Initial commit: perc v0.0.0 - percentage calculatorv0.0.0

Amp-Thread-ID: https://ampcode.com/threads/T-e4f4a959-8cc6-4ac0-b6fb-2779867e8b2a
Co-authored-by: Amp <amp@ampcode.com>

3 files changed, 351 insertions, 0 deletions

diff --git a/internal/calculator/calculator.go b/internal/calculator/calculator.go
new file mode 100644
index 0000000..ee1ff6f
--- /dev/null
+++ b/internal/calculator/calculator.go
@@ -0,0 +1,81 @@
+package calculator
+
+import (
+	"fmt"
+	"regexp"
+	"strconv"
+	"strings"
+)
+
+func Parse(input string) (string, error) {
+	input = strings.ToLower(strings.TrimSpace(input))
+	input = strings.ReplaceAll(input, "what is ", "")
+	input = strings.TrimSpace(input)
+
+	if result, ok := parseXPercentOfY(input); ok {
+		return result, nil
+	}
+
+	if result, ok := parseXIsWhatPercentOfY(input); ok {
+		return result, nil
+	}
+
+	if result, ok := parseXIsYPercentOfWhat(input); ok {
+		return result, nil
+	}
+
+	return "", fmt.Errorf("unable to parse input. See usage for examples")
+}
+
+func parseXPercentOfY(input string) (string, bool) {
+	re := regexp.MustCompile(`^(\d+(?:\.\d+)?)\s*%\s*(?:of\s+)?(\d+(?:\.\d+)?)$`)
+	matches := re.FindStringSubmatch(input)
+
+	if matches == nil {
+		return "", false
+	}
+
+	percent, _ := strconv.ParseFloat(matches[1], 64)
+	base, _ := strconv.ParseFloat(matches[2], 64)
+
+	result := (percent / 100.0) * base
+	return fmt.Sprintf("%.2f%% of %.2f = %.2f", percent, base, result), true
+}
+
+func parseXIsWhatPercentOfY(input string) (string, bool) {
+	re := regexp.MustCompile(`^(\d+(?:\.\d+)?)\s+is\s+what\s*%\s*(?:of\s+)?(\d+(?:\.\d+)?)$`)
+	matches := re.FindStringSubmatch(input)
+
+	if matches == nil {
+		return "", false
+	}
+
+	part, _ := strconv.ParseFloat(matches[1], 64)
+	whole, _ := strconv.ParseFloat(matches[2], 64)
+
+	if whole == 0 {
+		return "", false
+	}
+
+	percent := (part / whole) * 100.0
+	return fmt.Sprintf("%.2f is %.2f%% of %.2f", part, percent, whole), true
+}
+
+func parseXIsYPercentOfWhat(input string) (string, bool) {
+	re := regexp.MustCompile(`^(\d+(?:\.\d+)?)\s+is\s+(\d+(?:\.\d+)?)\s*%\s*(?:of\s+)?what$`)
+	matches := re.FindStringSubmatch(input)
+
+	if matches == nil {
+		return "", false
+	}
+
+	part, _ := strconv.ParseFloat(matches[1], 64)
+	percent, _ := strconv.ParseFloat(matches[2], 64)
+
+	if percent == 0 {
+		return "", false
+	}
+
+	whole := (part / percent) * 100.0
+	return fmt.Sprintf("%.2f is %.2f%% of %.2f", part, percent, whole), true
+}
diff --git a/internal/calculator/calculator_test.go b/internal/calculator/calculator_test.go
new file mode 100644
index 0000000..defbd13
--- /dev/null
+++ b/internal/calculator/calculator_test.go
@@ -0,0 +1,267 @@
+package calculator
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestParseXPercentOfY(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    string
+		expected string
+	}{
+		{
+			name:     "20% of 150",
+			input:    "20% of 150",
+			expected: "20.00% of 150.00 = 30.00",
+		},
+		{
+			name:     "what is 20% of 150",
+			input:    "what is 20% of 150",
+			expected: "20.00% of 150.00 = 30.00",
+		},
+		{
+			name:     "50% of 200",
+			input:    "50% of 200",
+			expected: "50.00% of 200.00 = 100.00",
+		},
+		{
+			name:     "decimal percent",
+			input:    "12.5% of 80",
+			expected: "12.50% of 80.00 = 10.00",
+		},
+		{
+			name:     "decimal base",
+			input:    "20% of 75.5",
+			expected: "20.00% of 75.50 = 15.10",
+		},
+		{
+			name:     "without 'of'",
+			input:    "25% 400",
+			expected: "25.00% of 400.00 = 100.00",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result, err := Parse(tt.input)
+			if err != nil {
+				t.Fatalf("Parse(%q) returned error: %v", tt.input, err)
+			}
+			if result != tt.expected {
+				t.Errorf("Parse(%q) = %q, expected %q", tt.input, result, tt.expected)
+			}
+		})
+	}
+}
+
+func TestParseXIsWhatPercentOfY(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    string
+		expected string
+	}{
+		{
+			name:     "30 is what % of 150",
+			input:    "30 is what % of 150",
+			expected: "30.00 is 20.00% of 150.00",
+		},
+		{
+			name:     "50 is what % of 200",
