//! Implements `builtins.derivation`, the core of what makes Nix build packages.
use nix_compat::derivation::{Derivation, Hash};
use nix_compat::{hash_placeholder, nixhash};
use std::cell::RefCell;
use std::collections::{btree_map, BTreeSet};
use std::rc::Rc;
use tvix_eval::builtin_macros::builtins;
use tvix_eval::generators::{self, GenCo};
use tvix_eval::{AddContext, CoercionKind, ErrorKind, NixAttrs, NixList, Value};

use crate::errors::Error;
use crate::known_paths::{KnownPaths, PathKind, PathName};

// Constants used for strangely named fields in derivation inputs.
const STRUCTURED_ATTRS: &str = "__structuredAttrs";
const IGNORE_NULLS: &str = "__ignoreNulls";

/// Helper function for populating the `drv.outputs` field from a
/// manually specified set of outputs, instead of the default
/// `outputs`.
async fn populate_outputs(
    co: &GenCo,
    drv: &mut Derivation,
    outputs: NixList,
) -> Result<(), ErrorKind> {
    // Remove the original default `out` output.
    drv.outputs.clear();

    for output in outputs {
        let output_name = generators::request_force(co, output)
            .await
            .to_str()
            .context("determining output name")?;

        if drv
            .outputs
            .insert(output_name.as_str().into(), Default::default())
            .is_some()
        {
            return Err(Error::DuplicateOutput(output_name.as_str().into()).into());
        }
    }

    Ok(())
}

/// Populate the inputs of a derivation from the build references
/// found when scanning the derivation's parameters.
fn populate_inputs<I: IntoIterator<Item = PathName>>(
    drv: &mut Derivation,
    known_paths: &KnownPaths,
    references: I,
) {
    for reference in references.into_iter() {
        let reference = &known_paths[&reference];
        match &reference.kind {
            PathKind::Plain => {
                drv.input_sources.insert(reference.path.clone());
            }

            PathKind::Output { name, derivation } => {
                match drv.input_derivations.entry(derivation.clone()) {
                    btree_map::Entry::Vacant(entry) => {
                        entry.insert(BTreeSet::from([name.clone()]));
                    }

                    btree_map::Entry::Occupied(mut entry) => {
                        entry.get_mut().insert(name.clone());
                    }
                }
            }

            PathKind::Derivation { output_names } => {
                match drv.input_derivations.entry(reference.path.clone()) {
                    btree_map::Entry::Vacant(entry) => {
                        entry.insert(output_names.clone());
                    }

                    btree_map::Entry::Occupied(mut entry) => {
                        entry.get_mut().extend(output_names.clone().into_iter());
                    }
                }
            }
        }
    }
}

/// Populate the output configuration of a derivation based on the
/// parameters passed to the call, flipping the required
/// parameters for a fixed-output derivation if necessary.
///
/// This function handles all possible combinations of the
/// parameters, including invalid ones.
///
/// Due to the support for SRI hashes, and how these are passed along to
/// builtins.derivation, outputHash and outputHashAlgo can have values which
/// need to be further modified before constructing the Derivation struct.
///
/// If outputHashAlgo is an SRI hash, outputHashAlgo must either be an empty
/// string, or the hash algorithm as specified in the (single) SRI (entry).
/// SRI strings with multiple hash algorithms are not supported.
///
/// In case an SRI string was used, the (single) fixed output is populated
/// with the hash algo name, and the hash digest is populated with the
/// (lowercase) hex encoding of the digest.
///
/// These values are only rewritten for the outputs, not what's passed to env.
fn populate_output_configuration(
    drv: &mut Derivation,
    hash: Option<String>,      // in nix: outputHash
    hash_algo: Option<String>, // in nix: outputHashAlgo
    hash_mode: Option<String>, // in nix: outputHashmode
) -> Result<(), ErrorKind> {
    // We only do something when `digest` and `algo` are `Some(_)``, and
    // there's an `out` output.
    if let (Some(hash), Some(algo), hash_mode) = (hash, hash_algo, hash_mode) {
        match drv.outputs.get_mut("out") {
            None => return Err(Error::ConflictingOutputTypes.into()),
            Some(out) => {
                // treat an empty algo as None
                let a = if algo.is_empty() {
                    None
                } else {
                    Some(algo.as_ref())
                };

                let output_hash = nixhash::from_str(&hash, a).map_err(Error::InvalidOutputHash)?;

