package build

import (
	"git.akyoto.dev/cli/q/src/build/expression"
	"git.akyoto.dev/cli/q/src/build/token"
	"git.akyoto.dev/cli/q/src/errors"
)

// CompileVariableDefinition compiles a variable definition.
func (f *Function) CompileVariableDefinition(expr *expression.Expression) error {
	if len(expr.Children) < 2 {
		return errors.New(errors.MissingAssignValue, f.File, expr.LastChild().Token.End())
	}

	name := expr.Children[0].Token.Text()

	if f.identifierExists(name) {
		return errors.New(&errors.VariableAlreadyExists{Name: name}, f.File, expr.Children[0].Token.Position)
	}

	reg, exists := f.CPU.FindFree(f.CPU.General)

	if !exists {
		panic("no free registers")
	}

	err := f.ExpressionToRegister(expr.Children[1], reg)

	if err != nil {
		return err
	}

	variable := &Variable{
		Name:     name,
		Register: reg,
	}

	f.addVariable(variable)
	f.useVariable(variable)
	return nil
}

func (f *Function) addVariable(variable *Variable) {
	variable.UsesRemaining = countIdentifier(f.Body, variable.Name)
	f.Variables[variable.Name] = variable
	f.CPU.Use(variable.Register)
}

func (f *Function) useVariable(variable *Variable) {
	variable.UsesRemaining--

	if variable.UsesRemaining < 0 {
		panic("incorrect number of variable use calls")
	}

	if variable.UsesRemaining == 0 {
		f.CPU.Free(variable.Register)
	}
}

func countIdentifier(tokens token.List, name string) int {
	count := 0

	for _, t := range tokens {
		if t.Kind == token.Identifier && t.Text() == name {
			count++
		}
	}

	return count
}