// SQLite3_DDL
//
// All of the SQLite3 specific DDL helpers for renaming/dropping
// columns and changing datatypes.
// -------

import Promise from 'bluebird';
import { assign, uniqueId, find, identity, map, omit } from 'lodash'

// So altering the schema in SQLite3 is a major pain.
// We have our own object to deal with the renaming and altering the types
// for sqlite3 things.
function SQLite3_DDL(client, tableCompiler, pragma, connection) {
  this.client = client
  this.tableCompiler = tableCompiler;
  this.pragma = pragma;
  this.tableName = this.tableCompiler.tableNameRaw;
  this.alteredName = uniqueId('_knex_temp_alter');
  this.connection = connection
}

assign(SQLite3_DDL.prototype, {

  getColumn: Promise.method(function(column) {
    const currentCol = find(this.pragma, {name: column});
    if (!currentCol) throw new Error(`The column ${column} is not in the ${this.tableName} table`);
    return currentCol;
  }),

  getTableSql() {
    return this.trx.raw(
      `SELECT name, sql FROM sqlite_master WHERE type="table" AND name="${this.tableName}"`
    );
  },

  renameTable: Promise.method(function() {
    return this.trx.raw(`ALTER TABLE "${this.tableName}" RENAME TO "${this.alteredName}"`);
  }),

  dropOriginal() {
    return this.trx.raw(`DROP TABLE "${this.tableName}"`);
  },

  dropTempTable() {
    return this.trx.raw(`DROP TABLE "${this.alteredName}"`);
  },

  copyData() {
    return this.trx.raw(`SELECT * FROM "${this.tableName}"`)
      .bind(this)
      .then(this.insertChunked(20, this.alteredName));
  },

  reinsertData(iterator) {
    return function() {
      return this.trx.raw(`SELECT * FROM "${this.alteredName}"`)
        .bind(this)
        .then(this.insertChunked(20, this.tableName, iterator));
    };
  },

  insertChunked(amount, target, iterator) {
    iterator = iterator || identity;
    return function(result) {
      let batch = [];
      const ddl = this;
      return Promise.reduce(result, function(memo, row) {
        memo++;
        batch.push(row);
        if (memo % 20 === 0 || memo === result.length) {
          return ddl.trx.queryBuilder()
            .table(target)
            .insert(map(batch, iterator))
            .then(function() { batch = []; })
            .thenReturn(memo);
        }
        return memo;
      }, 0);
    };
  },

  createTempTable(createTable) {
    return function() {
      return this.trx.raw(createTable.sql.replace(this.tableName, this.alteredName));
    };
  },

  _doReplace (sql, from, to) {
    const matched = sql.match(/^CREATE TABLE (\S+) \((.*)\)/);

    const tableName = matched[1];
    const defs = matched[2];

    if (!defs) { throw new Error('No column definitions in this statement!'); }

    let parens = 0, args = [ ], ptr = 0;
    let i = 0;
    const x = defs.length;
    for (i = 0; i < x; i++) {
      switch (defs[i]) {
        case '(':
          parens++;
          break;
        case ')':
          parens--;
          break;
        case ',':
          if (parens === 0) {
            args.push(defs.slice(ptr, i));
            ptr = i + 1;
          }
          break;
        case ' ':
          if (ptr === i) {
            ptr = i + 1;
          }
          break;
      }
    }
    args.push(defs.slice(ptr, i));

    args = args.map(function (item) {
      let split = item.split(' ');

      if (split[0] === from) {
        // column definition
        if (to) {
          split[0] = to;
          return split.join(' ');
        }
        return ''; // for deletions
      }

      // skip constraint name
      const idx = (/constraint/i.test(split[0]) ? 2 : 0);

      // primary key and unique constraints have one or more
      // columns from this table listed between (); replace
      // one if it matches
      if (/primary|unique/i.test(split[idx])) {
        return item.replace(/\(.*\)/, columns => columns.replace(from, to));
      }

      // foreign keys have one or more columns from this table
      // listed between (); replace one if it matches
      // foreign keys also have a 'references' clause
      // which may reference THIS table; if it does, replace
      // column references in that too!
      if (/foreign/.test(split[idx])) {
        split = item.split(/ references /i);
        // the quoted column names save us from having to do anything
        // other than a straight replace here
        split[0] = split[0].replace(from, to);

        if (split[1].slice(0, tableName.length) === tableName) {
          split[1] = split[1].replace(/\(.*\)/, columns => columns.replace(from, to));
        }
        return split.join(' references ');
      }

      return item;
    });
    return sql.replace(/\(.*\)/, () => `(${args.join(', ')})`).replace(/,\s*([,)])/, '$1');
  },

  // Boy, this is quite a method.
  renameColumn: Promise.method(function(from, to) {
    return this.client.transaction(trx => {
      this.trx = trx
      return this.getColumn(from)
        .bind(this)
        .then(this.getTableSql)
        .then(function(sql) {
          const a = this.client.wrapIdentifier(from);
          const b = this.client.wrapIdentifier(to);
          const createTable = sql[0];
          const newSql = this._doReplace(createTable.sql, a, b);
          if (sql === newSql) {
            throw new Error('Unable to find the column to change');
          }
          return Promise.bind(this)
            .then(this.createTempTable(createTable))
            .then(this.copyData)
            .then(this.dropOriginal)
            .then(function() {
              return this.trx.raw(newSql);
            })
            .then(this.reinsertData(function(row) {
              row[to] = row[from];
              return omit(row, from);
            }))
            .then(this.dropTempTable)
        })
    }, {connection: this.connection})
  }),

  dropColumn: Promise.method(function(column) {
    return this.client.transaction(trx => {
      this.trx = trx
      return this.getColumn(column)
      .bind(this)
      .then(this.getTableSql)
      .then(function(sql) {
        const createTable = sql[0];
        const a = this.client.wrapIdentifier(column);
        const newSql = this._doReplace(createTable.sql, a, '');
        if (sql === newSql) {
          throw new Error('Unable to find the column to change');
        }
        return Promise.bind(this)
          .then(this.createTempTable(createTable))
          .then(this.copyData)
          .then(this.dropOriginal)
          .then(function() {
            return this.trx.raw(newSql);
          })
          .then(this.reinsertData(row => omit(row, column)))
          .then(this.dropTempTable);
      })
    }, {connection: this.connection})
  })

})


export default SQLite3_DDL;