                // construct the algo string. Depending on hashMode, we prepend a `r:`.
                let algo = match hash_mode.as_deref() {
                    None | Some("flat") => format!("{}", &output_hash.algo),
                    Some("recursive") => format!("r:{}", &output_hash.algo),
                    Some(other) => {
                        return Err(Error::InvalidOutputHashMode(other.to_string()).into())
                    }
                };

                out.hash = Some(Hash {
                    algo,
                    digest: data_encoding::HEXLOWER.encode(&output_hash.digest),
                });
            }
        }
    }

    Ok(())
}

/// Handles derivation parameters which are not just forwarded to
/// the environment. The return value indicates whether the
/// parameter should be included in the environment.
async fn handle_derivation_parameters(
    drv: &mut Derivation,
    co: &GenCo,
    name: &str,
    value: &Value,
    val_str: &str,
) -> Result<bool, ErrorKind> {
    match name {
        IGNORE_NULLS => return Ok(false),

        // Command line arguments to the builder.
        "args" => {
            let args = value.to_list()?;
            for arg in args {
                drv.arguments.push(strong_coerce_to_string(co, arg).await?);
            }

            // The arguments do not appear in the environment.
            return Ok(false);
        }

        // Explicitly specified drv outputs (instead of default [ "out" ])
        "outputs" => {
            let outputs = value
                .to_list()
                .context("looking at the `outputs` parameter of the derivation")?;

            drv.outputs.clear();
            populate_outputs(co, drv, outputs).await?;
        }

        "builder" => {
            drv.builder = val_str.to_string();
        }

        "system" => {
            drv.system = val_str.to_string();
        }

        _ => {}
    }

    Ok(true)
}

async fn strong_coerce_to_string(co: &GenCo, val: Value) -> Result<String, ErrorKind> {
    let val = generators::request_force(co, val).await;
    let val_str = generators::request_string_coerce(co, val, CoercionKind::Strong).await;

    Ok(val_str.as_str().to_string())
}

#[builtins(state = "Rc<RefCell<KnownPaths>>")]
mod derivation_builtins {
    use super::*;
    use tvix_eval::generators::Gen;

    #[builtin("placeholder")]
    async fn builtin_placeholder(co: GenCo, input: Value) -> Result<Value, ErrorKind> {
        let placeholder = hash_placeholder(
            input
                .to_str()
                .context("looking at output name in builtins.placeholder")?
                .as_str(),
        );

        Ok(placeholder.into())
    }

    /// Strictly construct a Nix derivation from the supplied arguments.
    ///
    /// This is considered an internal function, users usually want to
    /// use the higher-level `builtins.derivation` instead.
    #[builtin("derivationStrict")]
    async fn builtin_derivation_strict(
        state: Rc<RefCell<KnownPaths>>,
        co: GenCo,
        input: Value,
    ) -> Result<Value, ErrorKind> {
        let input = input.to_attrs()?;
        let name = generators::request_force(&co, input.select_required("name")?.clone())
            .await
            .to_str()
            .context("determining derivation name")?;

        // Check whether attributes should be passed as a JSON file.
        // TODO: the JSON serialisation has to happen here.
        if let Some(sa) = input.select(STRUCTURED_ATTRS) {
            if generators::request_force(&co, sa.clone()).await.as_bool()? {
                return Err(ErrorKind::NotImplemented(STRUCTURED_ATTRS));
            }
        }

        // Check whether null attributes should be ignored or passed through.
        let ignore_nulls = match input.select(IGNORE_NULLS) {
            Some(b) => generators::request_force(&co, b.clone()).await.as_bool()?,
            None => false,
        };

        let mut drv = Derivation::default();
        drv.outputs.insert("out".to_string(), Default::default());

        // Configure fixed-output derivations if required.

        async fn select_string(
            co: &GenCo,
            attrs: &NixAttrs,
            key: &str,
        ) -> Result<Option<String>, ErrorKind> {
            if let Some(attr) = attrs.select(key) {
                return Ok(Some(strong_coerce_to_string(co, attr.clone()).await?));
            }

            Ok(None)
        }

        populate_output_configuration(
            &mut drv,
            select_string(&co, &input, "outputHash")
                .await
                .context("evaluating the `outputHash` parameter")?,
            select_string(&co, &input, "outputHashAlgo")
                .await
                .context("evaluating the `outputHashAlgo` parameter")?,
            select_string(&co, &input, "outputHashMode")
                .await
                .context("evaluating the `outputHashMode` parameter")?,
        )?;

        for (name, value) in input.into_iter_sorted() {
            let value = generators::request_force(&co, value).await;
            if ignore_nulls && matches!(value, Value::Null) {
                continue;
            }

            let val_str = strong_coerce_to_string(&co, value.clone()).await?;

