use std::rc::Rc;

use crate::schema::{BTreeTable, Column, Type};
use crate::translate::optimizer::optimize_select_plan;
use crate::translate::plan::{Operation, QueryDestination, Search, SelectPlan};
use crate::vdbe::builder::CursorType;
use crate::{
    bail_parse_error,
    schema::{Schema, Table},
    util::normalize_ident,
    vdbe::builder::{ProgramBuilder, ProgramBuilderOpts},
    SymbolTable,
};
use turso_sqlite3_parser::ast::{self, Expr, ResultColumn, SortOrder, Update};

use super::emitter::emit_program;
use super::optimizer::optimize_plan;
use super::plan::{
    ColumnUsedMask, IterationDirection, JoinedTable, Plan, ResultSetColumn, TableReferences,
    UpdatePlan,
};
use super::planner::bind_column_references;
use super::planner::{parse_limit, parse_where};
/*
* Update is simple. By default we scan the table, and for each row, we check the WHERE
* clause. If it evaluates to true, we build the new record with the updated value and insert.
*
* EXAMPLE:
*
sqlite> explain update t set a = 100 where b = 5;
addr  opcode         p1    p2    p3    p4             p5  comment
----  -------------  ----  ----  ----  -------------  --  -------------
0     Init           0     16    0                    0   Start at 16
1     Null           0     1     2                    0   r[1..2]=NULL
2     Noop           1     0     1                    0
3     OpenWrite      0     2     0     3              0   root=2 iDb=0; t
4     Rewind         0     15    0                    0
5       Column         0     1     6                    0   r[6]= cursor 0 column 1
6       Ne             7     14    6     BINARY-8       81  if r[6]!=r[7] goto 14
7       Rowid          0     2     0                    0   r[2]= rowid of 0
8       IsNull         2     15    0                    0   if r[2]==NULL goto 15
9       Integer        100   3     0                    0   r[3]=100
10      Column         0     1     4                    0   r[4]= cursor 0 column 1
11      Column         0     2     5                    0   r[5]= cursor 0 column 2
12      MakeRecord     3     3     1                    0   r[1]=mkrec(r[3..5])
13      Insert         0     1     2     t              7   intkey=r[2] data=r[1]
14    Next           0     5     0                    1
15    Halt           0     0     0                    0
16    Transaction    0     1     1     0              1   usesStmtJournal=0
17    Integer        5     7     0                    0   r[7]=5
18    Goto           0     1     0                    0
*/
pub fn translate_update(
    schema: &Schema,
    body: &mut Update,
    syms: &SymbolTable,
    mut program: ProgramBuilder,
) -> crate::Result<ProgramBuilder> {
    let mut plan = prepare_update_plan(&mut program, schema, body)?;
    optimize_plan(&mut plan, schema)?;
    // TODO: freestyling these numbers
    let opts = ProgramBuilderOpts {
        num_cursors: 1,
        approx_num_insns: 20,
        approx_num_labels: 4,
    };
    program.extend(&opts);
    emit_program(&mut program, plan, schema, syms, |_| {})?;
    Ok(program)
}

pub fn translate_update_with_after(
    schema: &Schema,
    body: &mut Update,
    syms: &SymbolTable,
    mut program: ProgramBuilder,
    after: impl FnOnce(&mut ProgramBuilder),
) -> crate::Result<ProgramBuilder> {
    let mut plan = prepare_update_plan(&mut program, schema, body)?;
    optimize_plan(&mut plan, schema)?;
    // TODO: freestyling these numbers
    let opts = ProgramBuilderOpts {
        num_cursors: 1,
        approx_num_insns: 20,
        approx_num_labels: 4,
    };
    program.extend(&opts);
    emit_program(&mut program, plan, schema, syms, after)?;
    Ok(program)
}

