--------------------------------------------------------------------------------
-- Title:               Finder.lua
-- Description:         Like a square peg in a round hole
-- Author:              Raphaël Szwarc http://alt.textdrive.com/lua/
-- Creation Date:       January 30, 2007
-- Legal:               Copyright (C) 2007 Raphaël Szwarc
--                      Under the terms of the MIT License
--                      http://www.opensource.org/licenses/mit-license.html
--------------------------------------------------------------------------------

-- import dependencies
local Template = require( 'Template' )

local io = require( 'io' )
local string = require( 'string' )

local assert = assert
local error = error
local getmetatable = getmetatable
local ipairs = ipairs
local loadstring = loadstring
local pairs = pairs
local pcall = pcall
local require = require
local setmetatable = setmetatable
local tonumber = tonumber
local tostring = tostring
local type = type

--------------------------------------------------------------------------------
-- Finder
--------------------------------------------------------------------------------

module( 'Finder' )
_VERSION = '1.0'

local self = setmetatable( _M, {} )
local meta = getmetatable( self )

--------------------------------------------------------------------------------
-- DDL
--------------------------------------------------------------------------------

local function Path( anExtension )
    return ( '%s%s.%s' ):format( require( 'Bundle' )(), self._NAME, anExtension )
end

local function Load( anExtension )
    local aPath = Path( anExtension )
    local aFile = assert( io.open( aPath, 'rb' ) )
    local aContent = assert( aFile:read( '*a' ) )
    local aContent = ( 'return { %s }' ):format( aContent )
    local aChunk = assert( loadstring( aContent ) )
    local aStatement = assert( aChunk() )
    
    aFile:close()
    
    return aStatement
end

local DDL = Load( 'ddl' )
local DML = Load( 'dml' )
local PartitionCount = 10 

--------------------------------------------------------------------------------
-- DB
--------------------------------------------------------------------------------

local function Try( aFunction, aDB, ... )
    local ok, aResult = pcall( aFunction, aDB, ... )
    
    if ok then
        return aResult
    end
    
    pcall( function() aDB( DML[ 'Rollback' ] ) end )
    
    error( aResult )
end


local function HexDecode( aString )
    local aCoder = function( aValue )
        return string.char( tonumber( aValue, 16 ) )
    end

    return aString:gsub( '(%x%x)', aCoder )
end

local function PartitionName( aNumber )
    return ( 'P%02d' ):format( aNumber )
end

local function Partition( aDocument )
    local crypto = require( 'crypto' )
    local aValue = HexDecode( crypto.sha1( aDocument ) )
    local aHash = 0
    
    for anIndex = 1, 4 do 
        aHash = aHash * 256 + aValue:byte( anIndex )
    end
    
    aHash = ( aHash % PartitionCount ) + 1

    return PartitionName( aHash )
end

local function PartitionPath( aURL )
    local URL = require( 'URL' )
    local aURL = URL( aURL )
    local aPath = aURL.path
    
    aPath.absolute = false
    
    return tostring( aPath )
end

local function CreateText( aDB, aPartition )
    local aCall = function()
        local aStatement = Template( DML[ 'CreateText' ] )
    
        aStatement[ 'partition' ] = aPartition
    
        aDB( aStatement )
    end
    pcall( aCall )
end

local function NewDB( aURL )
    local DB = require( 'DB' )
    local aDB = DB( aURL )
    local aPath = PartitionPath( aURL )
    
    for anIndex = 1, PartitionCount do
        local aStatement = Template( DML[ 'Attach' ] )
        local aPartition = PartitionName( anIndex )
        
        aStatement[ 'path' ] = ( '%s%02d' ):format( aPath, anIndex )
        aStatement[ 'name' ] = aPartition
        
        aDB( aStatement )
        
        for anIndex, aStatement in ipairs( DDL ) do
            local aStatement = Template( aStatement )
            
