// Copyright (C) 2019  Frank Rehberger
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0>
extern crate glob;
extern crate proc_macro;

use proc_macro::TokenStream;

use self::glob::{glob, Paths};
use quote::quote;
use std::path::PathBuf;
use syn::parse::{Parse, ParseStream, Result};
use syn::{parse_macro_input, Expr, ExprLit, Ident, Lit, Token};

const CONTENT_MAX_LEN: usize = 100;

// Remove from string punctuation/delimiters and special characters
fn canonical_fn_name(s: &str) -> String {
    // remove delimiters and special characters
    s.replace(
        &['"', ' ', '.', ':', '-', '*', '/', '\\', '\n', '\t', '\r'][..],
        "_",
    )
}

/// Concatenate two token-streams
fn concat_ts(
    accu: proc_macro2::TokenStream,
    other: proc_macro2::TokenStream,
) -> proc_macro2::TokenStream {
    quote! { #accu #other }
}

/// Parser elements
struct GlobExpand {
    glob_pattern: Lit,
    lambda: Ident,
}

/// Parser reading the Literal and function-identifier from token-stream
impl Parse for GlobExpand {
    fn parse(input: ParseStream) -> Result<Self> {
        let glob_pattern: Lit = input.parse()?;
        input.parse::<Token![;]>()?;
        let lambda: Ident = input.parse()?;

        Ok(GlobExpand {
            glob_pattern,
            lambda,
        })
    }
}

/// Prefix for each generated test-function
const PREFIX: &str = "gen_";

// Compose a new function-identifier from input
fn fn_ident_from_path(fn_ident: &Ident, path: &PathBuf) -> Ident {
    let path_as_str = path
        .clone()
        .into_os_string()
        .into_string()
        .expect("bad encoding");

    // prefixed name & remove delimiters and special characters
    let stringified = format!("{}_{}", fn_ident.to_string(), &path_as_str);

    // quote! requires proc_macro2 elements
    let gen_fn_ident = proc_macro2::Ident::new(
        &canonical_fn_name(&stringified),
        proc_macro2::Span::call_site(),
    );

    gen_fn_ident
}

// Compose a new function-identifier from input
fn fn_ident_from_string(fn_ident: &Ident, name: &str) -> Ident {
    // use at most CONTENT_MAX_LEN
    let safe_len = std::cmp::min(name.len(), CONTENT_MAX_LEN);
    let safe_name = &name[0..safe_len];

    // prefixed name & remove delimiters and special characters
    let stringified = format!("{}_{}", fn_ident.to_string(), safe_name);
    // quote! requires proc_macro2 elements
    let gen_fn_ident = proc_macro2::Ident::new(
        &canonical_fn_name(&stringified),
        proc_macro2::Span::call_site(),
    );

    gen_fn_ident
}

// Stringify the expression: arrays are enumerated, identifier-names are embedded
fn expr_stringified(expr: &Expr, int_as_hex: bool) -> String {
    let stringified = match expr {
        Expr::Lit(lit) => match lit {
            ExprLit {
                lit: litval,
                attrs: _,
            } => match litval {
                Lit::Int(lit) => {
                    let val = lit.value();
                    if int_as_hex {
                        // if u8-range, use two digits, otherwise 16
                        if val > 255 {
                            // not a u8
                            format!("{:016x}", val)
                        } else {
                            format!("{:02x}", val as u8)
                        }
                    } else {
                        format!("{:010}", val)
                    }
                }
                Lit::Char(lit) => {
                    let val = lit.value();
                    format!("{}", val)
                }
                Lit::Str(lit) => {
                    let val = lit.value();
                    val
                }
                Lit::Float(lit) => {
                    let val = lit.value();
                    format!("{}", val)
                }
                _ => panic!(),
            },
        },
        Expr::Array(ref array_expr) => {
            let elems = &array_expr.elems;
            let mut composed = String::new();
            // do not
            let mut cnt: usize = 0;
            // concat as hex-numbers, group by 8
            for expr in elems.iter() {
                // after 8 elements, always insert '_', do not begin with '_'
                if cnt > 0 && cnt % 8 == 0 {
                    composed.push_str("_");
                }
                cnt = cnt + 1;

                let expr_str = expr_stringified(&expr, true);
                composed.push_str(&expr_str);
            }
            composed
        }
        Expr::Path(ref expr_path) => {
            let path = &expr_path.path;
            let leading_colon = path.leading_colon.is_some();
            let mut composed = String::new();

            for segment in &path.segments {
                if !composed.is_empty() || leading_colon {
                    composed.push_str("_")
                }
                let ident = &segment.ident;
                composed.push_str(&ident.to_string());
            }
            composed
        }
        Expr::Reference(ref reference) => {
            let ref_expr = &reference.expr;

            expr_stringified(&ref_expr, int_as_hex)
        }
        _ => panic!(),
    };
    stringified
}

