// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//go:build !tinygo
// +build !tinygo

package memory

import (
	"fmt"
	"os"
	"runtime"
	"strconv"
	"strings"
	"sync"
	"sync/atomic"
	"unsafe"
)

type CheckedAllocator struct {
	mem Allocator
	sz  atomic.Int64

	allocs sync.Map
}

func NewCheckedAllocator(mem Allocator) *CheckedAllocator {
	return &CheckedAllocator{mem: mem}
}

func (a *CheckedAllocator) CurrentAlloc() int { return int(a.sz.Load()) }

func (a *CheckedAllocator) Allocate(size int) []byte {
	a.sz.Add(int64(size))
	out := a.mem.Allocate(size)
	if size == 0 {
		return out
	}

	ptr := uintptr(unsafe.Pointer(&out[0]))
	pcs := make([]uintptr, maxRetainedFrames)

	// For historical reasons the meaning of the skip argument
	// differs between Caller and Callers. For Callers, 0 identifies
	// the frame for the caller itself. We skip 2 additional frames
	// here to get to the caller right before the call to Allocate.
	runtime.Callers(allocFrames+2, pcs)
	callersFrames := runtime.CallersFrames(pcs)
	if pc, _, l, ok := runtime.Caller(allocFrames); ok {
		a.allocs.Store(ptr, &dalloc{pc: pc, line: l, sz: size, callersFrames: callersFrames})
	}
	return out
}

func (a *CheckedAllocator) Reallocate(size int, b []byte) []byte {
	a.sz.Add(int64(size - len(b)))

	oldptr := uintptr(unsafe.Pointer(&b[0]))
	out := a.mem.Reallocate(size, b)
	if size == 0 {
		return out
	}

	newptr := uintptr(unsafe.Pointer(&out[0]))
	a.allocs.Delete(oldptr)
	pcs := make([]uintptr, maxRetainedFrames)

	// For historical reasons the meaning of the skip argument
	// differs between Caller and Callers. For Callers, 0 identifies
	// the frame for the caller itself. We skip 2 additional frames
	// here to get to the caller right before the call to Reallocate.
	runtime.Callers(reallocFrames+2, pcs)
	callersFrames := runtime.CallersFrames(pcs)
	if pc, _, l, ok := runtime.Caller(reallocFrames); ok {
		a.allocs.Store(newptr, &dalloc{pc: pc, line: l, sz: size, callersFrames: callersFrames})
	}

	return out
}

func (a *CheckedAllocator) Free(b []byte) {
	a.sz.Add(int64(len(b) * -1))
	defer a.mem.Free(b)

	if len(b) == 0 {
		return
	}

	ptr := uintptr(unsafe.Pointer(&b[0]))
	a.allocs.Delete(ptr)
}

// typically the allocations are happening in memory.Buffer, not by consumers calling
// allocate/reallocate directly. As a result, we want to skip the caller frames
// of the inner workings of Buffer in order to find the caller that actually triggered
// the allocation via a call to Resize/Reserve/etc.
const (
	defAllocFrames       = 4
	defReallocFrames     = 3
	defMaxRetainedFrames = 0
)

// Use the environment variables ARROW_CHECKED_ALLOC_FRAMES and ARROW_CHECKED_REALLOC_FRAMES
// to control how many frames it skips when storing the caller for allocations/reallocs
// when using this to find memory leaks. Use ARROW_CHECKED_MAX_RETAINED_FRAMES to control how
// many frames are retained for printing the stack trace of a leak.
var allocFrames, reallocFrames, maxRetainedFrames int = defAllocFrames, defReallocFrames, defMaxRetainedFrames

func init() {
	if val, ok := os.LookupEnv("ARROW_CHECKED_ALLOC_FRAMES"); ok {
		if f, err := strconv.Atoi(val); err == nil {
			allocFrames = f
		}
	}

	if val, ok := os.LookupEnv("ARROW_CHECKED_REALLOC_FRAMES"); ok {
		if f, err := strconv.Atoi(val); err == nil {
			reallocFrames = f
		}
	}

	if val, ok := os.LookupEnv("ARROW_CHECKED_MAX_RETAINED_FRAMES"); ok {
		if f, err := strconv.Atoi(val); err == nil {
			maxRetainedFrames = f
		}
	}
}

type dalloc struct {
	pc            uintptr
	line          int
	sz            int
	callersFrames *runtime.Frames
}

type TestingT interface {
	Errorf(format string, args ...interface{})
	Helper()
}

func (a *CheckedAllocator) AssertSize(t TestingT, sz int) {
	a.allocs.Range(func(_, value interface{}) bool {
		info := value.(*dalloc)
		f := runtime.FuncForPC(info.pc)
		frames := info.callersFrames
		var callersMsg strings.Builder
		for {
			frame, more := frames.Next()
			if frame.Line == 0 {
				break
			}
			callersMsg.WriteString("\t")
			// frame.Func is a useful source of information if it's present.
			// It may be nil for non-Go code or fully inlined functions.
			if fn := frame.Func; fn != nil {
				// format as func name + the offset in bytes from func entrypoint
				fmt.Fprintf(&callersMsg, "%s+%x", fn.Name(), frame.PC-fn.Entry())
			} else {
				// fallback to outer func name + file line
				fmt.Fprintf(&callersMsg, "%s, line %d", frame.Function, frame.Line)
			}

			// Write a proper file name + line, so it's really easy to find the leak
			callersMsg.WriteString("\n\t\t")
			callersMsg.WriteString(frame.File + ":" + strconv.Itoa(frame.Line))
			callersMsg.WriteString("\n")
			if !more {
				break
			}
		}

		file, line := f.FileLine(info.pc)
		t.Errorf("LEAK of %d bytes FROM\n\t%s+%x\n\t\t%s:%d\n%v",
			info.sz,
			f.Name(), info.pc-f.Entry(), // func name + offset in bytes between frame & entrypoint to func
			file, line, // a proper file name + line, so it's really easy to find the leak
			callersMsg.String(),
		)
		return true
	})

	if int(a.sz.Load()) != sz {
		t.Helper()
		t.Errorf("invalid memory size exp=%d, got=%d", sz, a.sz.Load())
	}
}

type CheckedAllocatorScope struct {
	alloc *CheckedAllocator
	sz    int
}

func NewCheckedAllocatorScope(alloc *CheckedAllocator) *CheckedAllocatorScope {
	sz := alloc.sz.Load()
	return &CheckedAllocatorScope{alloc: alloc, sz: int(sz)}
}

func (c *CheckedAllocatorScope) CheckSize(t TestingT) {
	sz := int(c.alloc.sz.Load())
	if c.sz != sz {
		t.Helper()
		t.Errorf("invalid memory size exp=%d, got=%d", c.sz, sz)
	}
}

var _ Allocator = (*CheckedAllocator)(nil)