            // handle_derivation_parameters tells us whether the
            // argument should be added to the environment; continue
            // to the next one otherwise
            if !handle_derivation_parameters(&mut drv, &co, name.as_str(), &value, &val_str).await?
            {
                continue;
            }

            // Most of these are also added to the builder's environment in "raw" form.
            if drv
                .environment
                .insert(name.as_str().to_string(), val_str)
                .is_some()
            {
                return Err(Error::DuplicateEnvVar(name.as_str().to_string()).into());
            }
        }

        // Scan references in relevant attributes to detect any build-references.
        let references = {
            let state = state.borrow();
            if state.is_empty() {
                // skip reference scanning, create an empty result
                Default::default()
            } else {
                let mut refscan = state.reference_scanner();
                drv.arguments.iter().for_each(|s| refscan.scan_str(s));
                drv.environment.values().for_each(|s| refscan.scan_str(s));
                refscan.scan_str(&drv.builder);
                refscan.finalise()
            }
        };

        // Each output name needs to exist in the environment, at this
        // point initialised as an empty string because that is the
        // way of Golang ;)
        for output in drv.outputs.keys() {
            if drv
                .environment
                .insert(output.to_string(), String::new())
                .is_some()
            {
                return Err(Error::ShadowedOutput(output.to_string()).into());
            }
        }

        let mut known_paths = state.borrow_mut();
        populate_inputs(&mut drv, &known_paths, references);

        // At this point, derivation fields are fully populated from
        // eval data structures.
        drv.validate(false).map_err(Error::InvalidDerivation)?;

        let tmp_replacement_str =
            drv.calculate_drv_replacement_str(|drv| known_paths.get_replacement_string(drv));

        drv.calculate_output_paths(&name, &tmp_replacement_str)
            .map_err(Error::InvalidDerivation)?;

        let actual_replacement_str =
            drv.calculate_drv_replacement_str(|drv| known_paths.get_replacement_string(drv));

        let derivation_path = drv
            .calculate_derivation_path(&name)
            .map_err(Error::InvalidDerivation)?;

        known_paths
            .add_replacement_string(derivation_path.to_absolute_path(), &actual_replacement_str);

        // mark all the new paths as known
        let output_names: Vec<String> = drv.outputs.keys().map(Clone::clone).collect();
        known_paths.drv(derivation_path.to_absolute_path(), &output_names);

        for (output_name, output) in &drv.outputs {
            known_paths.output(
                &output.path,
                output_name,
                derivation_path.to_absolute_path(),
            );
        }

        let mut new_attrs: Vec<(String, String)> = drv
            .outputs
            .into_iter()
            .map(|(name, output)| (name, output.path))
            .collect();

        new_attrs.push(("drvPath".to_string(), derivation_path.to_absolute_path()));

        Ok(Value::Attrs(Box::new(NixAttrs::from_iter(
            new_attrs.into_iter(),
        ))))
    }

    #[builtin("toFile")]
    async fn builtin_to_file(
        state: Rc<RefCell<KnownPaths>>,
        co: GenCo,
        name: Value,
        content: Value,
    ) -> Result<Value, ErrorKind> {
        let name = name
            .to_str()
            .context("evaluating the `name` parameter of builtins.toFile")?;
        let content = content
            .to_str()
            .context("evaluating the `content` parameter of builtins.toFile")?;

        let mut refscan = state.borrow().reference_scanner();
        refscan.scan_str(content.as_str());
        let refs = {
            let paths = state.borrow();
            refscan
                .finalise()
                .into_iter()
                .map(|path| paths[&path].path.to_string())
                .collect::<Vec<_>>()
        };

        // TODO: fail on derivation references (only "plain" is allowed here)

        let path =
            nix_compat::derivation::path_with_references(name.as_str(), content.as_str(), refs)
                .map_err(Error::InvalidDerivation)?
                .to_absolute_path();

        state.borrow_mut().plain(&path);

        // TODO: actually persist the file in the store at that path ...

        Ok(Value::String(path.into()))
    }
}

pub use derivation_builtins::builtins as derivation_builtins;

#[cfg(test)]
mod tests {
    use super::*;
    use tvix_eval::observer::NoOpObserver;

    // TODO: These tests are commented out because we do not have
    // scaffolding to drive generators during testing at the moment.

