// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package unix

import (
	"sync"
	"sync/atomic"
	"unsafe"
)

// soError describes reasons for shared library load failures.
type soError struct {
	Err     error
	ObjName string
	Msg     string
}

func (e *soError) Error() string { return e.Msg }

// Implemented in runtime/syscall_solaris.goc.
func rawSysvicall6(trap, nargs, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err Errno) // TODO: export
func sysvicall6(trap, nargs, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err Errno)    // TODO: export
func dlclose(handle uintptr) (err Errno)                                                    // TODO: export
func dlopen(name *uint8, mode uintptr) (handle uintptr, err Errno)                          // TODO: export
func dlsym(handle uintptr, name *uint8) (proc uintptr, err Errno)                           // TODO: export

// A so implements access to a single shared library object.
type so struct {
	Name   string
	Handle uintptr
}

// loadSO loads shared library file into memory.
func loadSO(name string) (*so, error) {
	namep, err := BytePtrFromString(name)
	if err != nil {
		return nil, err
	}
	h, e := dlopen(namep, 1) // RTLD_LAZY
	if e != 0 {
		return nil, &soError{
			Err:     e,
			ObjName: name,
			Msg:     "Failed to load " + name + ": " + e.Error(),
		}
	}
	d := &so{
		Name:   name,
		Handle: uintptr(h),
	}
	return d, nil
}

// mustLoadSO is like loadSO but panics if load operation fails.
func mustLoadSO(name string) *so {
	d, e := loadSO(name)
	if e != nil {
		panic(e)
	}
	return d
}

// FindProc searches shared library d for procedure named name and returns
// *proc if found. It returns an error if the search fails.
func (d *so) FindProc(name string) (*proc, error) {
	namep, err := BytePtrFromString(name)
	if err != nil {
		return nil, err
	}
	a, _ := dlsym(uintptr(d.Handle), namep)
	if a == 0 {
		return nil, &soError{
			Err:     ENOSYS,
			ObjName: name,
			Msg:     "Failed to find " + name + " procedure in " + d.Name,
		}
	}
	p := &proc{
		SO:   d,
		Name: name,
		addr: a,
	}
	return p, nil
}

// MustFindProc is like FindProc but panics if search fails.
func (d *so) MustFindProc(name string) *proc {
	p, e := d.FindProc(name)
	if e != nil {
		panic(e)
	}
	return p
}

// Release unloads shared library d from memory.
func (d *so) Release() (err error) {
	return dlclose(d.Handle)
}

// A proc implements access to a procedure inside a shared library.
type proc struct {
	SO   *so
	Name string
	addr uintptr
}

// Addr returns the address of the procedure represented by p.
// The return value can be passed to Syscall to run the procedure.
func (p *proc) Addr() uintptr {
	return p.addr
}

// Call executes procedure p with arguments a. It will panic, if more then
// 6 arguments are supplied.
//
// The returned error is always non-nil, constructed from the result of
// GetLastError.  Callers must inspect the primary return value to decide
// whether an error occurred (according to the semantics of the specific
// function being called) before consulting the error. The error will be
// guaranteed to contain unix.Errno.
func (p *proc) Call(a ...uintptr) (r1, r2 uintptr, lastErr error) {
	switch len(a) {
	case 0:
		return sysvicall6(p.Addr(), uintptr(len(a)), 0, 0, 0, 0, 0, 0)
	case 1:
		return sysvicall6(p.Addr(), uintptr(len(a)), a[0], 0, 0, 0, 0, 0)
	case 2:
		return sysvicall6(p.Addr(), uintptr(len(a)), a[0], a[1], 0, 0, 0, 0)
	case 3:
		return sysvicall6(p.Addr(), uintptr(len(a)), a[0], a[1], a[2], 0, 0, 0)
	case 4:
		return sysvicall6(p.Addr(), uintptr(len(a)), a[0], a[1], a[2], a[3], 0, 0)
	case 5:
		return sysvicall6(p.Addr(), uintptr(len(a)), a[0], a[1], a[2], a[3], a[4], 0)
	case 6:
		return sysvicall6(p.Addr(), uintptr(len(a)), a[0], a[1], a[2], a[3], a[4], a[5])
	default:
		panic("Call " + p.Name + " with too many arguments " + itoa(len(a)) + ".")
	}
	return
}