pub fn prepare_update_plan(
    program: &mut ProgramBuilder,
    schema: &Schema,
    body: &mut Update,
) -> crate::Result<Plan> {
    if body.with.is_some() {
        bail_parse_error!("WITH clause is not supported");
    }
    if body.or_conflict.is_some() {
        bail_parse_error!("ON CONFLICT clause is not supported");
    }
    let table_name = &body.tbl_name.name;
    if schema.table_has_indexes(&table_name.to_string()) && !schema.indexes_enabled() {
        // Let's disable altering a table with indices altogether instead of checking column by
        // column to be extra safe.
        bail_parse_error!(
            "UPDATE table disabled for table with indexes is disabled by default. Run with `--experimental-indexes` to enable this feature."
        );
    }
    let table = match schema.get_table(table_name.0.as_str()) {
        Some(table) => table,
        None => bail_parse_error!("Parse error: no such table: {}", table_name),
    };
    let iter_dir = body
        .order_by
        .as_ref()
        .and_then(|order_by| {
            order_by.first().and_then(|ob| {
                ob.order.map(|o| match o {
                    SortOrder::Asc => IterationDirection::Forwards,
                    SortOrder::Desc => IterationDirection::Backwards,
                })
            })
        })
        .unwrap_or(IterationDirection::Forwards);

    let joined_tables = vec![JoinedTable {
        table: match table.as_ref() {
            Table::Virtual(vtab) => Table::Virtual(vtab.clone()),
            Table::BTree(btree_table) => Table::BTree(btree_table.clone()),
            _ => unreachable!(),
        },
        identifier: table_name.0.clone(),
        internal_id: program.table_reference_counter.next(),
        op: Operation::Scan {
            iter_dir,
            index: None,
        },
        join_info: None,
        col_used_mask: ColumnUsedMask::default(),
    }];
    let mut table_references = TableReferences::new(joined_tables, vec![]);
    let set_clauses = body
        .sets
        .iter_mut()
        .map(|set| {
            let ident = normalize_ident(set.col_names[0].0.as_str());
            let col_index = table
                .columns()
                .iter()
                .enumerate()
                .find_map(|(i, col)| {
                    col.name
                        .as_ref()
                        .filter(|name| name.eq_ignore_ascii_case(&ident))
                        .map(|_| i)
                })
                .ok_or_else(|| {
                    crate::LimboError::ParseError(format!(
                        "column '{}' not found in table '{}'",
                        ident, table_name.0
                    ))
                })?;

            let _ = bind_column_references(&mut set.expr, &mut table_references, None);
            Ok((col_index, set.expr.clone()))
        })
        .collect::<Result<Vec<(usize, Expr)>, crate::LimboError>>()?;

    let mut result_columns = vec![];
    if let Some(returning) = &mut body.returning {
        for rc in returning.iter_mut() {
            if let ResultColumn::Expr(expr, alias) = rc {
                bind_column_references(expr, &mut table_references, None)?;
                result_columns.push(ResultSetColumn {
                    expr: expr.clone(),
                    alias: alias.as_ref().and_then(|a| {
                        if let ast::As::As(name) = a {
                            Some(name.to_string())
                        } else {
                            None
                        }
                    }),
                    contains_aggregates: false,
                });
            } else {
                bail_parse_error!("Only expressions are allowed in RETURNING clause");
            }
        }
    }
    let order_by = body.order_by.as_ref().map(|order| {
        order
            .iter()
            .map(|o| (o.expr.clone(), o.order.unwrap_or(SortOrder::Asc)))
            .collect()
    });

