use std::io::{BufRead, BufReader, BufWriter, Write};
use std::path::Path;

use git2::{Patch, Repository};
use regex::Regex;
use serde::Deserialize;
use thiserror::Error;


#[derive(Debug, Error)]
pub enum Error {
}

#[derive(Debug, PartialEq)]
enum LineEnding {
    Lf,
    CrLf,
}

#[derive(Debug, Deserialize)]
pub struct Suggestion {
    #[serde(rename = "diff_hunk")]
    diff: String,

    #[serde(rename = "body")]
    comment: String,

    #[serde(rename = "original_commit_id")]
    commit: String,

    path: String,

    original_start_line: Option<usize>,

    #[serde(rename = "original_line")]
    original_end_line: usize,
}

impl Suggestion {
    // TODO: Rename to `diff`
    pub fn patch(&self) -> String {
        let mut diff: Vec<_> = self.diff.lines()
            .filter(|l| !l.starts_with("-"))
            .map(|l| {
                if l.starts_with("+") {
                    return l.replacen("+", " ", 1);
                }

                l.to_owned()
            })
            .collect();

        let last = diff.len() - 1;
        diff[last] = diff.last().unwrap()
            .replacen(" ", "-", 1);

        diff.push(self.suggestion_patch());

        diff.join("\n")
    }

    pub fn diff(&self) -> String {
        let repo = Repository::open(".").unwrap();

        self.diff_with_repo(&repo)
    }

    fn diff_with_repo(&self, repo: &Repository) -> String {
        let commit = repo.find_commit(self.commit.parse().unwrap()).unwrap();

        let path = Path::new(&self.path);

        let object = commit
            .tree().unwrap()
            .get_path(path).unwrap()
            .to_object(&repo).unwrap();

        let blob = object.as_blob().unwrap();

        let blob_reader = BufReader::new(blob.content());
        let mut new = BufWriter::new(Vec::new());
        self.apply_to(blob_reader, &mut new).unwrap();
        let new_buffer = new.into_inner().unwrap();

        let mut diff = Patch::from_blob_and_buffer(
            blob,
            Some(&path),
            &new_buffer,
            Some(&path),
            None,
        ).unwrap();

        diff.to_buf()
            .unwrap()
            .as_str()
            .unwrap_or("")
            .to_owned()
    }

    fn suggestion_patch(&self) -> String {
        let re = Regex::new(r"(?s).*(?-s)```\s*suggestion.*\n").unwrap();
        let s = re.replace(&self.comment, "+");
        s.replace("```", "")
    }

    fn suggestion(&self) -> String {
        self.suggestion_with_line_ending(&LineEnding::Lf)
    }

    fn suggestion_with_line_ending(&self, line_ending: &LineEnding) -> String {
        let re = Regex::new(r"(?s).*(?-s)```\s*suggestion.*\n").unwrap();
        let s = re.replace(&self.comment, "");
        let s = s.replace("```", "");

        // Suggestion blocks use CRLF by default.
        if *line_ending == LineEnding::Lf {
            return s.replace('\r', "");
        }

        s
    }

    pub fn apply(&self) -> Result<(), Error> {
        let repo = Repository::open(".").unwrap();

        let diff_text = self.diff_with_repo(&repo);
        let diff = git2::Diff::from_buffer(diff_text.as_bytes()).unwrap();

        repo.apply(
            &diff,
            git2::ApplyLocation::WorkDir,
            None,
        ).unwrap();

        Ok(())
    }

    fn apply_to<R: BufRead, W: Write>(
        &self,
        reader: R,
        writer: &mut W,
    ) -> Result<(), Error> {
        let mut line_ending = LineEnding::Lf;

        for (i, line) in reader.lines().enumerate() {
            let line_number = i + 1;

            match line {
                Ok(l) => {
                    // Determine which line endings the file uses by looking at
                    // the first line.
                    if line_number == 1 && is_line_crlf(&l) {
                        line_ending = LineEnding::CrLf;
                    }

                    if line_number == self.original_end_line {
                        write!(
                            writer,
                            "{}",
                            self.suggestion_with_line_ending(&line_ending),
                        ).unwrap();
                    } else if self.original_start_line.is_none()
                            || line_number < self.original_start_line.unwrap()
                            || line_number > self.original_end_line {
                        writeln!(writer, "{}", l).unwrap();
                    }
                },
                Err(e) => panic!(e),
            }
        }

