1 files changed, 344 insertions, 0 deletions
diff --git a/modules/templates/eval/eval.go b/modules/templates/eval/eval.go
new file mode 100644
index 00000000..5d4ac915
--- /dev/null
+++ b/modules/templates/eval/eval.go
@@ -0,0 +1,344 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package eval
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+
+	"code.gitea.io/gitea/modules/util"
+)
+
+type Num struct {
+	Value any // int64 or float64, nil on error
+}
+
+var opPrecedence = map[string]int{
+	// "(": 1, this is for low precedence like function calls, they are handled separately
+	"or":  2,
+	"and": 3,
+	"not": 4,
+	"==":  5, "!=": 5, "<": 5, "<=": 5, ">": 5, ">=": 5,
+	"+": 6, "-": 6,
+	"*": 7, "/": 7,
+}
+
+type stack[T any] struct {
+	name  string
+	elems []T
+}
+
+func (s *stack[T]) push(t T) {
+	s.elems = append(s.elems, t)
+}
+
+func (s *stack[T]) pop() T {
+	if len(s.elems) == 0 {
+		panic(s.name + " stack is empty")
+	}
+	t := s.elems[len(s.elems)-1]
+	s.elems = s.elems[:len(s.elems)-1]
+	return t
+}
+
+func (s *stack[T]) peek() T {
+	if len(s.elems) == 0 {
+		panic(s.name + " stack is empty")
+	}
+	return s.elems[len(s.elems)-1]
+}
+
+type operator string
+
+type eval struct {
+	stackNum stack[Num]
+	stackOp  stack[operator]
+	funcMap  map[string]func([]Num) Num
+}
+
+func newEval() *eval {
+	e := &eval{}
+	e.stackNum.name = "num"
+	e.stackOp.name = "op"
+	return e
+}
+
+func toNum(v any) (Num, error) {
+	switch v := v.(type) {
+	case string:
+		if strings.Contains(v, ".") {
+			n, err := strconv.ParseFloat(v, 64)
+			if err != nil {
+				return Num{n}, err
+			}
+			return Num{n}, nil
+		}
+		n, err := strconv.ParseInt(v, 10, 64)
+		if err != nil {
+			return Num{n}, err
+		}
+		return Num{n}, nil
+	case float32, float64:
+		n, _ := util.ToFloat64(v)
+		return Num{n}, nil
+	default:
+		n, err := util.ToInt64(v)
+		if err != nil {
+			return Num{n}, err
+		}
+		return Num{n}, nil
+	}
+}
+
+func truth(b bool) int64 {
+	if b {
+		return int64(1)
+	}
+	return int64(0)
+}
+
+func applyOp2Generic[T int64 | float64](op operator, n1, n2 T) Num {
+	switch op {
+	case "+":
+		return Num{n1 + n2}
+	case "-":
+		return Num{n1 - n2}
+	case "*":
+		return Num{n1 * n2}
+	case "/":
+		return Num{n1 / n2}
+	case "==":
+		return Num{truth(n1 == n2)}
+	case "!=":
+		return Num{truth(n1 != n2)}
+	case "<":
+		return Num{truth(n1 < n2)}
+	case "<=":
+		return Num{truth(n1 <= n2)}
+	case ">":
+		return Num{truth(n1 > n2)}
+	case ">=":
+		return Num{truth(n1 >= n2)}
+	case "and":
+		t1, _ := util.ToFloat64(n1)
+		t2, _ := util.ToFloat64(n2)
+		return Num{truth(t1 != 0 && t2 != 0)}
+	case "or":
+		t1, _ := util.ToFloat64(n1)
+		t2, _ := util.ToFloat64(n2)
+		return Num{truth(t1 != 0 || t2 != 0)}
+	}
+	panic("unknown operator: " + string(op))
+}
+
+func applyOp2(op operator, n1, n2 Num) Num {
+	float := false
+	if _, ok := n1.Value.(float64); ok {
+		float = true
+	} else if _, ok = n2.Value.(float64); ok {
+		float = true
+	}
+	if float {
+		f1, _ := util.ToFloat64(n1.Value)
+		f2, _ := util.ToFloat64(n2.Value)
+		return applyOp2Generic(op, f1, f2)
+	}
+	return applyOp2Generic(op, n1.Value.(int64), n2.Value.(int64))
+}
+
+func toOp(v any) (operator, error) {
+	if v, ok := v.(string); ok {
+		return operator(v), nil
+	}
+	return "", fmt.Errorf(`unsupported token type "%T"`, v)
+}
+
+func (op operator) hasOpenBracket() bool {
+	return strings.HasSuffix(string(op), "(") // it's used to support functions like "sum("
+}
+
+func (op operator) isComma() bool {
+	return op == ","
+}
+
+func (op operator) isCloseBracket() bool {
+	return op == ")"
+}
+
+type ExprError struct {
+	msg    string
+	tokens []any
+	err    error
+}
+
+func (err ExprError) Error() string {
+	sb := strings.Builder{}
+	sb.WriteString(err.msg)
+	sb.WriteString(" [ ")
+	for _, token := range err.tokens {
+		_, _ = fmt.Fprintf(&sb, `"%v" `, token)
+	}
+	sb.WriteString("]")
+	if err.err != nil {
+		sb.WriteString(": ")
+		sb.WriteString(err.err.Error())
+	}
+	return sb.String()
+}
+
+func (err ExprError) Unwrap() error {
+	return err.err
+}
+
+func (e *eval) applyOp() {
+	op := e.stackOp.pop()
