core/server/sandbox/routing_module.go

package sandbox

// routing_module.go
//
// Starlark routing module — a generic rule-based decision engine.
// Always available (pure computation, no I/O).
//
// Starlark API:
//   result = routing.evaluate(rules, data)
//   # result → "target_string" or None

import (
	"fmt"
	"strings"

	"go.starlark.net/starlark"
	"go.starlark.net/starlarkstruct"
)

// BuildRoutingModule creates the "routing" Starlark module.
// No permission required — pure computation.
func BuildRoutingModule() *starlarkstruct.Module {
	return MakeModule("routing", starlark.StringDict{
		"evaluate": starlark.NewBuiltin("routing.evaluate", routingEvaluateBuiltin()),
	})
}

// routingRule is the generic equivalent of workflow.Condition.
// Uses "target" instead of "target_stage" to be domain-agnostic.
type routingRule struct {
	Field  string
	Op     string
	Value  any
	Target string
}

func routingEvaluateBuiltin() func(*starlark.Thread, *starlark.Builtin, starlark.Tuple, []starlark.Tuple) (starlark.Value, error) {
	return func(_ *starlark.Thread, b *starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
		var rulesVal, dataVal starlark.Value
		if err := starlark.UnpackPositionalArgs(b.Name(), args, kwargs, 2, &rulesVal, &dataVal); err != nil {
			return nil, err
		}

		// Convert rules list → []routingRule
		rulesList, ok := rulesVal.(*starlark.List)
		if !ok {
			return nil, fmt.Errorf("routing.evaluate: rules must be a list, got %s", rulesVal.Type())
		}

		rules := make([]routingRule, rulesList.Len())
		for i := 0; i < rulesList.Len(); i++ {
			ruleDict, ok := rulesList.Index(i).(*starlark.Dict)
			if !ok {
				return nil, fmt.Errorf("routing.evaluate: rules[%d] must be a dict, got %s", i, rulesList.Index(i).Type())
			}
			m := DictToMap(ruleDict)

			field, _ := m["field"].(string)
			op, _ := m["op"].(string)
			target, _ := m["target"].(string)
			if field == "" || op == "" || target == "" {
				return nil, fmt.Errorf("routing.evaluate: rules[%d] must have field, op, and target", i)
			}
			rules[i] = routingRule{
				Field:  field,
				Op:     op,
				Value:  m["value"],
				Target: target,
			}
		}

		// Convert data dict → Go map
		dataDict, ok := dataVal.(*starlark.Dict)
		if !ok {
			return nil, fmt.Errorf("routing.evaluate: data must be a dict, got %s", dataVal.Type())
		}
		data := DictToMap(dataDict)

		// Evaluate rules — first match wins
		for _, rule := range rules {
			if evaluateRoutingCondition(rule, data) {
				return starlark.String(rule.Target), nil
			}
		}

		return starlark.None, nil
	}
}

// ── Evaluation helpers (mirrored from workflow/routing.go) ─────────
//
// These are pure functions copied from the workflow package to avoid
// a sandbox → workflow import cycle. The workflow package continues
// using its own copy for ResolveNextStage.

// evaluateRoutingCondition checks if a single rule matches against data.
func evaluateRoutingCondition(rule routingRule, data map[string]any) bool {
	val, exists := data[rule.Field]

	switch rule.Op {
	case "exists":
		return exists
	case "not_exists":
		return !exists
	}

	if !exists {
		return false
	}

	switch rule.Op {
	case "eq":
		return routingCompareEq(val, rule.Value)
	case "neq":
		return !routingCompareEq(val, rule.Value)
	case "gt":
		return routingCompareNum(val, rule.Value) > 0
	case "lt":
		return routingCompareNum(val, rule.Value) < 0
	case "gte":
		return routingCompareNum(val, rule.Value) >= 0
	case "lte":
		return routingCompareNum(val, rule.Value) <= 0
	case "in":
		return routingCompareIn(val, rule.Value)
	case "contains":
		return routingCompareContains(val, rule.Value)
	default:
		return false
	}
}

func routingCompareEq(a, b any) bool {
	return fmt.Sprintf("%v", a) == fmt.Sprintf("%v", b)
}

func routingCompareNum(a, b any) int {
	af := routingToFloat(a)
	bf := routingToFloat(b)
	if af == nil || bf == nil {
		return 0
	}
	switch {
	case *af < *bf:
		return -1
	case *af > *bf:
		return 1
	default:
		return 0
	}
}

func routingToFloat(v any) *float64 {
	switch n := v.(type) {
	case float64:
		return &n
	case int:
		f := float64(n)
		return &f
	case int64:
		f := float64(n)
		return &f
	case string:
		var f float64
		if _, err := fmt.Sscanf(n, "%f", &f); err == nil {
			return &f
		}
	}
	return nil
}

func routingCompareIn(val, list any) bool {
	arr, ok := list.([]any)
	if !ok {
		return false
	}
	vs := fmt.Sprintf("%v", val)
	for _, item := range arr {
		if fmt.Sprintf("%v", item) == vs {
			return true
		}
	}
	return false
}

func routingCompareContains(val, target any) bool {
	s := fmt.Sprintf("%v", val)
	t := fmt.Sprintf("%v", target)
	return strings.Contains(s, t)
}