// Compose a new function-identifier from input
fn fn_ident_from_expr(fn_ident: &Ident, expr: &Expr) -> Ident {
    let stringified = expr_stringified(expr, false);

    fn_ident_from_string(fn_ident, &format!("{}", &stringified))
}

/// Function-Attribute macro expanding glob-file-pattern to a list of directories
/// and generating a test-function for each one.
///
/// ```
/// #[cfg(test)]
/// mod tests {
///   extern crate test_generator;
///   test_generator::glob_expand! { "data/*"; test_exists }
///
///   fn test_exists(filename: &str) { assert!(std::path::Path::new(filename).exists()); }
/// }
/// ```
/// The macro will expand the code for each subfolder in `"data/*"`, generating the following
/// code. This code is not visible in IDE. Every build-time, the code will be newly generated.
///
///```
///mod tests {
///    #[test]
///    fn gen_data_set1() {
///        test_exists("data/testset1");
///    }
///
///    #[test]
///    fn gen_data_set2() {
///        test_exists("data/testset2");
///    }
///}
///
///```
#[proc_macro]
pub fn glob_expand(item: TokenStream) -> TokenStream {
    let GlobExpand {
        glob_pattern,
        lambda,
    } = parse_macro_input!(item as GlobExpand);

    let pattern = if let Lit::Str(s) = glob_pattern {
        s.value()
    } else {
        panic!();
    };

    let empty_ts: proc_macro2::TokenStream = "".parse().unwrap();

    let paths: Paths = glob(&pattern).expect("Failed to read testdata dir.");

    /// helper, concatting two token-streams
    fn concat(
        accu: proc_macro2::TokenStream,
        ts: proc_macro2::TokenStream,
    ) -> proc_macro2::TokenStream {
        quote! { # accu # ts }
    }

    // for each path generate a test-function and fold them to single tokenstream
    let result = paths
        .map(|path| {
            let path_as_str = path
                .expect("No such file or directory")
                .into_os_string()
                .into_string()
                .expect("bad encoding");

            // remove delimiters and special characters
            let canonical_name = path_as_str
                .replace("\"", " ")
                .replace(" ", "_")
                .replace("-", "_")
                .replace("*", "_")
                .replace("/", "_");

            // form an identifier with prefix
            let mut func_name = PREFIX.to_string();
            func_name.push_str(&canonical_name);

            // quote! requires proc_macro2 elements
            let func_ident = proc_macro2::Ident::new(&func_name, proc_macro2::Span::call_site());

            let item = quote! {
                # [test]
                fn # func_ident () {
                    let f = #lambda;
                    f( #path_as_str );
                }
            };

            item
        })
        .fold(empty_ts, concat);

    // transforming proc_macro2::TokenStream into proc_macro::TokenStream
    result.into()
}

/// Parser elements
struct ExpandPaths {
    fn_ident: Ident,
    glob_pattern: Lit,
}

/// Parser
impl Parse for ExpandPaths {
    fn parse(input: ParseStream) -> Result<Self> {
        let fn_ident: Ident = input.parse()?;
        input.parse::<Token![; ]>()?;
        let glob_pattern: Lit = input.parse()?;

        Ok(ExpandPaths {
            glob_pattern,
            fn_ident,
        })
    }
}

