use std::collections::HashMap;
use std::path::Path;

use crate::DomainError;

#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub struct ModuleName(String);

/// How a module name was assigned to a source file.
#[derive(Debug, Clone)]
pub enum ModuleAssignment {
    /// Matched an explicit user-configured mapping in `archlens.toml`.
    Explicit(ModuleName),
    /// Derived from file path structure by heuristic (e.g. `crates/<name>/...`).
    Inferred(ModuleName),
    /// No mapping matched and the heuristic could not determine a module.
    Unresolved(&'static str),
}

impl ModuleAssignment {
    pub fn module_name(&self) -> Option<&ModuleName> {
        match self {
            Self::Explicit(m) | Self::Inferred(m) => Some(m),
            Self::Unresolved(_) => None,
        }
    }

    pub fn into_module_name(self) -> Option<ModuleName> {
        match self {
            Self::Explicit(m) | Self::Inferred(m) => Some(m),
            Self::Unresolved(_) => None,
        }
    }

    pub fn reason(&self) -> Option<&'static str> {
        match self {
            Self::Unresolved(r) => Some(r),
            _ => None,
        }
    }
}

impl ModuleName {
    pub fn new(value: &str) -> Result<Self, DomainError> {
        let trimmed = value.trim();
        if trimmed.is_empty() {
            return Err(DomainError::EmptyValue("ModuleName"));
        }
        Ok(Self(trimmed.to_string()))
    }

    /// Assign a module to a file path, returning a typed assignment that
    /// distinguishes explicit mappings, heuristic inference, and failure.
    pub fn assign(
        file_path: &str,
        root: &Path,
        module_mappings: &HashMap<String, String>,
    ) -> ModuleAssignment {
        let canonical_root = root.canonicalize().unwrap_or_else(|_| root.to_path_buf());
        let root_str = canonical_root.to_str().unwrap_or("");
        let relative = file_path
            .strip_prefix(root_str)
            .unwrap_or(file_path)
            .trim_start_matches('/');

        // 1. Explicit mapping
        for (pattern, module_name) in module_mappings {
            if relative.starts_with(pattern.as_str())
                && let Ok(m) = Self::new(module_name)
            {
                return ModuleAssignment::Explicit(m);
            }
        }

        // 2. Heuristic inference from path structure
        let parts: Vec<&str> = relative.split('/').collect();
        if parts.len() <= 1 {
            return ModuleAssignment::Unresolved("path has no directory component");
        }

        let module_dir = if (parts[0] == "crates" || parts[0] == "src") && parts.len() > 2 {
            parts[1]
        } else if parts[0] != "src" && parts.len() > 1 {
            parts[0]
        } else {
            return ModuleAssignment::Unresolved("path under src/ with no further structure");
        };

        match Self::new(&Self::capitalize(module_dir)) {
            Ok(m) => ModuleAssignment::Inferred(m),
            Err(_) => ModuleAssignment::Unresolved("inferred directory name was empty"),
        }
    }

    /// Convenience wrapper — returns None for Unresolved.
    /// Prefer `assign()` when you want to distinguish strategies.
    pub fn from_path(
        file_path: &str,
        root: &Path,
        module_mappings: &HashMap<String, String>,
    ) -> Option<Self> {
        Self::assign(file_path, root, module_mappings).into_module_name()
    }

    pub fn from_directory_group(member_path: &str) -> Option<Self> {
        let parts: Vec<&str> = member_path.split('/').collect();
        if parts.len() < 3 {
            return None;
        }
        let group = parts[parts.len() - 2];
        Self::new(&Self::capitalize(group)).ok()
    }

    pub fn capitalize(s: &str) -> String {
        s.split('-')
            .map(|seg| {
                if seg.is_empty() {
                    String::new()
                } else {
                    format!("{}{}", seg[..1].to_uppercase(), &seg[1..])
                }
            })
            .collect::<Vec<_>>()
            .join("-")
    }

    pub fn as_str(&self) -> &str {
        &self.0
    }
}