use anyhow::{anyhow, Result};
use bytes::Bytes;
use oci_spec::image::{Arch, Descriptor, ImageIndex, ImageManifest, MediaType, Os, ToDockerV2S2};
use reqwest::{Client, RequestBuilder, Response};
use tokio::{fs::File, io::AsyncWriteExt};
use url::Url;

const MANIFEST_PICKER_PLATFORM: Os = Os::Linux;
const MANIFEST_PICKER_ARCHITECTURE: Arch = Arch::Amd64;

pub struct RegistryClient {
    agent: Client,
    url: Url,
}

impl RegistryClient {
    pub fn new(url: Url) -> Result<RegistryClient> {
        Ok(RegistryClient {
            agent: Client::new(),
            url,
        })
    }

    async fn call(&mut self, req: RequestBuilder) -> Result<Response> {
        self.agent.execute(req.build()?).await.map_err(|x| x.into())
    }

    pub async fn get_blob(&mut self, name: &str, descriptor: &Descriptor) -> Result<Bytes> {
        let url = self
            .url
            .join(&format!("/v2/{}/blobs/{}", name, descriptor.digest()))?;
        let response = self.call(self.agent.get(url.as_str())).await?;
        Ok(response.bytes().await?)
    }

    pub async fn write_blob_to_file(
        &mut self,
        name: &str,
        descriptor: &Descriptor,
        mut dest: File,
    ) -> Result<u64> {
        let url = self
            .url
            .join(&format!("/v2/{}/blobs/{}", name, descriptor.digest()))?;
        let mut response = self.call(self.agent.get(url.as_str())).await?;
        let mut size: u64 = 0;
        while let Some(chunk) = response.chunk().await? {
            dest.write_all(&chunk).await?;
            size += chunk.len() as u64;
        }
        Ok(size)
    }

    async fn get_raw_manifest_with_digest(
        &mut self,
        name: &str,
        reference: &str,
    ) -> Result<(ImageManifest, String)> {
        let url = self
            .url
            .join(&format!("/v2/{}/manifests/{}", name, reference))?;
        let accept = format!(
            "{}, {}, {}, {}",
            MediaType::ImageManifest.to_docker_v2s2()?,
            MediaType::ImageManifest,
            MediaType::ImageIndex,
            MediaType::ImageIndex.to_docker_v2s2()?,
        );
        let response = self
            .call(self.agent.get(url.as_str()).header("Accept", &accept))
            .await?;
        let digest = response
            .headers()
            .get("Docker-Content-Digest")
            .ok_or_else(|| anyhow!("fetching manifest did not yield a content digest"))?
            .to_str()?
            .to_string();
        let manifest = serde_json::from_str(&response.text().await?)?;
        Ok((manifest, digest))
    }

    pub async fn get_manifest_with_digest(
        &mut self,
        name: &str,
        reference: &str,
    ) -> Result<(ImageManifest, String)> {
        let url = self
            .url
            .join(&format!("/v2/{}/manifests/{}", name, reference))?;
        let accept = format!(
            "{}, {}, {}, {}",
            MediaType::ImageManifest.to_docker_v2s2()?,
            MediaType::ImageManifest,
            MediaType::ImageIndex,
            MediaType::ImageIndex.to_docker_v2s2()?,
        );
        let response = self
            .call(self.agent.get(url.as_str()).header("Accept", &accept))
            .await?;
        let content_type = response
            .headers()
            .get("Content-Type")
            .ok_or_else(|| anyhow!("registry response did not have a Content-Type header"))?
            .to_str()?;
        if content_type == MediaType::ImageIndex.to_string()
            || content_type == MediaType::ImageIndex.to_docker_v2s2()?
        {
            let index = serde_json::from_str(&response.text().await?)?;
            let descriptor = self
                .pick_manifest(index)
                .ok_or_else(|| anyhow!("unable to pick manifest from index"))?;
            return self
                .get_raw_manifest_with_digest(name, descriptor.digest())
                .await;
        }
        let digest = response
            .headers()
            .get("Docker-Content-Digest")
            .ok_or_else(|| anyhow!("fetching manifest did not yield a content digest"))?
            .to_str()?
            .to_string();
        let manifest = serde_json::from_str(&response.text().await?)?;
        Ok((manifest, digest))
    }

    fn pick_manifest(&mut self, index: ImageIndex) -> Option<Descriptor> {
        for item in index.manifests() {
            if let Some(platform) = item.platform() {
                if *platform.os() == MANIFEST_PICKER_PLATFORM
                    && *platform.architecture() == MANIFEST_PICKER_ARCHITECTURE
                {
                    return Some(item.clone());
                }
            }
        }
        None
    }
}