/// Generate a test-function call for each file matching the pattern
/// ```
/// extern crate test_generator;
/// #[cfg(test)]
/// mod tests {
///   test_generator::test_expand_paths! { test_exists; "data/*" }
///
///   fn test_exists(dir_name: &str) { assert!(std::path::Path::new(dir_name).exists()); }
/// }
/// ```
/// Assuming  `"data/*"` expands to "data/set1", and "data/set2" the macro will expand to
///```
///mod tests {
///    #[test]
///    fn test_exists_data_set1() {
///        test_exists("data/set1");
///    }
///
///    #[test]
///    fn test_exists_data_set2() {
///        test_exists("data/set2");
///    }
///}
///```
#[proc_macro]
pub fn test_expand_paths(item: TokenStream) -> TokenStream {
    let ExpandPaths {
        fn_ident,
        glob_pattern,
    } = parse_macro_input!(item as ExpandPaths);

    let pattern = if let Lit::Str(s) = glob_pattern {
        s.value()
    } else {
        panic!();
    };

    let empty_ts: proc_macro2::TokenStream = "".parse().unwrap();

    let paths: Paths = glob(&pattern).expect("Invalid 'paths' pattern.");

    // for each path generate a test-function and fold them to single tokenstream
    let result = paths
        .map(|path| {
            // check for error, shadow the name
            let path = path.expect("No such file or directory");

            // form a function identifier, each path is unique => no index required
            let gen_fn_ident = fn_ident_from_path(&fn_ident, &path);

            let path_as_str = path.into_os_string().into_string().expect("bad encoding");

            let item = quote! {
                # [test]
                fn #gen_fn_ident () {
                    #fn_ident ( #path_as_str );
                }
            };

            item
        })
        .fold(empty_ts, concat_ts);

    // transforming proc_macro2::TokenStream into proc_macro::TokenStream
    result.into()
}

/// Generate a benchmark-function call for each file matching the pattern
/// ```
/// extern crate test_generator;
/// #[cfg(test)]
/// mod tests {
///   test_generator::bench_expand_paths! { bench_exists; "data/*" }
///
///   fn bench_exists(bencher: &mut test::Bencher, filename: &str) {
///        let path = std::path::Path::new(filename);
///        b.iter(|| { path.exists() });
///    }
/// }
/// ```
/// Assuming  `"data/*"` expands to "data/set1", and "data/set2" the macro will expand to
///```
///mod tests {
///    #[bench]
///    fn bench_exists_data_set1(bencher: & mut test::Bencher) {
///        bench_exists(bencher, "data/set1");
///    }
///
///    #[bench]
///    fn bench_exists_data_set2(bencher: & mut test::Bencher) {
///        bench_exists(bencher, "data/set2");
///    }
///}
///```
#[proc_macro]
pub fn bench_expand_paths(item: TokenStream) -> TokenStream {
    let ExpandPaths {
        fn_ident,
        glob_pattern,
    } = parse_macro_input!(item as ExpandPaths);

    let pattern = if let Lit::Str(s) = glob_pattern {
        s.value()
    } else {
        panic!();
    };

    let empty_ts: proc_macro2::TokenStream = "".parse().unwrap();

    let paths: Paths = glob(&pattern).expect("Invalid 'paths' pattern.");

    // for each path generate a test-function and fold them to single tokenstream
    let result = paths
        .map(|path| {
            // check for error, shadow the name
            let path = path.expect("No such file or directory");

            // form a function identifier, each path is unique => no index required
            let gen_fn_ident = fn_ident_from_path(&fn_ident, &path);

            let path_as_str = path.into_os_string().into_string().expect("bad encoding");

            let item = quote! {
                # [bench]
                fn #gen_fn_ident (bencher: & mut test::Bencher) {
                    #fn_ident (bencher, #path_as_str );
                }
            };

            item
        })
        .fold(empty_ts, concat_ts);

    // transforming proc_macro2::TokenStream into proc_macro::TokenStream
    result.into()
}

/// Parser elements
struct ExpandList {
    fn_ident: Ident,
    listing: Expr,
}

/// Parser
impl Parse for ExpandList {
    fn parse(input: ParseStream) -> Result<Self> {
        let fn_ident: Ident = input.parse()?;
        input.parse::<Token![; ]>()?;
        let listing: syn::Expr = input.parse()?;

