_cursor)
        if prev_keyword and prev_keyword.value == "(":
            # Suggest datatypes
            return suggest_based_on_last_token("type", stmt)
        else:
            return (Keyword(),)
    else:
        token_v = token.value.lower()

    if not token:
        return (Keyword(),)
    elif token_v.endswith("("):
        p = sqlparse.parse(stmt.text_before_cursor)[0]

        if p.tokens and isinstance(p.tokens[-1], Where):
            # Four possibilities:
            #  1 - Parenthesized clause like "WHERE foo AND ("
            #        Suggest columns/functions
            #  2 - Function call like "WHERE foo("
            #        Suggest columns/functions
            #  3 - Subquery expression like "WHERE EXISTS ("
            #        Suggest keywords, in order to do a subquery
            #  4 - Subquery OR array comparison like "WHERE foo = ANY("
            #        Suggest columns/functions AND keywords. (If we wanted to
            #       be really fancy, we could suggest only array-typed columns)

            column_suggestions = suggest_based_on_last_token("where", stmt)

            # Check for a subquery expression (cases 3 & 4)
            where = p.tokens[-1]
            prev_tok = where.token_prev(len(where.tokens) - 1)[1]

            if isinstance(prev_tok, Comparison):
                # e.g. "SELECT foo FROM bar WHERE foo = ANY("
                prev_tok = prev_tok.tokens[-1]

            prev_tok = prev_tok.value.lower()
            if prev_tok == "exists":
                return (Keyword(),)
            else:
                return column_suggestions

        # Get the token before the parens
        prev_tok = p.token_prev(len(p.tokens) - 1)[1]

        if (
            prev_tok and prev_tok.value and
            prev_tok.value.lower().split(" ")[-1] == "using"
        ):
            # tbl1 INNER JOIN tbl2 USING (col1, col2)
            tables = stmt.get_tables("before")

            # suggest columns that are present in more than one table
            return (
                Column(
                    table_refs=tables,
                    require_last_table=True,
                    local_tables=stmt.local_tables,
                ),
            )

        elif p.token_first().value.lower() == "select":
            # If the lparen is preceeded by a space chances are we're about to
            # do a sub-select.
            if last_word(stmt.text_before_cursor,
                         "all_punctuations").startswith("("):
                return (Keyword(),)
        prev_prev_tok = prev_tok and p.token_prev(p.token_index(prev_tok))[1]
        if prev_prev_tok and prev_prev_tok.normalized == "INTO":
            return (Column(table_refs=stmt.get_tables("insert"),
                           context="insert"),)
        # We're probably in a function argument list
        return _suggest_expression(token_v, stmt)
    elif token_v == "set":
        return (Column(table_refs=stmt.get_tables(),
                       local_tables=stmt.local_tables),)
    elif token_v in ("select", "where", "having", "order by", "distinct"):
        return _suggest_expression(token_v, stmt)
    elif token_v == "as":
        # Don't suggest anything for aliases
        return ()
    elif (token_v.endswith("join") and token.is_keyword) or (
        token_v in ("copy", "from", "update", "into", "describe", "truncate")
    ):

        schema = stmt.get_identifier_schema()
        tables = extract_tables(stmt.text_before_cursor)
        is_join = token_v.endswith("join") and token.is_keyword

        # Suggest tables from either the currently-selected schema or the
        # public schema if no schema has been specified
        suggest = []

        if not schema:
            # Suggest schemas
            suggest.insert(0, Schema())

        if token_v == "from" or is_join:
            suggest.append(
                FromClauseItem(
                    schema=schema, table_refs=tables,
                    local_tables=stmt.local_tables
                )
            )
        elif token_v == "truncate":
            suggest.append(Table(schema))
        else:
            suggest.extend((Table(schema), View(schema)))

        if is_join and _allow_join(stmt.parsed):
            tables = stmt.get_tables("before")
            suggest.append(Join(table_refs=tables, schema=schema))

        return tuple(suggest)

    elif token_v == "function":
        schema = stmt.get_identifier_schema()

        # stmt.get_previous_token will fail for e.g.
        # `SELECT 1 FROM functions WHERE function:`
        try:
            prev = stmt.get_previous_token(token).value.lower()
            if prev in ("drop", "alter", "create", "create or replace"):

