1 files changed, 156 insertions, 0 deletions
diff --git a/src/expand.rs b/src/expand.rs
new file mode 100644
index 0000000..2bcbd06
--- /dev/null
+++ b/src/expand.rs
@@ -0,0 +1,156 @@
+use std::{collections::HashMap, mem::replace};
+
+use just_fmt::snake_case;
+
+use crate::Template;
+
+const IMPL_AREA_BEGIN: &str = "@@@ >>> ";
+const IMPL_AREA_END: &str = "@@@ <<<";
+
+const IMPL_BEGIN: &str = ">>>>>>>>>>";
+
+const PARAM_BEGIN: &str = "<<<";
+const PARAM_BEND: &str = ">>>";
+
+impl Template {
+    pub fn expand(mut self) -> Option<String> {
+        // Extract template text
+        let expanded = replace(&mut self.template_str, String::default());
+
+        let (expanded, impl_areas) = read_impl_areas(expanded)?;
+        let expanded = apply_impls(&self, expanded, impl_areas)?;
+        let expanded = apply_param(&self, expanded)?;
+        Some(expanded.trim().to_string())
+    }
+}
+
+/// Read all ImplAreas (HashMap<Name, Codes>)
+fn read_impl_areas(content: String) -> Option<(String, HashMap<String, String>)> {
+    let mut striped_content = String::new();
+    let mut impl_areas: HashMap<String, String> = HashMap::new();
+
+    let mut current_area_name = String::default();
+    let mut current_area_codes: Vec<String> = Vec::new();
+
+    for line in content.split("\n") {
+        let trimmed_line = line.trim();
+
+        // Implementation block end
+        if trimmed_line.starts_with(IMPL_AREA_END) {
+            // If the current ImplArea name length is less than 1, it means no block is being matched,
+            // so matching fails, exit early
+            if current_area_name.len() < 1 {
+                return None;
+            }
+
+            // Submit Impl Area
+            let name = replace(&mut current_area_name, String::default());
+            impl_areas.insert(name, current_area_codes.join("\n"));
+            current_area_codes.clear();
+            continue;
+        }
+
+        // Implementation block start
+        if trimmed_line.starts_with(IMPL_AREA_BEGIN) {
+            // If the current ImplArea name length is greater than 0, it means we are already inside a block,
+            // since nesting is not allowed, matching fails, exit early
+            if current_area_name.len() > 0 {
+                return None;
+            }
+
+            // Get a snake_case name
+            let snake_name = snake_case!(line.trim_start_matches(IMPL_AREA_BEGIN).trim());
+            current_area_name = snake_name;
+
+            // Continue to next line
+            continue;
+        }
+
+        // During implementation block
+        if current_area_name.len() > 0 {
+            // Add to current block code
+            current_area_codes.push(line.to_string());
+            continue;
+        } else {
+            // Add to remaining content
+            striped_content += "\n";
+            striped_content += line;
+        }
+    }
+
+    Some((striped_content, impl_areas))
+}
+
+/// Apply Template parameters to implementation block areas
+fn apply_impls(
+    template: &Template,
+    content: String,
+    impl_areas: HashMap<String, String>,
+) -> Option<String> {
+    let mut applied_content = String::new();
+
+    let mut impled_areas: HashMap<String, Vec<String>> = HashMap::new();
+    for (impl_area_name, impl_area_template) in impl_areas {
+        // Get user-provided parameters
+        let impl_items = template.impl_params.get(&impl_area_name);
+
+        // No parameters, return early
+        let Some(impl_items) = impl_items else {
+            impled_areas.insert(impl_area_name, Vec::new());
+            continue;
+        };
+
+        let mut impled_area_code_applied = Vec::new();
+
+        // Split items
+        for item in impl_items {
+            // Get base template
+            let mut template = impl_area_template.clone();
+
+            // Extract parameters
+            for (param_name, param_value) in item {
+                // Apply parameter
+                template = template.replace(
+                    &format!("{}{}{}", PARAM_BEGIN, param_name, PARAM_BEND),
+                    param_value,
+                );
+            }
+
+            // Add applied template
+            impled_area_code_applied.push(template);
+        }
+
+        impled_areas.insert(impl_area_name, impled_area_code_applied);
+    }
+
+    for line in content.split("\n") {
+        let trimmed_line = line.trim();
+
+        // Recognize implementation line
+        if trimmed_line.starts_with(IMPL_BEGIN) {
+            let impl_name = snake_case!(trimmed_line.trim_start_matches(IMPL_BEGIN).trim());
+
+            // Try to get implementation code block
+            let Some(impled_code) = impled_areas.get(&impl_name) else {
+                continue;
+            };
+
+            applied_content += "\n";
+            applied_content += impled_code.join("\n").as_str();
+        } else {
+            // Other content directly appended
+            applied_content += "\n";
+            applied_content += line;
+        }
+    }
+
+    Some(applied_content)
+}
+
+fn apply_param(template: &Template, content: String) -> Option<String> {
+    let mut content = content;
+    for (k, v) in template.params.iter() {
+        content = content.replace(&format!("{}{}{}", PARAM_BEGIN, k, PARAM_BEND), v);
+    }
+    Some(content)
+}