package compiler

import (
	"errors"
	"go/ast"
	"go/types"
	"strings"

	"github.com/nspcc-dev/neo-go/pkg/vm/emit"
	"github.com/nspcc-dev/neo-go/pkg/vm/opcode"
)

var (
	// Go language builtin functions.
	goBuiltins = []string{"len", "append", "panic"}
	// Custom builtin utility functions.
	customBuiltins = []string{
		"FromAddress", "Equals",
		"ToBool", "ToByteArray", "ToInteger",
	}
)

// newGlobal creates new global variable.
func (c *codegen) newGlobal(pkg string, name string) {
	name = c.getIdentName(pkg, name)
	c.globals[name] = len(c.globals)
}

// getIdentName returns fully-qualified name for a variable.
func (c *codegen) getIdentName(pkg string, name string) string {
	if fullName, ok := c.importMap[pkg]; ok {
		pkg = fullName
	}
	return pkg + "." + name
}

// traverseGlobals visits and initializes global variables.
// and returns number of variables initialized.
func (c *codegen) traverseGlobals() int {
	var n int
	c.ForEachFile(func(f *ast.File, _ *types.Package) {
		n += countGlobals(f)
	})
	if n != 0 {
		if n > 255 {
			c.prog.BinWriter.Err = errors.New("too many global variables")
			return 0
		}
		emit.Instruction(c.prog.BinWriter, opcode.INITSSLOT, []byte{byte(n)})
		c.ForEachFile(c.convertGlobals)
	}
	return n
}

// countGlobals counts the global variables in the program to add
// them with the stack size of the function.
func countGlobals(f ast.Node) (i int) {
	ast.Inspect(f, func(node ast.Node) bool {
		switch n := node.(type) {
		// Skip all function declarations.
		case *ast.FuncDecl:
			return false
		// After skipping all funcDecls we are sure that each value spec
		// is a global declared variable or constant.
		case *ast.ValueSpec:
			i += len(n.Names)
		}
		return true
	})
	return
}

// isExprNil looks if the given expression is a `nil`.
func isExprNil(e ast.Expr) bool {
	v, ok := e.(*ast.Ident)
	return ok && v.Name == "nil"
}

// indexOfStruct returns the index of the given field inside that struct.
// If the struct does not contain that field it will return -1.
func indexOfStruct(strct *types.Struct, fldName string) int {
	for i := 0; i < strct.NumFields(); i++ {
		if strct.Field(i).Name() == fldName {
			return i
		}
	}
	return -1
}

type funcUsage map[string]bool

func (f funcUsage) funcUsed(name string) bool {
	_, ok := f[name]
	return ok
}

// lastStmtIsReturn checks if last statement of the declaration was return statement..
func lastStmtIsReturn(decl *ast.FuncDecl) (b bool) {
	if l := len(decl.Body.List); l != 0 {
		_, ok := decl.Body.List[l-1].(*ast.ReturnStmt)
		return ok
	}
	return false
}

func (c *codegen) analyzeFuncUsage() funcUsage {
	usage := funcUsage{}

	c.ForEachFile(func(f *ast.File, pkg *types.Package) {
		isMain := pkg == c.mainPkg.Pkg
		ast.Inspect(f, func(node ast.Node) bool {
			switch n := node.(type) {
			case *ast.CallExpr:
				switch t := n.Fun.(type) {
				case *ast.Ident:
					usage[t.Name] = true
				case *ast.SelectorExpr:
					usage[t.Sel.Name] = true
				}
			case *ast.FuncDecl:
				// exported functions are always assumed to be used
				if isMain && n.Name.IsExported() {
					usage[n.Name.Name] = true
				}
			}
			return true
		})
	})
	return usage
}

func isGoBuiltin(name string) bool {
	for i := range goBuiltins {
		if name == goBuiltins[i] {
			return true
		}
	}
	return false
}

func isCustomBuiltin(f *funcScope) bool {
	if !isInteropPath(f.pkg.Path()) {
		return false
	}
	for _, n := range customBuiltins {
		if f.name == n {
			return true
		}
	}
	return false
}

func isSyscall(fun *funcScope) bool {
	if fun.selector == nil || fun.pkg == nil || !isInteropPath(fun.pkg.Path()) {
		return false
	}
	_, ok := syscalls[fun.selector.Name][fun.name]
	return ok
}

func isInteropPath(s string) bool {
	return strings.HasPrefix(s, "github.com/nspcc-dev/neo-go/pkg/interop")
}