feat: add Citation.cff

CITATION.cff

@@ -0,0 +1,34 @@
+cff-version: 1.2.0
+message: "If you use ptfkit in your research, please cite it using these metadata."
+title: "ptfkit: Pedotransfer functions for estimating soil hydraulic properties"
+type: software
+abstract: >-
+  ptfkit is a specification-driven collection of pedotransfer functions for
+  estimating soil hydraulic properties through consistent Python, Rust, C,
+  and C++ interfaces.
+authors:
+  - family-names: Fomin
+    given-names: Dmitry
+    email: "fomin_ds@esoil.ru"
+    orcid: "https://orcid.org/0000-0003-3733-0284"
+  - family-names: Shumilin
+    given-names: Petr
+    email: "shumpet03@yandex.ru"
+  - family-names: Tolstygin
+    given-names: Kirill
+    email: "tolstygin_kd@esoil.ru"
+    orcid: "https://orcid.org/0009-0005-1395-3745"
+  - family-names: Tsymbarovich
+    given-names: Petr
+    email: "tpr@esoil.ru"
+    orcid: "https://orcid.org/0000-0001-8591-2612"
+version: 0.2.0
+date-released: "2026-08-20"
+license: MIT
+repository-code: "https://github.com/AgroDT/ptfkit"
+url: "https://agrodt.github.io/ptfkit/"
+keywords:
+  - pedotransfer functions
+  - soil hydraulic properties
+  - soil science
+  - scientific software

README.md

@@ -98,20 +98,6 @@ specification must preserve.
 
 ## Citation
 
-### APA
-
-```text
-AgroDT lab (2025). ptfkit repository [Computer software]. https://github.com/AgroDT/ptfkit
-```
-
-### BibTeX
-
-```bibtex
-@misc{ptfkit,
-  author       = {AgroDT lab},
-  title        = {ptfkit repository},
-  year         = {2025},
-  howpublished = {\url{https://github.com/AgroDT/ptfkit}},
-  url          = {https://github.com/AgroDT/ptfkit}
-}
-```
+If you use ptfkit in research, cite the software using the metadata in
+[`CITATION.cff`](./CITATION.cff). On GitHub, select **Cite this repository** in
+the repository sidebar to export the citation in APA or BibTeX format.

codegen/src/version.rs

@@ -5,10 +5,12 @@ use anyhow::{Context, Result, bail};
 const RUST_MANIFEST: &str = "targets/ptfkit-rs/Cargo.toml";
 const PYTHON_VERSION: &str = "targets/ptfkit-py/src/ptfkit/_version.py";
 const NATIVE_VERSION: &str = "targets/ptfkit-native/cmake/ptfkitVersion.cmake";
+const CITATION_FILE: &str = "CITATION.cff";
 
 pub(crate) fn run(root: &Path, version: &str) -> Result<()> {
     validate(version)?;
     update_rust_manifest(root, version)?;
+    update_citation_file(root, version)?;
     fs::write(
         root.join(PYTHON_VERSION),
         format!("# @generated by ptfkit-codegen; do not edit.\n__version__ = '{version}'\n"),
@@ -63,3 +65,59 @@ fn update_rust_manifest(root: &Path, version: &str) -> Result<()> {
     fs::write(path, output).with_context(|| format!("writing {RUST_MANIFEST}"))?;
     Ok(())
 }
+
+fn update_citation_file(root: &Path, version: &str) -> Result<()> {
+    let path = root.join(CITATION_FILE);
+    let citation = fs::read_to_string(&path).with_context(|| format!("reading {CITATION_FILE}"))?;
+    let output = replace_citation_version(&citation, version)?;
+
+    fs::write(path, output).with_context(|| format!("writing {CITATION_FILE}"))?;
+    Ok(())
+}
+
+fn replace_citation_version(citation: &str, version: &str) -> Result<String> {
+    let mut output = String::with_capacity(citation.len());
+    let mut updated = false;
+
+    for line in citation.lines() {
+        if line.starts_with("version: ") {
+            output.push_str(&format!("version: {version}\n"));
+            updated = true;
+        } else {
+            output.push_str(line);
+            output.push('\n');
+        }
+    }
+
+    if !updated {
+        bail!("missing version in {CITATION_FILE}")
+    }
+
+    Ok(output)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::replace_citation_version;
+
+    #[test]
+    fn replaces_top_level_citation_version() {
+        let citation = "cff-version: 1.2.0\ntitle: ptfkit\nversion: 0.2.0\n";
+
+        let updated = replace_citation_version(citation, "0.3.0").unwrap();
+
+        assert_eq!(
+            updated,
+            "cff-version: 1.2.0\ntitle: ptfkit\nversion: 0.3.0\n"
+        );
+    }
+
+    #[test]
+    fn rejects_citation_without_version() {
+        let citation = "cff-version: 1.2.0\ntitle: ptfkit\n";
+
+        let error = replace_citation_version(citation, "0.3.0").unwrap_err();
+
+        assert_eq!(error.to_string(), "missing version in CITATION.cff");
+    }
+}