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

use serde::{Deserialize, Serialize};
use syn::{punctuated::Punctuated, Expr, Item, Lit, Meta, Token};
use thiserror::Error;

use crate::{discover_environments, environment::EnvironmentError, EnvironmentResource};

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

#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
pub struct ProjectModel {
    pub root: PathBuf,
    pub environments: Vec<EnvironmentResource>,
    pub entrypoints: BTreeMap<String, Entrypoint>,
    pub default_entrypoint: String,
    pub required_config_file: Option<PathBuf>,
}

#[derive(Clone, Debug, Error, PartialEq, Eq)]
pub enum ProjectModelError {
    #[error("environment discovery failed: {0}")]
    Environment(String),
    #[error("Disasmer entrypoint discovery failed: {0}")]
    EntrypointDiscovery(String),
    #[error(
        "no Disasmer entrypoint is declared; add `#[disasmer::main]` to a function under src/"
    )]
    NoEntrypoints,
    #[error("unknown Disasmer entrypoint `{name}`; available entrypoints: {available:?}")]
    UnknownEntrypoint {
        name: String,
        available: Vec<String>,
    },
}

impl ProjectModel {
    pub fn discover_without_config(root: &Path) -> Result<Self, ProjectModelError> {
        let environments = discover_environments(root).map_err(|err| {
            ProjectModelError::Environment(match err {
                EnvironmentError::Read { path, source } => {
                    format!("failed to read {}: {source}", path.display())
                }
            })
        })?;
        let entrypoints = discover_entrypoints(root)?;
        let default_entrypoint = if entrypoints.contains_key("build") {
            "build".to_owned()
        } else {
            entrypoints.keys().next().cloned().unwrap_or_default()
        };
        Ok(Self {
            root: root.to_path_buf(),
            environments,
            entrypoints,
            default_entrypoint,
            required_config_file: None,
        })
    }

    pub fn select_entrypoint(&self, name: Option<&str>) -> Result<&Entrypoint, ProjectModelError> {
        if self.entrypoints.is_empty() {
            return Err(ProjectModelError::NoEntrypoints);
        }
        let name = name.unwrap_or(&self.default_entrypoint);
        self.entrypoints
            .get(name)
            .ok_or_else(|| ProjectModelError::UnknownEntrypoint {
                name: name.to_owned(),
                available: self.entrypoints.keys().cloned().collect(),
            })
    }
}

fn discover_entrypoints(root: &Path) -> Result<BTreeMap<String, Entrypoint>, ProjectModelError> {
    let source_root = root.join("src");
    if !source_root.is_dir() {
        return Ok(BTreeMap::new());
    }

    let mut source_files = Vec::new();
    collect_rust_sources(&source_root, &mut source_files)?;
    source_files.sort();

    let mut entrypoints = BTreeMap::new();
    for path in source_files {
        let source = fs::read_to_string(&path).map_err(|error| {
            ProjectModelError::EntrypointDiscovery(format!(
                "failed to read {}: {error}",
                path.display()
            ))
        })?;
        let syntax = syn::parse_file(&source).map_err(|error| {
            ProjectModelError::EntrypointDiscovery(format!(
                "failed to parse {}: {error}",
                path.display()
            ))
        })?;
        collect_entrypoint_items(&syntax.items, &path, &mut entrypoints)?;
    }
    Ok(entrypoints)
}

fn collect_rust_sources(
    directory: &Path,
    files: &mut Vec<PathBuf>,
) -> Result<(), ProjectModelError> {
    let entries = fs::read_dir(directory).map_err(|error| {
        ProjectModelError::EntrypointDiscovery(format!(
            "failed to read {}: {error}",
            directory.display()
        ))
    })?;
    for entry in entries {
        let entry = entry.map_err(|error| {
            ProjectModelError::EntrypointDiscovery(format!(
                "failed to inspect {}: {error}",
                directory.display()
            ))
        })?;
        let path = entry.path();
        let file_type = entry.file_type().map_err(|error| {
            ProjectModelError::EntrypointDiscovery(format!(
                "failed to inspect {}: {error}",
                path.display()
            ))
        })?;
        if file_type.is_dir() {
            collect_rust_sources(&path, files)?;
        } else if file_type.is_file() && path.extension().is_some_and(|ext| ext == "rs") {
            files.push(path);
        }
    }
    Ok(())
}