                # Suggest functions from either the currently-selected schema
                # or the public schema if no schema has been specified
                suggest = []

                if not schema:
                    # Suggest schemas
                    suggest.insert(0, Schema())

                suggest.append(Function(schema=schema, usage="signature"))
                return tuple(suggest)

        except ValueError:
            pass
        return tuple()

    elif token_v in ("table", "view"):
        # E.g. 'ALTER TABLE <tablname>'
        rel_type = \
            {"table": Table, "view": View, "function": Function}[token_v]
        schema = stmt.get_identifier_schema()
        if schema:
            return (rel_type(schema=schema),)
        else:
            return (Schema(), rel_type(schema=schema))

    elif token_v == "column":
        # E.g. 'ALTER TABLE foo ALTER COLUMN bar
        return (Column(table_refs=stmt.get_tables()),)

    elif token_v == "on":
        tables = stmt.get_tables("before")
        parent = \
            (stmt.identifier and stmt.identifier.get_parent_name()) or None
        if parent:
            # "ON parent.<suggestion>"
            # parent can be either a schema name or table alias
            filteredtables = tuple(t for t in tables if identifies(parent, t))
            sugs = [
                Column(table_refs=filteredtables,
                       local_tables=stmt.local_tables),
                Table(schema=parent),
                View(schema=parent),
                Function(schema=parent),
            ]
            if filteredtables and _allow_join_condition(stmt.parsed):
                sugs.append(JoinCondition(table_refs=tables,
                                          parent=filteredtables[-1]))
            return tuple(sugs)
        else:
            # ON <suggestion>
            # Use table alias if there is one, otherwise the table name
            aliases = tuple(t.ref for t in tables)
            if _allow_join_condition(stmt.parsed):
                return (
                    Alias(aliases=aliases),
                    JoinCondition(table_refs=tables, parent=None),
                )
            else:
                return (Alias(aliases=aliases),)

    elif token_v in ("c", "use", "database", "template"):
        # "\c <db", "use <db>", "DROP DATABASE <db>",
        # "CREATE DATABASE <newdb> WITH TEMPLATE <db>"
        return (Database(),)
    elif token_v == "schema":
        # DROP SCHEMA schema_name, SET SCHEMA schema name
        prev_keyword = stmt.reduce_to_prev_keyword(n_skip=2)
        quoted = prev_keyword and prev_keyword.value.lower() == "set"
        return (Schema(quoted),)
    elif token_v.endswith(",") or token_v in ("=", "and", "or"):
        prev_keyword = stmt.reduce_to_prev_keyword()
        if prev_keyword:
            return suggest_based_on_last_token(prev_keyword, stmt)
        else:
            return ()
    elif token_v in ("type", "::"):
        #   ALTER TABLE foo SET DATA TYPE bar
        #   SELECT foo::bar
        # Note that tables are a form of composite type in postgresql, so
        # they're suggested here as well
        schema = stmt.get_identifier_schema()
        suggestions = [Datatype(schema=schema), Table(schema=schema)]
        if not schema:
            suggestions.append(Schema())
        return tuple(suggestions)
    elif token_v in {"alter", "create", "drop"}:
        return (Keyword(token_v.upper()),)
    elif token.is_keyword:
        # token is a keyword we haven't implemented any special handling for
        # go backwards in the query until we find one we do recognize
        prev_keyword = stmt.reduce_to_prev_keyword(n_skip=1)
        if prev_keyword:
            return suggest_based_on_last_token(prev_keyword, stmt)
        else:
            return (Keyword(token_v.upper()),)
    else:
        return (Keyword(),)


def _suggest_expression(token_v, stmt):
    """
    Return suggestions for an expression, taking account of any partially-typed
    identifier's parent, which may be a table alias or schema name.
    """
    parent = stmt.identifier.get_parent_name() if stmt.identifier else []
    tables = stmt.get_tables()

    if parent:
        tables = tuple(t for t in tables if identifies(parent, t))
        return (
            Column(table_refs=tables, local_tables=stmt.local_tables),
            Table(schema=parent),
            View(schema=parent),
            Function(schema=parent),
        )

    return (
        Column(table_refs=tables, local_tables=stmt.local_tables,
               qualifiable=True),
        Function(schema=None),
        Keyword(token_v.upper()),
    )


def identifies(id, ref):
    """Returns true if string `id` matches TableReference `ref`"""

    return (
        id == ref.alias or id == ref.name or
        (ref.schema and (id == ref.schema + "." + ref.name))
    )


def _allow_join_condition(statement):
    """
    Tests if a join condition should be suggested

    We need this to avoid bad suggestions when entering e.g.
        select * from tbl1 a join tbl2 b on a.id = <cursor>
    So check that the preceding token is a ON, AND, or OR keyword, instead of
    e.g. an equals sign.

    :param statement: an sqlparse.sql.Statement
    :return: boolean
    """

    if not statement or not statement.tokens:
        return False

    last_tok = statement.token_prev(len(statement.tokens))[1]
    return last_tok.value.lower() in ("on", "and", "or")


def _allow_join(statement):
    """
    Tests if a join should be suggested

    We need this to avoid bad suggestions when entering e.g.
        select * from tbl1 a join tbl2 b <cursor>
    So check that the preceding token is a JOIN keyword

    :param statement: an sqlparse.sql.Statement
    :return: boolean
    """

    if not statement or not statement.tokens:
        return False

    last_tok = statement.token_prev(len(statement.tokens))[1]
    return last_tok.value.lower().endswith("join") and \
        last_tok.value.lower() not in ("cross join", "natural join",)