+	if op == "not" {
+		num := e.stackNum.pop()
+		i, _ := util.ToInt64(num.Value)
+		e.stackNum.push(Num{truth(i == 0)})
+	} else if op.hasOpenBracket() || op.isCloseBracket() || op.isComma() {
+		panic(fmt.Sprintf("incomplete sub-expression with operator %q", op))
+	} else {
+		num2 := e.stackNum.pop()
+		num1 := e.stackNum.pop()
+		e.stackNum.push(applyOp2(op, num1, num2))
+	}
+}
+
+func (e *eval) exec(tokens ...any) (ret Num, err error) {
+	defer func() {
+		if r := recover(); r != nil {
+			rErr, ok := r.(error)
+			if !ok {
+				rErr = fmt.Errorf("%v", r)
+			}
+			err = ExprError{"invalid expression", tokens, rErr}
+		}
+	}()
+	for _, token := range tokens {
+		n, err := toNum(token)
+		if err == nil {
+			e.stackNum.push(n)
+			continue
+		}
+
+		op, err := toOp(token)
+		if err != nil {
+			return Num{}, ExprError{"invalid expression", tokens, err}
+		}
+
+		switch {
+		case op.hasOpenBracket():
+			e.stackOp.push(op)
+		case op.isCloseBracket(), op.isComma():
+			var stackTopOp operator
+			for len(e.stackOp.elems) > 0 {
+				stackTopOp = e.stackOp.peek()
+				if stackTopOp.hasOpenBracket() || stackTopOp.isComma() {
+					break
+				}
+				e.applyOp()
+			}
+			if op.isCloseBracket() {
+				nums := []Num{e.stackNum.pop()}
+				for !e.stackOp.peek().hasOpenBracket() {
+					stackTopOp = e.stackOp.pop()
+					if !stackTopOp.isComma() {
+						return Num{}, ExprError{"bracket doesn't match", tokens, nil}
+					}
+					nums = append(nums, e.stackNum.pop())
+				}
+				for i, j := 0, len(nums)-1; i < j; i, j = i+1, j-1 {
+					nums[i], nums[j] = nums[j], nums[i] // reverse nums slice, to get the right order for arguments
+				}
+				stackTopOp = e.stackOp.pop()
+				fn := string(stackTopOp[:len(stackTopOp)-1])
+				if fn == "" {
+					if len(nums) != 1 {
+						return Num{}, ExprError{"too many values in one bracket", tokens, nil}
+					}
+					e.stackNum.push(nums[0])
+				} else if f, ok := e.funcMap[fn]; ok {
+					e.stackNum.push(f(nums))
+				} else {
+					return Num{}, ExprError{"unknown function: " + fn, tokens, nil}
+				}
+			} else {
+				e.stackOp.push(op)
+			}
+		default:
+			for len(e.stackOp.elems) > 0 && len(e.stackNum.elems) > 0 {
+				stackTopOp := e.stackOp.peek()
+				if stackTopOp.hasOpenBracket() || stackTopOp.isComma() || precedence(stackTopOp, op) < 0 {
+					break
+				}
+				e.applyOp()
+			}
+			e.stackOp.push(op)
+		}
+	}
+	for len(e.stackOp.elems) > 0 && !e.stackOp.peek().isComma() {
+		e.applyOp()
+	}
+	if len(e.stackNum.elems) != 1 {
+		return Num{}, ExprError{fmt.Sprintf("expect 1 value as final result, but there are %d", len(e.stackNum.elems)), tokens, nil}
+	}
+	return e.stackNum.pop(), nil
+}
+
+func precedence(op1, op2 operator) int {
+	p1 := opPrecedence[string(op1)]
+	p2 := opPrecedence[string(op2)]
+	if p1 == 0 {
+		panic("unknown operator precedence: " + string(op1))
+	} else if p2 == 0 {
+		panic("unknown operator precedence: " + string(op2))
+	}
+	return p1 - p2
+}
+
+func castFloat64(nums []Num) bool {
+	hasFloat := false
+	for _, num := range nums {
+		if _, hasFloat = num.Value.(float64); hasFloat {
+			break
+		}
+	}
+	if hasFloat {
+		for i, num := range nums {
+			if _, ok := num.Value.(float64); !ok {
+				f, _ := util.ToFloat64(num.Value)
+				nums[i] = Num{f}
+			}
+		}
+	}
+	return hasFloat
+}
+
+func fnSum(nums []Num) Num {
+	if castFloat64(nums) {
+		var sum float64
+		for _, num := range nums {
+			sum += num.Value.(float64)
+		}
+		return Num{sum}
+	}
+	var sum int64
+	for _, num := range nums {
+		sum += num.Value.(int64)
+	}
+	return Num{sum}
+}
+
+// Expr evaluates the given expression tokens and returns the result.
+// It supports the following operators: +, -, *, /, and, or, not, ==, !=, >, >=, <, <=.
+// Non-zero values are treated as true, zero values are treated as false.
+// If no error occurs, the result is either an int64 or a float64.
+// If all numbers are integer, the result is an int64, otherwise if there is any float number, the result is a float64.
+func Expr(tokens ...any) (Num, error) {
+	e := newEval()
+	e.funcMap = map[string]func([]Num) Num{"sum": fnSum}
+	return e.exec(tokens...)
+}