fn collect_entrypoint_items(
    items: &[Item],
    path: &Path,
    entrypoints: &mut BTreeMap<String, Entrypoint>,
) -> Result<(), ProjectModelError> {
    for item in items {
        match item {
            Item::Fn(function) => {
                let Some(attribute) = function.attrs.iter().find(|attribute| {
                    let segments = attribute
                        .path()
                        .segments
                        .iter()
                        .map(|segment| segment.ident.to_string())
                        .collect::<Vec<_>>();
                    segments.as_slice() == ["disasmer", "main"]
                }) else {
                    continue;
                };
                let function_name = function.sig.ident.to_string();
                let default_name = function_name
                    .strip_suffix("_main")
                    .unwrap_or(&function_name);
                let name = entrypoint_name(attribute, default_name);
                let entrypoint = Entrypoint {
                    name: name.clone(),
                    function: function_name,
                };
                if let Some(existing) = entrypoints.insert(name.clone(), entrypoint) {
                    return Err(ProjectModelError::EntrypointDiscovery(format!(
                        "duplicate entrypoint `{name}` in {}; it was already declared by `{}`",
                        path.display(),
                        existing.function
                    )));
                }
            }
            Item::Mod(module) => {
                if let Some((_, nested)) = &module.content {
                    collect_entrypoint_items(nested, path, entrypoints)?;
                }
            }
            _ => {}
        }
    }
    Ok(())
}

fn entrypoint_name(attribute: &syn::Attribute, default: &str) -> String {
    let Meta::List(_) = &attribute.meta else {
        return default.to_owned();
    };
    let Ok(arguments) = attribute.parse_args_with(Punctuated::<Meta, Token![,]>::parse_terminated)
    else {
        return default.to_owned();
    };
    arguments
        .into_iter()
        .find_map(|meta| {
            let Meta::NameValue(name_value) = meta else {
                return None;
            };
            if !name_value.path.is_ident("name") {
                return None;
            }
            let Expr::Lit(expression) = name_value.value else {
                return None;
            };
            let Lit::Str(value) = expression.lit else {
                return None;
            };
            Some(value.value())
        })
        .unwrap_or_else(|| default.to_owned())
}

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

    use super::*;

    #[test]
    fn project_works_without_hand_written_configuration_file() {
        let temp = tempfile::tempdir().unwrap();
        fs::create_dir_all(temp.path().join("envs/linux")).unwrap();
        fs::create_dir_all(temp.path().join("src")).unwrap();
        fs::write(
            temp.path().join("envs/linux/Containerfile"),
            "FROM alpine\n",
        )
        .unwrap();
        fs::write(
            temp.path().join("src/main.rs"),
            "#[disasmer::main]\npub fn build_main() {}\n",
        )
        .unwrap();

        let model = ProjectModel::discover_without_config(temp.path()).unwrap();

        assert_eq!(model.required_config_file, None);
        assert_eq!(model.environments[0].name, "linux");
        assert_eq!(model.select_entrypoint(None).unwrap().name, "build");
    }

    #[test]
    fn project_can_define_multiple_default_entrypoints() {
        let temp = tempfile::tempdir().unwrap();
        fs::create_dir_all(temp.path().join("src/nested")).unwrap();
        fs::write(
            temp.path().join("src/lib.rs"),
            "#[disasmer::main(name = \"check\")]\npub fn test_main() {}\n",
        )
        .unwrap();
        fs::write(
            temp.path().join("src/nested/release.rs"),
            "#[disasmer::main]\npub fn release_main() {}\n",
        )
        .unwrap();
        let model = ProjectModel::discover_without_config(temp.path()).unwrap();

        assert_eq!(
            model.select_entrypoint(Some("check")).unwrap().function,
            "test_main"
        );
        assert_eq!(
            model.select_entrypoint(Some("release")).unwrap().function,
            "release_main"
        );
    }

    #[test]
    fn unknown_entrypoint_lists_available_choices() {
        let temp = tempfile::tempdir().unwrap();
        fs::create_dir_all(temp.path().join("src")).unwrap();
        fs::write(
            temp.path().join("src/main.rs"),
            "#[disasmer::main]\npub fn build_main() {}\n",
        )
        .unwrap();
        let model = ProjectModel::discover_without_config(temp.path()).unwrap();
        let error = model.select_entrypoint(Some("deploy")).unwrap_err();

        assert!(matches!(error, ProjectModelError::UnknownEntrypoint { .. }));
    }

    #[test]
    fn project_without_declared_entrypoint_does_not_invent_product_surfaces() {
        let temp = tempfile::tempdir().unwrap();
        fs::create_dir_all(temp.path().join("src")).unwrap();
        fs::write(temp.path().join("src/main.rs"), "fn main() {}\n").unwrap();

        let model = ProjectModel::discover_without_config(temp.path()).unwrap();

        assert!(model.entrypoints.is_empty());
        assert_eq!(model.default_entrypoint, "");
        assert_eq!(
            model.select_entrypoint(None).unwrap_err(),
            ProjectModelError::NoEntrypoints
        );
    }
}