// expressionValues evaluates a slice of expressions and returns a []*cd.Variable
// containing the results.
// If the result of an expression evaluation refers to values from the program's
// memory (e.g., the expression evaluates to a slice) a corresponding variable is
// added to the value collector, to be read later.
func expressionValues(expressions []string, prog debug.Program, vc *valuecollector.Collector) []*cd.Variable {
	evaluatedExpressions := make([]*cd.Variable, len(expressions))
	for i, exp := range expressions {
		ee := &cd.Variable{Name: exp}
		evaluatedExpressions[i] = ee
		if val, err := prog.Evaluate(exp); err != nil {
			ee.Status = errorStatusMessage(err.Error(), refersToBreakpointExpression)
		} else {
			vc.FillValue(val, ee)
		}
	}
	return evaluatedExpressions
}

// condTruth evaluates a condition.
func condTruth(condition string, prog debug.Program) (bool, error) {
	if condition == "" {
		// A condition wasn't set.
		return true, nil
	}
	val, err := prog.Evaluate(condition)
	if err != nil {
		return false, err
	}
	if v, ok := val.(bool); !ok {
		return false, fmt.Errorf("condition expression has type %T, should be bool", val)
	} else {
		return v, nil
	}
}

// stackFrames returns a stack trace for the program.  It passes references to
// function parameters and local variables to the value collector, so it can read
// their values later.
func stackFrames(prog debug.Program, vc *valuecollector.Collector) ([]*cd.StackFrame, *cd.StatusMessage) {
	frames, err := prog.Frames(maxCapturedStackFrames)
	if err != nil {
		return nil, errorStatusMessage("Error getting stack: "+err.Error(), refersToUnspecified)
	}
	stackFrames := make([]*cd.StackFrame, len(frames))
	for i, f := range frames {
		frame := &cd.StackFrame{}
		frame.Function = f.Function
		for _, v := range f.Params {
			frame.Arguments = append(frame.Arguments, vc.AddVariable(debug.LocalVar(v)))
		}
		for _, v := range f.Vars {
			frame.Locals = append(frame.Locals, vc.AddVariable(v))
		}
		frame.Location = &cd.SourceLocation{
			Path: f.File,
			Line: int64(f.Line),
		}
		stackFrames[i] = frame
	}
	return stackFrames, nil
}

// programLoop runs the program being debugged to completion.  When a breakpoint's
// conditions are satisfied, it sends an Update RPC to the Debuglet Controller.
// The function returns when the program exits and all Update RPCs have finished.
func programLoop(c *debuglet.Controller, bs *breakpoints.BreakpointStore, prog debug.Program) {
	var wg sync.WaitGroup
	for {
		// Run the program until it hits a breakpoint or exits.
		status, err := prog.Resume()
		if err != nil {
			break
		}

		// Get the breakpoints at this address whose conditions were satisfied,
		// and remove the ones that aren't logpoints.
		bps := bs.BreakpointsAtPC(status.PC)
		bps = bpsWithConditionSatisfied(bps, prog)
		for _, bp := range bps {
			if bp.Action != "LOG" {
				bs.RemoveBreakpoint(bp)
			}
		}

		if len(bps) == 0 {
			continue
		}

		// Evaluate expressions and get the stack.
		vc := valuecollector.NewCollector(prog, maxCapturedVariables)
		needStackFrames := false
		for _, bp := range bps {
			// If evaluating bp's condition didn't return an error, evaluate bp's
			// expressions, and later get the stack frames.
			if bp.Status == nil {
				bp.EvaluatedExpressions = expressionValues(bp.Expressions, prog, vc)
				needStackFrames = true
			}
		}
		var (
			stack                    []*cd.StackFrame
			stackFramesStatusMessage *cd.StatusMessage
		)
		if needStackFrames {
			stack, stackFramesStatusMessage = stackFrames(prog, vc)
		}

		// Read variable values from the program.
		variableTable := vc.ReadValues()

		// Start a goroutine to send updates to the Debuglet Controller or write
		// to logs, concurrently with resuming the program.
		// TODO: retry Update on failure.
		for _, bp := range bps {
			wg.Add(1)
			switch bp.Action {
			case "LOG":
				go func(format string, evaluatedExpressions []*cd.Variable) {
					s := valuecollector.LogString(format, evaluatedExpressions, variableTable)
					log.Print(s)
					wg.Done()
				}(bp.LogMessageFormat, bp.EvaluatedExpressions)
				bp.Status = nil
				bp.EvaluatedExpressions = nil
			default:
				go func(bp *cd.Breakpoint) {
					defer wg.Done()
					bp.IsFinalState = true
					if bp.Status == nil {
						// If evaluating bp's condition didn't return an error, include the
						// stack frames, variable table, and any status message produced when
						// getting the stack frames.
						bp.StackFrames = stack
						bp.VariableTable = variableTable
						bp.Status = stackFramesStatusMessage
					}
					if err := c.Update(bp.Id, bp); err != nil {
						log.Printf("Failed to send breakpoint update for %s: %s", bp.Id, err)
					}
				}(bp)
			}
		}
	}

	// Wait for all updates to finish before returning.
	wg.Wait()
}