        Ok(ExpandList { fn_ident, listing })
    }
}

/// Generate a test-function call for each list-element
/// ```
/// extern crate test_generator;
/// #[cfg(test)]
/// mod tests {
///   test_generator::test_expand_list! { test_size; [ 10, 100, 1000 ]}
///
///   fn test_size(value: &usize) { assert!( *value > 0 ); }
///
///   const VEC1 = [ 1, 2, 3, 4 ]; /* speaking array names */
///   const VEC2 = [ 5, 6, 7, 8 ];
///   test_generator::test_expand_list! { test_array_size; [ &VEC1, &VEC2 ]}
///   test_generator::test_expand_list! { test_array_size; [ [1, 2, 3, 4], [ 5, 6, 7, 8 ]}
///
///   fn test_array_size<T>(ar: &[T]) {
///        assert!(ar.len() > 0);
///   }
/// }
/// ```
/// Will expand to test-functions incorporating the array-elements
///```
///mod tests {
///    #[test]
///    fn test_size_0000000010() { test_size(&10); }
///    #[test]
///    fn test_size_0000000100() { test_size(&100); }
///    #[test]
///    fn test_size_0000001000() { test_size(&1000); }
///
///    #[test]
///    fn test_array_size_VEC1() { test_array_size( &VEC1 ); }
///    #[test]
///    fn test_array_size_VEC2() { test_array_size( &VEC2 ); }
///
///    #[test]
///    fn test_array_size_01020304() { test_array_size( &[ 1, 2, 3, 4 ] ); }
///    fn test_array_size_05060708() { test_array_size( &[ 5, 6, 7, 8 ] ); }
///}
///```
#[proc_macro]
pub fn test_expand_list(item: TokenStream) -> TokenStream {
    let ExpandList { fn_ident, listing } = parse_macro_input!(item as ExpandList);

    let expr_array = if let Expr::Array(expr_array) = listing {
        expr_array
    } else {
        panic!();
    };

    let empty_ts: proc_macro2::TokenStream = "".parse().unwrap();

    let elems: syn::punctuated::Punctuated<Expr, _> = expr_array.elems;

    let item = elems
        .iter()
        .map(|expr| {
            let gen_fn_ident = fn_ident_from_expr(&fn_ident, expr);
            let ref_symbol_ts: proc_macro2::TokenStream = match expr {
                Expr::Reference(_) => "".parse().unwrap(),
                _ => "&".parse().unwrap(),
            };

            quote! {
                #[test]
                fn #gen_fn_ident() {
                    let local = #ref_symbol_ts #expr;
                    #fn_ident ( local );
                }
            }
        })
        .fold(empty_ts, concat_ts);

    // transforming proc_macro2::TokenStream into proc_macro::TokenStream
    item.into()
}

/// Generate a benchmark-function call for each list-element
/// ```
/// extern crate test_generator;
/// #[cfg(test)]
/// mod tests {
///   test_generator::bench_expand_list! { bench_size; [ 10, 100, 1000 ]}
///
///   fn bench_size(b: &mut test::Bencher, val: &usize) {
///      let input = val;
///      b.iter(|| { *input > 0 });
///   }
/// }
/// ```
/// Will expand to bench-functions incorporating the array-elements
///```
///mod tests {
///    #[bench]
///    fn bench_size_0000000010(bencher: & mut test::Bencher) {
///        bench_exists(bencher, &10);
///    }
///    #[bench]
///    fn bench_size_0000000100(bencher: & mut test::Bencher) {
///        bench_exists(bencher, &100);
///    }
///    #[bench]
///    fn bench_size_0000001000(bencher: & mut test::Bencher) {
///        bench_exists(bencher, &1000);
///    }
///}
///```
#[proc_macro]
pub fn bench_expand_list(item: TokenStream) -> TokenStream {
    let ExpandList { fn_ident, listing } = parse_macro_input!(item as ExpandList);

    let expr_array = if let Expr::Array(expr_array) = listing {
        expr_array
    } else {
        panic!();
    };

    let empty_ts: proc_macro2::TokenStream = "".parse().unwrap();

    let elems: syn::punctuated::Punctuated<Expr, _> = expr_array.elems;

    let item = elems
        .iter()
        .map(|expr| {
            let gen_fn_ident = fn_ident_from_expr(&fn_ident, expr);
            let ref_symbol_ts: proc_macro2::TokenStream = match expr {
                Expr::Reference(_) => "".parse().unwrap(),
                _ => "&".parse().unwrap(),
            };

            quote! {
                # [bench]
                fn #gen_fn_ident (bencher: & mut test::Bencher) {
                    let local = #ref_symbol_ts #expr;
                    #fn_ident (bencher, local );
                }
            }
        })
        .fold(empty_ts, concat_ts);

    // transforming proc_macro2::TokenStream into proc_macro::TokenStream
    item.into()
}