        Ok(())
    }
}

/// Determine the line ending for `line`.
///
/// If the second-to-last character on the first line is "\r", assume CRLF.
/// Otherwise, default to LF.
fn is_line_crlf(line: &str) -> bool {
    if let Some(c) = line.chars().rev().nth(2) {
        if c == '\r' {
            return true;
        }
    }

    false
}


#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn suggestion_patch_generates_patch() {
        // Diff from gabgodBB (https://github.com/gabgodBB) and suggestion from
        // probablycorey (https://github.com/probablycorey) in this pull
        // request: https://github.com/cli/cli/pull/1123

        let suggestion = Suggestion {
            diff: r#"@@ -1, 9 +1, 11 @@
 package command
 
 import (
+	"bufio" // used to input comment
 	"errors"
 	"fmt"
 	"io"
+	"os" // used to input comment"#.to_owned(),
            comment: r#"It's ok to leave these uncommented

```suggestion
	"os"
```"#.to_owned(),
            commit: "".to_owned(),
            path: "".to_owned(),
            original_start_line: Some(8),
            original_end_line: 8,
        };

        assert_eq!(
            suggestion.patch(),
            r#"@@ -1, 9 +1, 11 @@
 package command
 
 import (
 	"bufio" // used to input comment
 	"errors"
 	"fmt"
 	"io"
-	"os" // used to input comment
+	"os"
"#,
        );
    }

    #[test]
    fn unified_diff() {
        use unidiff::PatchSet;

        let diff = r#"--- a/command/pr.go
+++ b/command/pr.go
@@ -1,9 +1,11 @@
 package command
 
 import (
+	"bufio" // used to input comment
 	"errors"
 	"fmt"
 	"io"
+	"os" // used to input comment
"#;

        let mut patch = PatchSet::new();
        patch.parse(diff).unwrap();

        println!("{:?}", patch);
        println!("{}", patch);

        let lines = patch.files_mut()[0].hunks_mut()[0].lines_mut();

        // for line in &lines {
        //     if line.is_removed() {
        //     } else if line.is_added() {
        //         line.line_type = unidiff::LINE_TYPE_CONTEXT.to_owned();
        //     }
        // }

        lines
            .iter_mut()
            .filter(|l| !l.is_removed())
            // .map(|l| {
            .for_each(|l| {
                if l.is_added() {
                    l.line_type = unidiff::LINE_TYPE_CONTEXT.to_owned();
                }
            });

        lines[lines.len() - 2].line_type = unidiff::LINE_TYPE_REMOVED.to_owned();

        patch.files_mut()[0].hunks_mut()[0].append(unidiff::Line::new(
            r#"	"os""#,
            unidiff::LINE_TYPE_ADDED,
        ));

        println!("{}", patch);
    }

    #[test]
    fn read_git_blob() {
        use std::path::Path;

        use git2::Repository;

        let repo = Repository::open("./private/suggestion-test").unwrap();
        let commit = repo.find_commit("b58be52880a0a0c0d397052351be31f19acdeca4".parse().unwrap()).unwrap();

        let object = commit
            .tree().unwrap()
            .get_path(Path::new("src/server.rs")).unwrap()
            .to_object(&repo).unwrap();

        let blob = object
            .as_blob().unwrap()
            .content();

        println!("{:?}", commit);
        println!("{}", std::str::from_utf8(blob).unwrap());
    }

    #[test]
    fn suggestion_diff_with_repo_generates_diff() {
        use tempfile::tempdir;


        let git_root = tempdir().unwrap();
        let repo = Repository::init(git_root.path()).unwrap();

        let file = r#"
     ‘Beware the Jabberwock, my son!
      The jaws that bite, the claws that catch!
     Beware the Jubjub bird, and shun
      The frumious Bandersnatch!’

