extern crate askama_shared as shared;
extern crate proc_macro;
extern crate syn;

use proc_macro::TokenStream;

use std::borrow::Cow;
use std::path::PathBuf;

#[proc_macro_derive(Template, attributes(template))]
pub fn derive_template(input: TokenStream) -> TokenStream {
    let ast = syn::parse_derive_input(&input.to_string()).unwrap();
    match ast.body {
        syn::Body::Struct(ref data) => data,
        _ => panic!("#[derive(Template)] can only be used with structs"),
    };
    build_template(&ast).parse().unwrap()
}

/// Takes a `syn::DeriveInput` and generates source code for it
///
/// Reads the metadata from the `template()` attribute to get the template
/// metadata, then fetches the source from the filesystem. The source is
/// parsed, and the parse tree is fed to the code generator. Will print
/// the parse tree and/or generated source according to the `print` key's
/// value as passed to the `template()` attribute.
fn build_template(ast: &syn::DeriveInput) -> String {
    let meta = get_template_meta(ast);
    let (path, src) = match meta.source {
        Source::Source(s) => (PathBuf::new(), Cow::Borrowed(s)),
        Source::Path(s) => {
            let path = shared::path::find_template_from_path(&s, None);
            let src = shared::path::get_template_source(&path);
            (path, Cow::Owned(src))
        },
    };
    let nodes = shared::parse(src.as_ref());
    if meta.print == Print::Ast || meta.print == Print::All {
        println!("{:?}", nodes);
    }
    let code = shared::generate(ast, &path, nodes);
    if meta.print == Print::Code || meta.print == Print::All {
        println!("{}", code);
    }
    code
}

// Returns a `TemplateMeta` based on the `template()` attribute data found
// in the parsed struct or enum. Will panic if it does not find the required
// template path, or if the `print` key has an unexpected value.
fn get_template_meta<'a>(ast: &'a syn::DeriveInput) -> TemplateMeta<'a> {
    let attr = ast.attrs.iter().find(|a| a.name() == "template");
    if attr.is_none() {
        let msg = format!("'template' attribute not found on struct '{}'",
                          ast.ident.as_ref());
        panic!(msg);
    }

    let attr = attr.unwrap();
    let mut source = None;
    let mut print = Print::None;
    if let syn::MetaItem::List(_, ref inner) = attr.value {
        for nm_item in inner {
            if let syn::NestedMetaItem::MetaItem(ref item) = *nm_item {
                if let syn::MetaItem::NameValue(ref key, ref val) = *item {
                    match key.as_ref() {
                        "path" => if let syn::Lit::Str(ref s, _) = *val {
                            source = Some(Source::Path(s.as_ref()));
                        } else {
                            panic!("template path must be string literal");
                        },
                        "source" => if let syn::Lit::Str(ref s, _) = *val {
                            source = Some(Source::Source(s.as_ref()));
                        } else {
                            panic!("template source must be string literal");
                        },
                        "print" => if let syn::Lit::Str(ref s, _) = *val {
                            print = s.into();
                        } else {
                            panic!("print value must be string literal");
                        },
                        _ => { panic!("unsupported annotation key found") }
                    }
                }
            }
        }
    }

    match source {
        Some(s) => TemplateMeta { source: s, print },
        None => panic!("template path or source not found in struct attributes"),
    }
}

// Holds metadata for the template, based on the `template()` attribute.
struct TemplateMeta<'a> {
    source: Source<'a>,
    print: Print,
}

enum Source<'a> {
    Path(&'a str),
    Source(&'a str),
}

#[derive(PartialEq)]
enum Print {
    All,
    Ast,
    Code,
    None,
}

impl<'a> From<&'a String> for Print {
    fn from(s: &'a String) -> Print {
        use Print::*;
        match s.as_ref() {
            "all" => All,
            "ast" => Ast,
            "code" => Code,
            "none" => None,
            v => panic!("invalid value for print option: {}", v),
        }
    }
}