    // Sqlite determines we should create an ephemeral table if we do not have a FROM clause
    // Difficult to say what items from the plan can be checked for this so currently just checking if a RowId Alias is referenced
    // https://github.com/sqlite/sqlite/blob/master/src/update.c#L395
    // https://github.com/sqlite/sqlite/blob/master/src/update.c#L670
    let columns = table.columns();

    let rowid_alias_used = set_clauses.iter().fold(false, |accum, (idx, _)| {
        accum || columns[*idx].is_rowid_alias
    });

    let (ephemeral_plan, mut where_clause) = if rowid_alias_used {
        let mut where_clause = vec![];
        let internal_id = program.table_reference_counter.next();

        let joined_tables = vec![JoinedTable {
            table: match table.as_ref() {
                Table::Virtual(vtab) => Table::Virtual(vtab.clone()),
                Table::BTree(btree_table) => Table::BTree(btree_table.clone()),
                _ => unreachable!(),
            },
            identifier: table_name.0.clone(),
            internal_id,
            op: Operation::Scan {
                iter_dir,
                index: None,
            },
            join_info: None,
            col_used_mask: ColumnUsedMask::default(),
        }];
        let mut table_references = TableReferences::new(joined_tables, vec![]);

        // Parse the WHERE clause
        parse_where(
            body.where_clause.as_ref().map(|w| *w.clone()),
            &mut table_references,
            Some(&result_columns),
            &mut where_clause,
        )?;

        let table = Rc::new(BTreeTable {
            root_page: 0, // Not relevant for ephemeral table definition
            name: "ephemeral_scratch".to_string(),
            has_rowid: true,
            primary_key_columns: vec![],
            columns: vec![Column {
                name: Some("rowid".to_string()),
                ty: Type::Integer,
                ty_str: "INTEGER".to_string(),
                primary_key: true,
                is_rowid_alias: false,
                notnull: true,
                default: None,
                unique: false,
                collation: None,
                hidden: false,
            }],
            is_strict: false,
            unique_sets: None,
        });

        let temp_cursor_id = program.alloc_cursor_id(CursorType::BTreeTable(table.clone()));

        let mut ephemeral_plan = SelectPlan {
            table_references,
            result_columns: vec![ResultSetColumn {
                expr: Expr::RowId {
                    database: None,
                    table: internal_id,
                },
                alias: None,
                contains_aggregates: false,
            }],
            where_clause,       // original WHERE terms from the UPDATE clause
            group_by: None,     // N/A
            order_by: None,     // N/A
            aggregates: vec![], // N/A
            limit: None,        // N/A
            query_destination: QueryDestination::EphemeralTable {
                cursor_id: temp_cursor_id,
                table,
            },
            join_order: vec![],
            offset: None,
            contains_constant_false_condition: false,
            distinctness: super::plan::Distinctness::NonDistinct,
            values: vec![],
        };

        optimize_select_plan(&mut ephemeral_plan, schema)?;
        let table = ephemeral_plan
            .table_references
            .joined_tables()
            .first()
            .unwrap();
        // We do not need to emit an ephemeral plan if we are not going to loop over the table values
        if matches!(table.op, Operation::Search(Search::RowidEq { .. })) {
            (None, vec![])
        } else {
            (Some(ephemeral_plan), vec![])
        }
    } else {
        (None, vec![])
    };

    if ephemeral_plan.is_none() {
        // Parse the WHERE clause
        parse_where(
            body.where_clause.as_ref().map(|w| *w.clone()),
            &mut table_references,
            Some(&result_columns),
            &mut where_clause,
        )?;
    };

    // Parse the LIMIT/OFFSET clause
    let (limit, offset) = body
        .limit
        .as_ref()
        .map(|l| parse_limit(l))
        .unwrap_or(Ok((None, None)))?;

    // Check what indexes will need to be updated by checking set_clauses and see
    // if a column is contained in an index.
    let indexes = schema.get_indices(&table_name.0);
    let indexes_to_update = indexes
        .iter()
        .filter(|index| {
            index.columns.iter().any(|index_column| {
                set_clauses
                    .iter()
                    .any(|(set_index_column, _)| index_column.pos_in_table == *set_index_column)
            })
        })
        .cloned()
        .collect();

    Ok(Plan::Update(UpdatePlan {
        table_references,
        set_clauses,
        where_clause,
        returning: Some(result_columns),
        order_by,
        limit,
        offset,
        contains_constant_false_condition: false,
        indexes_to_update,
        ephemeral_plan,
    }))
}