    // static mut OBSERVER: NoOpObserver = NoOpObserver {};

    // // Creates a fake VM for tests, which can *not* actually be
    // // used to force (most) values but can satisfy the type
    // // parameter.
    // fn fake_vm() -> VM<'static> {
    //     // safe because accessing the observer doesn't actually do anything
    //     unsafe {
    //         VM::new(
    //             Default::default(),
    //             Box::new(tvix_eval::DummyIO),
    //             &mut OBSERVER,
    //             Default::default(),
    //             todo!(),
    //         )
    //     }
    // }

    // #[test]
    // fn populate_outputs_ok() {
    //     let mut vm = fake_vm();
    //     let mut drv = Derivation::default();
    //     drv.outputs.insert("out".to_string(), Default::default());

    //     let outputs = NixList::construct(
    //         2,
    //         vec![Value::String("foo".into()), Value::String("bar".into())],
    //     );

    //     populate_outputs(&mut vm, &mut drv, outputs).expect("populate_outputs should succeed");

    //     assert_eq!(drv.outputs.len(), 2);
    //     assert!(drv.outputs.contains_key("bar"));
    //     assert!(drv.outputs.contains_key("foo"));
    // }

    // #[test]
    // fn populate_outputs_duplicate() {
    //     let mut vm = fake_vm();
    //     let mut drv = Derivation::default();
    //     drv.outputs.insert("out".to_string(), Default::default());

    //     let outputs = NixList::construct(
    //         2,
    //         vec![Value::String("foo".into()), Value::String("foo".into())],
    //     );

    //     populate_outputs(&mut vm, &mut drv, outputs)
    //         .expect_err("supplying duplicate outputs should fail");
    // }

    // #[test]
    // fn populate_inputs_empty() {
    //     let mut drv = Derivation::default();
    //     let paths = KnownPaths::default();
    //     let inputs = vec![];

    //     populate_inputs(&mut drv, &paths, inputs);

    //     assert!(drv.input_sources.is_empty());
    //     assert!(drv.input_derivations.is_empty());
    // }

    // #[test]
    // fn populate_inputs_all() {
    //     let mut drv = Derivation::default();

    //     let mut paths = KnownPaths::default();
    //     paths.plain("/nix/store/fn7zvafq26f0c8b17brs7s95s10ibfzs-foo");
    //     paths.drv(
    //         "/nix/store/aqffiyqx602lbam7n1zsaz3yrh6v08pc-bar.drv",
    //         &["out"],
    //     );
    //     paths.output(
    //         "/nix/store/zvpskvjwi72fjxg0vzq822sfvq20mq4l-bar",
    //         "out",
    //         "/nix/store/aqffiyqx602lbam7n1zsaz3yrh6v08pc-bar.drv",
    //     );

    //     let inputs = vec![
    //         "/nix/store/fn7zvafq26f0c8b17brs7s95s10ibfzs-foo".into(),
    //         "/nix/store/aqffiyqx602lbam7n1zsaz3yrh6v08pc-bar.drv".into(),
    //         "/nix/store/zvpskvjwi72fjxg0vzq822sfvq20mq4l-bar".into(),
    //     ];

    //     populate_inputs(&mut drv, &paths, inputs);

    //     assert_eq!(drv.input_sources.len(), 1);
    //     assert!(drv
    //         .input_sources
    //         .contains("/nix/store/fn7zvafq26f0c8b17brs7s95s10ibfzs-foo"));

    //     assert_eq!(drv.input_derivations.len(), 1);
    //     assert!(drv
    //         .input_derivations
    //         .contains_key("/nix/store/aqffiyqx602lbam7n1zsaz3yrh6v08pc-bar.drv"));
    // }

    // #[test]
    // fn populate_output_config_std() {
    //     let mut drv = Derivation::default();

    //     populate_output_configuration(&mut drv, None, None, None)
    //         .expect("populate_output_configuration() should succeed");

    //     assert_eq!(drv, Derivation::default(), "derivation should be unchanged");
    // }

    // #[test]
    // fn populate_output_config_fod() {
    //     let mut drv = Derivation::default();
    //     drv.outputs.insert("out".to_string(), Default::default());

    //     populate_output_configuration(
    //         &mut drv,
    //         Some("0000000000000000000000000000000000000000000000000000000000000000".into()),
    //         Some("sha256".into()),
    //         None,
    //     )
    //     .expect("populate_output_configuration() should succeed");

    //     let expected = Hash {
    //         algo: "sha256".into(),
    //         digest: "0000000000000000000000000000000000000000000000000000000000000000".into(),
    //     };

    //     assert_eq!(drv.outputs["out"].hash, Some(expected));
    // }

    // #[test]
    // fn populate_output_config_fod_recursive() {
    //     let mut drv = Derivation::default();
    //     drv.outputs.insert("out".to_string(), Default::default());

