use crate::{CompileError, Config, Syntax};

use std::path::PathBuf;
use std::str::FromStr;

use quote::ToTokens;

pub struct TemplateInput<'a> {
    pub ast: &'a syn::DeriveInput,
    pub config: &'a Config<'a>,
    pub syntax: &'a Syntax<'a>,
    pub source: Source,
    pub print: Print,
    pub escaper: &'a str,
    pub ext: Option<String>,
    pub parent: Option<&'a syn::Type>,
    pub path: PathBuf,
}

impl<'a> TemplateInput<'a> {
    /// Extract the template metadata from the `DeriveInput` structure. This
    /// mostly recovers the data for the `TemplateInput` fields from the
    /// `template()` attribute list fields; it also finds the of the `_parent`
    /// field, if any.
    pub fn new<'n>(
        ast: &'n syn::DeriveInput,
        config: &'n Config,
    ) -> Result<TemplateInput<'n>, CompileError> {
        // Check that an attribute called `template()` exists and that it is
        // the proper type (list).
        let meta = ast
            .attrs
            .iter()
            .find_map(|attr| match attr.parse_meta() {
                Ok(m) => {
                    if m.path().is_ident("template") {
                        Some(Ok(m))
                    } else {
                        None
                    }
                }
                Err(e) => Some(Err(format!("unable to parse attribute: {}", e).into())),
            })
            .unwrap_or(Err(CompileError::Static("no attribute 'template' found")))?;

        let meta_list = match meta {
            syn::Meta::List(inner) => inner,
            _ => return Err("attribute 'template' has incorrect type".into()),
        };

        // Loop over the meta attributes and find everything that we
        // understand. Raise panics if something is not right.
        // `source` contains an enum that can represent `path` or `source`.
        let mut source = None;
        let mut print = Print::None;
        let mut escaping = None;
        let mut ext = None;
        let mut syntax = None;
        for item in meta_list.nested {
            let pair = match item {
                syn::NestedMeta::Meta(syn::Meta::NameValue(ref pair)) => pair,
                _ => {
                    return Err(format!(
                        "unsupported attribute argument {:?}",
                        item.to_token_stream()
                    )
                    .into())
                }
            };

            if pair.path.is_ident("path") {
                if let syn::Lit::Str(ref s) = pair.lit {
                    if source.is_some() {
                        return Err("must specify 'source' or 'path', not both".into());
                    }
                    source = Some(Source::Path(s.value()));
                } else {
                    return Err("template path must be string literal".into());
                }
            } else if pair.path.is_ident("source") {
                if let syn::Lit::Str(ref s) = pair.lit {
                    if source.is_some() {
                        return Err("must specify 'source' or 'path', not both".into());
                    }
                    source = Some(Source::Source(s.value()));
                } else {
                    return Err("template source must be string literal".into());
                }
            } else if pair.path.is_ident("print") {
                if let syn::Lit::Str(ref s) = pair.lit {
                    print = s.value().parse()?;
                } else {
                    return Err("print value must be string literal".into());
                }
            } else if pair.path.is_ident("escape") {
                if let syn::Lit::Str(ref s) = pair.lit {
                    escaping = Some(s.value());
                } else {
                    return Err("escape value must be string literal".into());
                }
            } else if pair.path.is_ident("ext") {
                if let syn::Lit::Str(ref s) = pair.lit {
                    ext = Some(s.value());
                } else {
                    return Err("ext value must be string literal".into());
                }
            } else if pair.path.is_ident("syntax") {
                if let syn::Lit::Str(ref s) = pair.lit {
                    syntax = Some(s.value())
                } else {
                    return Err("syntax value must be string literal".into());
                }
            } else {
                return Err(format!(
                    "unsupported attribute key '{}' found",
                    pair.path.to_token_stream()
                )
                .into());
            }
        }

        // Validate the `source` and `ext` value together, since they are
        // related. In case `source` was used instead of `path`, the value
        // of `ext` is merged into a synthetic `path` value here.
        let source = source.expect("template path or source not found in attributes");
        let path = match (&source, &ext) {
            (&Source::Path(ref path), None) => config.find_template(path, None)?,
            (&Source::Source(_), Some(ext)) => PathBuf::from(format!("{}.{}", ast.ident, ext)),
            (&Source::Path(_), Some(_)) => {
                return Err("'ext' attribute cannot be used with 'path' attribute".into())
            }
            (&Source::Source(_), None) => {
                return Err("must include 'ext' attribute when using 'source' attribute".into())
            }
        };

        // Check to see if a `_parent` field was defined on the context
        // struct, and store the type for it for use in the code generator.
        let parent = match ast.data {
            syn::Data::Struct(syn::DataStruct {
                fields: syn::Fields::Named(ref fields),
                ..
            }) => fields
                .named
                .iter()
                .find(|f| f.ident.as_ref().filter(|name| *name == "_parent").is_some())
                .map(|f| &f.ty),
            _ => None,
        };

        if parent.is_some() {
            eprint!(
                "   --> in struct {}\n   = use of deprecated field '_parent'\n",
                ast.ident
            );
        }

        // Validate syntax
        let syntax = syntax.map_or_else(
            || Ok(config.syntaxes.get(config.default_syntax).unwrap()),
            |s| {
                config.syntaxes.get(&s).ok_or_else(|| {
                    CompileError::String(format!("attribute syntax {} not exist", s))
                })
            },
        )?;

        // Match extension against defined output formats

        let extension = escaping.unwrap_or_else(|| {
            path.extension()
                .map(|s| s.to_str().unwrap())
                .unwrap_or("")
                .to_string()
        });

        let mut escaper = None;
        for (extensions, path) in &config.escapers {
            if extensions.contains(&extension) {
                escaper = Some(path);
                break;
            }
        }

        let escaper = escaper.ok_or_else(|| {
            CompileError::String(format!("no escaper defined for extension '{}'", extension,))
        })?;

        Ok(TemplateInput {
            ast,
            config,
            source,
            print,
            escaper,
            ext,
            parent,
            path,
            syntax,
        })
    }
}

pub enum Source {
    Path(String),
    Source(String),
}

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

impl FromStr for Print {
    type Err = CompileError;

    fn from_str(s: &str) -> Result<Print, Self::Err> {
        use self::Print::*;
        Ok(match s {
            "all" => All,
            "ast" => Ast,
            "code" => Code,
            "none" => None,
            v => return Err(format!("invalid value for print option: {}", v,).into()),
        })
    }
}