use proc_macro2::TokenStream;
use quote::{quote, ToTokens, TokenStreamExt};
use sha2::{Digest, Sha384};
use std::fs;
use syn::LitStr;

struct QuotedMigration {
    version: i64,
    description: String,
    sql: String,
    checksum: Vec<u8>,
}

impl ToTokens for QuotedMigration {
    fn to_tokens(&self, tokens: &mut TokenStream) {
        let QuotedMigration {
            version,
            description,
            sql,
            checksum,
        } = &self;

        let ts = quote! {
            sqlx::migrate::Migration {
                version: #version,
                description: std::borrow::Cow::Borrowed(#description),
                sql: std::borrow::Cow::Borrowed(#sql),
                checksum: std::borrow::Cow::Borrowed(&[
                    #(#checksum),*
                ]),
            }
        };

        tokens.append_all(ts.into_iter());
    }
}

// mostly copied from sqlx-core/src/migrate/source.rs
pub(crate) fn expand_migrator_from_dir(dir: LitStr) -> crate::Result<proc_macro2::TokenStream> {
    let path = crate::common::resolve_path(&dir.value(), dir.span())?;
    let mut s = fs::read_dir(path)?;

    let mut migrations = Vec::new();

    while let Some(entry) = s.next() {
        let entry = entry?;
        if !entry.metadata()?.is_file() {
            // not a file; ignore
            continue;
        }

        let file_name = entry.file_name();
        let file_name = file_name.to_string_lossy();

        let parts = file_name.splitn(2, '_').collect::<Vec<_>>();

        if parts.len() != 2 || !parts[1].ends_with(".sql") {
            // not of the format: <VERSION>_<DESCRIPTION>.sql; ignore
            continue;
        }

        let version: i64 = parts[0].parse()?;

        // remove the `.sql` and replace `_` with ` `
        let description = parts[1]
            .trim_end_matches(".sql")
            .replace('_', " ")
            .to_owned();

        let sql = fs::read_to_string(&entry.path())?;

        let checksum = Vec::from(Sha384::digest(sql.as_bytes()).as_slice());

        migrations.push(QuotedMigration {
            version,
            description,
            sql,
            checksum,
        })
    }

    // ensure that we are sorted by `VERSION ASC`
    migrations.sort_by_key(|m| m.version);

    Ok(quote! {
        sqlx::migrate::Migrator {
            migrations: std::borrow::Cow::Borrowed(&[
                #(#migrations),*
            ])
        }
    })
}