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use std::collections::{HashMap};


use anyhow::Result;
use crate::query::AlterTable;

use crate::query::AlterAction;
use crate::query::CreateIndex;
use crate::query::CreateTable;
use crate::schema::{Schema};
use crate::{Dialect, ToSql};

#[derive(Debug, Clone, Default)]
pub struct MigrationOptions {
    pub debug: bool,
}


pub fn migrate(current: Schema, desired: Schema, _options: &MigrationOptions) -> Result<Migration> {
    let current_tables = current.tables.iter().map(|t| (&t.name, t)).collect::<HashMap<_, _>>();
    let desired_tables = desired.tables.iter().map(|t| (&t.name, t)).collect::<HashMap<_, _>>();

    let mut debug_results = vec![];
    let mut statements = Vec::new();
    // new tables
    for (_name, table) in desired_tables.iter().filter(|(name, _)| !current_tables.contains_key(*name)) {
        let statement = Statement::CreateTable(CreateTable::from_table(table));
        statements.push(statement);
    }

    // alter existing tables
    for (name, desired_table) in desired_tables.iter().filter(|(name, _)| current_tables.contains_key(*name)) {
        let current_table = current_tables[name];
        let current_columns = current_table.columns.iter().map(|c| (&c.name, c)).collect::<HashMap<_, _>>();
        // add columns
        let mut actions = vec![];
        for desired_column in desired_table.columns.iter() {
            if let Some(current) = current_columns.get(&desired_column.name) {
                if current.nullable != desired_column.nullable {
                    actions.push(AlterAction::set_nullable(desired_column.name.clone(), desired_column.nullable));
                }
                if current.typ != desired_column.typ {
                    actions.push(AlterAction::set_type(desired_column.name.clone(), desired_column.typ.clone()));
                };
            } else {
                actions.push(AlterAction::AddColumn {
                    column: desired_column.clone(),
                });
            }
        }
        if actions.is_empty() {
            debug_results.push(DebugResults::TablesIdentical(name.to_string()));
        } else {
            statements.push(Statement::AlterTable(AlterTable {
                schema: desired_table.schema.clone(),
                name: desired_table.name.clone(),
                actions,
            }));
        }
    }

    Ok(Migration {
        statements,
        debug_results,
    })
}

#[derive(Debug)]
pub struct Migration {
    pub statements: Vec<Statement>,
    pub debug_results: Vec<DebugResults>,
}

impl Migration {
    pub fn is_empty(&self) -> bool {
        self.statements.is_empty()
    }

    pub fn set_schema(&mut self, schema_name: &str) {
        for statement in &mut self.statements {
            statement.set_schema(schema_name);
        }
    }
}

#[derive(Debug)]
pub enum Statement {
    CreateTable(CreateTable),
    CreateIndex(CreateIndex),
    AlterTable(AlterTable),
}

impl Statement {
    pub fn set_schema(&mut self, schema_name: &str) {
        match self {
            Statement::CreateTable(ref mut create_table) => {
                create_table.schema = Some(schema_name.to_string());
            }
            Statement::AlterTable(ref mut alter_table) => {
                alter_table.schema = Some(schema_name.to_string());
            }
            Statement::CreateIndex(ref mut create_index) => {
                create_index.schema = Some(schema_name.to_string());
            }
        }
    }
}

impl ToSql for Statement {
    fn write_sql(&self, buf: &mut String, dialect: Dialect) {
        use Statement::*;
        match self {
            CreateTable(c) => c.write_sql(buf, dialect),
            CreateIndex(c) => c.write_sql(buf, dialect),
            AlterTable(a) => a.write_sql(buf, dialect),
        }
    }
}

#[derive(Debug)]
pub enum DebugResults {
    TablesIdentical(String)
}