     He took his vorpal blade in hand:
      Long time the manxome foe he sought--
     So rested he by the Tumtum tree,
      And stood awhile in thought.
"#;

        let path = "poems/Jabberwocky.txt";

        let mut index = repo.index().unwrap();
        index.add_frombuffer(
            &git2::IndexEntry {
                ctime: git2::IndexTime::new(0, 0),
                mtime: git2::IndexTime::new(0, 0),
                dev: 0,
                ino: 0,
                mode: 0o100644,
                uid: 0,
                gid: 0,
                file_size: file.len() as u32,
                id: git2::Oid::zero(),
                flags: 0,
                flags_extended: 0,
                path: path.as_bytes().to_vec(),
            },
            file.as_bytes(),
        ).unwrap();
        let tree_oid = index.write_tree().unwrap();
        let tree = repo.find_tree(tree_oid).unwrap();

        let author = git2::Signature::now(
            "Oshino Shinobu",
            "oshino.shinobu@example.com",
        ).unwrap();

        let commit = repo.commit(
            Some("HEAD"),
            &author,
            &author,
            "Sample commit",
            &tree,
            &[],
        ).unwrap();

        let suggestion = Suggestion {
            diff: "".to_owned(),
            comment: r#"``` suggestion
     He took his vorpal sword in hand:
      Long time the manxome foe he sought—
```"#.to_owned(),
            commit: commit.to_string(),
            path: path.to_owned(),
            original_start_line: Some(7),
            original_end_line: 8,
        };

        let expected = r#"diff --git a/poems/Jabberwocky.txt b/poems/Jabberwocky.txt
index 89840a2..06acdfc 100644
--- a/poems/Jabberwocky.txt
+++ b/poems/Jabberwocky.txt
@@ -4,7 +4,7 @@
      Beware the Jubjub bird, and shun
       The frumious Bandersnatch!’
 
-     He took his vorpal blade in hand:
-      Long time the manxome foe he sought--
+     He took his vorpal sword in hand:
+      Long time the manxome foe he sought—
      So rested he by the Tumtum tree,
       And stood awhile in thought.
"#;

        assert_eq!(
            suggestion.diff_with_repo(&repo),
            expected,
        );
    }

    #[test]
    fn suggestion_apply_to_writes_patch_to_writer() {
        use std::io::Cursor;


        let mut original_buffer = Vec::new();
        let original = r#"
     ‘Beware the Jabberwock, my son!
      The jaws that bite, the claws that catch!
     Beware the Jubjub bird, and shun
      The frumious Bandersnatch!’

     He took his vorpal blade in hand:
      Long time the manxome foe he sought--
     So rested he by the Tumtum tree,
      And stood awhile in thought.
"#;

        write!(original_buffer, "{}", original).unwrap();

        let suggestion = Suggestion {
            diff: "".to_owned(),
            comment: r#"``` suggestion
     He took his vorpal sword in hand:
      Long time the manxome foe he sought—
```"#.to_owned(),
            commit: "".to_owned(),
            path: "".to_owned(),
            original_start_line: Some(7),
            original_end_line: 8,
        };

        let expected = r#"
     ‘Beware the Jabberwock, my son!
      The jaws that bite, the claws that catch!
     Beware the Jubjub bird, and shun
      The frumious Bandersnatch!’

     He took his vorpal sword in hand:
      Long time the manxome foe he sought—
     So rested he by the Tumtum tree,
      And stood awhile in thought.
"#;

        let original_reader = Cursor::new(original_buffer);
        let mut actual = Cursor::new(Vec::new());
        suggestion.apply_to(original_reader, &mut actual).unwrap();

        assert_eq!(
            std::str::from_utf8(&actual.into_inner()).unwrap(),
            expected,
        );
    }
}