+			input:    "50 is what % of 200",
+			expected: "50.00 is 25.00% of 200.00",
+		},
+		{
+			name:     "decimal values",
+			input:    "12.5 is what % of 50",
+			expected: "12.50 is 25.00% of 50.00",
+		},
+		{
+			name:     "without spaces around %",
+			input:    "75 is what% of 300",
+			expected: "75.00 is 25.00% of 300.00",
+		},
+		{
+			name:     "without 'of'",
+			input:    "100 is what % 400",
+			expected: "100.00 is 25.00% of 400.00",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result, err := Parse(tt.input)
+			if err != nil {
+				t.Fatalf("Parse(%q) returned error: %v", tt.input, err)
+			}
+			if result != tt.expected {
+				t.Errorf("Parse(%q) = %q, expected %q", tt.input, result, tt.expected)
+			}
+		})
+	}
+}
+
+func TestParseXIsYPercentOfWhat(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    string
+		expected string
+	}{
+		{
+			name:     "30 is 20% of what",
+			input:    "30 is 20% of what",
+			expected: "30.00 is 20.00% of 150.00",
+		},
+		{
+			name:     "50 is 25% of what",
+			input:    "50 is 25% of what",
+			expected: "50.00 is 25.00% of 200.00",
+		},
+		{
+			name:     "decimal values",
+			input:    "15 is 30% of what",
+			expected: "15.00 is 30.00% of 50.00",
+		},
+		{
+			name:     "without spaces around %",
+			input:    "75 is 25% of what",
+			expected: "75.00 is 25.00% of 300.00",
+		},
+		{
+			name:     "without 'of'",
+			input:    "40 is 20% what",
+			expected: "40.00 is 20.00% of 200.00",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result, err := Parse(tt.input)
+			if err != nil {
+				t.Fatalf("Parse(%q) returned error: %v", tt.input, err)
+			}
+			if result != tt.expected {
+				t.Errorf("Parse(%q) = %q, expected %q", tt.input, result, tt.expected)
+			}
+		})
+	}
+}
+
+func TestParseErrors(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+	}{
+		{
+			name:  "invalid input",
+			input: "hello world",
+		},
+		{
+			name:  "incomplete input",
+			input: "20%",
+		},
+		{
+			name:  "missing numbers",
+			input: "% of",
+		},
+		{
+			name:  "random text",
+			input: "calculate percentage",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			_, err := Parse(tt.input)
+			if err == nil {
+				t.Errorf("Parse(%q) expected error, got nil", tt.input)
+			}
+		})
+	}
+}
+
+func TestParseCaseInsensitive(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+	}{
+		{
+			name:  "uppercase WHAT IS",
+			input: "WHAT IS 20% OF 150",
+		},
+		{
+			name:  "mixed case What Is",
+			input: "What Is 20% Of 150",
+		},
+		{
+			name:  "uppercase IS WHAT",
+			input: "30 IS WHAT % OF 150",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			_, err := Parse(tt.input)
+			if err != nil {
+				t.Errorf("Parse(%q) should be case-insensitive, got error: %v", tt.input, err)
+			}
+		})
+	}
+}
+
+func TestParseDivisionByZero(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+	}{
+		{
+			name:  "X is what % of 0",
+			input: "30 is what % of 0",
+		},
+		{
+			name:  "X is 0% of what",
+			input: "30 is 0% of what",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			_, err := Parse(tt.input)
+			if err == nil {
+				t.Errorf("Parse(%q) should handle division by zero, expected error", tt.input)
+			}
+		})
+	}
+}
+
+func TestParseWhitespace(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    string
+		expected string
+	}{
+		{
+			name:     "extra spaces",
+			input:    "  20%   of   150  ",
+			expected: "20.00% of 150.00 = 30.00",
+		},
+		{
+			name:     "tabs and spaces",
+			input:    "30  is  what  %  of  150",
+			expected: "30.00 is 20.00% of 150.00",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result, err := Parse(tt.input)
+			if err != nil {
+				t.Fatalf("Parse(%q) returned error: %v", tt.input, err)
+			}
+			if !strings.Contains(result, "of") {
+				t.Errorf("Parse(%q) should handle whitespace properly, got %q", tt.input, result)
+			}
+		})
+	}
+}
diff --git a/internal/version.go b/internal/version.go
new file mode 100644
index 0000000..3fd5dc6
--- /dev/null
+++ b/internal/version.go
@@ -0,0 +1,3 @@
+package internal
+
+const Version = "v0.0.0"