orm/mapper.go

package orm

import (
	"fmt"
	"reflect"
	"sync"
)

// Prefix used for tagging
var Prefix = "db"

type mapper struct {
	lock *sync.Mutex
	wg   *sync.WaitGroup
	tbls tables
	cbs  *mapperCallbacks
	init bool
}

// Global mapper context
var ctx *mapper = &mapper{
	lock: &sync.Mutex{},
	wg:   &sync.WaitGroup{},
	tbls: make(tables),
	cbs: &mapperCallbacks{
		ch:   make(chan mapperCallback),
		list: make([]mapperCallback, 0),
		cond: sync.NewCond(&sync.Mutex{}),
	},
	init: false,
}

// Map a table (struct) that implements MappableInterface
// Note! Should be mapped in init-function from the that struct
func Map(tbl MappableInterface) *mapper {

	// Add to working group
	ctx.wg.Add(1)

	ctx.lock.Lock()

	// Kick off some routines on first call
	if !ctx.init {
		ctx.init = true
		// Go routine to receive mapping-calls between mapping routines
		go func() {
			for {
				//  Receive callback from tables during mapping

				select {
				case q := <-ctx.cbs.ch:
					// Add to callback queue until table is mapped
					ctx.wg.Add(1)

					ctx.cbs.lock()
					ctx.cbs.add(q)
					ctx.cbs.unlock()

					ctx.cbs.cond.Broadcast()
				}
			}
		}()

		// Routine to communicate between other mapping routines
		go func() {
			for {
				// Loop on condition as long as empty
				ctx.cbs.lock()
				for ctx.cbs.length() == 0 {
					ctx.cbs.cond.Wait()
				}

				// Loop through all new callbacks
				for i, l := 0, ctx.cbs.length(); i < l; i++ {
					cb := ctx.cbs.get(l - i - 1)

					// Ensure callback is ran when columns are mapped
					if t := ctx.getTbl(cb.to); t != nil && t.isMapped() {

						// Remove callback from slice
						ctx.cbs.remove(l - i - 1)

						// Kick off the callback; and lock table
						go func(t *table) {
							t.lock()
							defer t.unlock()
							defer ctx.wg.Done()
							cb.fn(t)
						}(t)
					}
				}
				ctx.cbs.unlock()
			}
		}()
	}

	ctx.lock.Unlock()

	// Start mapping of table
	go func() {
		t := ctx.addTbl(tbl)

		// Mapping should only occur once
		if !t.isMapped() {
			ctx.mapTbl(t)
			ctx.cbs.cond.Broadcast()
		}

		// Unclock write to allow reading
		t.unlock()
		ctx.wg.Done()
	}()

	return ctx
}

// WaitInit should be called in main() to wait for the mapping
// to complete before start using the tables
func WaitInit() {
	ctx.wg.Wait()
	// Debug print
	fmt.Println(ctx.tbls)
}

// hasTable checks for table
func (m *mapper) hasTbl(n string) bool {
	m.lock.Lock()
	defer m.lock.Unlock()

	_, ok := m.tbls[n]

	return ok
}

// getTbl should only be called controller; Must lock after
func (m *mapper) getTbl(n string) *table {
	m.lock.Lock()
	defer m.lock.Unlock()

	if t, ok := m.tbls[n]; ok {
		return t
	}

	return nil
}

// addTbl creates a new or returns an existing table; will write lock!
func (m *mapper) addTbl(t MappableInterface) *table {
	rt := reflect.TypeOf(t).Elem()

	m.lock.Lock()
	defer m.lock.Unlock()

	if t, ok := m.tbls[rt.Name()]; ok {
		return t.lock()
	}

	m.tbls[rt.Name()] = &table{
		rt:   rt,
		rv:   reflect.ValueOf(t).Elem(),
		l:    &sync.RWMutex{},
		tFn:  t.GetTableMapperFn(),
		cFn:  t.GetColumnMapperFn(),
		cols: make(columns, 0),
		rels: relations{
			m:    &sync.Mutex{},
			rmap: make(map[relType][]relation),
		},
		mapped: false,
	}

	return m.tbls[rt.Name()].lock()
}

// isPossibleRelation determine if fields in table implements MappableInterface
// then its possible a relation
func (m *mapper) isPossibleRelation(t reflect.Type) bool {
	return reflect.New(t).Type().Implements(
		reflect.TypeOf((*MappableInterface)(nil)).Elem(),
	)
}

// mapField will prepare any field in table struct for mapping
func (m *mapper) mapField(t *table, csf reflect.StructField, cv reflect.Value) field {
	switch csf.Type.Kind() {
	case reflect.Ptr:
		fallthrough
	case reflect.Slice:
		fallthrough
	case reflect.Map:
		if m.isPossibleRelation(csf.Type.Elem()) {
			return field{
				sf: csf,
				t:  csf.Type.Elem(),
				v:  cv,
			}
		}
	case reflect.Struct:
		if m.isPossibleRelation(csf.Type) {
			return field{
				sf: csf,
				t:  csf.Type,
				v:  cv,
			}
		}
	}
	return field{
		sf: csf,
		t:  csf.Type,
		v:  cv,
	}
}

// mapTbl will simply loop throug every field in the table
func (m *mapper) mapTbl(t *table) {
	for n := 0; n < t.getType().NumField(); n++ {
		if sf := t.getType().Field(n); !sf.Anonymous {
			t.addField(m.mapField(t, sf, t.getValue().Field(n)), m.cbs.ch)
		} else if t.getType().Field(n).Anonymous && t.getValue().Field(n).CanInterface() {
			cv := t.getValue().Field(n)
			csf := reflect.TypeOf(cv.Interface())
			for i := 0; i < csf.NumField(); i++ {
				if !csf.Field(i).Anonymous {
					t.addField(m.mapField(t, csf.Field(i), cv.Field(i)), m.cbs.ch)
				}
			}
		}
	}
	t.mapped = true
}

// mappcerCallbackFn is used to communicate between mapping routines
type mapperCallbackFn func(tbl *table)

// mappcerCallback is used to communicate between mapping routines
type mapperCallback struct {
	from, to string
	fn       mapperCallbackFn
}

// mappcerCallbacks holds the main channel from main thread
// and a queue for all callbacks
type mapperCallbacks struct {
	ch   chan mapperCallback
	list []mapperCallback
	cond *sync.Cond
}

/**
 * Below is just helper methods to make code cleaner
 */

func (m *mapperCallbacks) lock() *mapperCallbacks {
	m.cond.L.Lock()
	return m
}

func (m *mapperCallbacks) unlock() {
	m.cond.L.Unlock()
}

func (m *mapperCallbacks) add(mf mapperCallback) {
	m.list = append(m.list, mf)
}

func (m *mapperCallbacks) get(i int) mapperCallback {
	return m.list[i]
}

func (m *mapperCallbacks) remove(i int) {
	m.list = append(m.list[:i], m.list[i+1:]...)
}

func (m *mapperCallbacks) length() int {
	return len(m.list)
}