// A lazySO implements access to a single shared library.  It will delay
// the load of the shared library until the first call to its Handle method
// or to one of its lazyProc's Addr method.
type lazySO struct {
	mu   sync.Mutex
	so   *so // non nil once SO is loaded
	Name string
}

// Load loads single shared file d.Name into memory. It returns an error if
// fails.  Load will not try to load SO, if it is already loaded into memory.
func (d *lazySO) Load() error {
	// Non-racy version of:
	// if d.so == nil {
	if atomic.LoadPointer((*unsafe.Pointer)(unsafe.Pointer(&d.so))) == nil {
		d.mu.Lock()
		defer d.mu.Unlock()
		if d.so == nil {
			so, e := loadSO(d.Name)
			if e != nil {
				return e
			}
			// Non-racy version of:
			// d.so = so
			atomic.StorePointer((*unsafe.Pointer)(unsafe.Pointer(&d.so)), unsafe.Pointer(so))
		}
	}
	return nil
}

// mustLoad is like Load but panics if search fails.
func (d *lazySO) mustLoad() {
	e := d.Load()
	if e != nil {
		panic(e)
	}
}

// Handle returns d's module handle.
func (d *lazySO) Handle() uintptr {
	d.mustLoad()
	return uintptr(d.so.Handle)
}

// NewProc returns a lazyProc for accessing the named procedure in the SO d.
func (d *lazySO) NewProc(name string) *lazyProc {
	return &lazyProc{l: d, Name: name}
}

// newLazySO creates new lazySO associated with SO file.
func newLazySO(name string) *lazySO {
	return &lazySO{Name: name}
}

// A lazyProc implements access to a procedure inside a lazySO.
// It delays the lookup until the Addr method is called.
type lazyProc struct {
	mu   sync.Mutex
	Name string
	l    *lazySO
	proc *proc
}

// Find searches the shared library for procedure named p.Name. It returns an
// error if search fails. Find will not search procedure, if it is already
// found and loaded into memory.
func (p *lazyProc) Find() error {
	// Non-racy version of:
	// if p.proc == nil {
	if atomic.LoadPointer((*unsafe.Pointer)(unsafe.Pointer(&p.proc))) == nil {
		p.mu.Lock()
		defer p.mu.Unlock()
		if p.proc == nil {
			e := p.l.Load()
			if e != nil {
				return e
			}
			proc, e := p.l.so.FindProc(p.Name)
			if e != nil {
				return e
			}
			// Non-racy version of:
			// p.proc = proc
			atomic.StorePointer((*unsafe.Pointer)(unsafe.Pointer(&p.proc)), unsafe.Pointer(proc))
		}
	}
	return nil
}

// mustFind is like Find but panics if search fails.
func (p *lazyProc) mustFind() {
	e := p.Find()
	if e != nil {
		panic(e)
	}
}

// Addr returns the address of the procedure represented by p.
// The return value can be passed to Syscall to run the procedure.
func (p *lazyProc) Addr() uintptr {
	p.mustFind()
	return p.proc.Addr()
}

// Call executes procedure p with arguments a. It will panic, if more then
// 6 arguments are supplied.
//
// The returned error is always non-nil, constructed from the result of
// GetLastError.  Callers must inspect the primary return value to decide
// whether an error occurred (according to the semantics of the specific
// function being called) before consulting the error. The error will be
// guaranteed to contain unix.Errno.
func (p *lazyProc) Call(a ...uintptr) (r1, r2 uintptr, lastErr error) {
	p.mustFind()
	return p.proc.Call(a...)
}