use std::collections::BTreeSet;
use std::fs;
use std::path::{Path, PathBuf};

use serde::{Deserialize, Serialize};
use thiserror::Error;

use crate::{Capability, Digest, Os};

#[derive(Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Serialize, Deserialize)]
pub enum EnvironmentKind {
    Containerfile,
    Dockerfile,
    NixFlake,
}

#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
pub struct EnvironmentRequirements {
    pub os: Option<Os>,
    pub arch: Option<String>,
    pub capabilities: BTreeSet<Capability>,
}

impl EnvironmentRequirements {
    pub fn linux_container() -> Self {
        Self {
            os: Some(Os::Linux),
            arch: None,
            capabilities: BTreeSet::from([Capability::Containers, Capability::RootlessPodman]),
        }
    }

    pub fn windows_command_dev() -> Self {
        Self {
            os: Some(Os::Windows),
            arch: None,
            capabilities: BTreeSet::from([Capability::WindowsCommandDev]),
        }
    }

    pub fn unconstrained() -> Self {
        Self {
            os: None,
            arch: None,
            capabilities: BTreeSet::new(),
        }
    }
}

#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
pub struct EnvironmentResource {
    pub name: String,
    pub kind: EnvironmentKind,
    pub recipe_path: PathBuf,
    pub context_path: PathBuf,
    pub digest: Digest,
    pub requirements: EnvironmentRequirements,
}

#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
pub struct EnvironmentReference {
    pub name: String,
    pub byte_offset: usize,
}

#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
pub struct EnvironmentDiagnostic {
    pub reference: EnvironmentReference,
    pub message: String,
}

#[derive(Debug, Error)]
pub enum EnvironmentError {
    #[error("failed to read environment resources under {path}: {source}")]
    Read {
        path: PathBuf,
        #[source]
        source: std::io::Error,
    },
}

pub fn discover_environments(
    project_root: &Path,
) -> Result<Vec<EnvironmentResource>, EnvironmentError> {
    let envs_dir = project_root.join("envs");
    if !envs_dir.exists() {
        return Ok(Vec::new());
    }

    let mut resources = Vec::new();
    let entries = fs::read_dir(&envs_dir).map_err(|source| EnvironmentError::Read {
        path: envs_dir.clone(),
        source,
    })?;

    for entry in entries {
        let entry = entry.map_err(|source| EnvironmentError::Read {
            path: envs_dir.clone(),
            source,
        })?;
        let path = entry.path();
        if !path.is_dir() {
            continue;
        }
        let Some(name) = path.file_name().and_then(|name| name.to_str()) else {
            continue;
        };

        if let Some(resource) = discover_one(project_root, name, &path)? {
            resources.push(resource);
        }
    }

    resources.sort_by(|left, right| left.name.cmp(&right.name));
    Ok(resources)
}

pub fn diagnose_environment_references(
    source: &str,
    environments: &[EnvironmentResource],
) -> Vec<EnvironmentDiagnostic> {
    let known = environments
        .iter()
        .map(|environment| environment.name.as_str())
        .collect::<BTreeSet<_>>();

    find_env_macro_references(source)
        .into_iter()
        .filter(|reference| !known.contains(reference.name.as_str()))
        .map(|reference| EnvironmentDiagnostic {
            message: format!(
                "missing Clusterflux environment `{}`; expected envs/{}/Containerfile or envs/{}/Dockerfile",
                reference.name, reference.name, reference.name
            ),
            reference,
        })
        .collect()
}

fn discover_one(
    project_root: &Path,
    name: &str,
    env_dir: &Path,
) -> Result<Option<EnvironmentResource>, EnvironmentError> {
    let candidates = [
        ("Containerfile", EnvironmentKind::Containerfile),
        ("Dockerfile", EnvironmentKind::Dockerfile),
        ("flake.nix", EnvironmentKind::NixFlake),
    ];

    for (file_name, kind) in candidates {
        let recipe_path = env_dir.join(file_name);
        if !recipe_path.exists() {
            continue;
        }

