use crate::nix_hash;
use crate::output::Output;
use crate::write;
use serde::{Deserialize, Serialize};
use sha2::{Digest, Sha256};
use std::{collections::BTreeMap, fmt, fmt::Write, iter::FromIterator};
use tvix_store::nixbase32::NIXBASE32;
use tvix_store::nixpath::STORE_DIR;

#[derive(Serialize, Deserialize)]
pub struct Derivation {
    outputs: BTreeMap<String, Output>,
    input_sources: Vec<String>,
    input_derivations: BTreeMap<String, Vec<String>>,
    platform: String,
    builder: String,
    arguments: Vec<String>,
    environment: BTreeMap<String, String>,
}

impl Derivation {
    pub fn serialize(&self, writer: &mut impl Write) -> Result<(), fmt::Error> {
        writer.write_str(write::DERIVATION_PREFIX)?;
        writer.write_char(write::PAREN_OPEN)?;

        write::write_outputs(writer, &self.outputs)?;
        write::write_input_derivations(writer, &self.input_derivations)?;
        write::write_input_sources(writer, &self.input_sources)?;
        write::write_platfrom(writer, &self.platform)?;
        write::write_builder(writer, &self.builder)?;
        write::write_arguments(writer, &self.arguments)?;
        write::write_enviroment(writer, &self.environment)?;

        writer.write_char(write::PAREN_CLOSE)?;

        Ok(())
    }

    /// Returns the path of a Derivation struct.
    ///
    /// The path is calculated like this:
    ///   - Write the fingerprint of the Derivation to the sha256 hash function.
    ///     This is: `text:`,
    ///     all d.InputDerivations and d.InputSources (sorted, separated by a `:`),
    ///     a `:`,
    ///     a `sha256:`, followed by the sha256 digest of the ATerm representation (hex-encoded)
    ///     a `:`,
    ///     the storeDir, followed by a `:`,
    ///     the name of a derivation,
    ///     a `.drv`.
    ///   - Write the .drv A-Term contents to a hash function
    ///   - Take the digest, run hash.CompressHash(digest, 20) on it.
    ///   - Encode it with nixbase32
    ///   - Construct the full path $storeDir/$nixbase32EncodedCompressedHash-$name.drv
    pub fn calculate_derivation_path(&self, name: &str) -> String {
        let mut hasher = Sha256::new();

        // collect the list of paths from input_sources and input_derivations
        // into a sorted list, and join them by :
        hasher.update(write::TEXT_COLON);

        let concat_inputs: Vec<String> = {
            let mut inputs = self.input_sources.clone();
            let input_derivation_keys: Vec<String> =
                self.input_derivations.keys().cloned().collect();
            inputs.extend(input_derivation_keys);
            inputs.sort();
            inputs
        };

        for input in concat_inputs {
            hasher.update(input);
            hasher.update(write::COLON);
        }

        // calculate the sha256 hash of the ATerm representation, and represent
        // it as a hex-encoded string (prefixed with sha256:).
        hasher.update(write::SHA256_COLON);

        let digest = {
            let mut derivation_hasher = Sha256::new();
            derivation_hasher.update(self.to_string());
            derivation_hasher.finalize()
        };

        hasher.update(format!("{:x}", digest));
        hasher.update(write::COLON);
        hasher.update(STORE_DIR);
        hasher.update(write::COLON);

        hasher.update(name);
        hasher.update(write::DOT_FILE_EXT);

        let compressed = {
            let aterm_digest = Vec::from_iter(hasher.finalize());
            nix_hash::compress_hash(&aterm_digest, 20)
        };

        format!(
            "{}-{}{}",
            NIXBASE32.encode(&compressed),
            name,
            write::DOT_FILE_EXT
        )
    }
}

impl fmt::Display for Derivation {
    /// Formats the Derivation in ATerm representation.
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        self.serialize(f)
    }
}