            aStatement[ 'partition' ] = aPartition
            
            aDB( aStatement )
        end 
        
        CreateText( aDB, aPartition )
    end
    
    return aDB
end

--------------------------------------------------------------------------------
-- DML
--------------------------------------------------------------------------------

local function InsertDocument( aDB, aDocument, aContent )
    local aPartition = Partition( aDocument )
    local aStatement = nil
    
    aDB( DML[ 'BeginTransaction' ] )
    
    aStatement = Template( DML[ 'InsertDocument' ] )
    aStatement[ 'partition' ] = aPartition
    aDB( aStatement, aDocument )
    
    aStatement = Template( DML[ 'DeleteText' ] )
    aStatement[ 'partition' ] = aPartition
    aDB( aStatement, aDocument )

    aStatement = Template( DML[ 'InsertText' ] )
    aStatement[ 'partition' ] = aPartition
    aDB( aStatement, aContent, aDocument )
    
    aDB( DML[ 'EndTransaction' ] )
end

local function DeleteDocument( aDB, aDocument )
    local aPartition = Partition( aDocument )
    local aStatement = nil

    aDB( DML[ 'BeginTransaction' ] )

    aStatement = Template( DML[ 'DeleteDocument' ] )
    aStatement[ 'partition' ] = aPartition
    aDB( aStatement, aDocument )
    
    aStatement = Template( DML[ 'DeleteText' ] )
    aStatement[ 'partition' ] = aPartition
    aDB( aStatement, aDocument )
    
    aDB( DML[ 'EndTransaction' ] )
end

local function SelectDocument( aDB, aDocument )
    local aPartition = Partition( aDocument )
    local aStatement = Template( DML[ 'SelectDocumentContent' ] )
          aStatement[ 'partition' ] = aPartition
    local anIterator = aDB( aStatement, aDocument )
    
    return function()
        local aRow = anIterator()
        
        if aRow then
            return aRow.name, aRow.content
        end
    end
end

local function FindDocument( aDB, aQuery, aLimit )
    local aLimit = aLimit or 999
    local anIterator = nil

    aDB( DML[ 'BeginTransaction' ] )
    
    aDB( DML[ 'DeleteHit' ] )
    
    for anIndex = 1, PartitionCount do
        local aPartition = PartitionName( anIndex )
        local aStatement = Template( DML[ 'FindDocumentText' ] )
            
        aStatement[ 'partition' ] = aPartition
    
        aDB( aStatement, aQuery, aLimit )
    end

    aDB( DML[ 'EndTransaction' ] )
    
    anIterator = aDB( DML[ 'SelectHit' ], aLimit )
    
    return function()
        local aRow = anIterator()
        
        if aRow then
            return aRow.name, aRow.extract
        end
    end
end

--------------------------------------------------------------------------------
-- Metamethods
--------------------------------------------------------------------------------

function meta:__call( aURL )
    local aDB = NewDB( aURL )
    local aFinder = { db = aDB }

    setmetatable( aFinder, self )
    
    return aFinder
end

function meta:__concat( aValue )
    return tostring( self ) .. tostring( aValue )
end

function meta:__tostring()
    return ( '%s/%s' ):format( self._NAME, self._VERSION )
end

function self:__call( aQuery, aLimit )
    return Try( FindDocument, self.db, aQuery, aLimit )
end

function self:__index( aKey )
    return Try( SelectDocument, self.db, aKey )
end

function self:__newindex( aKey, aValue )
    if type( aKey ) == 'string' and type( aValue ) == 'string' then
        return Try( InsertDocument, self.db, aKey, aValue )
    elseif type( aKey ) == 'string' and type( aValue ) == 'boolean' and aValue == false then
        return Try( DeleteDocument, self.db, aKey )
    end

    error( ( 'Invalid parameters: %q = %q' ):format( tostring( aKey ), tostring( aValue ) ) )
end

function self:__concat( aValue )
    return tostring( self ) .. tostring( aValue )
end

function self:__tostring()
    return tostring( self.db )
end