'use strict';

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

var _       = require('lodash');
var Promise = require('../../../promise');

// 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(runner, tableCompiler, pragma) {
  this.formatter     = new client.Formatter();
  this.tableCompiler = tableCompiler;
  this.pragma        = pragma;
  this.runner        = runner;
  this.tableName     = this.tableCompiler.tableNameRaw;
  this.alteredName   = _.uniqueId('_knex_temp_alter');
}

SQLite3_DDL.prototype.getColumn = Promise.method(function(column) {
  var currentCol = _.findWhere(this.pragma, {name: column});
  if (!currentCol) throw new Error('The column ' + column + ' is not in the ' + this.tableName + ' table');
  return currentCol;
});

SQLite3_DDL.prototype.getTableSql = function() {
  return this.runner.query({sql: 'SELECT name, sql FROM sqlite_master WHERE type="table" AND name="' + this.tableName + '"'});
};

SQLite3_DDL.prototype.renameTable = Promise.method(function() {
  return this.runner.query({sql: 'ALTER TABLE "' + this.tableName + '" RENAME TO "' + this.alteredName + '"'});
});

SQLite3_DDL.prototype.dropOriginal = function() {
  return this.runner.query({sql: 'DROP TABLE "' + this.tableName + '"'});
};

SQLite3_DDL.prototype.dropTempTable = function() {
  return this.runner.query({sql: 'DROP TABLE "' + this.alteredName + '"'});
};

SQLite3_DDL.prototype.copyData = function() {
  return this.runner.query({sql: 'SELECT * FROM "' + this.tableName + '"'})
    .bind(this)
    .then(this.insertChunked(20, this.alteredName));
};

SQLite3_DDL.prototype.reinsertData = function(iterator) {
  return function() {
    return this.runner.query({sql: 'SELECT * FROM "' + this.alteredName + '"'})
      .bind(this)
      .then(this.insertChunked(20, this.tableName, iterator));
  };
};

SQLite3_DDL.prototype.insertChunked = function(amount, target, iterator) {
  iterator = iterator || function(noop) { return noop; };
  return function(result) {
    var batch = [];
    var ddl = this;
    return Promise.reduce(result, function(memo, row) {
      memo++;
      batch.push(row);
      if (memo % 20 === 0 || memo === result.length) {
        return new client.QueryBuilder()
          .connection(ddl.runner.connection)
          .table(target)
          .insert(_.map(batch, iterator))
          .then(function() { batch = []; })
          .thenReturn(memo);
      }
      return memo;
    }, 0);
  };
};

SQLite3_DDL.prototype.createTempTable = function(createTable) {
  return function() {
    return this.runner.query({sql: createTable.sql.replace(this.tableName, this.alteredName)});
  };
};

SQLite3_DDL.prototype._doReplace = function (sql, from, to) {
  var matched = sql.match(/^CREATE TABLE (\S+) \((.*)\)/);
  
  var tableName = matched[1],
      defs = matched[2];
  
  if (!defs) { throw new Error('No column definitions in this statement!'); }

  var parens = 0, args = [ ], ptr = 0;
  for (var i = 0, x = defs.length; 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) {
    var split = item.split(' ');

    if (split[0] === from) {
      // column definition
      if (to) {
        split[0] = to;
        return split.join(' ');
      }
      return ''; // for deletions
    }
    
    // skip constraint name
    var 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(/\(.*\)/, function (columns) {
        return 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(/\(.*\)/, function (columns) {
          return columns.replace(from, to);
        });
      }
      return split.join(' references ');
    }
    
    return item;
  });
  return sql.replace(/\(.*\)/, function () {
    return '(' + args.join(', ') + ')';
  }).replace(/,\s*([,)])/, '$1');
};
// Boy, this is quite a method.
SQLite3_DDL.prototype.renameColumn = Promise.method(function(from, to) {
  var currentCol;
  return this.ensureTransaction()
    .bind(this)
    .then(function() {
      return this.getColumn(from);
    })
    .tap(function(col) { currentCol = col; })
    .then(this.getTableSql)
    .then(function(sql) {
      var a = this.formatter.wrap(from);
      var b = this.formatter.wrap(to);
      var createTable = sql[0];
      
      var 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.runner.query({sql: newSql });
      })
      .then(this.reinsertData(function(row) {
        row[to] = row[from];
        return _.omit(row, from);
      }))
      .then(this.dropTempTable);
    })
});

SQLite3_DDL.prototype.dropColumn = Promise.method(function(column) {
   var currentCol;
   return this.ensureTransaction()
    .bind(this)
    .then(function() {
      return this.getColumn(column);
    })
    .tap(function(col) { currentCol = col; })
    .then(this.getTableSql)
    .then(function(sql) {
      var createTable = sql[0];
      var a = this.formatter.wrap(column);
      
      var 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.runner.query({sql: newSql});
        })
        .then(this.reinsertData(function(row) {
          return _.omit(row, column);
        }))
        .then(this.dropTempTable);
    })
});

module.exports = SQLite3_DDL;