        let recipe_bytes = fs::read(&recipe_path).map_err(|source| EnvironmentError::Read {
            path: recipe_path.clone(),
            source,
        })?;
        let relative_recipe = recipe_path
            .strip_prefix(project_root)
            .unwrap_or(&recipe_path)
            .to_string_lossy();
        let digest = Digest::from_parts([
            b"environment:v1".as_slice(),
            name.as_bytes(),
            format!("{kind:?}").as_bytes(),
            relative_recipe.as_bytes(),
            recipe_bytes.as_slice(),
        ]);
        let requirements = match kind {
            EnvironmentKind::Containerfile | EnvironmentKind::Dockerfile
                if name.eq_ignore_ascii_case("windows") =>
            {
                EnvironmentRequirements::windows_command_dev()
            }
            EnvironmentKind::Containerfile | EnvironmentKind::Dockerfile => {
                EnvironmentRequirements::linux_container()
            }
            EnvironmentKind::NixFlake => EnvironmentRequirements::unconstrained(),
        };

        return Ok(Some(EnvironmentResource {
            name: name.to_owned(),
            kind,
            recipe_path,
            context_path: env_dir.to_path_buf(),
            digest,
            requirements,
        }));
    }

    Ok(None)
}

fn find_env_macro_references(source: &str) -> Vec<EnvironmentReference> {
    let mut references = Vec::new();
    let mut cursor = 0;

    while let Some(index) = source[cursor..].find("env!(") {
        let start = cursor + index;
        let mut pos = start + "env!(".len();
        while source[pos..].starts_with(char::is_whitespace) {
            pos += source[pos..]
                .chars()
                .next()
                .map(char::len_utf8)
                .unwrap_or(1);
        }
        if !source[pos..].starts_with('"') {
            cursor = pos;
            continue;
        }
        pos += 1;
        let name_start = pos;
        while pos < source.len() && !source[pos..].starts_with('"') {
            pos += source[pos..]
                .chars()
                .next()
                .map(char::len_utf8)
                .unwrap_or(1);
        }
        if pos < source.len() {
            references.push(EnvironmentReference {
                name: source[name_start..pos].to_owned(),
                byte_offset: start,
            });
        }
        cursor = pos.saturating_add(1);
    }

    references
}

#[cfg(test)]
mod tests {
    use std::fs;

    use super::*;

    #[test]
    fn discovers_containerfile_environments_by_logical_name() {
        let temp = tempfile::tempdir().unwrap();
        let linux = temp.path().join("envs/linux");
        fs::create_dir_all(&linux).unwrap();
        fs::write(linux.join("Containerfile"), "FROM alpine\n").unwrap();

        let envs = discover_environments(temp.path()).unwrap();

        assert_eq!(envs.len(), 1);
        assert_eq!(envs[0].name, "linux");
        assert_eq!(envs[0].kind, EnvironmentKind::Containerfile);
        assert!(!envs[0].digest.as_str().is_empty());
    }

    #[test]
    fn missing_env_macro_reference_reports_clear_diagnostic() {
        let source = r#"fn main() { let _ = env!("windows"); }"#;
        let diagnostics = diagnose_environment_references(source, &[]);

        assert_eq!(diagnostics.len(), 1);
        assert!(diagnostics[0]
            .message
            .contains("envs/windows/Containerfile"));
    }

    #[test]
    fn windows_environment_name_uses_windows_development_requirements() {
        let temp = tempfile::tempdir().unwrap();
        let windows = temp.path().join("envs/windows");
        fs::create_dir_all(&windows).unwrap();
        fs::write(
            windows.join("Dockerfile"),
            "# user-attached windows dev contract\n",
        )
        .unwrap();

        let envs = discover_environments(temp.path()).unwrap();

        assert_eq!(envs[0].name, "windows");
        assert_eq!(envs[0].requirements.os, Some(Os::Windows));
        assert!(envs[0]
            .requirements
            .capabilities
            .contains(&Capability::WindowsCommandDev));
    }
}