    //     populate_output_configuration(
    //         &mut drv,
    //         Some("0000000000000000000000000000000000000000000000000000000000000000".into()),
    //         Some("sha256".into()),
    //         Some("recursive".into()),
    //     )
    //     .expect("populate_output_configuration() should succeed");

    //     let expected = Hash {
    //         algo: "r:sha256".into(),
    //         digest: "0000000000000000000000000000000000000000000000000000000000000000".into(),
    //     };

    //     assert_eq!(drv.outputs["out"].hash, Some(expected));
    // }

    // #[test]
    // /// hash_algo set to sha256, but SRI hash passed
    // fn populate_output_config_flat_sri_sha256() {
    //     let mut drv = Derivation::default();
    //     drv.outputs.insert("out".to_string(), Default::default());

    //     populate_output_configuration(
    //         &mut drv,
    //         Some("sha256-swapHA/ZO8QoDPwumMt6s5gf91oYe+oyk4EfRSyJqMg=".into()),
    //         Some("sha256".into()),
    //         Some("flat".into()),
    //     )
    //     .expect("populate_output_configuration() should succeed");

    //     let expected = Hash {
    //         algo: "sha256".into(),
    //         digest: "b306a91c0fd93bc4280cfc2e98cb7ab3981ff75a187bea3293811f452c89a8c8".into(), // lower hex
    //     };

    //     assert_eq!(drv.outputs["out"].hash, Some(expected));
    // }

    // #[test]
    // /// hash_algo set to empty string, SRI hash passed
    // fn populate_output_config_flat_sri() {
    //     let mut drv = Derivation::default();
    //     drv.outputs.insert("out".to_string(), Default::default());

    //     populate_output_configuration(
    //         &mut drv,
    //         Some("sha256-s6JN6XqP28g1uYMxaVAQMLiXcDG8tUs7OsE3QPhGqzA=".into()),
    //         Some("".into()),
    //         Some("flat".into()),
    //     )
    //     .expect("populate_output_configuration() should succeed");

    //     let expected = Hash {
    //         algo: "sha256".into(),
    //         digest: "b3a24de97a8fdbc835b9833169501030b8977031bcb54b3b3ac13740f846ab30".into(), // lower hex
    //     };

    //     assert_eq!(drv.outputs["out"].hash, Some(expected));
    // }

    // #[test]
    // fn handle_outputs_parameter() {
    //     let mut vm = fake_vm();
    //     let mut drv = Derivation::default();
    //     drv.outputs.insert("out".to_string(), Default::default());

    //     let outputs = Value::List(NixList::construct(
    //         2,
    //         vec![Value::String("foo".into()), Value::String("bar".into())],
    //     ));
    //     let outputs_str = outputs
    //         .coerce_to_string(CoercionKind::Strong, &mut vm)
    //         .unwrap();

    //     handle_derivation_parameters(&mut drv, &mut vm, "outputs", &outputs, outputs_str.as_str())
    //         .expect("handling 'outputs' parameter should succeed");

    //     assert_eq!(drv.outputs.len(), 2);
    //     assert!(drv.outputs.contains_key("bar"));
    //     assert!(drv.outputs.contains_key("foo"));
    // }

    // #[test]
    // fn handle_args_parameter() {
    //     let mut vm = fake_vm();
    //     let mut drv = Derivation::default();

    //     let args = Value::List(NixList::construct(
    //         3,
    //         vec![
    //             Value::String("--foo".into()),
    //             Value::String("42".into()),
    //             Value::String("--bar".into()),
    //         ],
    //     ));

    //     let args_str = args
    //         .coerce_to_string(CoercionKind::Strong, &mut vm)
    //         .unwrap();

    //     handle_derivation_parameters(&mut drv, &mut vm, "args", &args, args_str.as_str())
    //         .expect("handling 'args' parameter should succeed");

    //     assert_eq!(
    //         drv.arguments,
    //         vec!["--foo".to_string(), "42".to_string(), "--bar".to_string()]
    //     );
    // }

    #[test]
    fn builtins_placeholder_hashes() {
        assert_eq!(
            hash_placeholder("out").as_str(),
            "/1rz4g4znpzjwh1xymhjpm42vipw92pr73vdgl6xs1hycac8kf2n9"
        );

        assert_eq!(
            hash_placeholder("").as_str(),
            "/171rf4jhx57xqz3p7swniwkig249cif71pa08p80mgaf0mqz5bmr"
        );
    }
}